269
FXUS63 KDTX 270146
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
946 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.

&&

.UPDATE...

Convection, heavily modulated by short wavelength deformation, is
currently lifting northeastward through portions of the eastern Metro
Detroit and the Thumb. Strong moisture transport occurring in a
pseudo conveyor was able to bring 1 to 2 inches of rainfall for many
locations in Monroe, Wayne and Macomb counties. An interesting wind
bubble has developed with 30 to 35 knot winds on the upwind edge of
the precipitation. The gusty winds are occurring where precipitation
rates fall off and evaporation is increased, dragging momentum down
to the surface. These gusty winds will end quickly as precipitation
ceases.

Watching some deep tropospheric convection/thunderstorm activity over
the far southern rim of Lake Michigan. The thunderstorm is occuring
right at the crux/max of absolute vorticity vorticity advection at
lead edge of pivoting vigorous vorticity maximum. Not expecting this
convection to hold onto integrity and strength as it lifts
northeastward towards western Lower Michigan and the Tri Cities
region. There are two reasons: 1. Negligible CAPE this evening over
Lower Michigan. 2. Vorticity feature is shown to spread out and
become more diffuse as it lifts to the northeast. Will continue to
monitor.

&&

.PREV DISCUSSION...
Issued at 751 PM EDT Sun May 26 2024

AVIATION...

Arc of showers and thunderstorms with heavy rainfall has congealed
along a synoptic scale deformation zone that is now lifting
northeastward through Southeast Michigan. The rainfall rates have
supported LIFR visibility restrictions at times. Prevailing MVFR
cigs of approximately 2.0 kft agl are expected in the wake of the
convection tonight. A convective vorticity maximum will support an
additional round of showers and thunderstorms between 10-14Z Monday
morning. A cold front will sweep across Southeast Michigan between
15-19Z. West southwest winds of 20 to 35 knots will be possible late
Monday afternoon.

For DTW/D21 Convection...Thunderstorms are occuring through 01Z.
Another round of thunderstorm activity is possible between 10-14Z.

DTW THRESHOLD PROBABILITIES...

* Moderate in thunderstorms between 10-14Z Monday morning.

* High in ceilings aob 5000 feet tonight and Monday.

* Low in crosswind thresholds being exceeded Monday afternoon.

PREV DISCUSSION...
Issued at 353 PM EDT Sun May 26 2024

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.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
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.

&&

$$

UPDATE.......CB
AVIATION.....CB
DISCUSSION...MV
MARINE.......BC


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