NWS Forecast Discussion

FXUS63 KDTX 260003

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
703 PM EST Thu Feb 25 2021


A broad area of high pressure reaches into Lower MI as it builds
through the Ohio Valley tonight and to the Atlantic coast Friday.
This ensures dry weather, minimal cloud cover, and light southerly
wind during the period. The weak pressure gradient results in a few
hours of near calm or light SE wind in the DTW corridor around
sunrise which combines with clear sky and a melting snow cover for a
short period of entry level MVFR haze or shallow fog. Southerly wind
stays mostly above 5 knots farther north through Friday morning. The
dry boundary layer associated with the high pressure air mass then
provides plentiful sunshine with a slight uptick in south to SE wind
Friday afternoon.


* None.


Issued at 348 PM EST Thu Feb 25 2021


Resident thermal profile late this afternoon defined near the
climatological norm for the day - characterized by a modestly mixed
diurnally modulated 925 mb temperature near -4C. Subtle period of
cold air advection noted above this layer corresponding with a brief
increase in coverage of stratocumulus coincident with daytime
heating, likely augmented by some degree of downstream moisture flux
off lake Michigan. Moisture depth proving too lean to support
precipitation development despite the presence of weak convergence,
leaving simply a fleeting window for perhaps a sprinkle or two
across the north prior to sunset. Deep layer stability then grips
the area tonight as a 1030 mb high anchors over the Ohio valley.
This will prompt a steady clearing trend overnight in conjunction
with the loss of diurnal support. A fairly standard nocturnal
cooling environment, as a 5 kt southwest gradient provides a ceiling
to possible magnitude of radiational cooling. Lows mainly 15 to 20
degree range.

Steady stream of shortwave energy working through the central conus
within a general split flow configuration will prompt a transition
toward broad upper level west-southwest flow Friday into next
weekend. Pattern of modest mid level warm air advection initiates
starting during the daylight period Friday. This likely promotes
some increase in cloud coverage with time, but retention of a deep
dry low level environment as existing low-mid level ridging only
slowly vacates ensures dry conditions. The general moderation of the
thermal profile points to a slight upward trend in temperatures
relative to today, but with prospects for a greater diurnal response
limited by the east-southeast low level flow.

Southern expanse of height falls tied to a pv anomaly pivoting into
the northern great lakes will glance across the area Friday night.
This process engaging a period of stronger isentropic ascent within
favorable left exit region upper jet dynamics translates into a
period of light precipitation production overnight. Precipitation
onset met by a gradually warming thermal layer. Analysis of sounding
data and projected surface temperature trends suggest a limited
resident time for sub-freezing conditions to support patches of
light freezing rain before temps nudge above 32F. Outgoing forecast
will continue to simply call for a low end chance mention - mainly
from the Irish Hills/glacial ridge up through the I-69 corridor. A
slightly colder mid level warm layer with northward extent also
favors snow or a rain/snow mix across the Saginaw valley/northern
thumb - accumulation potential at less than an inch.

A more noteworthy warming trend emerges over the weekend, lead by
the incremental increase in upper heights within prevailing
southwest flow. A rapid downturn in precip potential by daybreak
Saturday as stability deepens with time under increasing low-mid
level ridging. Highs Saturday arriving well into the 40s, with the
overall response perhaps aided further should clearing commence
earlier in the day. Mean flow will tend to direct additional
shortwave energy northeastward during the latter half of the
weekend. Greater precipitation potential may tend to split the area
given the projected placement of governing forcing and the deeper
moisture plume in this case. The underlying isentropic ascent as an
elevated warm frontal zone takes residence could prove sufficient
toward offering a lower end probability for light rain within the
Sunday period. This could certainly undercut the diurnal heating
response - projected highs tempered somewhat at this stage with
readings again planted in the 40s.


An area of high pressure will be sliding across the southern Great
Lakes and Ohio Valley today through Friday resulting in fairly quiet
conditions across the waters. The caveat will be a weak little low
currently tracking east across Lake Huron this evening which will
bring a short period of snow showers and briefly higher westerly
wind gusts possibly up to 25 knots. As the high shifts east, the
door will open for winds to become southwesterly around 15 knots
gusting to 25 knots by Friday afternoon. The high will depart on
Friday off to the east coast with the next low lifting northeast
through the region Friday night. This will briefly flip winds to
southeasterly ahead of the warm front, with southwest winds
returning on Saturday ushering in a much warmer and more stable
airmass for the weekend.



Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.




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NWS DTX Office Area Forecast Discussion