Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 160733
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
333 AM EDT Mon Apr 16 2018

.DISCUSSION...

The large stacked low pressure system responsible for the winter
weather over the weekend will continue to slowly wobbling through
the Great Lakes today. The base of the upper level trough is
swinging eastward resulting in a more negatively tilted trough axis.
The upper low is re-establishing itself over northern MI with the
cold pool while a piece of it shears off to the east. The surface
trough will also lag being the exiting surface low, reaching
westward across northern lower. The shift in the entire pattern
eastward has allowed westerly flow to develop which will usher in
colder air through the day. Plenty of lingering boundary level
moisture wrapping around the backside of the low, combined with
steepening low level lapse rates due to cooling of the mid levels
will lead to some scattered light rain showers today. Drizzle may be
more dominate especially early on as moisture depth may be too
shallow to result in rain. Activity should peak this afternoon with
peak heating with best coverage farther north closer to the cold
pool. Looks like ptype could transition to a rain snow mix later
this evening as saturated layer cools into the DGZ and surface cold
air advection gets temps closer to freezing.

There is another chance of accumulating April snow tonight as the
surface trough rotates down through SE MI and the upper low center
releases southeastward through the area along with it. light snow
will be possible after 00Z with only a dusting to a couple tenths
expected. Most of the accumulation will occur between 06-12Z tonight
into Tuesday morning as these two features along with the trowal and
cold pool. Lapse rates will peak during this time with mixing depths
reaching 6kft allowing these favorable lapse rates to spread through
the DGZ and moisture extending well above that. QPF looks to come in
around a tenth of an inch so expectations are for accumulations
around an inch for most locations, but possibly up to 2 inches north
of about M-59.

Tuesday will be dry (outside of any lingering early morning
snow/rain showers) as the low finally exits the region. Mid level
shortwave ridge will slide through state with surface ridge axis as
well. The thermal ridge will lag back to the SW keeping Tuesdays
highs in the upper 30s to low 40s. Warmer temps will arrive on Wed
where upper 40s to possibly some 50s will be felt. Wednesday like
Tuesday should be mostly dry although a compact low will be just off
to the west during the day before tracking across southern MI
Wednesday night into Thursday. The track of this low will mean the
difference between rain (through mid MI) or snow (track through
northern OH).  At this point several days out will highlight more of
a rain/snow mix until we can resolve some track issues and figure
out a thermal profile. One thing models all seems to agree on is the
precip falling in a fairly narrow band across lower MI.

A bit of a pattern shift comes for the end of the week and weekend
as upper level ridge builds across the Plains and into the Great
Lakes. Though not a pure warm advective pattern, the airmass will
moderate through the weekend with increasing heights allowing highs
into the 50s. This is still a few degrees below normals for mid
April (Sunday April 22nd: DTW 62, FNT 60, MBS 59).

&&

.MARINE...

Easterly winds across Lake Huron will weaken this morning as low
pressure lifts across the southern Lake Huron basin. This low will
drift into Georgian Bay this evening, causing winds to turn
northwesterly. As the low departs to the east tonight, the northwest
gradient will increase and cold air advection will deepen the over-
lake mixed layer. This will result in an uptick in the winds, with
gusts around 25 knot possible across the open lake through Tuesday.
The surface gradient will then relax toward mid week, leading to a
drop in winds and waves.

&&

.PREV DISCUSSION...
Issued at 1205 AM EDT Mon Apr 16 2018

AVIATION...

Fog is becoming a greater component of LIFR during late evening and
will continue as the surface trough/occlusion pivots through SE
Michigan. These conditions will be accompanied by drizzle and rain
at times through the night as temperatures hover in the mid 30s. The
greatest concentration of LIFR is expected to migrate northward with
the surface trough as slightly increased westerly wind allows some
improvement in the DTW area. Ceiling improvement will struggle back
into MVFR later in the day as colder air moves in on moderate west
wind. The struggle will be due to moisture wrapping around the low
pressure system from the north that could bring lower ceiling and
snow back into by Monday evening.

For DTW... LIFR in low ceiling and briefly dense fog will improve as
light/variable wind becomes light west during the night. Upstream
observations indicate mostly IFR will hold with widely variable
ceiling possible during the morning.

/DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less through the forecast period.

* Moderate for ceiling 200 ft or less tonight.

* High for precipitation type as rain through tonight.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 10 AM EDT this morning for
LHZ421-441- 442.

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

$$

DISCUSSION...DRK
MARINE.......SC
AVIATION.....BT


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



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