470
FXUS63 KDTX 171937
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
337 PM EDT Mon Jun 17 2024

.KEY MESSAGES...

- A prolonged period of heat and humidity will continue through the
week. Excessive heat warnings and heat advisories are in effect.

- There will be periodic chances for thunderstorms throughout the
week. Locally heavy rainfall will be primary driver of impacts.

&&

.DISCUSSION...

Amplifying upper-level ridge episode over eastern North America and
correlated building heat dome is well underway. Surface dewpoints
are surging into the lower 70s with temperatures climbing to around
90 - pushing heat index values into the upper 90s. Furthermore, low
temperatures will only settle back to around 70 with higher readings
in the urban settings (mid-70s). These conditions will be the norm
for the balance of the work week and will take its toll on exposed
populations - hence the long duration heat advisory and excessive
heat warning.

Subsidence in the wake of the morning mesoscale convective vortex
and associated thunderstorms is starting to lose influence across
southern Lower Michigan. There is still evidence of a ribbon of anti-
cyclonic enhanced flow aloft over Southeast Michigan in the GOES-WV
imagery. Consequently, expect the suppression of deeper cumulus
development to continue over the next few hours. The scattered
activity along the periphery over the Saginaw Valley will continue
to bubble northeast across the thumb. While there is plenty of
instability to tap (MLCAPE > 2.5-kJ/kg) with adequate depth (>2-km),
there is very little flow and/or shear to support scaled growth.
Therefore, heavy rainfall is the primary outcome with some wet
microburst potential with hydrometeor loading in deeper cells.

The quality of instability on Tuesday will not be as good, but a
north-south oriented buoyancy gradient in the 1-2-km layer will
linger over Southeast Michigan. This in combination with better jet
level forcing rolling north into the region will help initiate
scattered thunderstorms once again. Precipitable water values will
increase to well over 1.75-inches - supporting intense downpours
once again. If the buoyancy gradient maintains integrity along the
mean flow vector, convective training and resultant flash flood
potential will be more likely. Still some variance in guidance
offerings, but a small cluster of heavy rainfall outcomes is very
evident.

The mid-levels do not get dramatically warm with this heat dome;
therefore, afternoon convection is possible each day through this
heat spell. Medium range guidance is now suggesting that the current
heat will grab another day on Saturday with the timing of the next
shortwave and cold front remaining questionable.

&&

.MARINE...

Southwest winds will continue to advect hot and humid air into the
Central Great Lakes through the mid week period. High degree of
surface stability with the cooler waters should keep wind speeds
under 25 knots through the rest of the work week. The exception will
be in and near and strong thunderstorms which develop. Timing and
location will be highly uncertain, but the typical peak heating of
the day into early evening hours will be favored. Indications are
the surface frontal boundary will be sinking south Thursday and
Friday as seasonably strong high pressure tracks through Ontario.
This will allow for light northeast/northerly flow (~15 knots) over
Lake Huron. Airmass will remain warm, thus any wave build up with
the longer fetch remains below 4 feet.

&&

.HYDROLOGY...

A moist and unstable airmass will be in place across the region
through Tuesday. Scattered thunderstorms are expected this afternoon
and again Tuesday afternoon. The most intense thunderstorms have the
potential to produce rainfall amounts in excess of 2 inches over a
short period of time, resulting in urban and low lying area
flooding. Uncertainty in specifics for both timing and potential for
flooding precludes issuance of a flood watch, at this time.

&&

.PREV DISCUSSION...
Issued at 157 PM EDT Mon Jun 17 2024

AVIATION...

VFR conditions will prevail the much of this TAF period with daytime
heating and the increased moisture supporting a cumulus field at
around 6kft this afternoon. There remains potential for
afternoon/early evening isolated/scattered thunderstorm development
supported mainly by the diurnal instability. The overall uncertainty
and anticipated pop up nature of activity will preclude mention in
TAFs at this time, but may require an amendment if confidence
increases for any terminal to be affected. Low VFR to possible MVFR
conditions would be possible with any heavier shower/thunderstorm.
Winds will be out of the southwest through this afternoon while deep
mixing is yielding gusts to around 20 knots. Winds back towards the
south for tonight before veering back towards the southwest tomorrow.

For DTW/D21 Convection... There remains a chance for isolated to
scattered showers and thunderstorms to develop this afternoon.
Confidence is not high enough that any D21 terminal will be
impacted, so will not include a tempo group at this time. The favored
time frame for activity is towards 22-00Z. Will continue to monitor
and amend if needed.

DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms this afternoon and evening.

* Low for ceiling at or below 5000 ft, conditional with convective
  development.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory until 8 PM EDT Friday for MIZ047>049-053>055-060-062-
     063-068-075-082-083.

     Excessive Heat Warning until 8 PM EDT Friday for MIZ061-069-070-076.

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

$$

DISCUSSION...Mann
MARINE.......SF
HYDROLOGY....Mann
AVIATION.....AA


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