Expert Forecast Opinion

376
FXUS63 KDTX 211928
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
328 PM EDT Sun Jun 21 2026

.KEY MESSAGES...


- Showers and thunderstorms increase coverage tonight, especially
south of Detroit where rainfall totals range from 1.0 to 1.25 inch.
Lesser amounts to the north.

- Showers linger Monday morning then dry weather follows in the
afternoon and evening.

- Cooler than normal temperatures continue through at least the
middle of next week.

&&

.DISCUSSION...

The hybrid baroclinic cyclone and mesoscale convective system is
currently tracking out of Missouri and into Illinois early this
afternoon. There has been a strong and very consistent model
consensus that supports a split in the forcing with deep boundary
rooted convection tracking to the southeast across far southern
Indiana into portions of Kentucky, while seasonably strong 850mb
and 700mb frontogenesis lifts northeastward towards the far western
Lake Erie basin. Confidence is high the main synoptic scale lift and
frontogenesis will favor this northern route as it is driven by
strengthening and very rapidly organizing right entrance region jet
dynamics. The low confidence portion for tonight remains how high up
or what level the frontogenesis will activate. The current NAM nest
suggests the center line of the 850mb fgen axis will set up to the
south of the Michigan Ohio stateline, whereas the 700mb fgen axis
tracks near Lenawee and Monroe counties while eclipsing Wayne
County. Consensus of models suggests QPF amounts of 1.00 to 1.33 of
inch will be likely with some peak amounts of 2.00 inch in isolated
locations mainly across south central to southwest Lower Michigan.
Was really agonizing over the decision to issue a Flood Watch,
however a number of factors argue against it. The factors include:
dry antecedent soil conditions, not expecting to reach 6 hour qpf
amounts exceeding Flash Flood Guidance of 2.25 inches, QPF axis
forecasted south of Metro Detroit, narrow QPF axis at a county wide
or less, and no connection to true surface based instability
reservoir.

Lead deformation/warm advection light rainfall chances begin after
22z across the Southern cwa, then increasing significantly after 01-
2z this evening. Early activity looks to have a more stratiform look
based on hires depictions. Subset of model guidance points to a wave
of low pressure causing a tighter cyclonic circulation to lift
northeastward at Monroe County between 8-12z. It is with this
compact convergence forcing that will bring the highest rainfall
rates especially if there is more localized deformation response
along the northern flank. Survey of model data suggests a top end of
rainfall rates could be up to 0.50" per hour. Breadth of upper level
jet forcing is expected to allow precipitation to expand over much of
the area through the M 46 corridor.

Last of shearing deformation is expected to push east of Southeast
Michigan by/after 18Z Monday. Guidance continues to suggest some
brief potential for a light shower over eastern sections of the
forecast area between 20-23z. Difficult to include a PoP later in
the day with only a brief opportunity to achieve some reasonable
convective depth with strong subsidence down to 7.0 kft agl. Spotty
at best. Winds should be come well mixed in the dry advection,
holding northeasterly to northerly at 15 to 25 mph into the early
evening. Winds are then expected to lie down quickly after 00-01z.

Surface ridge axis will build across Southeast Michigan Tuesday
through midday Wednesday. Highs are expected to be in the upper 70s
(2 to 5 degrees below normal) with modest surface dewpoints in the
middle 50s.

Longwave trough and upper level jet axis settles into the central
Great Lakes by late Wednesday. Models are suggesting a very broad
cyclonic circulation which limits predictability because of timing
in internal absolute vorticity maxima. At this vantage point,
interesting to look at the EPS dataset which has mean values
relatively close to the 75th percentile. Potential exists for a
mainly dry stretch of weather next weekend near normal summerlike
weather.

&&

.MARINE...

A compact low pressure system will travel east across the Ohio
Valley tonight into tomorrow morning. This will elevate east to
southeast flow across Lake Erie, bringing wind gust potential around
25 knots along with increasing wave heights. A Small Craft Advisory
remains in place. Some isolated wind gusts 20 to 25 knots will be
possible across Lake St. Clair overnight, with lower magnitude wind
speeds across Lake Huron and the Saginaw Bay. This system will also
bring widespread rain, heavy at times, across the southern Great
Lakes. Wind direction backs north to northwest in the wake of the
low through the early week period as high pressure builds in.
Lighter winds are expected Tuesday and Wednesday.

&&

.HYDROLOGY...

Compact low pressure system will bring widespread rain to Southeast
Michigan this evening and tonight. Total rainfall amounts of 1.00 to
1.25 inch appear likely for far southern sections of cwa with the
potential for isolated amounts of up to 2.00 inches. Peak of the
rainfall is expected between 3am to 8am. With no expectation for
rainfall to exceed Flash Flood guidance, flooding impacts are
expected to be limited to ponding of water on roadways and flooding
of poor drainage areas.

&&

.PREV DISCUSSION...
Issued at 101 PM EDT Sun Jun 21 2026

AVIATION...

Field of small scale cumulus has developed across much of the
Southeast Michigan airspace. Coverage is greatest across the
Detroit airspace where weak convergence funneled by the influence of
Lakes St Clair and Erie have pooled more near surface moisture to
act upon. The mixing process will introduce enough dry air in the
cloud layer to limit expansion and will start to degrade the cloud
integrity through the balance of the afternoon. Winds will remain
light through the daylight hours.

Rain with embedded convective elements will overspread the area
start around sunset. The greatest coverage and intensity will be
across the Detroit airspace - peaking in the 8-12z time window. MVFR
ceilings will cruise in after midnight with a window of IFR (aside
from MBS) with the peak rainfall rates. Otherwise, east/northeast
flow will establish tonight and persist through Monday - with
occasional gusts to 20 knots.

D21/DTW Convection... There is a chance of thunderstorms tonight
within a more widespread area of showers. These will be elevated in
nature making briefly heavy rainfall the primary hazard.

DTW THRESHOLD PROBABILITIES...

* Moderate for ceiling at or below 5000 ft today. High tonight and
most of Monday.

* Moderate for thunderstorms tonight.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...Small Craft Advisory from 4 AM to 5 PM EDT Monday for LEZ444.

&&

$$

DISCUSSION...CB
MARINE.......CB
HYDROLOGY....CB
AVIATION.....Mann


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