Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 150524
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
124 AM EDT Fri Mar 15 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 Monday night.
- 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 NIGHT THROUGH THURSDAY/...
Issued at 420 PM 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 that 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.

The primary weather maker approaches the region Friday night. The
event begins with a 55-60 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
rain/snow mix amounts light Fri night into Saturday. Northern and
eastern portions of the area are most likely to get precipitation in
the warm sector of this clipper, but precip amounts appear light
with minimal impacts expected. 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. The grand ensemble mean cools 850mb
temps below that threshold Saturday night and doesn`t warm temps
back above that threshold until sometime on Tuesday with the coldest
850 mb temps likely occurring late Sunday night into Monday morning
when most ensemble means have temps as cold as -16C. Model soundings
advertise synoptic moisture up to 15-25 kft with the convective
boundary layer extending to around 5 kft and cooling into the DGZ
later Sunday into Sunday night which should boost SLRs closer to
20:1. However, sfc-850 mb flow is becoming increasingly anticyclonic
with time as upstream ridging approaches the lake with an increasing
inverted-v signal Sunday night into Monday. All told, Grand Ensemble
means indicates 2 to 3 with locally 4 inches of 10:1 snowfall for
the 36 hour period between 8 PM Sat night and 8 AM Monday. If SLRs
end up closer to 20:1 then snowfall amounts may locally approach
advisory criteria when combined with the blustery NW to N winds and
some blowing snow potential. However, the current lack of snow cover
should limit blowing snow impacts.

Overall, expect N-NW flow LES to taper off quickly from west to east
late on Monday as the surface ridge axis and associated subsidence
build in from the west and 850 mb temperatures moderate. Forecaster
confidence diminishes by Tuesday when another clipper may track into
the area, but considerable differences exist between models.
Ensemble means are in good agreement with temperatures warming above
normal ahead of the clipper disturbance, but cooler conditions may
return by mid to late next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 123 AM EDT Fri Mar 15 2024

With satellite imagery showing unexpected low clouds developing over
portions of western Upper MI recently, fcst will reflect ocnl bkn
IFR cigs at IWD and bkn LIFR cigs at CMX for the next couple of hrs.
Meanwhile, at SAW, low MVFR cigs have developed as a stream of low-
level moisture from ne of the lake has spread into n central Upper
MI. These lower clouds should linger for the next several hrs with
VFR thereafter. VFR will then prevail at all terminals today into
this evening. On the backside of a passing sfc high pres ridge
overnight and this morning, guidance does suggest that an area of
stratocu in the 3500-5000ft range will spread across w and central
Upper MI this morning into aftn. Winds at IWD/CMX will become gusty
to around 20-25kt this aftn as pres gradient tightens btwn the
departing ridge and low pres dropping se toward northern Ontario. As
near sfc layer then stabilizes somewhat this evening, LLWS should
develop at IWD this evening. LLWS will be possible at CMX/SAW near
the end or just beyond this fcst period. As aforementioned low pres
system moves across northern Ontario tonight, brief shra will be
possible across western Upper MI late this evening, but potential is
too low to include mention at IWD/CMX attm.

&&

.MARINE...
Issued at 420 PM EDT Thu Mar 14 2024

A weak low pressure system tracks east across the Lower Great Lakes
tonight as a high pressure ridge settles across Lake Superior with
light north winds below 20 kts. Looking ahead, southwesterly winds
increase to gales up to 40 kts across western and north-central
portions of the lake Friday night as a low-level jet moves over the
area. There is a high probability (50-80 pct) of gales between Isle
Royale and the Keweenaw late Fri night, justifying issuance of a
gale watch. As colder and more unstable conditions move in behind
the clippers on Saturday, winds veer from SWerly to NWerly. Ensemble
probabilities indicate northwesterly gales are nearly certain (70 to
near 100 pct chance) across north central and the east half portions
late Sat through Sunday where a gale watch was also issued.

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...
  Gale Watch from this evening through late Saturday night for
     LSZ162-240>244-263-264.

  Gale Watch from Saturday morning through Sunday evening for
     LSZ245>251-265>267.

Lake Michigan...
None.

&&

$$

SHORT TERM...Jablonski
LONG TERM...EK
AVIATION...Rolfson
MARINE...EK


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