Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 220703

Area Forecast Discussion
National Weather Service Marquette MI
303 AM EDT THU SEP 22 2016

Issued at 902 PM EDT WED SEP 21 2016

Based on radar trends showing a sharp back wrn edge of the area of
showers moving thru nw WI, diminishing ltg trends within the showers
over Upr MI/adjoing nrn WI and more resilient dry air to the n,
lowered fcst pops by accelerated the drying trend fm the nnw as shown
by the latest HRRR model run. The new fcst still retains the
categorical/hier likely pops over the s half or so of the cwa. The
main reason this pcpn area wl not expand farther to the n and thus
diminish faster is the axis of robust convection dvlpg fm scentral MN
into central WI closer to h85 warm fnt/fgen axis/area of pwat aprchg
2 inches/sharper differential dvgc fm h85 thru h3/hier mucape aoa 2k
j/kg is robbing mstr inflow into Upr MI and lowering the chc for
deeper saturation over this area.

.SHORT TERM...(This evening through Thursday)
Issued at 358 PM EDT WED SEP 21 2016

Dry air exists over the northern CWA where a SFC ridge extends. A
SFC low over the central plains has an inverted trough extending NE
across WI and lower MI, with an area of convection along the
elevated portion of the warm front over a good portion of WI. Most
do not initialize well with the current convection, and those poorly
initializing models blow convection up across the SW CWA this
evening as the warm front moves north and LLJ ramps up. If the front
can move into the area with the LLJ, heavy rainfall would be a
significant issue this evening and tonight as warm cloud depths
would be over 11kft, PWATs near 1.75" and storm motion slow and
nearly parallel to the front. Several inches of rain would be
possible especially along the WI border. However, models that do
initialize well (or at least better) with the WI convection (HRRR,
HRRR-EXP, Canadian-Regional) keep heaviest precip will south of the
area as the LLJ will be hindered north of that convection and the
front may not even make it into the area. These models do bring
precip into the area, just not the heaviest. Could still see 0.50-
1.00 inches right along the WI border. Thu should see overall
diminishing precip chances, but isolate to scattered showers will
continue to be possible through the day, especially over the south.
The Keweenaw will see the lowest precip chances through tomorrow,
possibly being dry much of the time.

.LONG TERM...(Friday through Wednesday)
Issued at 303 AM EDT THU SEP 22 2016

Nam forecasts a 500 mb ridge over the plains with a closed 500 mb
low and trough over the central and southern Rockies 12z Fri. This
ridge moves into the upper Great Lakes 12z Sat and remains over the
area into 12z Sun while the 500 mb trough and low move northeast
into the northern Plains. The frontal zone and pcpn will get pushed
south and will be dry until late Fri night and Sat morning when a
wave will try to bring some pcpn into the west, but only have slight
chance pops for now. Next wave and chance for pcpn comes in for Sat
night and have chance pops in for the west half late. Overall, did
not make too many changes to the going forecast.

In the extended, GFS and ECMWF show a 500 mb ridge on the west
coast, a trough in the northern plains and a ridge in the Great
Lakes and sern U.S. 12z Sun. This trough moves slowly east 12z Mon
with it starting to affect the upper Great Lakes. Upper air pattern
becomes increasingly amplified with very little movement to the east
through the forecast period with a slow moving sfc low pressure and
several fronts affecting the area this forecast period. Looks wet
with a slow moving system and temperatures look to be at or slightly
above normal.

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 136 AM EDT THU SEP 22 2016

Although the more nmrs showers wl stay to the s of IWD and SAW, the
presence of more llvl mstr closer to a warm fnt to the s of Upr MI
wl allow for lower MVFR and then IFR cigs at both those sites for a
time thru this mrng and into the aftn. Since CMX is closer to the
drier air, expect cigs to fall no lower than MVFR at that site. The
arrival of drier air wl cause an improvement later in the TAF
period. The MVFR cigs wl be most tenacious at SAW, where the
expected llvl ne flow wl upslope and possibly maintain MVFR cigs
thru the end of this fcst period.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 358 PM EDT WED SEP 21 2016

NE flow over Lake Superior with SFC trough moving into Upper MI and
SFC ridge over Ontario could support some higher wind gusts to 25
knots over the western half of the lake into Thu and across the
entire lake Thu night into Fri. As the Canadian high builds more
over the Upper Lakes, winds will dip below 20 kts Friday night into
Saturday night. Southerly winds will increase late Sunday into Mon
to 25 to 30 knots over mainly the north central and eastern part of
the lake as a low pressure trough approaches from the west.

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


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