Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 201614

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1214 PM EDT WED JUL 20 2016


Light south wind today will back slightly during the evening as lake
breeze encompasses the area. Wind remains solidly below 10 kts
all the while. VFR through the period.

For dtw...FEW or possibly SCT clouds around 5kft before moisture
mixes up/out. Generally dry column and increasing boundary layer
dewpoint depressions suggest virtually nil potential for actual
ceiling at 4-5kft.

//DTW Threshold Probabilities...

* None


Issued at 256 AM EDT Wed Jul 20 2016


Big ridge over KS and OK will continue to dominate the weather over
the next couple of days as heights slowly build and peak for
Thursday and Friday. Dry and stable air in place for today will lead
to mostly sunny skies.  Only possible issue is some cirrus debris
clouds from small northern MN MCS, but that should weaken before the
clouds would get too thick. Away from the marine influenced air on
Tuesday, temps soared well above guidance. Given the flow turns to a
southerly component today, thinking that even more locations will
see temps climb today. Aiding that climb is relatively dry air with
surface dew points in the 50s to around 60, and 925 mb temps warming
a solid 2 to 4 C and 850 temps warming around 2 C. All of that leads
to forecast temps above MOS guidance and closing in around 90 for
Detroit, Flint and Saginaw.

All models hold on to the stable air over southern Lower Michigan
through tonight and most of Thursday, even with some increase in
surface dew points and 850 mb theta-e. A large part of this
stability comes from the warming of the entire column into Thursday
creating a decent cap. With more warming of the low level profile,
expect temps to take another step upward into the low to mid 90s
about a degree or two above MOS guidance. Surface dew points
increase to the upper 60s which raise our heat indices to near 100
and will likely bring about the first heat advisory of the season.

Late Thursday afternoon and Thursday night all of the models
strongly agree on the evolution of severe weather threat. A fairly
potent shortwave that was just over coastal northern CA and southern
OR will crest the ridge and move over lower Michigan. There will
likely be a well developed MCS from this evening`s convective
initiation over the high plains of ND and southern Canada. 850 mb to
300 mb thickness analysis would suggest this MCS and/or any new
development would make a right turn over Ontario/eastern Lake
Superior/eastern U.P. Thursday afternoon and move due south over
Lower MI Thursday night. By late Thursday ML CAPEs will likely be
around 2000 j/kg as the right rear entrance of an upper jet moves
over Lower MI. Wind fields increase as 850 mb winds try to get to
35 to 40 kts and 500 mb winds on the back side of any MCS may get as
high as 40 to 50 kts. Really like the SPC Day 2 outlook for
basically all of Lower MI.

Then on Friday we will be in the wake of that Thursday night MCS.
The warming aloft, shortwave ridging and subsidence may leave the
forecast area dry. Will leave the current pops around 20 to 30
percent to account for a lingering outflow boundary near the south
half of the forecast area with ML CAPE likely around 2000 J/kg.
Friday should see enough sun in the afternoon to allow temps to
climb again toward the mid 90s especially since we will be starting
from the mid 70s in the morning. The difference will be dew points
in the lower 70s creating heat indices from 100 to 105.

The more stable air remains for Saturday and will keep the forecast
dry. Hot conditions will remain with temps likely breaking 90 again,
albeit with lower dew points. Sunday is a little more of a question
for the heat. Dew points raise back into the lower 70s, but the
approach of the main shortwave and cold front may bring early
convection. Current guidance suggest around 90 again and will not
sway from that. This all may lead to heat advisories extending into
the weekend, especially considering the cumulative effects of the
heat over a 4 or 5 day span.  When that wave moves through Sunday
may have another round of strong storms, but that will also allow
the system to clear Lower MI for a dry and cooler Monday and Tuesday.


Surface high pressure will keep its grip on the central Great Lakes
today through much of Thursday as it retreats to the Mid Atlantic
region. Winds will remain light southeasterly or southerly today and
tonight before veering modest southwesterly Thursday afternoon.
Expect quiet marine weather during this time. The next chance for
thunderstorms will be Thursday night as a thunderstorm complex may
develop and track from the north to south directly across lower
Michigan. Shower and thunderstorm chances will decrease again Friday
and throughout much of Saturday before increasing again Sunday as
the main cold front approaches the region. The wind and wave
forecasts across the central Great Lakes region looks to be
relatively benign this weekend.


The potential is increasing for the development of a thunderstorm
complex over portions of the northern Great Lakes Thursday
afternoon. Conditions will then be favorable for a due southward
track of this mesoscale convective system into all or portions of
southeastern Michigan Thursday night. The potential exists for a
basin wide average of .50 inches or greater of rainfall Thursday
night through Friday morning conditional to the development of this
thunderstorm complex.


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



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