Area Forecast Discussion
Issued by NWS Gaylord, MI

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517
FXUS63 KAPX 182000
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
400 PM EDT Fri Aug 18 2017

.NEAR TERM...(Tonight through Saturday)
Issued at 400 PM EDT Fri Aug 18 2017

...Slow improving trend...

High Impact Weather Potential...gusty winds will lead to a high
swim risk on Lake Michigan through this evening. Otherwise...none.

Pattern Synopsis/Forecast...Afternoon surface map and satellite
imagery reveals our departing stacked surface low over SE Ontario
with abundant wrap around cloud cover draped through the Great
Lakes region. Larger scale spotty shower activity has ended across
the CWA for the moment. But...gusty W/NW winds and cool-ish air
air (tongue of +10C 850 MB air) flowing across the warm lakes is
producing spotty showers/drizzle...particularly across NW lower
Michigan. Upstream...yet another short is rotating into western
Wisconsin with additional showers.

Primary Forecast Concerns...clearing trend and lingering precip
chances.

Stacked low and wrap around cloud cover inch out of the region
tonight through Saturday. With loss of heating/diurnal component
tonight...still anticipate some sort of modest cloud thinning
trend for the southern/SW parts of the CWA...although upstream
short wave will bring some additional cloud cover into the region
later tonight through Saturday morning.

Meanwhile...thicker cloud cover will probably hang on tight for
the N/NE portion of the CWA into Saturday and there may another
reinforcing lobe of moisture/spotty showers that rotate down
through eastern upper Michigan/northern Lake Huron later tonight...
then down through NE lower Michigan on Saturday. In addition...we
may see a few showers/even isolated thunder pop along the Lake
Michigan lakeshore of the U.P. Saturday afternoon...with daytime
heating and afternoon lake breeze convergence. Upshot...not an
entirely perfect day Saturday...although a big improvement over
today with highs warming back through the 70s.

&&

.SHORT TERM...(Saturday night through Monday)
Issued at 400 PM EDT Fri Aug 18 2017

...Eclipse...

High impact weather potential...Thunderstorms for the eclipse?

Fast moving upper ridge moves east of region Sunday night. Trough
then moves in and deepens over the Upper Midwest and Great Lakes as
upper low over Manitoba sinks south. This drops a front into the
upper Midwest and northern Great Lakes by Monday.

Descent shortwave moves along the front Sunday night through the UP.
Area of deep moisture and warm advection/isentropic lift moves
across the eastern UP after midnight with the chance of
precipitation. Elevated CAPE values of near 1000 J/kg so mix of lift
and instability could produce thunderstorms.

Better shot Monday. 30-40kt LLJ pushing into the area Monday
afternoon with MUCAPE values around 2000 J/kg and sfc dewpoints in
the 60s. Wave moving through the mid level flow crosses northern MI
in the evening as well. Also pocket of cooler 500mb temperatures
moving in will increase lapse rates in the vicinity of the front.
Looks like a good chance of thunderstorms especially over our
southeast areas of our CWA where LIs around -6C are forecast and 30
to 40kt 0-6km bulk shear. Possibility of severe weather Monday?

&&

.LONG TERM...(Monday night through Friday)
Issued at 400 PM EDT Fri Aug 18 2017

The H5 pattern in the extended shows large scale troughing over
eastern Canada, dipping down across the Great Lakes through the
first half of the period.  The GFS is more impressed with this
feature than the Euro...showing it lingering longer with an
associated closed low deepening as it pulls into Quebec. That low
was modeled as deep as 978mb! Whereas the Euro shows a weaker
feature that`s a bit more transient.

It seems reasonable that showers and thunderstorms are in the
forecast Tuesday and Tuesday night.  Upper level support for
stronger storms is modeled in lower Canada.  Showers may linger in
northwest flow Wednesday in a spotty fashion.  As far as
temperatures go, flirting with 80 degrees is possible Tuesday
afternoon.  Below normal high temperatures, which are middle 70s for
this time of year, is the theme for the middle and end of the week.
40s at night are plausible Wednesday night, Thursday night, and
Friday night.

Berger/JP

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 253 PM EDT Fri Aug 18 2017

MVFR CIGS remain entrenched across northern lower Michigan this
afternoon...although some erosion/lifting in the CIGS is
beginning to take shape across the southern parts of the CWA. CIGS
are expected to gradually lift to VFR over the next few
hours...with more substantial thinning to the clouds near the
MBL/TVC terminal sites. SCT-BKN cloud cover will stick around
through Saturday...but CIGS should be VFR through the day.


&&

.MARINE...
Issued at 400 PM EDT Fri Aug 18 2017

Gusty W/NW winds will maintain small craft advisory conditions on
the Lake Michigan this evening...and on the Huron side through the
overnight hours. Weakening winds and diminishing waves through the
weekend.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...BEACH HAZARDS STATEMENT until 11 PM EDT this evening for MIZ016-
     019>021-025-031.
LH...SMALL CRAFT ADVISORY until 11 PM EDT this evening for LHZ345>349.
LM...SMALL CRAFT ADVISORY until 11 PM EDT this evening for LMZ323-341-
     342-344>346.
LS...SMALL CRAFT ADVISORY until 11 PM EDT this evening for LSZ321-322.
&&

$$

NEAR TERM...BA
SHORT TERM...KF
LONG TERM...KB
AVIATION...BA
MARINE...BA



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