Area Forecast Discussion
Issued by NWS Gaylord, MI

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650
FXUS63 KAPX 182336
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
736 PM EDT Tue Jul 18 2017

.NEAR TERM...(Tonight through Wednesday)
Issued at 250 PM EDT Tue Jul 18 2017

...Shot for some rain tonight...

High impact weather potential...Nothing looks too significant.
Isolated thunderstorms with some brief heavy rain and gusty
winds possible tonight.

Pattern synopsis/forecast...Energetic northern Conus flow pattern
continues between elongated southern plains heat dome and
unseasonably intense/well organized mid level cyclone spinning north
of Hudson Bay. Upper level flow between these features only becomes
more organized with time, with robust H2 jet core expected to mature
over the northern plains and southern Canada tonight and Wednesday.
Down low response features a developing cold front just to our
northwest, with a secondary cold front dropping southeast through
central Canada. Rather respectable, but somewhat narrow, deep layer
moisture channel accompanying the lead front, and when combined with
some mid level support via passing shortwave trough and that
developing upper jet core, is driving the development of showers and
thunderstorms back across the Upper Mississippi Valley/northwest
Lakes.

Lead front will initially push slowly east into our area this
evening and overnight, looking to get a more definitive push south
on Wednesday as support from that secondary cold front arrives.
Combination of frontal forcing and increasing deep layer moisture
will bring at least a few showers/perhaps embedded storms across our
area this evening and tonight.

Primary forecast concerns/challenges...Temporal and spatial
resolution of overnight showers and embedded thunderstorms.
Thunderstorm intensity will also have to be addressed.

Details...Area of showers/thunderstorms to our west expected to
further congeal with time the remainder of this afternoon and early
evening as diurnal instability is maximized. Instability looks to
fall off substantially as this line approaches our area overnight,
with eastern upper standing the best chance to see some decent and
organized thunderstorm activity before this occurs, bringing perhaps
some brief periods of heavy rain along with them. Still appears any
severe threat, however, will remain upstream. Decaying band of
showers, and perhaps a rumble or two of thunder, will slowly advance
southeast across the area overnight, although still not convinced
just how much rain will be realized across much of northern lower
Michigan given expected weakening trend (likely both in intensity
and areal coverage).

As mentioned, front looks to get a bit of a kick south Wednesday
morning as high pressure builds into the northern Lakes. A few
showers expected along and south of this front during the morning.
Some question on just how fast overhead moisture axis departs, with
some hints it may take much of the day to do so for southern areas.
If so, enhanced low level convergence via lake breeze development
may be just enough to spark a few afternoon showers down near
Saginaw Bay. Otherwise, thinking Wednesday afternoon is a dry one,
and despite frontal passage, not much cool air to be had so expect
temperatures once again to make a run into the upper 70s through
middle 80s.

&&

.SHORT TERM...(Wednesday night through Friday)
Issued at 250 PM EDT Tue Jul 18 2017

...Showers and thunderstorms possible...

Nearly zonal flow aloft through the period with seasonable
temperatures. Upper level disturbances moving through the flow could
bring a round or two of showers and thunderstorms. The most
favorable location for any mesoscale convective complexes (MCSs) to
track is off to our south where there is better instability and
moisture. However with that being said, still can not rule out some
activity making it this far north. The best time periods for
possible convection are late Wednesday night into Thursday morning
and later in the day on Friday. Highs Thursday in the upper 70s to
lower 80s and Friday in the upper 70s to middle 80s. Will undercut
guidance a bit at night with lows in the 50s to lower 60s with
Wednesday night likely being the cooler of the two nights.

.LONG TERM...(Friday night through Tuesday)
Issued at 250 PM EDT Tue Jul 18 2017

Guidance continues to show a rather progressive zonal flow across
the conus in the extended...with a few shots of energy traversing
the Great Lakes in rapid progression, to bring a chance for some
showers/thunderstorms for the weekend. As opposed to previous
runs...indications are now that a system could threaten rain as
early as Saturday (particularly south of M32) and then into Sunday
(which was previously thought of as the most likely day for rain).
The GFS is diverging from the others to keep unsettled conditions
around for the second half of the period, although I am reluctant to
buy into this...preferring more the euro solution of a transient
Canadian high moving across the area on Monday and Tuesday.  Either
way, my gut says we`ll be in for more rain free stretches than what
the blended solutions (thus grids) indicate, but not with enough
confidence to go against said guidance with so much space between
now and then.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 715 PM EDT Tue Jul 18 2017

Thunderstorms are moving into the forecast area and will move
across the region tonight. PLN will be the first to feel the
impact with the thunderstorms reaching the TAF site between 00z
and 01z. Thunder will still be possible afterwards, but more
likely rain showers and then MVFR, and possibly IFR, cigs after
the cold front moves through there. That also seems to be the
scenario with all of the TAF sites tonight, the only difference
being timing. TVC and MBL will see the onset of thunder between
01z and 02z, and APN closer to 03z.

&&

.MARINE...
Issued at 250 PM EDT Tue Jul 18 2017

Southwest winds, at times a bit gusty, this afternoon and early
evening will slowly veer more west and northwest and decrease in
speed overnight as a cold front makes slow progress across the
area. Light northwest winds expected Wednesday, with winds become
light and variable Wednesday night. A few thunderstorms are
possible this evening and overnight. While these thunderstorms are
not expected to be particularly intense, any storms will be
capable of producing brief gusty winds and heavy rain.


&&

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

$$

NEAR TERM...MB
SHORT TERM...AS
LONG TERM...KB
AVIATION...JL
MARINE...MB



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