013
FXUS63 KDTX 070357
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1157 PM EDT Mon May 6 2024

.KEY MESSAGES...

- There is a risk for isolated strong to severe storms Tuesday
  evening southwest of a Midland to Port Huron line between 6 PM
  and 11 PM.

- Some gusts to 60 mph are possible with potential for isolated
  large hail to 1 inch in diameter.

- Cannot rule out an isolated weak tornado or two Tuesday evening.

- Mainly dry, breezy, and warmer Wednesday, then cooler again
  Thursday with additional opportunities for showers and
  thunderstorms.

&&

.AVIATION...

A gradual transition away from high pressure influence takes place
late tonight and in the morning. Surface wind remains easterly while
cloud layer wind veers SW as a warm front organizes in the Ohio
valley. Low end VFR clouds along and ahead of the front are patchy
and disorganized at issuance time but are expected to fill in
nocturnally and begin moving into Lower Mi to as far north as FNT by
sunrise. Low end VFR holds into the afternoon while the ongoing line
of storms across the Plains makes it into Lower Mi on a weakening
trend by mid afternoon. A second round of thunderstorms is then
expected to develop as instability recovers across WI/IL/IN by late
afternoon. This leads to a stronger trend down into MVFR as the
activity increases coverage and intensity over SE Mi late in the day
into Tuesday evening. The best chance of thunderstorms is after 22Z
with very similar timing along the terminal corridor.

For DTW/D21 Convection... Thunderstorm potential increases across
the region in the afternoon through Tuesday evening. There is a
marginal to slight risk of severe intensity storms across the
DTW/D21 area. The first round of activity moves in on a weakening
trend by mid afternoon followed by a round of stronger storms after
22Z Tuesday evening.

DTW THRESHOLD PROBABILITIES...

* Medium for ceiling 5000 feet or less in the morning, high in the
  afternoon.

* Low for thunderstorms after 18Z Tuesday, moderate after 22Z
  Tuesday evening.

&&

.PREV DISCUSSION...
Issued at 356 PM EDT Mon May 6 2024

DISCUSSION...

Ridging with central surface pressure of 1018 mb continues to anchor
the Great Lakes by flanking the northward progression of scattered
showers and storms attributed to troughing over the Ohio Valley.
Locally, expect near seasonable temperatures and dry conditions the
rest of today and tonight with prevailing easterly flow and a
persistent stream of high cirrus.

Expansive closed low occupying the western two-thirds of CONUS
(producing widespread severe convection) retrogrades from the
western Dakotas into eastern Montana Tuesday while the wave broadens
meridionally. This pushes the system`s elongated warm front
northeastward into Lower Michigan with rapid moistening arriving
after 15Z. Mean 850-700 mb layer dewpoints jump from around -30C
early Tuesday morning to +5C after 18Z as the magnitude of water
vapor transport increases sharply with the transition to cyclonic
southwesterly flow. Current analysis depicts a line of convection
extending from the Mid-Mississippi Valley up to the southern
Canadian Prairies, closer to the actual surface low. CAMs highlight
a tendency for decay as storms cross Lake Michigan and interface
with a dry and stable ambient airmass. Most areas remain dry, at
least through 18Z.

Height field adjustments along the eastern periphery of the system
lend some uncertainty to the upstream evolution of convection as a
secondary shortwave emerges and shears into southern Lower. The warm
sector will fully encompass the region by 22Z, as a secondary (and
more robust response) convection response arrives with additional
storms track west to east. Given the slightly later arrival time and
flatter diurnal curve, confidence in SBCAPE has trended lower as the
main instability axis remains better centered over southwest Lower.
All hazards are in-play Tuesday evening for Southeast Michigan given
the +60 knots of 0-6 km bulk shear, southeasterly winds, and pockets
of higher instability as mid-level lapse rates cool. A secondary
surface low emerges as the triple point, and given the current
curvature reflected in forecast hodographs, isolated rotating
structures will be capable of generating some weak mesocyclones,
augmented by the frontal intersections. Cannot rule out a few
isolated weak tornados and some overachieving thunderstorm gusts.
SPC has upgraded the CWA to a Slight Risk near the MI/OH border with
a Marginal risk elsewhere (excluding The Thumb). Storms largely
depart/dissipate by 03Z with increasingly zonal flow aloft.

Warmer and more stable as dewpoints drop into the upper 40s to lower
50s Wednesday with decreasing sky opacity. Well-mixed boundary-layer
supports some decent afternoon gusts in the 25-30 mph range. The
next system crosses through Indiana and Ohio Wednesday with some
additional shower/storms possible for southern Lower. The primary
upper trough then splits again Thursday, taking aim at the Great
Lakes Thursday while the broader longwave jet pattern remains quasi-
stationary. Additional showers and storms are likely with much
cooler temperatures Thursday, related to cold frontal forcing. The
synoptic pattern unlocks Friday as an amplified ridge drops through
the Upper Midwest. Drier weather will be short lived as a trailing
PV anomaly drops into the region Saturday.

MARINE...

High pressure currently centered over Lake Huron gradually drifts
east into Ontario tonight through the first half of Tuesday
maintaining light easterly flow. Midwestern low pressure lifts a
warm front into the central Great Lakes Tuesday afternoon/evening
bringing widespread showers and thunderstorms with some strong to
severe storms possible over the southern Great Lakes. System`s cold
front quickly follows overnight setting up cooler westerly flow
Wednesday, turning northeasterly Wednesday night. Cooler airmass
combined with a tighter gradient due to secondary low development
over the Ohio Valley supports a moderate uptick in wind strength
Wednesday and Thursday with gusts topping out between 15-25kts each
day. Saginaw Bay could see gusts near 30kts Thursday due to
NE winds channeling down the bay.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.

&&

$$

AVIATION.....BT
DISCUSSION...KGK
MARINE.......KDK


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