Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 01/23/21
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
912 PM CST Fri Jan 22 2021
Issued at 910 PM CST Fri Jan 22 2021
No major changes made to the forecast tonight. Timing for snow
moving in late tonight/early Saturday morning still looks good, as
well as placement of Winter Weather Advisory headlines.
.SHORT TERM...(This Evening through Saturday Night)
Issued at 338 PM CST Fri Jan 22 2021
Low clouds have moved to the east of the James Valley this afternoon
and will continue to move out of the CWA into the evening hours.
Otherwise, for tonight and Saturday, we are still on track for
accumulating snowfall across most of the CWA. A shortwave trough
ejecting out of the southwest U.S. upper trough and across our
region through Saturday night will be the main influence in
bringing the snowfall. Also, the confluence of the southwest and
northwest airstreams over South Dakota will be the other big
influence on the lift for snowfall. A northwest to southeast xsct
through South Dakota shows the greatest deep layer lift mainly
across our far southern CWA and across southern South Dakota. WAA
increasing tonight along with mid level frontogenesis will
provide good lift in the snow growth zone into Saturday. The lapse
rates were favorable from 700-500H in the 7 to 8 degree C range.
Also, the RR quadrant of a jet streak to our northeast will
provide good upper divergence for lift. Therefore, all models and
ensembles point to snow developing after midnight in our southwest
CWA, then spreading northeast through Saturday. The northern edge
of the snow will still be tricky with north central SD looking to
get little to no snowfall. The Winter Weather Advisory still
looks fine, extending from southwest SD into northeast SD/west
central MN later tonight into Saturday night where 2 to 5 inches
are expected. The system will move out quickly Saturday evening
with colder air pushing in on north to northeast winds. Don`t
expect much for blowing snow with this system.
.LONG TERM...(Sunday through Friday)
Issued at 338 PM CST Fri Jan 22 2021
The extended period looks pretty inactive overall. The period
starts out with polar high pressure centered over southern
Saskatchewan/Manitoba and nudging down into the Dakotas and
Minnesota. The surface high doesn`t move much through the first
half of next week and results in below average temperatures through
The one question in regards to precipitation is presently Tuesday
night. Deterministic solutions are consistent in low pressure
developing over the Central Plains Tuesday and pushing off to the
northeast Tuesday night through Wednesday. That said, latest
model guidance maintains a system that either grazes the southern
forecast area or keeps it south altogether. Either way, it`s still
Day 5, so just something to monitor for now.
.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
Issued at 525 PM CST Fri Jan 22 2021
VFR conditions will prevail across the area tonight. An area of
snow, accompanied by IFR/MVFR cigs and MVFR vsbys, will spread
from southwest to northeast on Saturday.
SD...Winter Weather Advisory from 3 AM Saturday to midnight CST
Saturday night for SDZ018>023-035>037-045-048-051.
MN...Winter Weather Advisory from 3 AM Saturday to midnight CST
Saturday night for MNZ046.
Area Forecast Discussion
National Weather Service Caribou ME
1100 PM EST Fri Jan 22 2021
Low pressure will cross the region overnight. Low pressure will
then remain across the Maritimes Saturday through Monday. High
pressure will build toward the region Tuesday into early
Wednesday as low pressure passes well south of the region.
.NEAR TERM /THROUGH SATURDAY/...
11:07 PM Update: Light snow persists in northeastern parts of
our area supported by a weak inverted trough over the region.
The light snow will continue for a couple hours then dissipate
to snow showers as the trough moves away. Updated forecast to
reflect this and adjusted temps a bit.
Tonight...WAA continues w/light snow occurring across the
northern and western areas w/radar showing echoes weakening as
the sfc low pres weakens this evening as it lifts ne. Further s,
pretty quiet w/the regional radar showing some development of
light snow across swrn areas pushing ne. An inverted trof
extending back from the low e of Nova Scotia will act as a focus
mechanism for more snow with radar filling later tonight. The
steadiest snow will be across the northern 1/2 of the CWA as a
vigorous vort max provides the available lift for the light
snow. Additional inch or so of snow is expected w/this feature.
Across srn areas, an upper disturbance will move across the Gulf
of Maine waters w/precip expanding as it interacts w/the
inverted trof at the sfc. The latest HRRR and RAP were aligning
well w/this setup and show the precip shield to the s expanding
back toward the coast w/the far eastern side of Washington
County seeing some enhancement, as does the NMM and WRF. But,
these two sets of guidance have been overdoing the current
activity. The ECMWF has been very consistent w/showing this
feature but the 12z run did shift the precip shield a bit
further s, matching closer to the 12/18z NAM. Therefore, decided
to show a nose of enhanced precip moving into the coast and
Washington County w/potential of an additional inch or so of
snow by early Saturday morning. Above normal temps for tonight.
For Saturday, light snow in the morning will be transitioning to
snow showers as the upper trof swings through and forcing weakens.
Some CAA coupled w/a gusty NW flow off the open St. Lawrence will
set the stage for the potential for some snow showers and
perhaps streamer activity across the mtns and nrn areas. Plus, a
fairly potent vorticity max is forecast to slide se across the
region helping to trigger the snow shower/streamer activity.
Not expecting much additional accumulation from this activity.
NW winds will be picking up though w/sustained winds of 10-20
mph w/gusts up to 30 mph. Daytime temps near to slightly above
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
Saturday night into Sunday will be marked by windy conditions
generated by a tight pressure gradient between a large low
pressure complex in the Maritimes/North Atlantic and a sprawling
high pressure system over large portions of Canada and the
eastern US. Warmer air aloft will actually be wrapping around
the closed upper low from Labrador and northern Quebec into the
forecast area. This will generate clouds and snow showers
Saturday night and Sunday...mostly in northern zones. No
appreciable snow accumulations are expected and these warm air
advection events from the north usually don`t produce much. Wind
chills will be below zero for much of the area Sunday morning
and wind gusts will reach up to 30 mph on Sunday. The winds will
gradually decrease Sunday night into Monday as the low in the
Maritimes moves out and high pressure builds.
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
A large dome of high pressure over most of Canada and the
northern tier of the US builds Monday night and dominates
through Friday. The storm track will be well south of the area. In
general, temperatures look to be slightly above normal, but
have some concerns that nighttime model temps may be a bit warm
at night for areas with snow cover in northern zones. Went for
lower temps than guidance on Monday night. Did add some PoPs for
Tuesday night into Wednesday for another weak upper disturbance
rotating south from northern Quebec. This is primarily shown by
the ECMWF and confidence in this feature is not very high.
Again, any snowfall would be light. At this point, this January
ranks as the 4th least snowy on record at Caribou and there`s
not much on the horizon to suggest that`s going to change
.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
NEAR TERM: Predominately MVFR at the northern terminals
overnight in lower clouds and occasional light snow. Very brief
IFR visibility restrictions are possible. VFR for KBGR and KBHB
with a period of MVFR with isolated to scattered snow showers
possible after midnight. Light and variable wind less than 10
kts becoming NW by early Saturday morning at 10 kt.
For Saturday, MVFR continues for the northern terminals in light
snow/snow showers. VFR for KBGR-KBHB. NW winds increasing to
10-15 kt w/gusts to AOA 25 kt.
Saturday night into Sunday...MVFR tempo IFR in snow showers
north of HUL and GNR. VFR elsewhere. NW winds gusting to 30 kt.
Sunday night into Tuesday...VFR with light NW winds
Tuesday night into Wednesday...MVFR tempo IFR in snow showers
north of HUL and GNR. VFR elsewhere. Light NW winds.
NEAR TERM: Light winds WNW less than 10 kt increasing to 10-15
kt late tonight. Seas 1-2 ft, slowly building to 2-3 ft by
For Saturday, a Gale Warning as been posted for late Saturday
into Sunday including the intra-coastal zone. NW Winds will be
increasing to 20-25 kt w/gusts increasing to 35+ kts. Seas will
build to 3-4 ft.
SHORT TERM: Gale conditions are expected Saturday evening into
Sunday evening...followed by SCA conditions into Monday evening.
Month to date it has been the 2nd warmest January and 13th least
snowy January on record in Caribou, Maine. Weather records date
back to 1939.
MARINE...Gale Warning from 5 PM Saturday to 4 PM EST Sunday for
Area Forecast Discussion
National Weather Service Cleveland OH
1016 PM EST Fri Jan 22 2021
High pressure will build east across the Great Lakes
Saturday and Sunday. Low pressure will move northeast through the
Ohio Valley Monday into Tuesday with mixed wintry precipitation.
.NEAR TERM /THROUGH SATURDAY NIGHT/...
The flow across Lake Erie has shifted to more northwesterly this
evening with lake effect snow showers extending farther inland
across the snowbelt of NE Ohio. This has allowed for a weakening
trend although expecting light snow to continue for portions of
the overnight with moisture extending into the shallow dendritic
growth zone. A light powdery snow will be focused across favored
upslope areas, although single digit dewpoints spreading
southeast across Lake Erie will prove to be a limiting factor
as we progress through the night.
For Northwest Pennsylvania, lake effect snow bands seen in SW
New York are expected to shift westward with time into eastern
portions of Erie and Crawford Counties. These areas will see an
uptick in snow overnight with an additional 1 to 4 inches
expected while areas closer to the Ohio State line will see snow
shower activity decrease. The uncertain part of the forecast remains
the location of any more dominant band extending from Lake
Huron later tonight. Generally expecting enough movement of
this band that we did not issue an advisory but will need to be
Previous discussion... Lake effect snow continues across
Northeast Ohio and Northwest Pennsylvania this afternoon as
another trough axis swings east across Lake Erie. Snow intensity
has increased slightly over the past couple of hours,
especially in Lake, Geauga and Ashtabula Counties, prompting two
lake effect special weather statements highlighting the gusty
winds and reduced visibilities. Satellite and radar trends
suggest some of this snow is being enhanced by an upstream
connection from Lake Michigan and perhaps even as far north as
Lake Superior. Increased snow totals over the
Lake/Geauga/Ashtabula areas by about an inch or two through the
next 6 hours. Hires guidance from the HRRR suggests that low-
level moisture will be sufficient to sustain moderate lake
effect snow through at least 7 PM this evening. Will have to
monitor trends to see if a short-fused advisory is warranted for
Otherwise, as the trough swings east across the lake, flow aloft
becomes more northwest to north, with lake effect snow primarily
transitioning to Northwest Pennsylvania. In particular, will have to
keep an eye on southern Erie County to see if an upstream connection
to Lake Huron occurs. Did not have enough confidence to go with an
advisory at this point for southern Erie, but if the upstream
connection develops, an advisory will likely be needed overnight
through tomorrow morning.
High pressure builds in later on Saturday, with height rises and
drier air signaling an end to any residual lake effect snow across
Northeast Ohio and Northwest Pennsylvania. Areas west of I-77 may
have a decent shot at seeing sunshine during the day as high
temperatures reach the upper 20s to lower 30s.
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Generally quiet early Sunday as high pressure just to the east moves
farther east and cloudiness increases as warm advection overspreads
the region. There is a slight chance of light snow or perhaps mixed
wintry precipitation late in the day south of US Route 30.
On Sunday night moisture will continue to increase and there is a
slight chance again of light snow possibly mixed with freezing rain
generally south of US Route 30. Northeast Ohio and nw PA should
remain dry. On Monday mixed wintry precipitation with just snow on
the northeast edge will spread into the area but timing differences
appear as the GFS is more progressive(faster)than the ECMWF short
wave over the Mississippi Valley. The NBM pops have been used which
could be too low if the recent run of the GFS is correct. On Monday
night the low pressure area will be moving across the Ohio Valley
just south of the region and allow enough warm air aloft for mixed
wintry precipitation to prevail across the region. The GFS is faster
with the movement of the system and thus colder on the backside of
the system but will lean toward the slower Euro which is more
consistent with the NBM data.
.LONG TERM /TUESDAY THROUGH FRIDAY/...
The upper low will exit the region Tuesday evening with light mixed
wintry precipitation ending as snow showers Tuesday afternoon.
The southern stream jet persists across the country through the
remainder of the period with generally zonal flow with somewhat of a
repeat of the pattern with a system passing by to the south of the
region. The pattern is slightly colder and drier with little
precipitation expected in the form of snow showers.
High temperatures will be below normal from the upper 20s to lower
30s. Lows will be in the teens to lower 20s.
.AVIATION /00Z Saturday THROUGH Wednesday/...
Lake effect snow showers will continue across portions of the
Ohio and Pennyslvania snowbelt overnight and will be most likely
to impact YNG this evening and ERI after 06Z although could
briefly clip CLE. Visibilities could drop to a mile or less in
the heavier snow showers but that will be short lived at any
terminal. Otherwise ceilings will range from MVFR to VFR
overnight and expecting to start to see some clearing developing
across NW Ohio between 04-06Z with an eastward expansion into
Saturday. Winds will become more northwesterly with time and
some gusts to 20 knots may continue overnight at terminals near
Outlook...Non-VFR possible once again with snow Sunday night
through Tuesday, some mixed precipitation is possible Monday.
Northwest flow prevails across the region with a weak surface trough
persisting across the lake. Cold advection is allowing
northwest winds generally of 15-22 knots with higher gusts to
mix to the surface and this will likely continue into Saturday
afternoon. High pressure over the Iowa will gradually build east
over the lake by Saturday evening and allow winds to slacken.
The high pressure area will remain just northeast of the region
into Sunday night as low pressure develops over the Ozarks. The
low pressure area will move northeast into the lower Ohio
Valley Monday afternoon and upper Ohio Valley by Tuesday
morning. Northeast winds will increase early Monday and a small
craft advisory is likely that will persist through Tuesday. The
surface low will move off the Mid-Atlantic coast by Wednesday
morning as high pressure persists north of the lake.
MARINE...Small Craft Advisory until 4 PM EST Saturday for LEZ147>149.
Small Craft Advisory until 10 AM EST Saturday for LEZ145-146.
Area Forecast Discussion
National Weather Service Corpus Christi TX
551 PM CST Fri Jan 22 2021
Expect a transition to IFR/LIFR ceilings and MVFR/IFR
visibilities overnight/early Saturday morning followed by IFR/MVFR
ceilings and VFR visibilities during the late morning/afternoon
Saturday. Brief MVFR visibilities near isolated showers, mainly
Saturday afternoon over the Coastal Plains. Generally weak
onshore flow overnight/early Saturday, followed by weak to
moderate Saturday afternoon.
.PREV DISCUSSION... /Issued 253 PM CST Fri Jan 22 2021/
SHORT TERM (Tonight through Saturday Night)...
Afternoon satellite and surface data revealed a diffuse boundary
stalling offshore ahead of subsidence and drying aloft. Surface
dewpoints behind this boundary have remained largely unchanged, and
actually risen in some areas. This will help set the stage for
stratus and fog development later tonight as ENE winds pull
deeper moisture onshore. Although the odd model out, the NAM is
now slower in veering northerly winds to the east (thanks to drier
surface ridging arriving from the N TX) and as a result has
considerably less fog overnight compared to the SREF, HRRR and
RAP. This lends uncertainty to widespread dense fog development,
although later shifts will monitor trends for a possible Dense
Stratus overnight will gradually thicken through the day on Saturday
as moist isentropic ascent improves ahead of a developing warm
front. Even though models trended drier with PoPs for Saturday,
afternoon soundings across the Coastal Plains depict low stratus
thickening to at least 2000 feet which is usually a good threshold
for some drizzle or very light rain development. However, PoPs
were shaved back to just slight chance as much of this activity
may only produce a trace at best of precip. High temps tomorrow
were lowered a good 3-7 degrees below the suspiciously mild NBM
for this otherwise cloudy and cool easterly flow regime.
Additional PoPs remain intact Saturday night as the warm front
lifts north across the region, yet soundings still show saturated
layers confined to the lowest 2-4k feet beneath the EML/capping
layer, so only light rain or drizzle remains in the offing.
LONG TERM (Sunday through Friday)...
A deep trough over the desert Southwest will shift easterly over the
Southern Great Plains early next week, bringing a cold front through
the area late Sunday night into Monday morning. Models have slowed
the progression of the front lately, with the NAM being the slowest
showing the front reaching the coast around noon. In advance of the
front, isolated showers are possible as low-level moisture remains
high with PWAT values around 1.5". However, a strong cap is in place
on Sunday behind the warm front with warm dry southwesterly flow
above 850mb remaining in place. In addition, CIN values are well
into the triple digits, with much of the area less than -300 J/Kg.
Due to this combination, have removed thunderstorm potential and
have limited activity to isolated light showers with the aid of
isentropic lift across the Coastal Plains and Victoria Crossroads
Sunday. As the weak cold front approaches the area late Sunday
night into Monday morning, a similar situation is in place;
isolated showers are possible for the Coastal Plains and Bend but
thunderstorm chances remain silent as energy aloft remains focused
north and east of the area. Models have also been trending drier
and therefore have decreased PoPs from the NBM.
Drier conditions and high pressure take over in wake of the front,
persisting through Tuesday night ahead of the next weak cold front
passage on Wednesday. Rain chances remain only slight on Wednesday
for the Coastal Bend and waters as a surface trough over the
northwest Gulf of Mexico prohibits sufficient moisture advection
with PWATs below 0.75". Dry conditions return Thursday for all
In regards to temperature, Sunday will be the warmest with highs in
the upper 70s to mid 80s and lows in the 60s due to strong southerly
warm air advection and clouds at night. Otherwise, highs are
expected to remain in the 70s through the extended with lows in mid
40s to mid 50s.
Northeast winds will remain weak tonight before turning easterly
on Saturday and increasing to weak to moderate ahead of a warm
front. Sea fog is likely later tonight into Saturday morning
before dissipating in the afternoon. Dense fog is possible.
Occasional light rain or drizzle should develop Saturday through
Saturday night ahead of weak to moderate southeast flow overnight.
Additional sea fog is expected Saturday night, lingering over the
bays and nearshore waters through Sunday morning. Moderate onshore
flow Sunday morning will strengthen to moderate to strong in
advance of a cold front passage early Monday morning. Small Craft
Advisory conditions with seas building to near 10 feet are likely
Sunday night into Monday. Winds then weaken to moderate and rotate
counter clockwise through the day Monday, becoming northeasterly
by Monday night. Moderate north to northeasterly flow persists
through Thursday with another cold front passage on Wednesday.
Small Craft Exercise Caution conditions are possible Wednesday
through Thursday for the offshore waters. Isolated showers are
possible Sunday through Monday, and then again on Wednesday in
association with the fronts.
.PRELIMINARY POINT TEMPS/POPS...
Corpus Christi 59 67 64 78 65 / 10 20 20 20 10
Victoria 58 68 62 77 63 / 10 30 30 30 20
Laredo 59 70 66 84 61 / 10 10 10 10 10
Alice 57 68 64 83 64 / 10 20 20 20 20
Rockport 57 66 63 73 64 / 10 20 20 20 20
Cotulla 57 67 63 81 60 / 0 10 20 10 20
Kingsville 58 68 64 82 65 / 20 20 20 20 10
Navy Corpus 60 67 66 73 65 / 10 20 20 20 10
Area Forecast Discussion...Update
National Weather Service Hanford CA
518 PM PST Fri Jan 22 2021
...Update to Air Quality Issues Section...
.SYNOPSIS...A low pressure system will bring periods of light
rain and mountain snow to the area through early Saturday as it
moves across central California. A colder system will bring
precipitation to the area Sunday night and Monday. A potentially
strong storm will bring moderate to locally heavy precipitation
to the area on Wednesday and Thursday.
.DISCUSSION...The first of a series of at least three storm
systems is now impacting our area as an upper low which was off
the PAC NW coast yday is now centered over the SF Bay Area as
depicted by satellite imagery. As the associated trough deepened
over our area today, the airmass over our area has become unstable
enough for showery precipitation to spread southward into our
area with several spotters in the San Joaquin Valley reporting ice
pellets and radar imagery indicating some fairly strong (50 to 55
dBz) reflectivities. The convection itself is low based and very
shallow, but would not be surprised if a thunderstorm or two
briefly pops up in the valley this afternoon. Mesowest indicating
the snow level has been running from around 4000 feet near
Yosemite Park to around 5000 feet in Tulare County. We expect the
showery precipitation to continue through this evening then taper
off overnight as the HRRR is indicating the low will drop
southward to the Socal coast overnight the push inland south of
our area on Saturday. The low is progged to move east of our area
by Saturday night which in a dry period across our area Sunday
night and Sunday morning with brief shortwave ridging.
The second storm is progged to push southward into our area on
Sunday evening and bring a period of significant precipitation to
our area Sunday night and Monday. This system is also expected to
have more moisture with it than today`s system and we are
anticipating liquid equivalents of half and inch to an inch and a
quarter of liquid precipitation over the Sierra Nevada with this
system and a quarter to three quarters of an inch of liquid
precipitation over the Kern County Mountains. This second system
is also expected to be much colder with snow levels lowering to
1500 to 2500 feet by Monday afternoon. The main concern with this
second system will be snow at lower elevations that could
adversely impact travel over the mountains. Between 6 and 12
inches of snow are expected above 4000 feet in the Sierra Nevada
and between 3 and 6 inches of snow above 3000 feet in the Kern
County Mountains which would impede travel over the Tejon,
Tehachapi and Walker passes. With impacts to travel being a
concern we have issued a Winter Storm Watch for the Sierra Nevada
and the Mountains of Kern County from 1000 pm PST Sunday evening
until 400 pm PST Monday afternoon.
This second system will move out of our area by Tuesday morning.
Mother than some residual Mountain showers, Tuesday should be a
dry and chilly day across our area. Temperatures across much of
the San Joaquin Valley will likely be below the freezing mark for
a few hours on Tuesday morning.
That sets up the stage for the third storm which is expected to
be the strongest system to impact our area in several months on
Wednesday and Thursday. Confidence is improving in that it will
spread widespread precipitation into our area by Wednesday
morning and pick up some subtropical moisture Wednesday night and
Thursday. The NBM is indicating that this system could produce
1.5 to 3 inches of rain in the San Joaquin Valley and 4 to 6
inches of liquid precipitation in the Sierra Nevada on Wednesday
and Thursday. There is some uncertainty on where the snow level
will be with this system as any subtropical moisture that gets
pulled up will likely mean higher snow levels and increased
potential for runoff and possible flooding concerns. This storm
will move out of our area by Friday, but cyclonic flow behind it
will likely maintain a chance of showers across our area.
.AVIATION...Areas of MVFR and local IFR in low clouds and showers
over the San Joaquin Valley, West Side Hills and Sierra
foothills. Widespread mountain obscuring IFR over the Sierra
Nevada in low clouds and snow showers. Increasing areas of IFR
over the Tehachapi Mountains after 03Z Sat becoming widespread
mountain obscuring IFR by 06Z Sat in low clouds and showers.
Otherwise, VFR conditions will prevail over the central CA
interior during the next 24 hours.
.AIR QUALITY ISSUES...
On Saturday January 23 2021... Fireplace/Wood Stove Burning Status
is: No Burning Unless Registered in Fresno County. Further
information is available at Valleyair.org
The level of certainty for days 1 and 2 is medium.
The level of certainty for days 3 through 7 is medium.
Certainty levels include low...medium...and high. Please visit
www.weather.gov/hnx/certainty.html for additional information
an/or to provide feedback.
Winter Storm Watch from Sunday evening through Monday afternoon
Area Forecast Discussion
National Weather Service Marquette MI
709 PM EST Fri Jan 22 2021
.SHORT TERM...(This evening through Saturday)
Issued at 351 PM EST FRI JAN 22 2021
Very broad upper-level troughing covers all of the Great Lakes and
eastern Canada this afternoon. With 850 mb temps around -21 C, lake
effect snow showers continue in the NW wind snow belts of the east
half. However, MSAS analysis shows surface high pressure centered
over Iowa extending a ridge northward over western Lake Superior.
Low-level drying with this surface ridge (plus subsidence with mid-
level height rises) has allowed cloud cover to begin clearing from
south to north. As the low levels dry out, lake effect snow showers
have ended around Ironwood and diminished to mostly flurries over
the Keweenaw. Temps have been steady in the upper single digits and
low teens throughout the day and it seems that little bit of
sunshine hasn`t helped at all.
Tonight, NW flow aloft will continue and the surface ridge will
slide by to the south through Wisconsin and into northern Illinois.
A fast-moving short wave currently seen in water vapor satellite
over southern Alberta will reach western Lake Superior by about 09z
tonight just as the low-level flow is becoming SW over the western
U.P. The combination of lift from this wave and SW flow with
enhanced landbreezes will induce a convergence band over western
Lake Superior. This band will take full advantage of lake sfc-850 mb
delta T`s around 19-20 C and saturation to around 7 kft to produce a
classic "Bayfield Bomber" lake effect snow band across the western
half of the lake and into the Keweenaw. This will be the main story
of this short-term period. HRRR and other high-QPF CAMs have been
verifying well in this regime with multiple lake-effect events over
the past week, so with such a strong convergence signal and such
favorable parameters, felt confident to lean high on QPF. The slight
warming aloft will actually be a net positive for SLRs as it means
the DGZ will be thicker and overlap more with the low-level omega.
Therefore, SLRs > 20:1 are likely. The end result is a narrow band
of 6-12" of snow from about Twin Lakes north to about Delaware. The
exact placement will determine who sees how much snow, but it is
possible that this band stalls in one area long enough to produce
12"+ of snow. Right now the best bet for seeing those high-end
amounts would be north of Calumet and southwest of Eagle River. Have
issued a new Winter Weather Advisory for Keweenaw and northern
Houghton counties for tonight and tomorrow. Amounts could justify a
warning but the small areal coverage of high amounts does not.
The eastern Winter Weather Advisory segment remains in effect
through 05z as previously scheduled. There is some concern that the
end of the aforementioned strong convergence band will reach the
eastern shoreline around Melstrand or Grand Marais. If it did, there
could be several inches more over a small area after midnight
tonight, but confidence in that happening is not particularly high.
As for temps tonight, it`s going to be a cold one. Lows should fall
into the single digits below 0 across the interior, although the
arrival of mid-level clouds overnight should keep temps from getting
Tomorrow, continued height rises and WAA aloft will lead to warmer
temps. There could even be some sunshine across the west half. This
will lead to temps rising into the low to mid 20s for highs. Over
the Keweenaw, the ongoing LES band will begin weakening by midday as
temps continue to warm and lake-based instability decreases. The
snow there should be done by about sunset tomorrow evening.
.LONG TERM...(Saturday night through Friday)
Issued at 332 PM EST FRI JAN 22 2021
Models suggest a split flow developing across the CONUS through much
of the extended with a progressive northern stream affecting the
northern Great Lakes. After a brief period of slightly below normal
temps this weekend, expect temperatures to slowly moderate through
next week with above normal temperatures by the end of the week.
Beginning late Sat night and Sun, models still in reasonable
agreement that a northern stream shortwave and associated inverted
sfc trough will bring an area of snow through the region from late
Sat night into Sun. Forecast 280k-290k isentropic lift and 1.5-2
g/kg moisture available were consistent with the 0.10-0.20 inches of
model QPF given the quick movement of the system. With SLR values
likely in the 15/1 to 20/1 range, expect 1 to 3 inches of snow,
highest south central and southeast. South to southeast winds and
850 mb temps around -11C may also bring the potential for some lake
enhancement off of Lake Michigan into locations from MNM/ESC/ISQ
where models suggest low level convergence will develop. This could
maybe boost local snow accumulations in these areas close to 4
Mon-Fri, increasingly confluent split flow and mean ridging into
midweek will result in mostly dry conditions. Only exception will be
some light LES in developing north-northeast flow for west and north
central U.P. Mon-Wed. Strengthening southerly flow and WAA by late
week, especially Fri, under mid-upper level ridging will
continue dry conditions as 850 mb temps climb to 0 to
-2C. Expect highs by Friday to reach near 30F across much of the
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 709 PM EST FRI JAN 22 2021
VFR conditions are expected at IWD as light southwest flow and land
breezes keep lake clouds off to the north.
MVFR cigs at SAW should also give way to VFR overnight with most of
the lake clouds remaining to the north. However, the clouds may
remain close enough so that confidence in clearing is lower.
CMX will be the challenging location. Models suggest that a moderate
to heavy lake effect snow band will develop over western Lake
Superior and move into the CMX area after about 02z. This band may
initially lift to the north before moving back south and setting up
to the south. Signficant variabitily in conditions will be possible
with vsby at or below mins possible for a brief time. LES bands will
likely persist into Saturday morning before gradually diminishing by
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 351 PM EST FRI JAN 22 2021
25 kt NW winds east half will subside below 20 kts tonight. A few
pockets of 20-25 kt winds are possible across the lake on Sunday.
Otherwise light winds 20 kts or less are expected across the lake
through at least the middle of next week.
Winter Weather Advisory until midnight EST tonight for MIZ006-
Winter Weather Advisory until 4 PM EST Saturday for MIZ001-003.
Area Forecast Discussion
National Weather Service Las Vegas NV
347 PM PST Fri Jan 22 2021
.SYNOPSIS...An active weather pattern will bring multiple low
pressure systems across the region. The first will continue to
impact our region this afternoon and evening with elevated southerly
winds areawide and scattered showers and thunderstorms in
southeastern Nevada and northwestern Arizona. A much colder system
will arrive early next week bringing measurable snow to the
mountains, rain for many of the valleys and the chance of low
elevation snowfall. Late in the week, systems will take advantage of
moisture from the atmospheric river, allowing the Sierra Nevada to
accumulate significant snowfall.
.SHORT TERM...Today through Sunday.
The first of several systems will continue to push through the area
today before a reinforcing area of low pressure spins up and around
the previous low, to bring lingering impacts. Wind Advisories remain
in effect for western San Bernardino County up through Death Valley,
eastward including western Clark County through 6pm PST tonight.
Lake Wind Advisories for Lake Mead Recreation Area continue through
6pm as well as southerly wind gusts persist through sunset.
Other than windy conditions, precipitation chances enter the
forecast for much of Lincoln, Clark and Mohave counties this
evening, with the best chances between 4pm and midnight PST tonight.
Looking at forecast RAP and HRRR soundings for KLAS and KIGM (Las
Vegas and Kingman), there exists a decent amount of CAPE as well as
shear this evening. Though 250 J/kg of CAPE would be nothing to
write home about in the Midwest or even during monsoon season, it is
a decent amount to have in winter, particularly when coupled with
upper level shear. Are we expecting severe thunderstorms tonight?
No, but a rumble of thunder is not out of the question. For
elevations below 6000 ft, the bulk of the precipitation expected
tonight will be in the form of rain. However, above 6000 ft, snow is
expected. Further, if a convective cell forms over higher elevation,
convective snow has the capability of dropping a substantial amount
of snow in a short period of time, with potential rain rates 2-
3"/hour. For this reason, confidence is moderate regarding snowfall
totals tonight, as isolated higher amounts are possible underneath a
stronger cell. All in all, this event will shape up to be relatively
minor compared to next week`s systems. Widespread precipitation
amounts between 0.10" and 0.30" expected tonight, though when the
reinforcing area of low pressure swings around, so will additional
chances of precipitation along southern Mohave County and
southeastern San Bernardino County, that could amount to an
additional 0.10" to 0.25" Saturday and Sunday. Otherwise, most areas
can enjoy a break with dry weather on Sunday as we gear up for what
the coming work week has in store.
Winds will be overall calmer through the weekend than today, though
elevated southerly winds can be expected. Temperatures will drop
about 10 degrees between today`s highs and tomorrow`s highs, as the
cold front pushes through the region tonight.
Impacts are overall anticipated to be minor, but it is important to
note that grime, oil and dirt build up on the roadways due to months
without widespread wetting rains need very little rain to become
incredibly slick. Double the distance between you and the car in
front of you when driving, if you can, than you normally do.
.LONG TERM...Monday through Thursday.
The parade of weather continues. Monday morning, the next system
will dip down the Western CONUS. Originating from Alaska, this
system is substantially colder than its predecessors. As such, snow
levels will drop to 3000 feet or lower, potentially reaching valley
floors in some areas. As a result, measurable snowfall can be
expected above 3500 ft, with a dusting to an inch possible even
lower. Snow chances continue to remain elevated across the region on
Monday, particularly, Monday morning. Looking at probabilistic NBM
resources, valleys such as Las Vegas, Yucca Valley, and Bishop can
expect to see snow in some capacity on Monday, with 40%, 72% and 78%
respectively. ECMWF ensemble members are increasing in confidence as
well regarding measurable snowfall here in Las Vegas, with only one
member keeping all of the precipitation as rain. What does this mean
for impacts? What about the roads? Though snow is possible,
accumulating snow is not as likely, with Las Vegas sporting a
whopping 1% chance of snow greater than 1 inch (though Yucca Valley
and Bishop have better odds with 35% and 55% respectively).
Additionally, ambient temperatures are not expected to drop low
enough in Las Vegas to cool roadways and allow snow to accumulate.
What could be a potential concern is black ice, depending on how
much rain Las Vegas gets during the day on Monday, followed by how
cold it gets Monday night/Tuesday morning. There is a nonzero chance
of isolated spots of black ice around the valley if temperatures dip
low enough for long enough. Chances of this at this time are low.
The "Shift of Tails" from the Ensemble Situational Awareness Table,
continues to indicate climatologically significant rainfall amounts
across southern Nevada and northwestern Arizona Monday, further
enhancing confidence. What is also shows, of note, is a
climatologically significant amount of CAPE across the forecast area
on Monday. This would indicate that there may be enough dynamics in
place to overcome potentially meager moisture amounts... and would
increase rain rates if there is a substantial amount of moisture
left over from the weekend system. Regarding snowfall...confidence
is not currently high enough to warrant any Winter Weather headlines
at this time. Additionally, we want to avoid putting out any
headlines this afternoon for Monday, as we don`t want people to
confuse the headlines with tonight`s event. Snowfall rates will be
highest Monday morning, decreasing through the event, with
measurable amounts expected above 3500 ft. Due to low confidence in
moisture potential, there is low confidence in precise snow totals
at this time, but are trending upward for higher elevations and
lower for the valleys.
Wind does not look to be a major impact for most of the area for
this system, but elevated southerly breezes can be expected. That
said, areas with lower anticipated rain rates can expect stronger
wind gusts. Areas that fit this description include cities south of
I-40 including Barstow-Daggett and Lake Havasu City as well as
potentially Yucca Valley and Twentynine Palms. Lake Wind products
for Lake Havasu will be reevaluated as we get closer and have
increased confidence, as these winds could result in waves 1.5-2.5
feet if they come to fruition. Additionally, local wind guidance as
well as CONSMOS continue to trend upward for western San Bernardino
County, so wind headlines may be necessary as we get closer and
But wait, there`s more. The next system to drop down will coincide
with a surge of moisture as a fairly robust atmospheric river
funnels into the western CONUS. This system has the potential to
dumb a substantial amount of snow on the Sierra Nevada and White
Mountain ranges with chances of light rainfall elsewhere.
.AVIATION...For McCarran...Clouds continue to this
afternoon as chances for rain increase into this evening. A few
showers and isolated thunderstorms can be expected through the
evening hours, ending by midnight. The greatest potential for
showers and isolated thunderstorms impacting the terminal area will
be between 01z-08z. Clouds as low as 4k-6k feet will be possible
with heavier shower activity. Southerly winds will continue at
around 15 kts gusting to 25 kts through 06z when wind will begin to
For the rest of southern Nevada, northwest Arizona and southeast
California...Windy conditions prevail over much of the area this
evening as a weather system moves through the area. Southerly winds
of 10-15 kts gusting to over 25 kts has been common, particularly
along the Colorado River Valley. This will continue through the
evening before winds begin to decrease after about 08z. Showers
and isolated thunderstorms are possible this evening with the
greatest chance between 01z and 08z. CIGs as low as 3-5kft are
expected along the Colorado River and in areas through 08z and in
areas with ongoing precipitation. Over southeast California, cloud
bases will be higher, AOA 15kft except in areas of showers and
precipitation will be more isolated.
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
For more forecast information...see us on our webpage:
https://weather.gov/lasvegas or follow us on Facebook and Twitter