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776
FXUS63 KDTX 251940
AFDDTX

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

.KEY MESSAGES...

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- Dry conditions tonight through most of Sunday.

- Showers are likely 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 cooler, more seasonable
temperatures with scattered showers and thunderstorms Monday.
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&&

.DISCUSSION...

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Strong subsidence in the wake of this morning`s midlevel shortwave
and associated showers and thunderstorms has caused high pressure to
build into the area with skies clearing out for the late afternoon.
A pleasant and warm Saturday evening is in store with a westerly
breeze around 15 mph winding down gradually. Dry conditions prevail
overnight as a convectively enhanced shortwave over the Plains
induces downstream ridging over the Great Lakes into much of Sunday.
Some high clouds likely stream in after midnight through Sunday
morning with lows falling to the 50s to upper 40s.

Convective trends upstream that carry a good amount of uncertainty
at this stage hold a lot of influence over the Sunday evening and
overnight forecast. The 12z guidance does continue to highlight a
negatively tilted lead shortwave emerging from tonight`s convection
over the Plains which then tracks overhead around/after 00z Monday.
This feature will likely sustain a complex of storms across IL and
IN through the morning/afternoon along a warm front as a surface low
lifts in from the west. Models then show the warm front stalling
across SW MI with much of SE MI remaining north of it during the
late afternoon and early evening. Instability will need to be
advected in which is anything but certain as the nose of the LLJ
looks to initially hold south across the Ohio Valley - where ongoing
convection and associated outflows may block what`s available.
Storms tied to that initial shortwave Sunday evening look to arrive
from the west after 7pm or so, and may outpace the instability and
begin to weaken as they move through. Still, a conditional severe
threat exists if instability does advect in given effective wind
shear increasing to around 40 kt. Large hail and damaging wind gusts
as well as heavy downpours would be possible in the strongest storms
with the most likely area south of I-69.

Additional rounds of showers and storms are likely after midnight
into Monday morning as forcing from the primary shortwave moves in
and continued moisture advection pushes PWATs to around 1.50 inches.
Instability continues to look lean during this period (HREF ensemble
mean MUCAPE holding below/near 500 J/kg), but bears watching as the
surface low tracks into west Michigan which places the triple point
and attendant localized low-level shear max in the vicinity. Given
the nocturnal timing, the overall severe threat remains conditional
on the instability being able to advect in. Event QPF still carries
a considerable amount of uncertainty but has trended down from the
previous model run. Areas that do see heavier storm(s) may receive
over an inch of rain, but most areas will likely see around a half
inch or less.

The surface low will continue to track across northern lower MI
through the daytime Monday, keeping an unsettled forecast in place
for some of the holiday. The upper dry slot looks to cut into
moisture depth but troughing overhead will induce some instability
so scattered showers and storms will likely be around along with
mostly cloudy skies, especially for the first half of the day. Post
cold-frontal drying may then bring an end to the showers with some
daylight to spare. Temperatures should be seasonable in the 70s with
a gusty west wind up to 30 mph developing behind the front.

A shortwave over Manitoba gets pulled southeast behind the departing
wave on Tuesday, bringing another opportunity for scattered showers
and storms conditions as another cold front moves through. This
marks the start of a period of relatively cooler temperatures next
week with highs in the 60s and 70s. High pressure builds in on
Thursday with warmer conditions then returning by next weekend as
southerly return flow develops behind it.
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&&

.MARINE...

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Light winds veer southeast overnight as brief high pressure
solidifies itself over the area early Sunday. The next low pressure
system is expected to impact the region Sunday evening, where a warm
front is expected to strengthen winds over the lake and bring
chances for showers and storms. Low level flow will be quite strong
with this system, reaching up to 40 knots 1000 feet above the
surface. Small temperature inversion will keep some of the wind at
bay, but stronger gusts should still have little trouble mixing
down, especially if the surface stays a bit warmer than forecasted.
Monday the cold front will move through, bringing further chances
for showers/storms as well as surface winds up to 20 knots over
Saginaw Bay and northern Lake Huron. Winds will have a harder time
mixing down on Monday, but errant gusts to 30 knots are still
possible. Small Craft Advisories will likely be needed for Sunday
and Monday, but there is still uncertainty in the timing and extent
of the impacts.
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&&

.HYDROLOGY...

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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 basin average rainfall
amounts range between a quarter inch to three quarters of an inch,
but higher amounts in excess of 1 inch will be possible in any
heavier storms. 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.
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&&

.PREV DISCUSSION...
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Issued at 1238 PM EDT Sat May 25 2024

AVIATION...

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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&&

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

$$

DISCUSSION...TF
MARINE.......BC
HYDROLOGY....TF
AVIATION.....SC


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