969
FXUS63 KDTX 050811
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
411 AM EDT Wed Jun 5 2024

.KEY MESSAGES...

- Elevated showers and thunderstorms are possible this morning,
  severe weather is not anticipated.

- A line of showers and thunderstorms is expected to track west to
  east across the area between 1 PM and 9 PM this afternoon. Some of
  these storms may be strong to severe.

- Damaging wind gusts in excess of 60 mph, isolated large hail to one
  inch diameter, and heavy downpours will be possible with these
  storms.

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

&&

.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.

&&

.PREV DISCUSSION...
Issued at 1144 PM EDT Tue Jun 4 2024

AVIATION...

Deep layer moisture will advance across Se Mi during the early
morning hours. Isolated showers are possible within this moisture
feed. The better chances will be later in the morning as some added
larger scale ascent and increasing instability expand across the
area. An upper level trough and associated surface cold front will
traverse Se Mi late Wed afternoon. Ample moisture and weak to
moderate instability ahead of this system will support widespread
showers and thunderstorms. The most probable time period for
thunderstorms will be between 19Z and 24Z Wednesday.

For DTW/D21 Convection...An initial influx of moisture will arrive
after early this morning. This combined with increasing instability
will support isolated thunderstorms between 12Z and 17Z Wednesday.
The probabilities for thunderstorms then becomes high during the 20Z
to 24Z time frame. Current indications suggest a slow moving line or
cluster of thunderstorms oriented north-south impacting the airspace
during this time period.

DTW THRESHOLD PROBABILITIES...

* Moderate in thunderstorms Wednesday afternoon and evening.


&&

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

$$

DISCUSSION...MV
MARINE.......AM
HYDROLOGY....MV
AVIATION.....SC


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