571
FXUS63 KDTX 220257
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1057 PM EDT Fri Jun 21 2024

.KEY MESSAGES...

- Marginal risk of severe thunderstorms late 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.

&&

.AVIATION...

An isolated shower or thunderstorm remains possible overnight, but
overall convective potential remains minimal as greater nocturnal
stability gains traction with time. Attention overnight turns to
prospects of fog development as winds lighten and saturation
improves at the surface. MBS appears the most susceptible to a
meaningful visibility restriction in fog, but any location may
witness a brief dip in visibility during the pre-dawn hours. A
northward advancing frontal zone will offer renewed focus for shower
and thunderstorm development Saturday afternoon, particularly across
central lower Mi including the MBS area. Forecast will offer a tsra
mention at MBS/FNT, with diminishing potential with southward extent
from this corridor.

For DTW/D21 Convection...Greater potential for thunderstorms will
focus north of the airspace Saturday afternoon and evening. An
approaching cold front may bring renewed potential late Saturday
night.

DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms impacting the airspace Saturday night.

&&

.PREV DISCUSSION...
Issued at 316 PM EDT Fri Jun 21 2024

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.

&&

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

$$

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


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