ACUS11 KWNS 072059
SWOMCD
SPC MCD 072059
OHZ000-INZ000-ILZ000-072300-

Mesoscale Discussion 1683
NWS Storm Prediction Center Norman OK
0359 PM CDT Mon Sep 07 2020

Areas affected...central Illinois through central Ohio

Concerning...Severe potential...Watch unlikely

Valid 072059Z - 072300Z

Probability of Watch Issuance...20 percent

SUMMARY...A few thunderstorms may produce locally strong wind gusts
and some hail from central Illinois through central Ohio into the
early evening. Overall threat does not appear to warrant a WW
issuance at this time.

DISCUSSION...Corridor of thunderstorm development associated with
warm advection persists from central IN through central OH. A small
cluster of storms over central OH appears to has transitioned to
surface based with a gust front becoming oriented more perpendicular
to the mean flow evident on radar advancing east southeast. The warm
sector south of this activity has destabilized as temperatures rise
through the 80s F with 1000-1500 J/kg MLCAPE, and this moist and
unstable inflow has contributed to modest storm intensification.
Farther west, visible imagery shows cumulus increasing along a cold
front across central IL and surface based development may occur by
22Z. The atmosphere in this region is moderately unstable with
2000-2500 J/kg MLCAPE, but modest vertical shear from 25-35 kt will
support multicell storm modes with isolated locally strong wind
gusts and hail possible with the stronger cells.

..Dial/Thompson.. 09/07/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...PBZ...CLE...ILN...IND...ILX...

LAT...LON 40208561 40428323 40738223 40898150 40468119 40158149
39988207 39668532 39308829 39648942 40208561
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ACUS11 KWNS 081421
SWOMCD
SPC MCD 081421
NEZ000-SDZ000-COZ000-WYZ000-081815-

Mesoscale Discussion 1686
NWS Storm Prediction Center Norman OK
0921 AM CDT Tue Sep 08 2020

Areas affected...Northern Colorado...southeast Wyoming...and western
Nebraska

Concerning...Heavy snow

Valid 081421Z - 081815Z

SUMMARY...Moderate, to at times heavy, snow rates will continue
through the mid to late morning hours before conditions gradually
improve across northern Colorado, southeastern Wyoming, and western
Nebraska.

DISCUSSION...Mid-morning regional radar loops continue to show a
broad region of banded precipitation across the central Rockies.
Sub-freezing temperatures continue to advect southward along the lee
of the Rockies, and wet-bulb cooling within the Rockies has allowed
for several locations to fall below freezing. The 12 UTC RIW
sounding shows a saturated, sub-freezing profile that supports
snowfall, and the DNR sounding revealed a similar thermodynamic
profile above ~2 kft. As a result, snowfall continues for northern
CO into southeast WY and western NE, with a few locations briefly
reporting heavy snow and visibility down to one-half mile.

These conditions are expected to continue over the next couple of
hours as lift ahead of the main synoptic low continues to be
augmented by frontogenetical lift in proximity to a strong
baroclinic zone between 850-700 mb. Heavy precipitation should shift
into western CO over the next few hours as main zone of ascent
translates southwestward with the upper-level low. Although profiles
will continue to evaporatively cool across western CO, the snowfall
potential is uncertain below higher elevations due to warm
near-surface temperatures.

The baroclinic zone is expected to undergo some degree of
frontolysis during the early to mid afternoon hours, and the main
low should begin to stall near the Four Corners region. This should
lead to a gradual reduction in lift and in the potential for
precipitation banding and heavy snow rates. There are some
indications in morning guidance that a small region of mid-level
frontogenesis may develop across southern CO/northern NM and support
moderate to heavy precipitation, but surface wet-bulb temperatures
in the upper 30s and low 40s across this region cast uncertainty
into the snowfall potential. Trends will be monitored heading into
the afternoon hours.

..Moore/Thompson.. 09/08/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...UNR...BOU...CYS...GJT...

LAT...LON 39810725 40040758 40530736 41140696 42000568 42630446
43030346 42800300 42260301 41220406 40420498 39930552
39520614 39620663 39810725
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ACUS11 KWNS 082049
SWOMCD
SPC MCD 082048
COZ000-NMZ000-090045-

Mesoscale Discussion 1688
NWS Storm Prediction Center Norman OK
0348 PM CDT Tue Sep 08 2020

Areas affected...Central to Southern Colorado

Concerning...Heavy snow

Valid 082048Z - 090045Z

SUMMARY...The potential for heavy snow will increase heading into
the late afternoon and evening hours across southern Colorado.
Snowfall rates between 1-2 inches/hour appear likely, and heavier
rates are possible at higher elevations.

DISCUSSION...Afternoon water vapor imagery continues to show the
gradual southward progression of an upper-level low along the CO/UT
border. An embedded impulse can be identified propagating around the
southern periphery of the low into the Four Corners region. Stronger
mid and upper-level flow associated with this impulse (as noted in
regional VADs) is increasing convergence along a frontogenetical
baroclinic zone between 850-700 mb. The slowing of the upper-level
low has decreased broad lift ahead of the wave somewhat, but strong
mesoscale lift along the baroclinic zone is compensating for this
weakness and will continue to favor widespread precipitation.
Elevated instability has allowed for several lightning strikes and
areas of heavier precipitation over the past hour, and RAP forecast
soundings suggest that 50-100 J/kg MUCAPE may remain in place across
the region through 00 UTC.

As thermodynamic profiles continue to cool via evaporative cooling
and low-level cold advection, this combination of mesoscale ascent
and instability should be sufficient for heavy snowfall rates
between 1-2 inches/hour with heavier rates possible at higher
elevations by the late afternoon/early evening hours.

..Moore.. 09/08/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...PUB...BOU...ABQ...GJT...

LAT...LON 37480390 37100406 36850474 36740514 36800569 37010626
37290656 37610673 38270689 38690692 39090686 39300664
39510574 39400471 39150418 38440399 37480390
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ACUS11 KWNS 161909
SWOMCD
SPC MCD 161908
GAZ000-FLZ000-162115-

Mesoscale Discussion 1697
NWS Storm Prediction Center Norman OK
0208 PM CDT Wed Sep 16 2020

Areas affected...Parts of northern Florida and the Florida Panhandle
and adjacent southwestern Georgia

Concerning...Tornado Watch 491...

Valid 161908Z - 162115Z

The severe weather threat for Tornado Watch 491 continues.

SUMMARY...At least isolated thunderstorms capable of producing
tornadoes remain possible through 7 PM EDT. It is unclear how much
longer an appreciable risk for tornadoes will continue thereafter,
but it is possible that a new tornado watch may be needed for this
evening across parts of southern Georgia and northern Florida.

DISCUSSION...Substantive boundary-layer warming has now occurred as
far north as the southern tier counties of Georgia (including the
Valdosta, Thomasville and Bainbridge areas), where surface dew
points have increased into the mid 70s F. This is focused along a
remnant frontal zone, where near surface vertical shear may now be
maximized, near the eastern periphery of the core of stronger
southerly 850 mb flow.

There may be considerable further weakening of this flow into early
evening, with little eastward progression, as the low-level
circulation center of Sally only very slowly migrates
east-northeastward near the western Alabama/Florida state border
vicinity. However, despite these trends, the environment remains
potentially conducive to occasionally strengthening low-level
mesocyclones within and ahead of bands of convection to the east of
the circulation center. This may be accompanied by a risk for
tornadoes, particularly in any rapidly intensifying storms aided by
increasing inflow of boundary-layer CAPE on the order of 1000-2000
J/kg, in the peak late afternoon warmth.

..Kerr.. 09/16/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...JAX...TAE...

LAT...LON 31168491 31208470 31458351 30808292 29998360 30088407
30028477 30488471 30978482 31168491
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ACUS11 KWNS 180911
SWOMCD
SPC MCD 180910
WAZ000-ORZ000-181115-

Mesoscale Discussion 1705
NWS Storm Prediction Center Norman OK
0410 AM CDT Fri Sep 18 2020

Areas affected...Northwest Oregon...Far Southwest Washington

Concerning...Severe potential...Watch unlikely

Valid 180910Z - 181115Z

Probability of Watch Issuance...5 percent

SUMMARY...An isolated severe threat is expected to continue across
parts of northwest Oregon and may affect far southwest Washington as
well. Hail and strong wind gusts will be possible but the threat is
expected to be too marginal for weather watch issuance.

DISCUSSION...The latest surface analysis shows a narrow corridor of
maximized low-level moisture from south-to-north in the Willamette
Valley of northwestern Oregon. Surface dewpoints along this corridor
are in the lower 60s F, which is contributing to MLCAPE estimated by
the RAP in the 500 to 750 J/kg range. A small cluster of
thunderstorms is ongoing along the instability axis. These storms
have formed in response to a band of large-scale ascent that is
spreading northward across western Oregon according to the
water-vapor imagery and RAP 500 mb analysis. The storms are located
in moderate deep-layer shear. The latest WSR-88D VWP at Portland has
0-6 km shear near 35 kt with some speed shear in the mid-levels.
This combined with the instability should be enough for an isolated
severe threat over the next few hours. Hail and marginally severe
wind gusts may occur with the stronger rotating storms.

..Broyles/Edwards.. 09/18/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...SEW...PQR...

LAT...LON 45182201 45772216 46252249 46372272 46392277 46422318
46162360 45672375 45252368 44582342 44252300 44532227
45182201
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ACUS11 KWNS 211822
SWOMCD
SPC MCD 211822
TXZ000-212045-

Mesoscale Discussion 1706
NWS Storm Prediction Center Norman OK
0122 PM CDT Mon Sep 21 2020

Areas affected...portions of the middle and upper Texas Coast

Concerning...Severe potential...Watch unlikely

Valid 211822Z - 212045Z

Probability of Watch Issuance...20 percent

SUMMARY...A couple of brief tornadoes are possible through this
evening across the middle and upper Texas coastal vicinity. A
tornado watch does not appear likely at this time, given an overall
marginally supportive environment. However, trends will continue to
be monitored over the next several hours.

DISCUSSION...Stronger bands associated with T.S. Beta will continue
to move onshore near Galveston Bay of the next several hours. Radar
imagery over the last 30-60 minutes has shows some modest mid-to-low
level rotation in mini-supercells over the near-shore Gulf waters.
Most of this activity has been weak, with rotational velocity
signatures less than 20 kts. Overall, the environment appears only
weakly supportive for tornadoes. MLCAPE has increased marginally
along the coast, but is generally 500 J/kg or less. This is partly
due to the cloud shield from Beta limiting insolation, but also
partly due to lower surface dewpoints than would typically be
expected along the Texas coast ahead of a landfalling tropical
system. Low level shear has strengthened this afternoon, with VWP
data from KHGX indicating around 200 m2/s2 0-1 km SRH when corrected
for storm motion, though deep layer shear in only marginally
supportive of supercells. Given the overall modest environment,
expect weak supercell activity and associated waterspouts/tornadoes
to be short-lived and transient.

..Leitman/Guyer.. 09/21/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...HGX...

LAT...LON 28819516 28419575 28439610 28839642 29269641 29759582
29959529 29969489 29679446 29359439 29109457 28819516
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ACUS11 KWNS 241444
SWOMCD
SPC MCD 241444
FLZ000-ALZ000-241645-

Mesoscale Discussion 1710
NWS Storm Prediction Center Norman OK
0944 AM CDT Thu Sep 24 2020

Areas affected...western FL Panhandle into southern AL

Concerning...Severe potential...Watch unlikely

Valid 241444Z - 241645Z

Probability of Watch Issuance...20 percent

SUMMARY...A brief tornado or two is possible into the afternoon
hours. The overall threat should remain confined and rather
transient, and a watch is not expected at this time, but trends will
continue to be monitored.

DISCUSSION...A band of low level convergence across the western FL
Panhandle into southern AL is sustaining showers and thunderstorms
this morning. A warm front extends southeast from a surface low over
central MS to near the FL/AL border. Surface dewpoints in the low to
mid 70s are noted across the FL Panhandle. Pockets of clearing skies
is allowing temperatures to quickly warm into the upper 70s to 80s
along the immediate coast, and low to mid 70s further north toward
the FL/AL border. North of the warm front, denser cloud cover is
limiting heating, with temperatures generally in the mid 60s to near
70 F.

Near and south of the front, MLCAPE around 500-1200 J/kg in noted in
latest mesoanalysis. Southeasterly low level winds are also
enhancing low level shear, with 0-1 km SRH values around 150-250
m2/s2 noted in mesoanalysis fields as well as observed via regional
VWP data. Furthermore, modest 0-6 km shear around 30 kt will aid in
storm organization, though poor lapse rates and weakening shear with
eastward extent will likely limit longevity of strong cells,
maintaining more transient supercell structures. Given favorable low
level shear and a moist environment in the vicinity of the warm
front, a couple of brief tornadoes cannot be ruled out.

Given the narrow warm sector and transient nature of any low level
rotation, a watch is not immediately anticipated. Trends will
continue to be monitored into the afternoon. Some guidance suggests
the warm front may develop further northward than currently
expected, leading to a broader warm sector and potential threat
area. In the short term, the main threat for a brief tornado or two
will remain confined to a small portion of the western FL Panhandle.

..Leitman/Guyer.. 09/24/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...TAE...MOB...

LAT...LON 30928792 31288779 31488697 31388645 31228561 30558526
30128542 29788566 29898607 30118692 30108755 30248780
30928792
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ACUS11 KWNS 261629
SWOMCD
SPC MCD 261628
KSZ000-OKZ000-TXZ000-262030-

Mesoscale Discussion 1757
NWS Storm Prediction Center Norman OK
1128 AM CDT Mon Oct 26 2020

Areas affected...portions of north Texas into west-central Oklahoma
and far southeast Kansas.

Concerning...Freezing rain

Valid 261628Z - 262030Z

SUMMARY...Ongoing freezing rain and mixed precipitation is forecast
to continue for at least the next several hours. Ice and sleet
accumulation is likely.

DISCUSSION...1530z observations showed widespread freezing rain and
mixed precipitation ongoing across portions of north Texas and
west-central Oklahoma. To the southwest of the ongoing precipitation
shield, a new zone of elevated thunderstorms has developed in
response to continued mid-level warm air advection and isentropic
ascent ahead of a diffuse shortwave trough. The shallow arctic
airmass across much of Oklahoma is forecast to continue to gradually
creep southward through this afternoon. Model soundings show much of
the ongoing and developing precipitation will remain in an airmass
favorable for periods of freezing rain and mixed precipitation
types. While much of the heavier precipitation from the initial
shortwave trough earlier this morning will remain on the warmer side
of the boundary, the threat of icing and perhaps accumulating sleet
will likely continue for at least the next several hours.
Precipitation intensity is forecast to gradually decrease through
this afternoon as upper-level support wains behind the passage of
the initial shortwave trough. However, the saturated shallow arctic
airmass and weak mid-level warm advection will likely support light precipitation in the form of freezing mist or sleet through the
evening.

..Lyons/Thompson.. 10/26/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...SGF...TSA...ICT...OUN...SJT...LUB...AMA...

LAT...LON 34699757 33969850 33859859 33489935 33129994 33050056
33330067 34490022 35099969 36009872 37059715 37599616
37619584 37569539 37359502 37129498 36709536 36339584
35739648 35499668 35119704 34699757
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ACUS11 KWNS 151633
SWOMCD
SPC MCD 151633
PAZ000-NYZ000-OHZ000-151730-

Mesoscale Discussion 1798
NWS Storm Prediction Center Norman OK
1033 AM CST Sun Nov 15 2020

Areas affected...north-central and northeast OH...far northwest PA

Concerning...Severe potential...Watch possible

Valid 151633Z - 151730Z

Probability of Watch Issuance...40 percent

SUMMARY...A broken band of linear segments will potentially be
capable of isolated to widely scattered 55-70 mph gusts across
north-central into northeast OH through 2pm EST.

DISCUSSION...Radar imagery as of 1120am EST shows a broken band of thunderstorms near the I-75 corridor from Cincinnati north to
Toledo. Surface observations across northern OH show temperatures
in the mid 50s and surface dewpoints ranging from the upper 40s in
northeast OH to the lower 50s in central OH. Both ASOS at Lima, OH
and Findlay, OH recently observed measured 57-kt and 53-kt gusts
with the convective band.

Visible-satellite imagery shows a relatively narrow but significant
area of cloud breaks immediately ahead of the convective band from
southwest OH northward to west-central Lake Erie. The zone of cloud
breaks will likely shift eastward and be maintained due in part to
mid-level dry air (reference water-vapor imagery) wrapping
cyclonically through the base of the mid-level shortwave trough over
the Great Lakes.

Given the above mentioned factors influencing destabilization, it
appears at least 100-300 J/kg MLCAPE will probably develop northeast
from central OH into northeast OH during the next several hours.
Given the 60-kt flow at 2-km AGL at KCLE VAD, it seems plausible a
risk for severe thunderstorms will continue into north-central OH
during the next hour and eventually into northeast OH. It is more
uncertain whether a risk will eventually spread into parts of
northwest PA. However, some short-term CAM guidance does indicate a
low-topped convective band moves through this region this afternoon.

..Smith/Grams.. 11/15/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...BUF...CTP...PBZ...CLE...ILN...

LAT...LON 41458327 42128159 42437979 41787944 41267969 40608096
39908395 41458327
#
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ACUS11 KWNS 272238
SWOMCD
SPC MCD 272237
ALZ000-MSZ000-LAZ000-280030-

Mesoscale Discussion 1818
NWS Storm Prediction Center Norman OK
0437 PM CST Fri Nov 27 2020

Areas affected...Southeast Louisiana...southern Mississippi...and
southwest Alabama

Concerning...Severe potential...Watch unlikely

Valid 272237Z - 280030Z

Probability of Watch Issuance...20 percent

SUMMARY...Strong to severe winds, and perhaps a brief tornado, will
remain possible for portions of southeast Louisiana, southern
Mississippi, and far southwest Alabama as a line of thunderstorms
continues to push southeast and new convection develops along a warm
frontal zone.

DISCUSSION...Recent radar imagery from southeast LA, southern MS,
and southwest AL has shown shallow discrete convection developing
along a surface warm front that is draped from southern LA into
southern AL. These storms should remain relatively discrete, and
strong deep layer shear has allowed for a few storms to take on
supercell characteristics. Additionally, transient, but weak,
velocity couplets have been noted with this activity, and given
around 150 m2/s2 0-3 km SRH (per the KMOB and KLIX VWPs) along with
ambient surface vorticity along the warm front, a brief tornado
associated with this activity appears possible over the next few
hours.

To the west, a line of storms continues to push to the southeast
into southern and southeastern LA. The environment ahead of this
line continues to feature ample (around 50 knots) deep layer shear
and sufficient instability (500-1000 J/kg MLCAPE), suggesting that
storm organization and intensification remains possible - especially
for segments of the line that can become more meridionally oriented
and normal to the deep shear vector. However, this potential may be
limited spatially as the storms begin to exit LA into the northern
Gulf. Increasing inhibition with the onset of diurnal cooling within
the next 2-3 hours may also limit the severe potential. Given these
concerns a watch is not anticipated.

..Moore/Grams.. 11/27/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...MOB...JAN...LIX...LCH...

LAT...LON 30169246 30469181 30589100 30759011 31008965 31278877
31338813 31168778 30788782 30428796 30308840 30188912
29908922 29578971 29349031 29319095 29459165 29639213
29849242 30169246
#
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ACUS11 KWNS 022157
SWOMCD
SPC MCD 022157
OKZ000-KSZ000-TXZ000-030200-

Mesoscale Discussion 1829
NWS Storm Prediction Center Norman OK
0357 PM CST Wed Dec 02 2020

Areas affected...Portions of far northwestern Oklahoma...far
southwestern Kansas

Concerning...Heavy snow

Valid 022157Z - 030200Z

SUMMARY...Moderate to heavy snow is expected to continue into the
evening hours, with up to 1 inch/hr rates possible in some of the
heavier bands.

DISCUSSION...MRMS regional radar imagery has shown a recent uptick
in precipitation intensity across portions of northern OK, with up
to 40 dBZ reflectivity values noted on the 0.5 degree tilt mosaics
(mainly over Alfalfa/Grant Counties in northern OK). In addition,
increasing snowfall rates have been noted by KLBL/KGAG METARs. As a
500 mb low slowly moves eastward, a belt of 925-700 mb
warm-air/moisture advection continues to pivot around the northern
side of the low, promoting adequate moisture and deep-layer ascent
to support additional moderate to heavy wintry precipitation. The
21Z Mesoanalysis depicts near saturation of an 800+ m deep -12 to
-17C dendritic growth zone over far northwest Oklahoma, where
efficient snowfall production is possible. Mesoanalysis trends over
the past few hours have also shown a westward advection of around
100 J/kg MUCAPE towards northwest OK. As such, some slantwise
convection supporting locally higher snowfall rates (up to 1 inch/hr
in some cases) is also possible, especially given the aforementioned
low-level warm air advection. 12Z HREF suggests that 1 inch/hr
snowfall rates would be most likely across far northwestern OK,
mainly within the 23-04Z period.

..Squitieri.. 12/02/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...OUN...DDC...AMA...

LAT...LON 36350113 37060118 37240078 37259971 37169894 36619877
36309896 36079965 36090033 36350113
#
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ACUS11 KWNS 041937
SWOMCD
SPC MCD 041937
GAZ000-FLZ000-042200-

Mesoscale Discussion 1832
NWS Storm Prediction Center Norman OK
0137 PM CST Fri Dec 04 2020

Areas affected...Portions of the FL Panhandle and far southwestern
GA

Concerning...Severe potential...Watch unlikely

Valid 041937Z - 042200Z

Probability of Watch Issuance...5 percent

SUMMARY...Isolated strong/gusty winds and perhaps a brief tornado
may occur with a line of storms this afternoon. Watch issuance is
not expected at this time.

DISCUSSION...A low-topped line of showers with occasional embedded
lightning has shown signs of weak low-level rotation and modest
organization across parts of the FL Panhandle early this afternoon.
Low-level moisture return ahead of this convection has remain muted,
with low 60s surface dewpoints having advanced as far north as the
FL/GA line vicinity. Combined with poor mid-level lapse rates, this
modest low-level moisture is limiting instability over land so far.
Still, with weak diurnal heating occurring amid some breaks in a low
stratus deck ahead of the line, up to 250-500 J/kg of MLCAPE may
ultimately develop by peak afternoon heating in a couple of hours
across the warm sector, with slightly greater instability present
with southward extent (near Apalachicola).

The VAD wind profile from KTLH shows veering/strengthening with
height through mid levels in association with an approaching
shortwave trough over the Mid-South. Enough mid-level flow is
present to support around 35-40 kt of effective bulk shear, which
will continue to encourage storm organization. At this point, it
appears that the weak instability will serve as the primary factor
acting to limit a greater severe threat across parts of the FL
Panhandle and far southwestern GA this afternoon. Even so, isolated strong/gusty winds may occur with the line through convective
downdraft processes. A brief tornado also cannot be ruled out, as
around 100-200 m2/s2 of effective SRH should be present across the
warm sector. With the overall severe threat expected to remain
rather isolated/marginal, watch issuance is not anticipated at this
time.

..Gleason/Dial.. 12/04/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...TAE...

LAT...LON 30148410 29808442 29538501 29618540 29998560 30258586
30638567 31018491 31108457 31148425 31068400 30678392
30148410
#
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ACUS11 KWNS 051252
SWOMCD
SPC MCD 051252
MEZ000-NHZ000-MAZ000-CTZ000-VTZ000-051645-

Mesoscale Discussion 1834
NWS Storm Prediction Center Norman OK
0652 AM CST Sat Dec 05 2020

Areas affected...Northern CT to southwest ME

Concerning...Heavy snow

Valid 051252Z - 051645Z

SUMMARY...Moderate rain will transition to heavy snow with rates
likely reaching 1-2 in/hr through midday.

DISCUSSION...12Z surface analysis places a cyclone just off the DE
coast which is expected to undergo pronounced deepening on its
approach towards Cape Cod through this afternoon. As this occurs,
850-mb winds will strengthen on the backside of the cyclone as well
as gradually back from northeast to north and increase low-level
cold advection. This will be coupled with further cooling from
intense upward vertical motion and likely yield a rapid changeover
to heavy snow. This process should occur first in the central
MA/Worcester vicinity just to the west of the pronounced bright band
evident on KBOX radar, and then rapidly increase in areal coverage
(mainly to the northeast) through midday. Deep, nearly isothermal
thermodynamic profiles beneath the dendritic growth zone that is
between 600-500 mb should yield large aggregates capable of
producing 1-2 in/hr snow rates, that could locally reach 2-3 in/hr
towards early afternoon. These rates are broadly supported by 09Z
SREF and 00Z HREF guidance.

..Grams.. 12/05/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...GYX...BOX...ALY...

LAT...LON 42227312 43027253 44017125 44367055 44427023 44227006
43867030 43117103 42507146 42057186 41727277 41907326
42227312
#
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ACUS11 KWNS 051657
SWOMCD
SPC MCD 051657
MEZ000-NHZ000-MAZ000-052300-

Mesoscale Discussion 1835
NWS Storm Prediction Center Norman OK
1057 AM CST Sat Dec 05 2020

Areas affected...Central Massachusetts...New Hampshire...western
Maine

Concerning...Heavy snow

Valid 051657Z - 052300Z

SUMMARY...Heavy snow will continue to develop today with the
heaviest rates of 1-2 in/hr expected from New Hampshire into western
Maine.

DISCUSSION...Temperature profiles are on the warm side over much of
the area as of 17Z, but precipitation has changed to snow especially
above 1000 ft. As deep frontogenetical forcing northwest of the
surface low persists and shifts slowly north, the heavier
precipitation will continue to cool the column, with rain changing
to snow, especially in the higher elevations of NH into western ME.
Hourly liquid-equivalent rates of 0.10 to 0.25 have already been
measured near the bright-banding areas, suggesting 1 to 2 in/hr
rates will be possible.

..Jewell.. 12/05/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...CAR...GYX...BOX...

LAT...LON 46196973 46376908 46236877 45626876 44816939 44337001
43877060 43327103 42997128 42647166 42607201 42727216
43007214 44217165 44867119 46196973
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ACUS11 KWNS 161857
SWOMCD
SPC MCD 161857
PAZ000-MDZ000-VAZ000-WVZ000-170000-

Mesoscale Discussion 1854
NWS Storm Prediction Center Norman OK
1257 PM CST Wed Dec 16 2020

Areas affected...Northeast West Virginia...northern
Virginia...western Maryland...and central to eastern Pennsylvania

Concerning...Heavy snow

Valid 161857Z - 170000Z

SUMMARY...Heavy snowfall rates around 2 inches per hour are expected
to increase in coverage through the mid to late afternoon hours
across portions of the Mid-Atlantic. Heavy snowfall will likely
continue into the overnight hours for portions of
eastern/northeastern Pennsylvania.

DISCUSSION...Precipitation continues to gradually increase in
coverage across much of the Mid-Atlantic region within a broad swath
of strong warm air advection between 850-700 mb (per recent RAP
soundings and mesoanalysis). Mixed precipitation types continue to
be reported within the precipitation transition zone along the
Roanoke to Fredericksburg, VA line. While a wintry mix, including
pockets of freezing rain, will continue in the near term, this zone
should become more limited spatially through the mid/late afternoon
hours. Further north, moderate, to at times heavy, snowfall rates
have been observed (as evidenced by visibility reductions to
one-quarter mile and observed snow rates around 2 inches per hour
for some locations in northeast WV).

Heading through the afternoon, the low that is currently advancing
northward along the Carolina coast will continue to deepen. As this
occurs, mid-level winds will strengthen and begin to tighten the
850-700 mb baroclinic zone and augment warm advection across the
region. As isentropic and frontogenetical lift increase, snowfall
rates will see a corresponding uptick in intensity. Lift within the
dentritic growth zone and weak instability closer to the coast will
help further augment snowfall rates. Widespread snowfall rates above
1 inch per hour over the region are likely, and the potential for
widespread snowfall rates exceeding two inches per hour will
increase through 00 UTC as the potential for organized frontogenetical/deformation-driven snow bands increases.

..Moore.. 12/16/2020

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...PHI...BGM...CTP...LWX...

LAT...LON 39387921 40367890 40907814 41177723 41227627 41087554
40717526 40257540 39857630 39497679 39097723 38737763
38477811 38707904 39387921
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ACUS11 KWNS 231342
SWOMCD
SPC MCD 231342
MNZ000-SDZ000-NDZ000-231845-

Mesoscale Discussion 1863
NWS Storm Prediction Center Norman OK
0742 AM CST Wed Dec 23 2020

Areas affected...eastern SD...west-central MN

Concerning...Heavy snow

Valid 231342Z - 231845Z

SUMMARY...Occasional heavier bursts of snow with rates near 1 inch
per hour are expected to begin this morning into the midday.

DISCUSSION...Radar mosaic shows a band of moderate to locally heavy
snow over parts of eastern SD into far southeast ND as of 745am CST.
Short-term models indicate this zone of heavier snow is associated
with frontal forcing in the 850-700 mb layer. As a mid-level
shortwave trough over the north-central Great Plains moves eastward
today, strengthening low- to mid-level ascent will support moderate
to occasionally heavy snow with rates around 1 inch per hour during
the heavier periods. The onset of heavier snow near the MN/SD
border is expected later this morning (10am-12pm). Strong sustained
winds (25-35 mph) with higher gusts and reduced visibility's within
the heavier bursts may yield intermittent, marginal blizzard
conditions.

..Smith.. 12/23/2020

ATTN...WFO...MPX...FGF...FSD...ABR...

LAT...LON 43949847 46039662 46219562 45539561 43559680 43289747
43369809 43949847
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ACUS11 KWNS 231539
SWOMCD
SPC MCD 231538
MNZ000-IAZ000-NEZ000-SDZ000-232045-

Mesoscale Discussion 1864
NWS Storm Prediction Center Norman OK
0938 AM CST Wed Dec 23 2020

Areas affected...Mid-MO Valley to central MN

Concerning...Blizzard

Valid 231538Z - 232045Z

SUMMARY...Blizzard conditions will spread east across portions of
the Mid-Missouri Valley north-northeast into southwest and central
Minnesota through mid-afternoon. Bursts of heavier snow with rates
of 1-1.5 in/hr is expected just ahead of the blizzard across
northwest Iowa through central Minnesota.

DISCUSSION...Widespread blizzard conditions are ongoing across a
swath of the northern Great Plains to Upper Midwest, centered on central/northern NE north-northeast into west-central/northwest MN.
Numerous observation sites within this corridor have measured 40-55
kt strong to severe gusts for several hours. As a 990-mb cyclone in
far north-central IA slowly deepens while tracking towards
west-central WI, a very tight surface pressure gradient should
become centered on the Mid-MO Valley to central MN during the 18-21Z
period amid 60+ kt 850-mb winds. In addition, falling surface
temperatures will be common through the afternoon with intense cold
air advection.

A swath of probable moderate to heavy snow will persist just ahead
and accompany the leading plume of blizzard conditions, likely
becoming centered on the Spencer, IA to Saint Cloud, MN corridor by
20-21Z. Steep mid-level lapse rates (around 8 C/km from 700-500 mb)
along the northern periphery of an elevated mixed layer, as sampled
by 12Z regional soundings will support embedded convective bursts of
heavier snow around 1-1.5 in/hr.

..Grams.. 12/23/2020


ATTN...WFO...DLH...MPX...DMX...FGF...FSD...OAX...ABR...

LAT...LON 45679586 46409528 46759498 46819400 46499366 46169366
45549369 44279419 43129474 42569532 42329603 42329665
42529713 43209725 44779632 45679586
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