Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 211722
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1222 PM EST Tue Feb 21 2017


.AVIATION...

Shower activity continues to weaken along an also weakening front.
Expect shower chances to continue in southern taf sites through
about 20z. Cloud bases have been all over the place but majority of
ceilings are quite high (aoa 5k ft) with some pockets of mvfr.  The
surface front will continue to weaken as it lays more east west
across the southern border of the state. Wind field will become very
light tonight with an area of low level moisture advecting southward
into the area with most of the moisture pooling in the proximity of
the nearly washed out front across the south. Expecting thin but
shallow stratus to form overnight along with fog as dewpoints will
remain high especially for this time of year. Still uncertain on the
extent of the stratus and fog that will develop. Might end up with a
wide varying of visibilities and ceilings.  Wind should pick up late
morning from the southwest scouring away and fog and low stratus for
the afternoon.


For DTW...Expect light showers for about the first two hours of taf
period then just overcast will varying ceilings that will be mostly
vfr.  Stratus and fog will likely form tonight with very light
surface flow.  Stratus and fog will scour out late Wednesday
morning as southwest flow increases.

//DTW THRESHOLD PROBABILITIES...

* Low for ceilings at or below 5000 ft this afternoon. High for
  tonight and Wednesday morning.

* Low in ceilings/visibilities below 200 ft and/or 1/2 mile tonight
  through Wed morning.

&&

.PREV DISCUSSION...
Issued at 300 AM EST Tue Feb 21 2017

DISCUSSION...

Band of showers stretches from the Gulf of Mexico to Northwest
Ontario at press time, the northern branch of which is undergoing a
steady weakening phase as forcing peels away to the northeast.
Extrapolation puts light rain showers on the doorstep of the Saginaw
valley at 12z. Diminishing trend is then forecast to accelerate
through the morning as the northern branch wave currently over
northern Wisconsin and Lake Superior peels away and the LLJ weakens
and veers out. As a result, took another whack at the inherited pops
as confidence in showers reaching the SE half of the CWA in any
organized fashion is reduced since yesterday. High and mid-level
overcast will dominate in the wake of any light rain. 925mb temps
increasing to the high single digits over the SW portion of the CWA
combined with reduced rain potential will make for a good
opportunity for highs to reach the low 60s once again.

The low-level moisture axis will remain in place tonight as the lead
edge of energy presently coming onshore in the Pacific Northwest
forces lee cyclogenesis over the northern Great Plains this evening.
Steady southwest gradient at the surface will support dewpoints
perhaps reaching the low 50s while strengthening westerly flow atop
the strengthening inversion layer sets up a decent shear layer for
enhanced forcing of drizzle development. With support from existing
upstream obs this morning and the addition of better forcing
tonight, added both fog and drizzle to the forecast for the latter
half of tonight.

Aforementioned lee cyclone will track well north of the area on
Wednesday, the 00z EC indicating a slightly flatter solution as it
grapples with energy offshore in the eastern Pacific. Strengthening
southwest gradient as the low approaches the western Great Lakes may
support some gusts upward of 20 mph. Meanwhile, late Feb insolation
and low-level warming should help mix out low clouds/drizzle/fog by
mid to late Wednesday morning. Mid 60s seem like a sure bet with
warmer spots potentially making a run toward all-time February marks
of...

DTW...70 (1999)
FNT...68 (1999)
MBS...67 (1930)

Weak height falls associated with the passing wave is modeled to
force the cold front just south of the Michigan/Ohio border for
Thursday allowing temps to fall back toward sub-record values.
During this time, jet energy digging south along the West Coast will
deepen the existing trough as it translates across the Rockies.
Strong cyclogenesis will result. Weakly coupled jet structure will
emerge as longwave pattern amplifies, dominated by the southern jet,
allowing isentropic ascent to ramp up in full force immediately to
the south. Baroclinic zone will lift back north bringing widespread
stratiform rain Thursday night into early Friday with a few rumbles
of thunder possible as h7-h5 lapse rates steepen coincident with
strengthening LLJ nosing into the area. Consensus is essentially set
on a warm track to the west of the CWA with the vast majority of
variability attributable to different intensity outcomes. Several
low amplitude features over Canada and the eastern Pac appear to be
playing havoc with larger scale trough evolution. Thus, while
confidence is sufficient for a high pop scenario, confidence in
Friday afternoon high temperatures and Friday evening/night severe
weather variables remains low. This is largely a result of
uncertainty in surface warm front progress. Worth noting that the
potential exists for another run all-time February highs will be
possible given that Wednesday`s airmass will simply be re-surging
back into the area.

MARINE...

The southeasterly gradient has been increasing overnight with the
approach of a frontal boundary. Meanwhile, an influx of very warm
low level air atop the shallow cool layer over the lake is greatly
limiting stability. Nonetheless, south-southeasterly winds across
Lake Huron will gust up to 25 to possibly 30 knots at times during
the pre dawn hours given the strength of the gradient. The front is
forecast to pass across Lake Huron this afternoon and into Lake Erie
this evening. There will actually be a weakening of the gradient as
the front passes through today before washing out over Lake Erie
tonight. The result will be a marked weakening in the winds during
the course of the day and evening.

Modest south-southwest winds will then develop late tonight and
persist into Wednesday night as a slow moving low pressure system
and frontal boundary pushes into the northern Great Lakes. A
strengthening low pressure system is forecast to lift into the Great
Lakes region on Friday, potentially bringing gale force winds Friday
through Saturday.

&&

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

$$

AVIATION.....DRC
DISCUSSION...JVC
MARINE.......SC


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