763
FXUS63 KDTX 131700
AFDDTX

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

.KEY MESSAGES...

- There will be several windows for thunderstorms Sunday through
Tuesday. Severe weather and heavy rainfall will be possible with
these systems but with relatively low confidence on timing and
location.

- A period of hot and humid conditions is forecasted for Sunday and
Monday with temperatures reaching near 90 and heat index in the mid
90s.

- Cooler and drier weather will move in Wednesday through the rest
of the week.

&&

.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.

&&

.PREV DISCUSSION...
Issued at 345 AM EDT Sat Jul 13 2024

DISCUSSION...

Quiet weather today before multiple chances of showers and
thunderstorms enter the forecast starting Sunday morning. Hot and
muggy today as temperatures climb into the mid/upper 80s with
dewpoints in the mid 60s. This will lead to heat indices close to 90
this afternoon.

On Sunday the weather begins to get more active. A persistent strong
ridge centered over the SW conus will hold as a series of weak
shortwave troughs ripple through the nearly zonal mid level flow
with the jet located up along the international border. The first
trough will arrive on Sunday with all models pointing to some kind
of convective complex developing upstream over MN/WI then tracking
east into the Great Lakes Sunday morning. Plenty of different
flavors to the CAMS as to where to track this complex. Synoptic
features of note will be the strong piece of vorticity pivoting NE
through the northern Lakes while the better low level jet resides
well south over IA into IL which is positioned over the area of
strong instability so one would think the complex would turn SE
along the instability gradient with fuel from the LLJ. There is a
strong theta e gradient pushing east across the area early Sunday
afternoon though. So even if the complex can skirt us to the west
through SW MI and N IN, we could see convective development along
this strong gradient with around 20 knots of shear locally and
roughly 1500 J/kg of CAPE. So a couple scenarios that could play out
Sunday. SPC stretched the Marginal Risk area across southern MI to
account for the morning complex possibly sustaining itself across the
area. This would bring the risk of strong wind gusts and hail. Heavy
rain will also be possible once again owning to PWATS approaching 2
inches and dewpoints back up into the 70s. Temperatures will make a
run at 90 as the heat plume to the west gets forced into the Great
Lakes. This of course will depend on cloud cover through the
afternoon.

Monday will be another hot and humid day with 850mb temps still
hovering around 20C and dewpoints still in the 70s. Models are
starting to key in on little better defined mid level wave that
would track across southern MI through the day Monday. This would
provide a good focus for convection chances through the afternoon.
It is a fairly compact system so any deviation in track would change
chances quite a bit for any one location.

Little better setup on Tuesday with some well defined synoptic
features to key on. A stronger vort max rotating through the broader
Canadian trough will sweep by the northern Great Lakes with the nose
of a strengthening upper level jet feeding into it. This will all
help force a cold front across the area with a chance of
thunderstorms along it. This system will be strong enough to
displace the resident hot and humid airmass and allow a cooler
Canadian high pressure system to build into the region for the end
of the week. High will be in the 70s to around 80 with lows in the
50s to near 60.

MARINE...

High pressure migrates further east today while a secondary (and
more diffuse) ridge lifts toward the Tri-State area offering
continued weak gradient flow and gusts AOB 15 knots. Marginal Small
Craft Advisory conditions will be possible Sunday afternoon as flow
shifts southwesterly over Saginaw Bay and peak gusts approach 25
knots. Broader coverage of showers/storms to follow Sunday and
Monday with the arrival of a warm front and approaching upper level
trough from the west. Stronger storms are possible both days which
could pose a heightened risk for locally higher winds/waves and some
hail.

&&

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

$$

AVIATION.....Mann
DISCUSSION...DRK
MARINE.......KGK


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