Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 241913

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
313 PM EDT Sat Jun 24 2017


Lead upper wave/cold pool tracking through this afternoon, going
generally as planned with highest coverage north of I-69, as dew pts
have mixed down into the 50 to 55 degree range. Unfortunately,
continued regeneration of thunderstorms in and around Tri-cities
region/Midland county leading to some additional flood concerns.
Majority of activity should be done by 00z, exception being northern
Thumb region where some activity may persist into the evening.

Parent cold pool (-25 C at 500 MB/-6 C at 700 MB)/circulation
exiting Minneapolis area this afternoon will already be arriving
over southeast Michigan just past sunrise Sunday, and thus will have
limited surface based/low level instability (capes aob 500 J/kg) to
work with, which is good news, as 50-60 knot 0-6 KM bulk shear/jet
core tracks through. 850-700 MB Theta-E ridge/and corresponding
steep lapse rates tracking through 9-12Z, with drying and subsidence
occuring after 12z. Airmass looks cold enough for lake induced
instability to come into play, especially over Saginaw Bay where
water temps are approaching 70 degrees.

Upper level shortwave ridging building in and gradual warming 500 MB
temps Sunday afternoon. None-the-less, still some modest diurnal
instability, SBcapes of 500-1000 J/kg, worthy of scattered
showers/isolated thunderstorms (numerous pops over Thumb region once
again) despite the overall negative/subsident environment with just
subtle surface troughing indicated, as well mixed boundary layer in
the afternoon should support gusts up around 25 knots. Guidance temps
in line with inherited forecast, and no changes made to highs,
around 70/lower 70s.

Yet another upper wave and associated cold pool (-23 to -24 C
at 500 MB) to work through the Central Great Lakes on Monday, with
large scale troughing encompassing the entire Great Lakes region,
and indications of Lake aggregate Low/troughing developing with
the cold airmass over the Great Lakes, as 850 MB temps drop into
the low single numbers, which may be just enough to hold maxes in
the upper 60s, especially if scattered-numerous showers blossom as
expected with the cold front.

A broad surface high pressure in association with an upper-level
ridge will move east across the Great Lakes both Tuesday and
Wednesday, which will act to keep conditions dry while bringing a
fair amount of sunshine to the region. The next activity for rain,
thunderstorms, and potentially localized flooding will return
Thursday, with precipitation chances continuing into the weekend.

To start, surface low pressure will head east from North Dakota into
the U.P Wednesday into Thursday, which will act to push a warm front
through southern Michigan throughout Thursday. Lift from the front
in additional to an impressive amount of moisture advected into the
region (PW averaging 1.7 in) will bring the first chance to see rain
showers and thunderstorms. Confidence is moderate regarding rain and
thunder chances on Thursday as several long-range models are in
agreement with the location of the low pressure system. Rain and
thunderstorm chances will continue into the weekend, however,
confidence is lowered regarding PoP and location as model solutions
start to diverge. The ECMWF run pushes a weak low from Iowa into
Michigan through Friday which would act to bring rain and thunder,
which is absent from the GFS and GEM runs. The GFS and GEM does
however develop and push a weak surface low through Michigan
throughout Saturday, however, location and timing differ between
runs. In any case, with a warm and humid air mass expected to be in
place late next week, the chance for rain and thunder will be there.



Moderate westerly flow will continue through Sunday. Gusts will
continue to approach 25kts this afternoon and evening. Gusts will
emerge somewhat stronger on Sunday behind a cold front - especially
across the Lake Erie basin. The offshore nature to the flow will
help keep wave heights manageable in most locations. The exception
will likely be Lake Erie, where the gusts will be the highest.
Therefore, a small craft advisory will be posted for the balance of
the day on Sunday.



Showers and thunderstorms are producing localized heavy rainfall
across portions of flood impacted Midland County. Some locations
have received up to an inch of additional rain. The coverage of the
most intense rainfall has remained limited. However, given the
oversaturated soils across the area from this past week`s extreme
rainfall, any additional rain will immediately result in quick
expansion of already partially flooded areas.

As for the area rivers, the Tittabawassee River water levels are
nearing the crest at Midland. Today`s rainfall will take some time
to affect the flooded river system. The main impact will be to slow
the recession of the water. The flood wave is expected to work
through the Saginaw River channel through Monday.


Issued at 117 PM EDT Sat Jun 24 2017


Rapid build up of shower and embedded thunder underway across
central Lower Michigan. The greatest coverage will be across the far
north - which is also where the better chances for thunder will
reside. The wave of forcing will swing through this afternoon and
coverage should quickly wane before sunset. West/southwest winds
will remain rather gusty - especially near showers.  Some isolated
shower activity is also possible tonight with an additional robust
mid-level wave - coverage too limited to assign in the forecast
right now.

For DTW...cumulus field is becoming agitated west of Ann Arbor.
Expect a few showers to break out of this cloud mass for the first
couple hours of the forecast period. Not anticipating enough depth
to support thunder, at this time. Otherwise, gusty westerly winds
will continue through the daylight hours and resume once again on
Sunday with diurnal heating.


* Medium confidence in ceilings around 5kft this afternoon.

* Low confidence in thunderstorms at DTW this afternoon and evening.


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



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