005
FXUS63 KDTX 261505
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1105 AM EDT Sun May 26 2024

.KEY MESSAGES...

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

- There is a Marginal Risk of severe weather late today into tonight
  from I-69 south with a Slight Risk for Lenawee and Monroe
  counties. Isolated damaging wind gusts are the main threat.

- 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...

Advertised line of thunderstorms extends from roughly northern
Illinois to western Kentucky and has taken on an increasingly
northeastward trajectory as slow-moving upper level features on the
northern flank of the system stall near the Iowa-Wisconsin border.
Line motion is currently southwest to northeast around 40 mph which
brings the line into Lenawee County between 3-5 PM and through the
rest of the forecast area between 4 PM and 10 PM this evening.

Despite neutral to weakly stable conditions over eastern Illinois
currently, this line of storms has produced gusts of 40+ mph and is
moving into an increasingly favorable environment over Indiana. The
expectation is that as the line moves into Indiana, it will
eventually overtake the warm front before reaching SE Michigan. This
will dramatically increase dry air entrainment into storm inflow, as
the 12z sounding depicts very dry and statically stable conditions
below 500mb, which will likely contribute to some weakening of the
line. For reference, forecast MLCAPE struggles to reach 500 J/kg
before the line arrives, with highest instability located downstream
of Lake Erie (generally from Detroit to Ann Arbor and points south).
For any updrafts that can maintain their strength, steep mid and low
level lapse rates combined with increasing mid-level flow would
support the chance for storm organization and strong downdrafts,
highlighting isolated wind gusts as the primary severe threat for
today alongside frequent lightning and heavy downpours. Cannot rule
out a rotating storm, but shallow equilibrium levels and dry low
levels keep probabilities low for large hail or tornadoes.
Stratiform rain fills in behind the leading line, but the primary
strong to severe storm threat ends by 10 PM this evening. A Marginal
Risk is in place south of I-69 with a Slight Risk for Lenawee and
Monroe Counties.

&&

.PREV DISCUSSION...
Issued at 603 AM EDT Sun May 26 2024

AVIATION...

VFR to start the day with just varying degrees of high cloud debris
shed off upstream convection. A strong low pressure system will then
force a band of showers and thunderstorms northeast through the
region after 21Z. Confidence is high enough to keep a prevailing
group going for thunderstorms between roughly 21-01Z as this band
arcs up through the area. Likely a period of subsidence will bring a
short dry period before another round of showers and possible
thunderstorms works through the area. Less confidence with this
timeframe due to scattered nature of the precipitation. Winds will
be southeasterly most of the day but will increase out of the
southwest early Monday.

For DTW/D21 Convection...The potential for thunderstorm activity
will increase after 21Z Sunday at DTW and 23Z at KMBS/KFNT. Looks to
be about a 2-3 hour window for convection with this first band that
works through. Some storms may become strong to severe while
tracking northeast around 20 knots. Less confidence with later
rounds of showers and thunderstorms as they likely become more
scattered.

DTW THRESHOLD PROBABILITIES...

* Moderate for thunderstorms in the 22-01Z window. Low through
  Monday morning.

* Low for ceilings aob 5kft before 22Z.  Moderate tonight.

PREV DISCUSSION...
Issued at 314 AM EDT Sun May 26 2024

DISCUSSION...

A strong shortwave will eject from NE/KS into the western/northern
Great Lakes late today into tonight. This mid level feature will
become negatively tilted as it pivots around upper low pressure
centered near Lake Winnipeg. This shortwave will induce cyclogenesis
over WI late today with the surface low then tracking into northern
lower MI and deepening to near 990mb by Monday morning. A band of
convection is expected to arc into the area along this trough axis
later today (arriving between 4pm-6pm).

Initially, this band of showers and thunderstorms will tap some
degree of surface instability along/south of a warm front lifting
north through the Ohio Valley. This front, however, will struggle to
lift into lower MI late in the day and band of convection will have
to rely increasingly on the advection of elevated instability into
its flank as a southwesterly LLJ pivots into the area by evening.

While this will limit severe potential, given the fact that wind
shear increases to near 40 knots as the wind field strengthens in
response to the encroaching shortwave, any notable push of unstable
air into the region (surface based or not) should support a small
chance of severe weather into at least portions of the forecast
area. As such, the areas north to the I-69 corridor are outlooked
for a marginal risk of severe weather with the far southern part of
the area outlooked for a slight risk in anticipation for spotty
large hail and/or damaging wind gusts with a few of the storms.

The most concentrated convective activity will focus on the evening
period with just scattered showers and a few thunderstorms possible
overnight into Monday as the surface low pressure reaches northern
lower MI and begins to occlude. Mild weather will continue Monday,
but a cold front will pivot east through the area during the day.
This will set up a temperature gradient from the mid/upper 60s over
the Saginaw Valley to the lower/mid 70s over east/southeastern parts
of the area. Gusty southwest to west winds will accompany this front
with wind gusts to 30 mph or so by afternoon.

The aforementioned upper low pressure system near Lake Winnipeg will
pivot southeast into the area into the midweek period in the wake of
a fast moving Pacific shortwave that races into the deepening upper
trough over the area. This will bring cooler temperatures in the 60s
to near 70 from Tuesday into Thursday. There will also be a chance
of showers and a few thunderstorms from Monday night into Tuesday
night, but peaking late Tuesday as the remnants of this main upper
low shift through the area.

A substantial upper level ridge shifts east over the area by late in
the week bringing a return of temperatures in the 70s to around 80
from Friday into next weekend. The next notable Pacific shortwave
will more than likely impinge on the area by sometime next weekend.
This will bring some chance of showers/thunderstorms back into the
forecast towards the tail end of this 7 day forecast.

MARINE...

Easterly winds today as brief high pressure moves across the region.
The next low pressure system is expected to impact the region
beginning this evening. Warm frontal passage overnight 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 will still have little trouble mixing down. 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 Monday, but there is
still uncertainty in the timing and extent of the impacts.

HYDROLOGY...

Showers and thunderstorms are expected late today into tonight as a
strong low pressure system lifts into the area. Locally heavy rain
will be possible with some of the thunderstorms as moisture quality
within the atmospheric column improves into this evening. Forecast
basin average rainfall amounts range between one quarter of an inch
to three quarters of an inch, but higher amounts in excess of 1 inch
will be possible in a few stronger storms. Forecast adjustments are
likely due to the convective nature of the rain. The 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.
&&

$$

UPDATE.......MV
AVIATION.....DRK
DISCUSSION...DG
MARINE.......BC
HYDROLOGY....DG


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