Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 021135

Area Forecast Discussion
National Weather Service Marquette MI
635 AM EST Tue Mar 2 2021

.SHORT TERM...(Today and tonight)
Issued at 512 AM EST TUE MAR 2 2021

Water vapor imagery and RAP analysis show yesterday`s sharp trof and
associated surge of arctic air now well to the e over New England.
With that trof well to the e and another shortwave moving across the
Canadian Prairies, 500mb heights have rebounded around 200m over the
northern Great Lakes during the last 24hrs. Strengthening
waa/isentropic ascent regime shifting eastward in response to the
upstream shortwave has already spread an ovc mid cloud deck across
much of the fcst area. Prior to the arrival of the clouds, temps
dropped to around -10F at some of the traditional cold spots over
interior western Upper MI. Current temps across the fcst area are
generally in the upper single digits to upper teens F, coldest east
where skies have temporarily become mostly clear.

Strong waa/isentropic ascent will spread into the area today,
powered by a 50-60kt low-level jet translating into the Upper Lakes.
Question is whether or not this isentropic ascent will lead to
sufficient pcpn generation aloft to overcome dry low-levels and
allow pcpn to reach the ground. Fcst soundings suggest low-levels
will probably remain too dry with better chc of sufficient low-level
moistening a little farther e, deeper into the retreating cold air.
Will be close over the tip of the Keweenaw and far eastern fcst area
though. So, opted to retain a mention of flurries/sprinkles or schc

Bigger story today will be the wind associated with the low-level
jet. As is typically the case, the question is how deep into the
inversion will the mixed layer build to tap stronger winds. In
general, fcst soundings suggest mixed layer will be able to tap 30-
40kt winds. So, much of the area should see 30+mph gusts today with
some locations up to around 40mph. The highest gusts should occur in
the downslope areas around Marquette to Munising to Grand Marais,
and from near the Lake Michigan shoreline to around Newberry. The
brisk winds up Lake Michigan will build waves to around 8-12 feet.
So, a Lakeshore Flood Advy remains in effect along the shoreline of
Schoolcraft County today. Quite a bit of high cloudiness and at
times broken mid clouds will be over the area today. Still, temps
will be able to rebound into the 30s and lower 40s F, warmest w and
coolest downwind of Lake MI (around 34F there). If there is more sun
than anticipated, some locations over the w could reach the mid 40s.

Cold front will move s across Upper MI tonight. Fcst soundings show
a few thousand ft of low-level moisture developing after the front
passes. Temps in this moist layer may not reach -10C, increasing the
prospect of potential -fzdz. Where postfrontal n to nw winds upslope
the sharpest (mainly western Upper MI e to Marquette County),
maintained a schc mention of -fzdz/-shsn overnight tonight.

.LONG TERM...(Wednesday through Monday)
Issued at 415 AM EST TUE MAR 2 2021

Wednesday will start off with an inverted surface trough developing
over the lakes. This will be in response to a very weak upper level
shortwave disturbance propagating along the nw flow at the H5
levels. Model soundings show the potential for some light
precipitation onshore via northerly flow in the east half off Lake
Superior, and ne flow for the west half of Upper Michigan. An
inversion aloft does present the possibility of a warm nose scenario
for Upper Michigan per model soundings. Could be a couple hours
between sunrise and late morning of light drizzle to freezing
drizzle Wednesday. Amounts don`t appear to be concerning at this
time. Cloud cover should transition to the east half of Upper
Michigan by late afternoon. Weak CAA from Ontario toward the eastern
third of the CWA will keep the clouds around through the remainder
of Wednesday. High temperatures will be near seasonal averages
ranging from the upper 200s to upper 30s. Warmest areas will be over
south central Upper Michigan closest to the WI/MI state line.

Wednesday night into Saturday will see steep upper level ridge
amplification occur over the Central CONUS. Amplification of ridge
will begin to take on the appearance of an omega block, with two
pronounced longwave troughs on the west/east side of North America.
This will create nw flow aloft, and any energy riding along the east
half of this ridge axis will propagate quickly toward the northern
Great Lakes region and over to the New England area. Additional
weather feature to take note of is that the occluded upper level Low
over Quebec will continue to ebb and flow with shortwave impulses
propagating along the main jet stream. This solution is modeled in
solid agreement with the extended guidance. Long story short is that
it will impinge on Upper Michigan`s gradual warming trend and delay
it by at least 24-48 hours. A couple of days looked like a slam dunk
for highs in the 40 to 50 degree range for the entire weekend over
the CWA. Now looking like that will happen Sunday into the first
part of next week.

The upper level ridge axis will slowly shift east over the Great
Lakes by Sunday and Monday. This will result in above average
temperatures for several areas. The anomalously warm temperatures
will play their part in helping the extended range forecast become
tricky. Several shortwave troughs are progged to propagate over the
CONUS next week. Depending on the storm system tracks, the warm air
that is in place could result in scenarios where Upper Michigan sees
all rain, albeit a cold rain. However, if colder air is advected
south over the CWA ahead of the weather systems, we could see
additional chances of a rain/snow to all snow solution. The gradual
warming trend will be pushed back slightly for the extended period,
with an active weather pattern creating above average chances of
precipitation as well.

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 634 AM EST TUE MAR 2 2021

VFR conditions are expected at KIWD/KCMX/KSAW thru this evening. A
strong low-level jet translating across the area will result in LLWS
at all terminals thru the morning hrs. Then, as mixed layer builds,
LLWS will end with sfc winds becoming gusty to around 35kt. A cold
front will drop s across the area tonight. In its wake, MVFR cigs
will develop at KCMX/KSAW, and IFR cigs will develop at KIWD.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 512 AM EST TUE MAR 2 2021

Tight pres gradient btwn low pres tracking e to northern Ontario and
high pres dropping se thru the Ohio Valley will result in sw gales
of 35-40kt developing across the w half of Lake Superior today. Some
gale force gusts will probably occur at times across eastern Lake
Superior this aftn as well. Air mass will be warming today, but
until it warms sufficiently this morning, hvy freezing spray will be
possible. Winds will begin to diminish late aftn and more so tonight
despite a cold frontal passage. Winds from Wed thru the end of the
week should mostly be under 20kt. However, there may be a few
periods during that time frame where winds will gust to around 25kt
over eastern Lake Superior.

Upper Michigan...
  Lakeshore Flood Advisory from noon today to 10 PM EST this
     evening for MIZ014.

Lake Superior...
  Heavy Freezing Spray Warning until 9 AM EST /8 AM CST/ this
     morning for LSZ162-240>251-263>267.

  Gale Warning until 5 PM EST /4 PM CST/ this afternoon for LSZ162-

Lake Michigan...
  Gale Warning until 7 PM EST this evening for LMZ248-250.



SHORT TERM...Rolfson
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