NWS Forecast Discussion

000
FXUS63 KDTX 232341 CCA
AFDDTX

Area Forecast Discussion...CORRECTED
National Weather Service Detroit/Pontiac MI
641 PM EST Sun Feb 23 2020

.AVIATION...

Clear skies across the lowest 10k ft now expected to hold through
Monday morning, as the passage of a weak front offers little more
than a wind shift toward daybreak. Prevailing pre-frontal southwest
winds will ease through the night, before veering to north-
northeasterly with the fropa. The diminishing gradient could allow
for a brief disruption of visibility in shallow fog, but confidence
in anything below 6SM remains low. Thickening and gradually lowering
mid cloud will define most of the daylight period, with arrival
of deeper low level moisture likely holding off until Monday
evening.

For DTW...confidence in low stratus development with a weak frontal
passage Monday morning too low to highlight this taf issuance.
Outgoing forecast favors a more optimistic outlook on cigs remaining
above 5000 ft through Monday afternoon.

DTW THRESHOLD PROBABILITIES...

* Low for cigs aob 5kft prior to Monday evening, high thereafter.

&&

.PREV DISCUSSION...
Issued at 323 PM EST Sun Feb 23 2020

DISCUSSION...

A mid level short wave now advancing across Lake Superior will drive
a weak cold front into Se Mi tonight. Moisture and forcing has been
so limited along this boundary that it has been unable to even
generate clouds. The front will weaken/wash out across Se Mi late
tonight/Mon morning. The main effects of the passage of this
boundary will be the development of light east-northeast winds off
the lakes on Monday which will support a little cooler daytime temps
in comparison to today, especially along the lakeshores.

The upper wave now diving into the Pacific northwest is forecast to
move into the central Rockies by Monday afternoon. There is good
model agreement that there will be enough separation between this
wave and the upper low now churning over the CO/NM border to cause
the CO/NM low to accelerate toward the northeast and into the Ohio
valley Monday night. This system is forecast to undergo considerable
weakening as it does so. It will drive decent moisture northward
into srn Lower Mi late Mon afternoon/Mon night. This moisture
transport along steepening low-mid level isentropic surfaces will
support a good chance of precipitation Mon night, mainly south of
the I-69 corridor. The NAM solution suggests precip will quickly
transition to snow due to wet bulb cooling. While the increasing
easterly flow does raise this prospect, the boundary layer temps on
the NAM have been much too cold with the airmass now overhead. So
preference with respect to precip type Mon Night and even into Tues
morning will be rain or rain/melting snow. Model solutions,
particularly the ECMWF actually indicate the moist ascent falling
apart late Mon night as the wave weakens.

The next phase of this complex system has the potential to be a
little more impactful. Model solutions continue to show long wave
trough amplification over the Rockies evolving into a closed mid
level circulation over the Central Plains and Mid Mississippi Valley
Tues into Tues night. This wave is forecast to take on a negative
tilt as it lifts across the Great Lakes Wednesday, eventually
phasing with a another northern stream impulse diving into the
western Great Lakes Wed night. This will cause a deepening of the
associated sfc low is it lifts from the Ohio Valley across the ern
Great Lakes on Wednesday.

A robust region of mid level deformation is forecast to develop
along the remnant mid level front over Se Mi on Tuesday aftn/Tues
night. The ECMWF/Canadian/Ukmet solutions, which are a little farther
south with the upper low, suggest a stronger/faster dynamic response
as the wave lifts into Lower Mi Wednesday. These solutions contract
the baroclinic zone right over Se Mi, thus pivoting the mid level
deformation overhead and giving a good portion of Se Mi accumulating
snow, particularly Tues night through Wed. The NAM and GFS are a
little farther north/faster. These solutions suggest this
intensification occurring farther north, leading to a more
progressive mid level deformation axis that strengthens mainly north
and west of the forecast area. The NAM/GFS solutions are also a
little warmer over Se Mi with much less snow (with the mid level dry
slot possibly affecting portions of the area). So obviously there is
a good deal of forecast uncertainty at this time. Later forecast
cycles as we near this event will narrow down the uncertainty. Both
camps do hit the Saginaw Valley and thumb regions with a good period
of forcing, suggesting higher probabilities of accumulating snow in
the north attm.

Much colder air will pour into the region in the wake of the
Wednesday storm system. This and lingering moisture/mid level short
wave impulses will sustain chances for snow showers Thurs and
Friday.

MARINE...

Southwest flow will weaken and rotate to westerly tonight before
veering to northeasterly Monday evening out ahead of the next
approaching low. Northeasterly winds will pick up Tuesday, though as
of right now, wind gusts are looking to stay below gales. There is
still a fair amount of uncertainty in the exact track of the low
center. The GFS takes it across west Michigan and north-central Lake
Huron, whereas the Euro takes it from western Lake Erie north along
the eastern shores of Lake Huron. The track will affect the main
precip type (further west more snow, further east more rain) and
wind speed/direction over Lake Huron. There is fairly good consensus
that the low will track across the region during the day Wednesday,
so expect rapidly changing wind directions Wednesday with northwest
flow setting up behind the low Wednesday night into Thursday.

HYDROLOGY...

A complex storm system will move into the region Monday night and
persist into Wednesday. Any precipitation Monday night will be
light. Precipitation is forecast to increase in coverage on Tuesday.
There is some uncertainty with the storm track of this system. A
farther east storm track will bring warmer air into the region, thus
more rain, but suggests lower total QPF; under a half inch. If the
storm system tracks farther east, total QPF up to three quarters of
an inch is possible, much of which will be in the form of snow.

As low pressure meanders across the Ohio Valley on Tuesday, east-
northeast winds may lead to some flooding along the lakeshores.
Depending on the track of this expected low pressure system, strong
northeast winds off Lake Huron may persist into Wednesday. This of
course would worsen shoreline flooding concerns along Lake Huron.

&&

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

$$

AVIATION.....MR
DISCUSSION...SC
MARINE.......KDK
HYDROLOGY....SC


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NWS DTX Office Area Forecast Discussion