Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 201858

Area Forecast Discussion
National Weather Service Marquette MI
258 PM EDT Sat May 20 2017

.SHORT TERM...(Today and tonight)
Issued at 509 AM EDT SAT MAY 20 2017

Latest water vapor imagery shows a developing closed low and well-
defined shortwave over the KS/NE border lifting slowly northward
through the Central Plains. Deepening moisture and lift out ahead of
the closed low/shortwave was supporting showers early this morning
from MO into central IA and southern MN, but very dry low-level air
mass in place was breaking apart the leading edge of showers into
northern IL and southern WI.

Latest regional radar trends and very dry airmass in place across
much of the Upper Midwest and Great Lakes region as depicted by the
00z GRB and APX soundings support 00z models slower progression of
pcpn into Upper Mi today. Thus, only have low chc pops for rain just
reaching into the the Wi border counties by 18z. With increasing
upper diffluence ahead of shortwave and increasing 295-300k
isentropic ascent ahead of occluded front, especially from 21-03z,
expect very dry low-levels to finally moisten and allow rain to
spread northeastward across the rest of west and central Upper Mi.
Despite increasing q-vector convergence and upper diffluence ahead
of the approaching shortwave trough late evening into the overnight,
mid-level dry slotting and a transition to isentropic descent as
depicted by models will cause a general diminishing trend to showers
from late evening into the overnight hours.

With more sunshine expected in the morning hours, bumped up high
temps today into the mid to upper 50s across much of the cwa, except
around 50f over the Keweenaw in strengthening onshore easterly flow.
Followed CONSAll guidance tonight under expected clouds and steady
ese winds with min temps in the lower to mid 40s.

.LONG TERM...(Sunday night through Saturday)
Issued at 258 PM EDT SAT MAY 20 2017

Overall forecast highlights include a cooler start to the week with
periodic chances for rain showers as cut off energy lingers across
the Upper Great Lakes region. Towards the end of the work week
temperatures will begin to warm back up to near normal for this time
of year with minimal chances for precipitation. We could see a few
nights early in the week where overnight lows drop low enough to
possibly warrant frost headlines.

Expect rain showers to linger across the area Sunday night and
through the day on Monday as the surface low lifts northeast across
the area and the main upper-level low remains becomes anchored
across the Upper Great Lakes. If the pressure gradient can maintain
some of its strength across Upper Michigan, Monday could also be a
breezy day. Given the cool and cloudy conditions expected, did bump
afternoon high temperatures for Monday down a bit. This cool and
cloudy weather will continue through Tuesday as a shortwave digs
south across the Upper Mississippi River Valley and brings a
reinforcing shot of cooler Canadian air. Given the lingering cloud
cover and enhanced lift as vorticity maxes dig south across the
area, we could see scattered rain showers linger through the day on
Tuesday. No concerns for thunder through this time period as mid-
level lapse rates only approaching 6.0-6.5C/km at best and the
atmosphere remains stable.

Through the day on Wednesday, skies are expected to finally clear
from west to east, and precipitation chances will come to an end.
The best chance for any additional precipitation during the day on
Wednesday will be across south central and eastern portions of the
area. As the main 850mb low slowly rotates about the Ohio River
Valley, even though we will still be under a modified cooler
airmass, the increasing insolation should allow temperatures to warm
up into the mid/upper 50s across much of Upper Michigan. Thursday
through Friday, as moist and warmer 850mb air pivot back northeast
into the Upper Great Lakes, temperatures will warm back up to near
normal for this time of year. Not expecting any precipitation as
subsidence should be dominant with upper-level heights building
across the region, allowing a narrow area of surface high pressure
to impact Upper Michigan.

Friday night through Saturday, as troughing continues to traverses
and begins to eject out across the west, surface ridging will shift
east of the region and a lee cyclone is progged to develop across
the High Plains. As a result, low-level moisture will try to make a
return to the Upper Great Lakes. There is some uncertainty among the
medium range models in how regards to how quickly this moisture
return will occur, with the GFS being the most robust this far
north. Depending on how much moisture can get this far north, we
could see the return of some thunderstorm activity to the region for

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 139 PM EDT SAT MAY 20 2017

VFR conditions will prevail through this afternoon. Rain showers
will begin to lift north across the area as low pressure lifts north
towards the area. Conditions will fall to MVFR at all sites this
evening as the rain becomes more widespread, and as rain begins to
taper off overnight tonight conditions will lower to IFR. There may
even be a period of LIFR conditions at KSAW late tonight in a moist
upslope ese flow. A period of tsra may also be possible btwn 09z-
15z, as a disturbance lifts through the area. However, confidence
was not high enough to include mention in the TAF at this time.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 320 AM EDT SAT MAY 20 2017

Ene winds 10 to 20 kts this morning will increase up to 25 to 30 kts
over the w half of Lake Superior this afternoon as the pres gradient
ahead of lo pres approaching from the sw tightens sharply over that
area and where terrain influences will accentuate the ne flow. The
sharper pres gradient and strong winds up to 30 kts will overspread
the rest of the lake tonight. Not out of the question there could be
some gales over the far w where the funneling of the ene flow will
continue. As the lo pres passes into Ontario on Sun and drags a
trough across Lake Superior, expect the winds to diminish and shift
to the w-sw by Sun night. Winds under 20 kts should then be the rule
on Mon into Wed as a relatively flat pres gradient dominates the
Upper Lakes.

Upper Michigan...
Lake Superior...
Lake Michigan...


LONG TERM...Ritzman
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