Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 210747

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
347 AM EDT Wed Jun 21 2017


Quiet weather day across the state today as surface high pressure
slides through lower MI with low amplitude ridging aloft increasing
heights slightly. More active pattern starts late tonight, lasting
through the end of the work week.

As of 07Z there remained a band of mid clouds south of I94, but
satellite shows this scouring out which should lead to clear skies
by morning. Most locations will see an increase in temperature over
Tuesday with highs reaching into the mid/upper 70s. Low level
thermal trough lingering over the Great Lakes will keep 850mb temps
in the single digits, preventing much additional heating, but will
finally slide off to the east this evening.

Late tonight is when more active stretch of weather begins. A
shortwave tracking through nearly zonal flow across the northern
Plains will excite a surface low over the central plains today which
will lift through mid MI tonight. A strong low level jet, speeds
possibly reaching 50 knots at 850mb, will surge up through western
MI into northern MI around 06-12Z tonight into Thursday morning.
Models continue to advertise convection developing on the attendant
warm front at the nose of the jet over western MI, spreading
eastward along the front while lifting north through lower MI.
Likely pops look good for the mid MI area closer to the nose of the
jet, but questions remain as to how far east and south the
precipitation will spread along the front. Fgen will be
strengthening over mid MI adding confidence there but there is a
notable theta e minimum surging across southern lower MI which may
help lessen precip chances there. SPC currently highlights a
Marginal Risk area across lower MI with Slight Risk nosing into SE

The system will track off to the NE through the morning hours
leaving a cold frontal boundary draped from northern MI back into
the central Plains. Southwesterly warm air advection in the warm
sector will put a cap in place over SE MI through the day Thursday
possible. MLCAPE and shear (1000 J/kg and 30ish knots respectively)
will both be decent enough for organized storms, but the cap may
prevent this from coming to fruition. Best chance will come late in
the day with peak heating maxing out. Something to keep an eye on.

Better chance for showers and thunderstorms will come around Friday
morning as the positively tilted cold front gets pulled through SE
MI as the pattern becomes more progressive. The next jet max will
dive further south across the Midwest which will force the front
eastward. This dynamic system will feature a strong shortwave and
vorticity lobe rotating around the parent low over Ontario. Best jet
level forcing is further north but the right entrance region will be
inching closer to lower MI. The biggest threat with this setup will
be heavy rainfall as the east-west oriented front will be slow to
move at first while it lays across mid MI. With PWATS over 1.5
inches, and nearing 2 inches in some models, some locations could
end up with a couple inches of rain by the time it moves off. Model
soundings are quite messy, many of which keep the cap in place with
only elevated convection developing. The frontal passage in the
early morning hours Friday will also work against stronger storms
from developing. Temperatures will soar back into the upper 80s
across southern lower MI Thursday as strong southwesterly flow
brings a very warm airmass in ahead of the front. Models have 850mb
temps rising back into the mid to upper teens.

Could see some lingering showers and storms Friday as the front
works east out of the area. Cooler air will filter back in the
region as longwave trough sets back up over the Great Lakes. Look
for highs only in the 70s Saturday through the end of the forecast.
Could see a few rounds of showers through the weekend as well as
troughs rotate around the parent low to the north.



Light westerly flow will persist in the wake of passing cold front
with high pressure bringing relatively calm conditions to the area

Additional showers and thunderstorms can be expected late tonight
into Thursday as a warm front lifts into the area. This front will
also bring in southerly flow to much of the area. However, it will
stall and then sink back south Thursday night into Friday morning as
low pressure tracks along it. This will maintain a good chance of
showers and thunderstorms. Modest southwest flow will persist to the
south of this front with winds veering to the north northwest over
Lake Huron to its north.



Showers and thunderstorms will be possible late Wednesday night into
Thursday as a warm front lifts north into lower Michigan. The main
focus for this activity appears to set up along and north of I-69 at
this time. With precipitable water levels climbing to around 1.50",
heavy rainfall will be possible, especially in area where frontal
forcing is maximized.

This warm front stalls over lower Michigan late in the day with a
low pressure then tracking east into the area Thursday night. As the
front slowly sinks south with the passage of this low, showers and
thunderstorm chances will increase significantly southward through
the remainder of the forecast area. Precipitable water levels will
remain high, 1.50"-1.75", so the potential for relatively widespread
heavy rainfall will persist until the front drops south of Southeast
Lower Michigan Friday morning.

All told, some bands of 1 to 2 inches of rainfall can be expected
with the best chance of 2 inch amounts along and north of I-69.


Issued at 1148 PM EDT Tue Jun 20 2017


High pressure will provide VFR conditions through the TAF period.
Lake breezes moving inland will provide a wind shift and increase in
speed Wednesday afternoon for Detroit-area terminals, but otherwise
winds will be light. Scattered diurnal cu field is also expected.

For DTW...Lake breeze will likely cause a wind shift to the
southeast somewhere in the 19-21Z window Wednesday afternoon.


* None


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



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