226
FXUS63 KDTX 011715
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
115 PM EDT Wed May 1 2024

.KEY MESSAGES...

- Mainly dry and slightly warmer today with afternoon gusts of 25-35
  mph.

- Above normal temperatures continue through the rest of the week
  and into the weekend.

- Daily precipitation chances exists, but the main shower/storm
  threat arrives Friday.

&&

.AVIATION...

VFR conditions are expected this forecast with just an isolated
shower possible early as nose of higher moisture plume shifts east
through the area. Otherwise, just varying degrees of cirrus into
Thursday with scattered diurnal cumulus again by midday Thursday.
Gusty southwest flow will veer to west and weakening into early
evening and then shift to north and then east overnight into
Thursday as a weak frontal boundary settles south through the area
as low pressure passes to the north late today and high pressure
follows.

For DTW/D21 Convection...Thunderstorms are not expected through the
TAF period.  .

DTW THRESHOLD PROBABILITIES...

* Low for crosswinds late this afternoon.

* Low for ceilings at or below 5kft early this afternoon.

&&

.PREV DISCUSSION...
Issued at 402 AM EDT Wed May 1 2024

DISCUSSION...

A negatively tilted shortwave trough quickly closes off through the
mid-levels over western Lake Superior this morning. This feature
sustains more robust convective activity in the vicinity of the wave
feature while longwave ridge amplification ensues further upstream.
Because of the ridge builds northward while tracking toward the
east, the aforementioned trough should remain displaced to the north
throughout the day. This generally keeps Southeast Michigan dry
today as the system`s warm sector spreads northeastward across Lower
Michigan. 01.00Z KILX (Lincoln, IL) RAOB sampled an H8 temp of +13C,
and although low-level southwest flow lessens toward the north,
still expect local values of +11C to +12C by this afternoon. A
rather dry and well-mixed boundary-layer favors highs peaking in the
mid to upper 70s. Additional boost possible should low clouds clear
ahead of schedule with Metro Detroit and a few other spots across
the far east potentially breaking 80F (see ECMWF MOS for
DTW/DET/TTF). Latest temperatures reflect slight upward adjustments.
Winds also become gusty once profiles mix as enhanced LLJ winds push
gusts into the 25-35 mph range. Could see some peak winds pop to
around 40 mph along the front.

Main question with this system is whether or not the warm advection
sufficiently moistens the column by the time its attendant cold
front crosses through. Surface progs show the boundary working west
to east across the forecast area from 15-21Z today with preceding
FGEN convective activity. An analysis of representative forecast
soundings show winds from 950-700 mb backing from NW to SW as the
ThetaE plume tracks east, but mid-level drying due to approaching
anticyclonic flow greatly inhibits convective depths. Any rainfall
that manages to arise from the decaying line should be brief with
lowering confidence east of US-23. Areas along/north of M-46 align
with the nose of the moisture arc, thus Slight Chance PoPs were
included. Also added a low-end Chance PoP for the Tri-Cities while
areas further south and west now have mentions for Sprinkles as the
line moves through. Dry and increasingly sunny skies arrive after
21Z with winds decreasing quickly after sunset. Clear skies early
tonight, becoming more opaque after midnight as mid and high clouds
spill in slowing nocturnal cooling. Should still see most areas drop
below 50F for overnight lows.

Surface high pressure encompassing the Great Lakes Thursday morning
eventually gets displaced by low pressure lifting northeast from The
Plains. Uncertainty exists regarding the extent and timing of
renewed the warm/moist conveyor as it pertains to southern Lower
Michigan. Isentropic ascent along the next warm front offers
potential for a leading band of clouds while some clearing may occur
later in the day. 00Z model spread is unusually high regarding local
shower activity, therefore decided to maintain dry PoPs for most
areas until the evening timeframe. Main push of CVA holds further
west until the inflection point in the longwave pattern arrives.
Thermal ridge still in place Friday morning before competing
boundaries interact with the main low pressure system located well
off to the north. A large swath of convection can be expected
upstream with coverage from central Ontario down the Mississippi
while a secondary low develops over the Ohio Valley, south of the
triple point. NAM and GFS differ greatly in lapse rates and
instability characterization, but with 0-6 km bulk shear near 35
knots, thunderstorm potential increases as the day progresses,
especially if diurnal timing aligns with the FROPA. Most of the
showers/storms should exit by midnight, but some signal exists for
a deformation response.

A bit cooler, but still warmer than normal for the weekend with
decreasing precipitation chances Saturday as subsidence arrives with
surface high pressure. Moist low-levels and perturbed mid-level flow
could provide some isolate showers Sunday with northeast flow
component. Low amplitude shortwave crosses the Ohio Valley Monday
clipping southern Lower with shower potential while an amplified
pattern lingers across Central CONUS. The next broad-form low tracks
into the High Plains Tuesday and Wednesday lending downstream
rain/storm chances for Michigan.

MARINE...

Increasing south-southwest winds today as low pressure tracks
through Lake Superior. Wind gusts this afternoon do look to reach 20-
25 knots over the nearshore waters, especially over Saginaw Bay and
along the shoreline areas of the Thumb region. Banking on the warm
air (925 mb temps up to 17 C) ahead of the cold front to provide
just enough stability to keep gusts mostly around 25 knots. Despite
the offshore winds and waves remaining aob 4 feet, will err on the
side of caution and carry a small craft advisory for Saginaw Bay and
the northern tip of the Thumb region. Winds veering to the west over
Saginaw Bay by early evening should also help to keep wind speeds in
check, vs the more favorable southwest wind.

Steady stream of cold advection behind the front Wednesday night
into Thursday, and outside of the north half of Lake Huron,
expecting wind speeds look to remain light, under 20 knots. Even
over northern Lake Huron, wind speeds look to peak at 25 knots to
perhaps up to 30 knots, centered around midnight per local
probabilistic guidance.

A return to light and variable winds for Thursday as surface high
builds over Lake Huron.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 9 PM EDT this evening for LHZ421-422-441.

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

$$

AVIATION.....DG
DISCUSSION...KGK
MARINE.......SF


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.