Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 201048
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
648 AM EDT Wed Sep 20 2017

.UPDATE...
Issued at 611 AM EDT Wed Sep 20 2017

A few showers have popped up over ne lower MI and Lk Huron. The
question /why/ is a challenge to answer, but there is a nearly
stationary vort max hanging over the Thumb area and southern Lk
Huron (left over from last nights convection). Recent Rap runs
hang onto some showers over ne lower MI and vicinity thru mid
morning before diminishing, and will have something similar in the
updated grids/fcst.

&&

.NEAR TERM...(Today through Tonight)
Issued at 337 AM EDT Wed Sep 20 2017

...Shower and thunderstorm threat increases tonight...

High impact weather potential...some non-svr t-storms tonight,
especially overnight.

Upstream cold front is pushing across central MN early this
morning. Line of deep convection accompanies this front. Parent
forcing shortwave is lifting nne toward Hudson Bay. So the cold
front will become a bit mushier by the time it is pushing into
eastern upper and approaching nw lower MI very late tonight.
Still, there is a respectable chance for precip ahead of this
front tonight.

In the meantime, cloud cover and temps are the main challenges for
the daylight hours. Stratus has advected into the region on ese sub-
850mb winds. Downsloping is keeping this deck is bit tattered along
the nw lower MI coast, but elsewhere it`s pretty solid. We`ll be
able to get diurnal heating around its edges and thru thin spots to
erode this deck, but our sun angle isn`t what it used to be, and
this will take time. Will generally hang onto mostly cloudy skies
into early afternoon east of I-75 in both peninsulas, with rapid
improvement thereafter. With the above in mind, will also cut
down on guidance max temps a touch in eastern sections.
Improvement will be faster west of I-75.

Highs will be mid 70s to lower 80s, warmest west of M-66. Immediate
TVC area may hit the mid 80s.

Prominent pre-frontal instability plume will develop across WI and
western/central upper MI this afternoon, in a relatively narrow zone
of deeper moisture return. Shower/thunderstorm activity is expected
there, per SPC day 1 outlook. This activity not be as vigorous as it
is presently, as again better forcing is lifting nne into Canada.
Low-level convergence will be less, and mid-level cooling/height
falls will diminish, leading to some concerns about capping. Still,
some activity is likely upstream, organizing into linear segments.
Instability plume will pivot into northern MI tonight, especially
overnight, as 1000-850mb sw flow increases. MuCape values will push
1k j/kg in nw lower MI, less elsewhere.

Expect a chance of convection reaching far western Mack Co, and w of
TVC-CAD, by mid/late evening. Chance for showers/storms will
gradually expand eastward across northern MI during the night. Will
have likely pops only for a portion of eastern upper MI, centered on
midnight to early overnight. Elevated nature of convection, and
decreasing instability with time, will limit any svr threat this far
east. Better shear (0-6 km bulk shear of 30-40kt) is in eastern
upper MI overnight, displaced spatially and temporally from better
instability.

A warm and sticky night, with min temps near 60f to the mid 60s.
Some foggy spots are likely overnight, especially where it rains.

&&

.SHORT TERM...(Thursday through Friday)
Issued at 337 AM EDT Wed Sep 20 2017

...Weak Frontal Passage to provide a little rain Thursday...

High Impact Weather Potential...Minimal, as thunder threatens on
Thursday/Thursday night.

Pattern Synopsis/Forecast...Thursday morning around 12z, the cold
front looks to be about half way through the forecast area, and will
probably have a few showers around in the morning. However, during
the afternoon the sfc high has moved NE and the next sfc low pushes
the cold front north as a warm front. Both the ECMWF and the GFS,
not to mention the SREF kick off the rain showers and thunderstorms
over the state. The dirty ridge idea overnight that the GFS has been
advertising, the ECMWF now shows overnight as well. Friday looks to
be more precipitation free as the models continue to pump up the
ridge as the ECMWF was advertising over the last few days. This sets
us up for a drier weekend.

Primary Forecast concerns...This idea of a "dirty" ridge with the
moisture getting into it, and weak spokes of vorticity setting off
showers and thunderstorms, really is the question mark of the next
two days. While the Thursday looks more likely than Friday, the GFS
has shown little dots of qpf during Friday. Still think that the
ECMWF pumping up the ridge is the better idea, but based on the
evolution of the models over the Thursday/Friday time frame the last
few nights, won`t be surprised if isolated showers pop up on Friday.

.LONG TERM...(Friday night through Tuesday)
Issued at 337 AM EDT Wed Sep 20 2017

...Above Normal Temperatures and Relatively Precipitation Free
Through the Weekend...

Extended (Saturday through Tuesday)...I`m sounding like a broken
record as the GFS continues the look of a "dirty" ridge and the
ECMWF continues to keep the weekend dry as it pumps up the 500 mb
ridge. The ECMWF is still looking good into the early part of the
week and it seems that the GFS is beginning to latch onto the ECMWF
idea of Maria absorbing the remnants of Jose and going into Mid
Atlantic states helping to break down the ridge and allow the 500 mb
low in the N Plains begin to move east into the Upper Great Lakes.
So this will continue to pump up the heat in the Upper Great Lakes
into Tuesday (numbers still trending almost 10 to 15F above normal)
with little precipitation until probably Tuesday or maybe Wednesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 648 AM EDT Wed Sep 20 2017

IFR to LIFR stratus deck (and some associated fog) blankets
northern lower MI. This will tend to erode from w to e this
morning and early afternoon, taking longest at APN. All sites will
eventually become VFR this afternoon. Incoming cold front will
spawn some showers and a few thunderstorms tonight, as well as a
return to some lower cigs (especially toward dawn).

Light se to s surface winds today, becoming light/variable
tonight.

&&

.MARINE...
Issued at 337 AM EDT Wed Sep 20 2017

Current easterly winds will veer se today, and s tonight, ahead of
a cold front that will reach eastern upper MI and surrounding
waters late tonight. Front will stall and wash out Thursday,
leading to south winds continuing on Huron, with light/variable
winds elsewhere. Winds/waves will remain below advisory levels.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...NONE.
LM...NONE.
LS...NONE.
&&

$$

UPDATE...JZ
NEAR TERM...JZ
SHORT TERM...JL
LONG TERM...JL
AVIATION...JZ
MARINE...JZ



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