Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 201949
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
349 PM EDT Sun Aug 20 2017

.NEAR TERM...(Tonight through Monday)
Issued at 345 PM EDT Sun Aug 20 2017

...Scattered showers/thunderstorms through Monday/And spotty
eclipse viewing Monday afternoon...

High Impact Weather Potential: Some scattered convection
tonight...better potential with daytime heating Monday.  Some severe
potential for northern Lower Monday.

Pattern Synopsis/Forecast: Generally partly-mostly sunny skies
across northern Michigan at mid afternoon...with some diurnal CU
around and CI blowoff from a remnant MCS (and associated MCV) moving
across northern IL.  A cold/occluded front stretches across
northwest Ontario/far northwest Wisconsin/southern Minnesota...with
mid/upper 60s dew points ahead of the front and steep mid level
lapse rates associated with an eastward advancing elevated mixed
layer resulting in scattered convection developing across western
Upper/northwest Wisconsin where MLCAPE values in the 1000-2000J/kg
reside.

Upstream cold front will get stretched west-east as it moves into
the upper Lakes this evening...and will lie across northern Lower
Michigan during the day Monday beneath zonal low-mid level flow.

Primary Forecast Concerns: Cloud cover for Monday of course...and
precipitation evolution through Monday afternoon.  As cold front
spreads into the area tonight...low level theta-e ridge and
steepening mid level lapse rates will result in an axis of
instability extending across northern Wisconsin/northern Michigan.
Weak but persistent moisture convergence along this boundary should
bring the threat of at least scattered elevated convection tonight
to eastern Upper and far northern Lower Michigan.  May not see much
activity south of the M-72 corridor initially.  This boundary
lingering across the area on Monday will continue the potential for
seeing convection developing along it...especially tied to the
diurnal heating cycle and perhaps aided by lake breeze development
within what will be a humid air mass.  NAM-WRF trying to depict an
MCV associated with anticipated MCS development tonight across Iowa
to roll across Lower Michigan during the afternoon (and provide
another focus for precipitation).  While a reasonable idea (the MCV
that is)...whether such a feature would impact northern Lower
depends on how convection evolves upstream overnight.  Bottom line
from a precipitation standpoint...chance/scattered PoPs for the most
part through tonight (eastern Upper) and through Monday for northern
Lower.  Marginal severe risk depicted for Day 2 across southwest
quarter of the forecast area not unreasonable given potential
instability and southern edge of stronger flow aloft impinging upon
northern Michigan.

As for the pesky cloud cover issues...not going to be a total Debbie
Downer on this.  Certainly not the most ideal potential eclipse
viewing conditions given the proximity of the lingering front and
potential for "junk" cloud cover.  But model mass fields suggest
that there could be some openings here and there...so will be
optimistic that there will be some viewing potential at least early
on prior to afternoon convective cloud development.

&&

.SHORT TERM...(Monday night through Wednesday)
Issued at 345 PM EDT Sun Aug 20 2017

...Showers and storms late Monday night into Tuesday morning...

High impact weather potential...thunderstorms with locally heavy
rain possible Monday night (mainly late) into Tuesday morning.

Period of active wx ahead, as we transition from above-normal temps
to cooler wx. Low pressure will rapidly deepen as it crosses the
northern lakes region and heads for Quebec Mon night-Tue. Very good
chance for associated showers/t-storms. Cold front will exit by
early Tue afternoon. Post-frontal airmass will cool us off and dry
us out (mostly).

Monday Night/Tuesday morning...500mb heights will be on a steady
fall, as an upper low moves southward into northern Ontario. Primary
shortwave trof will move over northern MI Tue afternoon, with the
surface low deepening well ahead of this wave. Spotty convection may
be ongoing Mon evening, the main show will be overnight as the low
level jet ramps up to our s and sw. This will advect a moist and
unstable airmass northward into the central lakes.

But...there are some indications we will see something of a `split`
around northern MI when it comes to heavier precip. Organized
convection seems most likely to march across southern lower MI in
the late evening/overnight hours. This is along the northern
periphery of the deepest instability. The low-level jet will veer
with time, especially overnight, not helping this activity make
northward progress. Meanwhile, low- to mid-level deformation just nw
of the developing surface low will impact upper MI and adjoining
parts of Lk Superior and northern Ontario, very late Monday night
into Tue morning.

Do expect some precip between these two primary areas, and high pops
are still very much justified late Mon night into Tue morning. But
most vigorous convection may well pass to our south, while secondary
area of best QPF impacts eastern upper MI and points north. Given
the above scenario, our svr threat Tue night doesn`t appear too
impressive.

A warm night, especially in northern lower. Min temps near 60f
to the upper 60s.

Tuesday afternoon into Wednesday...low pressure migrates to Quebec,
while large high pressure in the plains and prairies eventually heads
toward western Superior. Diurnal heating may be enough to produce a
stray post-frontal shower to two Tue afternoon, otherwise the
incoming high will promote a cooling/dry trend into Tuesday night. A
spoke of energy rotating around the stacked Quebec low will push a
secondary cold front and a band of enhanced moisture on Wednesday. A
few showers could result, especially over eastern upper MI.
Otherwise, Tue afternoon will see decreasing cloud cover, with Wed
seeing more sun than clouds in the majority of northern MI.

Max temps Tue mainly in the 70s. Min temps Tue night near 50f to the
mid 50s. Highs Wed in bit cooler, mid 60s to lower 70s.

&&

.LONG TERM...(Wednesday night through Sunday)
Issued at 345 PM EDT Sun Aug 20 2017

The extended in a word..."uneventful".  Broad upper level troughing
will be pulling out Wednesday and Thursday with high pressure
building in for at least the first half of the weekend.  The story
will be "the taste of fall"...with very cool readings, especially
overnight lows Wednesday night and Thursday night.  Someone in the
favored cold spots of the interior lower peninsula may even see
readings dip below 40 for the first time this season.  But even
then, temperatures will be moderating into the weekend (though still
remaining below climo).  The latest model runs are starting show the
next weather maker moving in on Sunday, with chance pops as early as
Saturday.  However, I really think this might be a little ambitious.
I would favor a mainly dry Saturday into Sunday... and pushing POP`s
into Late Sunday/Monday. Alas, we`re talking day 7...and that`s a
long way off.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 150 PM EDT Sun Aug 20 2017

Anticipating a line of showers/thunderstorms to move into northern
Lower Michigan later this evening...perhaps thinning out toward
daybreak with additional convection possible along a stationary
front that will lie across northern Lower Michigan during the day
Monday.

&&

.MARINE...
Issued at 345 PM EDT Sun Aug 20 2017

Lingering gusty south/southwest winds ahead of an approaching cold
front will allow for continued Small Craft Advisories within some
Lake Michigan and Whitefish Bay nearshore zones. Weak gradient
expected Monday but winds are expected to increase form the
northwest heading into Tuesday which will likely necessitate
another round of Small Craft headlines.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY from 7 PM this evening to 5 AM EDT Monday
     for LHZ347.
LM...SMALL CRAFT ADVISORY from 7 PM this evening to 5 AM EDT Monday
     for LMZ341-342.
     SMALL CRAFT ADVISORY until 5 AM EDT Monday for LMZ344>346.
LS...SMALL CRAFT ADVISORY from 7 PM this evening to 5 AM EDT Monday
     for LSZ321.
&&

$$

NEAR TERM...JPB
SHORT TERM...JZ
LONG TERM...KB
MARINE...JPB



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