271
FXUS63 KDTX 080006
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
806 PM EDT Tue May 7 2024

.KEY MESSAGES...

- A Tornado Watch is in effect for Lenawee, Monroe, and Washtenaw
  Counties until 11 PM this evening.

- Scattered strong to severe thunderstorms have moved in this
  evening, mainly along/south of M-59.

- Damaging winds, large hail, and isolated tornadoes are possible.

- Warm and breezy conditions are expected Wednesday, followed by
  cooler conditions with a chance of rain Thursday.

&&

.AVIATION...

Ceilings have struggled to lower this evening as storms arrive from
the southwest. These clusters of storms have shown signs of
weakening as the available instability transitions from surface
based to elevated. This presents increased risk for large hail, in
addition to standard aviation convective hazards. Areas from PTK
south are at greatest risk for lightning strikes given the vicinity
of the surface warm front while storms near FNT/MBS ride the
elevated frontal boundary. Most of the storms should depart or
dissipate by 11 PM this evening. Clouds try to scour out after
midnight offering potential for a bit of MVFR fog as the humid
airmass cools. Sunny and breezy conditions in store Wednesday
afternoon with afternoon gusts in excess of 25 knots.

For DTW/D21 Convection...

Multicell thunderstorms are approaching the terminals this evening
with potential for some strong to severe storms capable of 40+ mph
gusts and large hail. A tornado cannot completely be ruled out, yet.

DTW THRESHOLD PROBABILITIES...

* High for thunderstorms until 03Z this evening.

* Low for ceiling at or below 5000 feet this evening.

&&

.PREV DISCUSSION...
Issued at 346 PM EDT Tue May 7 2024

DISCUSSION...

Previous forecast reasoning offered by Area Forecast Discussions
issued earlier today remains valid. Initial arc of elevated shower
activity forced by lead system relative isentropic ascent and 850-
600mb thetae advection is now lifting northward through Southeast
Michigan. After this initial evaporative cooling response, will be
monitoring for the surface temperature and dewpoint recovery to
gauge for the potential of surface based, severe thunderstorms
between 6-11 pm local time. As forecasted, dewpoints have been slow
to rise and will have to overcome a due easterly trajectory off of
Lake Erie. A strong convergence bullseye on the nose of a deep
kinematic field and upper level diffluence is forecasted to
lift/pivot directly into portions of south central and southeast
Michigan this evening. Quality of large scale forcing is expected to
result in numerous to widespread showers and thunderstorms after. 22Z
The main threat this evening will be a potential for a tornado
(mainly for areas south of I 94) conditional to surface instability.
The secondary threat with thunderstorm activity (all areas) this
evening will be large hail. Modest midlevel lapse rates of 6-6.5C/km
should limit hail diameter potential, but any non-hydrostatic force
provided by mesocyclones could cause for hail diameters to exceed 1
inch. Again, the time period for potential severe weather is between
6-11 pm.

The zonal gradient orientation in the wake of the upper level trough
release will then set the stage for a relatively breezy day on
Wednesday. West winds of 20 to 30 mph. Little to no northward
advection will yield a sneaky warm day Wednesday with a dry, well
mixed boundary layer. No humidity to speak of but sunny conditions
and temperatures reaching the middle 70s to low 80s.

A very complex upper level height configuration is then expected to
develop for the Thursday and Friday time frame. An atypical
elongated trough axis is expected to reside in a largely west to
east fashion from the Central Plains to the Central Great Lakes. Not
a whole lot of confidence to be garnered from the setup as various
shortwaves digging southward from central Canada will have the
opportunity to disrupt the troughing. As it stands, Southeast
Michigan looks to be in a fairly close proximity to deeper
deformation forcing. Coupled jet forcing is also expected to eject
trough providing for an ageostrophic response and increased
frontogenesis. PoPs for Thursday are in the numerous to likely
category for much of the area and is warranted.

Various, lobes of modest planetary/potential vorticity are
forecasted to dig through Southeast Michigan for this upcoming
weekend. Given the trajectory, the predictability to the timing of
the shortwaves may prove difficult, but current trends suggest
Saturday is the most likely of time periods for precipitation.
Temperatures will be strongly dependent on cloud cover, with
current forecast suggesting temperatures of approximately 5 degrees
below normal.

MARINE...

Warm front tied to Midwestern low pressure continues to lift into
the central Great Lakes this afternoon supporting widespread showers
as well as scattered thunderstorms into this evening. A few strong
to severe storms are possible for areas south of Port Huron with all
hazards on the table. System`s cold/occluded front crosses the
region overnight setting up modest (~15-20kt) westerly flow for
Wednesday. Secondary low development over the Ohio Valley Wednesday
night results in a turn to northeasterly flow locally. Marginally
cooler airmass is drawn south, combined with the still tightened
gradient, is expected to allow for peak gusts 20-25kts over the
central portion of Lake Huron with near 30kts possible over Saginaw
Bay (lesser gusts over the remainder of the region). Additional
showers are also likely daytime Thursday before the low vacates.

&&

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

$$

AVIATION.....KGK
DISCUSSION...CB
MARINE.......KDK


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