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LU9DCE > ALERT 21.11.20 15:10z 194 Lines 11000 Bytes #999 (0) @ WW
BID : 41488_LU9DCE
Read: GUEST
Subj: STORM PREDICTION CENTER 21 11
Path: HB9ON<IW8PGT<IZ3LSV<DB0ERF<DB0RES<ON0AR<GB7CIP<N7HPX<LU9DCE
Sent: 201121/1501Z 41488@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 1148
PM CST Fri Nov 20 2020
Valid 211200Z - 221200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY... The risk for severe thunderstorms appears negligible
across the U.S. through tonight.
...Synopsis... A shortwave trough is forecast to amplify and
move southeastward from the northern Rockies this morning into
the central Plains by late tonight. At the surface, a cold front
will sag southward across the southern Plains and Ozark Plateau,
as a weak surface wave develops along the boundary and moves
northeastward toward the mid-MS Valley by Sunday morning.
...South-central Plains into the Ozark Plateau/Mid-MS Valley...
In advance of the primary shortwave trough moving into the central
Plains, one or more lower-amplitude vorticity maxima will likely
traverse the central Plains into the mid-MS Valley this afternoon
into tonight. Ascent attendant to these features will likely
result in the development of primarily elevated convection to the
north of the cold front. The most robust convection is currently
anticipated from northeast OK into the Ozark Plateau this evening,
where modest low-level moisture and relatively steep midlevel lapse
rates may support MUCAPE up to 500 J/kg. Small hail may occur with
the strongest storms, but the severe risk appears low at this time.
Convection should spread into the mid-MS Valley late tonight.
...South FL... While very dry air aloft and a warm layer based
roughly around 700 mb will continue to suppress attempts at
deep convection during much of the day, a gradual increase in
moisture/instability across south FL may support the potential
for isolated thunderstorm development by late afternoon/evening,
primarily across the southeast portion of the peninsula.
..Dean.. 11/21/2020
SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1200
AM CST Sat Nov 21 2020
Valid 221200Z - 231200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY... Organized severe thunderstorms appear unlikely across
the contiguous United States on Sunday.
...Synopsis and Discussion... An upper trough initially over the
Plains and Upper Midwest Sunday morning will progress eastward
across the MS/OH Valleys to the eastern states by the end of
the period. At the surface, a weak low over the mid MS Valley
should develop northeastward across the OH Valley and into the
Mid-Atlantic/Northeast by late Sunday night while slowly deepening. A
cold front attendant to this surface low is forecast to sweep
east-southeastward across much of the southern Plains, lower MS
Valley/Southeast, and eastern states through early Monday morning.
Limited low-level moisture, characterized by 50s surface dewpoints,
should be present in a narrow corridor ahead of the front across
parts of TX to the Mid-South. Isolated showers and thunderstorms may
be ongoing at the start of the period over these areas along/behind
the front, although instability should remain rather weak owing to
poor mid-level lapse rates. Thunderstorm potential should quickly
diminish by Sunday afternoon as the forcing associated with the
upper trough departs this region. Negligible instability forecast
across the OH Valley/Mid-Atlantic suggests thunderstorm potential
should remain very low as the upper trough moves over these areas.
Along much of the East Coast, surface ridging should generally
hinder the inland advance of substantial low-level moisture. One
exception may be eastern NC/SC late Sunday night into early Monday
morning. Here, upper 50s to low 60s surface dewpoints may be present
ahead of the eastward-advancing cold front. As modest mid-level
height falls associated with the approaching upper trough overspread
this region, at least isolated thunderstorms may develop. Although
deep-layer shear appears sufficient to support organized storms,
current expectations are for greater instability to remain confined
to immediate coastal areas, with any meaningful strong to severe
storm potential probably remaining offshore.
Elsewhere, isolated thunderstorms may occur Sunday across parts
of the FL Peninsula and the Keys as weak low-level easterly flow
continues, and the Four Corners vicinity into western CO as upper
troughing amplifies over the western CONUS late in the period.
..Gleason.. 11/21/2020
SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0212
AM CST Sat Nov 21 2020
Valid 231200Z - 241200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY... Organized severe thunderstorms are not expected
across the contiguous United States on Monday.
...Synopsis and Discussion... A pair of large-scale upper troughs
will move eastward across the CONUS on Monday. Strong low-level
warm/moist advection ahead of the upper trough over the eastern
states may support just enough elevated instability to generate
isolated lightning flashes across parts of coastal MA/ME early
in the period. Any thunderstorm potential should shift quickly
east-northeastward and offshore through the day in tandem with the
progression of the upper trough.
The upper trough over the western CONUS should likewise progress
eastward, with the southern portion of this trough perhaps closing
off near the Four Corners late Monday night. Although moisture
will likely remain quite limited, cooling mid-level temperatures
and strong forcing for ascent associated with the upper trough
should support isolated thunderstorms across parts of the
southern/central Rockies through the period. At the surface, lee
cyclogenesis is forecast to occur across the central High Plains,
with modest low-level moisture return occurring across portions of
the southern/central Plains ahead of the developing low. Isolated
thunderstorms may also occur across this area, mainly Monday night
into early Tuesday morning. Instability should remain fairly weak,
with any storms that form likely remaining elevated.
..Gleason.. 11/21/2020
Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK
0345 AM CST Sat Nov 21 2020
Valid 241200Z - 291200Z
...DISCUSSION... At least an isolated/marginal severe threat should
exist on Day 4/Tuesday across parts of the southern Plains into the
Ozarks and lower MS Valley as an upper trough/low ejects eastward
over these regions. Low-level moisture return ahead of a surface low
and related cold front may be sufficient to support surface-based
storms from Tuesday afternoon onward. Deep-layer shear appears more
than sufficient for organized severe storms, but some uncertainty
exists regarding how much instability will ultimately develop. Given
this uncertainty, will hold off for now on including a 15% severe
area on Day 4/Tuesday across any portion of the southern Plains
vicinity, but will reevaluate this possibility in future outlooks.
As the upper trough/low continues east-northeastward across the
central/eastern CONUS on Day 5/Wednesday, a low-end/marginal
severe threat may continue across parts of the lower MS Valley
and Southeast. However, medium-range guidance begins to diverge in
the placement and amplitude of the upper trough/low by Wednesday
evening. It also appears possible that any storms ongoing Wednesday
morning across the lower MS Valley/Mid-South may outpace the
low-level moisture return across the Southeast through the day.
Given these large-scale pattern predictability issues and concerns
about sufficient instability across the warm sector, a 15% severe
area has not been included across the lower MS Valley into the
Southeast for Day 5/Wednesday.
Substantial differences in the synoptic-scale pattern across the
CONUS continue from Day 6/Thursday through the end of the forecast
period. Even so, there appears to be some signal for another
large-scale upper trough to move from the western CONUS to the
Plains in the Day 7/Friday to Day 8/Saturday time frame. Depending
on the evolution of this upper trough/low and how much low-level
moisture return occurs ahead of it, there may be an increase
in severe potential across portions of the southern Plains and
lower MS Valley from Day 7/Friday into Day 8/Saturday. Regardless,
predictability remains far too low to delineate any severe areas
at this extended time frame.
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK
1243 AM CST Sat Nov 21 2020
Valid 211200Z - 221200Z
...Synopsis... An upper trough is forecast to amplify over the
central U.S. today, as upstream shortwave troughs move into southern
CA and also the Pacific Northwest by tonight. At the surface, a
ridge will remain in place across the interior Northwest, resulting
in a weak offshore flow regime across portions of southern CA.
...Southern CA... Elevated fire weather conditions are expected to
develop as early as this morning, primarily across terrain-favored
areas of Los Angeles and Ventura counties, as the offshore gradient
gradually increases. Sustained winds of 15-20 mph (with higher
gusts) are expected, as RH values drop to near or below 15%. Poor
RH recovery is expected tonight across the higher terrain, where
elevated conditions may linger into Sunday morning.
..Dean.. 11/21/2020
...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
1244 AM CST Sat Nov 21 2020
Valid 221200Z - 231200Z
...Synopsis... As an upper trough moves from the central into
the eastern CONUS on Sunday, an upstream trough is forecast to
amplify over much of the West. The surface ridge centered over the
interior Northwest is forecast to weaken and shift eastward during
the day. Weak offshore flow may persist into early Sunday across
portions of southern CA before weakening late in the day.
...Southern CA... Elevated fire weather conditions may persist into
at least the first part of Sunday across terrain-favored regions
of Los Angeles and Ventura counties, before the offshore gradient
weakens later in the day. Sustained winds of 15 mph with higher gusts
will be possible in wind-prone areas, while RH recovery from Saturday
night into Sunday morning will be poor across the higher terrain.
..Dean.. 11/21/2020
...Please see www.spc.noaa.gov/fire for graphic product...
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