314
FXUS63 KDTX 051748
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
148 PM EDT Wed Jun 5 2024

.KEY MESSAGES...

- Widespread showers and thunderstorms this afternoon, ending early
this evening. Some of these storms may be strong to marginally
severe.

- Localized rainfall totals of 1 to 2 inches are possible for areas
that see multiple storms this afternoon.

- Pattern shift for the latter half of the week brings below normal
temperatures  through at least the end of the week along with
periodic chances of rain.

&&

.AVIATION...

Convection has begun to perk up this afternoon ahead of the
approaching cold front. Will include a VCTS for the scattered
activity from 18-20Z before a convection cluster over northern
Indiana brings a more solid line of storms which a tempo will cover
for now. Biggest risk with these storms will be heavy rainfall, wind
gusts to 50-60 mph and large hail. Some question as to whether there
could be redevelopment behind the leading storms or not. Will keep a
couple hours of showers lingering and adjust as needed. An
additional period of showers will be possible from about 06-10Z
overnight as a secondary cold front drops through.

For DTW/D21 Convection...Scattered showers and thunderstorms are
ongoing as of 18Z around the area but the better coverage remains
off to the west and southwest. A cluster of storms currently lifting
into MI will impact DTW generally 20-23Z. Storms will be moving NE
at 30 mph while the cold front pushes everything east over time.
Storms will be capable of brief heavy downpours reducing
visibilities, strong winds to 50-60 mph and some large hail.

 DTW THRESHOLD PROBABILITIES...

* Moderate in thunderstorms this afternoon/evening.

&&

.PREV DISCUSSION...
Issued at 1023 AM EDT Wed Jun 5 2024

UPDATE...

Moist airmass in place, as 12z DTX sounding indicated a PW value of
1.5 inches, with further moisture pooling today ahead of cold front
expected to produce PW value of 1.75 inches. With a negative tilted
shortwave trough lifting through the Central Great Lakes, seems
reasonable widespread showers and scattered thunderstorms will
develop this afternoon, despite the less than stellar
instability/capes/mid level lapse rates. Surface dew pts generally in
the 67-72 degree range across southern Lower Michigan/Indiana this
morning. In the upper range, surface capes will reach 2000 J/kg with
highs in the lower 80s, but lower dew pt range will result in capes
more in the 500-1000 J/kg range. Adequate shear 0-6 KM bulk shear of
35-40 knots if the higher instability is realized to support a few
marginally severe storms (mainly wet micro-burst), favored mostly in
the 3-7 PM window. Overall, accounting for some modest mixing out of
dew pts, preference is to hold dew pts in the 68-70 degree range.
Zone update was mainly cosmetic, and do not anticipate any change
with SPC Day 1 outlook.

PREV DISCUSSION...
Issued at 411 AM EDT Wed Jun 5 2024

DISCUSSION...

Main forecast concern for today is several opportunities for showers
and thunderstorms across SE Michigan, including strong to severe
potential as a line of storms tracks through this afternoon-evening.
Leading the way is the warm front, which will lift into the cwa
through the early morning hours. The fropa so far has just been
producing virga locally, as better forcing and moisture transport are
to our west invof a 35-40 knot nocturnal low level jet. This low
level jet will eventually reach the western edge of the forecast area
between 12-15z (8am-11am), driven primarily by eastward progress of
an expansive surface trough and mid-level wave that arc from low
pressure near central Saskatchewan-Manitoba to Texas. Diurnal
weakening of the jet should lead to a decaying convective complex by
the time it reaches SE Michigan, but some degree of remnant elevated
showers/storms is likely. PoPs are highest near the Tri Cities and
decrease with southeastward extent away from the LLJ forcing,
although presence of elevated instability (500-1000 J/kg) does keep a
chance for scattered convective potential through the morning for
all of SE Michigan.

Trends in radar mosaic over the past 3 hours have shown significant
dissipation of radar returns along the upstream surface front, which
is currently over western Wisconsin/Illinois. Meanwhile, GOES-16 WV
loop depicts the lead edge of the mid-level wave catching up to the
surface feature, and will be the mechanism to watch heading into the
afternoon for redevelopment of linear convection. With the warm
front already well into the cwa and 00z KDTX RAOB observing 750 J/kg
MUCAPE ahead of the warm sector last night, should be able to
realize model forecast instability this afternoon even if we get
clipped by elevated convection this morning. With temperatures
reaching into the low 80s and dewpoints in the mid to upper 60s,
this equates to MLCAPE up to 1000-1500 J/kg by the time the mid-
level forcing arrives with minimal capping.

Timing of the wave and phased surface troughing continue to align
well with CAM output in bringing a line of thunderstorms west to
east across SE Michigan between roughly 1pm-9pm tonight.
Environmental parameter space will be favorable both from a
thermodynamic (discussed above) and kinematic perspective, with mid-
level flow increasing to 35-40 knots this afternoon for a Marginal
Risk of severe weather (SPC SWODY1). Linear mode suggests damaging
wind gusts in excess of 60 mph will be the main severe weather
threat, although heavy rainfall is also a concern considering the
seasonably high moisture content of this airmass (PWAT to 1.75") and
depth of the warm layer. Heavy downpours owing to very good
precipitation effiency could lead to localized rainfall totals of 1
to 2 inches should training storms develop ahead of the main line.
The speed and orientation of the line however are fairly progressive,
bringing an end to heavy rainfall potential late this evening as a
dry slot moves in aloft.

A notable pattern transition occurs for the late week period as the
parent closed upper low spreads southeast toward the Great Lakes. H8
temperatures drop into the single digits, corresponding to daytime
highs generally in the 70s with coolest temperatures on Friday
capped in the upper 60s. Several additional shortwaves ripple
through the flow, including a pair of waves Thursday that keep low
chances for showers and thunderstorms in the forecast.

MARINE...

A ridge of high pressure now resides across Lake Ontario, with
attention now turning to the cold front which currently resides just
west of Lake Michigan. This front is projected to move across the
eastern Great Lakes through the afternoon and evening hours, which
will likely bring numerous to widespread rain showers along with
embedded thunderstorms. There will be a marginal risk for severe
weather across all of the eastern Great Lakes given the building
instability, where wind gusts in excess of 30 knots and hail to an
inch will be possible with the strongest storms. While much less
likely, an isolated waterspout cannot be ruled out with the
thunderstorms.

Passage of the front will veer wind direction from the southeast to
the southwest this evening. A cooler air mass will then gradually
setup over the Great Lakes through at least the end of the week. The
enhanced mixing depths will bring some breezy conditions,
particularly for the nearshore zones. Small Craft Advisories may be
needed tomorrow, with the Saginaw Bay having higher probabilities to
reach criteria given the southwest flow. The favorable fetch will
allow wave heights to near the three ft threshold while wind gusts
near 25 knots.

HYDROLOGY...

A line of showers and thunderstorms is expected to track west to
east across SE Michigan between 1 PM and 9 PM today ahead of a cold
front. The airmass will seasonably warm and moist, helping this
storms become efficient rain makers with widespread rainfall amounts
up to a half inch expected. Localized higher amounts are possible if
several storms pass over any single location, in which amounts will
be closer to 1 to 2 inches. Minor flooding of prone urban and low-
lying areas, ponding of water on roadways, and rises in area rivers
will all be possible.

&&

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

$$

AVIATION.....DRK
UPDATE.......SF
DISCUSSION...MV
MARINE.......AM
HYDROLOGY....MV


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