613
FXUS63 KDTX 220000
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
800 PM EDT Tue May 21 2024

.KEY MESSAGES...

- Isolated storms are possible this afternoon/evening south of I-69,
while locations along I-69 are most favored for development.

- Strong to severe storms are unlikely, but cannot rule out an
overachieving storm or two that pose a marginally severe wind (60
mph gust) or hail (up to 1 inch diameter) threat.

- Marginal to Slight Risk of severe storms remains for Southeast
Michigan late tonight for damaging wind potential, but latest model
trends support weakening activity upon arrival.

- One more chance for showers/storms Wednesday before a cooler and
less humid airmass arrives late Wednesday into Thursday.

- Brief warm-up Friday with some additional chances for showers and
storms through the weekend.

&&

.AVIATION...

An isolated thunderstorm or two did initiate along the Lake Huron-
Lake St Clair composite lake breeze boundary the past couple of
hours. Convective activity has since waned along with boundary layer
cumulus with downtrend in diabatic solar heating. A very strong
anticyclonic vorticity dipole coupled to the strong low pressure
system will pass directly through much of Lower Michigan tonight.
Active downward vertical motion in addition to warming in the 5.0 to
10.0 kft agl layer will yield VFR conditions throughout tonight.
Rolled back much of the precipitation mention in the tafs. Old
convective remnant showers are expected to approach the northern taf
sites 11-14Z and the Detroit tafs 13-16Z. Very low confidence in
coverage and have included the mention as a Prob30. Non convective
low level wind shear in the lowest 2.0 kft agl tonight and southwest
winds Tuesday of 15 to 25 knots.

For DTW/D21 Convection... No thunder anticipated tonight. Low
confidence in showers impacting DTW between 13-16Z 5/22.
Questionable coverage.

DTW THRESHOLD PROBABILITIES...

*  Low for thunderstorms 13-16Z Wednesday morning.

&&

.PREV DISCUSSION...
Issued at 343 PM EDT Tue May 21 2024

DISCUSSION...

A strong differential heating boundary has setup along I-69 this
afternoon as clouds struggled to mix out north of the interstate
where 2m temperatures are still in the 70s (60s for The Thumb). Near-
full insolation further south has helped guide readings into the mid
80s as dewpoints across Southeast Michigan settle in the low to mid
60s. 21.12Z KDTX RAOB revealed another low-level inversion which
initially caps surface-based convection, but given that the 925 mb
inversion is 3C cooler than Monday`s with a higher 2m Td, SBCAPEs
should eventually build into the 1000-1750 J/kg range (see 12Z HREF
ensemble mean and SPC MesoAnalysis). Main limiting factors are
attributed to the initial synoptic setup and the 750-550 mb lapse
rates.

Regarding the former, shortwave ridging is in-place for the start of
the forecast period which delayed the development of a diurnal
cumulus field. Resultant subsidence signal is well-defined in
forecast soundings and contributes to a muted convection response in
the 12Z CAMs. The mid-level lapse rate issue suggests very isolated
coverage of thunderstorms late this afternoon as a secondary/weak
warm layer could further suppress convective depths and CAPE values.
All told, the afternoon forecast narrative lends heavily on a
surface convergence axis tied to the aforementioned thermal
gradient. This serves as the primary focus for CI, but weak 0-6 km
bulk shear limits overall lifecycles as storms generally drift
toward the northeast. Did make some slight adjustments to PoPs to
include a minimum of Slight Chance mentions across the region and a
wider swath of Chance PoPs along the boundary. Additional convective
development is also possible further south where free-convection may
arise from the strongest surface heating. Localized outflow
boundaries and lake breezes interactions could also spur additional
convective action late today. Strong to severe storms are unlikely
based on the current setup, but cannot rule out an overachieving
storm or two that pose a marginally severe wind or hail threat.

Any afternoon/evening convective development should decay by 10 PM
followed by a period of dry/calm conditions. Attention then turns
upstream to a negatively tilted amplifying shortwave trough closing
off over SD/IA/MN. Impressive flow within its broad cyclonic shield
will spread eastward overnight driving a flanking boundary and a
line of well-organized convection across Lake Michigan, into western
Lower. Questions remain regarding the integrity/longevity of the
expected QLCS, but SPC has maintained the Marginal to Slight Risk of
severe storms for Southeast Michigan through the early morning hours
on Wednesday. With the exception of the FV3, CAMs are quite bearish
on storms (and even showers) surviving to the western CWA border
late tonight as the boundary washes out and moisture quality
degrades rapidly.

Upper level pattern becomes more progressive Wednesday as the upper
low interacts with a stalled trough over Saskatchewan, a unified jet
streak and the associated height falls work across Lower Michigan as
the main cold frontal boundary gets shoved into the Great Lakes.
Can`t rule out a bit of shower activity, but a low-impact FROPA is
most likely. Post-frontal conditions offer a drier and cooler
forecast for Thursday.

A well-advertised Pacific wave crosses the High Plains into
Minnesota Friday with the warm advection arm extending into Southern
Lower. Ensembles have trended higher with max temperatures Friday
peaking in the mid 80s. Storms are also possible during the evening
and overnight hours with the next cold front. Surface ridge builds
in across the eastern Plains Saturday morning, expanding into
Michigan as the day progresses. This draws a cooler and drier
airmass until a VortMax ejects across the Mid-Mississippi Valley and
into the Ohio Valley Sunday bringing areas of rainfall to close out
the weekend with near-seasonable temperatures. Thermal troughing
hangs around early next week before strong longwave ridge
amplification gets underway across western CONUS. Omega block
configuration is possible through the end of next week.

MARINE...

A strengthening low pressure system will lift from Iowa through
western Lake Superior Wednesday morning while pulling a warm front
northward through lower Michigan. There is a chance of some isolated
showers or thunderstorms this afternoon and evening but chances
increase tonight ahead of an approaching cold front. The cold front
will pass through on Wednesday with showers and thunderstorms
possible tonight and Wednesday ahead of it. Winds increase out of
the south to 25 knots ahead of the associated cold front Wednesday,
then veer to the west Wednesday night into Thursday but settling
back down to 15 knots. A small craft advisory will be needed for
Saginaw Bay Wednesday as the winds funneling out of the bay have a
higher chance to reach 25 knots.

CLIMATE...

Here are the record high temperatures for May 21-22:

May 21st:
Detroit                92 (set in 1977)
Flint                  93 (set in 1921)
Saginaw/Tri-Cities     94 (set in 1977)

May 22nd:
Detroit                90 (set in 1994)
Flint                  91 (set in 1934)
Saginaw/Tri-Cities     89 (set in 1992)

Here are the record high low temperatures for May 21-22:

May 21st:
Detroit                71 (set in 2013)
Flint                  67 (set in 1934)
Saginaw/Tri-Cities     66 (set in 2021)

May 22nd:
Detroit                67 (set in 1941)
Flint                  65 (set in 1977)
Saginaw/Tri-Cities     68 (set in 1977)

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory from 8 AM to 10 PM EDT Wednesday for LHZ421-
     422-441.

Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

AVIATION.....CB
DISCUSSION...KGK
MARINE.......DRK
CLIMATE......KGK


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