Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 202014

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

.SHORT TERM...(This evening through Sunday)
Issued at 413 PM EDT SAT MAY 20 2017

WV imagery and RAP analysis indicated a mid/upper level trough
through the plains with a well-defined shortwave over ern Nebraska.
At the surface, low pressure was located over wrn IA with a warm
front through cntrl IL. 300k-305k(800-650mb) isentropic lift ahead
of the shrtwv and low supported a large area of rain from srn MN
through cntrl WI that was lifting slowly northward. Very dry low
level air ahead of the rain area has delayed the progress of the
pcpn into Upper Michigan.

Tonight into Sunday, expect the pcpn to gradually spread through
Upper Michigan btwn 21z-00z with the main area lifting north of the
area after 03z. As aggressive mid level dry slotting moves in
overnight, the rain should diminish to drizzle as lower level 285k-
295k (900-800mb) isentropic continues. As the shortwave approaches
Upper Michigan btwn 09z-15z with stronger qvector conv and steeper
mid level lapse rates, expect another period of showers with some
isold tsra possible. The pcpn should then diminish during the later
morning into the afternoon with even a few peeks of sun possible as
drier air movesino from the west. However, some additional wrap-
around shra may move into the west late. Temps will recover into the
mid and upper 50s .

.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 PM Lake Superior forecast issuance)
Issued at 413 PM EDT SAT MAY 20 2017

An increasing pres gradient ahead of low pressure lifting toward
Lake Superior will result in strong winds up to 30 kts and a few
gale force gusts to 35 knots. As the low 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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