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LU9DCE > ALERT 31.12.20 19:00z 235 Lines 13186 Bytes #999 (0) @ WW
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Subj: STORM PREDICTION CENTER 31 12
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Sent: 201231/1700Z 842@LU9DCE.TOR.BA.ARG.SOAM LinBPQ6.0.21
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ESTACION DE PACKET RADIO - BUENOS AIRES (GF05OM)
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LU9DCE@GMX.COM
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MD 1892 CONCERNING HEAVY SNOW FOR PORTIONS OF SOUTHWEST
TX...INCLUDING THE BIG BEND REGION
Mesoscale Discussion 1892 NWS Storm Prediction Center Norman OK
0216 AM CST Thu Dec 31 2020
Areas affected...Portions of southwest TX...including the Big
Bend region
Concerning...Heavy snow
Valid 310816Z - 311415Z
SUMMARY...Heavy snow, with rates of 1 to 2 inches per hour, will
likely continue this morning.
DISCUSSION...An upper low evident on water vapor satellite imagery
over northern Mexico will continue to move slowly eastward this
morning. Low-level thermal profiles will likely remain cold enough
behind a surface front to support mainly snow, with perhaps a little
sleet mixed in based on some bright banding in reflectivity and
lowered CC values in recent radar imagery from KMAF. Strong low to
mid-level frontogenetic forcing along with saturation through the
dendritic growth zone will likely support heavy snow in a relatively
narrow southwest to northeast band from the Big Bend into parts of
southwest TX through the early morning. Snowfall rates of 1-2 inches
per hour appear likely for several hours within this slow moving
band, particularly in the higher terrain of the Big Bend region into
the Stockton Plateau, where orographic lift should enhance snowfall
rates. Dry mid-level air on the back side of this band and the upper
low should provide a fairly sharp cut off to the heavy snow across
west TX. With time, this band should pivot slowly east-northeastward
in tandem with the eastward progression of the upper low.
..Gleason.. 12/31/2020
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...EWX...SJT...MAF...
LAT...LON 29570435 30040416 30870333 31400261 31980164 32030119
31700087 31420107 31170124 30860144 30460148 30050154 29740153
29750186 29760222 29630265 29240279 28930313 29270405 29570435
SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1200
AM CST Thu Dec 31 2020
Valid 311200Z - 011200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST
TEXAS INTO SOUTHERN LOUISIANA AND SOUTHWEST MISSISSIPPI...
...SUMMARY... Severe thunderstorms -- including potential for
tornadoes -- are possible today through tonight from southeast Texas
into the lower Mississippi Valley and central Gulf Coast States.
...Southeast Texas through the lower Mississippi Valley...
Cold front will stall from the TX coastal area through northern LA
and central MS. This boundary might advance slightly northward as
a warm front or remain stationary through a portion of southeast
TX and the lower MS Valley today into the evening. Cyclogenesis
will commence along the front near the central TX coast later this
morning. This cyclone will subsequently develop northward through
east TX within corridor of deep forcing for ascent associated with
a northward-ejecting shortwave trough.
A moist warm sector will reside south of the front with mid to upper
60s F dewpoints from southeast TX into southern LA and MS. However,
widespread clouds and weak lapse rates will support only a modest
thermodynamic environment with MLCAPE from 500-1000 J/kg. Deeper
forcing for ascent will begin to overtake the western portion of the
warm sector across southeast TX later this morning. This will result
in more robust thunderstorm development in vicinity and east of the
developing surface low near the central TX coast and southward along
the cold front into the western Gulf. Activity will subsequently
spread into southeast TX and southwest and central LA during the
day before reaching southwest LA by early evening. Vertical wind
profiles will strengthen as a coupled jet structure overspreads the
warm sector in association with the ejecting shortwave trough. Mixed
storm modes are likely. Large low-level hodographs with 300-500
m2/s2 0-1 km storm relative helicity and 50+ kt effective bulk
shear will support organized storms, including bowing line segments
and supercells with low-level mesocyclones capable of producing
tornadoes and damaging wind.
...Central Gulf Coast states...
A subtle warm front will move onto the central Gulf coast later
today. The boundary layer will moisten with dewpoints increasing to
the mid to upper 60s F. Showers and thunderstorms are expected to
gradually increase and develop northward through the evolving warm
advection regime later today into the overnight. Primary severe
threat is expected during the evening and tonight as low-mid level
winds increase downstream from the shortwave trough that will remain
well west of this region. Hodograph size will increase substantially
overnight, along with effective bulk shear supporting potential for
a few supercells. The deeper forcing for ascent will remain west of
this region, and most storms might remain slightly elevated given the
most favorable wind profiles will evolve overnight. Nevertheless,
the environment will support a supercell/tornado threat, assuming
updrafts can root in the boundary layer.
..Dial/Wendt.. 12/31/2020
SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1251
AM CST Thu Dec 31 2020
Valid 011200Z - 021200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS
OF THE OHIO AND TENNESSEE VALLEYS INTO THE SOUTHEAST AND SOUTH
CAROLINA...
...SUMMARY... Thunderstorms associated with isolated severe wind
gusts and a marginal tornado threat will be possible on Friday from
the Florida Panhandle northward to the Ohio Valley and northeastward
into South Carolina.
...Ohio and Tennessee Valleys.... An upper-level low will move
through the mid Mississippi Valley on Friday as southwest mid-level
flow remains over the Southeast and Carolinas. At the surface,
a low will be located in the lower Ohio Valley at the start of
the period with a cold front extending southward across middle
Tennessee into western Alabama. This front will move eastward
during the day. Thunderstorms appear likely to be ongoing along
and just ahead of the front Friday morning with this convection
moving eastward across Kentucky, Tennessee and Alabama into early
afternoon. Although surface dewpoints ahead of the front are forecast
to be in the lower to mid 60s F from middle Tennessee southward,
instability should remain weak along the moist axis due to abundant
cloud cover and minimal surface heating.
At mid-levels, a 60 to 80 kt jet is forecast to move northeastward
across the mid Mississippi Valley during the day. This feature
will create strong deep-layer shear profiles which will support
a marginal severe threat along and just ahead of the cold front.
The greatest threat will likely be in the late morning and early
afternoon from western Kentucky southward into middle Tennessee,
before the mid-level jet moves away from the moist sector. A
marginal wind damage/tornado threat may develop with the stronger
rotating cells.
...Southeast/South Carolina... An upper-level trough will move
northeastward across the Gulf Coast States Friday morning as a cold
front advances eastward across the region. Thunderstorms will be
possible on Friday across the moist sector, from near the front
in Alabama eastward across Georgia and South Carolina. Instability
across the moist sector is forecast to remain weak. However, strong
deep-layer shear will be in place due to influence of a mid-level
jet to the northwest. This combined with strong low-level flow will
create conditions supportive of marginally severe wind gusts. A
marginal tornado threat will also be possible with cells that rotate.
..Broyles.. 12/31/2020
SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0206
AM CST Thu Dec 31 2020
Valid 021200Z - 031200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS
OF THE SOUTHEAST AND EASTERN CAROLINAS...
...SUMMARY... Thunderstorms associated with marginally severe wind
gusts will be possible on Saturday from parts of the eastern Gulf
Coast to the southern Atlantic Seaboard.
...Eastern Gulf Coast/Southern Atlantic Seaboard... An upper-level
low is forecast to move northeastward across the Ozarks on
Saturday as southwest mid-level flow remains from the Southeast
into the Carolinas. At the surface, a cold front is forecast to
become quasi-stationary on Saturday from the Florida Panhandle
northeastward into far eastern North Carolina. Ahead of the front,
surface dewpoints in the lower to mid 60s F will allow for weak
destabilization by afternoon. Thunderstorm development will be
possible along the axis of instability as low-level convergence
increases during the day. The presence of strong deep-layer shear
may be enough for an isolated wind damage threat, with the threat
maximizing across the northwestern edge of the moist sector from
the Florida Panhandle to eastern South Carolina. The threat may
also affect far eastern North Carolina during the evening as a
low-level jet translates northeastward.
..Broyles.. 12/31/2020
Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK
0344 AM CST Thu Dec 31 2020
Valid 031200Z - 081200Z
...DISCUSSION... ...Sunday/Day 3 to Monday/Day 5... An upper-level
trough is forecast to move northeastward across the central
Appalachians on Sunday and across New England on Monday. A cold
front is forecast to move southward across the Florida Peninsula on
Sunday, along which thunderstorm development may take place during
the day. Behind the front, surface high pressure is forecast to
settle in across much of the southern half of the nation. As a
result, thunderstorm activity is expected to be minimized from
Sunday night into Monday.
...Tuesday/Day 6 to Thursday/Day 8... On Tuesday, the medium-range
models are in good agreement, moving an upper-level trough quickly
eastward into the southern Rockies. Under that scenario, moisture
advection would increase across the Texas Coastal Plain. Marginally
severe storms can not be ruled out over south-central Texas as the
upper-level trough approaches the southern Plains Tuesday night.
On Wednesday and Thursday, the upper-level trough is forecast to
progress quickly eastward across the Gulf Coast States. At this time,
moisture return is forecast to remain weak ahead of the trough. That
would limit the potential for severe storms to coastal areas from
Louisiana to the Florida Panhandle. The current thinking is that
any severe threat with this system will remain isolated. However,
uncertainty is substantial at this range in the forecast period.
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK
0116 AM CST Thu Dec 31 2020
Valid 311200Z - 011200Z
...NO CRITICAL AREAS...
...Synopsis... A shortwave trough will pivot through Deep
South Texas today. In the West, a shortwave trough will drop
down the California coast before forming a closed circulation
in the Southwest. In its wake, an upper-level ridge will amplify
across northern California and the Northwest. Cool temperatures
and precipitation will minimize fire weather concerns across
much of the CONUS. However, moderately strong offshore flow is
probable in southern California as a surface high intensifies in
the Great Basin toward early Friday morning. Despite the increase
in northerly/northeasterly winds, RH is not expected to fall to
critical levels and no highlights will be added.
..Wendt.. 12/31/2020
...Please see www.spc.noaa.gov/fire for graphic product...
SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK
0118 AM CST Thu Dec 31 2020
Valid 011200Z - 021200Z
...NO CRITICAL AREAS...
...Synopsis... The upper ridge across the West will shift into the
central Rockies with the southwestern trough accelerating into the
southern Plains on Friday. Broad areas of cooler temperatures and
precipitation will continue to minimize fire weather concerns across
most of the CONUS. Lingering high pressure in the Great Basin along
with enhanced northeasterly mid-level winds will produce a period of
stronger offshore flow during the early portions of the day. While
RH is expected to fall to 15-20% by the afternoon, the lower humidity
values appear somewhat offset from the stronger winds. An hour or two
of elevated meteorological conditions are possible in the typical
terrain-favored locations of LA/Ventura Counties. Confidence in
the duration of these conditions is low as well as fuel moisture
being less than optimal due to recent precipitation.
..Wendt.. 12/31/2020
...Please see www.spc.noaa.gov/fire for graphic product...
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The documentation is in Japanese. Good luck.
-- Rich $alz
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