Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 171939

Area Forecast Discussion
National Weather Service Gaylord MI
339 PM EDT Wed May 17 2017

.NEAR TERM...(Tonight through Thursday)
Issued at 338 PM EDT Wed May 17 2017

...Showers and storms possible tonight...

High impact weather potential...Thunderstorms will be possible
tonight across northern Michigan. A storm or two could become severe
with small hail and gusty winds.

Pattern Synopsis/Forecast...A vertically-stacked potent system out
over the Plains will lift into the Upper Midwest this evening,
reaching the Upper Great Lakes Thursday morning. This system will
generate a few rounds of showers and thunderstorms tonight into
Thursday as it makes steady progress to the northeast. The first
round has already blossomed across western WI in an area of strong
upper divergence and instability. Short-term hi-res model guidance
has done a decent job handling this initial round and continue to
show it skirting western Chippewa/Mackinac counties through the
evening. A second round tied to strong DPVA is developing out over
Iowa and is expected to track northeast into northern Michigan
overnight. Finally, the low itself tracking through the UP Thursday
morning will generate additional showers and storms.

For the APX CWA in particular, eastern Upper will generally be
grazed by the bulk of the shower/storm activity passing through
central Upper this evening. Instability looks marginal (less than
1000 J/kg of SBCAPE) with a continued capping inversion aloft.
However, 40-50 knots of 0-6km shear will be in place as a modest LLJ
noses into northern MI. This may be enough to support a few better
organized storms through this evening, and SPC continues to include
our far western CWA in a marginal risk. Small hail and some isolated
gusty winds would be the main threat, but does not look to be a
significant event for us by any means.

The second round of activity passing through the region overnight
will likely have a better chance of impacting northern Lower, though
it will probably be on a weakening trend as it approaches the
western CWA after midnight. The best chance for more "widespread"
(using that term loosely since shower/storm coverage just doesn`t
look that impressive for northern MI) rain will come as the core of
the system passes through on Thursday. By then, instability will be
rapidly declining as a cold front approaches, so expecting mainly
showers. That front will push east through the area by late
afternoon with strong CAA behind it ushering in a much drier and
significantly colder airmass.

Tonight looks to be another mild night over northern Lower with
dewpoints stuck in the mid to upper 50s. Lows will range from the
50s over eastern Upper to low 60s over most of northern Lower. SW
winds will stay breezy overnight over northern Lower, but eastern
Upper could see a bit of patchy fog development. Thursday`s highs
will occur earlier in the day, especially across the western CWA due
to the cold front passing through. Highs will range from the 50s to
low 60s across eastern Upper to 60s/70s across northern Lower
(increasing from west to east).


.SHORT TERM...(Thursday night through Saturday)
Issued at 338 PM EDT Wed May 17 2017

...Return of more seasonal temperatures...

High Impact Weather Potential: Will need to monitor some frost
potential Thursday night.

Pattern Synopsis/Forecast: Amplified pattern of late set to continue
through the mid period of the forecast (and likely beyond) as strong
shortwave currently diving southeast through the Intermountain West
simply reinforces western trough. Downstream response will be as one
would expect, with building mid and upper level ridging up and
through our area into the start of the weekend. Very much like its
predecessor, Intermountain West wave eventually ejects out into the
Central Plains (likely drumming up another significant severe
weather outbreak in the process), with it eyes set on the Northern
Mississippi Valley region by early Sunday morning. This system will
drive another surge of deep layer moisture into the Western Lakes,
bringing additional shower and thunderstorm chances to our area this

Primary forecast concerns/challenges: Cloud and temperature trends
through the period. Addressing that increasing shower potential on

Details: Current system will be exiting stage right early Thursday
evening, taking any lingering showers along with it. Return of that
mid level ridging and an expansion of its surface likeness into the
Northern Lakes will bring clearing skies overnight Thursday into
Friday. Post system cold air advection and those clearing skies does
set the stage for some rather chilly temperatures by early Friday
morning. Widespread lows Thursday night in the mid and upper 30s
look easily attainable northwest of Saginaw Bay, with perhaps some
lower 30s north of the big bridge. If winds can completely decouple,
we may see readings even a touch cooler than currently anticipated.
This cooler airmass hangs through Friday and Friday night, although
plenty of sun on Friday will do its best to modify the environment.
Increasing high clouds should temper the temperature fall-off some
Friday night, but once again may be dealing with some patchy frost
in those traditional ice box locations.

Current trends support a dry start to Saturday as top-down
saturation is slow to complete ahead of the next vigorous shortwave.
Just how fast this saturation becomes complete is still a source of
guidance contention. Slow is usually better with such an amplified
pattern, with initial collocation of deepest moisture and forcing
remaining just to our southwest. Given uncertainty, will need to
carry at least some Saturday afternoon shower wording, with still
plenty of time to work on the finer timing details in the coming
days. Increasingly gusty southeast winds will help usher in a touch
milder airmass, with temperatures returning to more normal levels.


.LONG TERM...(Saturday night through Wednesday)
Issued at 338 PM EDT Wed May 17 2017

High impact weather potential: There is a slight chance of
thunderstorms across a portion of northeast Lower Michigan Saturday

Fairly active pattern setting up for the extended period of the
forecast. At the start of the period, low pressure is progged to be
moving through the Midwest accompanied by rain/thunderstorm chances
Saturday night into early Sunday. Brief reprieve to end the weekend
into the start of next week before another system dives southward
out of Canada into the plains and eventually Great Lakes region
during the Tuesday-Wednesday timeframe.

Temperatures a couple degrees above normal Sunday fall back to near
to slightly below normal readings for days 5-7.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 200 PM EDT Wed May 17 2017

Breezy, dry, VFR conditions expected to continue at the TAF sites
the rest of this afternoon with showers staying mainly over
eastern Upper Michigan. Shower and thunderstorm chances will
increase this evening and overnight as the system out over the
Plains lifts into the Upper Midwest. Confidence in time of arrival
of the showers/storms at a given terminal is rather low. Although
widespread rain is not expected, the extent of coverage is also
still somewhat uncertain. The arrival of stronger winds aloft will
lead to some LLWS overnight. Some showers will still be found
across northern Lower MI Thursday morning, with MVFR ceilings and
breezy SW winds arriving mid to late morning.


Issued at 350 AM EDT Wed May 17 2017

...Small craft advisory conditions through Thursday night...

Breezy SW flow will be felt on the Great Lakes today with small
craft advisory gusts and waves on a good portion of Lakes Michigan
and Huron. Winds veer into the west and eventually NW through the
day Thursday as a strong cold front passes through the region.
Gusty winds persist behind the front into Thursday
night...diminishing heading into Friday.


LM...SMALL CRAFT ADVISORY until 6 AM EDT Thursday for LMZ323-344>346.
     SMALL CRAFT ADVISORY until 6 PM EDT this evening for LMZ341-342.


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