Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 210800

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
300 AM EST Tue Feb 21 2017


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

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.



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.


Issued at 1158 PM EST Mon Feb 20 2017


VFR will continue through the night as high clouds thicken and lower
ahead of the next frontal system. This will be accompanied by
southeast surface wind holding in the 5 to 10 knot range which the
latest model soundings indicate will be marginal for a LLWS mention
through the morning.

Expectations for the cold front remain on track for late morning
through the afternoon. Low pressure parent to the cold front will be
well north over Hudson Bay and moving away from the Great Lakes. The
trailing cold front that is left behind shows signs of weakening in
model data as it approaches SE Michigan but appears able to produce
MVFR rain showers at MBS from about mid morning through early
afternoon. The front will then struggle to support rain later in the
day but borderline MVFR/IFR ceiling will linger with the higher
boundary layer moisture content indicated upstream. Surface dewpoint
in the lower to mid 50s into southern Wisconsin is projected to
reach Lower Michigan and could produce a more aggressive intrusion
of IFR by Tuesday evening. The dissipating frontal wind shift will
be favorable for maintenance of low clouds and fog in light and
variable or light southwest wind over the region.

For DTW... Easterly flow that lingered around the 100 degree
direction during the evening will veer toward the south during the
night with speed 10 knots or less. The veering trend will at least
help switch runways back to southwest traffic operations during the
morning. VFR will otherwise persist until the remains of the cold
front arrive during afternoon.


* High for ceiling 5000 ft or less late morning into Tuesday


Lake Huron...Small Craft Advisory until noon EST today for LHZ441-442.

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



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