Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 210818
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
418 AM EDT Mon Oct 21 2019

.SHORT TERM...(Today and tonight)
Issued at 307 AM EDT MON OCT 21 2019

Busy forecast is beginning as the calm before the storm occurs.
Upper air pattern consists of a deep 500 mb trough in the central
U.S. with a closed low over the central plains. This closed low will
head slowly northeast into the western U.P. by 12z Tue. Nam brings
in some deeper moisture and 850-500 mb q-vector convergence this
morning with a dry slot moving in tonight. ECMWF and GFS show about
the same thing. Looks like rain will spread into the area during the
morning with a period of rain in the afternoon before the dry slot
moves in by evening and the wraparound part of the storm comes in
late tonight. Kept some thunder in this evening across the far
southern cwa in the dry slot...otherwise did not make too many
changes to the going forecast except continued the trend of delaying
the pops moving in for this morning. Everything still looks on track
for lakeshore flood advisory and will be updating the statements for
that.

.LONG TERM...(Tuesday through Sunday)
Issued at 417 AM EDT MON OCT 21 2019

The weather in the medium range continues to be focused on the
strong fall low pressure system causing wind and water issues.
Models are in good agreement in depicting a slowly filling ~986-990
mb low over far northern Wisconsin by Tuesday morning, with the
strong surface pressure gradient/40+ kt LLJ oriented more or less S
to N over Lake Michigan, the eastern U.P., and far eastern Lake
Superior. Despite this being southerly flow, the system will be
wrapped up enough by this point that colder air will be advecting in
aloft, steepening lapse rates and aiding in the mixing of higher
gusts down to the surface. Going off model progs of pressure falls
and the implied isallobaric response, the strongest winds would be
Tuesday morning, about 12z-15z. Think 40-45 kt gusts on Lake
Michigan and the Bay of Green Bay are likely during this period,
with 30-40 mph gusts make it into Escanaba, Manistique, and
surrounding areas as well. This long southerly fetch also means
lakeshore flood concerns continue. With the wind and wave direction
now from the SW, this not as much of a concern for the M-35
shoreline south of ESC, but it is a concern for ISQ. Current wave
forecasts exceed warning criteria for lakeshore flood (12 feet) so
the potential for lakeshore flooding in ISQ on Tuesday is something
that needs to be watched closely.

Gusty winds continue on land as
well, especially Tuesday afternoon as the low pulls away to the
north, though 25-30 mph should be about as high as they get away
from the immediate shorelines. There will also be numerous wrap-
around showers around on Tuesday, with perhaps some lake enhancement
over the east (using a lake surface temp of 50 F, we`d have about a
9 C sfc-850 mb delta T) as well as upslope/lake-enhancement over the
west and Keweenaw. Precip amounts through Wednesday morning
generally total 0.1-0.25", except 0.25-0.5" in those aforementioned
areas.

The low continues to slowly drift northward away from us on
Wednesday, but leave behind plenty of wrap-around moisture for
clouds and scattered showers. With flow out of the west, Wednesday
looks like an all-day supermarket drizzle for the higher terrain
from MQT on west where upslope flow will be lake-enhanced under 850
mb temps falling to about -5 C by late afternoon. Temps aloft drop
even more Wed night into Thursday morning, so this becomes the
window for some bona fide lake-effect rain/snow. With lows right
around freezing over the Keweenaw, and in the upper 20s to around 30
over the interior west, this would probably be some light
accumulating snow. Right now amounts look like less than an inch,
but as we get closer we`ll see if any of the hi-res guidance picks
up on any areas of more enhanced QPF. The deeper moisture is progged
to exit by about 15z-18z Thursday, bringing an end to lake-effect
precip except over far eastern Lake Superior.

Surface high pressure then builds in to the Upper Mississippi Valley
late Thursday, passing by to our south through Wisconsin on Friday.
With 850 mb temps at their coldest in the long-term, around -8 C,
and light winds and clearing skies away from Lake Superior, Friday
moring looks quite chilly. Dropped MinT`s several degrees below NBM
guidance, relying on MOS and the bias-corrected CMC which usually
handles chilly morning lows well. This gives some low 20s in the
notoriously cold spots, and as we get closer, would not be surprised
to end up seeing teens in a few spots. Ditto for Saturday morning.
The trade-off is that, as of right now, the weekend looks mostly dry.
&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 103 AM EDT MON OCT 21 2019

With easterly winds, fog/stratus on Lake Superior will continue to
upslope across the Keweenaw, impacting KCMX. Expect LIFR conditions
at that terminal thru the night with conditions blo airfield landing
mins at times. The fog/stratus should clear out by mid morning. At
KIWD/KSAW, VFR conditions will prevail overnight. However, given an
upslope ese wind developing at KSAW, not out of the question that a
low stratus deck (LIFR or IFR) could develop for a few hrs before
sunrise. Attention today turns to a deepening low pres system moving
toward the Upper Great Lakes. Expect shra to spread nne across the
area, impacting all terminals. IFR to LIFR conditions will accompany
the showers. In addition, winds will strengthen, gusting to 25-35kt
in the aftn, strongest at KCMX. LLWS is also expected as strong low-
level jet translates over the area. Conditions will begin to improve
this evening.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 307 AM EDT MON OCT 21 2019

The 00z model runs came in with stronger winds than previous
forecast, but still looks like a strong gale event out of this
incoming deepening low pressure system. There will be two strong
wind events with this low pressure system. The wind will increase
quickly late this morning and go to a strong gale this afternoon and
evening on Lake Superior. Could be a few storm force wind gusts in
the western part of Lake Superior with the funneling taking place in
a northeast wind regime. As the low approaches, the strongest winds
move out overnight tonight. The winds then get up close to gale
force on Tue into Wed as the low moves away and this would be the
second strong wind event for this forecast period. Hard to say right
now if gale force winds will be met with this second event as the
low pressure system is weakening in the Tue to Wed time frame and is
moving away from the area. Will keep the gale warnings going.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Lakeshore Flood Warning from 5 PM this afternoon to midnight EDT
     tonight for MIZ001-003.

  Lakeshore Flood Advisory from 4 PM this afternoon to 10 PM EDT
     this evening for MIZ013-014.

Lake Superior...
  Gale Warning from 2 PM this afternoon to 1 AM EDT Tuesday for
     LSZ263-264-266-267.

  Gale Warning from 2 PM this afternoon to midnight EDT tonight
     for LSZ265.

  Gale Warning from 3 PM this afternoon to midnight EDT tonight
     for LSZ243>245-249>251.

  Gale Warning from 3 PM this afternoon to 11 PM EDT this evening
     for LSZ246>248.

  Gale Warning from 10 AM EDT /9 AM CDT/ this morning to 10 PM EDT
     /9 PM CDT/ this evening for LSZ162.

Lake Michigan...
  Gale Warning from noon today to 11 PM EDT this evening for
     LMZ221-248-250.

&&

$$

SHORT TERM...07
LONG TERM...RJC
AVIATION...Rolfson
MARINE...07


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