Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 212000
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
400 PM EDT Fri Jul 21 2017

.SHORT TERM...(This evening through Saturday)
Issued at 400 PM EDT FRI JUL 21 2017

The main impact during the short-term portion of the forecast will
be severe weather potential Saturday afternoon into Saturday evening.

Tonight: A convectively induced shortwave is progged to slide across
southern WI this evening into the overnight hours. Models have been
steadily trending a bit farther to the south with this over the past
couple days, with the latest 12Z data continuing that trend. The
best moisture convergence is progged to remain across central to
south-central WI, which again lends more support to keeping the more
concentrated area of convection south of the U.P. It is still
possible that a few showers an maybe an isolated thunderstorm may
make it into the U.P., along the WI border, but the chances look to
be fairly limited. Southern Menominee county would have the best
chance of seeing some precipitation out of this, but it would be
fairly fast moving during the overnight hours, with very little
severe potential. Instability in the U.P. looks to be fairly limited
to the north of the Theta-e gradient across WI with only around 100 -
 200 J/kg expected along the southern portions of the U.P. this
evening. Outside of that, not really expecting much in the way of
widespread precipitation tonight. There could be a few rain showers
that slide across the rest of the area overnight tonight as another
area of decaying showers and thunderstorms/shortwave slides across
northern MN toward the U.P. Again, the lack of instability and
limited moisture convergence across the northern half of the U.P.
would help to steadily diminish the coverage and intensity of any
showers as shown by most of the hi-res model guidance.

Saturday: Cloud cover will steadily increase across the area through
the afternoon hours. This will be along and ahead of an approaching
cold front from the northwest. In addition, a stronger shortwave
will push into the western portion of Lake Superior by early evening
as the cold front progresses through the west half of the U.P.
Dewpoints will steadily increase ahead of the cold front, reaching
into at least the mid 60s by Saturday afternoon. The increasing
moisture advection along with heating of the day and increased
forcing along the front will help to touch off showers and
thunderstorms over the west half of the U.P. by late Saturday
afternoon into the evening hours. Some of the thunderstorms ahead of
the cold front could be strong to severe with the main threats being
gusty winds and large hail from the strongest storms. Instability is
progged to be around 1000-1500 J/kg along with shear values around
35 to 45 knots perpendicular to the front, which again lends support
to better organized storm structure during peak heating.

.LONG TERM...(Saturday night through Friday)
Issued at 355 PM EDT FRI JUL 21 2017

Not expecting any high impact weather in the long term. There is
some potential for some lingering stronger storms over the far south-
central Lake Saturday, but the strength of any convection will be
diminishing pretty quickly.

As the shortwave passes, convection will exit E early Sunday, with
upslope drizzle/showers Sun morning and afternoon in NW-N favored
areas.

A shortwave and weak cold front may bring some convection late Tue
into Tue night, but after that high pressure dominates with no
precip expected.

Did not need to make any changes from the blended initialization.
&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 137 PM EDT FRI JUL 21 2017

Ceilings are expected to remain VFR trough the afternoon into this
evening; however, low-level moisture will steadily increase late
this evening through the overnight hours, allowing ceilings to drop
to at least the MVFR category, with the best chance being at the
KIWD TAF site. Showers and thunderstorms are expected to remain
south of the area through tonight; however there could be a few pop
up showers and maybe a stray thunderstorm this afternoon near the
KSAW TAF site. The better chance of showers and thunderstorms will
perhaps push into the far western TAF sites toward the very end of
this issuance. At this point did not include mention in the TAF as
the chances increase even further after 18Z/22. Some fog is possible
late tonight as the low level moisture increases, with the best
chance again being over the KIWD TAF site will moisture increase
more rapidly.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 400 PM EDT FRI JUL 21 2017

Late tonight through Saturday afternoon winds across the western
half of the lake will increase to around 20 to 25 knots ahead of an
approaching cold front. Expect winds of 15 to 20 knots to spread
across much of the lake before diminishing to around 15 knots by
Saturday evening. Sunday afternoon expect the winds to increase
across the lake to around 20 to 25 knots. These winds will diminish
to under 15 knots by mid-morning on Monday. Through the rest of the
week, winds will remain under 20 knots.
&&

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

$$

SHORT TERM...KEC
LONG TERM...Titus
AVIATION...KEC
MARINE...KEC



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