263
FXUS63 KDTX 130811
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
411 AM EDT Thu Jun 13 2024

.KEY MESSAGES...

- Scattered showers and isolated thunderstorms arrive from the west
this morning. Severe weather is not anticipated with this activity.

- Warmer than normal today with high temperatures in the mid to
upper 80s and noticeably higher humidity.

- Scattered showers and thunderstorms develop this afternoon and
evening with potential for severe weather. Damaging wind gusts to 60
mph will be the main threat between 3pm and 10pm. Southeast MI is
outlined in a Marginal to Slight Risk from SPC.

- Higher than usual confidence in hot and humid conditions much of
next week. Temperatures well into the 90s Monday and beyond with
relatively high humidity will likely bring the highest heat indices
we have seen so far this year.

&&

.DISCUSSION...

Conditions this morning characterized by weak warm/moist advection
within southwest flow ahead of a cold front tracking across NW
Wisconsin at press time. A west-southwesterly LLJ is directing a
theta-e ridge across WI into northern lower MI, causing nocturnal
convection to fire all along western lower MI within the gradient of
elevated instability. As the LLJ progresses eastward and veers
westerly, this convection will arrive across the Saginaw Valley over
the next few hours, with a slight boost in forcing arriving after
sunrise as a remnant MCV currently over northern Lake Michigan
tracks in. With very little elevated instability in place this far
east, expectation is for scattered showers with a few rumbles of
thunder, mainly in the Tri-Cities and Thumb, this morning. Most of
the activity should move out and/or dissipate by late morning as the
LLJ steers the better moisture north and east.

Weak subsidence looks to work into the area through early afternoon
in the wake of the morning convective disturbance aloft. This will
bring increasing amounts of sunshine and should help boost temps
into the mid to upper 80s. We are still on track for a round of
showers and thunderstorms to develop this afternoon and evening as
instability builds in along a SW to NE oriented corridor of moisture
convergence. Dew points within this area from SW lower MI to the
Thumb are forecast to reach the mid to upper 60s. A plume of higher
mid-level lapse rates (6.5 to 7 C/km) will arrive from the west
simultaneously, resulting in MLCAPE on the order of 1000 to 2000
J/kg. Respectable height falls ahead of a potent shortwave moving
into the northern Great Lakes will time favorably with cold frontal
positioned over southern WI early this afternoon, providing the most
likely scenario for convective initiation with support among much of
the latest hi-res guidance.

This convection then tracks east across Lake MI into southern lower
MI and may be strong to severe by the time it arrives locally. Wind
shear will initially be lacking but will increase as the upper jet
works in the from the west, increasing 0-6km bulk shear to 40 to 50
kt and supporting organized updrafts. Damaging wind gusts will be
the main threat with timing most likely between 3pm and 10pm.
Secondary threats will be large hail and an isolated tornado. SPC
has designated areas west of I-75 within a Slight Risk (2/5) while
eastern areas are in a Marginal Risk (1/5) for severe weather. The
cold front then sinks across the area late tonight and ushers
precipitation south and east.

The mid-level trough axis passes overhead Friday morning with an
accompanying surge of lower 850mb temps around 10 C within drier
northwest flow. This brings cooler, more comfortable weather for
Friday and Saturday with seasonable highs in the 70s and lower 80s.
There will be a low chance for an isolated shower within the diurnal
cumulus field Friday afternoon as weak instability develops with a
boost from the cooling mid-levels. Otherwise, inbound high pressure
maintains dry and tranquil weather through Saturday. Uncertainty
remains with shower/storm chances by Sunday when a shortwave rides
across the ridge axis in place. Most model solutions carry the
better moisture and attendant precipitation chances to our north, so
will hold on to the inherited slight chance PoPs on Sunday and
Sunday night.

Significantly warmer and muggier weather remains in the forecast for
next week as a 594 dam 500mb ridge develops over the SE CONUS on
Sunday then expands north and east through the mid-week. This
directs a plume of 850mb temps of around 20 C (near the 99th
climatological percentile per NAEFS) into the Great Lakes and favors
high temps in the 90s as well as a humid air stream tied to the Gulf
of Mexico. This pattern will prove to be stubborn with ensemble mean
500mb height fields showing strong positive anomalies through the
week. Differing ensemble systems do begin to vary in handling the
ridge by late week however with the GEFS and CMCE steering the ridge
axis over New England before having it begin to break down.
Meanwhile, the EPS holds on to the ridge directly overhead through
the bulk of the week and thus advertises hotter late week temps.
Will note that 500mb vorticity progs do show several shortwaves
riding into the ridge from the west which would bring potential for
periods of showers and storms which, depending on diurnal timing,
could short circuit the current temperature forecast.

&&

.MARINE...

A cluster of showers and storms is expected to wane through the
morning across Lake Huron. Southwest flow will then become
reinforced over the lake through the day today as a warm airmass sets
up across the Great Lakes. This will continue to promote stable
over-lake conditions considering the cooler waters, however, gusts
20-25 knots will be possible immediately along the nearshore, given
well mixed southwest flow coming right off the land. These localized
higher gusts will be most likely across the inner Saginaw Bay with
the southwest fetch funneling into the Bay.

At this time, will continue to preclude the issuance of any Small
Craft Advisories, taking into account the stable marine layer,
noting the chance to reach isolated 25 knot gusts immediately along
the shoreline. The issuance of a short-fused Small Craft Advisory
will be considered this afternoon and evening if surface
observations support stronger wind gusts having a farther reach into
the open waters relative to current projections.

Otherwise, redeveloping showers and thunderstorms, some strong, will
be possible this afternoon and evening, south of the central portion
of Lake Huron. Wind gusts to or in excess of 34 knots and small hail
will be the main threats with any strong to severe thunderstorm
development. The passage of a cold front late tonight into Friday
morning will veer wind direction from southwest to northwest as high
pressure builds in behind the front. This will bring lighter winds
to the Great Lakes by Friday.

&&

.PREV DISCUSSION...
Issued at 1157 PM EDT Wed Jun 12 2024

AVIATION...

A combination of thunderstorm remnants moving in from the west and
new showers developing overhead are expected to affect MBS down
toward Flint late tonight and early in the morning. The ongoing
activity weakens enough for conditions to remain VFR while any new
showers are also high based and light. The plume of mid level
moisture tracks east mid to late morning which gives daytime heating
a chance to recover for the afternoon. Thunderstorm timing,
coverage, and intensity the become the forecast highlights for the
afternoon into Thursday evening. There is a wide range of model
projections on timing/location of storm initiation, however earlier
and/or farther north solutions are favored as the larger scale mid
level trough and upper level jet approach from the upper Midwest.
Storms are expected to affect all terminals beginning around 20Z at
MBS then spreading southeast toward DTW during late afternoon.

For DTW/D21 Convection... An approaching low pressure system and
cold front bring a chance of thunderstorms later in the afternoon. A
general NW to SE progression with increasing coverage is expected
across the area, primarily affecting DTW after 22Z.

 DTW THRESHOLD PROBABILITIES...

* Moderate for thunderstorms impacting the terminal after 22z
  Thursday.


&&

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

$$

DISCUSSION...TF
MARINE.......AM
AVIATION.....BT


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at www.weather.gov/detroit.