SPC MD 1874


MD 1874 Image

Mesoscale Discussion 1874
NWS Storm Prediction Center Norman OK
1211 PM CST Thu Dec 24 2020

Areas affected...Central/eastern FL Panhandle and southwest GA

Concerning...Severe potential...Watch unlikely 

Valid 241811Z - 241945Z

Probability of Watch Issuance...20 percent

SUMMARY...The threat for locally damaging winds and a brief tornado
will exist along a pre-frontal QLCS that should progress east from
the central to the eastern FL Panhandle and southwest GA. The
magnitude of these threats are expected to be small enough to
preclude a weather watch issuance in the near-term, but
observational trends will continue to be monitored.

DISCUSSION...The northern portion of a short QLCS depicted some
organized structure in radar reflectively as it moved onshore in
Gulf County, FL with overshooting CB tops in 1-min visible satellite
imagery, before waning farther inland. The KTLH VWP continues to
sample 50-60 kt southwesterlies through the 1-3 km AGL layer.
However, the boundary layer has struggled to warm greatly in this
portion of the Panhandle and southwest GA with surface temperatures
holding from 65-70 F. This suggests strong gusts capable of
localized tree damage should be the primary hazard with the line.

Convection just east of the Tallahassee area has shown broad and
weak low-level rotation at times. This activity remains on the
leading edge of surface-based buoyancy, which will likely limit
potential for more sustained supercell development. The overall
tornado threat may remain low this afternoon.

..Grams/Guyer.. 12/24/2020

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


LAT...LON   30478480 30778456 31018433 31068418 31268400 31248319
            30918293 30278319 29998338 29848395 29688476 29688515

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SPC MD 1806


MD 1806 Image

Mesoscale Discussion 1806
NWS Storm Prediction Center Norman OK
0837 PM CST Sun Nov 15 2020

Areas affected...Portions of Long Island New
York...Connecticut...Massachusetts...Rhode Island

Concerning...Severe Thunderstorm Watch 512...

Valid 160237Z - 160430Z

The severe weather threat for Severe Thunderstorm Watch 512

SUMMARY...The severe threat continues across Severe Thunderstorm
Watch 0512. Damaging gusts are expected to accompany a fast-moving
squall line to the Atlantic coastline.

DISCUSSION...A progressive squall line, with 18 dBZ echo tops
occasionally exceeding 25 kft, continues to pose a damaging wind
threat across portions of southern New England. Numerous
damaging/measured severe gusts have been noted farther west across
southeast New York into New Jersey over the past couple of hours.
Strong low-level Warm air advection continues ahead of the squall,
fostering up to 250 J/kg MUCAPE (mainly within the 850-500 mb
layer), as shown by the latest Mesoanalysis and RAP forecast
soundings. Though buoyancy is mediocre, 50+ kt 925-850 mb wind
fields are in place, and any downward momentum transport that occurs
with the more pronounced downdrafts will support damaging gusts. The
squall is expected to maintain intensity while on land, and is
expected to move out into the Atlantic over the next 2-3 hours.

..Squitieri/Thompson.. 11/16/2020

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


LAT...LON   40457391 41437333 42277328 42777309 42847214 42867121
            42807071 42487036 41986994 41677008 41337048 40747197

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SPC MD 1804


MD 1804 Image

Mesoscale Discussion 1804
NWS Storm Prediction Center Norman OK
0552 PM CST Sun Nov 15 2020

Areas affected...far eastern Pennsylvania...eastern
Maryland...Delaware...New Jersey

Concerning...Severe Thunderstorm Watch 511...

Valid 152352Z - 160145Z

The severe weather threat for Severe Thunderstorm Watch 511

SUMMARY...The threat for damaging gusts continues across Severe
Thunderstorm Watch 0511. Damaging gusts will be primarily associated
with a line of storms.

DISCUSSION...A low-topped squall line is currently moving across
eastern PA and northeast MD, with a history of at least scattered
wind damage from Cumberland to Lebanon and Lancaster Counties in PA,
down to Frederick County MD. Storm tops barely reach 25 kft, and the
anticipated line is expected to continue in an ambient thermodynamic
environment characterized by surface temperatures exceeding 60F and
very marginal buoyancy (with the latest RAP forecast soundings
showing 100-150 J/kg MUCAPE, mainly within the 850-600 mb layer).
Despite the weak, elevated instability, very strong forcing for
ascent and intense low-level wind fields suggest that any downward
momentum transport would support damaging gusts with the more mature
segments of the squall. The damaging wind threat is expected to
continue until the squall moves offshore, which will likely be
within the next 2.5-3.5 hours.

..Squitieri/Thompson.. 11/15/2020

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


LAT...LON   38617500 38537632 38687733 38917813 39707706 40667612
            41397569 41487488 41367427 40987403 40507387 39787390
            39397419 38937458 38617500 

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SPC Nov 2, 2020 0830 UTC Day 3 Severe Thunderstorm Outlook

SPC 0830Z Day 3 Outlook

Day 3 Outlook Image

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
1232 AM CST Mon Nov 02 2020

Valid 041200Z - 051200Z


Severe thunderstorms are not forecast across the contiguous United
States on Wednesday.

A low-amplitude upper-air pattern is forecast across the Lower 48 on
Wednesday.  A powerful upper jet is forecast to nose into the
Pacific Northwest on Wednesday.  Showers and isolated convective
showers are likely for coastal WA into the northern Cascades.  A few
lightning flashes may occur with the deeper convective showers. 
Elsewhere, generally dry/stable conditions will prevail across much
of the CONUS and preclude thunderstorm development.  The exception
may be far south FL where a couple of showers/thunderstorms could
develop during the day.

..Smith.. 11/02/2020

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SPC Nov 2, 2020 0700 UTC Day 2 Convective Outlook

SPC 0700Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1209 AM CST Mon Nov 02 2020

Valid 031200Z - 041200Z


Severe thunderstorms are not forecast for the contiguous United
States on Tuesday.

A mid-level ridge initially over the High Plains Tuesday morning
will deamplify as a zonal-flow regime encompasses much of the Lower
48.  A weak mid-level trough will move across the southern NV/UT
vicinity during the period while a series of disturbances move
across the northwestern CONUS.  A few thunderstorms are possible
over parts of UT on Tuesday in association with the weakening
mid-level trough.  Elsewhere, relatively dry/stable conditions will
preclude thunderstorm development.

..Smith.. 11/02/2020

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SPC MD 1761


MD 1761 Image

Mesoscale Discussion 1761
NWS Storm Prediction Center Norman OK
1101 AM CDT Tue Oct 27 2020

Areas affected...Eastern Kansas and far western Missouri

Concerning...Freezing rain 

Valid 271601Z - 271830Z

SUMMARY...Light to moderate freezing rain will be possible through
the late morning hours for east/southeast Kansas and into far
western Missouri.

DISCUSSION...Regional radar trends show a broad region of
precipitation moving from northern OK into southeast KS and western
MO. Surface temperatures across this area are largely in the upper
20s and low 30s. Aloft, morning regional soundings as well as recent
RAP forecast soundings show a 3-5 C warm nose between 800-700 mb
that is fostering a mixture of freezing rain along with some sleet -
as supported by recent surface observations and mPING reports across
the area. Although most forecast guidance shows temperatures
climbing above freezing by early afternoon, the onset of
precipitation prior to this warm up will allow for at least a couple
hours of light to perhaps moderate freezing rain and sleet.
Temperature trends will be monitored through the day for the
expected warm up, which, if delayed, could result in a prolonged
period of freezing rain.

..Moore.. 10/27/2020

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


LAT...LON   39139593 39559556 39739487 39449444 38969425 38609428
            38019436 37369467 37039517 37059559 37089607 37349629
            37939615 38489603 39139593 

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SPC MD 1760


MD 1760 Image

Mesoscale Discussion 1760
NWS Storm Prediction Center Norman OK
0840 AM CDT Tue Oct 27 2020

Areas affected...Northwest Texas...central and western
Oklahoma...and far southern Kansas

Concerning...Freezing rain 

Valid 271340Z - 271745Z

SUMMARY...Freezing rain and sleet will continue from central
Oklahoma into the eastern Texas Panhandle through the remainder of
the morning.

DISCUSSION...Recent mPING reports from central OK and northwest
Texas indicate that freezing rain with embedded pockets of sleet
continue to overspread the region. The recent 12 UTC Norman, OK
sounding reveals a 7-8 C warm nose between 800-700 mb on top of a ~1
km deep sub-freezing level (with a minimum temperature near -6 C).
This thermodynamic profile supports the observed precipitation
trends, and with little change expected in the next few hours,
should continue to favor freezing rain with embedded sleet. The
strong 850-700 mb isentropic ascent that is the primary forcing of
this morning's precipitation is expected to persist into the early
afternoon hours, especially across central OK per recent guidance.
This will also act to reinforce the warm nose aloft and continue to
support freezing rain. Although models do show a signal for surface
temperatures to warm just above freezing by around 18 UTC for
central OK, there is some uncertainty in the temperature forecast
given widespread cloud cover, persistent northerly winds/weak cold
advection at the surface, and only modest warm advection at around
925 mb. As such, confidence in ice accumulations will remain highest
along and west of the I-44 corridor where precipitation along the
mid-level warm front is most likely to overlap with sub-freezing
surface temperatures through the early afternoon. Due to the early
timing of this winter storm, fall foliage remains on most trees,
which when combined with ice accumulation and 10-15 mph surface
winds will increase the potential for widespread power outages
through the day.

..Moore.. 10/27/2020

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


LAT...LON   35860061 36839954 37339883 37819762 37999674 37679610
            37019568 36269616 35329695 34959710 34199742 33699837
            33339891 33309939 33510018 33840067 34530084 35370079

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SPC Oct 27, 2020 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0748 AM CDT Tue Oct 27 2020

Valid 271300Z - 281200Z


Severe thunderstorms are not expected across the contiguous United
States through tonight.

The main upper-air feature influencing this period's forecast is a
well defined synoptic-scale cyclone, currently centered over
southern AZ per moisture-channel imagery.  The associated 500-mb low
is forecast to pivot roughly eastward and reach southwestern NM by
00Z, then move to near ROW by 12Z tomorrow.  An extensive fetch of
cyclonic flow aloft will accompany this feature from the
southeastern Great Basin and Colorado Plateau across northern MX,
the southern Rockies, and the southern Great Plains.

At the surface, 11Z analysis showed a wavy, quasistationary frontal
zone across northern FL, extreme southeastern LA, and the TX shelf
waters of the Gulf.  A slow-moving but strong cold front was drawn
from the southern Appalachians across western MS, western LA, the
middle TX coastal waters, and deep south TX, merging with part of
the southern baroclinic zone over the northwestern Gulf.  The
western Gulf part of the combined boundary will move little for most
of the period, while the eastern part remains stationary to
northward drifting.

...Southern Plains...
Large-scale forcing for ascent (elevated low-level warm advection
already in place at first, then DCVA aloft shifting in from the
west), juxtaposed with a favorable corridor of moisture transport,
will spread eastward over the southern Plains through the period. 
These will contribute to multiple episodes of thunderstorms rooted
atop the elevated frontal surface, beginning with the ongoing widely
scattered thunderstorms embedded in a large area of convective
precip offering winter mixed precip across parts of OK and northwest
TX.  Another major precip episode in the form of a coarsely north-
south convective plume is likely late overnight across northwest,
central and north-central TX into OK, also containing sporadic
thunder. By that time, isolated thunderstorms may also begin across
east TX and the Arklatex region, in a moistening regime of marginal
buoyancy between the southern Plains plume and the Gulf activity
discussed below.

...Gulf Coast States, Southeast...
Tropical Storm Zeta (as of this writing) is forecast by NHC to
reinvigorate to hurricane strength over the Gulf north of the
Yucatan Peninsula today, its path curving toward a day-2 landfall
across the southeastern LA area.  Associated wind fields favorable
for potentially tornadic supercells are expected to remain offshore
through this period, but will affect portions of the Gulf Coast east
of its track on Wednesday; see the SPC day-2 convective outlook for
more details.

In the meantime, the boundary-layer response to the approaching
hurricane -- and indirectly, the ejecting Southwestern cold-core
cyclone -- will foster early stages of an inland spread of
increasingly well-modified return-flow air, both at and above the
surface.  This will support at least isolated general thunder
potential over a broad swath of the Gulf Coast States and Southeast,
in addition to antecedent potential across the FL Peninsula. 
Weaknesses of lapse rates, buoyancy and shear will preclude
organized severe.  See NHC advisories for latest track/intensity
guidance and tropical watches/warnings related to Zeta.

..Edwards/Mosier.. 10/27/2020

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SPC Oct 27, 2020 Day 4-8 Severe Weather Outlook

Day 4-8 Outlook

Day 4-8 Outlook Image

Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0332 AM CDT Tue Oct 27 2020

Valid 301200Z - 041200Z

A quiescent period for severe thunderstorms will begin on Friday
(day 4) and continue through next Tuesday (day 8) as the large-scale
upper-air pattern features a mean trough over the eastern U.S. for
much of the extended period.  Dry offshore flow will occur over the
Gulf of Mexico through the period and lead to hostile conditions for
thunderstorm development.

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SPC Oct 27, 2020 0730 UTC Day 3 Severe Thunderstorm Outlook

SPC 0730Z Day 3 Outlook

Day 3 Outlook Image

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0208 AM CDT Tue Oct 27 2020

Valid 291200Z - 301200Z


A conditional risk for a tornado may exist Thursday morning for
adjacent parts of Alabama, Georgia, and the Florida Panhandle in
association with tropical cyclone Zeta.  An isolated threat for
damaging thunderstorm gusts may develop over the Carolinas and
southern Virginia Thursday night.

A fairly complex scenario with relative higher uncertainty is
forecast for the day 3 period over the Southeast into the Carolinas
and VA.  Tropical cyclone Zeta will move from the AL/GA vicinity
west of Atlanta and accelerate rapidly northeastward reaching
Chesapeake Bay by early Thursday evening according to the latest
National Hurricane Center forecast.  The risk for a tornado may
linger during the morning from parts of the FL Panhandle
northeastward into central GA before low-level flow veers as Zeta
becomes increasingly displaced from the region.  Only marginal
instability is expected to penetrate the areas north of the
immediate coastal counties with less-available instability farther
north into southwest GA.  Nonetheless, a conditional risk for a
supercell or two capable of a tornado could continue from the late
Day 2 period into Day 3 across this region.  

By early evening, a mid-level low will open and feature a
strengthening jet (100 kt at 500 mb) moving from northern AL
northeastward across the Carolinas into southeast VA by early Friday
morning.  Significant mid-level height falls (120-180 m at 500 mb)
will overspread central NC Thursday night.  Concurrently, a cold
front is forecast to sweep eastward across the southern Appalachians
with intensifying frontal forcing in lee of the higher terrain. 
Model guidance currently indicates a moist boundary layer will
become conditionally unstable with a cluster or band of storms
potentially developing after dark.  The transport of higher momentum
aloft to the surface could materialize with a risk for damaging

..Smith.. 10/27/2020

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