Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 270518
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
118 AM EDT Fri Apr 27 2018


.AVIATION...

Very light winds and clear skies below 20 kft will continue
overnight. Mainly VFR clouds with a weak cold front passage late
Friday morning/early Friday afternoon. Window for rain showers at
each terminal will be short, 1-2 hours, if showers do in-fact
develop. A wind shift will occur with the front from southwest to
northwest, but winds ahead and behind should be relatively light, 10
knots or less. Much better chance for lower ceilings (mvfr) and rain
by midnight Friday over the southern TAF sites as low pressure
tracks across far southern Michigan and northerly winds usher in
colder air, with Lake Huron stratus likely developing.

For DTW...Airmass will become marginally unstable and very low
chance of a thunderstorm early Friday afternoon as front tracks
through. Slightly better chance if the front comes through a
little later in the day.

.DTW THRESHOLD PROBABILITIES...

* Low for CIGS below 5000 ft today, high by midnight Friday.

* Very low for a thunderstorm Friday afternoon.

* High for precip type being rain through tonight.

&&

.PREV DISCUSSION...
Issued at 318 PM EDT Thu Apr 26 2018

DISCUSSION...

Clear skies to continue well into the afternoon and evening hours as
a ridge of high pressure expands across the Great Lakes region. This
clearing will allow temperatures in the 60s to diminish into the
upper 30s to lower 40s by the mid-morning for most of SE MI (mid-30s
across the Thumb), before an advancing trough expands across
Michigan. This advancing upper-level trough with multiple embedded
shortwaves will produce overcast conditions filling in from
northwest to southeast through the mid to late morning hours, and
will also bring several chances for precipitation Friday into
Saturday.

The first PV anomaly will swing through SE MI through Friday
afternoon into early evening and will bring the chance to see
isolated to scattered rain showers across the region. A rumble of
thunder will be possible during the 18 - 00Z timeframe, mainly across
the southern Metro region, as MUCAPE values reside between 100 - 250
J/kg and mid-level lapse rates average 7.5 C/km. However, have opted
to leave thunder out of the official forecast as overall forcing for
rain chances remain poor. Precipitation chances will diminish
throughout Friday evening but will return again throughout Saturday
morning as embedded shortwaves on the backside of the trough coupled
with an advancing cold front moves in across SE MI.

Stronger forcing coupled with left exit region jet dynamics and
saturated low-levels show much better promise to see rain Friday
late night into early Saturday morning as an upper-level closed low
pushes east across northern lower MI. A thermal trough will build in
overhead behind the cold front, pooling in temperatures averaging -
2C by Sat 9Z and -6C by 18Z. This will allow overnight lows to dip
into the low to mid-30s north of I-69 and upper 30s across the Metro
region. With the cold column of sub-freezing air aloft and dewpoints
hovering between 30 - 32 degrees across the Thumb, wet-bulbing will
bring the chance to see rain mixed with melting snow throughout the
early to mid-morning hours. Precipitation chances will quickly
diminish throughout the late morning hours as an expansive high
pressure system builds in across the Midwest and pushes southeast
across the Ohio Valley. Northerly flow will cap daytime high
temperatures in the upper 40s to lower 50s for a high on Saturday,
with a clearing trend allowing for lows to dip into the upper 20 to
lower 30s for overnight lows as a lack of cloud cover
allows for radiational cooling.

As the upper trough departs to the east on Sunday, surface high
pressure will dominate the region while upper level ridging builds
in from the west. With thermal troughing lingering through much of
the day, expect another cool day as temperatures rise into the upper
50s under full late April solar insolation. The upper ridge will
then build into the region early next week allowing dry conditions
to prevail while increasing southerly flow will allow a warming
trend with highs rising into the 70s by Tuesday. The next chance for
showers and some thunderstorms will return during the middle part of
next week as a series of disturbances lift across the region ahead
of a cold front slowly pushing east.

MARINE...

High pressure over the region is resulting in light winds minimal
wave heights today. An approaching cold front will cause winds to
become southerly tonight. The front will pivot through the region on
Friday first affecting northern Lake Huron early Friday morning,
then passing through the southern end of the basin along with lakes
St Clair and Erie Friday evening. A second area of low pressure will
follow quickly behind it diving across the southern Great Lakes
Friday night. A period of light rain will accompany the front and
low. Winds will flip from southerly to northwesterly behind the
front with gusts approaching 25 knots by Saturday behind the exiting
low. The long fetch of Lake Huron along with cold air advection
allow these gusty winds to build wave heights across the southern
half of the lake. Small craft advisory may be needed Saturday for a
portion of Saginaw Bay and nearshore waters of Lake Huron to account
for the gusty winds and increased waves along the shore.

&&

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

$$

AVIATION.....SF
DISCUSSION...AM/JD
MARINE.......DRK


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