Ann Arbor, Michigan 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

297
FXUS63 KDTX 210748
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
248 AM EST Thu Nov 21 2024

.KEY MESSAGES...

- Scattered to numerous light snow showers around this morning.

- Scattered to numerous rain showers return tonight but especially
Friday, and mainly for areas east of U.S. 23.

- Dry weather expected for most of the weekend.

&&

.DISCUSSION...

Brisk westerly flow this morning with temperatures mostly in the mid
30s. The 00z KMPX raob indicated an 850 MB of -12 C, a bit colder
than model initializations. However, this cold pool previously over
Minneapolis is tracking southeast through Central Illinois this
morning, with just a glancing blow of the cold air extending over
southern Lake Michigan and southern Lower Michigan. Still expecting
light scattered-numerous snow shower activity to move across
southeast Michigan, especially for areas along and south of M-59,
but the DGZ is struggling to saturate based off the soundings, and
accumulations look to be minor (dusting to around half an inch).
None-the-less, latest radar and satellite trends upstream over
southwest lower Michigan are encouraging for snow showers, and expect
the bulk of the activity to fall during the morning commute.

Surface low pressure ended up tracking just north of the Straights,
and is now turning the corner and will be dropping south through
Lake Michigan and into the Central Ohio Valley this evening,
weakening in the process as the low near/off the southern New
England coast takes over. The airmass over the Central Great Lakes
will be modifying tonight and Friday as heights slowly rise and a
weak shortwave ridge axis attempts to arrive toward 00z Saturday.
However, Cyclonic flow around the backside of the departing upper
level low and Atlantic moisture wrapping in from Eastern Canada will
support rain showers tonight into Friday, especially over eastern
areas.

500 MB low over Manitoba on Friday tracks into northwest Ontario on
Saturday, and there is an attempt for some colder air (-5 C at 850
MB) to filter back into the southeast Michigan, with a rather sharp
low level baroclinic zone moving through. Still looks like just
enough upper level confluent flow/surface riding/anticylonic flow to
keep the forecast dry for most/all of the weekend.

Next low coming out of the Midwest leads to solid warm advection
pattern for Sunday, with the isentropic ascent used up to saturate
the mid levels and produce clouds during the day, with a low chance
of just enough moisture transport Sunday night to wring out a little
light rain. Better chance for rain showers on Monday as an amplified
northern Stream trough helps spin up/deepen the low over the Central
Great Lakes. Although, once again, the euro ensemble members are
indicating two different camps (Lake Superior vs Lake Huron) with
respect to the position of the low by 00z Tuesday. These differences
will have to be worked out before we can get any clarity on the
potential for snow showers on Tuesday, with the marginally cold
enough airmass progged. The colder air airmass (upper 30S/around 40
for highs) then looks to hold on through Thursday.

&&

.MARINE...

Low pressure is just now pivoting over the Straits, and will descend
along Lake Michigan today. A relaxed pressure gradient on the east
side of this system allows southwest winds and waves to subside
through the morning, but wrap around moisture keeps rain-snow
showers ongoing. A second low pressure system will be drawn westward
toward the Great Lakes today as the parent upper low slides into New
England. This will first flip winds to the north, followed by
renewed moisture and rain chances. An uptick in onshore flow then
begins early Friday as the pressure gradient tightens overhead. This
sets up a borderline gale scenario Friday, especially given ~100
J/kg or so of lake-induced instability in the boundary layer. That
said, the forecast magnitude of the available wind field (30-35
knots) just does not provide the needed confidence to issue a Gale
Watch. Regardless of exact magnitude, boaters should be prepared for
gusty northerly flow over the southern half of Lake Huron on Friday
with at least high-end Small Craft Advisories likely. The upper low
maintains unsettled conditions through Saturday before a brief ridge
of high pressure builds in on Sunday.

&&

.PREV DISCUSSION...
Issued at 1130 PM EST Wed Nov 20 2024

AVIATION...

Ongoing cold air advection along with a region of moisture now
advancing toward Se Mi will result in MVFR based clouds
overspreading Se Mi between 06Z and 09Z. An expansion of snow
showers into Se Mi will also occur. These snow showers will persist
well into the morning. Snowfall rates are likely not to be enough to
overcome air temperatures above freezing and relatively warm ground
temperatures. So accumulations onto paved surfaces are not expected.
An upper low and associated surface low drop from north to south
across Lake Michigan on Thursday. This will actually place a little
region of subsidence/drier air over Se Mi during the afternoon,
likely leading to a high variability in ceiling heights.

DTW THRESHOLD PROBABILITIES...

*   High in ceilings aob 5000 ft overnight and Thursday.

*   High in snow as the precipitation type overnight and Thursday
    morning.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 4 AM EST early this morning for LHZ442-
     443.

     Small Craft Advisory until 10 AM EST this morning for LHZ421-422-
     441.

Lake St Clair...Small Craft Advisory until 4 AM EST early this morning for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 4 AM EST early this morning for LEZ444.

     Low Water Advisory until 7 AM EST this morning for LEZ444.

&&

$$

DISCUSSION...SF
MARINE.......MV
AVIATION.....SC


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