Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 181821

Area Forecast Discussion
National Weather Service Marquette MI
221 PM EDT Tue Jul 18 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 219 PM EDT TUE JUL 18 2017

A weak cold front was draped across western Lake Superior and down
into central Minnesota this afternoon. Along this frontal boundary
showers and thunderstorms have developed across western Lake
Michigan and northwest Wisconsin and has slowly pushes east-
northeast early this afternoon. Ahead of the front, differential
heating across central Upper Michigan has allow a few isolated
showers to pop up as well. Dew points have increased ahead of this
boundary into the lower 70s, so conditions have become increasingly
humid this afternoon.

The main forecast concern is how convection will evolve through the
afternoon and evening hours across Upper Michigan as the cold front
pushes eastward, and the chance for strong to severe storms. As the
afternoon progresses, models are in fairly good agreement with
convection increasing in coverage across the west and central as the
warm, moist air continues to spread northeast and works with diurnal
heating to allow capping to erode. With a very moist air mass in
place and high freezing levels, expect any convection to be
efficient rainfall producers with high precipitation rates. With
storm motion only being around 10-15 knots, flooding may be possible
especially across areas that see prolonged precipitation. With
shear only progged to be around 30 knots, the main threat will be
strong downburst winds and small hail as storms may struggle to
remain organized at times. The best chances for strong to severe
storms looks to be across western and portions of central Upper
Michigan this afternoon, and then as the cold front pushes east
and storms begin to congeal into a line the threat will shift east
into the evening hours.

Tonight, the cold front will gradually push across the area and
showers and thunderstorms will diminish from west to east. Wednesday
things will dry out as high pressure moves overhead and skies clear.

.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 18Z TAFS through 18Z Wednesday afternoon)
Issued at 140 PM EDT TUE JUL 18 2017

Challenging aviation forecast with the arrival of a cold front and
expected showers and thunderstorms. These storms will impact
KIWD/KCMX this afternoon and then KSAW later this afternoon/evening.
There is some uncertainty in regards to the exact location of where
the stronger convection will move; therefore, amendments may be
needed to fine tune as the afternoon/evening progresses. The main
threats will be locally heavy rain, which will likely lead to
reduced visibilities, and gusty winds. Later tonight as the cold
front pushes south of the area, showers and storms will vacate the
area. There is the potential for some fog in areas that see heavier
rainfall this afternoon, but with a drier air mass progged to move
into the region wasn`t confident enough to include mentions at this

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 219 PM EDT TUE JUL 18 2017

Winds will remain around 20 knots just ahead of the cold front
currently pushing east across Lake Superior as an enhanced pressure
gradient remains in place. As the front moves across the lake, there
will be a transient area of lighter winds, before 15 to 20 knot winds
fill in behind the front tonight into Wednesday. High pressure
quickly moving across the region on Wednesday and allow winds to
remain around 10 to 15 knots. Through the rest of the week into the
first half of the weekend, winds will remain less than 15 knots
across the lake. Towards the later half of the weekend, depending on
the track of another storm system moving across the region winds
could increase to around 20 knots across the lake.

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


SHORT TERM...Ritzman
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