Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 11/06/21
Area Forecast Discussion
National Weather Service Columbia SC
1052 PM EDT Fri Nov 5 2021
.SYNOPSIS...
Low pressure will move across central FL tonight and into the
Atlantic basin toward daybreak then slowly along the coast of
the Carolinas Saturday and Sunday. This will result in rain
chances returning to the area on Saturday along with breezy
conditions. The low will move away from the region Sunday
allowing upper level ridging along with drier air and
moderating temperatures to return to the region early next
week.
&&
.NEAR TERM /UNTIL 7 AM SATURDAY MORNING/...
Satellite and radar imagery show extensive cloudiness blanketing
the region with rain stretching from the SC Coast through
Florida. Overnight the low currently crossing the FL Peninsula
to move offshore toward daybreak with models indicating a bit
more northerly track. This will create increasing northeasterly
winds during the early morning hours along with gusts reaching
20 mph during the early morning hours and slightly higher on
area lakes...especially in the eastern Midlands. Along with the
increasing winds Atlantic moisture will also be quickly advected
into the area. Much of the current radar returns continue to be
virga with a dry layer in the low and mid levels which will take
several hours to overcome before rain moves into the central
Midlands toward daybreak. As such have adjusted pops lower over
the next couple of hours then adjusted upward in the central and
eastern Midlands toward daybreak. With the cloud cover and
increasing moisture overnight lows will generally be in the low
to mid 40s.
&&
.SHORT TERM /7 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
By early Saturday morning the surface low pressure will be off
the coast of Georgia with a tightening pressure gradient
across the forecast area. Increased moisture transport that will
begin late Saturday night will continue with low levels
continuing to moisten as PWATs increase to around 1.2 inches in
the SE forecast area. With increased confidence in the low
traveling closer to the coast, have raised pops to likely across
around the eastern half of the forecast area and to chance
elsewhere. Highest QPF will still be offshore and along the
immediate SC coast but still potential for between a half inch
to an inch of rain through Saturday night. With increase cold
advection on the west side of this low as well as clouds and
rain, have also lowered temperatures for Saturday with highs in
the low to mid 50s. As the coastal low continues to deepen
Saturday, expect increasing NE winds over the area with gusts
exceeding 30 mph possible in the eastern forecast area and over
25 mph elsewhere through much of the day. Lake wind advisory
will be in place through the first half of Sunday as a result.
Winds will remain elevated overnight, highest on lakes where
mixing will continue with water temperatures still reasonably
warm.
By Sunday, surface low pressure will shift off the coast of the
Carolinas with lingering pressure gradient continuing to slowly
weaken over the course of the day. Some lingering moisture will
wrap around the low pressure system with chances for additional
rain in the far eastern area, with rain chances diminishing over
the course of the day. Temperatures recover, mainly in the west
with highs in the low to mid-60s where the sun will break out of
the clouds and temperatures in the upper 50s in the far east.
Sunday night temperatures drop into the upper 30s to low 40s.
&&
.LONG TERM /MONDAY THROUGH FRIDAY/...
Upper heights will continue to rise Monday with surface high
pressure building into the forecast area with ensembles favoring
PWATs dropping below .7 inch and drier air remaining in place
through the middle of the week. A weak upper trough passes
mainly north of the area which may lead to some increased clouds
but low levels will remain to dry to support any precipitation.
As the axis of the upper ridge shifts to the coast, moisture
will begin to increase Thursday into Friday. Have introduced
some chance pops for the end of the week as a result.
&&
.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
0250z update...latest AMDAR sounding at CAE indicating 35 kt at
2k ft, decided to add LLWS.
Previous discussion...Upper trough will cut off over the Gulf
Coast and move slowly east. Resultant surface low developing
near central FL along an old frontal boundary will shift slowly
NE to the Atlantic offshore NE FL and offshore SC
Saturday/Saturday night. This will eventually spread rain and
flight restrictions into our TAF sites but it will take a while,
as low levels still very dry. Current returns on radar virga
over our FA, with some PIREPs indicating some turbulence and
icing at mid to upper levels. Light rain is reaching the ground
along the S SC coast and SE GA. Will expect light rain to slowly
spread north overnight falling from a mid level deck, with CIGs
remaining above VFR level. Increasing boundary layer winds
tonight. LLWS possible, though surface winds may stay up enough.
Latest AMDAR sounding at CHS indicates 36kt around 1k ft, with
expectation of lower speeds farther north at our TAF sites. Will
monitor for possible inclusion of LLWS later tonight. Expect
winds to increase due to the developing low Saturday, with
breezy conditions expected. Some differences in model guidance,
so utilized SREF and latest hi res models, providing conditions
deteriorating to MVFR Sat afternoon.
EXTENDED AVIATION OUTLOOK...Increasing chances for rain and
lowering flight categories Saturday night into early Sunday,
under continued breezy conditions. Rain expected to move out
Sunday afternoon with gradual improvement to VFR but continued
breezy. No significant impacts to aviation expected Sunday night
through Wednesday except some late night/early morning shallow
ground fog possible at fog prone AGS and OGB Tue/Wed.
&&
.CAE WATCHES/WARNINGS/ADVISORIES...
GA...Lake Wind Advisory from 5 AM EDT Saturday to 2 PM EST Sunday
for GAZ040-063>065-077.
SC...Lake Wind Advisory from 5 AM EDT Saturday to 2 PM EST Sunday
for SCZ016-018-020>022-025>031-035-037-038-041-115-116-
135>137.
&&
$$
Area Forecast Discussion...CORRECTED
National Weather Service Reno NV
346 PM PDT Fri Nov 5 2021
.SYNOPSIS...
A trough of low pressure remains over the northeast Pacific through
the middle of next week. Two weak systems arrive Friday and Saturday
with breezes and chances for light rain and mountain snow; some
Sierra pass impacts are possible Saturday afternoon and evening.
Late Monday and Tuesday a much stronger system arrives with winds
along with heavier rain and snow.
&&
.SHORT TERM...
Unsettled weather continues through the weekend as a large-scale
trough of low pressure remains over the northeast Pacific. Two low
amplitude, fairly weak disturbances will move around the trough into
the West, impacting northeast California and western Nevada with
valley breezes, moderate (in a relative sense) ridge winds, and
periods of light rain and higher elevation snow.
Through tonight, the first wave currently off the northern California
coast skirts the region. The best lift with the wave is expected
to remain north of the area with rain and higher elevation snow
focused mainly on northern and northwestern CA. However, the wave
will bring increase flow aloft along with breezes working down into
valleys this afternoon and Saturday afternoon. Sierra ridgetop gusts
could reach 60-90 mph while valley winds are likely to top out around
20-30 mph today and Saturday for most spots. A bit higher gusts are
possible in wind prone locations with up to around 40 mph, especially
along the Highway 395/580 corridor.
By Saturday afternoon and evening, light precipitation moves into
northeast California and the Sierra down into Alpine County,
tapering to little or nothing farther south. For western Nevada
from about Highway 50 north, while forcing looks rather limited
there is a decent but narrow plume of moisture transport showing
up in the EPS and GEFS down to between 38N and 40N. If the timing
of the plume`s passage over western NV coincides with the best
upper forcing (not great in any case this far south), then there
may be a brief window for some light spillover into western NV.
Latest ensemble guidance indicates many runs with lower QPF than
in previous runs. Numbers have eased down to generally ~0.35" or
less for the Tahoe area crest southward with only a 20% chance
for 0.50" in the most recent NBM. This makes some sense given the
rapid progression of the wave and weak-ish upper forcing, although
that may be a bit better across northeast CA across Plumas and
Lassen counties. Lesser amounts up to 0.10" are expected for
northeast California east of Susanville. In western NV, amounts
would likely be on the light side at less than 0.10" (only a
20-30% chance for more than a tenth), highest west of I-580 as
well as out across north-central and northeastern NV (better
frontogenesis).
Colder air filters into northeast CA Saturday afternoon and
Saturday night, dipping down to 5000-6000 feet north of Tahoe and
6000-7000 feet from Tahoe. However, except in the orographically
favored areas near and west of the Sierra crest, precipitation
looks to mostly cut off behind the upper wave`s passage Saturday
evening. Being in a favored area, travel over the main Sierra
passes of I-80 and Hwy 50 could be impacted starting mid to late
Saturday afternoon with anywhere from 1-4" of snow possible through
Saturday night. Be prepared for slow downs and travel restrictions/
chain requirements if planning travel over the Tahoe area Sierra
later on Saturday.
It dries out again Sunday before another system early next week.
Please see the long term below for additional details.
-Snyder
.LONG TERM...Monday and beyond.
Its becoming clear that this strong low-pressure system moving
across northern CA/NV later Monday into Tuesday will pack somewhat a
significant fetch of Pacific moisture from a moderate AR event
sweeping east into the western US. Confidence remains somewhat
guarded as to timing and precipitation amounts with this next
system. Any uncertainty at this time should moderate over the next
couple model runs as Hi-Res guidance begins to play a more
significant role in the forecast. Any concerns with regards to wind
speed projections have become less a factor as ensemble guidance is
trending gusts consistently between 35-45 mph for most valley
locations and 80+ mph at higher Sierra ridges through Tuesday.
* Snow levels have trended even lower with the current NBM
guidance Monday night-Tuesday morning. Snow levels will increase
going into Monday evening and range between 4500-5500
across northeast CA, and as low as 5500-6,500 in the Tahoe
Basin. Winter driving impacts are a real possibility for the
higher Sierra passes across northeast CA, such as at Fredonyer
Pass along CA State Route 36, and also real possible for higher
portions of Highway 395 through Mono County, such as at Conway
Summit and Deadman passes where snow levels could drop into the
6500-7000 range. A foot or two of new snow is possible over
higher Sierra ridges above 9000`.
* The real wild card centers around varying solutions for
precipitation storm totals with ensemble guidance showing a
trend upwards over different locations across the Sierra Crest.
National Blend of Models (NBM 72-hr QPF Percentile) shows storm-
total liquid amounts ranging from around 4.0" at the Sierra
crest (50th percentile) up to around 8.0" at the Sierra crest
(90th percentile). Spillover amounts into western NV show an
even wider range of possibilities between a tenth to as much as
half an inch.
* Breezy south-to-southwest winds in valleys along with strong
ridge winds look more likely Monday as a strong 110kt jet core
noses over northern CA/NV Monday night-Tuesday bringing some
potential for very strong winds. Some ensemble members show
strong wind gusts to 50 mph Tuesday, especially from I-80 north,
with a few members indicating very strong, potentially damaging
winds over the Sierra and far western NV.
Wednesday onward...ensemble cluster guidance leans heavily towards a
drier more mild solution as the EPAC High ridges into the western
US. Much of the West Coast could see a return to more mild
temperatures with highs forecasted to climb back into the 60s for
western NV and into the 50s for some Sierra locations. While we are
fairly confident in the return of the ridge with the trend for
warming and drying, there are a handful of simulations that maintain
a flatter, less impressive ridge enabling the entrance of weak upper
waves over the region weeks end. -Amanda
&&
.AVIATION...
* Winds aloft and over Sierra ridges will remain elevated and then
increase this evening ahead of the next weather system. Of note is
turbulence persisting into the evening hours over the Sierra and
east into western NV. Turbulence and low-level wind shear should
still continue to trend upward through this evening into Saturday
morning. Arriving and departing aircraft in the areas east of the
Sierra Crest could expect bumpy conditions between 3000-12000
AGL through this evening.
* Increasing clouds and moisture from the west later this evening
into Saturday morning will act as the vanguard of next low
pressure system reaching across the Sierra east into western NV.
Increasing chances of rain and mountain snow will follow from
midnight onward into Saturday morning.
* Measurable precipitation should remain most likely north of
US-50 Saturday morning, but by midday shift east into western
NV, and southeast along the Sierra Front to KMMH. This will also
bring another round of mountain terrain obscuration with some
MVFR conditions possible at KTRK and KTVL. These Sierra
terminals could even see a brief period of rain/snow mixed early
morning Saturday between 12Z-16Z. No significant accumulating
snow is expected during this period. -Amanda
&&
.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&
$$
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