Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 220139
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
939 PM EDT Mon Aug 21 2017

.UPDATE...
Issued at 939 PM EDT Mon Aug 21 2017

Upstream cold front remains west of Michigan late this evening...
extending from near the arrowhead of Minnesota thru western Iowa
into Kansas. Plenty of warm/moist air streaming northward ahead of
this front continues to interact with a large axis of instability
to generate several areas of convection across the Western Great
Lakes and the Upper Mississippi Valley. Area of convection
quickly developed over the past hour or two across portions of
Northern Lower Michigan...featuring some thunder and heavy
rainfall. Marginal severe threat appears to be largely finished
with loss of instability in agreement with latest SPC Day 1
Outlook which now puts all of Michigan in only general thunder for
the remainder of the night. Latest short term models show this
initial wave of convection lifting off to our NE over the next
couple of hours... with a more widespread wave of precip
developing later tonight just head of the approaching cold front.

&&

.NEAR TERM...(Tonight through Tuesday)
Issued at 330 PM EDT Mon Aug 21 2017

Ill-defined and stalling cold front is draped across the Straits
region. This front connects with low pressure in Nebraska, which
will intensify as it lifts ne along the front. Intensification
will be most rapid over and downstream of northern MI, overnight
into Tuesday. This coincides with falling heights aloft, and the
eventual arrival of an upper trof Tuesday.

Diurnal heating was interrupted this afternoon by the eclipse
(temps fell by a few degrees in many locales), but has resumed.
Steamiest surface parcels are found from PLN to APN (with APN
81/69f), leading to MlCape values near 1500j/kg along that axis.
Earlier cu field here faded with the eclipse, but some mid-clouds
are approaching which indicate some weak mid-level forcing and
erosion of any capping. HRRR runs are becoming inconsistent as to
whether something can pop in ne lower MI this afternoon/early
evening. If it does, earlier discussions about favorable
shear/instability for supercells and svr wx remain valid. We are
seeing some cells cook off sw of CAD, which is not handled well by
the CAMs. There is certainly a nose of better instability (MlCape
just above 1k j/kg) poking into that region, but there is much
less in the way of shear down that way.

More widespread convective activity is still expected to break out
tonight, with the arrival of stronger forcing (to counter
decreasing instability). Last several runs of the HRRR show this
occurring in the 8-9pm range in nw lower MI, which would probably
be soon enough to support a strong/svr threat before instability
wanes too much. Will maintain an evening mention of strong/svr
storms in northern lower MI.

Very juicy airmass (PWATs around 1.75in) will support locally
heavy rainfall. This will become a bigger player overnight, as
forcing and precip coverage increases. 0.50-1.0 inch amounts
should be common, and locally higher amounts are anticipated.
Numerous to widespread pops in order for the overnight.

Showers will end from nw to se on Tuesday, as the low departs and
associated cold front swings thru. By mid-afternoon, only hanging
onto a slight chance of a shower for OSC/Tawas. We will be on the
breezy side from about late morning onward. Decreasing cloud
cover, though with enough diurnal heating and cool air aloft to
support a cu field (especially away from Lakes MI/Superior).

Min temps tonight quite mild, ranging thru the 60s. Max temps
Tuesday mainly in the 70s, some upper 60s near Superior.

&&

.SHORT TERM...(Tuesday night through Thursday)
Issued at 330 PM EDT Mon Aug 21 2017

...Much cooler weather for midweek...

High Impact Weather Potential:  Nothing.

Longwave pattern becomes more amplified for the midweek period as
deep fall-like trough digs into the Great Lakes and Northern CONUS.
Embedded shortwave energy rotating through the trough may bring some
light scattered precipitation to eastern areas Wednesday, otherwise
quiet weather.

Deep layer drying Tuesday night behind the front as much cooler air
sweeps into northern Michigan.  Early Wednesday, a well-defined
shortwave pinwheels around the stacked low now over Quebec, pushing
a secondary cold front and associated band of deeper moisture across
northern Michigan. A few scattered/light showers could result,
mainly over eastern Upper.  Otherwise, even cooler temperatures will
headline the midweek portion of the forecast with high temps ranging
from the low-mid 60s north to the upper 60s to 70 degrees
elsewhere...some 10 or so degrees below normal for the third week of
August.

Additional shortwave energy may pinwheel through the eastern lakes
on Thursday, possibly brushing Lake Huron areas with an isolated
shower.  Otherwise, large Canadian high pressure will slowly slide
southeast into the area resulting in lots of sunshine but still cool
temperatures.

.LONG TERM...(Thursday night through Monday)
Issued at 330 PM EDT Mon Aug 21 2017

High pressure will be over the Great Lakes region through Saturday
along with dry air, mostly clear skies, and rain free weather
through Saturday night. Sunday will see increased cloudiness and
rain chances throughout the day as an upper level area of low
pressure and surface reflection develops over the southern Great
Lakes with accompanying moisture. Rain chances will stick around
Monday as well as said area of low pressure remains over the
forecast area. Temperatures will only be around 70 Friday and warm a
bit the remainder of the period...in the low to mid 70s. Friday
morning has an opportunity to see some frost, with clear skies and
light winds...some mid to upper 30s are not out of the question for
our colder locales. The rest of the forecast period will see lows in
the mid 40s Saturday morning and warming to the mid 50s by Monday
morning.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 703 PM EDT Mon Aug 21 2017

Showers and thunderstorms will develop across Northern Michigan late
this evening and overnight ahead of an approaching cold front.
Conditions will deteriorate to MVFR/IFR...especially within
heavier showers and thunderstorms. Convection will continue into
Tuesday morning before cold FROPA brings precip chances to a close
Tuesday afternoon. Light southerly winds this evening will become
SW late tonight...eventually shifting to the W/NW on Tuesday and
strengthening to 15 to 25 kts in the wake of the cold front.

&&

.MARINE...
Issued at 330 PM EDT Mon Aug 21 2017

Light sw winds will persist for much of tonight, ahead of low
pressure that will intensify as it crosses northern MI late
tonight. Winds will veer nw behind the low, becoming quite gusty
Tuesday into Wednesday. Small craft advisories will be hoisted
for many waters shortly.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...NONE.
LM...SMALL CRAFT ADVISORY from 6 AM Tuesday to 6 PM EDT Wednesday for
     LMZ323-342-344>346.
LS...NONE.
&&

$$

UPDATE...MR
NEAR TERM...JZ
SHORT TERM...JK
LONG TERM...TL
AVIATION...MR
MARINE...JZ



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