846
FXUS63 KDTX 121925
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
325 PM EDT Mon May 12 2025

.KEY MESSAGES...

- Above average temperatures persist through the week.

- Scattered showers/thunderstorm chances on Tuesday and Wednesday.

- Greater thunderstorm potential Thursday evening.

&&

.DISCUSSION...

A weakness in geopotential heights will coalesce within the high
amplitude ridge and begin to lift northward into central the Great
Lakes region tonight. Above normal temperatures and occasional
spotty shower and isolated thunderstorm activity will be possible
through Thursday. Highs are expected to be in the mid 70s Tuesday
and Wednesday (5 to 10 degrees above normal) and the lower 80s (10
to 15 degrees above normal) Thursday.

A lead arc of absolute vorticity collocated with weak mid to upper
level diffluence will spread northward after 00Z this evening.
Increased synoptic scale forcing will lead to lift and the potential
for some rainfall. Forecast soundings suggest it will take until
approximately 01z-02z before moistening occurs in the 1.0 to 5.0 kft
agl layer. The rain chances will steadily lift northward in a more
narrow corridor with the potential persisting then between 12-16Z
for areas north of M 46. Low variance exists amongst the EPS members
with the interquartile 24 hr amounts confined to less than 0.25 inch.

Some challenge to the Tuesday forecast regarding precipitation as
the plan view progs suggest broad/deep saturation with a lack of any
isentropic downglide. On the other hand, forecast soundings do show
some weak active subsidence developing in the 4.5 to 7.0 kft agl
layer, effectively capping much convective development. EPS data
remains very bearish on precipitation for Tuesday with 24 hour
values again below 0.25 inch. Chance Pops are fine for Tuesday. The
open trough axis will then lift northward directly into Lower
Michigan for Wednesday. The moist air mass in place with dewpoints
in the lower 60s and favorable background convergence forcing will
result in shower and thunderstorm activity chances. 70-50% chances
for precipitation appear reasonable with relatively higher potential
at the Michigan Ohio stateline.

The arrival of the next upper level jet exit region and returning
cyclonic flow influence will bring widespread support for shower and
thunderstorms sometime Thursday. Shortwave ridging in advance of
dynamic upper level low should keep conditions quiet for a good
portion of Thursday, until the cold front arrives. A considerable
amount of uncertainty exists regarding any strong to severe
thunderstorm threat as the best forcing could hold off until 06-12Z
Friday.

Cool northwest flow will then be possible for next weekend as deep
troughing remains in place over the Great Lakes. Depending on timing
of successive cold fronts or lake breeze boundaries, the temperature
forecast will be up for revision.

&&

.MARINE...

As broad high pressure moves off the Atlantic coast, modest
southeast return flow slowly advects moisture and instability
northward into the Great Lakes. Scattered showers and isolated
thunderstorms will spread across the southern lakes tonight through
Thursday as a weak upper low tracks overhead. Ambient winds will
remain light - mainly 10 to 15 kt - and predominantly out of the
east and southeast through mid-week. Low pressure then organizes
over the Midwest and sends a warm front across the region Thursday
night into Friday. This will bring stronger southerly wind and the
potential for more organized thunderstorms, some of which could be
strong.

&&

.PREV DISCUSSION...
Issued at 155 PM EDT Mon May 12 2025

AVIATION...

Area of high pressure remains over the region as it slowly drifts
eastward today. Meanwhile, a cutoff upper low over the southern
Mississippi Valley will lift northward today with the northern edge
of the cloud shield already advecting into the Great Lakes over the
surface high. As it draws nearer tonight, the lead band of moisture
will lift into the area producing a period of showers and MVFR/IFR
CIGS. The showers will lift north through the taf sites in the early
morning with improving conditions after 14-16Z. The rest of the
afternoon will have some isolated to scattered shower potential but
chances are too low to note a specific window at this time.
Soundings do suggest MVFR CIGs through Tuesday afternoon. Winds will
largely be easterly and less than 10 knots through the forecast.

For DTW/D21 Convection... No thunderstorms are expected through the
forecast period.

THRESHOLD PROBABILITIES...

* High in ceilings aob 5000 feet tonight through Tuesday.

* Low for cigs/vsby to fall below 200 ft and/or 1/2 SM Tuesday
  morning.


&&

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

$$

DISCUSSION...CB
MARINE.......TF
AVIATION.....DRK


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