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842
FXUS63 KDTX 251638
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1238 PM EDT Sat May 25 2024

.KEY MESSAGES...

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- Showers are likely again with a chance of thunderstorms Sunday
evening and Sunday night. There is a Marginal Risk of severe weather
with these storms.

- There is also a Marginal Risk of Excessive Rainfall Sunday
evening through Sunday night. See Hydrology section of the AFD.

- The Memorial Day outlook calls for cool temperatures with showers
likely Monday and Monday night.
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&&

.AVIATION...

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Post frontal dry air advection is well underway across the area.
Surface dewpoints along Lake Mi have dropped into the 40s. As the
dry air continues its eastward expansion into Se Mi this afternoon,
skies will undergo a clearing trend. Deepening of the afternoon
mixed layer will be supportive of wind gusts in the 15 to 20 knot
range. Winds will quickly decrease toward sunset as high pressure
expands across Lower Mi from the southwest. This high will maintain
dry and VFR conditions into Sunday afternoon as moves across Lower
Mi and into the eastern Great lakes and upstate New York.

For DTW/D21 Convection...Dry air and subsidence will hold across
metro Detroit this afternoon well into Sunday afternoon. The chance
for thunderstorms will increase across the airspace late Sunday
afternoon in the south, then expand northward across the airport and
northern portions of the airspace later in the evening Sunday.

DTW THRESHOLD PROBABILITIES...

* None.
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&&

.PREV DISCUSSION...
Issued at 341 AM EDT Sat May 25 2024

DISCUSSION...

Rain chances to start the morning off but drier conditions on the
way behind a passing cold front. The warm front has lifted through
the region with good push of theta e advection on a weakening low
level jet around 25-30 knots this morning. Ample moisture is/will be
in place with PWATs around 1.25 inches and surface dewpoints set to
rise from the mid 40s as of 5Z up to near 60 this morning. In
addition, the nose of a mid level jet max enter the Great Lakes with
the left exit region lifting NE through lower MI this morning. The
low level jet with good moisture advection combined with the mid
level jet support should all lead to a band of showers and
thunderstorms along the cold front passing through between 12-16Z.
best chances will be across the Saginaw Valley and Thumb with
decreasing chances toward the Ohio border as the larger scale
forcing pull northward. Surface ridge then builds northward the rest
of the day leading to drier conditions and temps rising into the mid
to upper 70s.

Zonal flow will gradually take on more of a ridge locally overnight
into Sunday as the next mid level system comes together over the
Central Plains, resulting in downstream ridging. Attention in this
period turns to the Plains system as it lifts into the Great Lakes
Sunday evening through Monday. The more dominate upper level vort
max centered over northwest Ontario will draw the developing
shortwave northeastward from Kansas to the UP. Question as this
surface low occludes sending the occlusion through SE MI Sunday
evening and overnight, is the evolution of the convection and the
implications on a developing triple point that would possible travel
through southern MI. As we get deeper into the CAMs, they all have
ongoing convective systems traveling from Iowa through northern
IL/IN drifting east/SE along the instability gradient. Meanwhile the
low and occluded front lift NE through MI. There is a chance the
northern periphery of the convective complexes can reach northward
into far southern MI. This will likely all be dictated by existing
outflows from earlier convection and any MCV that can form on the
north end of the complex that would affect MI. Overall though, there
is a very strong surface low, compact and strong mid level vort max,
elevated warm front bringing in PWATs in excess of 1.5 inches, 30
knots of bulk shear, and CAPE around 500 J/kg likely limited by
moist lapse rates. So the background is there to warrant a
conditional Marginal Risk per SPC Day 2 outlook with best chances of
severe storms closer to the Ohio border. The other concern due to
the wealth of moisture will be QPF amounts. Newest ERO Day 2 has
most of SE MI in a Marginal Risk area, with convectively driven
heavy shower potential. QPF totals between 00-06Z Monday in excess
of a half inch focus south of M59 due to potential for the upstream
convective system to clip it.

Memorial Day looks cloudy with a chance of showers and
thunderstorms. Though the initial mid level system will be pulling
away by Monday, we`ll be in the moist wrap around region with cold
air advection aloft steepening low level lapse rates while a
secondary mid level wave slides through the region. Highs will only
make it into the low 70s for most locations.

Cooler temps continue through mid week as longwave troughing sets up
over the region and a cool Canadian surface high slides down. Highs
in the 60s and lows in the 40s will carry us through Wednesday
before warmer temps start working back into the region later in the
week.

MARINE...

A low pressure system drifts from southeast Manitoba into western
Ontario today causing modest local gradient winds to veer toward the
southwest. The system`s LLJ extends across Lower Michigan and is now
crossing into the central Great Lakes. Forecast soundings highlight
a sharp low-level subsidence inversion limiting gust potential
during the initial stable period. A rouge gust or two could approach
the 25 knot threshold across Saginaw Bay where 30+ knot flow extends
below 750 ft AWL; infrequency warrants foregoing a Small Craft
Advisory. Meanwhile, the system`s cold front should make inroads
across the basins and maintain some thunderstorms, some of which
could generate locally higher winds/waves. Flow then flips northerly
behind the boundary as thermodynamic profiles become more unstable,
but a decrease in column winds keep speeds at-bay. An occluded low
then tracks across Wisconsin and The UP Sunday night with another
LLJ response. More showers and storms are expected, some of which
may be strong to severe. Small Craft Advisory conditions are
becoming increasingly likely Sunday evening and Monday as low-level
lapse rates steepen amidst cold advection. Latest NBM winds feature
a brief period of gusts to gales over Saginaw Bay which will need to
be monitored.

HYDROLOGY...

Thunderstorms are likely Sunday evening into Sunday night as a
strong low pressure system lifts into the region. Locally intense
rainfall rates are possible in some thunderstorms with a high
moisture environment in place. Forecast average rainfall amounts are
around a third of an inch north of I69 with over a half inch to the
south. Some locations south if I94 may receive over an inch of
rainfall. Forecast adjustments are likely due to convective nature
of the rainfall. Main concern would be for localized flooding of
prone urban areas across the Detroit Metro region.

&&

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

$$

AVIATION.....SC
DISCUSSION...DRK
MARINE.......KGK
HYDROLOGY....DRK


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at www.weather.gov/detroit.