Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 220537

Area Forecast Discussion
National Weather Service Marquette MI
137 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...(Thursday night through Wednesday)
Issued at 445 PM EDT WED SEP 21 2016

An amplified pattern will prevail with a prominent mid/upper level
ridge from the se CONUS through central Canada by this weekend and a
trough slowly moving through the wrn CONUS. Although the models were
in agreement with the development of a cutoff low over the cntrl
CONUS there were large inconsistencies and run to run variations
with the evolution and position of the low. So, uncertainty is
higher than usual for this time frame with low forecast confidence.

Thursday night into Friday, as the mid/upper level ridge builds to
the west, sfc high pres over nrn Ontario will build to the south
with drier air pushing into the nrn Great Lakes. This will push most
of the pcpn south of the cwa. However, there still may be some light
showers south central Thursday evening and far south overnight with
weak bands of fgen to the north of the 850 mb front.

Friday night and Saturday, the models were in better agreement that
a stronger band of 700-500 mb fgen will develop in response to the
amplifying ridge to the west and upper level div with the right
entrance of the 250-300 mb jet to the northeast. This will support
at least chance pops over most of the area by late fri night into
sat morning. There is still some uncertainty with the impact of the
antecedent dry airmass on the progression of the pcpn.

Sunday through Wednesday, the developing blocking pattern will slow
the advance of the pcpn associated with the strong moisture
transport and forcing ahead of the plains trough with the highest
pops mainly from sun night through mon. Even with the higher
uncertainty with the cutoff low, shra chances are expected to linger
through wed with the potential for the low lingering just to the
west, per 12z GFS/GEFS/ECMWF.

.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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