368
FXUS63 KDTX 050737
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
337 AM EDT Fri Jul 5 2024

.KEY MESSAGES...

- A Low pressure system arrives over lower Michigan this afternoon
and evening. This will bring scattered to numerous showers with
embedded thunderstorms, with highest coverage favored over the Tri-
Cities and Thumb.

- There is a Marginal Risk of severe thunderstorms in the afternoon
and evening for all of SE MI.

- The low pressure system lingers over the Great Lakes tomorrow
keeping a low chance (25%) of showers and thunderstorms in the
forecast.

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

&&

.DISCUSSION...

1008 mb low pressure system over southern Wisconsin will expand and
move into lower Michigan through this afternoon and evening. Prior
to the arrival of low pressure, moisture transport magnitude will
increase this morning and afternoon under favorable southwest flow,
increasing PW values to around 1.50 inches and h850 dew points aoa
12C. Isolated to scattered rain showers will initially be possible
through the late morning and early afternoon hours once daytime
heating starts and instability builds. Expansion to numerous showers
with embedded thunderstorms then turns increasingly likely through
the late afternoon and evening hours as the low and associated
triple point arrival over Michigan, coinciding with peak diurnal
heating, where modest CAPE values of 500-800 J/kg will be in place.
Latest model guidance places the low center around the Tri- Cities or
just north with the warm front extending into the Thumb by the
afternoon/early evening. This is where the bulk of the activity will
likely commence and thus where PoPs are greatest (70%). Expansion of
a cold front moves through after 21Z through late tonight, where
increasing shower and storm activity will then be possible for the
remainder of SE MI.

There will be plenty upstream mid and upper-level clouds filtering
in through the day which will not be a favorable factor for
instability. 0-6/1-6km shear around 30-35 knots will help support
some organized convection. The hodographs are quite impressive by 21Z
and are nearly straight through northern lower and portions of the
Tri-Cities and Thumb, with a bulk of strong shear noted in the 6-12
km layer. EL in modeled soundings fall within the 6-12 km layer so a
portion of this shear will not be realized with convection, but
overall it shows strong speed shear through the mid to upper-levels.
Pulse, multicell clusters and/or mini-lines with possible bowing
segments will all be in the realm of potential storm modes noting the
above. Hail to an inch (lower than average freezing levels, straight
hodographs) and/or gusts to 60 mph (wet microbursts) will be the
primary severe threats. SWODY1 highlights a marginal risk for severe
weather across SE MI today, with 2PM - 10 PM as the primary threat
window, noting the modest instability as an inhibiting factor.

Some isolated residual showers will be possible during the overnight
period as a trailing upper-level trough axis swings over the state.
Otherwise, passage of the low pressure system will have pushed the
cold front over SE MI, which will bring a little relief from the
heat as highs peak in the upper 70s tomorrow. A lower end chance
(25%) for a shower or storm will hold through the afternoon and
evening as a weaker shortwave pulses overhead while very modest
instability builds (mainly north of M59). A major inhibiting factor
to organized shower and storms activity will be a building mid-level
cap around h600 that increases in strength through the afternoon.

An brief shortwave ridge with an expanding surface high pressure
system will fill in over Michigan on Sunday limiting precipitation
as highs rise back into the low to mid 80s. A series of upper-level
waves will expand through the Plains through the early week period
with trough amplification commencing into the western portion of the
Midwest. This will draw in warm air downstream across SE MI, with
h850 temperatures peaking around 18C by Monday evening supporting
highs into the mid to upper 80s. Additionally this will mark
increasing chances for showers and thunderstorms by Monday, initially
along a leading shortwave, with increasing potential for showers and
storms on Tuesday as the trough axis moves over the state.

&&

.MARINE...

Relatively quiet conditions to start the day as a weak ridge passes
over the region this morning. This is followed by the arrival of a
low pressure system which sends a warm/occluded front eastward
across the central Great Lakes during the daylight hours. Scattered
showers and storms will accompany this system, and isolated storms
may become severe with gusts in excess of 35 knots and hail
possible during the afternoon and evening. The cold front moves
through this evening as the low slowly departs to the east which
will bring an end to much of the convection tonight. Lingering
showers may continue into parts of Saturday as weak troughing holds
over the region. A broad ridge of high pressure then fills in on
Sunday with mainly dry conditions and continued light winds. The
next frontal boundary moves into 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 scattered to 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 0.75 inch until activity
diminishes and exits eastward toward evening. Highly localized totals
between 1- 2 inches will be possible with repeated thunderstorms,
which will be most likely across the Tri-Cities and/or Thumb. Steady
motion of the system location and location of the higher end rainfall
totals mitigate any serious considerations of flooding, with threats
limited to ponding of water on roads and in areas prone to
collecting standing water.

&&

.PREV DISCUSSION...
Issued at 1202 AM EDT Fri Jul 5 2024

AVIATION...

Surface trough has now exited the airspace, leaving a lingering pool
of low level moisture that has started to materialize into shallow
MVFR to occasional IFR fog at PTK and DET. There is still low
confidence in if these conditions develop at other terminal sites,
so will maintain the inherited TEMPO groups. Early stages of the
diurnal heating cycle should be sufficient to mix out any morning
fog by around 11-12z. Attention then turns to convective potential
this afternoon-evening. 00z guidance has shifted back toward later
thunderstorm timing, unveiling two potential windows for convection.
The first would be along a pre-frontal trough that moves into the
airspace between 20z and 00z which would capitalize on peak heating.
The second would be along the cold front itself, which looks to
traverse the airspace west to east between 00z and 03z tonight.
Despite the less optimal forcing, the first window looks better
thermodynamically so will continue to carry roughly 20z to 00z
timing in the PROB30 groups for most likely thunderstorm timing. Any
thunderstorms that develop will have potential to become organized.

For DTW/D21 Convection...Scattered showers and thunderstorms
expected Friday as a pre-frontal trough and cold front track through
the area. The preliminary window for convective development still
looks to fall between 20z and 00z, although some recent guidance has
carried -TSRA as late as 03z tonight.

DTW THRESHOLD PROBABILITIES...

* Medium for thunderstorms between 20z and 00z Friday.


&&

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

$$

DISCUSSION...AM
MARINE.......TF
HYDROLOGY....AM
AVIATION.....MV


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