336
FXUS63 KDTX 132002
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
402 PM EDT Sat Jul 13 2024

.KEY MESSAGES...

- Two rounds of isolated strong to severe thunderstorms possible on
  Sunday, the first wave during the morning and the second in the
  late evening and overnight.

- The main hazards are large hail to one inch, damaging wind gusts
  to 60 mph, and heavy rainfall with localized flooding.

- Warm and humid on Sunday as well with heat indices reaching the
  low to mid 90s.

- Shower and thunderstorm chances continue Monday and Tuesday. There
  is a chance for isolated strong to severe thunderstorms both days.

&&

.DISCUSSION...

Resident high pressure has led to a quiet Saturday for SE Michigan,
although temperature readings in the upper 80s still sit a few
degrees above normal even as we approach the mid-July climatological
maximum. Dry and subsident conditions highlighted in the 12z KDTX
sounding hold through the evening, followed by a shift to an
increasingly humid and active pattern by Sunday morning.

Leading edge of the warm front currently extends NW-SE through
Chicago, followed by an enhanced theta-e plume boasting MLCAPE
values of 2000-3000 J/kg over southern WI and IL. This instability
plume will eventually pivot into SE MI by early Sunday morning on
the nose of a 20-25 knot low level jet. There are still details to
work out depending on upstream convective evolution, but the general
trend to the 12z model suite has been to bring a complex of decaying
thunderstorms to the Tri Cities/Thumb along the ensuing instability
gradient early Sunday morning. For most of the cwa, showers/storms
will occur during the diurnal minimum with questionable instability
prospects, so confidence is low in any severe potential prior to 15z
(11am local time). That said, the majority of CAMs do suggest some
updraft reinvigoration across the easternmost counties by mid-day,
presenting a highly conditional strong to severe thunderstorm threat
of large hail and/or damaging wind gusts to 60 mph between about 11
AM and 3 PM local time east of I-75 with potential for storms to
grow upscale.

There is increasing confidence in a period of post-convective
subsidence and drier conditions late Sunday afternoon, although
upper 60s-low 70s dewpoints will keep conditions muggy. Heat indices
Sunday afternoon may approach the low to mid 90s, though will depend
on positioning of any outflow boundaries and cloud cover as noted in
MOS guidance where max T differs by some 10 degrees.

There is an emerging signal in guidance for a second round of
convection to develop later Sunday evening-overnight along a
reinforced outflow/theta-e boundary that will gradually lift back to
the north through the late afternoon. How far north this boundary
reaches is still uncertain, with some guidance keeping it south of
the state line and other guidance bringing it as far north as I-94.
Should the northern solution play out, the urban Detroit corridor
will be at risk for both isolated strong-severe thunderstorms and
heavy rainfall amidst training thunderstorms. The west-east
orientation of the boundary and ~20-25 knot flow aloft will result
in slow-moving and likely training storms wherever the boundary sets
up, capitalizing on efficient warm rain processes. See the Hydrology
section for more details.

Showers and thunderstorms likely to linger through early Monday
morning with a continuation of unsettled weather through the early
half of the week. The strong ridge over the Four Corners region
maintains a storm track favorable for embedded shortwaves to impact
southeast Michigan each day, introducing thunderstorm chances
throughout the week amidst prolonged instability. Otherwise warm and
humid conditions will continue through mid-week ahead of a stronger
synoptic disturbance that will impact the region on Wednesday. This
will usher in a cooler/drier Canadian airmass, but the system itself
will be one to watch for more organized convection potential.

&&

.MARINE...

Diffuse high pressure congeals around the central/eastern Great
Lakes today offering a rather unimpressive surface gradient which
generally keeps prevailing winds AOB 10 knots through the rest of
today and overnight. The resident humid airmass could interact with
lake breeze and/or differential heating boundaries this evening
triggering some isolated convective activity. Should showers/storms
develop (more probable over land) a weakening trend will likely
ensure shortly after crossing into the waterways. Sunday features
the arrival of a warm front bringing with it a shift to southwest
flow and expanding coverage of thunderstorm activity. Previous
considerations regarding marginal afternoon Small Craft Advisory
conditions for Saginaw Bay remain similar, therefore decided to
forego a headline for isolated/occasional peak gusts near 25 knots.
The warm and muggy airmass holds across the region Monday and early
Tuesday offering several additional opportunities for thunderstorms
as packets of upper level energy arrive in staggered succession.
Periods of stronger storms are possible Sunday through Tuesday which
could pose a heightened risk for locally higher winds/waves and some
hail.

&&

.HYDROLOGY...

There is potential for two rounds of heavy rainfall as a warm and
humid airmass tracks into SE Michigan on Sunday. Thunderstorms will
be capable of producing torrential downpours with a quick inch or
more of rainfall possible Sunday morning and again Sunday evening in
a single storm. There is a chance for training thunderstorms to
impact the urban Detroit corridor Sunday evening and overnight as an
instability axis may settle west-east over the area. In this case,
rainfall amounts may exceed two inches although there is low
confidence in exactly where this boundary may set up. Heavy rainfall
will occur amongst already saturated soils and elevated rivers from
the previous week`s rain. Localized flooding, especially low-lying
and urban areas, will be possible. There are several additional
chances for showers and thunderstorms through Wednesday.

&&

.PREV DISCUSSION...
Issued at 100 PM EDT Sat Jul 13 2024

AVIATION...

The center of the near surface anti-cyclone is positioned near Lake
St Clair and the diurnal cumulus field is pinwheeling about this
feature. Cumulus response has been greatest where the soil moisture
content is higher from recent rains. Expect the axis of cloud
formation to drift eastward into the Detroit airspace though the
course of the afternoon. There is a low chance that an isolated
shower/storm will emerge from the region of better cloud coverage as
the afternoon wears on.

Upstream convection is expected to become quite active this evening
and overnight. Expectations are for remnant activity to approach
Southeast Michigan around daybreak and persist through the balance
of Sunday morning with an opportunity for thunderstorms to
rejuvenate in the Detroit region around midday before exiting to the
east. Details are difficult to come by regarding the character of
the activity - but the timing window has been rather consistent for
quite some time.

For DTW/D21 Convection... An isolated shower/storm possible late
this afternoon. Expanding storms upstream of Lake Michigan have a
chance to survive into SE MI/D21/DTW late tonight through Sunday
morning.

DTW THRESHOLD PROBABILITIES...

* Low for ceiling 5000 ft or less this afternoon.

* Medium for thunderstorms Sunday 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.....Mann


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at www.weather.gov/detroit.