Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 142005
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
405 PM EDT Thu Mar 14 2024

.KEY MESSAGES...

- Dry weather and above normal temps expected through Friday.
- A strong weekend storm system brings light rain/snow mix and
  blustery conditions Fri night into Saturday.
- Below-normal temperatures, continued blustery conditions into
  early next week and accumulating lake effect snow potential
  Saturday night into Tuesday.
- High-end northerly gales possible over north central and east half
  portions of Lake Superior Sat night into Sunday.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 404 PM EDT Thu Mar 14 2024

Current RAP analysis and GOES WV imagery show a mid level shortwave
over southern WI and an associated sfc low over northern IL which is
lighting up the radar mosaic in IA, southern WI, lower MI, and OH.
While this feature continues eastward along the southern end of the
Great Lakes Basin today into tonight, precip remains south of our
CWA as sfc ridging extending over Upper MI holds steadily overhead.
While high level clouds streaming over the east half of the U.P.
continue eastward with the low pressure system, a batch of low level
clouds that settled south across Lake Superior this morning
continues to cover the Keweenaw and north central. These will linger
into the evening hours supported by upslope flow before scattering
out tonight. Aided by cool northerly flow off Lake Superior, these
clouds will hold temps in the 30s the rest of the day along the
lakeshores. A few spots in the southern half of the U.P. may warm up
to near 50, otherwise where obs are currently at in the mid to upper
40s will be the peak temps for today.

The mid level shortwave/sfc low progress east over the Great Lakes
Basin tonight and a mid level trough begins settling south over Lake
Superior. Some low level clouds may linger early on over the west,
otherwise mostly clear skies return as weak sfc ridging also settles
south across the Upper Great Lakes. With CAA, lows will settle into
the 20s with warmer temps near the lakeshores. That being said, some
interior spots that get good clearing overnight could dip into the
teens. Northerly winds gusting up to 15-20mph early on this evening,
strongest winds over the east half of the U.P., will gradually
diminish tonight; some variable winds over the far west are likely
by late tonight.

Although the mid level shortwave drops south on Friday, the
weakening sfc ridge overhead and dry profile noted in the model
soundings will prevent any precip. That said, cloud cover will
increase from the northwest Friday morning primarily over the west
half of the U.P. Warmer than normal temps are expected with highs
mainly in the 40s with some low 50s possible along the WI/MI state
line. Model soundings indicate mixing up to 3-5kft on Friday,
keeping dew point temps down in the low to mid 20s. This results in
min RHs in the low to mid 30s. Luckily, wind gusts are not expected
to exceed 20 mph until later in the evening when RHs begin to
recover. Thus, elevated wildfire conditions are not forecast at this
time. Will monitor for any changes in potential wildfire risk.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 402 AM EDT Thu Mar 14 2024

A developing rex block building over the West Coast will result in
500mb positive height anomalies in British Columbia approaching 340m
(+3 st devs) this weekend. This blocking ridge forces a deepening
trough downstream across eastern North America Friday night through
Tuesday. This deepening trough provides most of the noteworthy
weather during this forecast period. The most impactful hazards
appear to be gusty west winds Saturday into Sunday followed by a
period of accumulating lake effect snow Saturday night into Monday
night. Meanwhile, behind a cold front moving through on Saturday
daily temperatures will trend blo normal for late weekend into early
next week.

Beginning Friday, a high pressure ridge settles across the area
allowing for light winds. Highs Friday under partly sunny skies will
be mostly in the 40s with perhaps a 50F reading south central.

The primary weather maker approaches the region Friday night. The
event begins with a ~50 kt westerly low level jet resulting in WAA,
isentropic ascent, and perhaps some weak frontogenesis as well.
Operational models have ~9 hour period of deep moisture aloft, but
the antecedent air mass is quite dry so this will likely keep any
mixed pcpn amounts light Fri night into Saturday with northern and
eastern sections of the cwa mostly likely to get precipitation in
the warm sector of this clipper. With evaporative cooling from the
dry low-levels much of the mixed pcpn may end up being mostly in the
form of the snow. Even if it ends up being more snow, amounts will
be light (less than an inch) with minimal impacts. The other thing
to watch for on Saturday is the potential for gusty west to
northwest winds in the wake of the clipper system`s cold front.
Models are advertising fairly deep mixing/destabilization behind the
cold front with fcst soundings indicating a potential for advisory
wind gusts of 45 or higher mixing down to the sfc across a good
portion of the west half of the U.P. with the highest gusts likely
over the Copper Country per EPS mean gust data.

Continued cold air advection increases lake effect snow potential
Saturday night as a secondary shortwave digs into the base of the
trough. This shortwave should enhance any ongoing LES while also
sending a reinforcing cold front that should cool temperatures below
normal for the first time since Feb 29th. With lake average
temperatures around 2-3C, the critical 850 mb temp threshold for
pure lake effect is around -11C. Ensemble means cool 850 mb temps
below that threshold Saturday night and don`t warm temps back above
that threshold until late Tuesday with the coldest 850 mb temps
likely occurring late Sunday night into Monday morning when most
ensemble means have it as cold as -16C. Model soundings advertise
deeper moisture through the DGZ later Sunday into Sunday night which
should help SLRs, but at the same time it also looks like sfc-850 mb
flow is becoming increasingly anticyclonic with time with ridging
upstream of the lake. This may end up drawing drier air in at low-
levels late Sun night into Monday as GFS soundings suggest
which would cut into LES amounts. All told, Grand Ensemble
probabilities suggest 1 to maybe locally 3 inches of LES
accumulation for any 24 hour period Sat night into Monday, so
overall expect sub-advisory amounts. In addition to the LES,
we`re also well into the time of year where cold upper level
troughing can support diurnal snow showers developing due to
daytime heating.

Generally expect N-NW flow LES to taper off quickly from west
to east late Monday into Tuesday as high pressure and associated
subsidence build in from the west and 850 mb temperature
gradually moderate. Broad mid-level ridging and continued
moderating temps will result in a drier and warmer day on
Wednesday with a likely return of above normal temps.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 137 PM EDT Thu Mar 14 2024

A batch of low level clouds has settled south across Lake
Superior this morning and will continue to yield MVFR cigs at
CMX through late this afternoon. Cigs at SAW will start IFR,
eventually lifting to MVFR this evening before scattering out
tonight. However, confidence in the exact timing is low. With
upslope flow off Lake Superior, it may take longer for cigs at
CMX and SAW to improve. IWD will remain in VFR conditions
through most of the TAF period. Northeast winds stay light today
with gusts holding below 20 kts through this evening. A
disturbance Friday morning increases available moisture and
provides forcing for increased cloud cover from the west,
potentially yielding some MVFR cigs during the day at all TAF
sites.

&&

.MARINE...
Issued at 402 AM EDT Thu Mar 14 2024

A weak low pressure system sliding through the Lower Great Lakes and
a high pressure ridge to the north will result in northeast winds 15-
25 kts across the lake today, highest west half. As the high
pressure ridge moves over the lake later tonight into Friday winds
across the lake will drop blo 20 kts. Looking ahead, southwesterly
winds will increase Friday night into Saturday as a low-level jet
moves over the area ahead of an approaching clipper low pressure
system with gusts 25 to 30 likely, highest west and north central.
There is a higher probability (50-80 pct) of gales between Isle
Royale and the Keweenaw late Fri night. As colder and more unstable
conditions move in behind the clipper on Saturday, ensemble
probabilities suggest northerly gales are a good bet (70 to near 100
pct chance) especially for north central and the east half portions
late Sat into Sunday where there is even a 60-90 pct chance of high-
end gales Sat night into Sun morning.

Winds come down quickly blo gales late Sun night into Monday as a
high pressure ridge begins to build in from the west. Unstable
conditions remain into the early part of next week, but winds should
diminish to 20 kts or less for Tuesday and Wednesday as high
pressure and warmer conditions move over the area.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Small Craft Advisory until 6 PM EDT /5 PM CDT/ this evening
     for LSZ240-241.

Lake Michigan...
None.

&&

$$

SHORT TERM...Jablonski
LONG TERM...Voss
AVIATION...Jablonski
MARINE...Voss


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