Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 251843

Area Forecast Discussion
National Weather Service Marquette MI
243 PM EDT Mon Sep 25 2017

.SHORT TERM...(Today and tonight)
Issued at 506 AM EDT MON SEP 25 2017

WV imagery and RAP analysis indicated a mid/upper level over Wyoming
embedded in a trough over the wrn CONUS and a ridge over the ne
CONUS resulting sw flow from the cntrl plains to the upper MS Valley
and wrn Lake Superior. At the surface, a cold front extended through
wrn Lake Superior through nw WI into se MN from low pressure over
nrn Ontario. Radars indicated an area of showers and a few tsra from
nw WI through e cntrl MN into nw IA supported by 850-600 mb fgen
behind the front.

Today and tonight, short range higher res models suggest that the
pcpn will remain mainly over wrn Lake Superior and far wrn Upper
Michigan this morning. However, from late this afternoon into this
evening expect the pcpn coverage to increase as a shortwave
trough lifts toward the area from the plains. With PWAT values to
around 1.5 inch, and the possibility for convection lifting
northeast along with an area of fgen behind the front, some
locally heavy rain may be possible over the west half of Upper
Michigan. However, confidence in the position of any heavier rain
band is still low. MUCAPE values mainly aob 1k J/Kg along with
modest shear values may support some small hail with any stronger
storms. By later tonight, the focus for the heavier pcpn is
expected to shift again to the nw of the cwa with the strongest
qvector conv and upper level div ahead of the shrtwv lifting out
of the nrn plains.

Temperatures will climb again to around 80 or the lower 80s cntrl
and east before falling off this afternoon with the front moving in.

.LONG TERM...(Tuesday night through Monday)
Issued at 242 PM EDT MON SEP 25 2017

Nam shows a shortwave over the upper Great Lakes 00z Wed and the
area remains in upper level troughing through 00z Fri. Nam shows
some 850-500 mb q-vector convergence and some moisture moving
through the area on Thu. Will keep some pops in for Tue night
through Wed morning and again for Thu afternoon.

In the extended, GFS and ECMWF show a 500 mb trough over the ern
U.S. with a ridge over the plains and a trough off the west coast
12z Fri. Ridging moves into the upper Great Lakes 12z Sat with
troughing in the western U.S. 12z Sat. Troughing moves into the
Rockies and northern plains 12z Sun and into the upper Great Lakes
12z Mon. Looks dry for most of the extended period with temperatures
starting to below normal and warming to above normal. Chances for
pcpn look to be Fri morning and again on Mon.

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 141 PM EDT MON SEP 25 2017

A cold front slowly moving across Upper MI combined with a wave of
low pres moving nne along the front will bring lowering cigs. with
front already passed KIWD/KCMX, lower cigs have already developed.
At KIWD, expect low MVFR cigs to fall to IFR later this aftn, then
to LIFR tonight as -shra coverage increases. At KCMX, MVFR cigs
should prevail into the evening before falling to IFR late tonight
as -shra coverage increases in nw Upper MI as well. At KSAW, VFR
conditions initially will likely fall to low MVFR or IFR this
evening under upslope nne winds. Further reduction to LIFR will
occur overnight thru mid morning. There could be some -shra around
KSAW beginning late this aftn. Not out of the question that there
could be a tsra at any of the terminals, though KSAW is more favored
due to build up of instability this aftn. As a result, mention of
thunder was only included at KSAW for the late aftn/early evening.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 506 AM EDT MON SEP 25 2017

A developing low pressure behind a cold front will bring increasing
ne winds to 25 knots over wrn Lake Superior tonight.
As the cold front moves across Lake Superior Tue night into Wed with
colder air moving in, wind gusts will increase to 20 to 30 knots.
Winds should also increase to 30 knots by Friday with some gales
possible over the east as another disturbance moves through the area
with additional cold air.

Low to mid 60s dewpoints sliding across Lake Superior are expected
to linger into Tue bringing patchy to areas of fog across the lake.
Some of the fog could be locally dense at times.

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


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