006
FXUS63 KDTX 211734
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
134 PM EDT Fri Jun 21 2024

.KEY MESSAGES...

- Marginal risk of severe thunderstorms this afternoon and late
  Saturday afternoon/evening, with damaging winds being the main
  hazard.

- Hot and humid through Saturday. High temperatures 85-90 today and 90-95 on
  Saturday, as heat indices peak out just under 100 degrees for
  Saturday.

&&

.AVIATION...

Early morning showers clear out, but isolated popup thunderstorms
are still expected across the CWA this afternoon and evening as a
stationary front remains overhead. Front migrates northward this
afternoon which in combination with daytime instability, creates the
environment for aforementioned storms to pop up. Have gone with a
TEMPO over PROB30 due to the imminent timing of the storms, but
confidence is low on the full extent of the event. Any storms that
do move overhead will produce MVFR to IFR conditions, based on the
strength of the downpour. All storms look to be clear of the area by
02Z tonight at the latest, shifting instead to the northern Lower
Peninsula and Lake Huron. Some light fog is possible overnight,
mainly at MBS where light winds off the lake produce favorable
conditions for sustained fog.

The next chances for showers and storms come on Saturday afternoon
and evening. MBS and FNT see the greatest chances for development
with the stationary front maintaining north/south position. Low
pressure center moves into the area on Sunday, dragging a cold front
across the region and bringing with it additional chances for
showers and storms. After frontal passage, the pattern of daily
isolated popup showers looks to be broken, with high pressure and
clearer weather filling in behind to start next week.

For DTW/D21 Convection... Conditions remain favorable for
thunderstorms with mid afternoon to evening timing. The combination
of Erie/St. Clair lake breeze and stationary front near the MI/OH
border provide the best chances for storm development until the
front moves north of DTW later tonight.

DTW THRESHOLD PROBABILITIES...

* Moderate for thunderstorms impacting the airspace this afternoon
  and evening.

&&

.PREV DISCUSSION...
Issued at 1040 AM EDT Fri Jun 21 2024

UPDATE...

Forecast message still largely unchanged from prior discussion with
only some minor adjustments this morning owing to the SPC update
expanding marginal risk north into the Saginaw Valley area. Humid
airmass remains firmly in place with 12Z KDTX RAOB showing 1.72" of
PW as well as ~900 J/kg of MUCAPE residing above the near-surface
nocturnal inversion. CAM guidance continues to advertise surface
based capes increasing to between 1000-1800 J/kg by this afternoon
supporting scattered convective development across the bulk of the
CWA. Shear is lacking (aob 25kts) limiting potential organization
though given the moisture availability, isolated strong downbursts
similar to the past few days will again be possible. Activity wanes
into the late evening period (by roughly 03Z) with the loss of
diurnal heating/instability in addition to remnant shortwave energy
finally fully pushing east of the area.

PREV DISCUSSION...
Issued at 300 AM EDT Fri Jun 21 2024

DISCUSSION...

Moist airmass in place, as the 00z DTX raob indicated a PW value of
1.78 inches with a 700 MB dew pt of 5 C. Similar moisture profiles to
hold through the day.

Last vestiges some shortwave energy/PV tracking through southeast
Michigan this morning (slight-low chance pops), with negative upper
level PV advection in the 18-00z window. Despite the unfavorable
environment/general subsidence late this afternoon, ill defined
leftover frontal boundary and diurnal instability (MLcapes of 1500
J/kg) still will likely prove worthy to fire up convection (bulk of
CAM solutions), but limited coverage (25-40%) expected. The normally
bullish NAM is actually indicating instability parameters a bit
lower compared to the past couple of days, but still potential for
isolated downburst damaging wind gusts, despite little in the way of
0-6 MB bulk shear (under 25 knots for majority of the CWA). Locations
south of I-69 stand the best chance with the greater cape build-up
south of the front. 850 MB temps of 17-19 C suggest airmass potential
in the upper 80s to lower 90s. But assuming clouds and scattered
convection develops, likely looking at temps in the 85-90 degree
range, in line with inherited forecast.

Warm (10+ C at 700 MB) and dry mid level dry slot pushes into
southern Lower Michigan this evening/around midnight, and hangs
around through a good portion of Saturday, likely capping activity
(south of I-69) and allowing for a warm and humid day with deep
southwest flow ahead of an approaching cold front. High temperatures
in the 90-95 degree range appear likely as 850 MB temps reach aoa 20
C, but mainly sub 70 degree dew pts expected to keep heat indices
just under 100 degrees.

Good 500 MB height falls (for summer standards) arrive around 00z
Sunday, which will weaken the cap and and potentially allow storms
to spread in late in the day or during Saturday evening. Increasing
0-6 KM bulk shear, reaching 30-40 knots by day`s end will bring the
potential of isolated severe storms with MLcapes at least around
1000 J/kg. SPC day 2 outlook puts southeast Michigan in marginal
risk. It should be pointed out, several model solutions (NAM/RAP)
suggest shower and thunderstorm activity holds off mostly until
Saturday night, which limits severe potential with leftover MUcapes
mainly under 1000 J/kg. Despite the unfavorable timing, the large
scale forcing is expected to support a broken to solid line of
showers and thunderstorms.

Modest cold advection to follow for Sunday, with 850 MB temps now
only progged to lower into the lower teens by Monday morning per 00z
Euro (vs 10 C indicated by 12z Euro). None-the-less, the 500 MB
trough axis swinging through the Central Great Lakes may still touch
off a few showers over the Thumb region as 500 MB cold pool (-15 C)
tracks through Lake Huron.

MARINE...

High pressures to the north and south of the Great Lakes result in
weak northerly flow across much of the region today. There remains a
weak stalled boundary across the southern Lakes which may try to be
a focus for strong storms once again today. Additional storms look
to track out of WI and across Mid MI into Lake Huron later today.
Mild air remains across the region resulting in stable conditions
across the waters minimizing wave heights into the weekend. Though
winds should remain generally light and out of the north, any
location in the vicinity of a stronger storm will have higher gusts
potential with it.  A more organized low pressure system will pass
through the northern Lakes Saturday night pulling a cold front
through the region on Sunday likely resulting in more widespread
convection and wind speeds then could reach or exceed 25 knots with
waves building to around 4 feet. Small craft advisories may be
needed.

HYDROLOGY...

A moist and moderately unstable airmass holds in place today.
Isolated to scattered thunderstorms are expected to develop once
again, capable of producing highly localized rainfall amounts in
excess of 2 inches in less than 3 hours due to the slow movement.
This amount of rain would result in urban/low lying flooding.

The daytime hours of Saturday look to be mostly dry before a line of
showers and thunderstorms track through southeast Michigan Saturday
evening/night. This activity will have potential to produce half an
inch to one inch of rain, especially if activity arrives in the
evening. Stronger thunderstorms will bring the potential for locally
higher amounts.

&&

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

$$

AVIATION.....BC
UPDATE.......KDK
DISCUSSION...SF
MARINE.......DK
HYDROLOGY....SF


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