Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 281920
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
320 PM EDT Fri Apr 28 2017

.DISCUSSION...

12Z DTX sounding revealed an 850 mb dew pt depression of 31 C, with
PW value of 0.42 inches. None-the-less, looks like there will be
just enough isentropic ascent (295 K) and moisture advection
working through southeast Michigan (mainly south of M-59) this
evening/overnight to support some light showers based on latest
satellite/radar trends and hi-res solutions of HRRR and Rap13.
Negative LI`s stay south of the border, and left thunder mention
out. Surface cold front sinking south and exiting jet forcing up
north will also support chance/scatter pops there.

Latest water vapor imagery shows highly amplified upper level
pattern over North America, with longwave trough over the Rockies
and excellent upper level jet energy tracking into Four Corners
region.

A convergence of Pacific Moisture/Pineapple connection, coupled with
the Gulf of Mexico/Caribbean moisture as large Bermuda High will
remain in place through the weekend, drawing flooding concerns by
Monday as large and powerful 500 MB low develops over the Central
Conus over the weekend. The system will be lifting northeast into
the Midwest (Iowa) by Monday Morning.

Moisture parameters will be record/near record for end of
April/start of May this far north, as 700 mb dew pts approach 5 C
toward Monday morning, nearing tropical status, with 850 mb dew pts
equally impressive checking in between 13-15 C. With sufficient
destabilization/convective elements, showalter index going slightly
negative and deep warm cloud layer, several inches of rainfall is
certainly possible for the second half of the Weekend into Monday,
which will create flood concerns. Unfortunately, placement of heavy
rain axis remains difficult, but good low level FGEN/isentropic
ascent will be established by Sunday, as strong high (1032-1034 MB)
remains parked over/near James Bay. Do think the surface warm front
will not clear much past the southern Michigan border during the day
on Sunday (Lake Erie influence), which should help showers persist
even in southern areas, but max mid level forcing does appear to be
lining up across northern sections of the CWA into northern lower
Michigan Sunday Night.

As of right now, it appears the robust max 6HR height fall center
will already be over Central Great Lakes Monday afternoon, thus
strong cold frontal/occlusion passage with good upper level support
will occur early in the day. Moisture/instability axis passing east
by around NOON, helping to mitigate any severe threat. Still not out
of the woods Sunday night with 65 knot jet at 850 MB, but meager
lapse rates within the moist airmass should be hindrance. Bottom-
line, Heavy rain remains the biggest concern, and flood watch will
likely be needed for the second half of the weekend.

Lingering precipitation and gusty conditions will be possible Monday
evening into Tuesday afternoon as low pressure travels northeast
from Wisconsin into the Upper Peninsula. Cooler air that is expected
to wrap around the low and push into Michigan throughout Monday
afternoon will help to increase stability, minimizing the chance for
thunderstorms, as conditions remain breezy. The low pressure system
will continue to push northeast through Quebec late Tuesday into
Wednesday, as a surface high edges eastward across the Great Lakes
region. This will act to keep us dry and will keep winds light
through the middle of the week, as temperatures remain moderate with
daytime highs capped in the mid-50s.

The next chance for rain will return Thursday into Friday as a warm
front slowly pushes north into the MI/OH border. The GEM model run
suggests that the warm front will protrude into Michigan, allowing
rain showers to fall over our southern counties that border Ohio,
however, several other long-range models hold the rain south of
Michigan through the end of the week.

&&

.MARINE...

Gusty southwesterly winds over the morning will slowly continue to
diminish this afternoon.  Relatively light winds are then expected
by early tonight before strong high pressure builds into Ontario and
low pressure begins to organize over the plains.  This will bring an
increase in north/northeast winds to the marine areas and
potentially allowing waves to build high enough to warrant a Small
Craft Advisory for nearshore waters of Lake Huron and Saginaw Bay.
Monday will then see wave heights decreasing as southerly winds take
over ahead of a cold front.  However, winds will once again gust up
to 30 knots.  As the low approaches the Great Lakes region this
weekend, an increasingly unsettled, wet pattern will set up.
Thunderstorms will also be possible Sunday into Monday.

&&

.PREV DISCUSSION...
Issued at 120 PM EDT Fri Apr 28 2017

AVIATION...

Denser coverage of mid and high level clouds will continue to work
up towards the north over the area this afternoon.  VFR conditions
will continue into the early evening before lower clouds and rain
showers move in.  Gusty winds over MBS and FNT will slowly subside
going into the late afternoon with weaker winds going through the
overnight hours.  A frontal boundary over the Ohio Valley will allow
for some rain showers to work up into the area tonight.  Still
expecting the most likely timing of showers to be around 01Z to 03Z
Saturday. Showers should exit the area by early Saturday morning as
winds veer to the north/northeast and MVFR clouds enter in.

//DTW THRESHOLD PROBABILITIES...

* High confidence for ceilings above 5000 ft through the late
  afternoon.

* High confidence for ceilings 5000 ft or less overnight.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from 3 AM Saturday to 6 AM EDT Monday for
     LHZ421-422.

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

$$

DISCUSSION...SF/AM
MARINE.......SS
AVIATION.....SS


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