382
FXUS63 KDTX 150403
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1203 AM EDT Mon Jul 15 2024

.KEY MESSAGES...

* A thunderstorm complex tracks into the central Great Lakes from
  Wisconsin early this morning.

* Isolated damaging wind gusts, large hail, and localized flooding
  will be possible with any thunderstorms this morning as storms
  track west to east at 40 mph.

* Warm and humid conditions expected Monday with heat indices in the
  mid 90s.

* Additional chances for strong to severe thunderstorms and flooding
  rainfall exist tonight and Tuesday.

&&

.AVIATION...

The apex of the MCS is moving over Chicago into southwest IN early
tonight with the northern extension of this complex likely to move
through southwest lower Michigan. Latest model guidance continues to
show portions of this system lasting into southeast Michigan, but in
a much more weakened state as environmental conditions are less
favorable for MCS maintenance with further eastward extent. Showers
and thunderstorms with the MCV on northern end of the complex will
move through by around 08Z with showers and thunderstorms further
weakening post sunrise. After convection comes to an end, lower VFR
to possible MVFR clouds should linger into the afternoon with a
period of dry conditions. Mixing depths by early tomorrow afternoon
bring potential for gusts up to 20 knots.

For DTW/D21 Convection...A thunderstorm complex has developed
upstream across WI and IL this evening and will move across Lower
Michigan through the early morning hours. Showers and thunderstorms
should be able to make it into southeast Michigan, but in a
weakening state. Moderate confidence exists in thunderstorm arrival
to D21 airspace by around 08Z with activity lasting through about
12-13Z. Strong wind gusts will be the main threat.

DTW THRESHOLD PROBABILITIES...

* Medium for thunderstorms early this morning.

* Medium for ceilings aob 5,000 feet mid/late morning and afternoon.

&&

.PREV DISCUSSION...
Issued at 359 PM EDT Sun Jul 14 2024

DISCUSSION...

Advertised active pattern is well underway this afternoon as a warm
and unstable airmass settles over the Upper Midwest and Ohio Valley.
The MCS has stayed comfortably to our south, accelerating toward the
instability reservoir over central Indiana-Ohio. This is in contrast
to the local environment where observed surface temperatures have
lagged behind models by 2-3 degrees, maintaining a weak but
effective capping inversion so far this afternoon in the absence of
strong forcing. Otherwise, dewpoints near or above 70 degrees have
resulted in muggy conditions despite near-normal temperatures in the
mid 80s.

While an isolated shower or thunderstorm is possible this evening as
currently noted over Lenawee-Monroe Counties, the more robust
convective response is expected overnight into early Monday morning
as an MCS again traverses into the Great Lakes. MCS initiation will
occur further east than last night, over Wisconsin, forming along a
frontal zone/convergence axis and propagating southeast along the
instability gradient. There will again be an attempt to lift this
gradient into lower Michigan with help from both a convectively-
enhanced shortwave and ~30 knot nocturnal low level jet. This
provides a more favorable environment for the MCS and/or its remnant
MCV to persist into SE Michigan compared to last night, supporting
primarily a heavy rainfall risk as any convection will exhibit high
precipitation efficiency and training potential. Localized rainfall
amounts in excess of 2 inches will be possible, please see the
Hydrology section for more details. Nocturnal timing will be
resistant to surface-based convection, but if elevated instability
materializes then cannot rule out a few stronger precipitation cores
capable of producing hailstones of 0.75" to 1" diameter mainly after
10 PM this evening.

Showers and thunderstorms linger for the first half of the day
Monday, along with convective debris to result in a chaotic and low
predictability cloud forecast. While the potential is there for
portions of SE Michigan to exceed 90 degrees, morning cloud cover is
expected to suppress daytime heating enough to keep majority of
locations below heat advisory criteria. That said, temperatures in
the upper 80s and dewpoints in the low 70s will produce heat indices
in at least the mid 90s for Monday. Pending any outflow interactions,
Monday afternoon-early evening generally remains dry.

The warm and unstable airmass holds steady Monday night and Tuesday,
with increasing large-scale support for organized convection as an
expansive upper trough and surface low move into the upper Midwest.
Eastward progression of the system will lift a warm front into the
area late Monday night, preceding yet another nocturnal MCS that
presents a more organized strong to severe threat late Monday-early
Tuesday morning. Nocturnal timing of the MCS suggests the system
will lose its surface-based inflow and weaken by the time it reaches
SE Michigan, but this is not a guarantee should the warm sector be
well-established by then. SPC has designated a Marginal Risk for
most of the cwa for Monday night, although areas west of I-75 are in
a Slight Risk for severe weather. Heavy rainfall will again be a
concern with these storms.

Final push of convective potential comes Tuesday as a cold front
tracks across the Great Lakes, which will eventually usher in a
cooler and drier Canadian high pressure system for the remainder of
the week.

MARINE...

Initial round of afternoon thunderstorm activity associated with a
forward propagating MCS has largely held just south of the Lower
Peninsula keeping the central Great Lakes dry, thus far. Low-end
convective potential still remains through the rest of the afternoon
before the next surge of storms pushes in late tonight or early
Monday morning. This activity likely takes on the form of a
secondary MCS/MCV originating from a more pronounced shortwave
trough aloft that will pivot over southern Lake Michigan and then
turn northeast, toward southern Lake Huron. Monday afternoon looks
to be rather quiet/stable before a more potent wave drives a better
organized convective line across the Great Lakes Monday night. Both
systems pose a heightened risk for locally higher winds/waves and
some hail. A cold front lags the convection Tuesday before it
eventually clears through, offering more seasonable temperatures and
quieter conditions by midweek.

HYDROLOGY...

Isolated thunderstorms are possible this evening ahead of a
thunderstorm complex that will track into the Great Lakes late
tonight through early Monday morning. This thunderstorm complex will
be capable of torrential downpours with a quick inch or more of
rainfall possible as several storms may move repeatedly over the
same area. There is still a signal for a moisture gradient to set up
near the Ohio Border to urban Detroit corridor, which could result in
even higher totals in excess of 2 inches south of I-94. Urban and
low-lying areas along with elevated river basins will be most
vulnerable to this heavy rainfall. Additional chances for
thunderstorms exist Monday night and Tuesday with similar heavy
rainfall concerns.

&&

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

$$

AVIATION.....AA
DISCUSSION...MV
MARINE.......KGK
HYDROLOGY....MV


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