167
FXUS63 KDTX 211916
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
316 PM EDT Fri Jun 21 2024

.KEY MESSAGES...

- Marginal risk of severe thunderstorms this afternoon and
  Saturday afternoon/evening, with damaging winds being the main
  hazard.

- Hot and humid through Saturday. High temperatures 85-90 today
  and 90-95 on Saturday, as heat indices peak out just under
  100 degrees for Saturday.

&&

.DISCUSSION...

Scattered convection has begun firing this afternoon across
central/southern MI which will continue through this evening as
diffuse shortwave energy transits the area atop the lingering
stalled frontal boundary. Overall environment remains the same from
prior days with MLCAPEs between 1000-1500 J/kg and mediocre shear
aob 25kts resulting in a continuation of pulse-type convection with
isolated damaging downbursts possible. With PW at 1.72" from the 12Z
DTX RAOB sounding, locally heavy rainfall is likely beneath any
thunderstorm especially given the slower storm speeds as background
flow is 30kts or less through ~400mb. Any lingering convection still
expected to taper off around 03Z early tonight as instability wanes
and shortwave energy vacates.

Stalled frontal boundary that has lingered over southern lower MI
the past couple days is forced back north tonight in response to
developing surface low pressure over the north-central Plains. While
associated shower and thunderstorm activity initially holds north of
the CWA Saturday morning, shortwave energy/mid-upper height falls
reaches SE MI by Saturday afternoon likely resulting in a southern
expansion of ongoing activity over northern lower MI into areas
along/north of I-69. Favorable diurnal timing with SBCAPEs around
1000 J/kg and slightly better kinematic profiles (relative to
previous days) as bulk shear tops out around 30-35kts supports the
potential for scattered, more organized thunderstorms during the
afternoon and evening hours. A few strong to severe storms will be
possible within this activity particularly over the Tri-Cities/Thumb
with isolated damaging wind gusts being the primary hazard. Given
the boundary looking to hang out near the Saginaw Valley, can`t
completely rule out the chance for an isolated brief tornado though
forecast hodographs are fairly marginal. Moisture rich environment
also supports heavy downpours likely leading to locally heavy
rainfall, see hydrology for more information. Low pressure
eventually tracks somewhere over central to northern lower MI late
Saturday-Sunday driving a respectable cold front across SE MI
through the overnight hours into Sunday morning. This timing falls
solidly within the diurnal minimum for instability limiting severe
potential with model guidance all generally favoring a gradually
decaying line of showers and thunderstorms moving across the area.
Shortwave clears the region by midday/early afternoon Sunday ending
further rain chances.

For the southern portions of SE MI which likely miss out on
afternoon-evening rain, persistent deep layer southwest flow in
advance of the approaching cold front pushes 850mb to into the upper
teens to near 20C. Highs in the low to mid 90s look likely though
with dewpoints generally holding in the upper 60s, heat indices
remain sub-advisory between 95-98F.

Upper trough slides over the Great Lakes Monday allowing 850mb temps
to fall to 10-12C (down from 18-20C on Saturday) keeping highs in
the lower to mid 80s. Cooldown is shortlived as troughing is
replaced by induced ridging in advance of another upper trough
beginning to dig south out of the Canadian Prairie. This allows
southwest flow to redevelop in the lower levels pushing 850mb temps
back into the upper teens with Tuesday highs returning to the upper
80s to lower 90s. Aforementioned trough arrives over the Great Lakes
midweek bringing the next chances for widespread showers and storms.

&&

.MARINE...

Generally high pressure spread across the region keeping a hot and
stable airmass in place through Saturday. A stalled weak front will
remain across the southern Great Lakes helping to touch off
scattered thunderstorms through this evening. Then the pattern gets
a little more progressive offering some mid level support for more
organized and frequent storms Saturday across much of Lake Huron.
The hot air will help minimizing wave heights through Saturday
outside of any thunderstorm wind gusts. A more organized low
pressure system will pass through the northern Michigan Saturday
night pulling a cold front through the region on Sunday likely
resulting in more widespread convection and wind speeds then could
reach or exceed 25 knots with waves building to around 4 feet. Small
craft advisories may be needed.

&&

.HYDROLOGY...

A moist and moderately unstable airmass holds in place today with
scattered thunderstorms continuing through this evening. These
storms will be capable of producing highly localized rainfall
amounts in excess of 2 inches in less than 3 hours due to their slow
movement. This amount of rain would result in urban/low lying
flooding.

Additional showers and thunderstorms are possible over areas
along/north of I-69 Saturday afternoon-evening. With an unchanged
airmass, locally heavy rainfall is likely from these storms with
rainfall rates near or in excess of 2 inches per hour. Additional
showers and storms work across the area overnight Saturday as a cold
front crosses the area. This activity likely weakens through the
night resulting lower totals- rain amounts between 0.1-0.5 inches
generally favored.

&&

.PREV DISCUSSION...
Issued at 134 PM EDT Fri Jun 21 2024

AVIATION...

Early morning showers clear out, but isolated popup thunderstorms
are still expected across the CWA this afternoon and evening as a
stationary front remains overhead. Front migrates northward this
afternoon which in combination with daytime instability, creates the
environment for aforementioned storms to pop up. Have gone with a
TEMPO over PROB30 due to the imminent timing of the storms, but
confidence is low on the full extent of the event. Any storms that
do move overhead will produce MVFR to IFR conditions, based on the
strength of the downpour. All storms look to be clear of the area by
02Z tonight at the latest, shifting instead to the northern Lower
Peninsula and Lake Huron. Some light fog is possible overnight,
mainly at MBS where light winds off the lake produce favorable
conditions for sustained fog.

The next chances for showers and storms come on Saturday afternoon
and evening. MBS and FNT see the greatest chances for development
with the stationary front maintaining north/south position. Low
pressure center moves into the area on Sunday, dragging a cold front
across the region and bringing with it additional chances for
showers and storms. After frontal passage, the pattern of daily
isolated popup showers looks to be broken, with high pressure and
clearer weather filling in behind to start next week.

For DTW/D21 Convection... Conditions remain favorable for
thunderstorms with mid afternoon to evening timing. The combination
of Erie/St. Clair lake breeze and stationary front near the MI/OH
border provide the best chances for storm development until the
front moves north of DTW later tonight.

DTW THRESHOLD PROBABILITIES...

* Moderate for thunderstorms impacting the airspace this afternoon
  and evening.


&&

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

$$

DISCUSSION...KDK
MARINE.......DRK
HYDROLOGY....KDK/SF
AVIATION.....BC


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at www.weather.gov/detroit.