722
FXUS63 KDTX 242004
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
404 PM EDT Mon Jun 24 2024

.KEY MESSAGES...

- A complex of showers and thunderstorms arrive early Tuesday
  morning bringing a low potential for an isolated strong to possibly
  severe wind gust. Locally heavy rainfall is also possible.

- An additional round of thunderstorms is possible Tuesday night
  into early Wednesday, mainly along and south of the I-94 corridor
  across Washtenaw and Wayne County.

- Cooler and less humid air moves back into the area late Wednesday
  and lasts through Thursday.

&&

.DISCUSSION...

Nearly full insolation this afternoon with a high pressure and
shortwave ridge moving through has allowed temperatures this
afternoon to climb mostly into the upper 70s and low 80s. The lower
humidity with dewpoints mostly in the lower to mid 60s should make
for a relatively pleasant evening free of any precipitation.
Temperatures tonight expected to fall into the 60s.

Attention turns toward the Upper Midwest tonight and the expectation
for upscale growth across Wisconsin. This system will be triggered
by a northern plains shortwave and move along a warm front.
Initiation will be near the triple point with a strong low level jet
of 50+ knots driving this MCS east/southeast. There still remains
some differences in the CAMs as to where the strongest portion of
this line sets up and moves into portions of western Michigan.
Greater consensus would be towards Chicago closer to the thermal
gradient. In any case, any northward extension of this system will
encounter a stable surface layer as it arrives into southeast
Michigan. There will be elevated instability to work with being
directed into the area via the strong low level jet, which will
support numerous to widespread coverage of thunderstorms spreading
across the area. Timing has activity reaching western portions of
the CWA between 09-11Z while continuing to weaken and push east
before 16Z with potentially trailing isolated to scattered showers
for the early portion of the afternoon. An outlook of general
thunderstorms is in place prior to 12Z tomorrow.

A Marginal Risk is in place for all of southeast Michigan post 12Z,
which would cover the bulk of these morning thunderstorms. While
expectation is for this MCS to be weakening, there remains at least
a low probability for an isolated strong to possibly severe wind
gust as this system rolls through. The greater surface moisture with
the warm sector arrives Tuesday afternoon in the wake of the early
morning system with dewpoints returning to the 70s. This will yield
strong afternoon instability, but indications are that there will be
a strong cap in place for the afternoon greatly limiting any the
potential for thunderstorms. Have cut back on PoPs from previous
cycle for tomorrow afternoon given this trend, but will continue to
monitor how things evolve post morning convection. The best
instability with the frontal boundary then sets up along the
southern Michigan border along with any potential outflow boundary
late in the day. This will be the focus for potential evening and
overnight convection as lower level jet ramps up again. Strongest
activity looks to hold south of the state, with uncertainty as to
how far north any activity develops. Low end PoPs will extend up
through I-69 corridor, but greatest chance for thunderstorms will
reside along and south of I-94. This activity could again pose a
Marginal Risk for severe weather if it materializes.

The next trough and cold front dropping out of the western/northern
Great Lakes arrives Wednesday morning and sweeps through during the
afternoon. This will keep chances for showers and weak thunderstorms
into Wednesday afternoon until the front pushes completely through.
High pressure is then expected to quickly build in Wednesday evening
through Thursday bringing with it dry and slightly temperatures into
the 70s for Thursday. Another shortwave and surface low is forecast
to organize over the plains and continue through the Midwest bring
the next chance of showers and thunderstorms on Friday.

&&

.MARINE...

High pressure holds directly overhead through this evening
maintaining light winds and minimal waves across the region. This
high eventually drifts off to the east overnight as low pressure
strengthens over the upper Midwest/northern Ontario. This low is
expected to result in a thunderstorm complex (a MCS) forming over
Wisconsin before rapidly moving into the Great Lakes late tonight
into Tuesday morning. Exact track this complex takes still carries a
bit of uncertainty though models are generally favoring it to dive
towards southern Lake Michigan resulting in a glancing shot of
showers and decaying thunderstorms for the central Great Lakes. A
few strong wind gusts will be possible within these storms.

Breezy southwest winds develop daytime Tuesday in advance of an
approaching cold front warranting the need for Small Craft
Advisories for all nearshore waters. Front gradually sags through
the area offering some potential (~20-30%) for additional showers
and storms Tuesday evening into early Wednesday morning- mainly
focused over the southern Great Lakes.

&&

.HYDROLOGY...

An active pattern of thunderstorms returns to Lower Michigan by
early Tuesday morning as warm and humid air surges back into the
region. Most of southeast Michigan will see at least a period of
showers during the morning as thunderstorms decrease intensity while
moving through. Rainfall totals average 0.25 to 0.50 inch.

The Tuesday morning activity is followed by a break in the afternoon
until the next round of storms becomes possible Tuesday night into
Wednesday morning. Current forecast trends suggest the best
thunderstorm potential along and south of I-94. Additional totals of
0.25 to 0.50 inch with up to 1 inch are possible with this activity
until it exits the area by Wednesday afternoon.

The potential for flooding in each event is greater where repeated
rounds of storms occur over the same area making ponding of water on
roads and in prone low lying areas possible. The Tuesday and
Wednesday activity collectively could lead to a brief response in
the level of streams and rivers across the area.

&&

.PREV DISCUSSION...
Issued at 152 PM EDT Mon Jun 24 2024

AVIATION...

High pressure maintains dry and VFR conditions this evening with
weak and variable winds organizing out of the south to southwest
tonight in response to an approaching frontal system from the upper
Midwest. Mid/high clouds will increase overnight ahead of this
system but will remain VFR. Confidence is increasing on a
thunderstorm complex to emerge from the system and track eastward
into the area Tuesday morning. Instability will be weak this far
east, so expect the storms to be elevated and weakening as they move
through mainly between 10z and 15z. The main impacts will be lowered
visibility in heavy downpours and an isolated strong wind gust.
Warmer air arrives on a breezy southwest wind Tuesday afternoon with
a slight chance for additional convection to develop as the cold
front moves through late.

For DTW/D21 Convection...Adjusted the Tuesday morning TSRA window an
hour earlier to 13-16z based on latest hi-res trends. Considered
adding a PROB30 TS mention for potential late Tuesday afternoon
convective redevelopment but confidence remains too low with model
soundings showing stability/capping concerns.

DTW THRESHOLD PROBABILITIES...

* Medium for ceilings aob 5kft Tuesday after after 12z.

* Medium in thunderstorms Tuesday morning mainly 13-16z. Low
  confidence late Tuesday afternoon.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory from 5 AM to 10 PM EDT Tuesday for LHZ421-422-
     441>443.

Lake St Clair...Small Craft Advisory from 8 AM to 4 PM EDT Tuesday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 8 AM to 4 PM EDT Tuesday for LEZ444.

&&

$$

DISCUSSION...AA
MARINE.......KDK
HYDROLOGY....AA
AVIATION.....TF


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