204
FXUS63 KDTX 181753
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
153 PM EDT Tue Jun 18 2024

.KEY MESSAGES...

- Hot and humid conditions will persist across most of the area
through the week.

- Chances of thunderstorms will continue each day of the week. Some
of these storms may be strong to severe with locally heavy
downpours.

&&

.AVIATION...

Complex aviation setup today with current cloud cover and possible
thunderstorms this afternoon. Extensive cloud cover due to mid level
wave passing over lower MI this afternoon has prevented temperatures
from rising as rapidly as previously thought which in turn will
likely cause storms to be delayed. Storms have already initiated
over CLE and north of MBS, both of which had less cloud cover and
cu`ed up already. With lake breezes already forming, and the back
edge of the denser clouds exiting in a couple hours, will hold onto
thunderstorm chances for now in a 20-23Z window. Winds will
generally be out of the south/southwest around 12 knots with a few
gusts to near 20 possible. Strong gusty winds and microburst
potential exists with the deepest convective storms. Otherwise VFR
conditions should hold the rest of the evening and overnight.

For DTW/D21 Convection...Storms currently going up east and
southeast of DTW in the areas where skies have remained mostly
clear. Looks like clouds could thin on the backside of the passing
wave allowing temps to peak and storms to be possible. Lake breezes
are already forming which should help any storms to develop later.
Bumped the timing of the storms back an hour to account for the
increased clouds, so looking around 20-23Z for best chance.
Potential for wet microbursts should stronger storms develop
over/near D21 airspace.

DTW THRESHOLD PROBABILITIES...

* Low to Moderate for thunderstorms from 20 to 23Z.

* Moderate for ceiling at or below 5000 ft, conditional with
  thunderstorms.

&&

.PREV DISCUSSION...
Issued at 901 AM EDT Tue Jun 18 2024

UPDATE...

One of the first tasks of the day was to update the grids to offer
some definition to precipitation chances.

This afternoon, absolute vorticity center/associated leafing now
centered over far northeastern sections of Illinois will lift
northward arriving west of the Saginaw Valley by 18Z. A modest but
organized kinematic field will push west to east in response of the
shortwave with an area of speed convergence pushing into eastern
sections of the cwa. Concurrently, a low-mid dry slot feature will
also impinge into Southeast Michigan from the west, setting the
stages for a coherent plume of low to midlevel thetae/moisture to
coalesce in place locally. There may also be a differential heating
component also at play, but overall the convergence axis and boundary
look to be synoptically forced from southern Lake Huron southward to
the Ohio River.

The MPAS runs and the HRW-ARW are all bullish on thunderstorm
activity across the far eastern 1/3rd of the cwa including Metro
Detroit between 18-22Z timeframe. This thunderstorm activity does
match up very well to the expected thetae plume. So did give some
thought about increasing PoPs to likely between 18-00Z. Thunderstorm
activity may lift northward into the eastern Thumb region then
between 22-01Z. Forecast soundings support around 1750 MLCAPE and
SBCAPE of around 2000 J/kg with all exhibiting weak to nil cap this
afternoon (700mb at only 7C). 0-6km bulk shear gets a little
interesting as the eastern edge of the kinematics arrive pushing 30
knots for a portion of the forecast area. Given the shear combined
with CAPE densities, the potential for strong to severe storms is
higher than yesterday. Much of the area is designated as a Marginal
risk for Severe Weather. The main threat will be strong to severe
windgusts from wet microbursts and water loading. Orientation of the
convergence forcing and resolved omega (parallel to mean flow) also
gives some real concern for heavy rainfall and isolated Flash
Flooding today over Metro Detroit. PWATS may exceed 2.0 inches this
afternoon.

PREV DISCUSSION...
Issued at 329 AM EDT Tue Jun 18 2024

DISCUSSION...

Amplification of the East Coast mid level ridge will be ongoing
today into Wednesday, with the ridge becoming more elongated as it
stretches across the Ohio Valley during the end of the week. Short
wave energy rotating along the western periphery of this ridge will
advance across western Lower Mi today. Hi res model solutions
generally suggest this will set up a thermal/instability gradient
across the western portions of the forecast area this afternoon.
This and potential lake breeze convergence zones across the eastern
portions of the area will provide enhanced boundary layer
convergence to support additional rounds of convection, mainly this
afternoon and evening. ML Cape values projected near 2k J/kg with
model soundings showing respectable CAPE density within an uncapped
environment will again be supportive of localized strong/severe
convection despite relatively week deep layer shear profiles. The
depth of the warm layer, with PWATs around 1.8 inches will support
some locally high rain totals as well.

Expectations are for temps to be a little cooler today compared to
yesterday given high clouds and the chances for an earlier
convective release. Forecast highs in the low 90s with dewpoints
near 70 will still push heat indices well into the 90s. The humidity
will sustain another warm night tonight as lows will likely hold in
the 70s. Some building/expansion of the mid level ridge across the
eastern lakes will sustain heat and humidity across Se Mi Wednesday.
Timing and coverage of convective development within a moderately
unstable and uncapped atmosphere will play heavily into forecast
highs. Thermal profiles suggest low to mid 90s for highs Wed with
heat indices well into the 90s to around 100. The potential for ML
CAPE values to exceed 2k J/kg with little to no capping inversion
will again support locally strong/severe convection.

A little more elongation in the mid level ridge noted in the 00Z
model suite increases the chances for a southward push of slightly
cooler air from the north on Thursday as high pressure expands
across the northern lakes. Short wave impulses embedded within the
westerly flow with a lingering instability gradient over southern
Lower Mi also looks favorable for additional convection. Therefore,
the heat headlines will extend only through Wednesday evening. A
longer wavelength trough forecast in the northern stream over the
weekend will attempt to drive the front back northward as a warm
front. The potential for convection will however support a low
confidence forecast on temps during the first half of the weekend.
The passage of the mid level trough and associated cold front will
then support cooler and less humid conditions by the end of the
forecast.

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 the end of the week. Scattered thunderstorms are expected
each day this week. 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.

&&

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

     Heat Advisory until 8 PM EDT Thursday for MIZ048-049-054-055-062-
     063.

     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.
&&

$$

AVIATION.....DRK
UPDATE.......CB
DISCUSSION...SC
MARINE.......SF
HYDROLOGY....SC


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