119
FXUS63 KDTX 161658
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1258 PM EDT Tue Jul 16 2024

.KEY MESSAGES...

* A slow moving cold front keeps scattered showers and non-severe
  thunderstorms in the forecast today mainly for areas north of I
  69. A few afternoon showers also possible Wednesday afternoon as a
  cooler airmass settles in.

* High pressure brings cooler and less humid weather into the region
  for the late week period.

&&

.AVIATION...

Weak cold front will slowly sink south through southeast through
this evening. Limited instability and moisture (dry mid levels) will
limit shower and any thunderstorm coverage. Best forcing/moisture
convergence looks to be across northern TAF sites this afternoon,
and have included showers, but low confidence with thunderstorms
developing. It remains possible for some shower/isolated
thunderstorm activity to reach southern tafs by early this evening
as well, but confidence not high enough to include in tafs.

Southwest winds briefly gusting in the 15-20 knot range
early this afternoon become lighter and shift to the northwest this
evening. Light northwest winds tonight into tomorrow will usher in
drier air in the low levels, but still expecting a SCT-BKN VFR cu up
during the day, with isolated showers also popping up.

For DTW/D21 Convection...Very low (<10 percent) chance for a pop up
thunderstorm late this afternoon into early evening.

DTW THRESHOLD PROBABILITIES...

* Low for ceilings aob 5000 ft this afternoon and tomorrow
  afternoon.

* Very low for a thunderstorm 20-3z.

&&

.PREV DISCUSSION...
Issued at 403 AM EDT Tue Jul 16 2024

DISCUSSION...

A secondary line of thunderstorm activity is currently settling east
southeastward across Northern Lower Michigan along a line from
Manistee to Alpena. This activity is anchored within a deep axis of
850-650mb thetae that is immediately ahead of an organizing synoptic
cold front. Plan view perspective of moisture fields suggest little
southward push of this thetae content this morning. Agreement
amongst CAM guidance with regional mosaic radar trends of slow storm
top movement suggests the activity will largely remain north of
Southeast Michigan early this morning.

A convective overturning of the air mass and subsidence in the wake
of this mornings MCS will contribute to strong static stability in
the 3.0 to 8.0 kft agl layer for areas south of I 69 through this
afternoon. System relative wind progs do support a broad and deep
cyclonic circulation/low pressure reflection tracking across far
southern Lower Michigan between 18-00Z this afternoon in response to
1000-500mb geopotential height falls. Warm advection redeveloping
ahead of this weak low will limit the active subsidence and at least
try to erode lower tropospheric CIN across the northern cwa
including the Tri Cities early this afternoon. MLCAPEs of up to 1500
J/kg will be available provided that updrafts will be able to bypass
some residual stability in the 4.0 to 5.0 kft agl level. To that
potential, consensus of CAMs suggest smaller updraft thunderstorm
activity develops north of M 46 in vicinity of Saginaw Bay after 19Z
this afternoon. Given the projected instability and 0-6km of 35-40
knots, an isolated severe thunderstorm will be possible along the
cold front mainly across the northern Thumb. The breadth of the low
circulation is expected to be great enough to shunt much of the rich
surface based instability recovery to the south of Lower Michigan
this afternoon. Southeast Michigan is designated as General
Thunderstorm in the SPC day 1 Outlook.

North flow and nocturnal cooling will help a cooler air mass to push
across all of the area tonight. The cold advection will jumpstart a
period of more comfortable weather that will continue at least
through the first half of the upcoming weekend. Will first need to
contend with the heart of the upper level trough and reservoir of
potential vorticity pushing into the area from the northwest
Wednesday afternoon. Much cooler midlevel temperatures and some
steepening of lapse rates will support shower activity and perhaps a
rumble of thunder during peak heating timeframe Wednesday afternoon.
Surface dewpoints remain in the lower 60s for another day on
Wednesday before a second night of northerly cold air advection
knocks the dewpoints into the 50s. Highlight for the end of the week
forecast is that daytime heat indices are expected to top out mainly
in the 70s with night time lows dipping into the lower to middle
50s. The night time lows will be some 10 to as much as 15 degrees
below normal for the time of year.

MARINE...

An organized thunderstorm complex continues to work across the area
over the next few hours before exiting into Ontario by mid-morning.
Pressure perturbations induced by this well-developed system may
produce a brief window of gusty winds even after precipitation has
ended this morning, and may necessitate a short-fused Small Craft
Advisory depending on observations. Meanwhile, a cold front has
drifted southeastward into northern lower Michigan and will serve as
a focus for a final round of shower and thunderstorm development
during peak heating this afternoon and evening. Once the front
clears to our south tonight, cooler northwest flow prevails. An
upper low trails behind the surface front, gaining influence for the
mid-week period and maintaining shower chances for Wednesday.
Canadian high pressure then fills in for the end of the week,
ushering in a quieter pattern into the weekend.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

AVIATION.....SF
DISCUSSION...CB
MARINE.......MV


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