Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 240829
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
429 AM EDT Sun Mar 24 2024

.KEY MESSAGES...

- Late season winter storm lifting northeast from Colorado
  brings accumulating snow and hazardous travel late Sunday
  into Monday.
- Westerly lake effect snow develops early Wednesday morning and
  continues through Thursday, mainly across the Copper Country.

&&

.SHORT TERM /THROUGH TODAY/...
Issued at 309 AM EDT Sun Mar 24 2024

Water vapor imagery and RAP analysis show mid-level troffing over s
central Canada into se Canada, anchored by a deep mid-level low
centered over southern Hudson Bay. To the w, a deep trof is over the
western U.S. In response to this trof, a strengthening
waa/isentropic ascent regime is spreading across the Plains, leading
to radar returns from ND across MN into WI. Northern and eastern
portions of the radar returns are not translating to -sn reaching
the sfc due to dry low-levels that need to be overcome. Closer to
home, it`s been a quiet night with sfc high pres drifting across the
area. Where high clouds have remained thin, temps have dropped well
down in the single digits above zero F across the interior n central
and e. A few of the traditional cold spots are nearing 0F e.

With sfc high pres exiting to the e, se to s winds will be
developing thru the early morning hrs. With 850mb temps across
northern Lake MI around -12C, flurries or -shsn may develop off of
the lake into portions of central Upper MI. Fcst will reflect a schc
mention, 15-20pct, during the morning hrs after 12z downwind of the
lake. Otherwise, attention turns to the strengthening waa/isentropic
ascent spreading ne into Upper MI today. It seems likely that the
weaker leading edge of the ascent will not be able to overcome the
dry low-levels this morning. Opted to hold off on any -sn mention
for the morning hrs. Even if some snow does ends up occurring, it
will be very light. Further strengthening of ascent this aftn will
lead to -sn developing from sw to ne, likely not reaching Luce
County until toward evening. Consensus of model guidance is for qpf
of about a tenth of an inch near the MI/WI stateline and tailing off
from there to the n and e. With SLRs ~14 to 1, snow accumulations by
00z will be 1 to 1.5 inches w to s central, and less to the n and e.
Expect high temps today of 30-35F.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 429 AM EDT Sun Mar 24 2024

The primary forecast challenge continues to be snowfall amounts with
the large winter storm lifting northeast across the region through
Tuesday. Snow will be ongoing at 00z this evening and continues into
Monday morning before transitioning to rain from south-to-north
during the day. Rain continues Monday night and much of Tuesday
before transitioning back to snow late Tuesday (west) or Tuesday
night (east) behind the cold front. Most of Upper Michigan begins
drying out behind Tuesday night`s cold front as below-normal
temperatures spill across the area. The exception to this will be
lake effect snow development for the west wind snow belts (mainly
Copper Country) late Tuesday night that continues through Thursday.
Non-lake effect areas stay dry from Tuesday night through at least
Friday night when light precipitation chances return to the area.

Starting at 00z this evening, light to moderate snow rates of 0.25
to 0.5 in/hr will be ongoing across most of central and western
Upper Michigan. HREF guidance highlights an embedded band of heavy
snowfall rates (1.0 to 1.5 in/hr) at the southern edge of the precip
shield where frontogenesis is maximized. However, this band appears
to weaken as it lifts north across the U.P. tonight but a burst of
heavier snowfall rates still appears likely before tapering off
Monday morning. By 12z Monday morning, HREF means advertise 0.50 to
0.75 inches of QPF at higher elevation western UP locations with
localized totals >0.75 inches on the Keweenaw where some lake
enhancement appears likely early on. A moisture laden late March
system should have SLRs below climatology (13:1) and this is
supported by environmental analysis. Thus, a general 4-8 inches with
localized amounts up to 10 inches seems most likely for higher
elevations of Marquette/Dickinson Counties and points westward.
Amounts decrease farther east with 2 inches or less for Luce County.

The warm front reaches the Keweenaw last indicating potential for a
few additional inches of snow Monday morning. Elsewhere, there
should be a lull in precip Monday morning as a dry slot moves
overhead south of the elevated warm front but another wave of precip
moves in during the afternoon and evening. The surface warm front is
harder to identify since easterly flow advects a dry air mass with
plenty of evaporative cooling potential. This raises concerns about
freezing rain potential at higher elevations, but the warm nose
aloft is much larger than the boundary layer inversion. Rain drops
will therefore be well above-freezing before falling into a
marginally cold surface layer which limits icing potential.
Additional factors limiting potential freezing rain impacts are the
diurnal timing, the inevitability that warm air advection will
eventually change precip to regular rain, and any ice falling on
fresh snow. This hazard should also be spatially limited to high
elevation locations that will be slowest to warm above freezing.

By 00z Tuesday, rain should be the only p-type and continues to be
the prevailing p-type until the cold front passage. Details of this
frontal passage are complicated by a pair of negatively tilted
shortwaves acting on the frontal surface Tuesday into Tuesday night.
The first shortwave brings widespread rain chances Monday night into
Tuesday and the second brings a chance for a secondary (and much
weaker) deformation zone to bring a burst of wet snow across the
west. Even if the secondary deformation zone doesn`t materialize,
wrap-around moisture combined with rapidly cooling 850 mb temps may
set the stage for a brief period of lake-enhanced snow. As deeper
moisture departs, strong cold air advection shifts attention to lake
effect potential for Tuesday night through Thursday as lake-850 mb
delta-T values increase into the upper teens. BUFKIT analysis of the
00z GFS shows a 12-18 hour period of deeper moisture Wednesday night
into Thursday that coincides with the lake inversion extending
through the DGZ. The prevailing wind direction varies from WSW to
WNW among model guidance, which has important implications for LES
coverage. Strong west winds gusting to at least 30-35 mph also
appear likely on the Keweenaw for Tuesday night into Wednesday. LES
gradually diminishes on Thursday as a warmer and drier air mass
moves over the lake. Much drier weather weather closes out the week
with near to slightly below normal temperatures and mostly dry
weather.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 117 AM EDT Sun Mar 24 2024

VFR conditions to prevail until early this afternoon. However, they
will quickly deteriorate to MVFR at that point when the next Plains
system moves closer to the Upper Peninsula.  Widespread MVFR
conditions will become predominant at all TAF sites with
visibilities dipping into the IFR range at times through Mon 05Z.
IFR will then become the prevailing flight category through the end
of the TAF period until the system weakens.  Meanwhile,
southeasterly winds will become strong at CMX this evening/tonight
with sustained speeds in the 12 to 15 kt range, gusting to 22 kts.

&&

.MARINE...
Issued at 357 PM EDT Sat Mar 23 2024

Light winds of 20 knots or less continue this afternoon into Sunday
morning before an approaching low pressure system progressively
increases winds from the east and southeast Sunday afternoon into
Monday; gales of 35 to 45 knots look to occur along the
International Border and over the western U.P. Monday into Monday
evening, with the highest winds being seen over the far western lake
near Minnesota. As the warm front of the low begins moving over the
lake Sunday night through Monday, we could see mixing decrease over
the lake and end the gales. However, if the warm air advection is
weak enough near the surface, we could see gales continue into
Tuesday, with the highest gales being seen near Whitefish Point.
Once the cold front moves through Tuesday night and Wednesday, we
could see westerly gales return across Lake Superior along and
behind it.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Storm Warning from 5 PM this afternoon to 2 PM EDT
     Monday for MIZ001-003.

  Winter Weather Advisory from 5 PM EDT /4 PM CDT/ this
     afternoon to 2 PM EDT /1 PM CDT/ Monday for MIZ002-004-
     005-009>012-084.

  Winter Weather Advisory from 5 PM this afternoon to 5 AM EDT
     Monday for MIZ006-013-014-085.

Lake Superior...
  Gale Warning from 8 AM EDT /7 AM CDT/ Monday to 8 AM EDT /7 AM
     CDT/ Tuesday for LSZ162-263.

  Small Craft Advisory from 8 AM EDT /7 AM CDT/ Monday to 6 AM
     EDT /5 AM CDT/ Tuesday for LSZ240-241.

  Small Craft Advisory from 8 AM to 8 PM EDT Monday for LSZ242.

  Small Craft Advisory from 2 AM to 11 AM EDT Monday for LSZ243.

  Gale Warning from 11 AM Monday to 2 AM EDT Tuesday for LSZ243-
     244-264.

  Small Craft Advisory from 8 PM this evening to 11 AM EDT
     Monday for LSZ244-245.

  Small Craft Advisory from 5 PM this afternoon to 6 AM EDT
     Tuesday for LSZ246>248.

  Small Craft Advisory from 5 AM to 2 PM EDT Monday for LSZ249-
     250.

  Small Craft Advisory from 8 PM this evening to 5 AM EDT
     Tuesday for LSZ251.

  Gale Watch from late Monday night through Tuesday afternoon
     for LSZ251-266-267.

Lake Michigan...
  Small Craft Advisory from 8 PM this evening to 5 PM EDT Monday
     for LMZ221-248-250.

&&

$$

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


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