Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 192006
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
406 PM EDT Wed Jul 19 2017

.DISCUSSION...

The update discussion regarding the late afternoon/early evening
shower and thunderstorm potential remains valid.

The governing feature for the region`s weather throughout the next
36 hours remains the deep column high pressure that will work from
western Lake Superior this afternoon through Ontario on Thursday.
Difficulty with this particular high pressure is that while it is
noteworthy and impressive in the midlevels it is not particularly
strong at the surface. As a result, will not have any signfiicant
cooling or drying at the surface, but models remains steadfast in a
significant amount of midlevel drying this evenign and overnight.
For tonight, expecting quiet but muggy weather with lows remaining
in the upper 60s to near 70 degrees outside of the Thumb.

Early Thursday morning - midday Thursday.

Quite a bit of uncertainty exists with how late tonight will play
out as various solutions continue to oscillate between a singular
northern MN/northern Wisconsin/Northern Lower Michigan MCS solution
and a dual solution with the northern MCS along with second area of
convection/MCS that will work southeastard through portions of
southern MN/southwestern WI/and eastern Iowa. The problem is that
some sof those solutions that have the southern activity suggest it
will become dominant and short circuit the north. Regardless,
feeling is this southern activity is irrelevant to to the forecast
for southeastern Michigan and instead attention will remain on
development that will initiate in vicinity of far northwestern
Wisconsin as late as 03Z. Forcing tucked immediately behind the
midlevel anticyclone will actually be well organized over the
northern Great Lakes tonight. Synoptic scale forcing will come in
the form of right entrance region dynamics on an anticylonnicaly
curved jetlet in addtion to more than adequate forcing alogn the
nose of the nocturnal low level jet.

Expectations are for a mature MCS to cross northern Lake Michigan
tonight with the southern edge sliding through the cwa in the 11-15Z
timeframe. Certianly questionable about how far south shower and
thunderstorm activity will make it here locally. Latest iterations
suggest a greater potential for the southern cwa. Regardless, this
potential will end fairly early in the day setting the region up in
the midlevel heating wake of the MCS. Models suggest as much as 1500
J/KG of SBCAPE will be avaible. The atmosphere is expected to be
signfiicantly capped with a subsidence inversion as deep as 2-10 kft
agl. Difficult to get specific on Day 2 severe threat wihtout
knowing how today will unfold. 0-6km bulk shear will climb with
increasing kinematics, with 40 -50 knots of bulk shear. Will
continue to monitor for the severe threat.

Did raise highs solidly into the upper 80s for the southern half of
the cwa. Well mixed condidtions are forecasted at the surface with
southwest winds to 30 mph possible.

Very quiet and outstanding mid summer weather on Friday as a
sprawling but quick moving high pressure passes through lower
Michigan. Increasing high cloud during the afternoon but
temepratures in the middle 80s.

Ahead of a weak low pressure system, southern Michigan will remain
under a warm, unstable airmass, which will act to bring rain and
thunderstorms to the region throughout Saturday. Additional rain and
thunderstorm chances will be possible heading into Sunday morning as
low pressure from the Central Plains slides east into Michigan. As
the low travels east across the state, a cold front will drag behind
it, bringing a final chance for pop-up showers and thunderstorms
throughout Monday, before drying out for an extended period. Behind
the front, temperatures will drop from the low to mid 80s
(Saturday/Sunday) into the mid to upper-70s (Monday/Tuesday) for
daytime highs. Likewise, dewpoints are expected to fall from the
upper 60s to lower 70s (Saturday/Sunday) into the upper 50s to lower
60s (Monday/Tuesday), thus major relief from warm and muggy
conditions will be seen behind the front. Lastly, a stable, dry air
mass and amplified ridge will reside across the Great Lakes both
Tuesday and Wednesday, bringing dry conditions and plenty of
sunshine to the region during the mid-week period.

&&

.MARINE...

A weak front draped across the southern Great Lakes through the end
of the week will bring periodic thunderstorms capable of producing
locally higher wind and waves. Winds along and behind the front
tonight will be weak with little impact on waves as the front
settles near western Lake Erie. The front is then expected to waver
between Lake Erie and southern Lake Huron Thursday through Friday
while weak high pressure develops over the northern Great Lakes. The
front will remain a focal point for thunderstorms through Saturday.

&&

.PREV DISCUSSION...
Issued at 116 PM EDT Wed Jul 19 2017

AVIATION...

A weak frontal boundary near the PTK corridor will slowly approach
the DTW corridor during the mid afternoon time period. Scattered to
broken cu development is expected to continue ahead of the frontal
boundary which will act as a focal point for isolated thunderstorm
development during the 18-22Z timeframe. Due to the isolated
coverage of thunderstorms, a VCTS group was added but will require
monitoring through the afternoon for any potential effects at
terminals from PTK southward. The front then looks to become nearly
stationary near the Ohio border before lifting slowly northward late
tonight. Regardless of frontal location, a moist low level air mass
with light winds across the region will keep the potential for MVFR
fog development late tonight through sunrise on Thursday. Upstream
thunderstorm complex development across Minnesota and Wisconsin will
need to be monitored late tonight as some model solutions hint at a
low potential for thunderstorms to push through the northern TAF
sites (MBS, FNT) tomorrow morning. A shift to southwesterly flow is
expected across the region Thursday morning.

For DTW... A frontal boundary expected to push slowly southward
through the DTW corridor will act as a focal point for isolated
thunderstorm development through late afternoon. Hi-res model
guidance has continued to favor 18-22Z as the most likely time window
for storms within D21 airspace. While the expected isolated coverage
makes any storms striking DTW unlikely, radar trends will need to be
monitored through the late afternoon.

//DTW THRESHOLD PROBABILITIES...

* Moderate for ceiling at or below 5000 ft during afternoon

* Low for thunderstorms during afternoon


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

DISCUSSION...CB/AM
MARINE.......CB
AVIATION.....JD


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at www.weather.gov/detroit.



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