Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 211903
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
303 PM EDT Fri Apr 21 2017

.DISCUSSION...
Mid level trough axis and weak surface troughing extends back from
yesterday`s system across central lower Michigan.  This combined
with plenty of low level moisture wrapping behind this system is
producing extensive cloud cover and some light rain showers earlier.
The trough will gradually swing through over night bringing gradual
clearing from the northwest to about the northern burbs of the
Detroit metro area by morning. Gradient wind will remain about 5 to
10 mph as surface high pressure center approaches.  This combined
with cloud cover for a good part of the night should hold temps up
in the upper 30s preventing any frost formation.

Upper level ridging and surface high pressure will slide in for the
weekend bringing plenty of sunshine and relatively light winds.  The
exception will be the southeast corner, from about the Detroit area
south for most of Saturday.  Large elongated closed 500mb
circulation across the Tennessee Valley will slowly push east with
mid and high level cloud shield extending north into the southeast
corner.  Depending how thick whether mostly cloudy or filtered
sunshine in that area.   Highs Saturday will be a few degrees below
average in the mid to upper 50s.

For Saturday night, large surface high pressure will be moving in
with weak surface gradient and plenty of dry air.  Winds  will
go near calm and with clear skies and dew points around or slightly
below freezing, expect possibility of frost, mainly west and north
of Detroit area. High pressure overhead Sunday will bring a wonderful
weather day with sunshine, light winds and highs mostly in the mid
60s.

Dry air is expected to hold in place throughout Monday as
temperatures rise into the mid-60s for a daytime high , with a
decent amount of sunshine expected through the afternoon. Cloud
cover will gradually increase as early as Monday evening, with
clouds filtering in through Tuesday as a weak low travels from the
North Central plains into southern Ontario. As the low travels north
of Michigan, winds will start to take on a S/SW component, pushing
temperatures into the lower 70s by Tuesday afternoon. Strong WAA in
addition to a series of upper-level disturbances will also bring the
chance for rain showers starting Tuesday afternoon. A second weak
low will then push in from MO/IL into MI Tuesday night through
Wednesday morning, bringing the continued chance for rain throughout
most of Wednesday.

Another round of rain and potential thunderstorms will be possible
by Friday, however, confidence remains low at this time track and
timing differences exist between the GEM and ECMWF models with the
associated low. Additionally, the GFS keeps the low pressure system
over the Central Plains, where-as the GEM and ECMWF models push the
low from around MO into Eastern WI by roughly Friday into Saturday.
PoP values will remain low through Friday as a result.

&&

.MARINE...

West to northwest winds will continue to decrease overnight as low
pressure lifts through Quebec. The Small Craft Advisory will be
cancelled as winds have already decreased below thresholds. Wave
heights will build into the 2 to 4 foot range for southern Lake
Huron this evening and late tonight as winds turn north, then
subside for Saturday as high pressure provides light winds. High
pressure over the Great Lakes will keep a quiet weather pattern and
favorable marine conditions over the area through the weekend.

&&

.PREV DISCUSSION...
Issued at 137 PM EDT Fri Apr 21 2017

AVIATION...

Moisture lingering behind exiting low pressure remains trapped under
an inversion this afternoon. Meanwhile, cold air advection filtering
into the area if offsetting daytime heating, and will help to keep
ceiling heights in the 2500-3500 range for the remainder of the
afternoon and evening. Skies will start to clear over the western
part of Michigan this evening, affecting MBS first. The remainder of
the TAF sites will take a little longer for stratus deck to scatter
out as moisture under the inversion is reinforced by north and then
northeast flow off Lake Huron. This adds some uncertainty with
timing the breakup of the stratus deck from FNT south. Gusty west-
northwest winds (270-290) will gradually turn more northwesterly by
late afternoon (290-330). The mixed layer does not look to support
gusts over 25 knots. Gusts will subside this evening as sustained
speeds also fall to less than 10 knots overnight.

For DTW...Stratus deck below 5000 feet is likely to hold through the
evening before scattering out overnight. Timing of the stratus break-
up is a little uncertain due to reinforcement as flow turns north-
northeast off Lake Huron. Most likely time still looks to be around
07Z. West-northwest gusts, just over 20 knots at best, should stay
below crosswind thresholds.

MVFR stratus will likely hold through the afternoon before
possibly lifting above 3kft. CIGS below 5kft should then scatter out
around 06z as high pressure builds into the region.

//DTW THRESHOLD PROBABILITIES...

* High in ceilings below 5000 ft through this evening then low late
  tonight.

* Low for reaching crosswind threshold this afternoon.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 8 PM EDT this evening for LHZ421-422-
     441>443.

Lake St Clair...Small Craft Advisory until 8 PM EDT this evening for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 8 PM EDT this evening for LEZ444.

&&

$$

DISCUSSION...DRC/AM
MARINE.......HLO
AVIATION.....HLO


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



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