Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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398
FXUS63 KDTX 220355
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1155 PM EDT Sun May 21 2017


.AVIATION...

Low level cold advection in the wake of the synoptic scale cold
front is leading to a good deal of saturation and cloud in the 4.0
to 5.0 kft agl layer. The cloud deck has been a little slow to move
into the Detroit Metro area, but will momentarily. Model RH show
little to no dry air advection in the 925-850mb layer supporting VFR
cloud tonight. Introduction of surface ridge should help in
preserving low level moisture given lack of airmass changeover. Low
RH makes inroads around midday for the southern half of the cwa.
This could lead to a break up in clouds during the late morning with
clouds developing again with diurnal cu response for the afternoon.
West gradient flow will be high enough during the late afternoon to
support winds of 20 to potentially 30 knots.


//DTW THRESHOLD PROBABILITIES...

* High for ceiling aob 5000 feet tonight.

&&

.PREV DISCUSSION...
Issued at 318 PM EDT Sun May 21 2017

DISCUSSION...

Large upper level low pressure, with multiple embedded vort lobes,
centered over northern Minnesota will slowly lift northward into
Ontario tonight. Additional shortwave energy over Alberta and
Saskatchewan will meanwhile drop down into the backside of the
system, enhancing the longwave trough over much of the U.S. and
eventually resulting in a closed low over the Upper Midwest by
Tuesday.

Showers and thunderstorms working across the area ahead of a cold
front and mid-level dry slot will exit the area over the next few
hours, with a fairly dry evening expected. SPC analysis shows 500-
1000 J/KG of SB CAPE over the far southeast corner of Michigan.
Cannot rule out some stronger storms with gusts to 45 mph, but so
far radar presentation has not suggested anything too strong.
Locally heavy rainfall looks to be the main threat for the rest of
the afternoon before storms exit. Cold air-advection below 850mb may
allow moisture to become trapped in the lower levels under a
strengthening inversion overnight, providing a fair amount of cloud
cover. This should limit radiational cooling, holding min temps in
the upper 40s to low 50s.

One of the stronger lobes of vorticity embedded within the upper
system to our north will swing across northern Michigan early
Monday. Forcing from this feature looks to remain primarily north of
the area, where better chance of showers will also reside. It will
however serve to elongate surface low pressure over Ontario, which
will provide breezy conditions across Southeast Michigan as the
gradient tightens between this surface low and high pressure
building into the Ohio Valley. Strong southwest flow and decent
mixing will help boost high temperatures into the mid to upper 60s,
just a little below normal.

Closed low over the Midwest will slowly sink southeast towards
Michigan Tuesday and Tuesday night, providing steadily increasing
chances for showers from Monday night through Tuesday night.

An amplified upper-level trough with a cut-off low situated over the
Ohio Valley will bring the chance for rain showers Wednesday into
Thursday, as daytime highs stick around in the upper 60s. A ridging
pattern is then expected to briefly enter across the Great Lakes
region which could provide some relief from rain chances, however,
the ECMWF model is hinting at rain potential as a shortwave moves
east across southern Michigan. Will leave PoP values low for now,
but may need to bump up over the next day or two if model
convergence is noted. Otherwise, low confidence regarding rain
potential for Memorial Day weekend. GFS runs hold on to some upper-
level ridging Friday into Saturday which holds precipitation south
of Michigan, however, ECMWF and GEM 12Z runs exhibit a series of
short waves along with a weak surface low which would bring the
chances for rain showers. Additionally, weak instability is
exhibited in the ECMWF run which could also bring the potential for
thunder if showers were to develop. Temperature-wise, daytime high
temperatures are expected to peak in the mid to upper-60s mid week,
with a warm-up into the 70s starting Friday and continuing into the
weekend.

MARINE...

Waves remain excited across Lake Huron with southeast flow in the 20
to 25 knot range. This direction keeps the bulk of the waves off
shore, but waves in the 3 to 5 foot range continue to clip a couple
nearshore zones along the Thumb thus small crafts will be issued
through this afternoon. A cold front then sweeps through the region
this evening bringing an abrupt wind shift to the southwest. This
may necessitate additional small craft advisories for Saginaw Bay
and/or the nearshore zones of Lake Huron as winds approach criteria.
Unsettled weather will remain over the region through midweek as
general troughing remains overhead with possible low pressure
systems developing within it.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from 10 AM to 8 PM EDT Monday for LHZ441>443.

     Small Craft Advisory until 8 PM EDT Monday for LHZ421-422.

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

$$

AVIATION.....CB
DISCUSSION...HLO/AM
MARINE.......BT


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.



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