Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 201726

Area Forecast Discussion
National Weather Service Marquette MI
126 PM EDT Thu Jul 20 2017

.SHORT TERM...(Today and tonight)
Issued at 339 AM EDT THU JUL 20 2017

Pretty quiet morning as complexes of showers and thunderstorms have
stayed well to the south of Upper Michigan along stationary front
and northern edge of much greater instability. As of 3 am EDT, bulk
of lightning is affecting southern MN into southern WI (where
there has been heavy rain and flooding reported) with a few isold
strikes only as far north as Oshkosh WI. A couple of showers have
drifted across the Bay of Green Bay early this morning and also
over eastern Lk Superior but that is about it. Have isold pops
over far scntrl and east through daybreak but went dry otherwise.
Sfc trough upstream over northwest MN will sweep across western
cwa this morning then over rest of the forecast area early to mid
aftn. Still warm and humid ahead of this front so went for another
warm day with readings into the upper 70s to even upper 80s,
warmest over scntrl with downsloping NW winds. Even as the front
runs into lingering warmth and moisture in low- levels, subsidence
in wake of convection this morning leads to atmosphere that will
be too dry to support any additional shra/tsra during peak
heating. Could be some pop up fair weather cu clouds but that is
all. Most areas should see temps warm quickly this morning with
mostly sunny skies, but expect temps to fall back some this aftn
along Lk Superior into the upper 60s to lower 70s with developing
onshore NW-N flow.

High pressure builds across tonight. Based on upstream temps this
morning in south central Canada vcnty of the high, think interior
areas have shot to drop below 50 degrees tonight which will be quite
refreshing. Temps near 60F will hang on close to the Great Lakes
though as proximity of warmer nearshore waters tempers the cooling.

.LONG TERM...(Friday through Wednesday)
Issued at 425 AM EDT THU JUL 20 2017

Models suggest that weak ridging and dry conditions on Fri will give
way to a stronger shortwave trough from Manitoba moving into the
Upper Great Lakes late Sat into Sun and bringing with it scattered
showers and t-storms. As the shortwave trough pushes east on Mon it
will be replaced by ridging and drier, cooler weather for the early
part of the next work week.  Temps will remain at or above normal
into Sat but then drop below normal from Sun-Tue.

Beginning Fri, Models indicate that the main sfc-850 mb front
remains far enough to the south so that the next shortwave progged
to move along this boundary and associated area of convection should
remain over WI with only lighter pcpn on the northern fringe
possibly brushing the southern cwa from the late afternoon into fri
night. It appears that the 00z GFS qpf field handles this best while
the 00z CMC and NAM look way too far north with showers. Given the
CMC and NAM recent poor performance handling convection have less
confidence in these models and will side more closely with the GFS

Sat-Sun, as the mid/upper level flow becomes more northwesterly, a
stronger shortwave trough is expected to drop from southern Manitoba
into the northern Great Lakes. Some minor timing differences still
exist with models on shortwave, but model consensus would suggest
that the initial band of showers with WAA and 700-300mb qvector conv
ahead of the shrtwv is expected to move in from the west-southwest
Saturday afternoon and then continue to spread east-northeast into
Saturday evening. With model fcst MUCAPEs of 800-1200 j/kg and deep
layer shear of 40-50 knots could see a few strong to possibly severe
storms along the WI border Sat afternoon into Sat evening. Shower
chances will persist Sat night through most of Sunday into Sunday
evening until the shortwave slides off to the east and building high
pressure from the north and west brings drier conditions late Sun
night. High temps in the 70s across Upper Mi on Sat will cool down
into the 60s on Sunday over the nw half with onset of northerly
winds behind departing low pressure.

Mon-Tue, Amplified mid-upper level ridge building in from the west
along with cool Canadian sfc high pressure over the area will result
in dry, cooler and pleasant weather. Highs will range from the upper
60s/lower 70s north to the lower 70s/mid 70s south Monday with
slightly warmer (widespread 70s temps across cwa) conditions

Wed, Model uncertainty increases as the 00z GFS more aggressive than
00Z ECMWF with showing a stronger shortwave riding over the mid-
level ridge through northern Ontario and bringing an associated cold
frontal boundary in from the west to initiate more showers/t-storms.
The 00z CMC on the other hand, shows the amplified mid-level ridge
and sfc ridge peristing continuing dry conditions over the Upper
Great Lakes on Wed. Perhaps the 00z GFS solution is too aggressive
while the 00z ECMWF fits closer with the GFS ensemble mean lagging
front farther to the west. The CMC solution seems like an outlier at
this point. A GFS/ECMWF blend would argue for keeping chc pops in
Wed fcst at least for afternoon and evening.

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 125 PM EDT THU JUL 20 2017

VFR conditions are expected to prevail thru the fcst period at each
TAF site. There may be some scattered fair weather clouds this
afternoon and some mid-level clouds that push into the TAF sites
late in the period, but there should be no restrictions from these.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 339 AM EDT THU JUL 20 2017

Expect winds 15 kts or less late this week into Sat. Next chance for
stronger winds from the N-NE over 20 kts will be on Sun in wake of
low pressure system crossing the Upper Great Lakes. High pressure
builds back over region by early next week with winds mainly 15 kts
or less.

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


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