Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 141122
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
722 AM 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 TONIGHT/...
Issued at 318 AM EDT Thu Mar 14 2024

GOES-16 Night Fog shows a few high clouds among otherwise clear
skies over the UP. North of Lake Superior, a cloud deck with ceiling
heights of 600-1100 ft is proceeding south. Well to the south of the
UP, high clouds with a shortwave and associated surface low are
advancing north through southern Wisconsin. While no deterministic
models show precipitation making it as far north as the UP (most
showing precipitation staying south of Green Bay), a convergence of
high clouds from the south and low clouds from the north should
create mostly cloudy conditions today. Cloud cover blocking
radiational heating in conjunction with continued cold advection
from 850mb will keep highs today mainly in the 40s. This is still 5-
10 degrees above normal for Pi Day, but will be the coolest highs of
the week thus far. RHs will only fall to around 40 for the interior
west today, helping keep fire weather concerns lower than earlier in
the week. Northeasterly winds will gradually back northerly to
northwesterly tonight in response to the low pressure passing
through the southern Great Lakes today.

&&

.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 /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 721 AM EDT Thu Mar 14 2024

VFR conditions are currently being observed at all TAF sites. These
conditions will continue at IWD and CMX, but some low clouds at SAW
may threaten lower flight categories.

Model trends have backed off significantly on the potential for MVFR
ceilings and vis for this morning at SAW but the majority (around
60%) of models show an afternoon to evening period of MVFR
ceilings. There is uncertainty about the ceiling forecast as
there is about a 20 percent chance ceilings could fall to as
low as IFR and about a 20% chance conditions remain VFR through
the day. This TAF will elect to go with high-end MVFR, but the
period from noon to sunset may need to be closely monitored for
changing ceiling conditions at SAW. Ceilings are expected to
scatter out tonight at roughly 2Z.

&&

.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...
None.
Lake Michigan...
None.

&&

$$

SHORT TERM...GS
LONG TERM...Voss
AVIATION...GS
MARINE...Voss


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