Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 180528
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
128 AM EDT Tue Jul 18 2017

.UPDATE...
Issued at 1008 PM EDT MON JUL 17 2017

Main tweaking to the forecast this evening is to bring in pops over
the west quicker as tsra complex moves out of MN. Have higher pops
starting up around 04-05z at IWD and slowly spreading across rest of
west half overnight. Even with higher MUCAPE upstream and adequate 0-
1km shear to keep cold pool balance going, think the complex should
gradually weaken as it moves into western U.P. That said, cannot
count out gusty winds to 50 mph, at least initially over the west
through the early overnight, and do not forsee the complex completely
falling apart. This complex will likely leave an outflow boundary
around somewhere in the southwest or scntrl forecast area which
could serve as a focus for more thunderstorm development through
the day.

Finally what a difference a night makes. With strong warm air
advection ahead of low over the Dakotas temps tonight will struggle
to fall to the mid 60s over parts of the west and will be in the
mid 50s to mid 60s elsewhere. Coolest temps in the east but
nothing close to the 30s and 40s readings seen last night and
early Tue morning.
&&

.SHORT TERM...(This evening through Tuesday)
Issued at 313 PM EDT MON JUL 17 2017

Another beautiful day across the Upper Peninsula, as the departing
high pressure was still influencing the weather with abundant
sunshine and temperatures in the upper 70s away from the lakes and
upper 60s closer to Lake Michigan shoreline. The focus for later
this evening into the overnight will turn towards the
west/northwest. A line of showers and thunderstorms has developed
upstream over Northern Minnesota, associated with the next upper
level lobe of vorticity. Low-level moisture has pooled north through
Wisconsin pushing Td`s this afternoon into the mid/upr 60s.
Fortunately for much of the U.P. mid-lvl heights are holding on, but
with the departing surface ridge to the southeast, expect height
falls to increase later tonight. This coupled with guidance
indicating a secondary lobe of vorticity pivoting southeast aft 5z,
will bring the chances for showers and thunderstorms east across the
U.P. There is a window overnight though that guidance indicates
height falls could slow, which may inhibit the chance for precip
overnight or shift it to the southwest away from the U.P. So have
made minor adjustments to the going forecast, with only a steady
increase in POPs after daybreak Tue.

Guidance then continues to flatten the longer 500mb wave Tue
morning, which would allow any upstream shortwaves to traverse the
northern latitudes towards the U.P. so have held onto the higher
chances for showers and thunderstorms. Temps tonight will remain
mild due to the slowly increasing low-level moisture and weak
southerly flow aloft. With lows in the lower 60s. Then Tue will
hinge upon cloud cover and precip, but have highs still warming into
the upper 70s to low 80s.

.LONG TERM...(Tuesday night through Monday)
Issued at 248 PM EDT MON JUL 17 2017

As upper-level ridging builds across the Plains flow will become
zonal across the northern Plains and northern Great Lakes regions
allowing for a number of shortwaves to track across the area. There
is quite a bit of uncertainty in how precipitation chances will play
out towards the latter half of the week and weekend, but there
should be a few days that remain mostly dry as transient areas of
high pressure quickly move across the area in between systems.
Temperatures wise we`re looking at seasonable temperatures, 70s to
lower 80s through the middle of the week, and then cooling down a
bit through the weekend.

Tuesday night through Wednesday morning, as a cold front continues
to push east across central and eastern portions of Upper Michigan,
showers and thunderstorms are expected to linger. There is some
disagreement in regards to the speed of this front, but right now it
looks like convection should linger across central and eastern
portions of the area into the overnight hours. By Tuesday night
convection should begin to congeal and grow upscale into an MCS as
it rolls across Upper Michigan and Wisconsin. This would allow the
threat for a hail to diminish, but strong winds and very heavy rain
will still be a concern. With PWATs progged to approaching 2+
inches, which is about 1.5-2 standard deviations above
climatological means, with a deep warm cloud layer, precipitation
will be highly efficient. Thankfully it looks like things will
remain fairly progressive and precipitation should move out of the
area through the overnight hours. Wednesday a transient area of high
pressure will push into the area following the surface trough
bringing dry conditions for much of the day.

Wednesday night through Thursday brings another potential for
showers and possible some thunderstorms as a shortwave is progged to
move across the upper Great Lakes region. There is quite the spread
among the medium range models in regards to how precipitation
chances will play out as this wave moves across the area. The
Canadian looks to be a bit too robust with surface high pressure
building across the region on Wednesday given the upper air-
pattern/shortwave activity, which would push the frontal boundary
and precipitation chances well south of the area Wednesday night
through Thursday. The ECMWF/NAM/GFS seem to be in much better
agreement with a complex of storms dropping out of the northern
Plains and into portions of Wisconsin. The big question will be if
convection will get this far north. Given the uncertainty, will
maintain at least chances mentions for a good portions of the
area.

For the most part, Friday looks like it will remain mostly dry as
another transient area of high pressure moves into the area. Given
the number of shortwaves progged to move across the area throughout
the week, it is not surprising that the models are diverging in the
speed/track of additional waves through the weekend. Right now, the
best chances across Upper Michigan for precipitation through the
weekend looks to be towards the latter half. However, this will all
depend on the speed and track of the more robust shortwave progged
to arrive, which still has considerable uncertainty in regards to
its strength, location, and track.
&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 127 AM EDT TUE JUL 18 2017

VFR to start the TAF period early in the overnight. May see some
showers affect IWD and CMX overnight but intensity has waned
considerably since late last evening. Last issue overnight will be
LLWS, mainly expected at IWD. Later this morning at IWD and CMX
expect cold front to work through, switching winds from SW to W/NW.
Could be MVFR cigs for a time behind the front. Signal emerging that
shower chances with some tsra as well develop in the aftn at IWD and
CMX. At SAW, could be some shra late morning into early aftn at SAW
before another round of shra/tsra develop late in the day. All shra
and tsra should be out of the TAF sites by late Tue evening.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 314 PM EDT MON JUL 17 2017

Winds will remain southerly tonight, with speeds ranging from 10-
15kt and occasional gusts to 20kt until sunset. High pressure will
continue to sag south away from the U.P. and the approach of a
frontal boundary will shift winds to the southwest Tue and
eventually northwest late Tue ngt into Wed. Winds will then mostly
be under 15kt from Tue aftn thru Fri as pres gradient will be weak
across the Upper Lakes.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

UPDATE...JLA
SHORT TERM...Beachler
LONG TERM...Ritzman
AVIATION...JLA
MARINE...Beachler



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