Area Forecast Discussion
Issued by NWS Gaylord, MI

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000
FXUS63 KAPX 191803
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
203 PM EDT Tue Sep 19 2017

.UPDATE...
Issued at 1048 AM EDT Tue Sep 19 2017

Messy looking satellite imagery over northern Michigan this
morning with mid-high clouds streaming northeast (associated with
convection downstate) and increasing low stratocu coming off Lake
Huron in the developing moist easterly flow. Models are showing
the potential for stratocu to continue increasing off Lake Huron
through the day. Have tweaked cloud cover forecast up a little bit
to account for this, but will have to monitor trends into early
afternoon. Expect more sun closer to Lake Michigan and over eastern
Upper. Otherwise models have been trending away from the idea of
afternoon spotty showers developing across the southeastern
forecast area. Have largely removed PoPs from the forecast today,
except for a slight chance down near Saginaw Bay late this
afternoon. Only minor tweaks made to temperature grids to keep
areas east of I-75 a tad cooler due to increased cloud cover and
easterly flow.

&&

.NEAR TERM...(Today through Tonight)
Issued at 327 AM EDT Tue Sep 19 2017

...Small rain chances, mainly for northeast lower MI...

High impact weather potential...none.

High pressure was a bit ne of Superior early this morning. A
shortwave and attendant weak surface low was moving across central
IL, with an associated area of showers, leading edge of which has
reached southern Lake MI. A more subtle upper disturbance was
lifting across Superior, again with some associated showers in ne
WI and central upper MI. Northern MI is seeing increasing mid/high
clouds with these features, but abundant dry air is present below
700mb (per 00Z APX sounding). Though there are radar echoes over
eastern upper MI, surface obs show the lowest cloud bases above
10k ft (and, not surprisingly, no precip).

Expect showers to our north to lift ne-ward with time this morning,
along with the driving vort maxima. Not anticipating needing a
shower in the forecast past 12z, but maybe a stray sprinkle is
possible in western Chip/Mack before then.

Decaying wave of low pressure in IL/IN will dissipate today.
However, the warm front along which this low is found will slowly
move north toward southern lower MI by late tonight. This will be
aided by the slow-moving 500mb shortwave moving into se lower MI
tonight. Deformation north of this feature may result in mid-level
radar returns that persist long enough to get some raindrops to the
ground. This could edge up into southeast sections of the forecast
area this afternoon (HTL-W Branch and south), and make a touch more
northward progress tonight (up to Mio). These rain chances aren`t
high - mostly in the slight chance (20 pop) category - with only
southern Gladwin Co warranting anything higher.

The above also results in a considerable cloud cover gradient for
this afternoon and evening, when the back edge of thicker mid/high
clouds heads east to some degrees. Expect lots of cloud cover se of
an HTL-APN line, with relatively little cloud cover for eastern
upper MI on down to TVC. Thicker cloud cover will eventually back up
westward overnight.

Max temps in the 70s, coolest near Lk Huron. Min temps 50s to around
60.

&&

.SHORT TERM...(Wednesday through Thursday)
Issued at 327 AM EDT Tue Sep 19 2017

...How Long do We have Rain Chances?...

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

Pattern Synopsis/Forecast...Wednesday, the 500 mb ridge begins to
break down as a 500 mb shortwave trough begins to move into the
Upper Great Lakes. A weak cold front is also associated with this
feature. The ECMWF continues to keep the forecast area dry, while
the GFS produces some pop up showers during the afternoon. However,
the real action gets going in the evening as the front moves through
northern Michigan and produces showers and some thunderstorms.
Thursday morning the front runs out of energy, until the sun begins
to heat the region, so that by the afternoon, isolated showers and
thunderstorms pop up. Things look to settle down by Thursday
evening, but with the GFS "Dirty" ridge idea, there is a low chance
probability of shower and thunderstorms overnight.

Primary Forecast concerns...The dirty ridge idea that the GFS is
promoting is also being seen in the SREF plume diagrams with the
MUCAPE and MLCAPE continuing to remain above 1000 J/kg through
12z/Fri. The ECMWF seems to have the NAM on its side (at least from
the way that the 84 hr prog trends). So think that it will remain
dry, but that there will be a very small chance for some rain
showers as we start Friday.

.LONG TERM...(Thursday night through Monday)
Issued at 327 AM EDT Tue Sep 19 2017

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

Extended (Friday through Monday)...The models haven`t changed much
since last night`s runs, with the GFS idea being a "dirty" ridge
with the front in Lake Superior and little spokes of energy dropping
across E Upper and N lower on Friday and a little on Saturday before
the 500 mb ridge pumps up some more and pushes the boundary a little
more north and keeps the shortwave troughs out of the region,
through Monday morning. The ECMWF on the other hand, pumps up the
500 mb ridge and keeps all of the energy out of the forecast area
and the moisture, for that matter, as well. This keeps the
chances of precipitation to near zero through Monday morning. It
looks like Monday afternoon, the ridge breaks down as both Jose
and Maria begin to interact with one another and the 500 mb trough
in the west begins to make its move to the east pushing the front
through northern Michigan. The later periods will be greatly
influenced on the movements of what`s left of Jose and Hurricane
Maria. For the time being, I`m hedging toward the ECMWF.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 203 PM EDT Tue Sep 19 2017

As daytime heating gets into full swing, starting to see a general
decrease in cloud cover across northern MI early this afternoon
with pockets of MVFR stratocu lingering at APN. Low pressure
currently over NW Indiana will slowly lift northeast this evening,
bringing an increase in clouds tonight. Low stratocu looking
pretty likely overnight given strong model agreement and IFR to
LIFR cigs observed downstate this morning. Good chance for some
IFR fog, especially if we decouple enough for winds to become
calm. Slight chance for an isolated light shower overnight at APN,
but dry otherwise. Visibilities would improve shortly after
daybreak Wednesday, but low cigs will likely improve only slowly
through late morning. Winds stay light out of the southeast
through the period.

&&

.MARINE...
Issued at 327 AM EDT Tue Sep 19 2017

Easterly winds will occur today, behind high pressure departing
northern MI to the ne. These winds will veer se tonight, and
southerly by Wed night. Winds/waves are expected to remain below
advisory levels.


&&

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

$$

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



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