FXUS63 KDTX 250803
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
403 AM EDT Sun Aug 25 2019
The west flank of surface high pressure remains over the central
Great Lakes and is set to provide a nice finish to the weekend
across SE Michigan. Expect conditions similar to Saturday with a
cool start across the region and some marine induced clouds during
the morning, only this time stratocu from Lake Erie instead of
Huron. This is followed by a transition to scattered fair weather
cumulus and nearly full late summer surface heating that helps lift
high temperatures into the mid 70s to near 80. These readings are a
few degrees warmer as the core of the cool high pressure air mass
An increase in high clouds tonight is the first sign of changes
ramping up for the early week period. Larger scale features are
progressing as expected from the Canadian Rockies into the southern
Plains where the lead upper level circulation is first to interact
with the surface front that has been stalled near the Gulf coast.
This system begins drawing Gulf moisture northward tonight while
phasing with the deepening upper trough over central Canada. These
upper level systems combine to enhance moisture transport into the
central Great Lakes during Monday to the extent that likely POPs
become warranted across SE Michigan by Monday evening. Model theta-e
depictions are in good agreement with the maintenance of a sharp
moisture gradient in the 850-700 mb layer suggesting elevated
portions of the front maintain integrity. The moisture axis matures
overhead as 700 mb dewpoint reaches around 5C and PW approaches 2
inches. This coincides with just enough elevated instability for a
chance of thunderstorms to go along with scattered to numerous
showers through about midnight.
A subtle dry slot follows for late Monday night which could reduce
coverage or produce a transition to drizzle before the cold front
moves in from the Midwest during Tuesday. The GFS and ECMWF are in
reasonable agreement with mid afternoon timing of the frontal
passage. GFS projections of MUCAPE around 1500 J/kg and MLCAPE less
than 1000 J/kg suggest a cloud laden moisture axis ahead of the
front as a limiting factor for instability. On the other hand, the
modest instability could be compensated for by strong forcing and a
favorable wind profile associated with the large low pressure system
spanning central Canada and the Midwest. Expectations lean toward at
least some convective organization with scattered to numerous
coverage before the front exits SE Michigan by Tuesday evening.
The rest of the mid week period turns breezy, slightly cooler and
less humid after the cold front through Wednesday. The unseasonably
strong low pressure system lingers over northern Ontario and fills
through Thursday with the bulk of any cold core showers located over
the northern Great Lakes.
High pressure will hold over the eastern Lakes one more day while
continuing to drift eastward toward the Canadian Maritime. This will
lead to a weak easterly wind field primarily below 15 knots. The
next trough currently over the central Plains will move into the
western Great Lakes on Monday. This will tighten the pressure
gradient in between the two systems bringing an increase to the
winds as they veer more southerly. Southeast winds around 15 to 20
knots with gusts of 25-30 knots will be possible and may require
Small Craft Advisories along the Lake Huron shoreline. This system
will bring the next chance for showers and thunderstorms during the
later half of Monday into Tuesday.
Issued at 1158 PM EDT Sat Aug 24 2019
Surface high pressure centered to the northeast of area will provide
VFR conditions this forecast period with just few-sct diurnal cu on
Sunday and some degree of cirrus arcing into the area around outer
portions of circulation associated with shortwave over the central
plains. Northeast flow will veer to southeast on Sunday as the
center of high pressure continues east into Quebec and return flow
around its western periphery begins.
DTW THRESHOLD PROBABILITIES...
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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