Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 191048

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
648 AM EDT Sat May 19 2018


Low pressure tracking through southwest Lower Michigan this morning
will support borderline IFR/MVFR cigs, along with showers, with the
highest concentration north of M-59. Warm and moist unstable air
will move in along/south of M-59 during peak heating, supporting
scattered thunderstorms during the late afternoon hours.  A trailing
cold front will help focus storms and usher in a renewed period of
MVFR ceiling Saturday evening, despite winds shifting the the
west/northwest by early evening. Light winds shifting to the
North-northeast by Sunday morning, which looks to support the
development of low MVFR cigs.

For DTW...Borderline IFR/MVFR cigs will lift into low VFR by early
this afternoon, with scattered thunderstorms likely developing late
this afternoon. Wind shift to the west toward 00z behind a cold
front, but clearing looks doubtful as low level moisture persists.


* High for ceiling 5000 ft or less into tonight, medium confidence
  Sunday morning

* Moderate for late afternoon thunderstorm coverage/timing Saturday.


Issued at 303 AM EDT Sat May 19 2018


A mid level trough now extending across Illinois will lift across
IL/OH/Lower MI today. There has been persistent deep layer moisture
advection into Lower Mi overnight proceeding this trough. Through
much of the night, the better isentropic ascent has focused the
greatest coverage of showers west of the forecast area. Low to mid
level flow has been veering toward the south, which will support a
little better isentropic ascent and mid level theta e push during
the early morning hours across Se Mi. This will lead to better
coverage of showers across the area, supported by recent hi res
solutions. The ascent is expected to transition from south to north
across the area which will cause more widespread showers to remain a
little more persistent across the Saginaw Valley/thumb region
through late morning. In fact, some degree of mid level deformation
may sustain a little higher intensity rainfall at times across
portions of the tri cities (latest HRRR suggests mainly Midland/nrn
Bay Counties).

Surface low pressure will accompany the mid level wave across Se Mi
this afternoon. There has been reasonable model agreement in
depicting a fairly tight instability gradient across the forecast
area as this sfc low and associated frontal boundary pass through
the area. Based on the forecast timing of the sfc cold front,
locations generally south and east of a Sandusky to Howell line
(within the prefrontal warm sector) will see the better daytime
instability. Expecting daytime highs in the low-mid 70s with sfc
dewpoints in the low 60s will support 0-1km MLCAPE just under 1k
j/kg. The overall weak instability and marginal wind shear will
hamper severe weather potential. Decent moisture (pwats up to 1.7
inches) and the overall slow movement of the upper trough and
associated sfc front may lend itself to locally intense rainfall.

Cooler air will filter into the remainder of the forecast area this
evening as the surface front slides to the east. Increasingly
confluent mid level flow across the northern lakes will allow sfc
high pressure to expand into nrn and cntl Lower Mi from the west on
Sunday. Model soundings suggest the resulting north-northeast low
level winds will advect a shallow cool airmass into Se Mi, while
remnant moisture gets trapped under the resulting inversion. This
will support overall cloudy and cool conditions (temps will likely
be stuck in the 50s along Lake Huron).

Sfc high is forecast to linger across the northern Great Lakes
Monday into Tuesday, while a stationary front extends across the
Ohio Valley. Numerous mid level short wave features are forecast to
track across the srn Great Lakes/Ohio Valley within the fast mid
level flow overhead. Better moisture/instability should remain south
of the state. Any stronger wave may however be able to draw some of
this instability a bit farther north into the southern portions of
the area, warranting chance pops. The medium range model suite
indicate mid level trough amplification across ern Canada driving the
sfc high across southern Mi by mid week, supporting dry conditions.


Much lighter winds around today as low pressure tracks through the
Central Great Lakes, with winds under 20 knots. Showers and
thunderstorms will be around however, with stronger winds possible
in and around any thunderstorm.  Light and variable winds are
expected for the second half of the weekend as weak high pressure
leads to dry conditions for the daytime hours of Sunday. Showers and
thunderstorms will then return to the forecast early next week, but
continued light winds.


Showers will persist today as low pressure and an associated warm
front lift slowly north into the southern Great Lakes. As this low
pressure crosses the area this afternoon and evening, scattered
thunderstorms may bring locally heavy rainfall. So, while average
rainfall amounts are expected to range from a quarter to half an
inch, locally higher amounts will be possible from thunderstorms.
Even with this rainfall, flooding is not expected at this time with
the exception of continued flooding along the Huron River in the
vicinity of Hamburg.

The next chance of rain showers arrives by Sunday night, although
amounts of a quarter of an inch or higher will likely be confined
toward the Ohio Border.


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



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