579
FXUS63 KDTX 170741
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
341 AM EDT Mon Jun 17 2024

.KEY MESSAGES...

- Heat and humidity will affect the area through the week. Excessive
heat warnings and heat advisories are in effect.

- There will be periodic chances for thunderstorms throughout the
week.

&&

.DISCUSSION...

A compact mid level MCV will traverse Se Mi during the early morning
hours. This wave has been responsible for clusters of strong to
severe convection upstream, with the more robust convective response
occuring closer to the sfc warm front. The passage of this wave and
influx of deep layer moisture and elevated instability will sustain
some degree of convection across Se Mi this morning, particularly
across the southern portions of the forecast area. Elevated
instability will be advecting into Se Mi from the west during the
course of the early morning, which may be enough support isolated
strong to marginally severe convection.

Some building of the mid level height field in the wake of this
mornings MCV will allow respectable diurnal heating to occur. High
temps upstream yesterday were in the lower to mid 90s, which look
reasonable across Se Mi this afternoon. Diurnal mixing will likely
hold sfc dewpoints in the 60s this afternoon which will cap heat
indices in the mid to upper 90s. Forecast soundings across Se Mi
this afternoon/evening are uncapped. Late day convective development
can therefore not be ruled out, especially considering lingering sfc
boundaries expected across Se Mi.

A building mid level ridge across the East Coast over the next
couple days will be responsible for the heat across the southern
lakes. Models have been very consistent showing 500mb heights rising
to 598-600dm as the mid level high becomes centered over the Mid
Atlantic Wednesday into Thursday, while the ridge axis builds
westward across the Ohio Valley and eastern Great Lakes. Thermal
profiles (with 850mb temps of +19 to +21C) across southern Michigan
will be supportive of high temps into the 90s.

There does remain considerable uncertainty as to the timing and
strength of numerous short wave impulses that will be circulating
around the large mid level ridge, especially Tuesday and Wednesday.
These short waves are likely to impact portions or all of Se Mi at
times and will continue to support a chance of showers and
thunderstorms. Moderate to possibly high instability with a little
bit of mid level flow along the northwestern side of the ridge will
support a chance for a few strong to severe storms both Tuesday and
Wednesday. Timing/coverage however remains highly uncertain. Medium
range model ensemble members show increasing spread in the Friday to
Sunday time frame with respect to the breakdown of the mid level
ridge across the Great Lakes resulting from northern stream energy.
This and the increasing potential for convection to bleed into
portions of Se Mi lead to some degree of uncertainty as to temps
late week into next weekend.

The excessive heat watch was issued due to multiple consecutive days
of hot weather as opposed to just one day of possibly breaking a
heat index of 100. This is due to the fact that heat stress worsens
with number of consecutive hot days. Per coordination with
surrounding offices, the heat watch is being replaced with a long
fused head advisory. The exception to this is the urban Detroit and
Flint areas (Wayne, Oakland, Macomb, Genesee Counties) where a
warning is being issued given the more adverse affects of heat on
these urban areas.

&&

.MARINE...

A warm and humid airmass will hold over the Great Lakes through the
week, which will support relatively stable near surface lake
conditions. The earlier passage of a warm front has reinforced south
to southwest flow, which will hold through at least the early week
period. Otherwise, there will be a couple of chances for showers and
thunderstorms today. The first through this morning, pending the
evolution of an upstream storm complex, with renewed chances
possible later this afternoon and evening. Additional development is
possible tomorrow, but this is more favored over land or along the
nearshore. Localized stronger wind speeds and gusts around 20 to 25
knots will be possible through the Saginaw Bay into central Lake
Huron with the favorable southwest fetch tomorrow.

&&

.HYDROLOGY...

A moist and unstable airmass will be in place across the region
through Tuesday. This will bring the potential of a few rounds of
showers and thunderstorms this morning through at least Wednesday.
Locations which experience strong thunderstorms will have the
potential for rainfall amounts to exceed 2 inches in a short period
of time, leading to urban/low lying flooding. There is too much
uncertainty both the timing and potential for localized heavy
flooding to issue any type of flood watch products at this time.

&&

.PREV DISCUSSION...
Issued at 1207 AM EDT Mon Jun 17 2024

AVIATION...

A large cluster of thunderstorms now represents both earlier surface
based activity plus new development farther west fed more by
nocturnal mechanisms. The parent MCV still makes storms possible
farther north toward MBS although radar trends at forecast issuance
clearly favor PTK and the DTW corridor for several hours of
borderline MVFR/IFR conditions depending on rainfall intensity.
Other observational trends will be monitored for signs of greater
coverage of ceiling or visibility restriction within the frontal
zone. The shower/storm pattern then moves eastward by late morning
and VFR cumulus follows within the inbound heat and humidity for the
afternoon. A stray pop-up shower or storm is possible in this air
mass but with predictability too low for a mention at this point in
the forecast.

For DTW/D21 Convection... The leading edge of thunderstorms inbound
from LAN to JXN weaken to lighter showers in favor of new storms
farther west. It is possible the later activity holds together for
scattered storm coverage across D21 and at DTW after 08Z until about
12Z. Localized heavy rainfall is the primary hazard with this
activity until moving east of D21 by late morning.

DTW THRESHOLD PROBABILITIES...

* Moderate for thunderstorms at the terminal late tonight into early
  morning.

* Moderate for ceiling 5000 ft or less mainly with convection late
  tonight and early morning.


&&

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

     Excessive Heat Warning from noon today to 8 PM EDT Friday for
     MIZ061-069-070-076.

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

$$

DISCUSSION...SC
MARINE.......AM
HYDROLOGY....SC
AVIATION.....BT


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