Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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641
FXUS63 KDTX 261953
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
353 PM EDT Sun May 26 2024

.KEY MESSAGES...

- A line of showers and thunderstorms moves into the region between
  5 PM and 10 PM this evening.

- There is a Marginal Risk of severe weather this evening from I-69
  south with a Slight Risk for Lenawee and Monroe counties. Isolated
  damaging wind gusts to 60 mph remain possible.

- There is also a Marginal Risk of excessive rainfall. See the
  Hydrology section of this AFD.

- The Memorial Day outlook calls for cooler, more seasonable
  temperatures with scattered showers and thunderstorms.

&&

.DISCUSSION...

Continuing to monitor a broken line of thunderstorms that extends
from roughly South Bend to Wilmington at press time. Thus far, the
line has remained sub-severe with recent gust observations ranging
between 35-45 mph. The enhanced forward propagation of the
southernmost portion of the line, which is well into southern Ohio at
this point, has effectively slowed progress of the northern line to
now reach southeast MI closer to 5 PM. As expected, MLCAPE has
struggled to build above 500 J/kg amidst dry boundary layer
conditions so not anticipating much intensification although
entrainment/evaporative cooling potential still does pose a threat
for strong to borderline severe gusts. The most widespread impacts of
this line will be frequent lightning and heavy downpours, with 6-
hour MRMS QPE values showing widespread rainfall totals of a half
inch to localized inch along this line.

The leading line of showers and thunderstorms exits into Lake Huron
by 10 PM this evening, leaving a much broader pool of low level
moisture in its wake while low level portions of the warm front lift
northward. The result is continued scattered shower activity
overnight, aided further by lingering elevated instability that will
maintain low end thunder chances through Monday morning. Heaviest
rainfall overnight looks to remain south and east of the state line,
with just the northern fringe of the low level jet and moisture axis
clipping SE MI. Widespread heavy rainfall potential will also be
mitigated by a strong post-convective push of mid level dry air.
Localized heavy downpours however remain possible in any stronger
convective cells, which could bump QPF over an inch in some spots.

Drier air arrives mid-day Memorial Day as the parent surface low
migrates into central lower Michigan, drawing a cold front west to
east across the state. This brings an end to shower activity around
noon, followed by a brief period of low amplitude ridging and deep
static stability above 3.0 kft agl through Monday evening. Trapped
low level moisture keeps a blanket of cloud cover overhead with a
few sprinkles possible in the afternoon, while post-frontal cold
advection brings H8 temperatures into the single digits and
corresponding daytime highs in the low 70s for the holiday.

Even as the surface low departs Monday night, broad upper troughing
maintains an unsettled pattern Tuesday and Wednesday with additional
shortwaves pivoting through the flow. Transient moisture accompanies
these systems to support glancing periods of precipitation before
the trough axis finally swings through mid-week. Deep northwest flow
throughout maintains cool thermal profiles with temperatures
settling in the upper 60s to low 70s for the early half of the week.
Conditions to then dry out latter half of the week with the arrival
of an amplified ridge axis.

&&

.MARINE...

Low pressure brings the first round of storms into the area this
evening. Strong low level easterly flow has already been able to mix
down 30 knot gusts, so a Small Craft Advisory has been issued for
the nearshore area of Lake Erie through 8pm tonight. Winds will
briefly die down overnight to 10-15 knots, but return to strength on
Monday evening with the passage of a cold front. Abundance of Small
Craft Advisories with this system, beginning with western Lake Erie
currently in effect through 8pm tonight. Conditions around the tip
of the thumb are expected to pick up tonight, so Small Craft
Advisory will go into effect beginning at 6pm tonight. All zones are
up to criteria by noon tomorrow, with the zones of Lake Erie, Lake
St. Clair, and nearshore areas of Lake Huron from Harbor Beach to
Port Huron expected to drop below criteria overnight Monday into
Tuesday. These advisories are set to drop off at 4am Tuesday.
Gustier conditions are expected to hang around a little bit longer
around the thumb, so the Saginaw Bay and Port Austin to Harbor Beach
zones have the advisory active until 4pm. Gale potential out over
the open waters looks marginal for now, and have decided not to go
with a gale watch at this time. Cooler conditions with westerly flow
are expected behind the front.

&&

.PREV DISCUSSION...
Issued at 1231 PM EDT Sun May 26 2024

AVIATION...

An upper level trough will lift across Se Mi between 21Z and 03Z
today. Despite the ample dry air currently over Se Mi, an axis of
deep layer moisture and elevated instability along region of ascent
will produce a line of thunderstorms as the trough moves across the
region. An influx of low level moisture within the warm sector of a
deepening sfc low combined with the development of a subsidence
inversion will support low cloud development tonight in the wake of
the evening convection. Model soundings are suggestive of low end
MVFR and IFR ceilings prevailing and trends have been increasing in
the latest probabilistic guidance. The cold front will move across
Se Mi early to mid morning on Monday. This front will provide a
chance for additional thunderstorms, limited by overall weak
instability.

For DTW/D21 Convection...A slow moving solid to broken line of
thunderstorms is expected to traverse the airspace this evening. The
line will move from southwest to northeast across the airspace
between 21Z and 02Z. A cold front will then produce a low chance for
additional thunderstorms, more likely to be scattered, between 08Z
and 15Z Monday.

DTW THRESHOLD PROBABILITIES...

* High in thunderstorms this evening. Low overnight and Monday
  morning.

* High in ceilings aob 5000 feet tonight and Monday.

* Low in crosswind thresholds being exceeded Monday afternoon.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement until 8 PM EDT this evening for MIZ083.

Lake Huron...Small Craft Advisory from noon Monday to 4 AM EDT Tuesday for
     LHZ442-443.

     Small Craft Advisory until 4 PM EDT Tuesday for LHZ421-441.

     Small Craft Advisory from noon Monday to 4 PM EDT Tuesday for
     LHZ422.

Lake St Clair...Small Craft Advisory from noon Monday to 4 AM EDT Tuesday for
     LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from noon Monday to 4 AM EDT Tuesday for
     LEZ444.

     Small Craft Advisory until 8 PM EDT this evening for LEZ444.

&&

$$

DISCUSSION...MV
MARINE.......BC
AVIATION.....SC


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