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LU9DCE > ALERT 12.12.20 16:01z 172 Lines 9520 Bytes #999 (0) @ WW
BID : 42874_LU9DCE
Read: GUEST
Subj: STORM PREDICTION CENTER 12 12
Path: HB9ON<IW8PGT<IZ3LSV<IK5FKA<IK5FKA<LU9HGS<LU9DCE
Sent: 201212/1600Z 42874@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 1839 CONCERNING HEAVY SNOW FOR PORTIONS OF CENTRAL AND EASTERN
IOWA
Mesoscale Discussion 1839 NWS Storm Prediction Center Norman OK
0119 AM CST Sat Dec 12 2020
Areas affected...portions of central and eastern Iowa
Concerning...Heavy snow
Valid 120719Z - 121315Z
SUMMARY...An area of heavy snowfall is forecast to evolve over the
next 2-3 hours, with snowfall rates around 1" per hour expected
-- likely peaking during a 3-5 hour period from roughly 08-09Z
through 12-14Z.
DISCUSSION...Latest radar loop shows a zone of light to moderate
snowfall occurring from eastern Nebraska eastward to eastern Iowa,
with the current rain/snow line extending roughly from KLWD (Lamoni
IA) to roughly KCWI (Clinton IA). This zone of snowfall is occurring
within a zone of deformation north of a well-defined vort max --
evident in current WV imagery over the Ozark Plateau of southern
Missouri -- which will continue moving east-northeastward with time
and reaching central Illinois around sunrise.
Favorable large-scale ascent will continue within the deformation
zone as the surface low -- now over northeastern Missouri --
continues to gradually deepen as it shifts east-northeastward
with time, in tandem with translation of the upper feature, and
strengthening of the cold conveyor belt. With moist/saturated
thermal profiles -- including within the favored dendritic growth
zone -- an increase in snowfall rates within the deformation zone is
expected, possibly aided by some weak convective enhancement given
steep lapse rates and even some minimal CAPE hinted at within model
forecast soundings.
Snowfall should increase over the next 2-3 hours, and continue
at around 1" per hour rates within the MD area for several hours,
before tapering gradually from west to east through mid morning.
..Goss.. 12/12/2020
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...DVN...ARX...DMX...
LAT...LON 41359369 42049372 42419298 42719181 42719091 42219068
41759143 41239217 41359369
SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0147
AM 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.
...Discussion... Within the belt of westerlies emanating from the
mid-latitude Pacific, models indicate that a lead short wave trough
will rapidly accelerate east-northeast of the southern Appalachians,
across the southern Mid Atlantic coast and into the western Atlantic
during this period. This is expected to occur to the southeast of
a vigorous short wave trough of Arctic origins, which is forecast
to accelerate eastward within strengthening cyclonic flow, from
the upper Great Lakes into the Canadian Maritimes.
While there may be at least some increase in phasing of these
perturbations, it appears that this will be mostly well east of
the Atlantic Seaboard, supporting a rapidly deepening cyclone over
the Atlantic to the south/southeast of the Canadian Maritimes
by 12Z Tuesday. Models do suggest that the onset of more rapid
cyclogenesis could occur as early as midday Monday, but generally
just offshore of the Mid Atlantic coast. Prior to this, it is
possible that low-level moistening and large-scale ascent may
contribute to very weak destabilization across parts of the middle
and south Atlantic Seaboard. However, forecast thermodynamic
profiles, at best, currently appear only marginally conducive to
convection capable of producing lightning. Primary thunderstorm
development seems likely to become focused closer to the Gulf stream,
as forcing for ascent spreads offshore Monday afternoon.
Meanwhile, upstream, models indicate considerable amplification of
another short wave trough of mid-latitude Pacific origins, across
the Rockies into the central and southern Great Plains by late
Monday night. However, preceded by expansive cold surface ridging,
building beneath a strongly confluent mid-level regime across
and east of the Mississippi Valley, models indicate that surface
cyclogenesis to the lee of the southern Rockies will be subdued.
Generally cold, dry and/or stable conditions likely will prevail
across most areas east of the Rockies, as well as across the West.
..Kerr.. 12/12/2020
Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK
0303 AM CST Sat Dec 12 2020
Valid 151200Z - 201200Z
...DISCUSSION... Medium-range model output suggests that initially
northwest flow across much of Canada will transition to a more zonal
regime, while a belt of westerlies emanating from the mid-latitude
Pacific remains a prominent influence across much of the U.S. through
the middle and latter portions of next week. As this occurs,
it appears that an initially amplified trough to the lee of the
southern Rockies will lose amplitude, with the most significant
embedded perturbation accelerating toward the Mid Atlantic, where
it may support significant surface cyclogenesis offshore Wednesday
into Thursday. An additional perturbation or two may follow within
this stream, inland across the Pacific coast and through the U.S. by
early next weekend. However, models indicate little in the way of
substantive surface cyclogenesis and inland return flow of moisture
off the Gulf of Mexico, resulting in the maintenance of generally
stable conditions and low convective potential.
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK
0129 AM CST Sat Dec 12 2020
Valid 121200Z - 131200Z
...Synopsis... A substantial mid-level wave - initially over Idaho
at 12Z Saturday - will make steady southeastward progress toward
the central Rockies during the forecast period. As this occurs,
mid/upper flow will intensify across the southern Rockies while a
surface low quickly organizes across central/eastern New Mexico.
West of the low, high pressure will build into the western Great
Basin and result in a 6-9 hour window of offshore flow late across
southern California and its coastal ranges.
...Southern New Mexico... The combination of a strengthening
surface pressure gradient and increasing flow at all levels will
result in areas of 20-30 mph surface winds across the southern half
of the state. These wind speeds will occur within areas of low RH
values ranging from 20-35% -lowest in lower elevations. Latest fuels
guidance suggests potential for fire spread across the region due
to dry fine fuels. The elevated delineation highlights areas most
likely to experience elevated fire-weather conditions for part of the
afternoon, though locally/briefly elevated fire-weather conditions
are possible farther west of these areas (into central/southwestern
New Mexico) as well.
...Southern California... Models indicate that offshore flow will
briefly intensify after around 06Z Sunday and remain strong through
around 12Z or so. Wind gusts exceeding 30 mph are possible -
locally higher in terrain-favored areas. This brief offshore wind
event will combine with areas of 20-30% RH values and very high
ERCs to promote rapid fire spread despite an unfavorable time of
day for very low RH. An elevated fire-weather delineation remains
in place to address this threat.
..Cook.. 12/12/2020
...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
0131 AM CST Sat Dec 12 2020
Valid 131200Z - 141200Z
...Synopsis... A vigorous, yet progressive mid-level wave
will migrate across Texas on D2/Sun and promote surface pressure
falls/cyclogenesis across southeastern Texas throughout the forecast
period. West of the strengthening surface low, very strong high
pressure will build southward across the southern Rockies/High
Plains. This will result in a favorable surface pressure pattern
for strong post-frontal winds across portions of south Texas, with
latest models indicating enough warming/drying for an elevated to
locally critical fire-weather threat.
...Portions of south Texas... Within the post-frontal airmass,
surface temperatures rising into the mid-70s will promote falling RH
values during the afternoon, with recent high-resolution guidance
suggestive of 15-25% minimum RH values. This dry airmass will
combine with areas of 20-30 mph northwesterly winds to promote
elevated to locally critical fire-weather conditions. Fuels guidance
suggests that marginally favorable ERCs are in place, which may
support fire spread given the dry/windy conditions. Models suggest
only briefly/locally critical fire-weather in any given location
across south Texas, with locally elevated fire-weather possible as
far east as the Austin/San Antonio areas through early evening.
..Cook.. 12/12/2020
...Please see www.spc.noaa.gov/fire for graphic product...
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Tonight's the night: Sleep in a eucalyptus tree.
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