Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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049
FXUS63 KDTX 260350
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1150 PM EDT Wed Apr 25 2018

.AVIATION...

Increasing stability under cool and gradually drying northerly flow
will minimize the potential for additional cloud cover going forward
overnight. The existence of clear skies and a generally weak
gradient will provide a brief window for shallow fog development mid
morning /10z-12z/. High pressure now anchored over the midwest will
then build into the region on Thursday. This will maintain a dry and
stable environment, supporting clear skies and modest west to
southwest winds through the day.

For DTW...noting some increase in cloud coverage just to the south,
as cold easterly flow lifts Lake Erie moisture inland. This will
provide at least a low probability for some lower stratus to creep
back in overnight. Very low confidence for occurrence. Any low cloud
would quickly mix out by late morning.

.DTW THRESHOLD PROBABILITIES...

* Very low for ceiling 5000 ft or less overnight.

&&

.PREV DISCUSSION...
Issued at 321 PM EDT Wed Apr 25 2018

DISCUSSION...

Partial clearing across the southern Metro region have allowed
temperatures to overachieve this afternoon as temperatures have
climbed into the lower 60s. Northerly flow off of Lake Huron have
kept temperatures capped in the 40s across the Thumb, while more
moderate temperatures have been observed from Pontiac up to Saginaw,
with highs in the 50s. Communities in the thumb, especially closer
to the shoreline, will have a slight chance to see brief showers
through the evening as a PV anomaly resides across central Lake
Huron. Cloud cover associated with this eastward moving PV anomaly
and diurnal heating will begin to diminish tonight and overnight as
incoming subsidence and dry air settles in across SE MI. Winds
gusting between 15 - 20 mph, isolated 25 mph, will also quickly
diminish tonight after diurnal mixing ceases after sunset. The cut-
off low and associated PV anomaly will push over New York by
Thursday 12Z and will continue to reinforce NW flow across Michigan,
allowing 850 mb temperatures to drop to an average of 1C overnight.
Clear skies will allow for strong radiational cooling overnight,
supporting lows in the lower 30s across SE MI and mid-30s across the
urban Metro region. A very slight chance for periods of patchy fog
to develop overnight across the Thumb, as winds diminish and dry air
moves in aloft, however, opted to leave patchy fog out of the
official forecast as latest high-resolution runs keep surface
conditions too dry to support fog chances.

Otherwise, a ridge of high pressure will then build across Michigan
throughout Thursday and will continue to keep conditions dry as
clear to partly clouds skies persist throughout the day. Copious
amount of sunshine will allow temperatures to push into the low to
mid-60s for a daytime high as a weak pressure gradient keep winds
calm to light.

The next chance for rain will enter late Friday morning into the
early afternoon as an upper-level trough and associated cold front
push through the Great Lakes region. Temperatures will remain below-
normal as a thermal trough and overcast conditions help cap daytime
highs to the mid to upper 50s Friday afternoon. For reference,
normal highs reside in the lower-60s for late April. Otherwise, a
brief lull in precipitation will be possible late Friday afternoon,
before an embedded shortwave located on the backside of a trough
coupled with left exit dynamics from a jet maxima aloft help support
a second round of showers. Rain chances will be centered across the
Metro region, late Friday into Saturday morning.

Any lingering showers will be on the way out by Saturday afternoon
as upper jet support and shortwave move off to the east. Strong
ridging through the troposphere will take over in the wake and high
pressure at the surface will dominate the weekend forecast. Thermal
trough with 850 mb temps in the negative single digits C will linger
through Saturday and limit surface highs to the low 50s. Quick
modification of this air mass in late April insolation will allow
Sunday`s highs to rise to the mid 50s. Dry and mostly sunny
conditions will prevail Saturday through late Tuesday as the high
pressure slowly drifts south and east. Warm air advection will
become established by Monday with southerly flow bringing highs to
the upper 60s that day, and the lower 70s by midweek. Chance for
rain returns on Wednesday due to low pressure over Ontario pushing a
cold front through the Great Lakes.

MARINE...

Small craft advisories remain in effect for Saginaw Bay and southern
Lake Huron through this evening. Peak gusts topping out near 25
knots will relax through the evening as low pressure tracks east to
southern Ontario but the long north fetch will keep waves elevated
in excess of 4 feet for several more hours. High pressure will build
overhead tonight and hold through Thursday resulting in light winds
backing from northwest to southwest. A cold front will then reach
northern Lake Huron late Thursday night and sweep across the rest of
the basin through the day Friday. This combined with an additional
low pressure system sweeping across the southern lakes will keep
unsettled conditions and gusty northerly flow through the weekend.

&&

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

$$

AVIATION.....MR
DISCUSSION...AM/TF
MARINE.......DK

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



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