065
FXUS63 KDTX 070935
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
535 AM EDT Sun Jul 7 2024

.KEY MESSAGES...

- The holiday weekend closes out with dry weather today under mostly
  sunny skies.

- Warming up into Monday with highs in the mid to upper 80s. Shower
  and thunderstorm chances return Monday and Tuesday.

- Remnants of Beryl may begin to impact parts of the area by Tuesday
  night and Wednesday.

&&

.AVIATION...

A ridge of high pressure will bring light winds along with VFR
conditions today. Diurnal heating will aid in what will likely be
just a SCT deck of cu this afternoon and evening, with cloud bases
around 6-7 kft. Any overachieving cu coverage approaching BKN would
likely be narrowly forced along any lake breezes, which will flow
inland during the late afternoon and evening hours. This will result
backing of wind direction from west to south-southeast.

For DTW/D21 Convection...No concerns at this time.

DTW THRESHOLD PROBABILITIES...

* None

&&

.PREV DISCUSSION...
Issued at 310 AM EDT Sun Jul 7 2024

DISCUSSION...

Upper level ridging will translate in the region today and provide
mostly sunny conditions with temperatures warming back into the low
80s in most locations (upper 70s over the Thumb). The upper ridge
axis will shift a bit east into Monday with strengthening south to
southwest flow developing between this feature and an encroaching
weak frontal boundary to the northwest. Temperatures will continue
to warm within this regime with middle 80s common by afternoon (and
upper 80s possible metro Detroit south).

The chance for scattered showers and thunderstorms will increase
into the afternoon and evening period as the aforementioned frontal
boundary shifts into the forecast area late Monday. At this time, it
appears convection will most likely be most prevalent over the north
to northwest one quarter to one half of the forecast area where the
best frontal forcing will reside along northwest edge of remaining
upper level ridge. This forcing will act on an increasingly unstable
airmass as surface dew points edge into the upper 60s to around 70.
This should promote SBCAPES nearing 1500 J/kg locally. Stronger mid
level flow will also translate into the area and increase deep layer
shear from about 20 knots midday to 30-40 knots into the evening.
So, the combination of these two modestly supportive parameters may
lead to a few stronger storms.

This frontal boundary will settle into the remainder of the forecast
area Monday night into Tuesday, but stall over/near the area as the
positive tilt upper level trough driving this front southeast minors
out as it crosses the area Tuesday. This will maintain rain chances
into Monday night and to some degree into Tuesday (although model
differences are substantial in terms of active convection along/near
this front by that time).

The largest forecast challenge that appears to be emerging is how
the remnants of Beryl will initially interact with this stationary
frontal boundary by the middle of the week (Tuesday night into early
Wednesday) as it is steered around the northwest periphery of the
western extension of the Bermuda high centered over the Atlantic and
then just where the remnant low ends up tracking as it rounds the
top of this ridge over the southern Great Lakes/northern Ohio Valley
later Wednesday into Wednesday night.

This general idea having Beryl impact the area was basically "new"
to the model suite at the 00z cycle Friday night and the 00z suite
for Saturday remains notably divergent in the exact progression of
events (although all models have the system over/near the area now).
This will be a significant rain producer for a rather wide swath of
the southern/eastern Great Lakes and/or northern Ohio Valley. While
details remain elusive, it appears that increasing the chance of
rainfall in this late Tuesday night to Wednesday night period seems
prudent.

MARINE...

A ridge of high pressure centered over the Ohio Valley maintains dry
conditions with light winds and low waves the rest of the weekend.
Southerly wind of around 10 knots develops on Monday ahead of the
next frontal system moving in from the Midwest. Scattered showers
and storms arrive over northern Lake Huron Monday morning before
expanding south and east into the evening. Additional showers and
storms will be possible into Tuesday as the system slowly continues
tracking through. The mid-week carries a considerable amount of
uncertainty but the potential exists for a period of heavy rain and
strong winds if the remnants of Tropical System Beryl track in the
vicinity.

HYDROLOGY...

The remnants of Beryl may very well begin to interact with a stalled
frontal boundary along the southern portion of the forecast area by
Tuesday night with the remnant low then tracking into the vicinity
Wednesday into Wednesday night. At this time, details on the track
of this system are difficult to determine. Suffice it to say that an
increased risk of heavy rainfall will exist as the system encroaches
on the area. If impacted directly, rainfall will most likely reach
or exceed 2 inches in some areas. Follow upcoming forecasts as the
forecast track into this general part of the country is fine tuned.

PREV DISCUSSION...
Issued at 346 PM EDT Sat Jul 6 2024

Pop up showers remain a consideration through tonight. Temperatures
have creeped up into the mid-to-upper-70s across the CWA today.
Isolated showers have already begun to develop, and further
development is expected throughout the evening. The best chances for
showers remains north of I-69, where CAPE values of 500 J/kg are
currently in place. 0-3km lapse rates of 7 C/km are the most
favorable ingredient for shower development currently, and not much
else supports anything more organized. CAPE values are not expected
to increase through the evening, and low shear values are a problem
for updrafts trying to organize further. PWAT values struggle to
reach 1", and showers that do develop are not expected to bring more
than a few hundreths of an inch. Warmer air at the 600mb level will
advect in this evening and bring lapse rates of around 5 to 5.5
C/km, below the moist adiabatic lapse rate and as a result, cutting
off convective access to the upper levels. With updraft potential
limited to the lower levels of the atmosphere, thunder is not
expected with these showers. However, an isolated rumble of thunder
cannot be ruled out.

High pressure ridge fills in briefly on Sunday keeping dry
conditions and few to scattered clouds through the day. As a result
temperatures will reach the 80s across the CWA tomorrow with urban
areas likely to push 85 degrees or better. The next chance for rain
comes Monday ahead of a weak front that will pass through. The
combination of frontal forcing and daytime heating will produce
decent chances for showers and storms. Hi-res models remain out of
range at this time, but looks from global models resolve CAPE values
between 1000-1500 J/kg. Trough axis will line up as well and place a
jet streak over the lower peninsula, giving the area a shot at some
decent speed shear of 30-40 knots.

Beyond Monday, models struggle to convincingly resolve rain chances
through the rest of the week. One of the main disagreements in the
deterministic models is the evolution of the negatively tilted
trough through the week. The ECMWF for example, keeps the trough
axis slightly further to the northwest than models like the GFS.
This is especially important when considering the potential for the
remnants of Tropical Storm Beryl to be picked up and brought over
the southern part of the CWA. Regardless of if Beryl makes its way
over the area or stays to the southeast, the setup will allow for
warm, moist air to advect in, pushing dew points into the upper
60s/low 70s and PWATs up to 2 inches. As a result, available
moisture in combination with daytime heating still provide chances
for showers to pop up in the mid-to-late week time frame even if the
more robust system stays to the southeast.

MARINE...

Light winds and low waves accompany the weak pressure gradient in
place through this weekend. Apart from a stray shower this afternoon
or early evening, dry conditions will prevail through Sunday as an
area of weak high pressure builds in over the Ohio Valley. Southerly
wind of around 10 knots then develops on Monday ahead of the next
frontal system moving in from the Midwest. This system will bring
scattered showers and storms late Monday into Tuesday as it tracks
through. Slightly cooler northerly flow follows for the mid-week.

&&

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

$$

AVIATION.....AM
DISCUSSION...DG
MARINE.......TF
HYDROLOGY....DG


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