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LU9DCE > ALERT 13.12.20 16:05z 272 Lines 15414 Bytes #999 (0) @ WW
BID : 42948_LU9DCE
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Subj: STORM PREDICTION CENTER 13 12
Path: HB9ON<IW2OHX<IR1UAW<IZ3LSV<IW8PGT<LU4ECL<ZL2BAU<PY2BIL<LU9DCE
Sent: 201213/1601Z 42948@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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MD 1842 CONCERNING HEAVY SNOW FOR SOUTHEASTERN
COLORADO...SOUTHWESTERN KANSAS...THE OKLAHOMA PANHANDLE AND NORTHERN
PORTIONS OF THE TEXAS PANHANDLE...AND NORTHWESTERN OKLAHOMA
Mesoscale Discussion 1842 NWS Storm Prediction Center Norman OK
0100 AM CST Sun Dec 13 2020
Areas affected...southeastern Colorado...southwestern Kansas...the
Oklahoma Panhandle and northern portions of the Texas Panhandle...and
northwestern Oklahoma
Concerning...Heavy snow
Valid 130700Z - 131300Z
SUMMARY...Snowfall rates near, or locally slightly in excess of,
1" per hour will likely spread across the discussion area over the
next 3 to 6 hours.
DISCUSSION...Heavy snow -- aided by easterly low-level upslope flow
-- has been falling for several hours across the Sangre de Cristo
mountains of southeastern Colorado, and will continue at rates in
excess of 1" per hour as an upper low over the southern Rockies
shifts east-southeastward into the southern High Plains with time.
As the low progresses, snowfall will continue spreading across
southeastern Colorado into southwestern Kansas and portions of the
Texas and Oklahoma Panhandles, where temperatures are now near or
just below freezing.
Aided by increasing large-scale ascent as the upper low progresses
east-southeastward, expect coverage and intensity of precipitation
ongoing across portions of the discussion area to increase gradually
through the early morning hours. Additionally, model point forecast
soundings hint at the potential for very weak CAPE through the
favored dendritic growth zone, which suggests some convective
enhancement may allow rates to exceed an inch per hour locally,
at times. Currently, it would appear that the heaviest snowfall
over the next few hours may occur over southwestern Kansas and into
the Oklahoma Panhandle, southeastward into northeastern portions of
the Texas Panhandle and adjacent northwestern Oklahoma, where radar
is exhibiting hints of a deformation band evolving across this area.
..Goss.. 12/13/2020
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...ICT...OUN...DDC...AMA...PUB...
LAT...LON 37890161 37090255 36370245 35480162 35649919 37199833
37929969 37890161
SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1148
PM CST Sat Dec 12 2020
Valid 131200Z - 141200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
MIDDLE/UPPER TX COAST INTO SOUTHEAST TX AND CENTRAL/SOUTHERN LA...
...SUMMARY... Isolated strong to severe thunderstorms may impact
parts of the Upper Texas Coast and southern/central Louisiana on
Sunday. Damaging wind gusts and perhaps a tornado or two are the
main threats.
...Middle/Upper Texas Coast into Southern/Central Louisiana...
Shortwave trough currently moving through the Four Corners region is
forecast to continue quickly southeastward, reaching the southern
High Plains by later this morning. This shortwave is then expected
to pivot more eastward across the southern Plains and Lower MS
Valley, while also obtaining a more neutral tilt. This transition
to a more neutral tilt will also be accompanied by strengthening
mid-level flow as well as increasing low-level flow throughout the
warm sector and surface cyclogenesis.
Surface low resulting from this cyclogenesis will likely develop
along the middle TX Coast before moving northeastward across central
LA and into central MS. This path will limit the inland penetration
of the warm sector, with low 60s dewpoints likely remaining confined
from the middle TX coast in southeast TX during the day. Later this
evening and overnight, low 60s dewpoints will likely reach central
portions of the Lower MS Valley and Southeast states.
Primary forecast concern is whether or not surface-based storms
will be able to establish within the warm sector over southeast
TX/Upper TX Coast. Based on forecast soundings, surface temperatures
likely need to reach the low/mid 70s for surface-based storms, which
appears most probable from the middle TX Coast into southwest LA in
the 18 to 21Z time frame. Given the impressive kinematic profiles,
the expectation is that any warm-sector storms that are able to
persist and maintain updraft continuity should be able to organize
into supercells. Primary threat would be damaging wind gusts, but
a tornado or two is also possible. One additional factor working
against tornadogenesis (in addition to limited instability and a
potentially elevated storm structure) is the anticipated veering
of the low-level winds during the afternoon ahead of the cold front.
A strongly forced, but narrow line of storms is anticipated along the
front in the wake of the earlier warm-sector activity. A few stronger
gusts are possible from the middle TX coast into southern LA as this
line moves through. Low-level stability will likely limit strong
gusts at the surface across much of east TX and northern/central LA,
but potential exists for a few gusts to be strong enough to penetrate
the stable layer. Overnight, storms should have a tendency to become
more elevated with eastern extent into the Southeast as the system
outpaces the low-level moisture along the coast.
..Mosier.. 12/13/2020
SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1120
PM CST Sat Dec 12 2020
Valid 141200Z - 151200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY... The risk for severe thunderstorms appears negligible
across the U.S., Monday through Monday night.
...Synopsis... A belt of westerlies emanating from the mid-latitude
Pacific will remain a prominent influence across much of the
U.S. through this period, with one embedded short wave trough
expected to be progressing into/across the southern Appalachians
vicinity by 12Z Monday. Models indicate a continued rapid
east-northeastward acceleration across the southern Mid Atlantic
coast by late Monday afternoon, accompanied by a still modest,
but deepening, surface cyclone.
This is forecast to occur as a more vigorous short wave trough,
on the leading edge of northwesterly flow emanating from the
northwestern Canadian Arctic latitudes, accelerates eastward within
strengthening cyclonic flow across the upper Great Lakes into the
Canadian Maritimes. There may be increased phasing of the two
perturbations east of the north Atlantic Seaboard, accompanied
by substantive further deepening of the surface cyclone to the
southeast of the Canadian Maritimes.
In the wake of these features, and in advance of another significant
amplifying mid-level trough digging across the southern Rockies
and central/southern Great Plains, a confluent mid-level regime is
forecast to support building cold surface ridging across and east
of the Mississippi Valley into the Atlantic Seaboard. This will
tend to suppress surface cyclogenesis to the lee of the southern
Rockies, with generally stable conditions being maintained across
most areas east of the Rockies, in addition to much of the West.
...Southern Mid Atlantic... Thermodynamic profiles characterized
by a stable boundary-layer and generally weak mid-level lapse rates
are expected to prevail along the warm frontal zone, ahead of the
developing cyclone expected to migrate into the western Carolinas
by 12Z Monday. However, at least some forecast soundings (perhaps
most notably the NAM) suggest that modest moisture return, in the
presence of lift aided by low-level warm advection, may contribute
to profiles at least marginally conducive to convection capable of
producing lightning. Any such activity probably will be focused
just ahead of strong mid-level subsidence warming, which is forecast
to accompany a strong cyclonic mid-level jet nosing across the
Carolinas by mid afternoon Monday.
Low-level and deep-layer shear may become strong by Monday
afternoon across the Outer Banks area of North Carolina, where
weak boundary-layer destabilization may not be entirely out of
the question. However, appreciable potential for strong to severe
thunderstorm activity still seems focused offshore, closer to the
Gulf stream, late Monday afternoon and evening.
..Kerr.. 12/13/2020
SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0132
AM CST Sun Dec 13 2020
Valid 151200Z - 161200Z
...NO THUNDERSTORM AREAS FORECAST...
...SUMMARY... The risk for thunderstorms appears negligible across
the U.S., Tuesday through Tuesday night.
...Discussion... Models indicate that initially amplified
mid/upper troughing digging to the lee of the southern Rockies by
12Z Tuesday may undergo considerable shearing during this period.
The primary embedded short wave perturbation, perhaps including
at least a transient closed mid-level low, is generally forecast
to pivot across the central and southern Great Plains, through
the middle and lower Mississippi Valley by the end of the period.
As it does, it is forecast to provide support for slowly deepening
surface troughing across and east of the Mississippi Valley.
Although initially expansive cold surface ridging across and
east of this region at the outset of the period will suppress
significant surface cyclogenesis, this may include the development
of a surface low over the lower Ohio Valley by 12Z Wednesday.
Otherwise, a frontal zone, initially extending across the central
Florida Peninsula into the northern Gulf of Mexico, probably will
become the primary focus for potential cyclogenesis. And models
indicate a couple of waves developing along it by late Tuesday night.
Boundary-layer moistening and destabilization within the warm sector
of one of these, across the north central into northeastern Gulf of
Mexico, could provide support for increasing thunderstorm activity
(well offshore) Tuesday night. Another wave, developing a bit
later, may be accompanied by at least increasing boundary-layer
destabilization off the south Atlantic coast.
Otherwise, across and inland of coastal areas, through most of
the U.S., generally stable conditions are likely to prevail with
negligible risk for thunderstorms.
..Kerr.. 12/13/2020
Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK
0307 AM CST Sun Dec 13 2020
Valid 161200Z - 211200Z
...DISCUSSION... A significant, remnant short wave perturbation,
accelerating out of the southern Great Plains by Tuesday, may
reach the southern Mid Atlantic coast by Wednesday evening. As it
approaches the coast, medium-range models indicate that it will
support substantive further deepening of a frontal wave initially
developing off the South Carolina coast by daybreak Wednesday.
It might not be entirely out of the question that a moistening and
destabilizing warm sector boundary layer could spread across parts of
the North Carolina Outer and Inner Banks vicinity Wednesday afternoon
or evening. However, at this point, this seems a low probability,
and it is not clear that this would support more than a low severe
thunderstorm risk.
Otherwise, mid/upper flow is forecast to become more zonal across
Canada later this week through next weekend, with much of the U.S.
remaining under the influence of branching westerlies emanating
from the mid-latitude Pacific. It appears that this may include a
number of relatively fast moving short wave perturbations. While the
potential for significant surface cyclogenesis appears low, even
if one of these is able to support at least modest cyclogenesis
near Gulf coastal areas, it is not clear that the Gulf boundary
layer will be able to modify sufficiently to support a substantive
inland return flow of moisture.
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK
0147 AM CST Sun Dec 13 2020
Valid 131200Z - 141200Z
...Synopsis... A vigorous shortwave trough will move quickly
east-southeastward across Oklahoma/Texas today while spreading
intense mid-level flow across the southern half of Texas. The lift
associated with these features will foster surface cyclogenesis
across southeastern Texas and eventually southern Louisiana late,
while a cold front shifts southward across south Texas and the Rio
Grande Valley. Meanwhile, strong high pressure will move into the
southern Rockies/High Plains behind the front. That same high will
foster offshore flow early in the day across southern California.
...South Texas... Behind the cold front across south Texas,
models depict a fairly focused axis of warming and drying during
peak heating hours that will extend generally from the Rio Grande
near Del Rio to the Austin/San Antonio corridor. In this area,
20-30 mph Uppernorthwesterly surface winds will develop, while
downslope flow and warming will lower RH values into the 15-30%
range during the afternoon. These conditions will exist across
dry fuels with marginal ERCs, supporting a risk of fire spread.
The quick movement of the front and cold advection across west
Texas will limit the duration of any elevated to locally critical
fire-weather conditions.
...Southern California... A lingering offshore pressure gradient
will foster a few areas of breezy winds exceeding 15 mph in the
12-18Z timeframe. The offshore flow will help maintain a dry
airmass across the region, however, with RH values falling in
the 10-15% range during the day (locally lower in a few areas).
Fuels remain receptive with high ERCs and several ongoing large
fires. An elevated fire-weather delineation is in place to address
the threat.
..Cook.. 12/13/2020
...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
0147 AM CST Sun Dec 13 2020
Valid 141200Z - 151200Z
...Synopsis... Fire-weather concerns on D2/Mon will be focused on
southern California coastal ranges as high pressure builds into
portions of the Great Basin and fosters an offshore flow regime.
This regime should take shape mainly after 06Z, however. Earlier
in the day, dry/breezy conditions will develop across portions
of Arizona and New Mexico, although cooling surface temperatures
should keep any fire-weather risk relatively localized and limited
to mid-afternoon.
...Southern California... As the aforementioned offshore gradient
develops in the Great Basin, a dry low-level airmass will return
overnight to coastal ranges across the region, with RH values as low
as 20% overnight (especially in the 06Z-12Z timeframe). Meanwhile,
a few areas will experience breezy conditions exceeding 15-25 mph in
tandem with the strengthening pressure gradient. These conditions
are consistent with elevated fire-weather thresholds, and an elevated
delineation is in place to address the threat.
..Cook.. 12/13/2020
...Please see www.spc.noaa.gov/fire for graphic product...
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