867
FXUS63 KDTX 110420
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1220 AM EDT Thu Jul 11 2024

.KEY MESSAGES...

- Scattered showers and thunderstorms develop during the afternoon
  both today and Friday.

- A period of above average temperatures begins this weekend into
  early next week.

&&

.AVIATION...

The back edge of lower clouds are clearing Michigan to the east
leaving mostly clear skies during the overnight. The abundant surface
moisture and clearing skies brings potential for patchy fog to
develop early tonight. However, the limiting factor will be the winds
which should stay slightly elevated to around 5 knots out of the
northwest. Will introduce a minor drop in VSBY at TAF sites as some
sites across Michigan are already experiencing lower VSBYs. Early
morning trends will be monitored and will maintain VFR conditions for
now. Any patchy fog will lift with the sunrise as winds hold out of
the northwest through this morning and afternoon. Good surface
moisture will support a low VFR to possible MVFR diurnal cumulus
field this afternoon. Scattered showers and thunderstorms are also
late this afternoon, with the greater chances towards MBS. Winds
will become southwesterly during the evening will staying mostly
below 10 knots.

For DTW/D21 Convection...Scattered thunderstorms will be possible
this afternoon, but current thinking is that that best chances will
hold west and north of DTW.

DTW THRESHOLD PROBABILITIES...

* Low for ceiling aob 5kft through early morning. Moderate this
  afternoon.

* Low for thunderstorms this afternoon.

&&

.PREV DISCUSSION...
Issued at 405 PM EDT Wed Jul 10 2024

DISCUSSION...

Mid afternoon observations and model analysis fields indicate near
surface based convection in the Detroit metro area has exited into
Ontario with the surface low remains of Beryl. That leaves the bulk
of deformation forcing to occur across the Thumb region for the
remainder of this event. Radar derived rainfall estimates and
surface reports show the heaviest rain has fallen along and west of
a line from Ann Arbor to Pontiac to Lapeer, including the Flint
metro area where cumulative rainfall from yesterday and today has
led to pockets of residential flooding. The Tri Cities and Thumb
regions meanwhile have been largely spared from excessive rainfall
with reports generally less than 1 inch since midnight. Model
consensus QPF that is now primarily east of the Tri Cities allows
cancellation of the Flood Watch there while continuing for the Thumb
region for up to 1 inch of additional rainfall through 8 PM.

Northerly wind gusting in the 30 mph range is the first sign of the
surface low associated with Beryl exiting into Ontario during late
afternoon and this evening. The other is showers gradually
diminishing around the western fringe of the system`s moisture field
while surface based convection holds across northern and western
Lower MI. Beryl moisture strips away later tonight, especially after
midnight, leaving just low clouds in place despite northerly wind
bringing in a cooler and less humid air mass into Thursday morning.

A smaller scale mid level circulation over the Midwest this
afternoon has northern stream origins from central Canada. It is
unrelated to Beryl but follows closely behind across the Great Lakes
during Thursday until nearly stalling overhead Thursday night into
Friday. This system has a cold core scattered convective appearance
in observations today which projects well to hold into Lower MI
Thursday afternoon and evening. Peak daytime instability generates
surface based CAPE across Lower MI but is projected to remain below
1000 J/kg in the 12Z HREF run, in line with the general thunder
convective outlook. Storm intensity diminishes to showers Thursday
evening and then coverage becomes isolated after midnight under the
lingering mid level circulation. Trends in today`s 12Z model package
slows the exit of this system into Friday afternoon requiring at
least an isolated shower/storm mention in the forecast.

Global/extended model runs offer mostly zonal solutions on the
larger scale mid to upper level flow pattern this weekend. The zonal
flow keeps predictability on the low side for shower/storm activity
but with a steady warming trend indicated in the data through
Sunday.

MARINE...

Post-Tropical Cyclone Beryl (or the remnants thereof) stream through
the central Great Lakes this evening fueling additional gusty
showers as the low tracks across the Ontario Peninsula. An uptick in
gradient wind is underway given the vicinity of the low pressure
center and strengthening of the surface pressure gradient.
Expectation for evening winds features a backing trend with time
while gustiness increases due to slightly steeper low-level lapse
rates augmented by the approach of a strong cyclonic lower column
wind field. Latest observations suggest additional isolated gusts to
gales may persist across portions of the Lake Huron nearshores, but
the general infrequency precludes an upgrade to Gale Warnings. Gusts
to around 30 knots will be more representative of prevailing
conditions through the evening hours. Further south, gradient winds
veer toward the northwest across Lake St. Clair and Lake Erie
producing Small Craft Advisory winds this evening, therefore the
current headlines will remain in effect. Winds decrease steadily
late tonight and into Thursday with northwest flow becoming weaker
and westerly by the afternoon hours. High pressure attempts to build
into the region Thursday and Friday while weak troughing may produce
some additional showers. Winds/waves hold below criteria through
Saturday and probably through the weekend time-frame.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 10 AM EDT this morning for LHZ421-422.

     Small Craft Advisory until 4 PM EDT this afternoon for LHZ441>443.

Lake St Clair...Small Craft Advisory until 10 AM EDT this morning for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 10 AM EDT this morning for LEZ444.

&&

$$

AVIATION.....AA
DISCUSSION...BT
MARINE.......KGK


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.