Area Forecast Discussion
Issued by NWS Marquette, MI

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000
FXUS63 KMQT 231817
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
217 PM EDT Sat Mar 23 2024

.KEY MESSAGES...

- A brief period of quiet and dry weather continues through tonight.
- Late season winter storm lifting out of Colorado through the early
part of the coming week will bring accumulating snow later Sunday
through Monday.
- Heaviest snow accumulations will be Sunday night, resulting in
hazardous travel into early Monday before a transition to rain for
late Monday and Tuesday.
- Westerly lake effect snow, mainly for the copper Country Wednesday
and Wednesday night.

- Late season winter storm lifting northeast from Colorado early
next week brings accumulating snow and hazardous travel late Sunday
into Monday.
- Westerly lake effect snow mainly for the Copper Country Wednesday
and Wednesday night.

&&

.UPDATE...
Issued at 931 AM EDT Sat Mar 23 2024

Scattered lake effect flurries and snow showers continue across the
eastern UP this morning, but some lake clouds are apparent to the
west on satellite, streaming into Keweenaw, Houghton, and Ontonagon
counties. So, will not rule out some activity there in spite of an
otherwise dry airmass. The only real changes have been made to
temperatures over hte next couple of hours, with most of the western
half of the UP coming in a few degrees cooler than forecast so far.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 217 PM EDT Sat Mar 23 2024

Water vapor imagery and RAP analysis show mid-level troughing over
central and eastern Canada, anchored by a deep mid-level low
centered on the Hudson Bay shore of Ontario. At the surface,
sprawling surface high pressure centered over Manitoba is building
into the Great Lakes.

In spite of very dry midlevel air, lake-induced stratocumulus is
apparent on satellite courtesy of chilly NW flow over Superior
(850mb temperatures hovering around -18 to -20C). The Day Cloud Type
RGB shows higher cloud tops across the eastern UP, with a longer
fetch off of Superior. There, weak, cellular, lake-induced snow
showers are apparent on radar with some drops in visibility noted in
ASOS sites as well. Elsewhere, lower-topped, patchy strato-cu across
much of the western and central UP, becoming somewhat more organized
over Marquette county along the lake breeze. Precipitation has yet
to develop there, but will not rule out some light snow showers as
cloud tops do appear to be climbing. Totals across northern
Marquette county and across the eastern UP should only peak at
around a quarter to half an inch, with just isolated flurries and
snow showers elsewhere. Otherwise, temperatures are climbing through
hte 20s this afternoon, and should peak in the upper 20s and lower
30s across most of the area.

Any lingering flurries should end by sunset. The surface high
continues drifting eastward overnight, resulting in a wind shift
over mainly to the SE. With 850mb temps across northern Lake MI
around -12C, some flurries may develop into portions of central
Upper MI late tonight. Otherwise, expect midlevel cloud cover to
increase from the south courtesy of warm air advection ahead of the
much-advertised deepening low pressure system over the Plains.
Precipitation should hold off until after 12Z Sunday. Increasing
clouds and a shift over to southerly flow likely means that
overnight lows will occur fairly early in the night; expect most of
the area to fall into the teens, with some cooler pockets possibly
bottoming out in the single digits by 06Z. After that, temperatures
hold steady and perhaps even increase towards morning.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 339 AM EDT Sat Mar 23 2024

The primary forecast challenge continues to be the impending wintry
mess late Sunday into Monday ahead of a Colorado low lifting
northeast across western Lake Superior on Tuesday. Wintry precip
transitions to rain on Monday that persists through Tuesday before
transitioning back to snow late on Tuesday. Lake effect potential
- mainly for west wind snow belts - develops on Wednesday before
tapering off Thursday. Above normal temperatures and synoptic
precipitation chances return late next week.

Beginning with Sunday morning, a ~1030 mb surface ridge positioned
across southern Ontario results in increasing southeasterly flow.
Upslope SE flow off Lake MI results in increasing low level
cloudiness and chances for light snow, mainly across higher
elevations of the western UP. Much of the cloud-bearing layer and
modeled lift resides in a deep DGZ with light low level winds
implying initially high SLRs. However, surface temps warming to
around freezing and relatively strong late March sun suggests minor
travel impacts until heavier precipitation arrives later on Sunday.

An impressive warm front lifts across Upper Michigan Sunday night
with a band of heavy precipitation rates developing within strong
isentropic ascent and frontogenesis along and north of the warm
front. As the heavier precip rates arrive late on Sunday, the DGZ
narrows and raises to roughly 12-16 kft AGL. Not only is this
positioned above the best forcing for ascent, but there also appears
to be considerable turbulence below the DGZ suggesting potential for
dendrite fracturing. All that is to say that even though there may
be a brief window of high SLR snowfall early in the event, I expect
SLRs closer to 10:1 for the bulk of the QPF and I edited the
forecast accordingly. Speaking of QPF, ensemble means advertise
a considerable west-to-east gradient due to a dry slot along and
south of the warm front. Ensemble means advertise up to 3/4" of
QPF across the western UP to less than 1/4" across the eastern
UP by 12z Monday when p-type issues arise. This gradient should
be even sharper in reality, but there`s uncertainty in where the
gradient sets up with the GEFS/CMCE noticeably farther east
than EPS guidance. There may also be some southeasterly lake
enhancement on the Keweenaw. In addition to instigating a QPF
gradient, the dry slot also delineates the first (all snow) and
second (wintry mix) waves of precipitation.

Monday`s forecast is tricky with meaningful model differences as the
low pressure approaches being vertically stacked/occluded over
northwestern Iowa. Model guidance is in good agreement that a
shortwave ripples northeast along the warm front draped across our
area resulting in considerable p-type challenges. This waves brings
light to locally moderate QPF with the best chance for all snow
being on the Keweenaw. With the surface low displaced well to the
southwest, stable low levels, and generally easterly flow makes me
skeptical of the magnitude of warming on Monday. While the RGEM is
most aggressive with Monday`s snow potential, the prospect of
accumulating snow persisting through Monday afternoon across
the northwest 1/3 of the U.P. shouldn`t be immediately
discounted. On the other hand, NAM guidance shows a sharp
boundary layer inversion with a warm nose aloft that raises
IP/ZR concerns. Regardless of the model, a northwest to
southeast gradient in QPF and p-type seems likely to cause
forecast issues on Monday.

Warm air advection eventually overwhelms the entrenched cold air
mass on Monday leading to a period of rain that continues until the
systems cold front moves through late on Tuesday. Importantly, an
energetic shortwave rounds of the base of the trough on Monday then
accelerates northeast toward the Great Lakes region Monday night and
Tuesday. This negatively tilted shortwave results in a renewed
period of cyclogenesis and intensifying precip as the low pressure
tracks across western Lake Superior on Tuesday. This wave of precip
appears to fall exclusively as rain and ensemble means advertise
another wave of locally moderate precip with the heaviest amounts
downwind of Lake Michigan. The cold front sweeps across the area
Tuesday night changing any lingering precip back to snow. The 12z
grand ensemble also shows probabilities of 850 mb temps cooling
below -11C increasing above 50% Tuesday night through Thursday
afternoon. This is sufficiently cold for lake effect snow and models
are in seemingly good agreement about LES mainly for the west wind
snow belts.

Another trough moves over the Pacific Northwest on Thursday that
emerges on the Plains on Friday. Ridging building ahead of this
system results in temps warming above normal on Friday then
precipitation chances returning on Saturday. Ensembles suggest the
trough and associated surface low weaken while approaching the area
suggesting mainly light precip amounts. The forecast low track near
or south of the UP indicates some wintry p-type potential, but it
doesn`t seem like it`s worth getting excited about at this time.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 113 PM EDT Sat Mar 23 2024

VFR is expected through the forecast period. With cold air moving
over the lake, a stratocumulus deck at around 4kft has developed
across the area. Clouds are thickest at SAW, where weak radar
returns also indicate a potential for some hit and miss snow showers
this afternoon. Clouds briefly scatter out tonight while winds turn
light, but another system moving out of the Plains will bring
increasing lower to midlevel cloud cover into the early hours of
Sunday. Expect ceilings to fall to around 4-6kft by the end of the
TAF period, while winds shift over to the SE.

&&

.MARINE...
Issued at 339 AM EDT Sat Mar 23 2024

North winds around 20-25 knots are occurring across most of Lake
Superior early this morning as a colder air mass flows across the
lake. Winds diminish to mostly under 15kt on Saturday as high
pressure builds over the lake. A deep low pressure develops over
eastern CO on Sunday and tracks across the western lake on Tuesday.
Ahead of the low pressure, SE to E winds increase to 20-30kt by late
Sunday afternoon, strongest across the western lake. Winds of 20-
30kt are expected across much of Lake Superior Sun night through
Monday night with gale potential increasing to 70-90% by Mon morning
- highest across western Lake Superior. Easterly gales of 35-40kt
are expected for Mon/Mon night, with 40-60% chance for high-end 40-
45kt gales. East winds diminish as the low pressure lifts across
western Lake Superior on Tue, but west winds increase as a much
colder air mass moves across the lake. West winds up to 30 kts are
expected late Tuesday night into Wednesday night as the low pressure
lifts north of the lake.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Storm Watch from Sunday afternoon through Monday
     afternoon for MIZ001>003-009.

Lake Superior...
  Gale Watch from Monday morning through late Monday night for
     LSZ162-243>245-251-263-264-266-267.

Lake Michigan...
None.

&&

$$

UPDATE...
SHORT TERM...LC
LONG TERM...EK
AVIATION...LC
MARINE...EK


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