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LU9DCE > ALERT 26.11.20 16:24z 223 Lines 12885 Bytes #999 (0) @ WW
BID : 41774_LU9DCE
Read: GUEST
Subj: STORM PREDICTION CENTER 26 11
Path: HB9ON<IW2OHX<IQ2LB<IR2UFV<N3HYM<N7HPX<LU9DCE
Sent: 201126/1600Z 41774@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 1149
PM CST Wed Nov 25 2020
Valid 261200Z - 271200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PORTIONS
OF FAR EASTERN TEXAS INTO LOUISIANA...
...SUMMARY... Isolated large hail may occur with thunderstorms that
develop across parts of far eastern Texas into Louisiana tonight
into early Friday morning.
...Synopsis... A compact mid-level shortwave trough will move
across the Northeast and eject into the Atlantic while modest
surface lee troughing will prevail along the East Coast through
the day into early Friday morning. Adequate moisture and lift
associated with this lee troughing will promote at least isolated
thunderstorm development. Meanwhile, a second trough aloft is
poised to traverse the Inter-mountain West while diverging from
the broader upper cyclonic flow regime and evolving into a 500 mb
cutoff-low. At the surface, a cold front will move across the Plains
states, preceded by a region of weak low pressure and associated
low-level WAA across the mid-South. Colder mid-level temperatures
associated with the approaching upper trough/cyclonic flow regime
will contribute to enough buoyancy to support a very isolated severe
threat early Friday morning.
...Portions of the mid Atlantic into the Carolinas... As the
aforementioned trough moves toward the Atlantic, a gradual veering
and weakening of the tropospheric wind profiles is likely.
Marginal instability will be in place to support isolated to
potentially scattered thunderstorm development, with strong enough
diurnal heating likely to promote some boundary-layer mixing.
However, the lack of both stronger buoyancy and flow aloft to be
transported to the surface suggests that severe gusts would be too
sparse for Marginal highlights at this time. Nonetheless, a strong
to marginally severe gust or two cannot be completely ruled out.
...Far eastern Texas into Louisiana... Within the roughly 06-12Z
time frame, a plume of steeper mid-level lapse rates (up to 8 C/km
based on 00Z NAM, GFS, and 03Z RAP forecast soundings) is expected
to overspread a modest moist/warm-air advection regime, promoting
over 1000 J/kg MUCAPE in spots. While much of this instability is
expected to be elevated, cellular convection may ingest air-parcels
down to 850 mb, within a layer of modestly veering low-level winds,
with around 150 m2/s2 effective SRH available to any storms that
form. As such, storms may become organized and long-lived enough
to support isolated large hail, with a Marginal risk for severe
storms maintained over the area.
..Squitieri.. 11/26/2020
SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1200
AM CST Thu Nov 26 2020
Valid 271200Z - 281200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS
OF CENTRAL/EAST TEXAS...LOUISIANA...AND SOUTHWESTERN MISSISSIPPI...
...SUMMARY... Isolated strong to severe thunderstorms may
occur Friday across parts of central/east Texas, Louisiana, and
southwestern Mississippi. Large hail and strong to damaging winds
should be the main threats.
...Texas into the Lower Mississippi Valley... Mainly elevated
thunderstorms will probably be ongoing to the north of a warm front
at the beginning of the period across parts of east TX and LA. This
activity will be supported by modest low-level warm advection, which
is forecast to weaken through Friday morning. Still, given the
forecast combination of MUCAPE around 500-1250 J/kg and 35-45 kt of
deep-layer shear, this convection may continue to pose an isolated
large hail threat across parts of LA and perhaps southwestern MS
through the morning hours before diminishing.
As a closed upper low slowly pivots across the Southwest and
towards the southern High Plains through the period, a belt of
enhanced west-southwesterly mid-level winds will remain over much
of central/east TX into parts of the lower MS Valley. A generally
southwest-northeast oriented surface boundary should be located
over these areas, with rich low-level moisture characterized by
upper 60s to perhaps low 70s surface dewpoints to its south. It
appears that this boundary will serve a focus for potentially robust
convection through the day, possibly beginning by early afternoon
across central TX as an upper jet overspreads this region. Up to
1000-1500 J/kg of MLCAPE may develop along/south the front. Coupled
with strong deep-layer shear, this should support some organized
convection. Isolated large hail and strong to locally damaging
wind gusts appear to be the main threats as storms move slowly
east-southeastward into coastal TX/LA in tandem with the surface
front through Friday evening.
..Gleason.. 11/26/2020
SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0210
AM CST Thu Nov 26 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 mid/upper-level low should
move slowly eastward across the southern Plains on Saturday. A
prolonged period of precipitation will likely have been ongoing
since Friday across much of central/east TX ahead of this feature,
limiting instability. A weak surface low is forecast to develop
from the lower TX Coast vicinity northeastward towards coastal
LA through the period. A cold front will probably move off the
TX Coast Saturday morning, with elevated, non-severe thunderstorms
possible to its north across parts of central/east TX. At this point,
it appears that a marine warm front extending east-northeastward
from the surface low will not make substantial progress inland
across coastal LA/MS/AL through late Saturday night. Accordingly,
the potential for surface-based thunderstorms posing even an
isolated/marginal severe risk across this area currently appears low.
..Gleason.. 11/26/2020
Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK
0300 AM CST Thu Nov 26 2020
Valid 291200Z - 041200Z
...DISCUSSION... It appears increasingly probable that a closed
upper low over the southern Plains will merge with a northern-stream
upper trough over the eastern CONUS on Day 4/Sunday, likely forming
a highly amplified upper trough/low by Day 5/Monday. Medium-range
guidance is in reasonably good agreement in depicting a deepening
surface low developing from coastal LA Sunday morning northeastward
to the Mid-Atlantic vicinity by Day 5/Monday.
As greater low-level Gulf moisture advances inland across parts
of the Southeast and Mid-Atlantic in tandem with the deepening
surface low, weak instability may develop across the warm sector of
this cyclone. Rapidly strengthening low and mid-level wind fields
suggest that organized severe storms capable of producing at least
isolated damaging winds may occur over parts of the Deep South into
the Carolinas on Day 4/Sunday, and from the Carolinas into eastern
portions of the Mid-Atlantic on Day 5/Monday.
At this point, it remains very uncertain how much surface-based
instability will ultimately develop across these regions, which will
have a large impact on overall severe potential. This uncertainty
precludes the introduction of 15% severe probabilities for now.
However, the severe potential for this system will be reevaluated
in later outlook updates. Once the cold front associated with this
cyclone clears the East Coast, severe thunderstorm potential appears
minimal across the CONUS on Day 6/Tuesday and Day 7/Wednesday.
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK
0157 AM CST Thu Nov 26 2020
Valid 261200Z - 271200Z
...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHERN CALIFORNIA...
...Synopsis... A mid-level shortwave trough will move across
the southwest CONUS as it evolves into a cut-off low through the
period. At the surface, a strong pressure gradient will persist
across central into southern California, with dry and breezy
offshore flow supporting a wildfire-spread threat, especially for
portions of the southern California Transverse Ranges. While upper
support will generally be lacking across the south-central U.S,
modest lee troughing and associated downslope westerly flow across
the southern High Plains is expected to precede an approaching cold
front, with dry conditions likely.
...Portions of central and southern California... Strong mid-level
flow and upper support will contribute to intensification of the
surface pressure gradient, with the latest guidance depicting
the LAX-DAG gradient to reach -3 to -5 mb before 00Z Friday, and
increase to over -6 mb early Friday morning. Across the southern
Transverse Ranges, particularly across the Ventura Valley and Santa
Ana mountains, dry and windy offshore flow conditions are expected
around 18Z and will continue to 12Z Friday. RH may dip to the 10-15%
range by late afternoon/early evening, coinciding with widespread
25+ mph sustained winds. Locally stronger winds, as well as gusts
exceeding 45 mph are possible across terrain-favoring locations
and at higher elevations. Critical fire weather highlights have
been maintained for areas of highest confidence in Critical to
high-end Critical surface conditions overlapping the relatively
more receptive fuels.
Just north of the Bay area across the lower Sacramento Valley,
mid-level northerly flow is expected to overspread a deep, dry
boundary layer. Widespread 15-25 mph sustained northerly surface
winds in association with downslope flow are likely along the eastern
slopes of the Coast Ranges, with RH dropping to near 20% in some
locales. Disagreement exists among guidance members regarding how
low RH will drop however. In addition, some spots have seen up to
2.0 inches of rain in the last two weeks. As such, an Elevated area
has been withheld this outlook given the uncertainties with RH and
fuel receptiveness.
...Southern High Plains... Weak downslope westerly flow is expected
across portions of eastern New Mexico into western Texas by afternoon
peak heating, with RH expected to drop into the 15-20% range. Despite
the favorable RH and modestly receptive fuels, the overall surface
wind field is expected to remain mainly below 15 mph through the
day given weak upper support, precluding Elevated highlights.
..Squitieri.. 11/26/2020
...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
0201 AM CST Thu Nov 26 2020
Valid 271200Z - 281200Z
...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHERN CALIFORNIA...
...Synopsis... Surface high pressure across the Inter-mountain
West will weaken somewhat as a mid-level cutoff low enters the
Plains states Day 2/Friday. The surface pressure gradient across
southern California will relax through the period, with offshore flow
gradually subsiding in strength, especially by Friday night. Early
Friday morning into mid-afternoon however, the strongest and driest
offshore flow will persist, promoting significant wildfire-spread
potential. Elsewhere across the CONUS, surface high pressure,
cooler temperatures, and moister low-level conditions will dominate,
with relatively quiescent fire weather conditions expected.
...Portions of southern California... The latest guidance consensus
shows a strong (i.e. LAX-DAG -5 to -7 mb) pressure gradient across
southern California, with widespread 25+ mph sustained offshore flow
overlapping 10-15% RH Friday morning. Gusts over 50 mph are possible
in terrain favoring areas, especially before noon. However, 00Z-12Z
Saturday, sustained surface winds are expected to decrease below
25 mph across the lower terrain areas, though some high-resolution
guidance suggests 25 mph offshore flow may persist across higher
elevations. Elevated highlights are in place through the entire
period for most of the southern Transverse Ranges, with a Critical
area introduced for locations that will most likely experience
widespread 25+ mph winds the longest, especially Friday morning.
..Squitieri.. 11/26/2020
...Please see www.spc.noaa.gov/fire for graphic product...
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