Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 180741

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

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...(Wednesday through Monday)
Issued at 339 AM EDT TUE JUL 18 2017

Upper-level ridging building over the Central and Southern Plains
will result in zonal flow dominating the northern Plains and
northern Great Lakes regions allowing for a number of shortwaves to
track across the area from mid to late week. 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 should be
seasonable with highs in the 70s to lower 80s through much of the
extended period, but then cooling down a bit Sunday into Monday.

Beginning the wake of Tue`s cold front, a transient area of
high pressure will push into the area bringing dry conditions for
much of the day.

Wednesday night through Thursday brings another potential for
showers and possibly some thunderstorms as a shortwave is progged by
models to move across the Upper Great Lakes region. There has been
quite a bit of spread among the medium range models in regards to
how precipitation chances will play out as this wave moves across
the area. The Canadian strongly builds surface high pressure
building across the region on Wednesday and pushes the frontal
boundary and precipitation chances well south of the area Wednesday
night through Thursday. The 00z GFS and NAM show the frontal
boundary setting up over southern WI with a complex of storms
initiating along the boundary and dropping out of the northern
Plains and into mainly southern and central portions of Wisconsin.
The big question will be if any of this convection reaches far
enough north to bring showers into our fcst area. Given the model
uncertainty, will continue at least chance pops for mainly south
central portions of the fcst area.

Fri into Mon...For the most part, Friday looks 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,
given the considerable model uncertainty in regards to the strength,
location, and track of shortwaves moving thru the area will continue
to keep chc pops in the fcst for Sat into Sun with the best chcs for
shra/tsra (likely pops) probably late Sat into Sat night. Monday
looks drier and cooler as Canadian high pressure builds back over
the Upper Great Lakes.

.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.

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


SHORT TERM...Beachler
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