Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 080414
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1214 AM EDT Sat May 8 2021


.AVIATION...

Northwest flow is underway tonight with steady gradient wind around
10 knots which should limit fog mentions. Models have fallen into
decent agreement with keeping overnight showers out of the Metro and
Tri-Cities terminals. Addressed KPTK/KFNT with a few hours of low-
potential -SHRA. Monitoring cloud edge interactions due to reservoir
of drier air barely west of the terminals where ceilings briefly cut
out during the past few hours. Moisture fields and satellite trends
generally support MVFR ceilings the rest of the night with only a
weak signal for brief dips to IFR (mainly at -SHRA sites), thus
forewent TAF mentions. Clouds partially scatter out this morning
before returning as higher-based afternoon stratocumulus with dry
conditions through the end of the cycle.

.DTW THRESHOLD PROBABILITIES...

* High for ceiling at or below 5000 ft tonight and early Saturday
  morning.

&&

.PREV DISCUSSION...
Issued at 343 PM EDT Fri May 7 2021

DISCUSSION...

High amplitude troughing emanating south of a closed mid level
circulation anchored over Hudson Bay will govern conditions over the
48 hours. Seasonably cool airmass derived from this setup clearly
evident this afternoon - characterized by a pocket of 500 mb
temperatures near -30C arriving concurrent with the passage of
shortwave energy working through the mean flow. Late day cold
frontal passage capitalizing on the underlying diurnally enhanced
steep lapse rate environment maintains a window for convective
development over the next several hours /particularly eastern
sections/ - instances of small hail or graupel and gusts to 40 mph still
a possibility within stronger cells.

Attention then turns to more substantial height falls now spilling
into northern lower Mi. This process arrives locally early tonight,
accompanied by a period of increasing mid level cold/moist air
advection. This may afford a general increase in deeper layer ascent
as a combination of dcva and the advective process engage the
advancing frontal slope. Recent hi res model guidance offers a
better signal for the maintenance and/or renewed development of
shower activity tonight - particularly across the thumb area. The
nocturnal timing may even allow for a few wet snowflakes overnight
across the north as freezing levels continue to fall. Inbound
thermal profile will net low temperatures Sat morning in the
mid/upper 30s despite some lingering cloud concerns and a modest
northwest gradient. Banking on this same environment limiting the
degree of frost production.

Dry and cool conditions define Saturday within deep layer northwest
flow. Typical insolation potential undercut slightly by some degree
diurnal stratocu expansion. This will afford a respectable diurnal
temperature response - afternoon readings arriving in the 50s.

Prototypical corridor of warm/moist air advection emerges upstream
this weekend, responding to the eastward propagation of low
amplitude shortwave energy out of the central rockies. This offers a
steady increase in high based cloud cover starting Saturday night
locally. Deeper layer saturation anchors within the northward
drifting elevated warm frontal slope during this time, likely
arriving in the vicinity of the Ohio border region by Sunday
morning. Uncertainty lies in the degree of additional northward
expansion of this moist axis throughout Sunday, differing model
opinion at this stage likely owing to subtle shifts in both
magnitude and track of the governing wave and corresponding
strength of the advective process. Southern sections certainly
better positioned for period of meaningful rainfall within a
combination of system relative isentropic ascent and perhaps some
trailing deformation forcing. Another cool day for all heightened by
lack of insolation within northeast low level flow - temperatures
across the south perhaps struggling to climb out of the 40s should a
widespread longer duration rainfall event materialize.

Another round of height falls tied to the aforementioned Hudson Bay
upper low arrives early next week. Extended period of deep layer
northwest flow ensures continued below average temperatures through
this time. Low finally releases eastward by the middle of next week,
but this ragged mid May pattern lends to another upper low
possibly taking residence late next week.

MARINE...

Numerous showers and thunderstorms will exist through the evening
hours as a cold front moves through the region. Winds shift to
northwesterly in the wake of this front overnight, gusting up to 20
knots at times through early Saturday. Winds then ease late Saturday
and Saturday night under building high pressure. Dry conditions
expected through the first half of the weekend. A low pressure
system tracking through the Ohio valley will bring an increasing
chance of rain Sunday, particularly across lake Erie and St Clair.
Winds will shift to an easterly direction during this time, but
limited strength and duration of onshore flow will maintain modest
wave conditions along the nearshore waters.

&&

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

$$

AVIATION.....KK
DISCUSSION...MR
MARINE.......IRL


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