Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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138
FXUS63 KDTX 271915
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
315 PM EDT Mon Mar 27 2017

.DISCUSSION...

Cloudy to mostly cloudy skies around today, but temps still able to
reach into the upper 40s north to lower 60s south.

Upper level wave/circulation currently over southern Missouri will
be unraveling/shearing out, with bulk of the upper level PV tracking
through to the Ohio River Tonight. Meanwhile, upper level trough
tracking through northern Great Lakes this Evening/Tonight, with
southeast Michigan caught in between two systems. Best chance of
rain looks to be toward Ohio Border with 700 MB
forcing/FGEN/deformation potentially getting that far north, but 12z
NAM/regional GEM are both mainly dry (local probabilistic SREF
weighted guidance trends are trending down as well, along with
latest HRRR), with maybe just some light showers with the weak cold
front/low level convergence dropping south through Lower Michigan.
Good drying out occuring during Tuesday as PW values drop into
the 0.25 to 0.5 inch range with stout subsidence/drying continuing
Tuesday Night underneath pronounced  upper level northwest confluent
flow as upper level ridge axis builds over the western Great Lakes.
Problem is northerly flow off Lake Huron may be sufficient for low
clouds trapped underneath the  strengthening low level inversion,
but it does drop below 3000 FEET late in the day Tuesday, likely
allowing for clearing skies toward sunset Tuesday. Favorable
radiating night with surface ridge extending from large high
centered over Ontario, sending temps at or below freezing,
with rural locations/good radiators potentially slipping into the
20s. Although, development of Lake Huron stratus could become an
issue, with these clouds potentially impacting the Wednesday
forecast (see 12z gfs 925 mb RH/temps). SREF plumes at Detroit
indicating highs anywhere from 40 to 60 degrees. As this time,
forecast will favor mostly sunny skies on Wednesday which will will
help ease the chill, but northeast flow at the surface off Lake Huron
and 925 mb temps averaging 3 C (per 12z Euro) points to highs in the
upper 40s to around 50 degrees, or close to normal.

Low pressure will continue to push from MO and into the Ohio Valley
Thursday morning into Friday, bringing the likely chance for
precipitation. Current thinking is precipitation seen throughout the
morning hours will have the chance to fall as snow or a rain/snow
mix as wet-bulb processes dominate due to a dry low level
environment. As the column saturates and temperatures warm up, a
transition to rain will take place throughout the afternoon, from
south to north. PoP values will increase throughout Thursday
afternoon into Friday morning as the low pushes east across IN.

The ECMWF and GEM models are exhibiting a more southerly track of
the low compared to yesterday`s run, and as a result, the column of
air is not quite as warm as what was seen yesterday heading into
Friday. This brings the possibility of seeing additional snow or a
rain/snow mix, mainly near the thumb, throughout the early morning
hours, as temperatures have the potential to dip near the freezing
mark. Any snow solution near the thumb is expected to be short-lived
as temperatures warm up quickly through the late morning and
afternoon, transitioning any remaining precipitation back to rain as
the low starts to exit the area. PoP values are expected to diminish
late Friday into Saturday, as high pressured starts to edge in from
the west. Dry conditions will then be expected through the weekend
as temperatures stick around in the low to mid-50s for a high.

&&

.MARINE...

Fog over Lake Huron will dissipate from north to south during the
late afternoon and evening as a cold front drops through the area.
The front will also switch winds to the north, but speeds will
remain fairly light overnight. Strong high pressure building into
Ontario will then increase north to northeast winds Tuesday and
Wednesday. The strongest gusts look occur over southern Lake Huron,
Lake St Clair, and western Lake Erie, but are expected to only just
top 20 knots. While sustained wind speeds are expected to stay in
the 10 to 20 knot range, the persistent northerly flow and long
fetch over the water will increase wave heights over southern Lake
Huron. Low-end Small Craft Advisories could be needed for portions
of the nearshore waters during the mid-week period. Approaching low
pressure will then prompt increased east winds Thursday night into
Friday, allowing waves to grow once again over southern Lake Huron
and western Lake Erie.

&&

.PREV DISCUSSION...
Issued at 213 PM EDT Mon Mar 27 2017

AVIATION...

Moisture locked under an inversion will keep stratus with breaks in
place through the afternoon. Drier air clipping extreme Southeast
Michigan should allow for some improvement and even short periods of
VFR near the Detroit-area terminals, but conditions are expected to
predominantly remain at MVFR. A weak cold front will drop through
Lower Michigan this evening, with low-level cold advection
strengthening the inversion and dropping ceilings to IFR overnight.
Light north to northeast gradient will favor low status over fog,
although some MVFR vis restrictions are expected. A low pressure
system will also track through the Ohio Valley this evening. The
chance for rain showers to impact terminals from PTK south is too
low to include in TAFS however.

For DTW...Low confidence in ceilings holding at VFR this afternoon.
This is supported by all model data and upstream observations over
the rest of Michigan and the Ohio Valley where ceilings are between
1500-2500 feet. Colder air funneling into the area tonight behind a
cold front will strengthen the low-level inversion. Moisture trapped
under this layer should result in IFR cloud deck and BR.

//DTW THRESHOLD PROBABILITIES...

* High for cigs below 5000 feet through the TAF period.

* High confidence any precipitation will be rain.


&&

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

$$

DISCUSSION...SF/AM
MARINE.......HLO
AVIATION.....HLO


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



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