Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/14/21
Area Forecast Discussion
National Weather Service Charleston SC
644 PM EST Mon Dec 13 2021
Dry high pressure will prevail through much of the week before
a cold front arrives over the weekend.
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Water vapor images showed a well-defined shortwave tracking
east across the Deep South early this evening. This feature was
contributing to an area of developing showers over the Gulf
Stream off the FL coast. HRRR indicates that additional showers
will develop off the GA/SC coast late tonight, remaining over
the Gulf Stream. However, cloud cover is expected to increase
from the east, resulting in at least partly cloudy conditions
over the coastal counties late tonight. Temperatures are on pace
to range from the mid 30s over inland GA to the mid to upper 40s
along the coast.
.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
Deep high pressure will prevail across the region and then make
an eastward shift on Thursday. A coastal trough will linger in
the vicinity. While a dry forecast is in place over land, there
could a few showers over the waters along the trough and where
moisture is slightly higher. Although, any showers that do form,
should generally be light and short-lived due to dry air aloft.
In regards to temperatures, Tuesday will be in the 60s and by
Thursday, temps will warm into the low to mid 70s across SE SC
and upper 70s across SE GA. Low temperatures on Tuesday night
will be in the upper 30s to mid 40s inland and upper 40s to low
50s just along the coast. Wednesday will be a few degrees
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
High pressure will remain offshore through Saturday followed by
a cold front. For Thursday and Friday, a dry forecast is in
place, except for a slight chance over the waters. Then, as
moisture increases ahead of the aforementioned cold front,
showers will be possible starting Saturday. The cold front will
move through the region overnight Saturday and into Sunday,
before stalling just offshore. Decent moisture and shortwave
energy will support isolated to scattered showers through early
week. Heights will support warm temperatures on Fri/Sat then
after the cold front, highs in the 60s will return. Lows will be
in the 40s to 50s.
.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
VFR conditions expected across the terminals through the 0z TAF
period. A ridge of high pressure will yield light northeast
winds through the period.
Extended Aviation Outlook: VFR is expected to prevail through
Tonight: The local waters will be situated between high
pressure to the north and a coastal trough located to the south.
This will drive northeasterly flow across the local waters with
wind speeds generally topping out in the 10-15 knot range. Seas
will average 2-3 feet, except up to 4 feet in the outer Georgia
Tuesday through Saturday: Northeasterly winds at 5 to 10 knots
will prevail through late week before becoming south-southwest.
Seas will start out around 2 to 4 feet before building to 3 to 5
feet by the weekend.
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
600 PM EST Mon Dec 13 2021
A weak front will sag south into the area overnight and stall. This
will bring nearly calm conditions late. The atmosphere is very dry,
but slightly moisture pooling along the boundary coupled with decent
cooling conditions may produce patchy MVFR to possible IFR fog a few
hours either side of sunrise. Winds will become east/southeast north
of along/north of this front on Tuesday.
.DTW THRESHOLD PROBABILITIES...
Issued at 352 PM EST Mon Dec 13 2021
Southeast Michigan resides on the anticyclonic shear side to a broad
+150 knot upper level jet streak that is in place across most of
north central North America. Absolute anticyclonic vorticity
advection across Southeast Michigan combined with very strong
statically stable conditions between 1.5 and 7.0 kft supports
surface high pressure influence extending out of the Carolinas back
to the northwest into Lower Michigan. No significant weather to
speak of throughout the next 36 hours with the persistent ridging
influence and dry ambient air mass.
The item to watch for tonight and Tuesday morning will be the
potential for shallow ground based fog. NAM soundings look way
overdone with a substantial low stratus signal while the RAP
soundings strictly point to a ground/surface layer signal. There is
uncertainty here for a couple of reasons, very high surface T to Td
depressions running some 15-20C today, and possibly some better
potential for frost formation over supercooled liquid droplets and
fog. Do think there is some possibility for visibility restrictions
but may be more of a haze at daybreak. Surface col region will push
to the east already by Tuesday morning that will cause some subtle
low column cold air advection. Biggest factor for Tuesday will be
change in wind directions to the southeast. Limited mixing depths
should keep moderation in check with afternoon highs in the middle
to upper 40s.
Surface warm front and plume of high thetae is forecasted to advect
into all of Southeast Michigan between 12-18Z. 800mb moisture
transport will be earlier, 06-12Z, which will provide low level
saturation in the lowest 3.0 kft agl. A significant environmental
wind profile through this cloud bearing layer points to a high end
drizzle light rain shower setup. Went ahead and increased PoPs into
the likely category for the latter half of Tuesday night. Tricky to
pin down highs on Wednesday given amount of cloud and moisture but
indications suggest a humid/damp middle 50s Wednesday.
A strong absolute anticyclonic vorticity signal off of the upper
Mississippi River Valley supports dry slotting by Wednesday evening
and night. Wednesday night is an interesting forecast period as the
potential exists for a well mixed layer from the surface to 2000 ft
agl. The progged low level jet is very impressive at over 65 knots.
Not expecting this to fully mix down to the surface but depending
on how this unfolds, the potential exists for wind gusts to reach
and exceed 40 knots during the Wednesday night period. Latest
indications suggests a slightly quicker timing of the surface cold
front through Southeast Michigan Thursday morning. The nam is a
little later compared to the ECMWF but even then the NAM shows a
veered wind profile just off of the deck with bulk of the cold air
advection at 800 to the southeast of the forecast area by 15Z.
Regardless, very windy conditions are expected as daytime heating
causes fresh mixing and downward momentum transport around late
morning. A wind headline may be needed for Wednesday and Thursday.
The main baroclinic zone is expected to stall out over portions of
the Ohio and Tennessee River Valleys Thursday/Friday before
advancing northward for the weekend. Latest forecast data suggests a
more winter like system for Southeast Michigan during the weekend.
Strong high pressure dropping out of northern Ontario builds over
the central Great Lakes tonight bringing light winds back to the
area. This high quickly moves into eastern Ontario Tuesday shifting
flow to the SE. An uptick in strength accompanies this shift with
gusts reaching 20-25kts by Tuesday night. Gradient tightens again
Wednesday as a warm front lifts through the region tied to a strong
developing low over the northern Plains. Warm front brings a chance
of showers throughout the day Wednesday as well as strengthening
southerly flow. This low looks to track into the upper
Midwest/western Lake Superior late Wednesday into Thursday. Peak
winds are expected during this timeframe with gales looking possible
across portions of Lake Huron (particularly central LH).
Record highs for Wednesday Dec 15th:
DTW 61 (1933)
FNT 60 (1971)
MBS 60 (1971)
Thursday Dec 16th:
DTW 65 (1984)
FNT 62 (1984)
MBS 60 (1984)
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
You can obtain your latest National Weather Service forecasts online
Area Forecast Discussion
National Weather Service New Orleans LA
400 PM CST Mon Dec 13 2021
.SHORT TERM (This evening through Wednesday Night)...
Nice and quiet evening to finish up a fresh start to the work
week. GOES-16 Ch2 VIS shows ongoing patchy low-level stratus
advecting east across the region. This was sampled well looking
at RAP/HRRR analysis and trends indicating a fetch of low-level
Gulf moisture riding north over a stationary frontal boundary
currently situated in the northern Gulf. Some of this took its
time getting too far north, which led to mostly sunny skies over
northern parts of the CWA, but slightly cooler by a few degrees
underneath thicker stratus south of I-10/12 including the
southshore. As mentioned in the morning update, the current
vertical thermal profile shows a distinct frontal inversion locked
in place from the surface to around 925mb/3kft AGL supported by
nearby high pressure anchored over the mid-Atlantic states helping
to promote light easterly surface to low-level winds. Above this
layer, winds transition from the southwest to eventual west which
has continued to pump moisture north in the from of stratus
clouds. There is some indication of towering Cu development
underneath a deeper vertical moisture plume over coastal central
LA pushing north. 18Z RAP illustrated this area well with the
center of a H7 ridge just to our south, helping to pull this plume
north. See a few isolated showers in this area of enhanced low-
level moisture, but HRRR trends continue to keep things quiet and
dry here tonight with no strong indication of Tamiko ascent at
play, other than subtle isentropic lift nearby the low-level front
but this should stay over southwestern parts of the CWA or around
the Atchafalaya basin. Not going to get cute by mentioning PoPs
in this region, as coverage potential looks too low.
Staying partly to mostly cloud tonight, mainly as this same
aforementioned H7 moisture plume pushes in along the northern
periphery of the ridge axis in the northern gulf, spreading low-
level moisture east. HRRR RICAPS keeps clouds in place tonight
within a thick/moist surface to low/mid-level layer, but what
degree of influence this might have in fog development daybreak
Tuesday is in question. For now, deterministic and probabilistic
guidance is not entirely confident on coverage and density, with
NBM probabilities only in the 15-20% range over most of the CWA.
While low cloud ceilings will definitely be possible tonight, just
looks like this will entrap any longwave radiation attempting to
escape reducing radiational cooling processes. However, checking
the MS river temperatures and comparing to forecast
temperatures/dewpoints, we may see some fog along the river or
around/nearby any other water sources come daybreak (greater
chances for northwestern areas where T/Td is closer to river
temps). Left in the mention of patchy fog for a large portion of
the area but refrained from mentioning thicker/denser coverage as
confidence is just too low. Will closely monitor updated guidance
this evening/early tonight and adjust where necessary.
Going into Tuesday, the stationary front to the south slowly
dissipates undergoing frontolysis with no distinguishable
frontogenetic characteristics anymore. Deeper surface to low-level
moisture takes over and spreads north, eroding the frontal
inversion placing us back in a subtle veering profile and well-
mixed PBL following daytime heating. We will see partly to mostly
cloudy skies again, but with more convective cloud development as
we build positive bouyancy from the LCL to mid-levels (eventually
striking a subsidence inversion at H5). Can`t rule out an
isolated shower, especially nearby coastal SE LA within deeper
moisture but again, expecting a mostly dry day. Temperatures
several degrees warmer, with a slight bias above deterministic NBM
which gets many areas into the mid to upper 70`s.
Nothing changes much going into Tuesday night with persistent
moisture locked in place the low-levels, leading to partly to
mostly cloudy skies. NBM VIS probabilities are again on the low
side which makes sense, but hints at patchy fog potential moreso
for northern and western areas. Letting the mention of patchy fog
ride for early Wednesday and will fine tune better as we get
closer. Overall, expect low clouds to persist, likely with low
ceilings into daybreak on Wednesday. The warming trend persist
as we climb into the daytime hours on Wednesday, this time with a
bit more upper-level cloud cover. Otherwise, subsidence takes over
by suppressing/warming the layer right above the LCL leading to a
pretty strong subsidence inversion between 925 and 800mb. This is
due to the same low-level ridge eventually weakening/stretching
and becoming absorbed within strengthening southerly low-level
flow. This presses a dry layer west with time so perhaps not as
much low-level clouds, but upper-level cirrus will persistently
continue spreading east as we reside along the northern periphery
of a deep upper-level ridge parked over the central Gulf, helping
to advect moisture in from the base of a deep longwave trough over
the intermountan West. But generally speaking, another nice day
with warm afternoon temperatures in the upper 70`s. Even when
adjusting to a warmer bias, this produces some areas flirting with
the 80`s which is nearing record highs. May be close, but if
guidance comes in warmer we might not be too far off daily
.LONG TERM (Thursday through Monday)...
The winter blowtorch continues late-week as deep Gulf ridging
continues to dominate our area leading to very warm afternoon
highs, likely reaching or surpassing daily records for a few
areas. Keeping a warmer bias above deterministic NBM going which
for now, hints at Thursday and Friday being the warmest days.
Won`t take much for areas to surpass the 80 degree mark, with
light onshore winds and patchy late morning/afternoon Cu or Cu
streets. Still a lot of influence from this ridge noticeable in
area model sounding guidance with persistent dry air in the middle
to lower troposphere, compressed down to the LCL above a well
mixed PBL meaning we will warm up fast while staying humid. NBM is
coming in with the mention of isolated PoPs Friday afternoon for
coastal SE LA and MS. Both the latest ECMWF and GFS illustrate
this possibility, perhaps with greater coverage coming from the
ECMWF. Investigating this closer, there appears to be a weak low
to mid-level impulse riding north from the north-central Gulf into
the northern Gulf coast states. The GFS shows some hint at this,
but is not entirely distinguishable (maybe somewhat of a weak
impulse at 850mb). Back-tracking the origin of this impulse shows
this to be a lingering piece of energy from an earlier weak
shortwave trough diving south of Florida around Wednesday. It goes
without saying that resolving such a small-scale impulse will be
hard to include in the forecast with confidence, especially so far
in advance. However, with persistent WAA, can`t rule out some
isolated showers but not overly excited about coverage just yet.
Riding with the NBM, but will be interesting to see if or how this
changes over the next few days.
By the upcoming weekend, things get challenging. The same deep
longwave trough mentioned earlier over the intermountan west
splits, with a piece of energy breaking off over the southern
Plains. With this shortwave closing off, we don`t really get much
in the way of an eastward push, meanwhile at the surface, we have
a slowing (yet strong) cold front ever so slowly pushing in from
the east into the southern Plains/mid MS valley region. With the
lead energy ejecting east off New England, the front becomes
parallel to upper-level flow meaning the front will attempt to
slow or completely stall to our north. Should this happen, we
will see a warmer weekend - perhaps warmer than currently forecast
as we continue underneath a warm/moist WAA flow regime. The model
solution really splits going beyond into next week, as a second
"kicker" shortwave trough dives into the northern US and helps to
phase up and press the closed low east. If it phases, we
eventually get surface cyclogenesis along the front with an
eventual eastward kick pushing through here with time. If it doest
not phase, and the upper-low is more south farther away from the
northern trough`s influence, it`ll meander east. Either way, will
have to watch for showers and storms again with this one, and
deepening on either solution will determine the potential for
some strong storms. Will favor/bias on the GFS due to recent
months model performance, and if so, we should see this upper-low
phase up a bit more helping to push east. Something to keep a
close eye on. KLG
.AVIATION (18Z TAF DISCUSSION)...
Low-level stratus deck continues spreading east over a large
portion of southeastern LA and coastal MS late this morning,
bringing intermittent MVFR CIG`s. Patchy to areas of stratus
should continue generally over the same areas through the
afternoon with CIGs lifting, but still could see periodic MVFR at
times. Otherwise, will need to monitor for the potential of
surface fog development after 06z tonight, primarily towards
daybreak between 10 and 12z for terminals along/near I-10 and 12.
Have included lowest VIS forecasts in TAF`s with higher confidence
for now. Conditions will steadily improve thereafter around 15Z
tomorrow with VFR/MVFR CIGs to follow. KLG
A weak frontal boundary will continue to dissipate going into
Tuesday, with easterly winds eventually transitioning to onshore
flow by mid-week. This will lead to a subtle increase in fetch
with time, building wave heights to around 3 to 5 feet for outer
Gulf zones. Some showers/storms possible Friday and into the
weekend, with the next cold front expected through here early next
.PRELIMINARY POINT TEMPS/POPS...
MCB 54 77 58 76 / 10 0 0 0
BTR 57 78 60 79 / 10 0 0 0
ASD 54 78 56 78 / 0 0 0 0
MSY 61 77 63 78 / 0 0 0 0
GPT 53 74 57 75 / 0 0 0 0
PQL 51 75 54 76 / 0 0 0 0
Area Forecast Discussion
National Weather Service Newport/Morehead City NC
1009 PM EST Mon Dec 13 2021
Strong high pressure will continue to build over the area
today and remain in control through the upcoming week. A cold
front will impact the area over the weekend.
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
As of 10 PM Mon...Forecast remains on track with no changes.
Prev disc...High pressure will remain over NC tonight but the
northern center will become the dominant circulation. This will
cause the flow to become N/NE by Tuesday morning. Tonight skies
will remain clear and winds will decouple early this evening
resulting in strong radiational cooling and rapidly falling
temps once again. Thus will undercut most MOS/NBM forecast lows
by 2-4 degrees with min temps in the upper 20s to low 30s. The
higher resolution models like the HRRR are indicating a stronger
signal for radiational fog tonight beginning around midnight
and becoming extensive especially over southern inland
locations. Have included this in the forecast since localized
dense fog did develop late last night.
.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
As of 215 PM Mon...High pressure will ridge into the area from
the north on Tuesday, with light winds and clear skies
continuing. Areas of morning fog should dissipate by 9 AM. Highs
will climb into the low to mid 60s.
.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
As of 240 AM Mon...A stretch of very quiet weather is expected
this week with temperatures initially around normal, increasing
through the week to well above average. By Friday, a cold front
will stall just north of the region, keeping the area dry, and
then another, stronger front will push through the area Sunday.
Wednesday and Thursday...By Wednesday strong high pressure
will rebuild off the New England coast and ridge down the
eastern seaboard. This will allow for southerly flow to develop
(though a weak coastal trough may briefly develop Wednesday,
keeping northerly flow present across the area), and low levels
heights will build both days. Expect highs to reach the mid to
upper 60s Wednesday, and low to mid 70s Thursday.
Friday through Sunday...High pressure will remain offshore
Friday, while a cold front moves eastward out of the Mid-South.
As the front tries to push east of the Appalachians it will
stall to the north and west of the area as high pressure holds
steady overhead, and most of the associated upper level energy
moves into New England. On Saturday this stalled front will lift
north in response to cyclogenesis along the front farther to
the west, and a developing low pressure system will move into
the Mid-Atlantic through the day. To the south of this
developing low, a stronger cold front will march into the
Southeast states by Saturday night, and cross through Eastern NC
Sunday morning. A period of wet weather is anticipated along
this front, but much uncertainty regarding rainfall amounts.
Low level heights will continue to build through Saturday
leading to very warm conditions both Friday and Saturday, with
highs reaching the low to mid 70s. Behind the cold front Sunday,
strong CAA will limit warming, keeping temps mostly in the low
to mid 50s for highs.
.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
SHORT TERM /through Tuesday/...
As of 630 PM Mon...Strong subsidence from high pressure directly
overhead tonight will keep skies clear and winds calm. As a
result, VFR conditions likely this evening with the threat of
fog early Tue AM. Hi res guidance is showing a stronger signal
for fog development across southern terminals. Though airmass
remains dry, strong radiational cooling will allow temps to drop
quickly tonight and fog to potentially develop. Though fog will
likely be predominantly shallow steam fog, some more substantial
development is possible. Localized IFR/LIFR fog in the TAFs this
morning for EWN/OAJ with MVFR fog elsewhere for the time being.
Any fog burns off after sunrise, giving way to high confidence
VFR conditions for the rest of Tuesday.
LONG TERM /Tuesday night through Saturday/...
As of 240 AM Mon...VFR conditions are expected to persist
through the week with high pressure in control.
SHORT TERM /through Tuesday/...
As of 215 PM Mon...Good boating conditions are expected through
Tue as high pressure remains over the waters. Winds are expected
to remain light through Tue morning mainly 10 kt or less with
the direction veering from W this evening to NE by Tue morning.
The NE flow could increase to 10-15 kt late Tue. Seas will be
2-3 ft through Tue though some 4 ft seas will be possible over
the outer waters late Tue in response to the increased northerly
LONG TERM /Tuesday night through Saturday/...
As of 240 AM Mon...NE winds will be strengthening to 10-15 kts
Tuesday night. A weak coastal trough likely develops Wednesday
with winds mostly out of the E/SE at 5-10 kts to the east of the
trough, and out of the NE at 5-10 kts right along shore.
Southerly flow then develops Thursday with winds 5-10 kts,
increasing to 10-15 kts Thursday night, and then coming around
to the west on Friday at 5-15 kts. Seas will be 2-3 ft Tuesday
and then 3-4 ft Tuesday night through Thursday. Seas then build
further Thursday night becoming 3-5 ft through Friday.
AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
935 PM EST Mon Dec 13 2021
High pressure will persist over the Carolinas and Mid Atlantic
.NEAR TERM /THROUGH TONIGHT/...
As of 935 PM Monday...
High pressure remains over southeastern North Carolina. The only
meaningful change to the forecast is to remove the patchy fog that
was possible across southeastern counties. Confidence in the fog
earlier was low, and the most recent model guidance shows a very low
chance of any visibility reductions occurring. Skies will remain
clear, and although winds should be relatively light overnight, the
fact that there should be a little bit of wind compared to
widespread calm conditions last night should allow overnight
temperatures to be slightly warmer than last night, ranging from the
mid 20s to mid 30s.
.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
As of 248 PM Monday...
Broad ridging will be in place Tue into early Wed at mid-levels. At
the surface, high pressure over southeastern Canada will move into
New England early Wed. Northeasterly flow at the surface will
commence during the daytime Tue as a result. Low-level thicknesses
remain about the same over the northern Piedmont and Coastal Plain
but warm slightly over the southern Piedmont and Sandhills. High
temperatures then to be about a degree or so warmer area-wide,
ranging from the upper 50s to 60 in the north to lower 60s in the
southwest. While it is difficult to discern if the surface high over
New England will bring the back door cold front all the way through
central NC, either way thicknesses will drop by early Wed with a
light northeast wind. In the low-levels, the east-northeast moist
flow from the western Atlantic may lead to some morning fog or low
stratus Wed morning, primarily over the eastern Piedmont and Coastal
Plain. Forecast soundings have been indicating this moistening at
low-levels, with the NAM the most aggressive. The HRRR has also been
consistent on the pattern. As a result, overnight lows to be a tad
warmer in the low to middle 30s under increasing clouds and slight
stirring in the wind.
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
As of 330 PM Monday...
A subtropical ridge aloft will remain across the Southeast US
through Friday, resulting in dry weather for central NC. However,
this will gradually get pushed southeastward as a series of
mid/upper disturbances moves across the Plains and Upper Midwest. At
the surface, a backdoor front will move through at least part of the
area Tuesday night and Wednesday morning. Behind this front,
easterly flow may result in low-level cloudiness and cooler
temperatures, particularly if the NAM were to verify, with the best
chance of this in the east. Thus increased forecast cloud cover and
cooled forecast highs a bit on Wednesday closer to the NAM,
generally mid-50s to near 60. Otherwise, surface high pressure
centered over the area on Wednesday will shift east and offshore,
resulting in southerly flow and warmer temperatures from Thursday
through Saturday. Forecast highs increase from mid-60s to lower-70s
on Thursday (around 15 degrees above normal) to 70s areawide on
Saturday (around 20 degrees above normal). Thus the record high of
72F at RDU on 12/17 (Friday) could be in jeopardy.
Precipitation chances increase for the weekend into early next week.
A strong cold front will cross the region late Saturday or early
Sunday, though timing of the front has slowed down in the latest
model runs. The front may be accompanied by some showers, and there
is enough model support to increase POPs to high chance during this
period. However, similar to recent frontal passages, there is no
wave along the front and it does not look to have a ton of moisture
associated with it, so rainfall amounts do not look impressive at
Confidence then greatly decreases for the rest of the period. There
will at least be a lull in precipitation on Sunday as the front
moves south of the area, but a shortwave trough will then move
across Texas and the lower Mississippi Valley on Sunday night into
Monday. The 12z ECMWF keeps the system suppressed well to the south
with high pressure over our region, but the 12z GFS continues to be
much wetter as it brings the system farther north. The Canadian is
more in line with the wetter GFS solution, though it holds off
precipitation until Monday night. Considering even a majority of 12z
ECMWF ensembles have at least some precipitation over the area, the
operational ECMWF appears to be an outlier, and have high chance
POPs again on Monday. While the 12z GFS is warmer than the 06z run,
it still has low-level thicknesses near 1300 m in the far northern
Piedmont at the onset of precipitation Monday morning. The event if
it occurs should be mainly liquid, but a bit of frozen precipitation
at the onset can`t be entirely ruled out. Temperatures will be much
cooler on Sunday and Monday, but exactly how much will depend on how
the overall pattern plays out. For now forecast highs are near
.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
As of 630 PM Monday...
High confidence in VFR conditions for the next 24 hrs across central
NC, as deep dry air sits atop the region, within surface high
pressure stretching across the area. This high will weaken later
tonight, while another high pressure area centered just north of
Lake Ontario begins to ridge southward into NC. This will result in
very light to calm winds tonight becoming mostly from the NE on
Tuesday, under 10 kts. Few to no clouds are expected through Tue,
with no vsby restrictions.
Looking beyond 00z Tue, VFR conditions will dominate through Fri,
although there is a risk of sub-VFR fog and low stratus late Tue
night/early Wed morning, and again late Wed night/early Thu morning,
with increasing easterly low level flow pulling moisture in from the
Atlantic. A chance for showers with sub-VFR conditions is expected
starting Sat. -GIH
Area Forecast Discussion
National Weather Service Reno NV
225 PM PST Mon Dec 13 2021
A major winter storm is bringing areas of strong winds and
significant snow in the Sierra, with rain changing to snow for
the lower elevations of western Nevada Monday night. Lengthy
travel delays in the Sierra are expected with full road closures
possible. Another colder winter storm is expected late Wednesday
into Thursday with additional travel impacts expected.
...RAPID DETERIORATION OF TRAVEL CONDITIONS IN THE SIERRA AND FAR
WESTERN NV BETWEEN 4 and 10 PM...
Impact-wise, no major changes to thinking through Tuesday with
the current storm system bringing heavy Sierra snow and gusty
winds, notable snow (tonight-Tuesday morning) for western NV, and
strong winds for portions of western NV.
Precipitation, mostly of the lighter variety, has been affecting
the Sierra/eastern CA today with moist upslope flow and some
upper forcing with a potent upper low off the northern CA and
Oregon coasts beginning to swing eastward. So far today, occasional
periods of precipitation have been spilling over into western NV
but nothing prolonged yet as that area waits for better forcing
tonight. As for snow levels, they are currently stuck around
5200 to 6200 feet from Lassen down to Tahoe/Reno, respectively,
with levels slower to 6500-7000 feet down in Mono County. Travel
difficulties are already underway in northeast CA with slushy and
snow-covered passes requiring chains and/or snow tires.
As we get into the late afternoon and evening, conditions are
expected to deteriorate substantially in the Sierra and across
northeast CA as a strong cold front (currently over northern CA)
approaches and ramps up snowfall rates and drives down snow
levels. At least the HRRR is definitely hinting at an NCFR (Narrow
Cold Frontal Rainband) advancing across the region through
tonight; indeed, there are already hints of one near Interstate 5
stretching down towards Ukiah, CA so confidence is increasing in
the HRRR solution. The HRRR has the NCFR pushing across the
majority of western and west-central NV by daybreak Tuesday.
Why is an NCFR significant? Well, intense snowfall rates of 2-3"
per hour or even higher can be associated with an NCFR. Also, the
NCFR typically drives the snow level down abruptly for a rapid
increase in the area of travel difficulties. Therefore, while some
areas even in the Sierra are currently just experiencing wet
roads, don`t be caught off guard when conditions deteriorate
rapidly (i.e. snow accumulating on roads quickly) later today.
Also, near the Sierra crest, there is even a low chance for a
brief thunderstorm tonight.
For western NV, while notable rainfall has spilled into the
immediate lee of the Sierra, most of the area is seeing more
impact from strong winds at this time. However, by between 7-10
PM, expect rain to change to snow in far western NV (even lower
valleys) with at least a few inches of snowfall possible by
morning. Farther east into the Lovelock, Fallon, and Hawthorne
areas, it looks to be well after midnight into Tuesday morning
before snow levels fall off enough to begin to cause travel
issues. Be prepared for travel slow downs and chain and/or snow
tire requirements across western NV for the Tuesday morning
commute...it would be wise not to wait until the last possible
minute to start your morning commute!
Late tomorrow morning into the afternoon, coverage and temporal
nature of snow showers is expected to decrease substantially,
although not end completely as a cold pool aloft settles overhead.
Tuesday night could be quite cold as winds diminish with a surface
high settling into the region (albeit, briefly), especially in
areas that receive at least a few inches of snowfall with the
current storm. However, models do show clouds already spreading
overhead ahead of the next system early Wednesday morning so the
current forecast lows are a bit moderated with that expectation.
.LONG TERM...Wednesday evening through early next week...
The next Pacific low pressure system will sweep across the Sierra
and western NV through Thursday afternoon. This quick moving shot
of winter weather will spread a fresh layer of new snow across
the region with considerable snowfall in the Sierra and Tahoe
Basin overnight Wednesday through Thursday afternoon. Lesser snow
accumulations are expected over western Nevada as the cold front
quickly passes to the east and southeast into the Great Basin.
Although ensemble model guidance is showing minor variances
between model simulation runs, precipitation and wind forecast
confidence still remains relatively moderate for this system.
* Abundant Mountain Snow: Although there will always a certain
amount of forecast uncertainty with snow forecasts, a moderate
level of confidence remains that 1-2 feet of accumulating snow
will fall across the Sierra. Areas above 7000 feet will be the
most favored areas for these higher snowfall totals. In western
Nevada, probabilistic snow guidance for lower valley areas will
range from a dusting to less than an inch of new snow. But
slightly higher areas above 5000 could see 3"- 6 of new
accumulating snow on the ground. This same model guidance shows
higher mountain communities receiving nearly a half to almost a
foot of fresh snow on the ground by early Thursday morning.
* Storm Impact Timing: From late Wednesday afternoon through early
Thursday morning, the largest snow impacts will be centered over
the Sierra. Lower valley locations of western Nevada could see
accumulations gathering on the ground shortly after midnight
Thursday and lasting through the early morning hours. Snow
impacts over Mono County could continue to till midday Thursday.
Anticipate travel impacts for both aviation
(turbulence/LLWS/icing) and ground (especially over Sierra
passes) during these noted time periods.
* Increasing Winds: Thermal and pressure gradients in advance of
this incoming cold front will begin to increase Wednesday
afternoon and peak around midnight into Thursday morning with
gradients gradually loosening through Thursday afternoon. Wind
gusts in the lower valleys will range 30-40 mph with a moderate
potential of seeing some gusts to 50 mph in the Sierra. Sierra
ridges could still see gusts greater than 100 mph. Gusty periods
could see localized wind impacts mainly confined to wind-prone
areas. Impacts on aviation, recreation, and high-profile vehicles
are likely especially along the US-395 and US-95 corridors.
Friday and beyond, an upper level ridge axis will extend across the
West Coast as high pressure strengthens over the Sierra into the
Great Basin region. Friday will see gusty northeast winds possibly
increasing along the Sierra crest with accompanying fair skies and
slightly colder temperatures. Early next week and onward, the
synoptic pattern continues to look a bit on the active side but
increased uncertainty in this extended forecast period warrants a
precautionary wait and see until model guidance shows less
disparity. Nonetheless, above normal precipitation and slightly
below normal temperatures are expected.
An ongoing major winter storm will continue through Tuesday.
Significant impacts to aviation are expected: (1) Wind-LLWS-
Turbulence; (2) Snowfall-obscurations-visibility; and (3) In- flight
* Mountain wave turbulence and LLWS are anticipated through at least
Tuesday morning. Currently, there is a SIGMET in effect over the
Sierra south of Lake Tahoe for turbulence due to strong up-drafts
and LLWS. Surface gusts look to range between 30-40 kts for most
area terminals, with some higher gusts possible in the northern
Sierra (TRK-TVL) terminals. West-central Nevada terminals,
especially HTH, could see a burst of strong wind gusts exceeding
50 kts into tonight.
(2) Snow-flight Conditions:
* Central northern Sierra terminals (TRK-TVL), snow will continue
into Tuesday morning, with the heaviest rates and IFR/LIFR
conditions expected 00Z-12Z Tuesday. Accumulations will likely
exceed 2 feet in these areas.
* Western Nevada terminals (RNO-CXP-MEV): A mix of light to moderate
rain will give way to snow later this evening. Snow should
accumulate later tonight as snow levels quickly drop to valley
floors overnight. Accumulations will likely exceed 2 inches, with
CXP-MEV having a moderate chance of exceeding 4 inches. RNO has a
moderate chance of exceeding 4 inches. IFR/LIFR conditions are
expected mainly between 03-06Z Tuesday in western Nevada.
* Eastern Sierra terminals (MMH): Heavy snow and long duration
IFR/LIFR conditions are expected through Tuesday morning.
Accumulations will likely exceed 1 foot.
(3) In-flight Icing:
* Icing impacts to aviation will be elevated across the Sierra and
into western Nevada through Tuesday morning. Be sure to check
forecast icing conditions and PIREPs at aviationweather.gov before
departing or arriving at area terminals.
NV...High Wind Warning until 10 PM PST this evening NVZ001.
Lake Wind Advisory until 6 PM PST this evening for Pyramid Lake
Winter Weather Advisory from 10 PM this evening to 10 AM PST
Winter Weather Advisory from 4 PM this afternoon to 10 AM PST
Winter Storm Warning until 10 PM PST Tuesday NVZ002.
Winter Storm Warning from 5 PM this afternoon to 10 AM PST
CA...Winter Storm Warning until 4 PM PST Tuesday CAZ071.
Winter Weather Advisory from 4 PM this afternoon to 10 AM PST
Winter Storm Warning until 10 PM PST Tuesday CAZ073.
Winter Storm Warning until 10 PM PST Tuesday CAZ072.
For more information from the National Weather Service visit...