Area Forecast Discussion
Issued by NWS Gaylord, MI

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595
FXUS63 KAPX 261403
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1003 AM EDT Tue Sep 26 2017

.UPDATE...
Issued at 1003 AM EDT Tue Sep 26 2017

Morning surface analysis reveals broad-ish low pressure across
Wisconsin and stalled front resting across far NW Wisconsin down
into the southern plains...and arcing northeastward through the
U.P. into Ontario. Upstream short wave trough has become a bit
more progressive with a couple vorticity centers pinwheeling
around each other northeastward through the Dakotas. Short wave
trough will swing up across the far northern lakes region and
finally kick the cold front through the western Great Lakes later
this afternoon and especially tonight...bringing an end to our
September heat wave.

As discussed by overnight forecaster...despite the impending
abrupt change in airmass...overall shower/thunderstorm chances
with FROPA don`t appear that impressive. Morning upper air
charts/regional soundings reveal a pocket of drier low-mid level
air across the region...a PWAT value under an inch on the 12Z APX
sounding/rapid drying just off the surface and a fairly capped
environment. A bit better low-mid level moisture is just upstream
ahead of the front and guidance continues to suggest a narrow
corridor of moisture/conditional instability on the order of a
few to several hundred J/KG MUCAPE pooling right ahead of the
front late this afternoon and this evening. Might see a few
showers bubble up late this afternoon mainly west of I-75 as low
level moisture begins to increase. But best chances will probably
be with FROPA and mainly this evening.

Severe weather chances...ambient wind fields do increase ahead of
the front with mid level flow ramping up close to 50 knots before
FROPA. But given the anticipated lackluster instability and only
modest forcing with the front...severe weather threat still
appears low.

&&

.NEAR TERM...(Today through Tonight)
Issued at 332 AM EDT Tue Sep 26 2017

...One final hot day...

High impact weather potential...few non-severe t-storms this
afternoon and tonight.

All good things must come to an end. One last, final, this-is-it
toasty day is ahead before autumn asserts itself. Upstream, stalled
front is lying across nw IL/eastern WI/central upper MI (just
east of ESC-Munising). This front will finally get kicked across
northern MI, as the upper ridge gets suppressed by a 500mb trof
passing just north of Superior this evening. Fropa timing will be
this evening. Temp and precip trends are the main concern.

One would think that, with such unseasonably warm air in place, and
a favorable evening fropa, we could potentially see some interesting
wx. One would be incorrect. Moisture is our primary limiting factor;
our airmass is warm but not terribly moist. 00z APX observed pwat
was only 1.03 inches (unimpressive for an airmass this warm), with
relatively dry air below 500mb except at the top of the mixed layer.
We do not see a substantial influx of moisture before fropa, though
there will still be a tendency toward pooling in the weakly
convergent zone just ahead of and along the front. Still, as
mixing deepens during the day today, we will be mixing down drier
air. Models are generally not enthusiastic about precip at all,
with chance to slight chance pops from guidance, and the GFS
looking a touch wetter than the Nam. Rap doesn`t have more than a
few showers during the daylight hours today.

So for today, we could see a few showers/perhaps a t-storm cook off
this afternoon in parts of both peninsulas. Highest pops (such as
they are) will be in western Chip/Mack Cos, and from CAD to GLR in
northern lower. MlCape values might reach 500j/kg, so difficult to
be enthusiastic about thunder chances at all, let alone anything
strong.

Somewhat higher pops tonight with fropa, though again nothing to get
terribly excited about. Narrow plume of somewhat higher
instability (MuCapes to 750j/kg) will cross the region from w to e
before 06Z, though that instability will be waning with time.
Limited instability, unimpressive forcing, and increasingly
elevated nature of convection will limit potential for strong/svr
storms. Best moisture in a relative sense is post-frontal, with a
several- hour window of near saturation up to 700mb (before moist
layer thins out very late). This will support plenty of clouds and
still some spotty showers post-fropa overnight.

Max temps today in the 80s to around 90f. All record highs are once
again threatened to some degree. Min temps tonight will be much
cooler, 50s in most places, closer to 60f near Saginaw Bay.

&&

.SHORT TERM...(Wednesday through Thursday)
Issued at 332 AM EDT Tue Sep 26 2017

...Much cooler temperatures for middle to late this week...

High Impact Weather Potential: Minimal.

Pattern Forecast: Ever so slowly flattening mid-upper level ridge
that brought us our late season heat over the past week will press
well off to our east this evening, followed by a mid level wave and
attendant surface low tracking across southern Ontario tonight. By
Wednesday morning, corresponding potent cold front tied to
aforementioned low pressure is expected to have cleared the forecast
area with lowering heights aloft and broad northwesterly flow
helping to usher in temperatures some 20-30 degrees cooler than this
past weekend. Broad upper troughing then remains in place through
the end of the work week with a secondary wave ushering in a
reinforcing cool shot of air aloft, along with the threat for
showers during the Thursday evening through Friday time frame.

Primary Forecast Concerns/Challenges: Significantly cooler
temperatures and the threat for scattered showers arriving late in
the day Thursday across some areas.

Aside from a lingering isolated shower or two across eastern Upper
early Wednesday morning, little in way of sensible weather is
anticipated for the remainder of the day. Certainly the headline
will be the cooler temperatures as highs struggle to reach the mid-
60s for most (a bit warmer across the southeastern CWA). Morning
clouds are expected to gradually thin, giving way to partly sunny
skies as weak surface ridging noses into the area as a result of
high pressure centered across the central plains.

A mostly sunny and cool start to the day Thursday gives way to
increasing cloudiness across eastern Upper/Tip of the Mitt and
eventually elsewhere Thursday evening as another shortwave
approaches the area from the northwest. This wave will usher in a
reinforcing shot of cool air with the coolest days of the week
expected to follow (Friday-Saturday). The combination of increased
mid level support and lake processes beginning to ramp up (delta T`s
of 15-18 C) may bring the possibility of a few showers to sections
of eastern Upper and northwest Lower as early as late Thursday
afternoon/evening with a greater threat for shower activity Thursday
night and early Friday.

.LONG TERM...(Thursday night through Monday)
Issued at 324 AM EDT Tue Sep 26 2017

High impact weather potential: Minimal.

The coolest temps (below normal) of the week are expected Friday and
Saturday as high temps struggle to reach the upper 50s to low 60s.
Lows in the 30s across inland locations may even promote a bit of
patchy frost both nights. Increased mid level support and lake
processes mentioned above should allow for shower activity to be
commonplace, most numerous across eastern Upper and northwest Lower
late Thursday night through early Friday morning. However, precip
chances begin to gradually wane by midday Friday as mid level
ridging and attendant surface high pressure impede on the region
from the west. Thus, mainly dry conditions are expected this weekend
with high temps gradually climbing a few degrees each day...
returning to near normal by the end of the weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 646 AM EDT Tue Sep 26 2017

Fog departing this morning. MVFR cigs possible tonight.

A stalled cold front just w of lower MI will finally get pushed
east this evening. Patchy morning fog will erode soon after
sunrise. Some showers and perhaps a t-storm could get kicked off
ahead of and with the front. Lower (mainly MVFR) cigs are
expected behind the front late tonight.

Sw winds today will veer nw by late tonight.


&&

.MARINE...
Issued at 324 AM EDT Tue Sep 26 2017

Fairly light southerly winds will be seen today, ahead of a cold
front that will finally cross the region this evening. Gusty w to
nw winds will arrive behind that front. Small craft advisories
will be needed on most waters as soon as very late tonight,
continuing into Wednesday.


&&

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

$$

UPDATE...BA
NEAR TERM...JZ
SHORT TERM...MG
LONG TERM...MG
AVIATION...JZ
MARINE...JZ



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