Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 201806

Area Forecast Discussion
National Weather Service Marquette MI
206 PM EDT WED JUL 20 2016

.SHORT TERM...(Today and tonight)
Issued at 435 AM EDT WED JUL 20 2016

The upper ridge and convectively induced shortwave moving along the
northern edge of the ridge continue to thwart the forecast process.
Ended up knocking POPs down significantly for today as the shortwave
previously anticipated to be moving out of MN completely dissipated.
Models now have some isolated convection this afternoon/early
evening firing mainly over western Upper Michigan as residual
shortwave energy passes. Models suggest SBCAPE of 2000-3000 J/kg and
effective shear around 30 KTS, so any storms that do develop could
quickly become strong to possibly severe. Partly cloudy skies are
expected, mainly from thin, high clouds leftover from upstream
convective. 850mb temps will increase to 21C west, 19C east, by this
evening, and that warm airmass will allow for temps to climb up to
90F over portions of the west half. Over the east half, south winds
will keep areas downwind of Lake Michigan cooler but mainly still in
the 80s.

Lots of uncertainty tonight as models suggest a couple shortwaves
could move through. The first shortwave looks to provide better
chances for scattered convection, but the second could produce
widespread convection that may be strong to severe, but that would
mainly occur during the first part of the long term forecast (see
long term for more details). Lots of issues to be resolved for the
forecast for tonight, but those will probably not be easily
determined until around 6 hours out due to shortwave energy.

.LONG TERM...(Thursday through Tuesday)
Issued at 352 AM EDT WED JUL 20 2016

Nam shows a 500 mb ridge across the central U.S. with a trough on
both coasts and the upper Great Lakes in the ring of fire with the
westerlies just to the north of the area. Any little shortwave that
tops the ridge could kick off some convection and this will be hard
to forecast and time these for this forecast period. For this
reason, confidence is low with this forecast for Thu. Forecast
hinges on MCS development tonight and how much clouds and
instability occur for Thu along with heating. Will go middle of the
road for now and go chance pops. Do not want to go with likely pops
for Thu at this point. WIll go with less convection right now which
will lead to more heating and ended up raising temperatures in a few
places. Heat indices get up close to 100 in a few spots and will
highlight this in the hwo product. The slight risk for Thu for our
area also seems warranted with large hail and damaging winds being
the main threat. Cold front moves through on Thu night and then
dries out Thu night into Fri and continued dry for Fri into Fri
night. Did not make too many other adjustments to the forecast for
temperatures beyond Thu.

In the extended, GFS and ECMWF show a broad 500 mb ridge over the
southern U.S. 12z Sat with a broad trough in the pacific nw and
northern Rockies. The shortwave in the northern Rockies heads east
into the upper Great Lakes and brings a cold front through the area
12z Sun with some cooler temperatures coming back for early next
week. This shortwave moves over the top of the ridge and digs into
the Great Lakes region on Mon into Tue with the ridge starting to
build up again in the Rockies on Tue, so a return of warmer air will
be in the near future. Temperatures will remain above normal for
this forecast period. Have some pops in for Sat into Sun with likely
pops in for Sat night. Starts to dry out Mon with cooler and drier
air moving in and have Mon night and Tue dry for now.

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 206 PM EDT WED JUL 20 2016

VFR conditions expected through the TAF period. Details for this TAF
issuance are difficult to pin down with exact timing of any showers
and thunderstorms being dependent on timing and track of
disturbances sliding into the area. Overall confidence in any one
solution is fairly low, so have decided to leave out of the TAF at
this point. There could be a couple of isolated showers and
thunderstorms this evening, but chances are minimal. The chance for
showers and thunderstorms will slide in very late tonight, but the
best potential for showers and thunderstorms will be toward the end
of the TAF period as a weak cold front passes through the area.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 314 PM EDT TUE JUL 19 2016

Winds will stay below 20 knots through the forecast period under
relatively a weak pressure gradient and high overwater stability.
Warm and humid air will flow across Lake Superior Wednesday through
Friday, which will allow fog to form, locally dense at times.

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


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