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

...NO SEVERE THUNDERSTORM AREAS FORECAST...

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

...Synopsis...
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

...NO SEVERE THUNDERSTORM AREAS FORECAST...

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

...Synopsis...
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 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

...NO SEVERE THUNDERSTORM AREAS FORECAST...

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

...Synopsis...
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

...DISCUSSION...
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

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
SOUTHEAST AND VIRGINIA...

...SUMMARY...
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.

...Synopsis...
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
gusts.

..Smith.. 10/27/2020

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SPC Oct 27, 2020 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1240 AM CDT Tue Oct 27 2020

Valid 271200Z - 281200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not expected across the contiguous United
States on Tuesday.

...Discussion...

Early-morning water-vapor imagery depicts a well-defined upper low
moving south toward the AZ/Mexico border. This feature is forecast
to begin advancing east along the international border later this
morning, then into extreme southwest NM by late afternoon. Very cold
continental surface high has settled into the central Plains with
the leading edge of this air mass now to the coastal plain of TX.
Latest model guidance continues to suggest low-level warm advection
will focus along a corridor from the Edwards Plateau-northwest
TX-central OK. This zone will be the primary area of concern for
elevated convection through the period.

Currently, the leading edge of large-scale forcing for ascent
appears to be spreading across the southern Rockies into far west
TX, per moistening observed at mid levels in water vapor imagery.
Scattered showers are now developing across the southern High Plains
in response, and these showers should eventually deepen sufficiently
for lightning. Much of this activity will develop atop sub-freezing
boundary-layer temperatures and significant icing may ultimately be
noted along the aforementioned corridor.

Farther southeast across the Gulf Coast region, a strong mid-level
Bermuda high will forcing deep southerly trajectories across the
Gulf Basin ahead of Hurricane Zeta. While Zeta will not reach the
central Gulf Coast during the day1 period, moisture will begin to
spread inland such that isolated thunderstorms will be possible,
despite the poor low-level lapse rates and overall weak buoyancy.

..Darrow.. 10/27/2020

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SPC Oct 27, 2020 0600 UTC Day 2 Convective Outlook

SPC 0600Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1226 AM CDT Tue Oct 27 2020

Valid 281200Z - 291200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR FAR SOUTHERN
ALABAMA AND THE WESTERN FLORIDA PANHANDLE...

...SUMMARY...
A couple tornadoes are possible beginning Wednesday afternoon
through Wednesday night over parts of the central Gulf Coast states
in association with Zeta.

...Central Gulf Coast...
Tropical cyclone Zeta will approach the coast and subsequently move
inland during the period.  The influx of a tropical airmass
(characterized by mid 70s surface dewpoints) will gradually spread
inland over southeast LA and the immediate coastal areas of MS/AL/FL
Panhandle during the day.  Forecast soundings show hodographs
enlarging initially over southeast LA and later along the MS/AL/FL
Panhandle coasts by late afternoon.  Sufficient buoyancy and
enlarged hodographs (0-1 km SRH 300-600 m2/s2) will probably yield
the development of several mini supercells in the outer bands of
Zeta.  It appears the greatest tornado risk will be confined to far
southern AL and the FL Panhandle where larger CAPE (500-1000 J/kg)
and SRH will spatiotemporally overlap.  Considerable uncertainty
remains how far inland a low/conditional supercell-tornado risk will
develop late overnight (i.e., east-central AL and adjacent parts of
GA).

..Smith.. 10/27/2020

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SPC Oct 27, 2020 0100 UTC Day 1 Convective Outlook

SPC 0100Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0740 PM CDT Mon Oct 26 2020

Valid 270100Z - 271200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Organized severe thunderstorms are not expected across the
contiguous U.S. through tonight.

...01z Update...

Minor changes have been made to the 20z outlook this evening, namely
to lower thunder probabilities across most of the FL Peninsula.
Earlier convection that developed across the southwestern portions
of the Peninsula have propagated northwest with most lightning now
offshore. 01z product will reflect this evolution.

Farther west across the south-central US, isentropic ascent atop
cold boundary layer will be the primary forcing mechanism for
elevated convection later tonight. Earlier thunderstorm activity
that developed across the southern Plains has moved into the Ozark
Plateau region and weakened with minimal lightning observed.
However, buoyancy remains across the southern Plains and the next
short-wave trough will approach this region after midnight. At that
time, renewed thunderstorm activity is expected.

..Darrow.. 10/27/2020

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SPC Oct 26, 2020 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0244 PM CDT Mon Oct 26 2020

Valid 262000Z - 271200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Organized severe thunderstorms are not expected across the
contiguous U.S. through tonight.

...20Z Update...
No major changes have been made to the ongoing forecast. Isolated to
scattered elevated thunderstorms will remain possible across parts
of the southern Plains into the Ozarks through tonight.

..Gleason.. 10/26/2020

.PREV DISCUSSION... /ISSUED 1108 AM CDT Mon Oct 26 2020/

...Southern Plains through Tuesday morning...
A shallow, cold air mass continues to move southward across central
TX.  Bands of elevated thunderstorms (some producing freezing rain
and sleet) are ongoing in association with warm advection and
frontogenesis in the 850-700 mb layer atop the frontal surface.  The
larger buoyancy aloft and stronger forcing for ascent are expected
to shift gradually southeast of the I-44 corridor in OK through this
afternoon into this evening.  Elevated convection should again
increase over northwest TX and spread northeastward into OK in
response to speed maxima ejecting northeastward in advance of the
closed mid-upper low forming over AZ.  Much of this convection after
06z will produce substantial sleet and freezing rain accumulations
where boundary-layer temperatures will be below 32F (along and
northwest of I-44).

...South FL this afternoon...
Daytime heating within a maritime tropical air mass will support
scattered diurnal thunderstorm development along and south of a weak
front across central FL.  The convection will be a little more
concentrated in the deeper moist profiles across southwest FL.

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SPC Oct 26, 2020 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1108 AM CDT Mon Oct 26 2020

Valid 261630Z - 271200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Organized severe thunderstorms are not expected across the
contiguous U.S. through tonight.

...Southern Plains through Tuesday morning...
A shallow, cold air mass continues to move southward across central
TX.  Bands of elevated thunderstorms (some producing freezing rain
and sleet) are ongoing in association with warm advection and
frontogenesis in the 850-700 mb layer atop the frontal surface.  The
larger buoyancy aloft and stronger forcing for ascent are expected
to shift gradually southeast of the I-44 corridor in OK through this
afternoon into this evening.  Elevated convection should again
increase over northwest TX and spread northeastward into OK in
response to speed maxima ejecting northeastward in advance of the
closed mid-upper low forming over AZ.  Much of this convection after
06z will produce substantial sleet and freezing rain accumulations
where boundary-layer temperatures will be below 32F (along and
northwest of I-44).

...South FL this afternoon...
Daytime heating within a maritime tropical air mass will support
scattered diurnal thunderstorm development along and south of a weak
front across central FL.  The convection will be a little more
concentrated in the deeper moist profiles across southwest FL.

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

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