593
FXUS63 KDTX 191944
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
344 PM EDT Wed Jun 19 2024

.KEY MESSAGES...

- Hot and humid conditions will persist across most of the area
today as a Heat Advisory is in-place for all of Southeast Michigan.

- Cooler temperatures arrive tomorrow, mainly confined across
  portions of the Tri-Cities and Thumb.

- Chances of thunderstorms continue each day of the week, some of
which may be strong to severe with locally heavy downpours and
isolated damaging wind gusts.

&&

.DISCUSSION...

Retainment of the anomalously strong subtropical airmass
characterized by ~594 dam h500 heights (99.5th percentile to outside
of all climatological values wrt CFSR data set) continues through the
day today. In terms of surface impacts, the return of temperatures
highs back into the lower 90s with dew points in the upper 60s to
lower 70s, have bolstered afternoon heat indices in the mid to upper
90s, where a heat advisory remains in effect. For the remainder of
the afternoon and evening, attention will be focused on
thunderstorms chances, specifically along land/lake differential
heating boundaries and from inland locations, where an enhanced
ribbon of h850-h700 theta-e will expand in from the Toledo area.
differential heating along the demarcation of clouds, and/or the
slight surface convergence along the glacial ridge can also be focal
point for initiation. In subtropical conditions with h850 dew points
aoa 10C, it will not take much for storm initiation, but confidence
on the exact initiation point is lowered.

The main hazard for any thunderstorm development will be
precipitation loading that can result in wind gusts up to 60 mph.
MUCAPE approaching 2,000 J/kg along with theta-a indices around 25
and PW values of 1.80 inches support heavy downpours with any
thunderstorms. Strong 0-3 km lapse rates around 9C/km and a mini-
inverted V sounding with DCAPE values aoa 1000 J/kg support strong
downward momentum transfer with evaporative cooling potential. Hail
to an inch would be a secondary concern, but as is common in humid
airmass, high freezing levels and warm rain processes will
contribute to melting. The overall kinematics are poor with bulk
shear values around 20 knots with pulse to multicell clusters as the
main storm mode. Last, LCL-EL (cloud layer) mean wind sits at around
15 knots. Slower storm motion with heavy downpour and thunderstorm
training potential brings the risk for highly localized
precipitation accumulation which may lead to localized flooding
concerns. Please see the hydrology section for additional details.
Any shower or storm development will taper off very late tonight.

Warm overnight lows continue with temperatures only dropping into
the mid to upper 60s overnight. Relief from hot temperatures will be
felt across the Tri-Cities and Thumb, especially along the
shorelines, as a backdoor cold front advects inland. Communities
along the shoreline will likely not break the 80 degree mark, while
locations more inland across the  Tri-Cities and Thumb have high
probabilities of staying capped below the 90 degree mark. There
remain uncertainties with how far inland the cooler air will expand
through, but the latest NBM output holds a 60% or higher probability
to achieve 90 degrees for a daytime high along and south of M59,
with increasing probabilities (near 100%) within urban Detroit and
closer to the MI/OH border. Heat indices will peak in the mid 90s
outside of the cold front. The heat advisory has been further
trimmed to reflect the locations that have high confidence to be
impacted by the cooler air. Renewed isolated to scattered
thunderstorm development will also be likely tomorrow afternoon and
evening. Surface convergence across the multiple boundaries
(northeast flow from Huron, west-northwest flow off of southern Lake
Michigan, southwest flow from northern Indiana) will provide
multiple chances for initiation. Wet microbursts with wind gusts up
to 60 mph and highly localized flooding will again be the main
concerns for any stronger thunderstorm development.

This pattern of above normal temperatures will continue to end the
week. Friday will again have cooler temperatures along and in the
vicinity of the lakes with the northeast flow in place along with
renewed rain and shower chances in the afternoon. For Saturday,
multiple shortwaves will ride along the periphery of the heat dome
and will advect some of the hottest air across the western Midwest
into the Great Lakes. This has the potential to support a boost back
into the mid-90s for the southern portion of the cwa and will
diminish the lake influence for the northern third as southwest flow
returns. As of right now the increased stability looks to keep the
greater portion of the cwa dry, but any slight modification of the
shortwave path to the south with new model output would put us in
the path of potential thunderstorms. Breakdown of this pattern looks
to commence on Sunday once a prefrontal trough and eventual cold
front swing over the state. Showers and storms will be likely along
the prefrontal trough.

&&

.MARINE...

Hot and stable conditions across the waters maintain low wind and
waves today outside of any thunderstorm activity. Timing and
location will be highly uncertain, but the typical peak heating of
the day into early evening hours will be favored. Some breakup in
the pattern occurs Thursday as high pressure builds across Ontario
which forces a cold front south through Lake Huron. This will flip
winds around to the north but warm temperatures remain across
region. A stronger cold front looks to be on track for the second
half of the weekend however, 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 unstable airmass will remain in place through the end of
the week. Isolated to scattered thunderstorm development are
expected across portions of SE MI this afternoon and evening. The
most intense thunderstorms will have the potential to produce highly
localized rainfall amounts of 1-2 inches in a 30-60 min period.
Thunderstorm training (repeated thunderstorms) can also provide the
chance see highly localized totals of 1-2+ inches. Uncertainty in
specifics of location and exact timing for any flooding precludes the
issuance of an flood watches. Additional storms with highly
localized flooding potential will again be possible on Thursday
during the afternoon and evening.

&&

.PREV DISCUSSION...
Issued at 118 PM EDT Wed Jun 19 2024

AVIATION...

A large lobe of 850-700mb thetae content is forecasted to lift
northward and pivot into far Southeast Michigan after 21Z.
Convergence along a secondary warm front feature within the northern
flank of the thetae air mass is expected to provide enough forcing
for shower and thunderstorm development this afternoon. Current
cumulus development south of Toledo is lined out generally along the
gradient. Additionally, model data does suggest some weak cyclonic
circulation or mesolow feature is possible leading to a scattered
coverage. Hires signal suggests the potential exists for
thunderstorms to develop and track northward through DTW/YIP
terminals. Less confidence exists with how far northward thunderstorm
activity will persist this evening.

For DTW/D21 Convection...The potential exists for thunderstorm
activity between 20-24Z today. The shower and thunderstorm activity
is expected to be scattered.

DTW THRESHOLD PROBABILITIES...

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


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory until 10 PM EDT this evening for MIZ047>049-053>055-
     060>063.

     Heat Advisory until 10 PM EDT Thursday for MIZ068>070-075-076-082-
     083.

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

$$

DISCUSSION...AM
MARINE.......AM
HYDROLOGY....AM
AVIATION.....CB


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.