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LU9DCE > ALERT 19.01.21 16:12z 233 Lines 13113 Bytes #999 (0) @ WW
BID : 2216_LU9DCE
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Subj: STORM PREDICTION CENTER 19 01
Path: HB9ON<IW2OHX<IR1UAW<IZ3LSV<DB0ERF<DB0RES<ON0AR<VK6HGR<GB7CIP<N7HPX<
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Sent: 210119/1600Z 2216@LU9DCE.TOR.BA.ARG.SOAM LinBPQ6.0.21
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SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1138
PM CST Mon Jan 18 2021
Valid 191200Z - 201200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY... A few thunderstorms may occur today across parts
of Texas as well as near the coast of southern California into the
lower Colorado River Valley. Severe thunderstorms are not expected.
...Texas... Shortwave ridging should build over the southern
Plains today as a surface cold front slowly moves southward over
parts of central/east TX. Partially modified low-level moisture,
with surface dewpoints generally in the low 60s, will reside to the
south of the cold front. Scattered, low-topped showers should be
ongoing at the start of the period along/near the front across parts
of central/east TX. Some of this convection may become deep enough
through the day to support isolated lightning flashes, even though
the presence of an inversion centered around 700 mb should generally
limit boundary-layer instability. A minor mid-level perturbation
approaching the southern Plains from northern Mexico may also
encourage continued convective development along the front through
the evening and overnight hours. Weak forecast instability and poor
lapse rates are expected to preclude an organized severe threat.
...Channel Islands/Southern California into the Lower Colorado
River Valley... A closed upper low over the western CONUS will
develop southward off the coast of southern CA and the northern
Baja Peninsula by tonight. Cool mid-level temperatures will
promote steepened mid-level lapse rates beneath the upper low. Lift
associated with multiple vorticity maxima should support shallow
convection. The deepest cores could reach sufficient height to induce
charge separation and isolated lightning flashes. The best potential
for thunderstorms will likely remain just off the CA Coast and over
the Channel Islands. Other isolated thunderstorms may also occur
in the mid-level moisture plume over parts of the lower CO River
Valley, but instability should remain rather weak across this region.
..Gleason/Moore.. 01/19/2021
SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 0101
AM CST Tue Jan 19 2021
Valid 201200Z - 211200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY... No severe storms are forecast across the continental
United States Wednesday or Wednesday night.
...Discussion... Fast west-northwesterly flow aloft is progged
across much of the U.S. Wednesday, except over the southwestern
U.S. and Great Basin area, where a cut-off low -- initially lingering
off the southern California/Baja coast -- will prevail. This low is
forecast to begin an eastward advance Wednesday, gradually moving
inland over southern California/northern Baja and then to the lower
Colorado Valley and adjacent northern Gulf of California by the
end of the period.
At the surface, high pressure will largely prevail over the southern
half of the CONUS, while farther north a clipper-type system moves
across southern Canada and the northern Plains, and later into the
Upper Midwest/Great Lakes region.
As the upper system moves into the southwestern U.S. with time,
showers are expected. As cold air/steep lapse rates aloft spread
inland, particularly into the second half of the period, sporadic
lightning may also occur, embedded within the broader area of
convection. Elsewhere, thunderstorms are not expected.
..Goss.. 01/19/2021
SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0231
AM CST Tue Jan 19 2021
Valid 211200Z - 221200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY... Severe weather is not expected across the U.S. on
Thursday.
...Discussion... Fast westerly/west-northwesterly flow aloft is
expected to continue across the U.S. on Thursday. An upper low
initially centered over the northern Gulf of California vicinity
is forecast to steadily weaken/deamplify as it shifts eastward
toward the southern Plains. Meanwhile, an area of troughing off
the coast of western Canada is progged to dig south-southeastward
with time, affecting the Pacific Northwest through the second half
of the period.
At the surface, a weakening clipper-type system will move across the
Northeast and adjacent eastern Canada with time, as high pressure
builds into the north-central U.S. in its wake. Very weak low
pressure is expected to move across the Southwest and into the
southern Plains, ahead of the dampening upper system.
Showers -- and possibly a few lightning flashes -- will spread
across the Southwest during the day, in tandem with the upper trough
and associated/weak surface system. A few flashes may also occur
later over east Texas and the Arklatex. Here, however, coverage
of any lightning appears as though it should remain below the 10%
threshold required for inclusion of a thunder area.
..Goss.. 01/19/2021
Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK
0359 AM CST Tue Jan 19 2021
Valid 221200Z - 271200Z
...DISCUSSION... Medium-range models appear to be in good agreement
day 4 (Friday 1-22), with respect to evolution of the large-scale
features, but subtle differences aloft begin to emerge day 5,
and then increase day 6 and beyond.
With that said, models generally agree that an upper system will
move slowly across the southwestern U.S. during the first half of
the period. Corresponding downstream surface development is expected
to occur over the southern Plains beginning day 5 (Saturday), but
particularly day 6 (Sunday), after which model divergence becomes
too substantial to make even general inferences regarding pattern
evolution.
With little convective potential evident Friday, an increase in
thunderstorm activity may occur later in the day Saturday over the
south-central U.S., and continuing into Sunday as an increase in
southerly low-level flow permits at least some theta-e advection
from the western Gulf of Mexico. While some corresponding increase
in convective activity is expected, degree of any severe-weather
potential remains uncertain, and thus too low to introduce a
risk area at this time. Beyond Sunday, decreasing predictability
precludes any reasonable assessment of convective potential.
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK
1235 AM CST Tue Jan 19 2021
Valid 191200Z - 201200Z
...CRITICAL FIRE WEATHER AREA FOR THE LOWER COASTAL HILLS OF CENTRAL
TO SOUTHERN CALIFORNIA...
...Synopsis... Recent water vapor imagery reveals a leading
upper-level shortwave trough off the southern California/Baja
California coast. This feature is preceding a more potent upstream
low associated with a meridional jet streak over the Pacific
Northwest. This stronger low will deepen further over the next
24 hours as it stalls off the southern CA coast. As this occurs,
surface pressure falls offshore juxtaposed with a building surface
high to the north will induce strong pressure-gradient winds over
much of the southern two-thirds of CA. These winds, coupled with
dry fuels, will support a fire weather concern today through early
Wednesday. Elsewhere across the CONUS, cool temperatures and/or
weak winds will limit most fire weather concerns.
...Coastal Southern California... Surface observations from
Santa Barbara, Ventura, and Los Angeles counties show winds
gradually beginning to increase with wind gusts into the 25-35 mph
range. Surface pressure analyses reveal low pressure developing
along the CA coast ahead of the approaching upper-level low to the
north. While the proximity to the surface trough is maintaining
somewhat reasonable winds early this morning, winds will begin
to increase through the day as the surface low deepens and moves
offshore. Peak winds are expected by early to mid afternoon, and
sustained winds near 30-50 mph and potentially damaging wind gusts
up to 60-80 mph remain likely (especially for portions of Ventura
and Los Angeles counties). As winds become more east/northeasterly
through the day, downslope effects will be maximized for the
coastal hills and lower mountains, allowing humidity reductions
to 15-20%. While RH values may not consistently meet critical
thresholds throughout the day, the strong winds and unseasonably
dry fuels should compensate and support a fire weather threat. The
offshore pressure gradient is forecast to remain in place into the
overnight hours, and may support at least elevated fire weather
conditions well into Wednesday morning (depending on overnight RH
recoveries in the coastal areas).
...Sacramento Valley region... Wind gusts into the 45-60 mph range
and humidity values as low as the mid teens have been noted in recent
observations from the greater San Francisco Bay area and southwestern
Sacramento Valley. While early morning RH recoveries are expected
for this region, winds will likely maintain intensity through the
late afternoon hours. Recent guidance has come into somewhat better
agreement in the potential for RH values to fall back into the low
20s and teens during the afternoon. Fuels across this region have
only recently begun to dry out after a few dry/windy days. However,
recent fuel moisture analyses suggest fine fuel moisture has fallen
into the single digits and may support fire spread. This factor,
combined with the strong winds and borderline humidity, warrants
the northward expansion of the elevated risk area.
..Moore.. 01/19/2021
...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
0146 AM CST Tue Jan 19 2021
Valid 201200Z - 211200Z
...Synopsis... A stalled synoptic low off the coast of southern
California/Baja California is forecast to weaken through Wednesday
evening, but will continue to support strong offshore flow and
a fire weather concern for southern California for much of the
day. Across the central CONUS, a surface trough associated with
a Canadian clipper low will move southeastward through the day,
ushering in breezy and dry conditions for portions of the Plains.
...Coastal southern California... Forecast guidance remains
in good agreement that a -5 to -6 mb LAX-DAG pressure gradient
will remain in place for much of Wednesday across southern CA as
the synoptic low stalls offshore. Sustained winds near 30-45 mph
(gusting to 50-60 mph) appear likely for portions of Los Angeles
and Ventura counties with slightly weaker winds in the peripheral
coastal areas. Winds will be strongest during the morning, and are
expected to gradually weaken through the evening/overnight hours.
Despite the persistent strong winds, relative humidities will likely
improve through the day as moist air filters into the region. Cloud
cover and scattered rain showers will further limit RH reductions
for far southern CA where winds will likely remain elevated.
Ensemble and deterministic guidance show humidity values will most
likely improve into the 20-30% range for most coastal areas, but
reductions as low as 15% are possible where downslope warming/drying
can persist. Given the expected RH improvements, elevated fire
weather conditions appear most likely, but transient/localized
critical conditions are possible during the afternoon.
...central Plains... Northwesterly winds are forecast to increase to
around 15-20 mph across the central Plains in the wake of a passing
surface trough. Although temperatures will remain on the cool side,
dry air advection and slight downsloping effects will allow RH
values to fall to near 20% across the broader WY/SD/NE region. This
may allow for areas of elevated fire weather conditions during the
afternoon hours when diurnal heating and boundary-layer mixing are
maximized. However, fuels across this region are only marginally
receptive (10-hour fuel moisture values in the low teens and ERC
values in the 50-60th percentiles) after light precipitation over
the past 24 hours. Because of this, no risk areas are introduced
for this outlook. Highlights may be needed in subsequent outlooks
if guidance trends windier or drier.
..Moore.. 01/19/2021
...Please see www.spc.noaa.gov/fire for graphic product...
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