363
FXUS63 KDTX 141721
AFDDTX

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

.KEY MESSAGES...

- There is a diminishing threat for severe intensity thunderstorms
this morning leaving an isolated storm possible this afternoon.

- Another round of strong to severe thunderstorms is possible
tonight from mid evening into the late night.

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

- Increasing heat and humidity fuel the storms while lifting high
temperatures into the upper 80s and lower 90s. Peak heat index
reaches the lower to mid 90s today and upper 90s Monday.

- Thunderstorms with potential for severe intensity and flooding
continue Monday and Tuesday. The primary time window for greater
storm activity is currently projected for later Monday night into
early Tuesday.

&&

.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.

&&

.PREV DISCUSSION...
Issued at 1037 AM EDT Sun Jul 14 2024

UPDATE...

Remnant MCV from the first wave of nocturnal convection is just now
exiting into Lake Huron, with cloud cover clearing in its wake. The
14.12z KDTX sounding observed just weak elevated instability with
MUCAPE values around 300 J/kg atop a strong capping inversion (CIN
around 100 J/kg) as two waves of nocturnal convection have delayed
theta-e advection into southern lower Michigan. Latest observational
trends however have shown some northeastward moisture transport ahead
of the upstream MCS, which in combination with developing pockets of
sunshine should bring MLCAPE values toward 1000-1500 J/kg by mid-
day.

Nearly all of the hi-res guidance is underestimating the longevity
of the MCS and the influence of its remnant MCV that will move
across SE Michigan during peak heating this afternoon. Locally
enhanced convergence and shear invof the MCV could trigger
thunderstorm redevelopment across SE Michigan this afternoon (about a 30%
chance between 1pm-6pm), although will be complicated by
reintensification of the MCS that will track just to our south.
Should any thunderstorms develop this afternoon, a wet microburst
with gusts of 40-60 mph or large hail up to an inch cannot be ruled
out. Will dive into the details of evening-overnight convection with
the afternoon forecast package.

Considering the effects of this MCS on expected moisture transport
for the afternoon, did lower dewpoints by several degrees to bring
heat indices down into the low 90s.

PREV DISCUSSION...
Issued at 417 AM EDT Sun Jul 14 2024

DISCUSSION...

Convective trends remain the highlight of this forecast cycle as an
active storm pattern is established from the northern tier of states
into the Great Lakes today. Storms are fueled by an increasingly hot
and humid air mass building high temperatures into the upper 80s
with heat index reaching the mid 90s today. Highs around 90 are
reachable Monday with heat index in upper 90s. These numbers
approach heat advisory levels but are also vulnerable to
interference from clouds and rain cooled air both today and Monday.
The larger scale zonal mid and upper level flow configuration
maintains the corridor for additional storm complexes Monday into
Tuesday when a stronger low pressure system and cold front bring a
pattern change for the late week period.

The ongoing SW Lower MI/IN/IL storm cluster is the remains of
yesterday`s surface based convection across the upper Midwest that
grew upscale into a respectable MCS. It is now past peak
organization having outrun a better shear profile while tracking
along the MLCAPE gradient. Remnants of this system graze SE MI early
this morning accompanied by a component of elevated showers and
storms feeding off 850-700 mb moisture transport extending toward
the Tri Cities and Thumb. This is followed closely by yet another
low level jet forced storm cluster also in progress from MN into WI
that at least remnants of which are expected to survive into western
Lower MI by mid morning as the larger scale instability axis builds
northward. Assuming a slightly farther north track does materialize,
then this system is also expected to outrun the better upstream
shear profile and follow a standard weakening trend in the
transition from nocturnal to surface based instability. It is then
prudent to assume some redevelopment is possible in SE MI on the
leading edge of any residual weak MCV and as surface based
instability recovers this afternoon. Negative factors to monitor are
too much persistence of clouds and stable air from the morning
shower/storm pattern and a lack of a defined surface based focusing
mechanism. These variables combined with a wide range of CAM and
regional model solutions this far east of larger scale weather
features present lower than average predictability in this part of
the forecast.

Assuming afternoon storms are able to form, they would move into
Ontario and Ohio and leave a short break for this evening. The weak
cold front analyzed roughly from the MN arrowhead into the central
Plains this morning then becomes the focus for yet another round of
storms in WI late today. This activity tracks through WI into Lower
MI tonight with improved potential for severe intensity given the
farther east initiation and several hours of earlier timing in the
convective cycle. The 00Z HREF mean MUCAPE gradient is in a similar
west to east position with an incrementally improved downstream wind
shear profile to support some longevity of upscale growth. A linear
convective mode is most likely by the time the potential system
reaches SE MI making damaging wind the primary hazard and which may
be the best fit for the new Day 1 convective outlook. The trailing
cold front stalls near the Ohio border region while still presenting
heavy rainfall potential from additional nocturnal development late
tonight and Monday morning (see hydrology section below).

The stalled front moves quickly northward during Monday as a larger
scale short wave and surface low pressure reflection arrive in the
upper Midwest. This wave precedes larger scale mid level height
falls across central Canada which offers improved predictability due
to improved organization of low pressure and frontal forcing. This
is reflected in a final round of thunderstorms Monday night and
Tuesday with continued heavy rainfall potential as the associated
cold front moves slowly through Lower MI. The front clears the area
Tuesday night and is followed by broad high pressure promising a
chance to dry out during the late week period.

MARINE...

The arrival of a warm front is expected to bring a shift to
southwest flow today and expanded coverage of both morning and
afternoon thunderstorm activity. Marginal afternoon Small Craft
Advisory conditions are possible for Saginaw Bay, but decided to
forego a headline due to the isolated/brief nature of peak gusts to
around 25 knots. The warm and muggy airmass holds firm across the
region Monday through at least the first half of 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. A
cold front arrives late Tuesday bringing more seasonable
temperatures and quieter conditions by midweek. Occasional waves
could approach 4 ft over Saginaw Bay Tuesday.

HYDROLOGY...

The potential for heavy rainfall and flooding continues in an active
thunderstorm pattern today through Tuesday. Storms today present a
decreasing heavy rainfall risk while activity tonight increases,
especially late tonight and Monday morning. Thunderstorms will be
capable of torrential downpours with a quick inch or more of
rainfall possible Sunday night and Monday morning as lines of storms
moves repeatedly over the same areas. The best chance for this to
occur is from the urban Detroit corridor to the Ohio border as a
front stalls west to 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 last
week`s rain. Localized flooding is possible, especially in low-lying
and urban areas. Heavy rainfall and flooding potential then
continues later Monday, Monday night, and into Tuesday as a corridor
of storms is maintained until a cold front sweeps through the region
by late Tuesday.

&&

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

$$

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


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