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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KDTX 191416
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1016 AM EDT Mon Apr 19 2021

.UPDATE...

Based on the radar representation and considering the low to mid
level frontogenetical forcing will increase as the front traverses
the forecast area this afternoon, a forecast update was issued to
increase precip chances. Also based on the latest observations and hi
res guidance, there will be a little tighter thermal gradient along
the front. Adequate daytime heating will boost highs well into the
60s across the eastern 1/3rd of the forecast area before temps plunge
into the 40s by late afternoon. The earlier forecast update also
made some minor adjustments to temperatures.

&&

.PREV DISCUSSION...
Issued at 631 AM EDT Mon Apr 19 2021

AVIATION...

Predominately VFR conditions through this TAF period which will be
maintained by a dry low level environment as a greater coverage of
mid level clouds spread into southeast Michigan today. Winds pick up
out of the west-southwest today in advance of a cold front that is
expected to pass through southeast Michigan this afternoon. Gusts of
20 to 25 knots are expected during the early to mid afternoon
period. Some lowering of cloud bases will accompany this front along
with light rain showers. Winds shift more towards the west-northwest
in the wake of the front for tonight.

DTW THRESHOLD PROBABILITIES...

* Low for ceiling at or below 5000 ft Monday afternoon through
  Monday night.

PREV DISCUSSION...
Issued at 338 AM EDT Mon Apr 19 2021

DISCUSSION...

Warm air advection will persist within west-southwest flow this
morning. A bit of elevated instability may even brief a brief
sprinkle/shower early this morning as nose of WSW 35 knots low level
jet works through southern Lower Michigan. Temperatures at the
surface will quickly respond as boundary layer mixing ensues after
sunrise. Expect temperatures to climb to near 60 by midday over the
southern half to two-thirds of the forecast area, say I-69 south
roughly.

By midday, a strong cold front will begin pushing south through the
area with temperatures never making it out of the 50s north and
falling back into the 50s in the mid afternoon further south.
Scattered light showers will accompany this front today and persist
into tonight over southern portions of the area as the front stalls
over the northern Ohio Valley. Temperatures will be much colder
tonight to the north of the front with lows ranging in the lower 30s
for the most part with some upper 20s possible over the Saginaw
Valley. The colder temperatures will hold into Tuesday as highs
struggle back towards 40 degree in most areas as rain/snow showers
increase across the area with the approach of a strong shortwave.

Overall model trends continue to shift the bulk of the strongest
lift/forcing associated with FGEN induced by this shortwave south
into far southern portions of the forecast area on into parts of the
Ohio Valley. It is within this general area that periods of heavy
snow will be most likely Tuesday evening/night. Modest lift will
extend further north through the area as coupled jet structure leads
to broad scale upper lift over the region. FGEN with also be forced
northward up the frontal surface to some degree as the shortwave
encroaches/reaches the area Tuesday night.

Air temperatures will become plenty cold enough for accumulating snow
as cold air will be pulled further south into the area and
temperatures fall into the mid/upper 20s north to the upper
20s/around 30 metro Detroit south. Ground temperatures (generally
in 45-50F range), on the other hand, will be more problematic for
accumulating snow, especially if much of the higher snowfall rates
remain south of the area. Generally expect to see a 2-4 inch swath
of snow I-69 south (especially on grassy areas) with locally higher
amounts possible, particularly over the higher elevations of the
Irish Hills from the M-59 corridor south. This snow will occur from
late Tuesday afternoon into the overnight hours before pulling east
early Wednesday morning.

A freeze warning will also likely be needed for much of the area
Tuesday night as the early warmup so far this spring has the green
up ahead of schedule by several weeks. Another cold night is also
expect in the make of this system on Wednesday night with another
period of hard freeze conditions expected as temperatures fall below
32F much of the night and bottom out in the middle 20s most areas.

Temperatures will then moderate for the remainder of the forecast as
highs return to the lower 50s on Thursday after another chilly day
on Wednesday. From late this week on through the weekend, upper 50s
to lower 60s will be common (which is rather average for late April).

MARINE...

Southwest flow to start the morning will back to the west following
the passage of a cold frontal boundary, which will sweep across the
Great Lakes from northwest to southeast through the better part of
the day. Cold air advection behind the front will increase mixing
depths and will tap into an energetic field field aloft, which will
increase wind speeds and elevate wave heights late Monday into
Tuesday. The highest wind speeds are expected across northern Lake Huron
given the westerly fetch and better proximity to a passing low
pressure system. Gusts to gales can be expected from this evening
into the overnight hours and a Gale Warning has been issued for the
northern portions of Lake Huron. Otherwise, locations south of
this will also see an uptick in wind trends following the passage of
the front. However, with gusts are expected to remain below headline
thresholds.

The passage of the cold front will bring about the chance of rain
showers through the day across the Great Lakes region, with the
likely chance for snow then entering late Tuesday into early
Wednesday due to an approaching low pressure system. Southern Lake
Huron and locations south will have the best chance to see
persistent snow during the overnight hours.

HYDROLOGY...

Low pressure lifting northeastward along a cold front will drive
heavy wet snow into portions of Southeast Michigan from Tuesday
afternoon into late Tuesday night. There has been an overall
southward trend in the axis of higher QPF. The latest model
consensus generally carries a quarter to half an inch of moisture
from the M-59 corridor south to the Michigan and Ohio state line.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning from 8 PM this evening to 6 AM EDT Tuesday for LHZ361-
     362.

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

$$

UPDATE.......SC
AVIATION.....AA
DISCUSSION...DG
MARINE.......DG
HYDROLOGY....DG


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