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LU9DCE > ALERT 28.11.20 17:14z 216 Lines 12729 Bytes #999 (0) @ WW
BID : 41912_LU9DCE
Read: GUEST
Subj: STORM PREDICTION CENTER 28 11
Path: HB9ON<IW8PGT<IZ3LSV<DB0ERF<DB0RES<ON0AR<GB7CIP<N7HPX<LU9DCE
Sent: 201128/1701Z 41912@LU9DCE.TOR.BA.ARG.SOAM LinBPQ6.0.20
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ESTACION DE PACKET RADIO - BUENOS AIRES (GF05OM)
BOLETINES INFORMATIVOS PROGRAMADOS (BIP)
CASTILLOEDUARDO@OUTLOOK.COM.AR
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SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1250
AM CST Sat Nov 28 2020
Valid 291200Z - 301200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS
OF THE LOWER MISSISSIPPI VALLEY...SOUTHEAST...AND CAROLINAS...
...SUMMARY... Isolated strong to severe thunderstorms may occur
Sunday into Sunday night across parts of the lower Mississippi
Valley, Southeast, and Carolinas. Damaging winds and perhaps a
couple of tornadoes should be the main threats.
...Lower Mississippi Valley into the Southeast and Carolinas...
A closed upper low centered over the southern Plains Sunday morning
will move eastward through the day. This upper low should begin to
merge with a positively tilted, northern-stream upper trough over
the eastern states Sunday evening into early Monday morning. A weak
surface low initially near the coast of southwestern LA is forecast
to develop northeastward across parts of LA/MS/AL through the day
while gradually deepening. Additional deepening of this surface
low should occur from Sunday night through the end of the period
as it continues developing northeastward along/near the spine of
the southern/central Appalachians. A warm front attendant to the
surface low will lift northward across parts of the Southeast and
Carolinas, while a trailing cold front sweeps eastward across these
regions through the period.
Most guidance indicates that storms will be ongoing Sunday morning
over the northern Gulf of Mexico near the LA Coast. Low-level warm
advection should be the primary forcing mechanism for this activity,
with the low-level jet forecast to shift northward across MS/AL
through the day. Some concern remains regarding how much low-level
moisture will be able to return inland given the potential for
numerous to widespread storms over the northern Gulf of Mexico Sunday
morning. If mid to upper 60s surface dewpoints can develop inland
across parts of southern LA/MS/AL and the FL Panhandle in tandem
with the deepening surface low and northward-advancing warm front,
then only modest diurnal heating would be needed to support weak
instability and surface-based storms. Strong effective bulk shear of
45-60 kt will easily support organized convection, with supercells
possible along/ahead of the cold front. Isolated strong to damaging
winds should be a concern given the strength of the low/mid-level
flow and potential for storms to grow upscale into a low-topped
line along the cold front by Sunday evening. Low-level shear also
appears strong enough for updraft rotation, with a couple tornadoes
possible across the warm sector with any semi-discrete storms.
This isolated severe threat will probably continue across parts of
GA into the Carolinas Sunday night and early Monday morning (end
of the Day 2 period), as low-level moisture return occurs from
the western Atlantic, and as a south-southwesterly jet rapidly
strengthens over these areas. However, even though the low-level
flow will likely be quite strong, instability is forecast to remain
rather weak (generally less than 500 J/kg of MLCAPE). The northern
extent of any meaningful damaging wind/tornado threat across the
Southeast remains unclear, as there is uncertainty in how far north
the mid 60s to upper surface dewpoints will advance. If confidence
increases in a narrow corridor of greater instability developing
across the warm sector on Sunday, then a Slight Risk for damaging
winds and/or tornadoes may be included across some portion of these
regions in a later outlook.
..Gleason.. 11/28/2020
SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0226
AM CST Sat Nov 28 2020
Valid 301200Z - 011200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS
OF FLORIDA/COASTAL GEORGIA INTO THE CAROLINAS AND MID-ATLANTIC...
...SUMMARY... Isolated strong to severe thunderstorms capable of
producing damaging winds and perhaps a couple of tornadoes appear
possible on Monday from parts of Florida and coastal Georgia into
the Carolinas and Mid-Atlantic.
...Florida/Coastal Georgia into the Carolinas and Mid-Atlantic...
A large-scale upper trough should evolve into a closed low over the
Midwest/OH Valley and central Appalachians on Monday. A mid-level
vorticity maximum embedded within this upper trough is forecast to
move quickly northeastward from the central Appalachians into the
Mid-Atlantic through Monday afternoon. A deep surface low should
likewise develop northeastward in tandem with this vorticity
maximum. A cold front trailing from this surface low will likely
sweep eastward across much of the FL Peninsula and the East Coast
through the day. A warm front extending northeastward from the
surface low will probably make some northward progress across parts
of the Mid-Atlantic through Monday afternoon as well.
A line of low-topped showers/storms along or just ahead of the cold
front should be ongoing at the start of the period from near the
surface low in WV/western VA southward to northern FL. Although
instability may remain modest across most of the warm sector ahead
of this line, generally low to mid 60s surface dewpoints should
be enough to support weak surface-based instability through the
day. A very strong (50-60+ kt) south-southwesterly low-level jet
should be present over the central/eastern Carolinas and southern
VA Monday morning, and this feature is forecast to shift northward
across the Mid-Atlantic through the day.
Given the strength of the low-level flow and sufficient, albeit
weak, forecast instability, strong to damaging winds may occur with
storms that either persist along the cold front or develop ahead
of it over the open warm sector. A couple tornadoes also appear
possible, mainly across parts of eastern SC/NC/VA to the Delmarva
Peninsula and perhaps NJ in associated with the low-level jet and
potentially greater low-level moisture and instability. Even so,
there is too much uncertainty regarding sufficient destabilization
to include higher severe probabilities for now.
Farther south, low-level convergence along the cold front and
deep-layer shear are both forecast to be somewhat weaker across
coastal GA and the FL Peninsula. Still, there may be isolated
strong/gusty winds with any storms through Monday afternoon.
..Gleason.. 11/28/2020
Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK
0300 AM CST Sat Nov 28 2020
Valid 011200Z - 061200Z
...DISCUSSION... Minimal severe potential is expected across
the CONUS on both Day 4/Tuesday and Day 5/Wednesday, as offshore
low-level trajectories should be maintained over the majority of
the Gulf of Mexico and western Atlantic. By late next week, there
is some disagreement in medium-range guidance regarding the possible
development and subsequent evolution of an upper trough/low over the
central/eastern states. Depending on how much low-level moisture
return occurs ahead of this feature, there might be some low-end
severe potential across parts of the central Gulf Coast and perhaps
FL from Day 6/Thursday into Day 7/Friday. But, low predictability
in the synoptic-scale pattern and weak forecast instability preclude
any 15% severe probabilities at this extended time frame.
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK
1237 AM CST Sat Nov 28 2020
Valid 281200Z - 291200Z
...Synopsis... An upper-level closed low will continue to gradually
shift eastward into the southern Plains through the day today,
bringing widespread precipitation and cloud cover. To the north,
a clipper low along the Canadian border will usher in a weak cold
front across the northern High Plains. Breezy conditions behind this
front could support brief fire weather concerns. Upper-level ridging
over the West will mitigate most fire weather concerns for today. One
exception will be the higher elevation of southern California where
continued offshore flow may support a fire weather threat.
...Southern California... Although early morning surface
observations show poor overnight RH recoveries across southern CA,
winds are weaker compared to 24 hours ago with the exception of a
few stations in the San Gabriel Mountains. This is largely due to
gradual upper-level ridging over the West coast and diminishing winds
throughout the column. Despite an approaching low-amplitude offshore
disturbance, mid-level winds will continue to be weak through the
day and limit the potential for widespread critical fire weather
conditions. However, persistent offshore pressure-gradient winds
will continue to support areas of elevated, to locally critical,
fire weather conditions for the higher elevation of southern CA. The
fire weather threat may be highest during the morning hours when
the LAX-DAG pressure gradient is forecast to be the strongest before
relaxing later in the day.
...Northern High Plains... Morning guidance continues to
show the potential for elevated fire weather conditions this
afternoon for western ND and eastern MT as winds increase behind a
southeastward moving cold front. Fuels remain dry and/or dormant
across this region and wind gusts upwards of 25-35 mph appear
possible. However, uncertainty remains somewhat high regarding the
degree of RH reductions with most guidance remaining above elevated
RH thresholds. Additionally, the temporal window for elevated
conditions appears limited to a couple of hours during the late
afternoon. Due to these concerns no highlights are introduced,
but conditions will continue to be monitored through the day.
..Moore.. 11/28/2020
...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
0136 AM CST Sat Nov 28 2020
Valid 291200Z - 301200Z
...Synopsis... An amplifying upper-level pattern over the CONUS will
feature a deepening trough over the East with upper-level ridging
over the West by the late weekend. While this pattern will feature
weak mid-level winds across the Southwest, where conditions have been
fairly dry, surface high pressure over the central CONUS will augment
pressure gradient winds over the Plains and portions of southern
California. This could lead to localized fire weather concerns.
...Southern California... Although upper-level ridging will continue
to support weak winds aloft for Sunday, a reinforced surface high
over the central Rockies and into the northern Great Basin will
continue to foster offshore pressure-gradient winds for southern
CA. Poor overnight RH recoveries are expected with RH values in the
teens likely for Sunday afternoon. The LAX-DAG pressure gradient
is forecast to be similar in magnitude as Saturday's, suggesting
that elevated, to locally critical, fire weather conditions will be
possible again for terrain-favored locations in the higher elevation
of southern CA. This idea is supported by recent high-res ensemble
guidance and deterministic model solutions.
...Central to Southern High Plains... Building surface high
pressure over the northern High Plains in the wake of a cold front
will help drive an increase in pressure-gradient winds through
the day on Sunday. Strong northerly 850 mb flow within a cold
advection regime over the central to southern Plains will help
mix stronger winds down to the surface with gusts up to 30-40
mph possible. Some deterministic solutions and high-res ensemble
members hint at the potential for RH reductions into the low 20s
across western KS and the OK/TX Panhandles during the afternoon
hours. However, confidence in this scenario is not high due to the
potential for cold advection to limit RH reductions. Additionally,
fuels across this region are only modestly receptive and portions
of the OK/TX Panhandles may see prior precipitation on Saturday. As
such, no highlights are introduced in this outlook, though trends
in guidance and precipitation on Saturday will be monitored.
..Moore.. 11/28/2020
...Please see www.spc.noaa.gov/fire for graphic product...
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