Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 230423
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1223 AM EDT Wed Aug 23 2017

.AVIATION...

Mostly clear skies and light winds expected to hold for the rest of
the night, but continued cold advection and steepening low level
lapse rates post sunrise expected to allow for a good VFR (possible
brief MVFR in late morning) CU up in clouds spreading from north to
south, with even isolated showers popping up during the afternoon,
mainly over the thumb region. Westerly winds increasing to around 15
knots by afternoon with diurnal mixing.

//DTW THRESHOLD PROBABILITIES...

* Low for cig aob 5000 feet this afternoon

&&

.PREV DISCUSSION...
Issued at 310 PM EDT Tue Aug 22 2017

DISCUSSION...

The surface cold front now sliding across Se Mi will exit east of
the forecast area between 21 and 23Z. This front has provided the
focus for a line of showers. Despite warming temps under afternoon
heating, ongoing low level dry air advection is limiting
instability, which in turn will limit chances for thunder out these
showers. Some of these showers will however be capable of producing
a quick burst of gusty winds, possibly over 40 MPH.

Ongoing deepening of the surface low over ern Quebec is associated
with a deepening upper low rotating across nrn Ontario. This upper
low will track into nrn Quebec on Wednesday, leaving a broad region
of low level cyclonic flow across the Great Lakes region. Low to mid
level west-northwest flow will result in persistent cold air
advection, beginning with the passage of the cold front this evening
and persisting into the day Thursday. The degree of deep layer post
frontal drying will support a good deal of clearing tonight. The
gradient flow will suppress the degree of nocturnal cooling, holding
min temps in the 50s. There will be enough moisture to cause an
expansion of diurnally driven strato cu on Wednesday given the cool
mid level temps (850mb temps in the high single digits). Model
soundings suggest convective cloud depths may be enough to support
some brief sprinkles or a light shower. Despite the cool air aloft,
mixing depths up toward 6k feet will support daytime highs on Wed in
the 70s.

The North American water vapor loop shows a mid level short wave
impulse over NW Saskatchewan. Model solutions indicate this feature
will rotate into the Great Lakes Wed night into Thursday, leading to
an amplification in the long wave trough across ern Canada/Great
Lakes.  There is general agreement that this wave will force a
secondary surge in cold air across the southern Great Lakes on
Thursday (850mb temps drop to +4 to +6 C). With some potential
northerly flow off Lake Huron, where the 0-1km theta e profile
suggests ample over-lake instability, some lake effect rain showers
will be possible across the thumb region. The expected cloud cover
with the added lake moisture will limit mixing depths, supporting
high temps only in the 60s. The magnitude of the cold air will also
warrant min temps down into the 40s (outside of urban Detroit) both
Wed night and Thurs night.

High pressure will remain in control over the Great Lakes region
through the weekend keeping dry, pleasant conditions in place.
Temperatures will remain slightly below average through the weekend
with highs in the low to mid 70s and lows in the upper 40s to mid
50s. A gradual moderation in temperatures will occur through early
next week with highs approaching 80 by Monday as ridging slowly
builds into the region. A wave tracking into the Western Great Lakes
early next week will bring the next low chance for showers to SE
Michigan on Monday.

MARINE...

Northwesterly gusts to marginal gales will continue through tonight
over the northern half of Lake Huron as colder air spreads across
the waters. Gusts to near-gales are forecast elsewhere and will
persist through Wednesday...especially over the open waters.The
fetch will build the highest waves east of the International Border
with maximum wave heights topping out between 12 and 14 feet in
favored areas of the American Waters. The influx of colder air will
make waterspouts likely over all marine zones today through
Thursday. The gradient will diminish considerably Wednesday night
supporting moderate north or northwesterlies for the remainder of
the week.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

Lake Huron...Gale Warning until 5 AM EDT early this morning for LHZ361-362.

     Small Craft Advisory until 5 AM EDT early this morning for LHZ421-
     441.

Lake St Clair...NONE.

Michigan waters of Lake Erie...NONE.

&&

$$

AVIATION.....BT
DISCUSSION...SC/JD
MARINE.......JVC


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