Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 210401
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1201 AM EDT Sat Apr 21 2018


.AVIATION...

VFR conditions will prevail as high pressure remains positioned over
the area. Only cirrus will thicken Saturday as an upper low pressure
system edges east into the southern plains. Winds will remain 5 kts
or less under this high.

.DTW THRESHOLD PROBABILITIES...

* None.

&&

.PREV DISCUSSION...
Issued at 300 PM EDT Fri Apr 20 2018

DISCUSSION...

Temps pretty much on target today rising into the low to mid 50s
except mid/upper 40s in the Thumb under full insolation. Extremely
dry 12z sounding fully supportive of cloud free skies for the
balance of the afternoon as surface dewpoints have fallen into the
teens with deep diurnal mixing. The dry boundary layer, clear skies,
and a gradient sufficiently weak to allow for decoupling early in
the evening will be supportive of another chilly night. Thin cirrus
already spreading across Lake Michigan will gradually spread over
the area and thicken through tonight, eventually putting a floor on
low temps in the upper 20s and low 30s per MET/MAV statistical
guidance, which were both on the cooler side of the solution
envelope.

Mid and high clouds are widespread over the central US today in
association with the closed low centered near the 4-corners at press
time. 12z NWP appears to have initialized well with mid/upper
tropospheric moisture fields and progged soundings for Saturday
suggest pessimism. Forecast soundings from the GFS indicate full
saturation from the troposphere down to 500mb. Overcast skies will
dominate for the balance of the day across the south. Given
virtually no change in the resident thermal profile from today,
temps have been lowered into the low 50s south of M59. Would not be
entirely surprised to see some locations stuck in the upper 40s, but
will give the mid shift a last minute opportunity to make that
adjustment if needed. Confluent flow pivoting through the Great
Lakes from the north will force the cloud shield south sufficiently
early in the day to allow temps to rebound in the Saginaw Valley.
The Thumb will be limited by cool onshore flow due to the strong
lake aggregate that will limit mixing depths.

As the closed low meanders from the 4-corners today into the Lower
MS Valley by late Sunday, northern stream energy will force upper
ridging over the Great Lakes for the latter half of the weekend.
Subsequent modification of the thermal field may be too late to make
too much of a difference as the 12z GFS indicates 850mb temps will
remain below 0C until 21z Sunday afternoon. Therefore suspect Sunday
will be quite similar to today with no expectation for clouds and
highs only limited by the cool airmass over the region. A stronger
easterly gradient as the lake aggregate translates east beneath
progressive upper ridging will support highs near 60 west of US-23
and in the mid 50s over the eastern CWA where mixing depths will be
more limited in the lake shadows.

The stretch of dry weather will continue through Tuesday with high
pressure remaining in control at the surface with a split-flow
pattern aloft. Heading into Wednesday, a closed upper low over the
southeast CONUS will open up and merge with incoming northern stream
shortwave energy diving across the northern Plains. The long range
guidance diverges significantly in the handling of this interaction,
but enough moisture advecting north across the region will lead to a
period of scattered showers late Tuesday and continuing into
Wednesday night. A secondary closed upper low amidst deepening
longwave troughing over the eastern CONUS will continue to lead to
unsettled weather conditions heading into the weekend.

Temperatures on Monday and Tuesday will be the warmest in quite some
time, with high temperatures reaching well into the 60s. As showers
overspread the region during the midweek period, temperatures will
cool, but still remain in the 50s for daytime highs.

MARINE...

High pressure will dominate the region for the next few days. High
will slowly drift eastward, resulting in weakening winds tonight
that will remain light and variable through the weekend. Light
southerly winds will emerge Monday as the high exits to the east.
Unsettled weather likely to return by late Tuesday into Wednesday as
an upper trough pivots through the Great Lakes.

&&

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

$$

AVIATION.....AA
DISCUSSION...JVC/IRL
MARINE.......MR


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at www.weather.gov/detroit.



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