473
FXUS63 KDTX 220439
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1139 PM EST Thu Nov 21 2024

.KEY MESSAGES...

- Scattered to numerous lake effect rain showers return Friday.

- Dry weather is then expected for most of the weekend.

&&

.AVIATION...

Ceiling heights have shown a wide variability from VFR to IFR
following the wake of the earlier region of precipitation. This
variability will persist into the predawn hours. Low level moisture
will then advance back into Se Mi from the northeast during the
course of the morning. This will trend ceilings heights to
predominately lower end MVFR. Areas of IFR ceilings can not be ruled
out. The degree of low level moisture may support areas of light
rain/drizzle. There will be an increase in the NNW gradient on
Friday. Despite limited mixing depths, the strengthening low level
wind fields will warrant forecast wind gusts in the 25 to 30 knot
range Friday afternoon.

DTW THRESHOLD PROBABILITIES...

*   Moderate in ceilings aob 5000 ft tonight. High on Friday.

*   High for precip type being all rain Friday.

&&

.PREV DISCUSSION...
Issued at 345 PM EST Thu Nov 21 2024

DISCUSSION...

Scattered rain and snow showers will wind down into the evening as
low pressure over Lake Michigan weakens and sweeps south into the
Ohio Valley. At the same time, secondary low pressure developing
along the eastern seaboard will retrograde back into far eastern New
York state. This will allow Atlantic moisture to wrap back around
the overall upper level low pressure to our east and pivot back
through Lake Huron into parts of SE lower MI overnight tonight into
Friday. Best rain chances will focus over the Thumb where northerly
flow from the lake will aid in the great Lake Effect coverage. Rain
chances will drop considerably westward with little/no rain from
U.S. 23 west. Temperatures will moderate into the mid 40s as the
coldest air associated with this system shifts southeast.

Generally dry conditions are expected over the weekend as this low
continues to shift east away from the region. Temperatures will hold
in the mid to upper 40s as a wavy zonal upper flow pattern becomes
established. A passing shortwave trough over southern Canada will be
shunting just north and east of the area as this generally westerly
flow overspreads the Great Lakes, but its close approach to the area
is only enough to limit warming into the 50s. A mid level shortwave
trough will translate through the developing zonal flow and bring
the next chance of rain showers Sunday night into Monday as warm air
advection in advance of this feature overspreads the area into late
Monday and Monday night as the system itself crosses the western to
central Great Lakes.

Rain and snow showers may linger into Tuesday depending on just how
trailing shortwave energy from Canada feeds southeast into this main
wave. In its wake, dry and colder conditions will become established
with highs edging closer to 40 for Tuesday and back into the 30s
into the midweek period.

MARINE...

An expansive upper low continues to govern Great Lakes conditions
today, with the surface low currently over southern Lake Michigan.
Locally the pressure gradient is relaxed with light northerly winds
over northern Lake Huron and southwest winds over the remaining
waterways. As the surface low drifts into the Ohio Valley tonight,
winds flip to the north across all waterways while the pressure
gradient tightens in response to strengthening New England low
pressure. By mid-Friday morning, gusts flirt with gale force
especially toward the southern end of the Lake Huron fetch and
around the tip of the Thumb. The latest guidance still keeps
frequent gusts just below 34 knots, noted in local probabilistic
guidance where there is nearly a 60% chance for peak gusts of 30
knots, but less than a 10% chance for gusts to 34 knots. Have opted
to maintain high-end Small Craft Advisories for now, but there is
still variability in model guidance right around decision thresholds.
Regardless of where frequent gusts fall in the 30-35 knot range,
northerly flow will be gusty on Friday especially over southern Lake
Huron. The presence of the upper low will also maintain rain-snow
showers tonight, changing to all rain showers for Friday and
Saturday. A brief ridge of high pressure then builds in Sunday ahead
of an unsettled early week period.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 10 PM EST Friday for LHZ422.

     Small Craft Advisory until 7 AM EST Friday for LHZ421-441>443.

     Gale Warning from 7 AM to 7 PM EST Friday for LHZ421-441>443-
     462>464.

Lake St Clair...Small Craft Advisory until 10 PM EST Friday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 10 PM EST Friday for LEZ444.

&&

$$

AVIATION.....SC
DISCUSSION...DG
MARINE.......MV


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