Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 201955
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
355 PM EDT Sat Apr 20 2019

.DISCUSSION...

A band of light to moderate rain ongoing during mid to late
afternoon is being driven by a mature trowal/deformation pattern
over SE Michigan. This component of forcing is shown in model data
as a sharp ridge of theta-e in the 850-700 mb layer tied to the
northwest flank of the upper level low moving slowly across the
upper Ohio valley. The strong dynamic forcing within the deformation
pattern is then also enhanced by elevated instability generated by
mid level theta-e advection through the trowal axis. Periods of
moderate rain supported by the pattern resulted in 6 hr rainfall
around 0.75 inch from the northern suburbs of Detroit to the Ohio
border during early afternoon which is expected to continue into
early evening as the band migrates northwestward. The slow but
steady northeast track of the upper low toward the central
Appalachians then slows the westward progression of the rain band
over SE Michigan as it brushes the Saginaw valley. Expect intensity
and areal coverage of the band to also diminish during the evening
with rain ending around midnight as the trowal shears into Ontario
and Quebec following the movement of the low and upper jet.

The short wave ridge supporting surface high pressure over the
Plains and Midwest today breaks across the Great Lakes tonight. The
approach and passage of the surface ridge axis displaces the low
level thermal trough and pushes any remaining low clouds out of SE
Michigan during Sunday morning. Sunshine filtered through a mix of
mid and high clouds combines with the rebounding low level thermal
profile for a notable warming trend through the afternoon. Guidance
temperatures in the mid to upper 60s look solid and leave the door
open for a few interior locations touching 70 Sunday afternoon. High
pressure moving eastward promotes light onshore wind that keeps
readings in check along the Thumb coastline.

The warming trend accelerates Monday as deeper southwest flow
develops over Lower Michigan ahead of new low pressure over the
Plains and Midwest. Model soundings show boundary layer mixing depth
similar to Sunday while the southwest flow warms produces a warmer
overall thermal profile below 700 mb. These developments, along with
less coverage of mid/high clouds and better surface heating, result
in highs making a run well into the 70s Monday afternoon. Mild
conditions hold as southwest flow continues and clouds thicken
Monday night. The bulk of shower activity remains to our north as
the surface low ripples along the front stalled across the central
Great Lakes. A better chance for showers and possibly a thunderstorm
accompanies the cold front as it moves through the region Tuesday.
Today`s model cycle offers a faster solution on the passage of this
system so that it is mostly through SE Michigan by midnight Tuesday
night.

Conditions look to dry out by the middle of the week and into the
start of next weekend. The only slight chance for precipitation may
come overnight on Thursday as current models are showing a weak wave
move across. Besides that, temperatures are expected to stay in the
60s for highs going through the end of the week.

&&

.MARINE...

Northerly winds will be on the decrease, but onshore flow through
this evening with gusts still elevated across Saginaw Bay will
continue to keep elevated waves across the nearshore zones of the
Thumb and Saginaw Bay. Therefore, small craft conditions will remain
in effect from Inner Saginaw Bay to Port Huron. As rain comes to an
end tonight and low pressure system exits the region, a weak high
pressure will begin building into the region. Winds will turn from
northerly to southerly by tomorrow afternoon with favorable marine
conditions. Light winds and low waves will continue into early
Monday before an approaching low pressure system brings rainfall and
slightly elevated southeasterly flow. Winds remain below 20 knots
and waves low. High pressure following the aforementioned low will
bring a return to quiet marine conditions for mid-week.

&&

.PREV DISCUSSION...
Issued at 203 PM EDT Sat Apr 20 2019

AVIATION...

Predominately MVFR with periodic IFR conditions will prevail through
this afternoon into the evening with steady rainfall lifting through
southeast Michigan. The exception being MBS where a sharp gradient
in cloud cover exists along with precipitation that will likely hold
to the southeast. IFR conditions will largely come from reduced
VSBYs under moderate to heavy rainfall that impacts terminals.
Rainfall along the deformation axis will gradually weaken throughout
the evening with only lighter rain showers remaining as the low
pressure system weakens and moves further northeast into tonight.
Winds will be out of the north through this evening around 10-15
knots with occasional gusts to around 20 knots. Winds gradual
weaken and turn to the NW tonight. Once precipitation comes to an
end tonight, light fog will have potential to develop during the
early morning hours across the Detroit Metro area.

DTW THRESHOLD PROBABILITIES...

* High for cigs aob 5kft through tonight.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...Lakeshore Flood Advisory until 10 PM EDT this evening for MIZ048-
     049-054.

Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422-
     441>443.

Lake St Clair...NONE.

Michigan waters of Lake Erie...NONE.

&&

$$

DISCUSSION...BT/SP
MARINE.......AA
AVIATION.....AA


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



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