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 Day 1 Fire Weather Outlook

SPC Day 1 Fire Weather Outlook

Day 1 Fire Weather Outlook Image

Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
1140 AM CDT Mon Oct 26 2020

Valid 261700Z - 271200Z

...EXTREMELY CRITICAL FIRE WEATHER AREA FOR PORTIONS OF THE SOUTHERN
TRANSVERSE RANGES IN SOUTHERN CALIFORNIA...
...CRITICAL FIRE WEATHER AREA FOR PARTS OF SOUTHERN CALIFORNIA...
...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF NORTHERN AND CENTRAL
CALIFORNIA...
...CRITICAL FIRE WEATHER AREA FOR PARTS OF SOUTHERN NEVADA INTO THE
COLORADO RIVER BASIN...

Current visible satellite depicts clear skies across California and
the Great Basin, allowing for ample boundary-layer heating and
continued mixing. As such, near-critical to critically low RH is
expected to persist across much of California into the southern
Great Basin through the day. Current METAR observations depict 20-30
mph sustained winds, with higher gusts from the Sacramento Valley in
northern California, down to the southern Transverse Ranges in
southern California and eastward into the Colorado River Basin. In
addition, 60-80 kt mid-level flow continues to overspread California
into Nevada. Upper support, downslope flow, and downward momentum
transport of the stronger mid-level flow will continue to foster
strong northerly/offshore flow across portions of the Sacramento/San
Joaquin Valleys and the southern Transverse Ranges in California
through the day, as also suggested by the latest model guidance
consensus. Critical/Extremely Critical Highlights have been
maintained across California, although widespread Extremely Critical
conditions in the southern Transverse ranges may gradually subside
by late afternoon. Critical conditions however, are still expected
to persist across southern California into tomorrow morning.

At the moment, temperatures are rather cool across parts of southern
Nevada, with temperatures in the upper 30s to mid 40s. However,
temperatures are expected to warm into the 50s by afternoon peak
heating, that combined with continued 25-40 mph sustained northerly
flow and 10-25% RH, will foster Critical wildfire-spread conditions
through the afternoon.

..Squitieri.. 10/26/2020

.PREV DISCUSSION... /ISSUED 0152 AM CDT Mon Oct 26 2020/

...Synopsis...
A very steep pressure gradient will persist across dry areas of the
West and Southwest today in response to 1) very strong high pressure
over the western Great Basin and 2) surface troughing from the
California coastline southeastward through Arizona and western New
Mexico.  Additionally, very strong flow aloft will persist across
these areas in response to a vigorous mid-level wave expected to be
centered over Utah at 12Z and Arizona in the evening.  Continued dry
fuels and areas of drought will continue to support higher-end
fire-weather conditions particularly in portions of California.

...Southern California...
Models/high resolution guidance continue to indicate very strong
flow across typical, terrain-favored areas of the southern
Transverse Ranges throughout the forecast period.  Northeasterly
surface flow will range from 25-35 mph, with gusts perhaps as high
as 70 mph in spots.  Meanwhile, very low RH will continue given the
dry airmass in place, with 5-15% values becoming common during the
day as surface heating commences.  Fuels remain dry and favorable
for fire spread given continued dry conditions over the past several
months.  Guidance suggests that these conditions will continue even
into the evening hours, owing to poor overnight recoveries and the
continued offshore gradient.

...Northern California and the Bay Area...
Elevated to critical fire-weather conditions will likely be ongoing
at the start of the period as current (05Z-06Z) observations
indicate areas of 25-35 mph northerly low-level flow and 7-15% RH
values, indicating very poor recovery.  The strong surface pressure
gradient and favorable upper support suggest that these conditions
will continue throughout the day, with RH values remaining low amid
surface warming.  A few areas may experience gusts to 70 mph.  Fuels
remain extremely dry/combustible, and a few areas will likely exceed
extremely critical thresholds at times - especially in areas between
Sacramento and San Francisco/Oakland and including the North Bay
Mountains and East Bay Hills.

...Southern Nevada through the Lower Colorado River Valley...
Recent high-resolution guidance indicates that enough surface
warming will occur for temperatures to reach the 60s F during peak
heating hours despite northerly surface flow and modest cold
advection.  The residing airmass across the region is quite dry, and
as temperatures increase, surface RH values will fall into the 5-15%
range during the afternoon.  Additionally, surface winds will
increase into the 25-35 mph range given the surface pressure
gradient across the region.  Critical fire-weather delineations
exist where the aforementioned conditions are most likely to occur
amidst dry fuels/fuel beds.

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

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SPC Day 2 Fire Weather Outlook

SPC Day 2 Fire Weather Outlook

Day 2 Fire Weather Outlook Image

Day 2 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
0203 PM CDT Mon Oct 26 2020

Valid 271200Z - 281200Z

...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF NORTHERN INTO CENTRAL
CALIFORNIA...
...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHERN CALIFORNIA...

Much of the previous forecast remains on track. Latest model
guidance consensus depicts 15-25 mph sustained northerly surface
winds amidst 10-20% RH across portions of the Sacramento and upper
San Joaquin Valley areas Tuesday afternoon, necessitating the
maintenance of a Critical area given exceptionally dry fuels in
place. Offshore flow and widespread 10-20% RH will continue all day
Tuesday across the southern Transverse Ranges in southern
California. The strongest winds (i.e. widespread 25+ mph with higher
gusts) are expected to occur mainly during the morning, with gradual
weakening expected through the afternoon into the overnight hours as
upper support continues to move away from California. 

The Elevated area across the Lower Colorado River Basin was expanded
farther north into far southern Nevada. Temperatures are forecast to
warm into the 50s, with widespread 15-25 mph sustained northerly
surface winds coinciding with critically low RH by afternoon peak
heating. While surface temperatures will remain cool overall, the
aforementioned favorable surface winds/RH overspreading very dry
fuels will compensate to support an Elevated wildfire-spread threat.

..Squitieri.. 10/26/2020

.PREV DISCUSSION... /ISSUED 0216 AM CDT Mon Oct 26 2020/

...Synopsis...
Elevated to critical fire-weather conditions will continue across
California and the Desert Southwest on D2/Tuesday as a persistently
strong surface pressure gradient resides in these areas.  There are
indications that this gradient will weaken midday as high pressure
over Nevada weakens slightly.  However, models also indicate a
restrengthening of the gradient in the latter half of the forecast
period, which should maintain areas of gusty northerly/northeasterly
surface winds and very low RH.

...Northern California and the Bay Area...
Given the continued favorable pattern for fire weather, it is likely
that elevated to critical fire-weather conditions (20-30 mph
northerly flow and 5-20% RH values) will be ongoing early in the
forecast period.  Winds will slacken only briefly in a few areas
during the day as temporary weakening of the surface pressure
gradient occurs.  This gradient will reintensify, however, with
strong winds returning during the afternoon and continuing
overnight.  Fuels remain very dry in this region, and ERCs remain
near record levels.  Thus, an environment favorable for rapid fire
spread will continue - especially in the critical delineation across
the Sacramento Valley and eastern portions of the Bay Area.

...Coastal ranges of Southern California...
The favorable offshore flow pattern will persist throughout the day
across the region, and although slightly weaker winds are expected
compared to D1/Monday, gusts to 50 mph or higher cannot be
completely ruled out in terrain-favored areas.  Fuels remain dry,
and RH values will also exhibit poor recovery overnight while
falling again into the 5-15% range amid peak heating.  Critical
fire-weather conditions are expected to persist throughout the day
and continue into the overnight hours.

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

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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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SPC Oct 26, 2020 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1215 PM CDT Mon Oct 26 2020

Valid 271200Z - 281200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

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

...Synopsis and Discussion...
A closed upper low over AZ/NM and adjacent northern Mexico is
forecast to move slowly eastward towards the southern High Plains on
Tuesday. Large-scale ascent preceding this feature will overspread
parts of the southern Plains through the period. Even though much of
this region will be to the north of a cold front, weak elevated
instability may still develop as mid-level temperatures gradually
decrease with the approach of the upper trough. Isolated
thunderstorms may occur in this regime. Farther south, substantial
low-level moisture will remain confined to parts of coastal TX and
the Southeast. Occasional storms may also occur across these regions
though the day, but generally weak low/mid-winds should limit both
deep-layer shear and organized severe thunderstorm potential. The
enhanced low-level wind field associated with Tropical Cyclone Zeta,
forecast by the National Hurricane Center to move northwestward to
northward across the central Gulf of Mexico on Tuesday, is not
expected to overspread portions of the central Gulf Coast until
after the end of the Day 2 period.

..Gleason.. 10/26/2020

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SPC MD 1755

MD 1755 CONCERNING WINTER MIXED PRECIPITATION FOR FAR EAST-CENTRAL NM…MUCH OF THE TX PANHANDLE…WESTERN OK/EASTERN OK PANHANDLE

MD 1755 Image


Mesoscale Discussion 1755
NWS Storm Prediction Center Norman OK
0117 AM CDT Mon Oct 26 2020

Areas affected...Far East-Central NM...Much of the TX
Panhandle...Western OK/Eastern OK Panhandle

Concerning...Winter mixed precipitation 

Valid 260617Z - 261015Z

SUMMARY...Mixed winter precipitation, predominantly sleet, is
expected this morning from far east-central NM across the TX
Panhandle into western OK.

DISCUSSION...Regional radar imagery has shown an increase in
precipitation coverage during the past few hours as isentropic
ascent persists across the southern Plains/southern High Plains. 00Z
AMA sounding sampled a shallow cold layer well, revealing a cold
layer extending to 850 mb (about 1 km deep). Above this cold layer,
warm temperatures associated with the persistent southwesterly flow
aloft resulted in a strong inversion, with 700 mb temperatures near
7 to 8 deg C. This results in a thermodynamic profile supporting
mixed precipitation, predominantly sleet, once the mid-level layer
moistens enough to erode the dry layer in place. The increase in
precipitation coverage noted in regional radars is likely evidence
of that ongoing moistening process, which is expected to continue
and will soon support precipitation reaching the surface over much
of this region. 

Given the anticipated persistence of the southwesterly flow aloft
and resulting maintenance of the warm layer aloft, the expectation
is for an area of mixed winter precipitation to develop from far
east-central NM across the TX Panhandle in western OK/eastern OK
Panhandle. Sleet is expected to be the dominant precipitation type.
Additionally, elevated instability, based the at the top of the warm
layer around 700 mb, could contribute to higher precipitation rates
as well as occasional lightning. Current observations show lightning
within the precipitation band from Potter County TX into Harper
County OK.

..Mosier.. 10/26/2020

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

ATTN...WFO...OUN...DDC...LUB...AMA...ABQ...

LAT...LON   35500332 36190236 37200002 36959882 36039911 35399962
            34630075 34150235 34130337 34390375 34850375 35500332 

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SPC MD 1744

MD 1744 CONCERNING SEVERE THUNDERSTORM WATCH 500… FOR SOUTHWEST IOWA…FAR NEBRASKA…FAR NORTHWEST MISSOURI

MD 1744 Image


Mesoscale Discussion 1744
NWS Storm Prediction Center Norman OK
1128 PM CDT Sun Oct 11 2020

Areas affected...Southwest Iowa...Far Nebraska...Far Northwest
Missouri

Concerning...Severe Thunderstorm Watch 500...

Valid 120428Z - 120600Z

The severe weather threat for Severe Thunderstorm Watch 500
continues.

SUMMARY...An isolated wind damage threat is expected to persist
across southwest Iowa and far northwest Missouri for another one to
two hours. Weather watch issuance is unlikely beyond the expiration
of Ww 500.

DISCUSSION...A line of strong to severe thunderstorms is ongoing
across western Iowa extending south-southwestward into far southeast
Nebraska. The RAP has weak instability ahead of the line with MLCAPE
of 500 to 1000 J/kg. This combined with strengthening low-level flow
will support continued thunderstorm development over the next few
hours. The Des Moines WSR-88D VWP currently has 60 kt of 0-6 km
shear which will be enough to continue an isolated severe threat a
little while longer with the stronger cells embedded in the line. A
few damaging wind gusts will be possible along the leading edge of
the line as it moves eastward across southwest Iowa and far
northwest Missouri. However, as instability continues to weaken
during the early overnight period, the severe threat will become
increasingly marginal.

..Broyles.. 10/12/2020

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

ATTN...WFO...DMX...EAX...OAX...TOP...

LAT...LON   42469435 42369485 42059510 41079543 40319581 39979575
            39869556 39819505 40029457 41049423 42059394 42469435 

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SPC MD 1743

MD 1743 CONCERNING SEVERE THUNDERSTORM WATCH 500… FOR EASTERN NEBRASKA AND FAR WESTERN IOWA

MD 1743 Image


Mesoscale Discussion 1743
NWS Storm Prediction Center Norman OK
0902 PM CDT Sun Oct 11 2020

Areas affected...eastern Nebraska and far western Iowa

Concerning...Severe Thunderstorm Watch 500...

Valid 120202Z - 120400Z

The severe weather threat for Severe Thunderstorm Watch 500
continues.

SUMMARY...The potential for severe wind will continue for portions
of central Minnesota as well as eastern Nebraska and far western
Iowa through at least 03 UTC.

DISCUSSION...Recent radar trends from MN show an organized squall
line, which suggests that 40-45 knot effective bulk shear is
compensating for relatively weak (around 500 J/kg MLCAPE)
instability. Convection will likely begin to diminish as it moves
eastward into the cool side of a diffuse surface warm front, but
will continue to pose a severe wind potential in the near term
(through at least 03 UTC) for central MN. With temperatures in the
mid 60s (and dewpoints in the 40s) across eastern MN, a downstream
watch is not anticipated at this time. 

Further south, the cold front has overtaken the main line of storms
per recent surface and radar observations from KOAX. This will
further favor a linear storm mode for the rest of the evening.
Despite increasing inhibition from nocturnal cooling, stronger
ascent associated with the cold front should maintain convection for
the next few hours. Downward trends in MRMS vertically integrated
ice and warming IR cloud top temperatures, combined with a
transition to a linear storm mode, suggest a downward trend in the
hail potential overall, though a few instances of severe hail can
not be ruled out with any stronger updraft pulses. Although severe
wind is possible along the entirety of the line, portions of
southeast NE may see a locally higher wind threat associated with
accelerating convection along the cold frontal surge.

..Moore/Dial.. 10/12/2020

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

ATTN...WFO...MPX...DMX...FSD...OAX...GID...

LAT...LON   40979791 42009666 42409634 42849593 43769563 44629550
            45269523 45759511 45929479 45859429 45329389 44969383
            44489390 43889416 43149459 42549494 41999520 41659539
            41169556 40739560 40459611 40429688 40569759 40979791 

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