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773
FXUS63 KDTX 070703
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
303 AM EDT Tue May 7 2024

.KEY MESSAGES...

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- There is a chance of isolated to scattered strong to severe
  thunderstorms south of a Midland to Port Huron line this evening,
  the greatest chances are along/south of the I-94 corridor.

- Damaging winds, large hail and isolated tornadoes are the severe
  weather risks.

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

.DISCUSSION...

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A strong mid to upper level jet core circulating around the deep
large scale upper low over the northern high plains will advance
from the Mid Mississippi Valley into the northern Ohio Valley/srn
Great Lakes today. Mid level isentropic ascent and deep layer
moisture transport along the lead edge of an 85kt 500mb speed max
will be driven across Lower Mi this afternoon and evening. The lead
edge of elevated frontal forcing is expected to weaken as it
advances into Se Mi early this afternoon given the lingering
influence of a departing low level anticyclone, likely causing the
lead edge of showers to diminish as the move into Se Mi. The RAP
then indicates a respectable ribbon of forced ascent developing
along an axis from west-central Ohio into Sw Lower Mi in the 21Z to
23Z time frame, in tandem with increasing upper level divergence
along the nose of a 120 kt upper jet streak. This will correlate
with an influx of sfc based instability (with sfc dewpoints in the
low 60s) lifting northward along an approaching sfc warm front. The
result will be the development of deep convection in the wake of the
initial band of showers. This convection is expected to move into Se
Mi during the course of the evening.

In terms of kinematics, 0-6 km bulk shear values are forecast to be
an impressive 60-80 knots across the northern Ohio Valley into Srn
Lower Mi this afternoon/evening. Rap and NAM hodographs also show
excellent low level curvature in the vicinity of the approaching sfc
warm front; 0-3km SR Helicity values over 350 m2/s3. The main caveat
for Southeast Michigan will be whether or not the surface based
instability is able to advect in from the southwest, especially
given the easterly component to the surface winds off Lake Erie.
While available SB CAPE is in question, 00Z model solutions still
drive anywhere from 500 to 1500 J/kg of elevated CAPE across Se Mi
this evening, with model soundings indicating respectable CAPE
density. These factors would suggest storms that develop upstream
will be rooted in the boundary layer, then become more elevated as
they move across Se Mi during the evening. Given the close proximity
to the sfc instability reservoir (as well as the instability
gradient), the southern portions of the forecast area remains in a
slight risk for all types of severe weather including tornadoes.
Severe weather risk will be more a result of hail and isolated
strong wind gusts risk farther north where the depth of the sfc
stable layer will become much greater. Upstream convective mode is
expected to be supercellular, transitioning to multi cell cluster
and/or linear as storms move across Se Mi.

Ample mid level drying will expand across the area in the wake of
the evening convection and will persist through Wednesday. This will
warrant a dry forecast as developing low pressure within an
amplifying short is forecast to remain focused across the northern
lakes. Deep mixing depth per model soundings and a respectable
westerly flow (25-30 knots within the mixed layer) will support
breezy conditions Wednesday. A low level thermal gradient will
extend across the forecast area, with highs across the thumb hard
pressed to break 70, while metro Detroit/Ann Arbor and points south
should break 80.

There continues to be ample spread among model ensemble members as
to the track of the remnants of the upstream upper low. There is at
least agreement that this system will quickly dampen/shear apart as
it tracks across the Ohio Valley and srn Great Lakes Thurs/Thursday
night. Model spread involves timing and the degree of interaction
with short wave impulses dropping down from Canada and precise
timing and location of the associated mid level deformation, which
leads to a low confidence rain forecast. Any instability will remain
well south and given the expected northeast surface flow, which will
be a cool rain wherever it sets up over southern Mi.
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&&

.MARINE...

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Influence of high pressure wanes over the course of today as
Midwestern low pressure lifts a warm front into the region late this
afternoon-evening. Some strong to severe storms will be possible
over the southern Great Lakes this evening. System`s cold front
quickly follows tonight setting up slightly cooler westerly flow
Wednesday that then turns 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.
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&&

.HYDROLOGY...

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Numerous showers and scattered thunderstorms will impact southeast
Michigan late this afternoon through this evening. Despite a very
dry start to the day, ample moisture advection into the area during
the latter half of the day will allow some of the thunderstorms to
produce locally heavy rainfall. As is typical in these type of
convective situations, rainfall amounts will be highly variable
across the region, with high end amounts up to a quarter to half
inch possible. Overall, basin average rainfall should not pose
flooding concerns.
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&&

.PREV DISCUSSION...
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Issued at 1157 PM EDT Mon May 6 2024

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.
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&&

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

$$

DISCUSSION...SC
MARINE.......KDK
HYDROLOGY....SC
AVIATION.....BT


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