Expert Forecast Opinion

038
FXUS63 KDTX 030826
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
426 AM EDT Thu Apr 3 2025

.KEY MESSAGES...

- Breezy today with gusts of 35 to 40 mph; briefly approaching 45
mph in the Thumb.

- The next round of widespread rain arrives Friday night into
Saturday. This rain may be heavy across the south with a 50%
probability for over 1 inch of rainfall.

- Cooler conditions ensue early next week with an opportunity for
some rain/snow showers Monday before high pressure settles in mid-
week.

&&

.DISCUSSION...

The strong upper low responsible for the active weather over the
past 24 hours is lifting north of Lake Superior into Ontario early
this morning. The bulk of the rainfall has moved off to the east
with SE MI currently residing in the warm sector with temps well
into the 60s for most locations. The cold front, marked by a narrow
line of convective showers along it, is positioned roughly from
Midland to Marshall and will track eastward through the area early
this morning. The dry slot follows, bringing a quick end to shower
chances. Broad synoptic subsidence brings welcome relief from the
rain as well as some afternoon sunshine today.

Our position in the crosshairs between the Ontario low and a ridge
off the coast of the Atlantic holds a strong pressure gradient
across the Great Lakes which will maintain gusty southwest winds
through the day. Soundings show the cold advection allowing mixing
up to the 900-850mb level where 40 to 45 kt flow will exist. This
produces gusts to the surface of 35 to 40 mph with a peak midday.
Slightly deeper mixing will be possible across parts of the northern
Thumb where gusts of 45 mph may occur for a brief period - latest
HREF guidance shows a 40% of this mainly between 9am and 2pm.
Overall, the trend in gust magnitude over recent hi-res model runs
has been decreasing so opted not to issue a Wind Advisory there
today. Temps will hold rather mild with highs in the 50s to lower
60s which then crash into the 30s and 40s tonight as the cold
advection takes greater hold. High pressure builds in Friday to
provide more tranquil weather.

A jet streak and shortwave emanating from a deep trough over the
Four Corners will ride in from the southwest Friday night, causing
the stalled frontal boundary over the Ohio Valley to lift northward
toward the southern Great Lakes. Model consensus shows the surface
frontal wave taking a track northeastward near or just south of the
MI/OH border and into Lake Erie by Saturday morning. This will
advect in a slug of Gulf moisture back into the vicinity with PWATs
creeping back up to around 1.25" - near the 99.5th climatological
percentile. Deformation forcing on the northwest side of the frontal
low and a convective component may result in some heavier rainfall
rates. However, there is still a relatively high amount of
north/south spread among guidance which will affect where the axis
of 1 to 2 inch rainfall totals ultimately set up. If confidence
increases on this axis affecting Southeast MI another Flood Watch
may be needed Friday night. Highest confidence in this potential
will be south of Metro Detroit where LREF ensemble guidance shows a
50 to 60% probability to exceed 1 inch by midday Saturday. The
frontal boundary maintains close proximity across the Ohio Valley
into the eastern Great Lakes through Sunday with low confidence in
whether additional waves riding along it will be able to produce
more rainfall as far north and west as SE MI.

A compact and potent upper shortwave will pivot across the area late
on Monday bringing a shot of late season cold air and scattered to
numerous rain and snow showers. Cold advection sends 850mb temps
down to -15C, well below average for early April. Surface temps fall
to the lower 20s Monday night and likely hold near 40 Tuesday within
this air mass. Moderation back to milder conditions is then expected
by midweek as southerly return flow sets up.

&&

.MARINE...

A strong low pressure system over Lake Superior this morning pulled
a cold front across Lake Huron. The tight pressure gradient over
northern Lake Huron this morning into the afternoon will bring a
period of westerly Gales through the Straits so a warning has been
issued. Farther south, it looks like winds may briefly reach into
the mid 30 knots, but confidence is higher in a period of offshore
winds up to 30 knots so Small Craft Advisories are in effect for
Saginaw Bay and the nearshore waters of Lake Huron. A weaker
gradient across Lake St Clair and Lake Erie will allow for winds
around 25 knots over land to bleed over the bodies of water so Small
Craft Advisories are in effect there as well. A front will then
stall across the Ohio River Valley through the end of the week as
high pressure builds back over the Great Lakes later today. Winds
will veer to northerly for Friday and hold below 20 knots. A couple
lows will ripple northeast along the front, wavering it northward
and brushing by southeast Michigan bringing chances of thunderstorms
this weekend.

&&

.HYDROLOGY...

Widespread heavy rainfall has moved out of the area this morning.
Most areas received between 1 and 2.5 inches of rain over the past
24 hours with localized reports of higher amounts up to near 3
inches. Flooding is ongoing along the Ecorse Creek at Dearborn
Heights and the Clinton River at Clinton Township with additional
reports of areal flooding across parts of Metro Detroit. A brief
period of showers is possible along a cold front this morning, but
otherwise dry conditions are expected to allow flood waters to
recede today.

The next round of widespread rainfall is expected Friday night into
Saturday as a low pressure system tracks up the Ohio Valley. This
system may bring a corridor of rainfall in excess of 1 inch to parts
of Southeast Michigan, but confidence is currently low on where this
may set up. This rainfall will likely cause additional rises on area
streams and rivers this weekend with potential for additional
flooding concerns.

&&

.PREV DISCUSSION...
Issued at 1230 AM EDT Thu Apr 3 2025

AVIATION...

Showers and a rumble of thunder linger between the trailing flank of
the exiting storms and the cold front inbound from Lake Michigan
until the front sweeps through SE Mi in the 07-10Z timeframe. A
hybrid warm sector/occlusion gives greater support for MVFR/IFR
ceiling to also fill in between the remaining showers and ahead of
the front. Rapid ceiling improvement then occurs post cold front
bringing VFR scattered coverage to MBS by 07Z and reaching DTW around
10Z. WSW wind becomes the weather highlight as modestly colder air
balances early April daytime heating for boundary layer growth into
30 knot gusts that last through afternoon into Thursday evening.

For DTW... A cold front sweeps any remaining showers east of the
terminal before sunrise. WSW then builds to 30 knots by mid morning
through the afternoon.

DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less late tonight.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Gale Warning until 4 PM EDT this afternoon for LHZ361.

Small Craft Advisory until 10 PM EDT this evening for LHZ421-422-
441>443.

Lake St Clair...Small Craft Advisory until 4 PM EDT this afternoon for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 4 PM EDT this afternoon for LEZ444.

&&

$$

DISCUSSION...TF
MARINE.......DRK
HYDROLOGY....TF
AVIATION.....BT


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