755
FXUS63 KDTX 131709
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
109 PM EDT Thu Jun 13 2024

.KEY MESSAGES...

- 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.

&&

.AVIATION...

Difficult convection forecast for late this afternoon into early
evening hours. The 12z DTX sounding indicated a lot of dry air below
800 MB, and thus will be counting on the steepening mid level lapse
rates/increasing cape to potentially trigger strong to severe
thunderstorms late today. At this point, will continue with the
inherited tempo group for TSRA at each taf site. Coverage and
location is still uncertain, and bulk of storms could end up closer
to the Michigan/Indiana border.

Cold front/wind shift will track through southeast Michigan tonight,
and low level convergence may be sufficient for a period of
borderline MVFR/VFR clouds. Unfortunately, the amount of showers and
thunderstorms that occur late this afternoon/this evening will be a
factor in determing this scenario. It appears the southern TAFS
stand the best chance and longest duration of low clouds, but should
clear around sunrise Friday regardless.

Light northerly flow tomorrow, with some sct-bkn mid cloud (5-10
kft) development expected with the cooler mid levels (zero at 700
MB) tracking through the Central Great Lakes.

For DTW/D21 Convection... A scattered-broken line of thunderstorms
looks to be developing/tracking through southeast Michigan late this
afternoon/early this evening. The primary window to affect DTW is
expected to arrive by 23Z and move east by around 02Z.

 DTW THRESHOLD PROBABILITIES...

* Moderate for thunderstorms impacting the terminal by around 23z
  today.

* Low for cigs aob 5000 ft this evening through tomorrow morning.

&&

.PREV DISCUSSION...
Issued at 1152 AM EDT Thu Jun 13 2024

UPDATE...

Morning showers dying out as cloud cover continues to progress
eastward allows for heating to take place and begin destabilizing
the profile in advance of a cold front passing through overnight.

Most of southeast Michigan is under a Slight risk for severe weather
this evening, mainly due to threats of wind and hail. An isolated
tornado has also not been ruled out for this evening. There remains
a level of uncertainty with how things are going to play out for
southeast Michigan, as hi-res models consistently shows a line of
storms to the southwest, but still have not converged well on how
this will evolve into southeast Michigan. The best chances for
severe weather currently look to be in the southern part of the CWA,
over Washtenaw, Wayne, Monroe, and Lenawee counties, but the
potential does exist for something to pop up over the Thumb as well.

Thermodynamics look favorable on paper, with SBCAPE reaching 1000-
1500 J/kg and lapse rates pushing 7 C/km. Shear will eventually
reach 40-50 knots, but the stronger shear pushes in behind the
storms overnight. Convergence along the front looks to be stronger
to the southwest, while storms that do form may outrun a relatively
narrow plume of instability. All this to say that should an updraft
develop, the ingredients are in place to see storm organization, but
confidence remains low on how widespread severe may be.

PREV DISCUSSION...
Issued at 411 AM EDT Thu Jun 13 2024

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.

&&

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

$$

AVIATION.....SF
UPDATE.......BC
DISCUSSION...TF
MARINE.......AM


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