NWS Forecast Discussion

773
FXUS63 KDTX 191100
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
600 AM EST Sun Jan 19 2020


.AVIATION...

CAA continues with strong westerly flow this morning as sufficient
moisture streams across lower MI to produce scattered lake effect
snow showers. Activity will temporarily wane this morning before a
cold front drops south. This front will maintain a semi-correlated
band of snow followed by a northerly wind shift on the back end.
Timing for snowfall beings with MBS around 12Z before exiting south
of DTW prior to 21Z. Gusty will be strongest this morning before
gradually diminishing during the course of afternoon, especially
after the frontal passage. MVFR conditions are expected outside of
any snow shower activity until expansive high pressure over the
northern Plains broadens into the Great Lakes this evening thinning
out the persistent stratus deck.

For DTW...Gusts initialize around 30 knots with westerly flow before
diminishing throughout the day, especially once a cold front clears.
A band of snow showers along said front may produce quick bursts of
dry snow with temporary IFR (or LIFR) vsby reductions. Otherwise,
MVFR continues until this evening with chilly temperatures.

 DTW THRESHOLD PROBABILITIES...

* High for ceilings under 5000 feet through Sunday afternoon.

* High in precipitation type as snow today.

* Low in exceeding crosswind threshold from 250-270 degrees tonight.

&&

.PREV DISCUSSION...
Issued at 241 AM EST Sun Jan 19 2020

DISCUSSION...

Trailing vorticity center on backside of sheared out upper system
will pivot southeast through the forecast area early this morning
and maintain light snow shower activity lift from this feature is
aided by moisture flux within westerly flow from Lake Michigan. A
secondary cold front will settle north to south through the area in
the wake of this upper wave. Convergence along this front will most
likely grab dominant Lake Superior/northern Lake Michigan snow band
and bring in southward. Early morning low level trajectories suggest
this feature will impact parts of the northern Thumb region as it
picks up just a bit more moisture crossing Saginaw Bay. Given radar
trends early this morning, will increase snow chances in this area
and up accumulations to at least an inch locally.

Some semblance of this band will persist as this front progresses
through the region today with timing from north to south still in
the 14z-22z window. Will adjust snow chances/amounts slightly based
on the expected progression of this feature. Outside the Thumb,
where additional lake effect activity from Lake Huron also pivots
onshore during the day, expect accumulations to be an inch or less.
Over the Thumb, particularly Huron county, would anticipate several
inches of new snow from early this morning into the afternoon. Aside
from lingering lake effect snow showers along the immediate shore of
Lake Huron early this evening, expect a much drier air mass to begin
shifting into the area as sprawling surface high pressure centered
over the northern plains/upper midwest gradually builds into the
Great lakes.

This drier pattern will hold into the middle of the week as said
high pressure settles into the Ohio Valley region by Wednesday
morning. Cold conditions will hold for the remainder of the weekend
on into Tuesday as temperatures actually drop below average for a
change this winter. Highs will range in lower/mid 20s into Monday
and edge up into the upper 20s Monday while lows settle into the
teens and in some cases single digits.

Upper ridging then expands over the eastern CONUS from mid to late
in the week as shortwave energy gradually digs into the plains from
the Pacific Northwest. Temperatures will moderate into the 30s and
eventually lower 40s in some locations by week`s end as this system
approaches the area. Precipitation chances will also increase in the
Friday to Saturday time frame with a mix of rain and snow showers as
the resultant upper low pressure system from this Pacific energy
shift east of the Mississippi Valley. At this time, this system
appears to remain largely cutoff from the northern stream storm
track as upper ridging encompasses much of Canada with upper
troughing displayed well east/northeast from area east of Hudson Bay
on into Greenland. This will limit any significant cool down with
(and in the wake of this system).

MARINE...

Colder air will continue to funnel across the lakes Sunday as a
strong low pressure system moves east away from the region.  West
southwest winds will continue to bring gales through the early
morning hours on Sunday. A trailing cold front will then be forced
south across the lake Sunday morning, with winds turning north-
northwest in the wake of the front. The post frontal gradient will
be weakening, so wind speeds/gusts will then actually decrease
slightly Sunday morning. Northerly winds then persist through the
day on Sunday.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 5 AM EST Monday for LHZ421-441>443.

Lake St Clair...Gale Warning until 7 AM EST this morning for LCZ460.

Michigan waters of Lake Erie...Gale Warning until 7 AM EST this morning for LEZ444.

     Low Water Advisory until 1 PM EST this afternoon for LEZ444.

&&

$$

AVIATION.....KK
DISCUSSION...DG
MARINE.......DG


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NWS DTX Office Area Forecast Discussion