NWS Forecast Discussion
FXUS63 KDTX 210448
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1148 PM EST Mon Jan 20 2020
A gradually backing low level wind will continue to draw lake
Michigan moisture into the region through Tuesday. Existing area of
stratus showing some signs of clearing now, suggesting a window for
partly cloudy or clear skies will exist during the morning period.
Lower stratus will then expand in coverage again Tuesday afternoon
in response to a prevailing westerly flow and some diurnal
enhancement. Winds generally aob 10 knots through the period.
For DTW...Existing low stratus will attempt to clear through the
morning hours. Additional stratus development will then be possible
again Tuesday afternoon.
DTW THRESHOLD PROBABILITIES...
* Medium for ceilings below 5000 ft late this evening into early
morning hours, otherwise low.
Issued at 353 PM EST Mon Jan 20 2020
Dry conditions continue through the early week with temperatures on
a multi-day below normal stretch for the first time in a while. We
have to go back into mid November to find a string of more than 2
below normal days in a row for the Detroit area. Lows tonight
generally in the single digits to lower teens and highs Tuesday
mainly in the upper 20s should make it 3 in a row before a warming
trend begins during mid week.
The main question in the short term forecast is regarding the
coverage of lake stratus extending into SE Michigan tonight and its
durability through Tuesday. Afternoon satellite imagery and surface
observations today show solid coverage across northern and western
Lower Michigan reaching into the Saginaw valley and Thumb. These
clouds are set to make additional eastward progress in backing low
level wind that results from high pressure sliding to our west and
south during the night. The wind field is on the light side which
means it will take while for clouds to reach all the way to Detroit
and also suggests some breaks will be possible during the night.
Both of these trends support holding the low temperature forecast on
the low end of the guidance range to allow for some spurts of
radiational cooling over fresh snow cover. The usually sheltered
interior locations reach the single digits while urban and shoreline
areas end up in the 10 to 15 degree range once again by sunrise
A mostly cloudy start Tuesday morning trends toward a greater amount
of sunshine during the afternoon as low level dry air helps
deactivate lake effect clouds. Any resulting increase in daytime
warming is likely too late to boost high temperatures past the upper
20s. Readings then begin a more notable moderation Tuesday night
through Wednesday as stronger south flow develops over the Great
Lakes on the west flank of surface high pressure migrating to the
Atlantic coast. Dry weather is also maintained by the system while
high clouds thicken over the region which may end up a factor in
limiting high temperatures to around 30.
Continued moderation in temperatures is accompanied by an uptick in
prospects for precipitation Thursday, at least a low probability for
the Saginaw valley and northern Thumb. During this time, a weak
front/surface trough settles into Upper Michigan from Canada
associated with a northern stream low pressure system. Weak
isentropic lift is shown occuring within the moisture axis along and
ahead of the boundary over Lower Michigan which brushes the Tri
Cities and northern Thumb. The combination of model soundings and
QPF suggest a low chance of a light rain/snow mix as the pattern
stalls during Thursday night. Entry level chance POPs in the
guidance database looks Ok for this time period.
The pattern Thursday over the Great Lakes stalls Thursday night as
the next low pressure system digs into the central Plains and
reaches the mid Mississippi valley by Friday. The sharp southward
track is helped by some lee side trough development in the southern
stream and progressive amplification of the larger scale upper air
pattern upstream over the eastern Pacific. Shortwave ridge
development centered over Lower Michigan then holds the stalled
front to our north and leaves SE Michigan effectively between
systems through much of Friday. Prefer holding on to entry level
chance POPs once again for a light rain/snow mix as the bulk of
low level cold air is confined to our north.
The latest runs of extended range models continue with the
preference of a closed solution on the mid Mississippi valley system
heading into the weekend. There also remain a few options on the
track of that system as it moves east of the Mississippi river
Friday night and Saturday. The stalled front/trough to our north
washes out in the meantime which allows some colder air to leak
southward leaning precipitation type toward snow. The question then
is if the closed low slides eastward more along the Ohio valley
which would allow the north flank of the precipitation shield to
reach SE Michigan, or if it takes a farther south track leaving just
a weak mid level deformation pattern over the central Great Lakes
through Saturday. A position about over the Ohio/West Virginia
border is favored in the latest deterministic runs by 12Z Saturday
which brings the northern fringe of the precipitation shield up to
about the M-59 corridor during Saturday. This is slightly faster and
farther south than the GEFS and NAEFS means and includes a northward
trend in the 12Z ECMWF track compared to its 00Z run.
A surface high pressure system will expand across the Midwest
tonight and will gradually settle over the Ohio Valley by Tuesday
afternoon which will allow a moderate pressure gradient to develop
across Lake Huron. The resulting pressure gradient will allow
prevailing northwest flow to hold through the night with gusts
around 25 knots across northern and central Lake Huron. Slight
backing of wind direction to the west-southwest expected Tuesday,
tied to the advancing high pressure system. Pressure gradient
strength to increase slightly during the midweek period, allowing
gusts to hold around 25 knots across Lake Huron, but otherwise, no
active weather expected until at least Wednesday night.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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