Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 251745

Area Forecast Discussion
National Weather Service Marquette MI
145 PM EDT SUN SEP 25 2016

.SHORT TERM...(Today and tonight)
Issued at 434 AM EDT SUN SEP 25 2016

Upper air pattern consists of a closed 500 mb low over ND embedded
in a longwave trough over the northern plains with a shortwave ridge
over the upper Great Lakes this morning. The trough and closed low
move east and affect the upper Great Lakes this afternoon and
tonight. Nam brings in some 850-500 mb q-vector convergence along
with deeper moisture today into tonight with a dry slot moving
through tonight across the western half of the cwa.

Overall, did not make too many changes to the going forecast for
temperatures. As for weather, slowed the progression of pops across
the cwa a bit today and delayed pcpn in the east a couple hours due
to drier air remaining over that area the longest for this morning.
Did go categorical pops in a narrow band that moves across the area
this afternoon and tonight and could see 0.50 to 1 inch of rain as
this band moves through.

.LONG TERM...(Monday through Saturday)
Issued at 400 AM EDT SUN SEP 25 2016

Main story in the long term is deepening low pressure system that
affects the Upper Great Lakes early this week as upper trough
deepens/closes off over Great Lakes and northern Ontario.

Strong and gusty winds should will occur at times though differences
in forecasted winds aloft keep confidence on widespread high impact
wind event on the lower side attm. Tightest pressure gradient and
925mb winds 35-40 kts would favor the Lk Superior shoreline of
western Upper Michigan and over all of the Keweenaw Peninsula for
west to northwest wind gusts up to 45 mph mid morning Mon into Mon
evening. Could also see similar wind gusts along Lk Superior from
Big Bay to Munising and Grand Marais Mon night, but model trends are
not as clear as they are over western cwa. Winds will remain gusty
into Tue over most cwa, but especially along Lk Superior. Waves will
be high on Lk Superior as well leading to high swim risk and the
potential for some beach erosion. Both of these items will be
mentioned in HWO. May not end up needing a Beach Hazard Statement
though as expected temps in the 50s and inclement weather with
frequent showers and blustery winds should keep most people away
from the beaches.

Due to the deepening upper level trough across the Great Lakes and
sufficient deep moisture/cyclonic low-level flow, cool air advection
with h85 temps down to 1-4c should result in plenty of showers due
to the system and/or lake enhancement with terrain upslope lifting
occuring as well. Likely pops or greater will start up on Mon morning
as wraparound moisture in the cyclonic low-level flow moves in and
the higher pops will last all the way through Tue afternoon. Only
scntrl cwa will escape the frequent showery weather, though should
see pops increase there as well on Tue helped along by daytime heating
and with upper low center settling closer by across east half Upper
Michigan to Georgian Bay. Through the period the lowest h85 temps are
over western Lk Superior and western Upper Michigan. This area is
also where sharpest cyclonic flow is too. The low-level convergence
along with sfc-h85 delta t/s nearing 13c signals potential for at
least moderate rainfall for western cwa, again helped along by
additional upslope lift.

With upper low in the vicinity and SI/s falling to around 0c, did
include slight mention of thunder Mon into Tue with the stronger
dynamics around.

Upper low and sfc low drift toward lower Great Lakes on Wed. North
winds will be weakening over Upper Michigan but the flow off Lk
Superior with daytime heating and some lingering low-level moisture
could help develop some light showers/sprinkles out of a cu/sc deck.
High pressure then builds in late this week into next weekend. Expect
dry weather with a gradual warming trend. Nighttime temps once the
high centers overhead late this week could drop into the upper 30s to
low 40s. Interesting side note that so far at NWS Marquette office
this month we have not recorded a temp blo 41 degrees. Last time this
site saw a reading in the 30s was back on July 16th (of course), when
we saw a low that morning of 39 degrees.

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 145 PM EDT SUN SEP 25 2016

Gusty sse winds wl advect a good deal of mstr into Upr MI ahead of
an aprchg cold fnt. The combination of this llvl mstr and showers wl
result in period of MVFR/hi end IFR conditions at the TAF sites. The
arrival of some drying following the cold fropa with a wshft to the
wsw wl then bring at least a brief improvement to VFR w-e this evng
into the overngt before more llvl mstr arrives and causes cigs to
drop into the MVFR category, earliest at IWD/CMX. Winds shifting to
the w wl become gusty over the wrn TAF sites on Mon mrng, especially
at the more exposed CMX location.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 434 AM EDT SUN SEP 25 2016

Tightening pressure gradient will happen across the area as high
pressure moves toward Quebec and New England and a low pressure
system lifts across Manitoba to northern Ontario. Southeast winds
may gust as high as 30 kts Sun into Sun evening over north central
and eastern sections of Lk Superior and will go with a gale warning
across the far eastern lake for gales to 35 knots tonight. The low
will move east of the region Mon into Tue and a cold front will
cross Lake Superior. With 850 Temperatures falling to 2 C and tight
pressure gradient on back side of surface low dropping southward
over the eastern lake...expect northwesterly gales to around 40
knots on Monday and Monday evening and a gale watch was issued for
this. Northwest winds to 30 kts continue on Tue then winds diminish
to 20 kts or less by Wed through Thu as high pressure crosses the
Great Lakes.

Upper Michigan...
Lake Superior...
  Gale Warning from 8 PM this evening to 4 AM EDT Monday for

  Gale Watch from Monday afternoon through late Monday night for

  Gale Watch from Monday morning through late Monday night for

Lake Michigan...


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