Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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170
FXUS63 KDTX 231943
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
343 PM EDT Sun Apr 23 2017

.DISCUSSION...

A cold front is currently dropping southward through Northern
Michigan and Lake Huron and has progressed into northern portions of
the Thumb this afternoon. This has occurred as a shortwave trough has
pivoted around an upper low over Hudson Bay, pushing a surface
trough down into the Northern Great Lakes. The frontal passage was
evidenced by a northerly wind shift and dramatic decrease in
temperature from 64 to 49 degrees between 17Z and 18Z at Port Hope
(P58). The front will progress through the remainder of the thumb
and Saginaw Valley this evening, dropping temperatures through the
evening, before sliding to about the I-69 corridor overnight. The
front looks to then stall there overnight as it loses upper support
and becomes parallel to upper flow. Very dry air already in place
(0.21-0.25 PW vales on KDTX and KAPX 12Z RAOBs), will limit clouds
with the front and no precipitation is expected. The most noticeable
effect aside from falling temperatures preceding sunset over the
Thumb will be a modest shift to northeast winds. Min temps tonight
will actually remain a few degrees warmer for most locations (mid
30s to low 40s) owing to the northeast gradient and influence from
the lake. Concern for frost formation is low, but if it did occur it
would be patchy over northern Oakland, Livingston, and rural areas
of Washtenaw County. Temperatures are very marginal for formation,
however, and did not even include a mention in forecast.

Canadian surface high pressure will expand back into Michigan late
tonight into Monday behind the surface trough and remain a dominant
influence on our weather tomorrow as it becomes centered over
Ontario and Quebec. Very dry airmass will remain in place, allowing
for a good amount of sunshine and a strong diurnal response to
temperatures to areas away from the lakeshores. Easterly flow off
the lakes will limit max temps to the 60s, allowing only areas only
well inland to reach 70. It will still be a nice spring day, as
seasonal averages for max temps are still in the low 60s.

Surface low pressure out ahead of lead energy ejecting out of the
trough over the West Coast will lift into the Upper Midwest and U.P.
of Michigan Monday night and Tuesday. This will bring an increase in
cloud cover and continue the stretch of warm weather into Tuesday as
southerly flow also increases.

WAA exhibited throughout Wednesday will allow daytime highs to peak
in the mid to upper-70s across SE MI as cloud cover remains
plentiful thanks to an advancing warm front. As low pressure
progresses from MO into the Great Lakes region Wednesday into
Thursday, PoP values will increase Thursday morning into afternoon,
as cooler air is wrapped around the low. Weak instability will also
bring the chance for thunder as the front drags through.

Otherwise, Friday is expected to stay relatively dry, although dry
conditions will be short-lived as a second warm front pushes into
southern Michigan Friday afternoon into Monday. This front will
provide enough lift and moisture to provide both the chance for rain
and thunderstorms through the weekend, while allowing temperatures
to peak in the upper 60s to lower 70s for a daytime high.

&&

.MARINE...

High pressure will shift slowly south this evening as a weakening
cold front settles into the area. The front will do little more than
shift winds to the north/northeast through tonight with a several
hour period of 20 knot gusts immediately behind the front. A Small
Craft Advisory will remain in place for Saginaw Valley as funneling
of the northeast flow will lead to somewhat enhanced wind and wave
action. Winds will turn to the east on Monday with gusts increasing
to 20 to 25 knots, mainly over far northern Lake Huron. SOutheast
flow will then become established into the middle of the week
between high pressure to the east and developing low pressure over
the plains.

&&

.PREV DISCUSSION...
Issued at 1245 PM EDT Sun Apr 23 2017

AVIATION...

The ridge of high pressure will settle south of the area into this
evening, allowing for light west flow around its northern periphery.
Strong subsidence and deep dry layer will maintain clear skies this
forecast period. A backdoor cold front will sweep into area this
evening (MBS) and overnight (I-94), bringing veering winds to the
northeast. With the earlier arrival at MBS (22z-23z), gusts of 20
knots will be possible for several hours with a steady 5-10 knot
"surge" immediately behind the front elsewhere. Light east/southeast
winds late tonight will increase to 10-12 knots mid/late Monday am.

//DTW THRESHOLD PROBABILITIES...

* None


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422.

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

$$

DISCUSSION...HLO/AM
MARINE.......DG
AVIATION.....DG


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