Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 030926

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
526 AM EDT Mon Aug 3 2020


Latest satellite trends show the healthy coverage of mid to high
levels clouds, which have kept visibilities at vfr and have
prevented the developing of low-lying stratus, now holds over
central Michigan. Observations have shown a quick degradation in
visibility and and development of ifr/lifr stratus across southwest
lower michigan with the removal of the mid and high based clouds.
These clouds will sweep from west to east through 09-12Z and may
produce this same brief development of mvfr/ifr stratus and
reduction to visibilities, however, this will also coincide with
sunrise which will help to counteract development of possible fog
and stratus. Otherwise, upper-level trough and passing cold front
will increase cloud coverage again this afternoon and will produce
widely scattered to numerous showers and thunderstorms, with
thunderstorm development confined to KFNT south into the Metro
terminals, mainly centered between 18Z-00Z. KMBS will likely remain
stuck under mvfr cigs through the better part of the day with closer
proximity to the aforementioned frontal boundary and trough. Quick
shift in wind direction from the SW to NNE will take place following
the passage of the front tonight, with mvfr cigs filling in behind
the front.

For DTW... Satellite trends show clearing from west to east which
may briefly produce mvfr/ifr cigs and a quick reduction to
visibility early this morning, with improvement in any reductions to
cigs/visibilities expected after sunrise. Otherwise, cold front to
produce rain and thunderstorm chances later this morning and into
the afternoon and evening, with best chance for thunderstorm
development centered between 19Z-00Z.


* Low for ceiling aob 5000 this morning and afternoon.

* Moderate for thunderstorms this afternoon.


Issued at 339 AM EDT Mon Aug 3 2020


Ongoing mid level height falls across the region are occuring ahead
of a broad mid level trough that will slowly advance across Lower Mi
today. A lead short wave impulse now over Central Lake Mi is
forecast to lift across nrn and central Mi this morning. This
feature is forecast to strengthen some low low level frontal forcing
along/north of a weak sfc cold front that is slowly inching
southward across the Saginaw Valley this morning. The result will be
an expanding region of showers with a few embedded thunderstorms
this morning, mainly along/north of the I-69 corridor. The
approaching upper trough will support the evolution of a weak sfc
low along this cold front as it settles into Se Mi today. The
expectation for showers and cloud cover across the north will temper
the diurnal heating and thus keep sfc based instability weak. South
of the I-69 corridor however, there is the potential for some
thinning of the mid/high clouds this afternoon, offering a better
opportunity for daytime heating to support weak/moderate surface
based instability. This will allow scattered to numerous
showers/thunderstorms to develop during the afternoon.

The RAP suggests 0-1KM ML CAPE will rise to 1000 to 1500 j/kg by
mid/late afternoon, with steep low level lapse rates. There will be
an increase in deep layer shear late in the day. So if convective
initiation in the south holds off until late afternoon/evening, a
few strong/severe storms can not be ruled out. Daytime temperatures
will be suppressed to the upper 60s/low 70s across the Tri Cities
given expected earlier coverage of showers and cloud cover, with
daytime heating offering an opportunity for metro Detroit and points
south to break 80.

The ECMWF/Canadian/UKMET solutions are notably stronger with a PV
feature dropping out of Georgian Bay today/tonight, which leads to a
deeper/more amplified upper wave to rotate across Lower Mi Tues/Tues
night in comparison to the NAM/GFS. Representation on satellite
would lend more support to the more amplified solutions. This
feature will drive much cooler air into the region, with 850mb temps
forecast to drop into the single digits by Tues night. The mid level
cold pool still looks to be far enough removed from Se Mi on Tuesday
to limit convective cloud depths, thus hindering thunder. Enough
moisture does however look present to support some light showers,
aided by diurnal heating Tues. The more amplified solutions give
better chances for this. The highest chances for showers will be
across the thumb as the cool airmass under northerly flow will
support some lake enhancement. Mid level subsidence/drying will
overspread the region on Wednesday as the upper wave departs to the
east. Surface high pressure will then take hold across the region and
looks to persist into the weekend, resulting in a dry forecast the
rest of the period. Seasonally cool conditions will prevail Tues and
Wed before airmass modification leads to a gradual warming trend
late week into the weekend.


Main surface low is now well east of the region over southern
Quebec. A broader weak surface trough has now settled over the Great
Lakes with a weak surface low at the base of the trough over
southern Lake Michigan that will work east across southern MI today
and the eastern Lakes tonight. This trough will bring cool air over
the relatively warm waters of the lakes which will result in a
chance of thunderstorms today and tonight along with a chance of
water spouts now through Tuesday morning. In addition, northeasterly
flow will increase once again tonight which may lead to another
round of small craft advisories along the Thumb. A cold front will
then swing down through the area Tuesday evening which will allow
high pressure to then build in for the mid week period.


Showers and scattered thunderstorms will develop across the area
today. Basin average rainfall amounts of two to four tenths of an
inch are expected. Some higher intensity convection may however
result in some locally higher rain totals.


Lake Huron...Small Craft Advisory from 8 PM this evening to 10 PM EDT Tuesday
     for LHZ441>443.

     Small Craft Advisory from noon today to 10 PM EDT this evening for

     Small Craft Advisory from noon today to 10 PM EDT Tuesday for

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



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