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LU9DCE > ALERT 27.11.20 16:43z 237 Lines 13609 Bytes #999 (0) @ WW
BID : 41825_LU9DCE
Read: GUEST
Subj: STORM PREDICTION CENTER 27 11
Path: HB9ON<IW2OHX<IQ2LB<IR2UFV<N3HYM<N7HPX<LU9DCE
Sent: 201127/1600Z 41825@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 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1147
PM CST Thu Nov 26 2020
Valid 271200Z - 281200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM SOUTH
TEXAS EAST-NORTHEASTWARD TO SOUTHERN MISSISSIPPI...
...SUMMARY... A couple of severe thunderstorms may affect areas
from South Texas east-northeast to southern Mississippi Friday, with
marginal hail and gusty winds the main threats with these storms.
...Synopsis... A northern-stream trough over central Canada and the
adjacent north-central U.S. is forecast to move quickly eastward,
while just south of the main belt of westerlies, a closed low will
move more slowly eastward across Arizona and, later, New Mexico.
Southeast of this low, a belt of moderately strong west-southwesterly
flow will persist from northern Mexico across southeast Texas
and into the Southeast. Within this flow field, several weak
perturbations will progress across the southeastern quarter of the
country and the adjacent Gulf of Mexico.
At the surface, a weak baroclinic zone will linger across the Gulf
Coast states through the day, though a southward surge will occur
across Texas as high pressure strengthens over the central Plains.
This baroclinic zone will loosely focus a persistent zone of showers
and storms through the period.
...South Texas east-northeastward to southern Mississippi...
Showers and thunderstorms -- likely ongoing across portions of
southern and eastern Texas and into Louisiana at the start of the
period -- are expected to evolve/increase in coverage through the
day, generally in an elevated sense near and north of the surface
baroclinic zone stretching across the area. Modest CAPE will support
the convective activity, but will largely remain insufficient for
particularly robust storms.
Still, with rather strong mid-level west-southwesterlies (40
to 60 kt) atop the region, cloud-layer shear could support some
organization/longevity of convection locally. Marginally severe hail
is possible -- particularly with any updraft which could acquire
transient rotation. Otherwise, locally gusty/perhaps damaging
winds would be possible, mainly with a stronger storm or two in
close proximity to the surface boundary.
Though convection will likely continue, gradually spreading
southeastward, through the second half of the period, severe threat
should diminish in most areas after dark, as the front shifts into
the Gulf, with the possible exception of the Texas portion of the
risk area.
..Goss/Moore.. 11/27/2020
SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1200
AM CST Fri Nov 27 2020
Valid 281200Z - 291200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY... Organized severe thunderstorms appear unlikely across
the contiguous United States on Saturday.
...Synopsis and Discussion... A closed upper low initially over
the southern High Plains should move slowly eastward across TX/OK
on Saturday. A weak surface low is forecast to form over the western
Gulf of Mexico ahead of this feature, eventually reaching the coastal
LA vicinity by early Sunday morning. Large-scale lift ahead of the
upper low and weak low-level warm advection will likely support
numerous to widespread showers and thunderstorms across central/east
TX Saturday morning, which should limit instability. The majority of
this convection is expected to remain elevated, as a surface front
should generally move off the middle/upper TX Coast through the
day. As the surface low develops northeastward over the western Gulf
of Mexico, increasing low-level moisture will begin to approach the
LA Coast late Saturday night into early Sunday morning as a marine
warm front develops slowly northward. At this point, it appears
that the potential for surface-based thunderstorms will probably
remain offshore from the LA Coast through the end of the period.
Accordingly, severe probabilities have not been included.
..Gleason.. 11/27/2020
SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0228
AM CST Fri Nov 27 2020
Valid 291200Z - 301200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS
OF THE LOWER MISSISSIPPI VALLEY/SOUTHEAST INTO THE CAROLINAS...
...SUMMARY... Isolated strong to severe thunderstorms may occur
Sunday across parts of the lower Mississippi Valley into the
Southeast and Carolinas.
...Lower Mississippi Valley into the Southeast and Carolinas...
A closed upper low over the southern Plains Sunday morning should
move eastward across the lower MS Valley and Southeast through the
day. This upper low should begin to merge with a northern-stream
upper trough over the eastern CONUS Sunday evening into early
Monday morning. A weak surface low initially near the coast of LA is
forecast to develop northeastward across the Southeast through the
day while gradually deepening. Additional deepening of this surface
low should occur Sunday evening through the end of the period as
it continues developing northeastward along/near the spine of the
southern/central Appalachians. A warm front should lift northward
across parts of the Southeast and Carolinas through the period,
while a cold front attendant to the surface low sweeps eastward
across these regions throughout the period.
A prior frontal intrusion over the northern Gulf of Mexico may
tend to limit the prospect for substantial inland destabilization
across the Southeast through Sunday evening. Even so, low to mid 60s
surface dewpoints should advance northward into parts of southern
LA/MS/AL and the FL Panhandle in tandem with the developing surface
low and warm front through the day. Forecast soundings from various
models suggest weak instability may gradually develop with modest
daytime heating across these areas along/south of the warm front.
Strong low-level and deep-layer shear appear likely given the
enhanced wind field associated with the approaching upper low. This
high-shear, low-instability setup typically favors isolated strong
to severe convection across the developing warm sector along/ahead
of the eastward-moving cold front. Damaging winds a perhaps a couple
tornadoes would be the main threats with both low-topped supercells
and linear convection given the forecast strength of the low-level
flow and shear.
This isolated severe threat may continue across parts of GA
into the Carolinas Sunday night and early Monday morning (end of
the Day 3 period), as low-level moisture return occurs from the
western Atlantic. However, even through the low-level flow across
these areas should be quite strong, surface-based instability is
forecast to remain rather weak. Given the potentially limiting
factor of modest instability, have opted to introduce a broad
Marginal Risk area from parts of the lower MS Valley/Southeast into
the Carolinas. The northern extent of any damaging wind/tornado
threat remains unclear, as there is uncertainty in how far north
the low to mid 60s surface dewpoints (which will probably be needed
for surface-based storms) will advance across the Southeast and
Carolinas. If confidence increases in a narrow corridor of greater
instability developing across the warm sector, a Slight Risk for
damaging winds and/or tornadoes may need to be included across some
portion of these regions in a later outlook update.
..Gleason.. 11/27/2020
Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK
0345 AM CST Fri Nov 27 2020
Valid 301200Z - 051200Z
...DISCUSSION... A continued isolated/marginal severe threat
may continue across mainly eastern parts of the Carolinas and
Mid-Atlantic as a large-scale upper trough/low moves slowly across
the eastern CONUS on Day 4/Monday. Strong low/mid-level flow is
forecast to be present over these regions ahead of a cold front,
but instability should remain weak across the warm sector owing
to fairly limited low-level moisture. Confidence in a more
substantial severe threat on Day 4/Monday remains too low to
include 15% severe probabilities at this time. Minimal potential
for organized severe thunderstorms is anticipated across the
CONUS for Day 5/Tuesday and Day 6/Wednesday, as offshore low-level
trajectories should be maintained over much of the Gulf of Mexico
and western Atlantic. Predictability of the synoptic-scale pattern in
medium-range guidance appears low by late next week, with any low-end
severe potential remaining confined to parts of the central/eastern
Gulf Coast vicinity and possibly FL.
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK
1239 AM CST Fri Nov 27 2020
Valid 271200Z - 281200Z
...CRITICAL FIRE WEATHER AREA FOR PARTS OF LOS ANGELES AND VENTURA
COUNTIES...
...Synopsis... Early morning water vapor imagery shows an
upper-level trough deepening as it digs southward into the Southwest
and northern Mexico. This feature will continue to provide mid and
upper-level support for strong winds across southern California
and into adjacent areas of Arizona and southern Nevada through the
morning hours. This should pose a continued fire weather concern
for portions of southern California for today. Winds will gradually
abate through the late afternoon hours as the wave translates east
through the day and the regional surface pressure gradient relaxes.
Widespread rain/clouds across the southern US and cool temperatures
across the dry regions of the Plains will limit the fire weather
potential elsewhere.
...Southern California... Early morning surface observations from
the higher terrain of Los Angeles and Ventura counties show elevated
to critical fire weather conditions already ongoing with RH values
in the low teens to single digits and wind gusts between 30-40 mph
in a few locations. These conditions should persist through at least
the mid to late morning hours due to the persistence of a 4-5 mb
DAG-LAX pressure gradient and 20-45 mph winds within the lowest 1
km. The regional surface pressure gradient is expected to gradually
weaken through the day as the main upper-level trough shifts to the
east. Elevated to critical fire weather conditions should become
somewhat more localized heading into the late afternoon hours,
but may persist well into the overnight and early morning hours on
Saturday for some locations - namely areas where terrain-augmented
winds are common.
Elevated to locally critical fire weather conditions will be possible
this afternoon for southeast CA and adjacent areas of southern
NV and far western AZ. This will largely be driven by 20-25 mph
pressure-gradient winds late this morning through the mid afternoon
hours as RH values fall into the teens. Conditions should improve by
the evening hours as the pressure-gradient winds begin to diminish.
..Moore.. 11/27/2020
...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
0138 AM CST Fri Nov 27 2020
Valid 281200Z - 291200Z
...Synopsis... An upper-level low over the southern High Plains,
along with a trough along the US/Canada border, will continue to
translate eastward through the day Saturday. These features will
bring rain chances to the south-central US and windy conditions
to the northern High Plains. Meanwhile, weak upper-level ridging
will become established over the southwestern US and along the West
Coast. While some fire weather concern will continue for portions
of southern CA, this ridging will aid in mitigating a more robust
fire weather threat.
...Southern California... Elevated to locally critical fire
weather conditions may be ongoing within the higher elevation of
Los Angeles and Ventura counties at the start of the period/early
Saturday morning. However, weakening mid-level winds (associated
with mid-level height rises through the day) will reduce the
potential for widespread critical conditions by the afternoon
hours. Despite these weaker winds aloft, persistent high pressure
over the northern Great Basin will continue to support offshore
winds at the surface. Given poor RH recoveries through Saturday,
this could maintain areas of elevated fire weather conditions through
the day for the higher elevation of Los Angeles and Ventura counties,
especially for locations that typically see terrain-enhanced winds.
...northern High Plains... Windy conditions are expected Saturday
afternoon in the wake of a cold front. Although wind speeds between
15-20 mph will be possible, cold air advection behind the front
will help maintain RH values above elevated thresholds. However,
some guidance suggests that deeper mixing and the introduction of
drier air could allow a few locations to experience RH values in
the low 20s. Confidence in these solutions is low, but if correct
then pockets of elevated conditions will be possible for eastern
MT and western ND.
..Moore.. 11/27/2020
...Please see www.spc.noaa.gov/fire for graphic product...
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