National Weather Service United States Department of Commerce


000
FXUS63 KDTX 290759
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
359 AM EDT Tue Sep 29 2020

.DISCUSSION...

High amplitude troughing now entrenched throughout the central U.S.
will take an increasing hold of local conditions this forecast
period. Southeast Michigan will maintain a position within the
immediately downstream flank of the mean trough axis today, leaving
low to mid level southwest flow to govern conditions during the
daylight period. Resident thermal profile generally characterized as
seasonable by late September standards - little noted thermal
advection and prospects for some peaks of sun affording modest
diurnal temperature recovery. Highs generally mid 60s. An area of
convergence will emerge late today, as the pressure gradient
responds to height falls associated with the inbound trough axis.
Moisture quality likely proves too limited to support a greater
response, but the underlying ascent within a steep lapse rate
environment held during peak heating may support a few showers from
the Flint area northward into the Saginaw Valley/northern thumb late
afternoon and evening.

Upper trough axis pivots into the area tonight, the eastward
movement aided by strong shortwave energy now noted over western
Quebec digging southeast into the existing height fall center. The
combination of increasing cva and deeper layer, albeit modest cold
air advection will maintain the chance for shower production this
period, primarily M-59 corridor northward. A deeper layer of cold,
moist cyclonic flow derived from the resident upper trough axis will
then define conditions Wednesday. This steep lapse rate environment
will yield the usual higher coverage of stratocumulus, while
maintaining the potential for periodic shower development. Greatest
window for rainfall will exist from mid afternoon into the evening
hours, focused within another period of stronger cold air advection
and an accompanying increase in downstream moisture flux off lake
Michigan as overlake instability grows. A scattered to numerous
coverage of showers likely during this time. The strongest updrafts
may offer a few instances of lightning, small hail and gusty winds
given the magnitude of lapse rates, suppressed freezing levels and a
very dry sub-cloud layer.

A similarly unsettled environment will exist Thursday, as a period
of even stronger cold air advection arrives during the back half of
daytime heating. The underlying deep layer ascent and overall
thermodynamic profile again points to a scattered to numerous
coverage of late day showers. Highs Thursday struggling to climb out
of the 50s. Prolonged period of cold air advection as deeper
northwest flow takes hold continues into Thursday night, allowing 850
mb temperatures to near the freezing mark by Friday morning.

Conditions Friday into the upcoming weekend remain governed by high
amplitude troughing. Stretch of well below normal temperatures
entrenched during this period - daytime highs solidly in the 50s.
Coldest conditions likely noted Saturday morning as high pressure
slips across the region, allowing lows to dip well into the 30s most
locations.

&&

.MARINE...

Low pressure departed the Great Lakes this morning, lifting north
toward James Bay today. A tightened pressure gradient remains in
place for the next few days as broad upper level troughing begins to
take hold of the region. Winds will remain out of the west to
southwest in the 15 to 20 kt range through the midweek period. Today
should be mostly dry, but periodic showers returns to the lakes on
Wednesday as another cold front pushes in. A much cooler air mass
filtering in for the late week will bring a chance for waterspouts,
especially over Lake Huron.

&&

.PREV DISCUSSION...
Issued at 1210 AM EDT Tue Sep 29 2020

AVIATION...

Model soundings show subsidence down into the 3.5 kft agl layer that
corresponds with dry slot. Given satellite trends scaled way back on
the clouds/cigs overnight. Daytime heating will lead to
stratocumulus increase by the late morning. A well organized
convergence axis is expected to push into the Saginaw Valley Tuesday
afternoon which could result into shower development. Decided to go
with a TEMPO group for showers at KFNT/KMBS 20-23Z.

DTW THRESHOLD PROBABILITIES...

* High for cigs less than 5000 ft agl.


&&

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

$$

DISCUSSION...MR
MARINE.......TF
AVIATION.....DRK


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