Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 03/21/21

Area Forecast Discussion

National Weather Service La Crosse WI

 1050 PM CDT Sat Mar 20 2021

.SHORT TERM...(This evening through Sunday)
Issued at 148 PM CDT Sat Mar 20 2021

Fitting weather today for the first day of spring. Departing high
pressure continues to provide an abundance of sunshine, with
breezy southerly winds in its wake courtesy of a tightening
pressure gradient. Temperatures are on their way to highs in the
50s to low 60s this afternoon, coolest within a swath of
diminishing snowpack from Dodge to Winneshiek counties.

Wind gusts will diminish towards sunset as the boundary layer
decouples, but winds will still remain a bit breezy in open areas
and higher elevations tonight as a low level jet develops
overhead. This will begin transporting some additional moisture
into the region overnight into Sunday with dewpoints slowly
climbing into the 30s and eventually low 40s for some. Look for
increasing cirrus tonight as well, which together with the
southerly winds will keep lows in the mid 30s to around 40.

Sunday`s biggest story will be even gustier southerly winds
across the area as the pressure gradient max drifts overhead.
Mixing and gusts will begin ramping up by mid-morning, with gusts
topping out in the afternoon around 35 to 45 mph. The strongest
gusts will be found in open areas of southeast MN. RAP suggests
potential for mixing down gusts as high as 45 knots at RST, but
looks like average mixed-layer gusts closer to 40 knots. Not
currently anticipating the need for a wind advisory, but will keep
a close eye on trends. Should warm up nicely across the area with
highs in the upper 50s to mid 60s.

.LONG TERM...(Sunday night through Saturday)
Issued at 148 PM CDT Sat Mar 20 2021

Still looking like a wet beginning to the upcoming work week as a
surface cold front stalls northeast to southwest across the area
Sunday night and a closed low system ejects out of the Desert
Southwest and moves through the area Tuesday into Wednesday. Good
amount of moisture with the system as NAEFS mean precipitable
water values climb toward 0.75", good for the 90th+ percentile of
climatology. Furthermore, deterministic runs suggest values could
be even higher, closer to 0.90", and linger in the area much of
Monday and through Tuesday. In addition, pretty solid signal that
moisture transport will be pointing directly into the forecast
area during the day Tuesday as the low approaches from the
southwest, making for a day of widespread, steady rainfall. The
low will pass through the area sometime Tuesday night into
Wednesday, with cold air wrapping around the back side and leading
to a change over to snow for at least part of the region.
Questions do remain on just how far south the coldest air, and
therefore snow extends...at this point it`s looking very possible
our forecast area stays all rain. Also some questions on how long
precip lingers Wednesday, but once it does exit, much of the area
looks like it will have received at least 1 inch of rain. Many
ensemble members also suggest a band of higher amounts (2+").
Still some spread on where exactly that would fall, however,
though consensus would seem to favor a swath from southeast
Nebraska, through central or northwest Iowa, and into southern
Minnesota. While soils would certainly be able to absorb some
rain, would expect at least some river rises.

Following that system, another looks to pass by just southeast of
the area on Thursday. Yet another then looks like it could bring
some more rain sometime Friday into Saturday, but lots of
differences in guidance regarding timing and strength. Otherwise,
expect fairly widespread highs in the 50s Monday and Tuesday,
followed by a cool down into the 40s for the middle of the week
behind that initial system. Then expect a gradual warm up heading
into the weekend as we get back to widespread 50s by Saturday,
pending precip of course.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1051 PM CDT Sat Mar 20 2021

Winds will be the main concern into Sunday evening. The pressure
gradient will remain tight across the region between the area of
high pressure over the Ohio River Valley and the approaching cold
front, currently over the Dakotas. Winds just above the surface
will be very strong overnight with low level wind shear for both
sites. This will end early Sunday morning once the low level
inversion breaks allowing some of these stronger winds to mix down
to the surface. Once this happens, gusts of 30 to 35 knots can be
expected for much of the day. The gradient will relax enough
around sunset Sunday evening to allow the gusts to diminish but by
this time, the front could be close enough to allow some MVFR
ceilings to develop. This would primarily impact KRST and these
should not arrive at KLSE until right around 22.06Z.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...Kurz
LONG TERM...CA
AVIATION...04



Area Forecast Discussion

National Weather Service Denver/Boulder CO

 928 PM MDT Sat Mar 20 2021

.UPDATE...
Issued at 857 PM MDT Sat Mar 20 2021

Overall there were no major changes to the forecast. A shortwave
is moving through northwest Colorado this evening with associated
precipitation and a surface cold front. There are strong winds
just behind the cold front with gusts to 50 mph being reported at
a couple locations. It seemed like the models were underestimating
winds tonight across the mountains so gusts were increased. As the
shortwave progresses northeastward, it will produce moderate snow
showers in the mountains especially along the western slopes.
Since there is not much QG ascent associated with this shortwave,
snow amounts won`t be very much so no highlights were issued for
tonight. The shortwave passes tomorrow morning with a brief break
in precipitation for the mountains and improved travel conditions.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 244 PM MDT Sat Mar 20 2021

There is fairly strong southwesterly flow aloft over the forecast
area at this time. There is plenty of high level cloudiness in
place. Temperatures are varied across the plains: with upper 50s
to mid 60s in the snow-less areas, and mid 40s to lower 50s where
snow is on the ground. It was interesting, DIA was 60 F earlier at
12:38 MDT then an easterly wind came in and the temperatures
dropped to 48 in a matter of minutes.

There should be 60-80 knot southwesterly flow at jet level over the
CWA tonight and Sunday.  There is upward vertical velocity in place
tonight and Sunday. Normal diurnal wind patterns are expected
tonight.  The cold front associated with this incoming trough moves
into the CWA from the north at about 10Z by the border to about
17Z for the southern CWA. Pretty strong north-northeasterly
upslope is in place behind the front.

Cross sections continue to indicate pretty decent alpine moisture
much of tonight, with a bit of a decrease towards dawn. The plains
just have some mid level clouds around tonight.  On Sunday, the
incoming upper trough will bring deep moisture to the mountains
through the morning, then over the plains by the afternoon.  Will go
with likely pops for snow in the mountains from 03Z tonight.  No
pops for the plains tonight. On Sunday, pops will increase to
80-90%s in the mountains by late morning. I will get the pops up
to "likely" over the eastern half of the plains by afternoon.
Sunday`s high temperatures will be in the mid teens and 20s in the
mountains, 30s in the foothills and 40s on the plains.

.LONG TERM...(Sunday night through Saturday)
Issued at 149 PM MDT Sat Mar 20 2021

Active pattern with persistent central US trough and welcome
periodic moisture in the extended period. Seasonably cool
temperatures through mid week...with highs about 10 degrees below
normal and lows near normal...will be a contrast to recent warmth.

Extended period picks up ongoing mountain/foothill snow Sunday
evening with axis of the 500mb trough just entering the western
part of Colorado and northeast surface flow on the plains. Trough
continues east through the night, reaching the plains by 12z
Monday morning. Will be cold enough for snow Sunday in the
mountains at the start, and rain changing to snow pretty quickly
after the 00z/6pm beginning of the extended period. High
resolution models, especially RAP & HRRR breaking out heavier
precipitation 00-03z in the foothills west of Denver and wrapping
around to the south side of the metro area. Model soundings show a
period from 00-12z Monday with saturation in the -12 to -18c
dendrite growth zone and upward vertical motion. Couple that with
NNE low level upslope flow at the onset from 00-03z for a good
start to the snow. Surface temperatures may not start cool enough
on the plains, but wet bulb effects and time of day will see a
speedy changeover to snow. Some model discrepancies, with GFS
trending the lowest at around a third of an inch of liquid and 3
inches of snow, with NAM double or triple those amounts. We have
confidence in the mountain & foothills areas to hoist a winter
storm warning. Some internal debate over advisory vs warning, but
with returning ski traffic on I-70 late Sunday we have opted to
nudge up to warning based on impacts. For the next stripe of
forecast zones...northern foothills, Denver Metro and Palmer
divide, given the later start and uncertainty of the model spread
have gone with a watch for those areas.

Light snow to continue Monday morning under cold pool aloft, then
shuts down Monday afternoon after trough passage and subsidence
begins. Next system for Tuesday follows quickly on the heels of
Monday`s departing system. A second shortwave trough digs into the
region, amplifying the full latitude trough developing over the
central US. Renewed chances for snow mainly in the mountains
Tuesday afternoon and overnight. No real warmup during this
period with us low heights under the upper trough and continued
cool northerly flow. Temperatures do warm to near normal on
Thursday in advance of next system

Next system on Friday drops into the western part of the trough,
sinking to the four corners area. This system may do more for the
western slope but still worth the likely in the mountains and
chance on the adjacent plains.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 857 PM MDT Sat Mar 20 2021

Drainage winds will continue until late tonight when a cold front
will begin to push through the terminals. This will turn winds to
the northeast during the day tomorrow with moderate gusts up to 20
knots. By the afternoon, ceilings will begin to lower as showers
develop over the mountains and foothills and push eastward over
the terminals. The heavier precipitation rates don`t begin until
the evening when IFR to potentially LIFR ceilings and visibilities
will develop.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Sunday evening through Monday afternoon
for COZ039>041.

Winter Storm Warning from noon Sunday to noon MDT Monday for
COZ033-034-036.

&&

$$

UPDATE...Danielson
SHORT TERM...RJK
LONG TERM....Hanson
AVIATION...Danielson



Area Forecast Discussion

National Weather Service Columbia SC

 910 PM EDT Sat Mar 20 2021

.SYNOPSIS...
Some possible showers over the eastern and southern Midlands
tonight and Sunday morning, otherwise cool and fair through
mid week. A warming trend is expected throughout the week as an
upper ridge builds over the region. Chances of rain will
increase after mid week as a low pressure system approaches the
region.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
A coastal trough combined with ridging from the north has
triggered some isentropic lift and weak showers across the
eastern Midlands and the CSRA this evening. Low level air
remains fairly dry so this precipitation is expected to remain
light. Hi-res guidance has trended towards stronger warm
advection and isentropic lift with a 40 knot 850mb easterly jet
developing along the coast. Based on current radar trends,
shower activity is out performing the hi-res suite along the
eastern FA.

The hi-res guidance picks shower activity up dramatically in
the next few hours. However, this is likely overdoing the
geographic extent of the shower activity a bit, as the hi-res
suite is not currently representing the low level moisture
field very well to west. So while shower activity will likely
become more widespread overnight as PWATs continue to increase,
expecting the majority to remain in eastern and southern
Midlands and CSRA. But given how the hi-res has been under-doing
the showers so far, and the current satellite and radar trends,
bumped PoPs up across the region to a chance, and likely across
some of the southern FA.

Winds will remain up at 5-10 knots from northeast throughout
the night.


&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY NIGHT/...
Sunday and Sunday night: What limited light rainfall that may be
occurring over the eastern cwa will quickly be moving back
towards the coast during the morning hours. Upper trough slowly
moves closer to the coast, while at the surface the coastal
trough will remain off the coast and high pressure builds in
from the north. Clouds through the day, along with continued
northeasterly flow, will keep temperatures on the cool side.
However they should still be warmer than Saturday, with highs
in the lower 60s. Slow warming trend continues into Sunday
night, with lows in the 40s.

Monday and Monday night: Upper trough will be pushing away from
the area, while upper ridging builds in briefly behind it.
Surface high pressure will continue, and dry conditions should
prevail through Monday night. There should be more sunshine with
the ridge moving through, and this will continue to allow
temperatures to moderate. highs are expected to be in the mid
to near 70. Overnight lows are expected to be slightly warmer
in the mid to upper 40s.

Tuesday and Tuesday night: The upper ridge axis will push east
of the area by Tuesday morning, allowing the upper flow pattern
to turn more southwesterly. Some weak wedging may still be
ongoing across the northwestern cwa early Tuesday, but that will
mix out quickly through the morning as the surface high moves
further offshore and low-level winds turn more easterly.
Moisture will be on the increase through the day, with low-
levels bringing in Atlantic moisture, while aloft the pattern
will bring Gulf moisture northeastward. Conditions through the
day Tuesday should remain dry as ti will take time to moisten
up. By Tuesday night, rain chances should increase across the
western cwa, with mainly slight chance pops expected for now.
Daytime highs in the upper 60s to lower 70s, while overnight
lows mainly in the 50s.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Deepening trough will setup into the middle of the country
Wednesday. East of that trough, deep southwesterly flow aloft,
and southeasterly surface flow, will continue to moisten the
atmosphere Wednesday through Friday. Weak shortwave energy
moving through aloft should allow for some scattered showers
Wednesday. By Thursday the upper trough will be lifting
northeastward towards the Mid-Atlantic, while at the surface a
cold front will be approaching the region. By Thursday afternoon
and into the early portions of the overnight, some thunderstorms
and heavy rainfall may become possible ahead of the front. Still
too far out to determine any severe potential. May see a brief
period of drying Friday afternoon and night, before isolated
showers once again enter the forecast for the weekend. Temperatures
are expected to be mainly in the 70s through period, with lows
in the 50s.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
Extensive strato-cumulus/alto cumulus across the region early
this evening. At the moment the ceilings are VFR. Strong
pressure ridge extending into the area from the Delmarva and
weak low developing east of Canaveral. Relatively tight pressure
gradient across the region so northeast winds will stay up
overnight around 10 knots with higher gusts. Showers have
developed in the coastal plain associated with relatively strong
warm advection and east moisture flux. This is in line with the
latest GFS guidance and HRRR guidance suggesting light showers
mainly in the eastern Midlands near OGB and near the AGS/DNL
terminals later tonight. The lamp and NBM ceiling guidance is
trending lower even at the CAE/CUB terminals late tonight so
lowered to MVFR developing after 043z from east to west. The
MVFR ceilings may linger through Sunday mainly at OGB. Northeast
winds 10 to 15 knots with gusts to around 20 knots through
Sunday expected as the pressure gradient remains tight with
weak surface low well offshore.

EXTENDED AVIATION OUTLOOK... Another low pressure system
approaches Tuesday into mid week with possible restrictions.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.

&&

$$




Area Forecast Discussion

National Weather Service Gray ME

 958 PM EDT Sat Mar 20 2021

.SYNOPSIS...
After a mild day today...high pressure will move overhead
tonight allowing temperatures to fall rapidly. Our warming
trend will continue on Sunday as the high pulls east into the
Canadian maritimes. This high looks to remain in control of our
weather through the middle of the week with temperatures
remaining above seasonal norms. By latter portions of the
week...chances for rain will increase as a series of frontal
systems approach from the west.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
9:55 PM Update... Very little change to the ongoing forecast
other than adjusting forecast temperatures some to better match
with surface observations. Locations that decouple will
continue to cool quite rapidly under mostly clear skies. A few
high level clouds may stream in across northern locations but
these should not have a major impact on temperatures.

Previously... 620 PM Update...Little change to the going
forecast. Clear skies are expected this evening with light to
calm winds. This will set the stage for good radiational
cooling.

High Impact Weather Potential: Minimal.

Pattern: Looking at mid level water vapor imagery this afternoon
shows troughing over the northeastern United States and maritime
Canada /the eastern member of a trough-ridge-trough setup
across the country/ lifting north and east. Beneath the ridge
there is a weak mid level trough over the southeastern states
with no significant sensible weather beneath this feature. The
near term period will be dominated by arriving mid level ridge
axis from the west and attendant surface high. This portends a
very quiet forecast period with our focus primarily on overnight
lows.

Through this Evening: Surface high pressure will continue to build
towards the region from the west with a very dry boundary layer and
slackening gradient favoring a quick temperature fall once we reach
sunset.  By 8pm expect most locations to have fallen back into the
30s under clear skies.

Tonight: Not much to consider overnight with surface and mid level
ridge directly overhead.  PWATs fall to right around 0.10" with a
dearth of moisture through the column suggesting a clear night. A
look at 1000 mb geostrophic winds among the deterministic guidance
suggest 10-15kts of flow...strongest over Maine.  With this
gradient...most valleys should decouple with some light winds
possibly continuing over the hills. Given this...inherited lows
that are at the lower end of the statistical guidance envelope
look good. This yields teens in the valleys and 20s elsewhere.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
High Impact Weather Potential: Minimal.

Pattern: High pressure overhead daybreak Sunday will continue to
move east into the Gulf of Maine through Sunday Night as mid level
ridge axis arrives from the west.  The aforementioned trough/cutoff
south of this ridge will slowly sharpen/organize through the period
with low pressure forming off the southeastern coast.  Given the
proximity of the high...very quiet weather will continue through
this period with our focus again being on temperatures...which will
be modulated during the daytime by seabreezes.

Sunday: A very spring like second day of spring is in store given
very dry airmass /PWATs nearing 10th percentile/ and T9s pushing to
around +7C just west of the surface high.  Light winds are expected
with T9s suggesting highs 55-60F are a good starting point.
Mixing heights are rather disparate across the guidance
suite...but feel that given the time of year...consensus height
around 900 mb is about right...which would boost these values a
degree or two...with another small boost likely from a surface-
based superadiabatic layer. Thus...followed close to inherited
highs...which follow the MET and NBM 75th percentile with
mid/upper 50s in the mountains and lower 60s to the south. With
high pressure now east of our longitude...expect robust
seabreeze development which is well shown by the longer range
HRRR cycles. Clearly this will keep temperatures lower in this
area.

Sunday Night:  High pressure still just to our east with lighter
gradient overhead suggests another good radiational cooling night
given dry airmass overhead.  Expect lows to be somewhat warmer than
the night previous given the much warmer afternoon highs...but still
expect a large diurnal range with a few valley locations very
possibly dropping below 20F.  Followed the coolest of the
statistical guidance for this.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
High pressure at the surface and above normal heights aloft
will keep our area dry with above normal temperatures for the
for much of next week. Onshore winds will keep coastal areas
several degrees cooler than inland areas where highs will be in
the uppers 50s to low 60s. A surface low associated with an
upper wave moving through the upper ridge will pass to our
southeast late Tuesday into Wednesday with the only sensible
weather impacts being increased onshore flow and more clouds
Wednesday. Towards the second half of next week above normal
heights over the Northeast will shift into the Atlantic while a
trough over the central US slides eastward. This trough will
generate several areas of low pressure that will track west of
the area. The first low in the series will track well to our
west Thursday with another low quickly following it that looks
to track close enough to bring widespread precipitation Friday.

On Monday, the area will be under the western edge of broad high
pressure centered in the western Atlantic. Our early spring warm
spell will continue with highs in the upper 50s to low 60s
under mostly sunny skies. Southwest winds will turn southerly
during the day leading to onshore flow bringing cooler
conditions to the coast. Tuesday will be fairly similar to
Monday with the exception of winds turning easterly. These
easterly will again bring cooler conditions along the coast
along with the potential some low marine stratus.

The center of high pressure will shift out into the Atlantic
Wednesday as a weak surface low meanders southeast of Nova
Scotia. Easterly flow will continue Wednesday along with an
increase in clouds. Easterly flow and more cloud cover will
limit high temperatures to the mid to upper 50s with coastal
areas in the upper 40s to near 50F. On Thursday the trough over
the central US will be progressing eastward with low pressure
systems tracking northeastward through the Great Lakes. These
systems look to pass to far to our west to bring appreciable
precipitation with mostly cloudy skies expected Thursday. By
Friday global models are in good agreement of tracking an area
of low pressure close to overhead bringing widespread rainfall.
There is also a strong signal in ensembles for widespread
precipitation Friday and have nudged PoPs above the NBM to
account for this signal.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
Short Term...

Summary: High pressure moves overhead tonight and into the Gulf of
Maine on Sunday / Sunday night with quiet weather expected.

Restrictions:  VFR conditions are expected to dominate the period
through Sunday night under clear/mostly clear skies.

Winds: Northwest winds around 10kts this afternoon will diminish to
calm/light-variable overnight with very light winds expected to
continue for Sunday and Sunday night with the exception of local
seabreezes for coastal terminals Sunday afternoon.

LLWS: LLWS is not expected through the period.

Long Term...Mainly VFR into the second half of the week.
Easterly winds Tuesday and Wednesday may lead to low stratus
developing at coastal terminals.

&&

.MARINE...
Short Term...High pressure in control through this
period...settling overhead tonight and pushing east into the
Gulf of Maine through Sunday night. This will lead to headline-
free conditions on the waters through the period.

Long Term...Winds and seas will remain below SCA thresholds
Monday through Tuesday night. Persistent easterly flow Tuesday
into Wednesday will lead to seas building to 5 feet by Wednesday
morning. Seas will remain at 5 feet into the second half of the
week, while wind gusts will be less than 20 kts.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...None.

&&

$$

NEAR TERM...Ekster/Tubbs
SHORT TERM...Arnott
LONG TERM...Schroeter



Area Forecast Discussion

National Weather Service Key West FL

 1015 PM EDT Sat Mar 20 2021

.DISCUSSION...
Clear to partly cloudy, dry and cool conditions prevail along the
Florida Keys on this Saturday evening. Areas of stratocu are
spreading SW from the mainland into the Upper Keys at this time,
while radar shows some light showers moving slowly south across
Biscayne Bay and the adjacent Atlantic waters. Temperatures along
the island chain are dropping through the upper 60s, and winds on
land are from the northwest at 10 to 15 mph. Surface analysis
shows a weak low pressure area centered between the Southeast
Florida coast and the northern Bahamas, with a reinforcing cold
front dropping southward across South Florida. A large area of
high pressure is centered over western New York State and
dominates the eastern CONUS. The 00Z Key West sounding sampled a
very dry and stable airmass, with a strong inversion based near
4000 feet and PW of only 0.66 inches. MIMIC-TPW imagery shows a
similarly dry airmass around and NW of the Keys, while somewhat
greater moisture (estimated PW values around one inch) curls
around the weak low to our northeast.

Overnight, the weak low pressure area is expected to drift slowly
to the northeast, while the reinforcing front continues to drop
southward, causing our surface winds to shift from NW to N late
tonight. A few of the showers currently over Biscayne Bay may
manage to reach the far Upper Keys from Ocean Reef to North Key
Largo, but otherwise expect dry conditions across the remainder of
the Keys. Temperatures appear to be on track for lows in the mid
60s by sunrise, along with very pleasant dewpoints in the upper
50s. The public forecast has been updated to make minor
adjustments to overnight sky cover and winds.

&&

.MARINE...
NW winds have surged above most of the guidance again this evening
across the Keys coastal waters, although there is a great deal of
variation among the various reporting sites, ranging from barely
over 10 knots at Sand Key to near 20 knots at Sombrero Key. Winds
are generally holding around 15 knots on the Gulf/Bay side,
except out near the Dry Tortugas where the NOAA research ship
Nancy Foster has been reporting N winds at 11 to 14 knots this
evening. HRRR guidance seems to be handling this wind surge the
best, and indicates that it will last a few more hours before
subsiding late tonight. Will post Small Craft Exercise Caution
headlines for parts of the Keys waters with the late evening
forecast issuance.

&&

.AVIATION...
VFR conditions will prevail overnight and Sunday at the EYW and
MTH terminals. Areas of BKN stratocu between 3500 and 5000 feet
will continue to spread SW from the mainland across the Keys
during the night. A brief MVFR ceiling around 2500 feet cannot be
ruled out, but the probability is too low to mention in the TAFs.
Sunday should see clearing skies once again with stratocu reducing
to FEW to SCT. Surface winds will remain from the NW at 10 to 15
knots this evening, becoming NNW late tonight, then becoming NW
again Sunday afternoon.

&&

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...None.
&&

$$

Public/Marine/Fire...Jacobson
Aviation/Nowcasts....Jacobson
Data Acquisition.....DR

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Area Forecast Discussion

National Weather Service Marquette MI

 628 PM EDT Sat Mar 20 2021

.SHORT TERM...(This evening through Sunday)
Issued at 358 PM EDT SAT MAR 20 2021

WV imagery and RAP analysis indicated a mid/upper level trough over
the western CONUS and a downstream ridge from the Southern Plains
into the Upper Mississippi Valley. At the surface, southerly winds
have increased from MN and WI into Upper MI with a tightening
gradient between high pressure over the eastern Great lakes and a
trough from central ND to western Nebraska. With the dry airmass in
place and plentiful sunshine, mixing to 3k-4k ft has dropped
dewpoints at or below 10F over much of the area with RH values into
the 10-20 percent range. Winds were also gusting to 20-25 mph
resulting in elevated fire weather conditions for locations that
have lost snow cover, especially grassy areas.

Tonight, a ssw low level jet of 50-60 kt will prevail keeping enough
low level mixing going despite increasing stability (surface temps
into the lower 30s inland) to maintain gusts to around 20 mph inland
and to around 30 mph for downslope locations near Lake Superior.

Sunday, expect incrasing mid/high clouds into the west half as the
mid level and sfc trough approaches. Given the antecedent dry
airmass, any pcpn with the approaching weak to moderate 700-300
qvector conv will remain to the west of Upper Michigan. Enough low
level moisture will move in to keep min RH values closer to 30
percent. However, forecast momentum transer with mixing again to
around 3k ft suggests gusts to around 35 mph will be likely. Temps
will also climb toward the higher end of guidance with highs in the
lower 60s, except downwind of the cooling from Lake Michigan.

.LONG TERM...(Sunday night through Saturday)
Issued at 353 PM EDT SAT MAR 20 2021

The longterm period looks to continue with above normal temperatures
through the beginning of this week. During the middle of next week
and through the weekend, models suggest temperatures fall back
closer to normal, but perhaps still slightly abv, to round out the
month of March.

Broad ridging over the ern CONUS will slowly slide to the east
through the weekend as a trof follows behind. By Monday, this trof
takes on more of a split-flow pattern with the northern stream
bringing a weak cold front across the UP with some light pcpn and a
southern stream wave gets cut off and drifts east through the 4
corners and into TX. Tuesday night into Wednesday, this wave lifts
northward, progged to pass through western to central Upper Michigan
by Wednesday afternoon, while bringing a pcpn shield of rain, bcmg
snow, Tuesday aftn through potentially mid-Thursday. Split flow and
broad troffing continue across much of the central and wern CONUS
behind this wave before model suggest another wave shifting from the
Pac NW through the Rockies and into the GL region on Sunday,
bringing another chance of pcpn, but still some time to shake out
the details.

Pretty breezy to start on Sunday night as a 60kt LLJ traverses from
west to east across the UP ahead of a weak cold front progged to
move in from the NW. Antecedent dry air may have something to say
about it, but models suggest some light pcpn in the form of rain on
Sunday night. The best window per model soundings appears to be in
the 03 to 09Z timeframe across the west and central and 06 to 12Z in
the east, though confidence is lower on pcpn, if any, across the
east. Cold front peters out across central UP Monday morning as a
warm front develops in central WI and starts pushing northward
towards the UP Monday evening.

As the warm front pushes across the UP Monday night, moisture is
marginal, as well as the WAA but models that show pcpn are
suggesting decent isentropic ascent that will bring a chance of
light rain. Behind this warm front, there looks to be a break in the
pcpn as dry air mixes into the profile, cutting off deeper moisture
as well. Better forcing for ascent and moisture profiles arrive
later in evening on Tuesday, as a shield of pcpn will shift over the
UP, bringing widespread rain with amounts most likely between 0.3
and 0.7 inches across the UP for the event. Models show the
strongest forcing, especially in the GFS, remaining off to the west
over Lake Superior and the Arrowhead of MN where the better fgen
forcing will be. This system looks to slowly shift over the UP
through Wednesday night, before shifting away into Thursday morning.
Some model differences in how this event ends, with the GFS
developing into a much stronger low as the result of its baroclinic
instability drops 850mb temps much colder than other deterministic
models to as low as -20C Thursday morning (EC at -6 and GEM at -3).
Something to monitor for the potential of snow on the backside of
this low, which at this point is more likely to remain as all rain
per ensemble trends and spread.

Models continue their differences behind this exiting low with the
GFS remaining the coldest of the 3 big deterministic players. A
second southern stream shortwave ejects to the NE from ern TX
Thursday night, lifting through the Central Plains and into the Ohio
River Valley. To the west, a positively tilted trof begins to
develop as a wave digs south from the Pac NW to SoCal Friday night,
shifting E to the 4 corners region Sat morning. At the same time,
the northern stream shifts ESE from the Canadian Rockies as a
building ridge pushes onto the West Coast Saturday. This trof
traverses over the UP on Sunday, bringing a some chance for some pcpn
across the UP. The best forcing is with the EC, and across the E
where a better gradient lines up. GFS is trending a little further
to the south with the better pcpn, but still over a week out so
something to watch this week.
&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 628 PM EDT SAT MAR 20 2021

TAFs will continue to be VFR. There will be LLWS at all terminals
tonight into Sunday morning as a strong low-level jet moves across
the region. SW winds will also be gusty at all of the terminals into
the 25-30 knot range.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 358 PM EDT SAT MAR 20 2021

Over the east half, southerly winds are expected to remain near 30
knots through Sunday evening. Winds on the west half will remain in
the 20-25 kt range through the weekend. Lighter winds are expected
Monday as a low pressure trough moves over the area. By Tuesday, a
low pressure system over the Mississippi Valley will result in winds
veering around to NE and increasing to 20-30 kts, greatest over the
western third of the lake. NE winds may even reach low-end gales
over the west end late Tuesday into Wednesday morning before backing
N and diminishing to 20 knots or less late Wednesday night into
Thursday as the low lifts northward across the lake and weakens.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...JLB
LONG TERM...JAW
AVIATION...07
MARINE...JLB