Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 201030

Area Forecast Discussion
National Weather Service Gaylord MI
630 AM EDT Sun Aug 20 2017

.NEAR TERM...(Today through Tonight)
Issued at 313 AM EDT Sun Aug 20 2017

High impact weather potential: A chance of thunderstorms overnight

Pattern synopsis and forecast:

A ridge of sfc high pressure extended across the western Great Lakes
early this morning, ahead of shallow mid level ridging. Weak WAA
aloft has started aloft, but a relatively drier air mass and no
other forcing aloft has resulted in mostly clear skies. The only
clouds around were associated with last evening`s pocket of light
rain that crossed nrn lower, as well as the fog and bit of stratus
across portions of eastern upper. Upstream, a shortwave trough and
associated cold front were encroaching on the Mississippi valley.
Not a whole lot of showers and storms ongoing there right now due to
a general lack of moisture, however there was a pocket of activity
in NE/western IA where the low level jet was relatively strong.
Also, some scattered showers were across SD. Both areas were
underneath 7c/km mid level lapse rates and in the vicinity of some
upper divergence.

The aforementioned shortwave trough will broaden out as it shoves
the mid level ridge east of the region. The air mass through the day
will remain on the dry side, and only few to scattered cumulus is
anticipated away from Lake Michigan where SW winds will be starting
to increase. Thus, mostly sunny skies are expected, with highs
reaching the upper 70s and lower half of the 80s. Moisture is never
really able to efficiently advance northward ahead of the front,
even through the night as the fast wave shoves the nrn end of the
front quickly, laying it out across far nrn Lake Michigan and
eastern upper overnight. We will have steepening mid level lapse
rates to 6.5c/km with some semblance of better WAA/LLJ and weaker
upper divergence, but not as good as what is currently upstream.
This combined with the front and MUCAPES of 500-1000j/kg ought to
bring at least the chance for showers and storms. Increased winds
just above the sfc will keep temps from falling too much. Lows will
be in the low to mid 60s.


.SHORT TERM...(Monday through Tuesday)
Issued at 313 AM EDT Sun Aug 20 2017

...Shower/storm chances to start the week...

High Impact Weather Potential: Thunderstorm chances at various times
Monday through Tuesday.  Locally heavy rain possible.

Pattern Forecast: Gradually lowering mid-upper level heights Monday
through Tuesday with several mid level shortwaves sliding along an
elongated surface frontal boundary draped across the Great Lakes.
This will result in unsettled weather to start the week.

Primary Forecast Concerns/Challenges: How much cloudiness for the
eclipse?  Shower/storm chances Monday through Tuesday.

Stalling frontal boundary will remain draped across northern Lower
Michigan on Monday with more clouds than not, and additional
scattered showers/storms at various times.  Very soupy airmass with
low level moisture pooling along and south of the boundary, pushing
surface dewpoints toward 70 degf in some areas.  This high dewpoint
air, combined with high temperatures pushing into the 80s, will
promote MLCAPEs of nearly 2,000 J/kg across much of northern lower
Monday afternoon.  Forcing is rather nebulous and not terribly
impressive during the day, but the development of afternoon lake
breezes should be enough to produce scattered storms.  Given the
amount of instability and with bulk shear values near 40kts, a few
organized strong-severe storms will be possible.

Eclipse viewing: Still looking like more clouds than sun across much
of the area early Monday afternoon as a frontal boundary bisects
northern lower.  Model trends are pointing toward afternoon deep
layer drying over upper Michigan (especially central and western
areas), where clouds will scatter out during the afternoon and allow
for better viewing.  Even south of the bridge, a few glimpses of
sunshine will be possible.

Still some model differences in the strength of any surface
reflection later Monday night into Tuesday as shortwave energy
slides along the quasi-stationary boundary across central Michigan.
Better forcing developing with upper level jet energy dropping into
the northern lakes coincident with surface low development along the
boundary.  Plenty of deep layer moisture in place with PWATs
approaching 2 inches.  Everything points to a fairly widespread rain
event later Monday night into the first half of Tuesday with pockets
of locally heavy rain possible (we are in the marginal excessive
rainfall area according to WPC).

.LONG TERM...(Tuesday night through Saturday)
Issued at 313 AM EDT Sun Aug 20 2017

Another deep upper level trough digs into the Great Lakes and
Northeast states for the middle and end of the week, pushing an
abnormally cool airmass into the area.  Deep layer drying and
subsidence Tuesday night behind the front, likely resulting in
mainly dry conditions but breezy and turning cooler.  Secondary
trough on Wednesday brings an uptick in H8-H7 moisture over northern
areas and possibly results in a few showers.  The remainder of the
week into the first part of the weekend looks quiet as a large area
of Canadian high pressure slowly builds south/east. Temperatures on
the cool side for August, although readings will moderate heading
into the weekend.  Ideal radiational cooling conditions on several
nights will likely result in some of the typically colder locations
dipping into the 30s.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 630 AM EDT Sun Aug 20 2017

Sfc high pressure will track east of the region today, while a
cold front approaches from the NW and nears PLN late in the TAF
period. S/SW winds will increase with the approach of the front,
with low end LLWS eventually being needed tonight. The atmosphere
has quite a bit of instability today, but moisture is rather
scant, with only few to scattered cumulus expected. No rainfall
until mainly after midnight when there`s a chance for showers and


Issued at 313 AM EDT Sun Aug 20 2017

Higher pressure slides east today with a cold front laying out
across nrn Michigan late tonight through later Tuesday. SW winds
increase to low end advisories over many of the nearshores later
this afternoon and tonight, before the gradient weakens
considerably. Chances for showers and storms will be associated with
this front late tonight through Tuesday. No severe weather is
expected. Then, a larger upper trough plows into the region and
shoves the cold front well south. The cold advection and stronger NW
winds will bring late Tuesday afternoon into Wednesday.


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 from 3 PM this afternoon to 5 AM EDT Monday
     for LMZ344>346.
LS...SMALL CRAFT ADVISORY from 7 PM this evening to 5 AM EDT Monday
     for LSZ321.


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