804
FXUS63 KDTX 042354
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
754 PM EDT Thu Jul 4 2024

.KEY MESSAGES...

- Patchy light rain or sprinkles continue this evening, mainly toward
  the Ohio border. A heavier shower remains possible across the Tri
  Cities and Thumb.

- A low pressure system in the Midwest brings a surge of showers and
  thunderstorms across all of Lower Michigan Friday. There is a
  Marginal Risk of severe thunderstorms in the afternoon and evening.

- The low pressure system lingers over the Great Lakes Saturday
  keeping a chance of showers in the forecast.

- The holiday weekend closes out with dry weather Sunday under
  partly sunny sky.

&&

.AVIATION...

Weak SE-moving surface trough has been the focus for very isolated
convection near MBS this evening. This convection has struggled to
obtain much organization or longevity, with just a decaying shower
reaching the MBS airspace at issuance. For the remaining terminals,
a mixture of virga and occasional sprinkles will continue through
the evening but dry low levels maintain VFR conditions. Passage of
the surface trough veers winds to the northwest overnight,
diminishing below 5 knots. Overnight clearing trend is still
expected to some degree, but lingering mid-level moisture in the most
recent model runs will likely mute radiational cooling with lower
confidence in fog potential Friday morning as a result. If fog does
develop, it will dissipate shortly after sunrise as winds organize
out of the south ahead of the next system arriving Friday afternoon.
Low pressure, currently centered ~100 miles west of Minneapolis, will
drive a pre-frontal trough through the area after 18z Friday. There
is moderate confidence for organized thunderstorm development along
the boundary Friday afternoon-evening with isolated damaging wind
gusts and large hail possible.

For DTW/D21 Convection...Scattered showers and thunderstorms
expected Friday as a pre-frontal trough tracks through the area.
Preliminary window for convective development looks to fall between
21z and 00z with potential for isolated strong to severe storms.

DTW THRESHOLD PROBABILITIES...

* Medium for thunderstorms between 21z and 00z Friday.

&&

.PREV DISCUSSION...
Issued at 358 PM EDT Thu Jul 4 2024

DISCUSSION...

Upstream convective complexes changed the mesoscale environment
considerably over the last 24 hours as activity grew upscale into a
well organized MCV now affecting Lower MI this afternoon and
evening. The mid level circulation is weakening with time but
remains capable of light showers across the area through early
evening. Dry air below 700 mb, shown in the 12Z DTX sounding and in
hi-res model soundings, is proving to be an effective obstacle for
greater coverage reaching the ground but is expected to be overcome
in pockets until the mid level MCV circulation moves into Ontario by
mid evening. Hourly mesoanalyses reflect the stabilizing influence
of the high cloud cover limiting MLCAPE to sub 500 J/kg farther
north toward the hybrid surface front/trough/lake breeze boundary
lingering in northern to central Lower MI. An isolated heavier
shower materialized there as of forecast issuance suggesting a
rumble of thunder is possible through late afternoon and early
evening peak heating.

A weak mid level short wave ridge follows passage of the evening MCV
circulation leading to a few hours of dry weather with some decrease
in cloud cover late tonight. A quick transition into the next low
pressure system then begins as the leading edge of mid level
moisture approaches Lower MI Friday morning. Model trends over the
last few forecast cycles indicate slower timing and much less
coverage of showers on the leading edge of weaker/less effective
moisture transport. While this salvages the morning mostly free of
rain in SE MI, it does open the door to greater potential for severe
thunderstorms in the afternoon. The upgraded outlook is mostly out
of respect for the seasonably strong forcing brought by the mid
level wave and upper level jet, and for the potential of surface
based instability capitalizing on the lack of morning activity. It
would not take much to enable overachievement of MUCAPE from sub
1000 J/kg HREF projections into the 1000-1500 J/kg range combined
with the inbound wind profile producing bulk shear in the 40-50 kt
range. The other moving part that may be a negative factor is
occlusion of the surface system which could pinch the instability
axis southward before or during the afternoon to early evening storm
window. As usual, timing will then be everything in the
determination of severe storm outcomes.

The mid level dry slot is projected with good model consensus to
punch through southern Lower MI Friday evening while still shrinking
the deformation pattern from SW to NE into northern Lower MI. This
occurs as the mid level circulation deamplifies rapidly leaving just
a stray shower possible and entry level chance POPs maintained for
the bulk of Saturday. The in-between mid level ridge then remains on
schedule for Saturday night bringing weak high pressure and a chance
to close out the holiday weekend with warm and dry weather through
Sunday.

MARINE...

A weak trough settles across the central Great Lakes this evening
with isolated showers possible mainly near the shoreline areas.
Otherwise, weak winds and dry conditions prevail through early
Friday. Low pressure arriving from the Midwest on Friday then brings
a more active pattern with scattered to numerous showers with
embedded thunderstorms expected after noon. Isolated storms may
become severe with wind gusts in excess of 35 knots and hail. The
low begins to move out Friday night with winds veering to the
northwest, but lingering troughing holds through Saturday with
additional showers possible. A broad ridge of high pressure then
fills in on Sunday with mainly dry conditions and continued light
winds. The next cold front moves across the Great Lakes on Monday,
bringing another period of unsettled weather to start the week.

HYDROLOGY...

Low pressure moving into the Midwest swings a frontal system through
Lower Michigan during Friday while supporting numerous showers and
scattered thunderstorms across the area. Locally heavy rainfall
could briefly reach rates of 1 inch per hour while basin average
totals come in closer to 0.25 to 0.5 inch until activity diminishes
and exits eastward toward evening. Steady motion of the system
mitigates any serious concerns with flooding potential limited to
ponding of water on roads and in areas prone to collecting standing
water.

&&

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

$$

AVIATION.....MV
DISCUSSION...BT
MARINE.......TF
HYDROLOGY....BT


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