161
FXUS63 KDTX 141959
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
359 PM EDT Sun Jul 14 2024

.KEY MESSAGES...

- Isolated thunderstorms are possible this evening, becoming more
  likely overnight into Monday morning as a thunderstorm complex
  tracks into the Great Lakes from Wisconsin.

- Isolated damaging wind gusts, large hail, and localized flooding
  will be possible with any thunderstorms today and tonight 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 Monday night and Tuesday.

&&

.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.

&&

.PREV DISCUSSION...
Issued at 121 PM EDT Sun Jul 14 2024

AVIATION...

One remnant meso convective vortex, MCV, was pushing from Lake Huron
into Ontario while another was near GRR.  At the same time, there is
a line of storms well to the south near FWA and points southwest
that continues to gain strength as it pushes into western OH. All of
this has left mostly broken chaotic skies across lower MI with
clouds at all levels. Where it has cleared to some extent, cumulus
around 3k feet was developing especially south of a GRR to DET line.
Expect this to continue through the afternoon along with the sw wind
with gusts into the lower 20kts. Still a small chance that a few
showers or storms may develop with a modest increase in instability
near the MCV over wester Lower as it moves across southeast MI. At
this point chances are too low to put into any TAF.

After that MCV exits the state around 21-22z, just expect some
cirrus mainly from debris from convection around Lower MI until the
next potential convective complex moves from the Chicago-land area
and affects Lower MI. Some building consensus that would likely hold
together enough to at least be in a diminish state over southeast MI
after midnight tonight. Upped the PROB30s to TEMPO for the TAF sites
from FNT south through the Detroit area.

In the wake of that convection overnight and early Monday morning,
expect much of Monday to be dry with just a residual sct-bkn cumulus
developing with a southwest wind again becoming gusty up to 20kts.

For DTW/D21 Convection...Isolated storms may fire anywhere in the
D21 area from 19z to 22z as the MCV tracks over the D21 air space
during the peak heating of the afternoon. Most likely chance of
thundestorms will be just after midnight to just before daybreak
Monday morning as the next convective system develop over IA, WI and
IL late this afternoon.

DTW THRESHOLD PROBABILITIES...

* Low for ceilings aob 5,000 feet this afternoon.

* Low for thunderstorms from 19z to 22z this afternoon. Medium after
  midnight into very early Monday morning.


&&

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

$$

DISCUSSION...MV
MARINE.......KGK
HYDROLOGY....MV
AVIATION.....RBP


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