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fxus63 kdtx 171051 
afddtx

Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
651 am EDT Wed Jul 17 2019



Aviation...

Remnant low level moisture associated with the sfc low over se mi
has led to the development of fog and low stratus. Ceilings and
visibilities have been highly variable across the region this
morning. That trend will continue with the onset of daytime heating.
Overall expect the daytime boundary layer growth will support a
predominate MVFR ceiling this morning, likely trending VFR during the
course of the afternoon. Slightly drier air will be advecting into
the region from the north in the wake of the departing sfc low this
afternoon. This will support a clearing trend during the late
afternoon/evening hours.

For dtw...the northwestern flank of the departing sfc low will
sustain showers in the vicinity this morning. The better chances for
morning thunderstorm activity will remain southeast of Metro. There
remains enough reports of IFR ceilings in the region to maintain the
mention in the taf through 15z.

Dtw threshold probabilities...

* moderate in ceilings at or below 5000 ft today.

&&

Previous discussion...
issued at 340 am EDT Wed Jul 17 2019

Discussion...

One more forecast cycle with talks of rainfall as a result of the
surface low that is the remnants of ts Barry. Cyclonic flow will
continue to reside over far southeast lower Michigan this morning before a
surface trough dropping from central Michigan early this morning, passes
east of the Detroit Metro around lunch time today. This trough will
push the last of the deeper moisture off to the east with northerly
flow filling in it's wake.

Until then, we still have a corridor of deep moisture on the
northeast flank of the weak surface low lifting which will lift from
central in toward Western Lake Erie this morning. Low level jet
lifting ahead of the low is sparking a new round of convection to
our south which may clip a portion of Southeast Michigan this morning before
pushing east. Current radar returns east of a line generally from
det to adg paints the area of concern where heaviest showers could
fill back in as the low level jet surges northeast. Expectations
based on current radar and model trends are for the bulk of the
heaviest rain to stay south of Detroit but Monroe County may get
clipped by it as it pivots north resulting in a couple hours of
heavy rain and possible flooding concerns. Luckily this area was
spared of the heaviest rains along i94 on Tuesday where 1 to 4
inches fell. Scattered showers and thunderstorms will cover a bid
broader of an area north and west. The trough looks to pass south of
Detroit by about 15z marking the end of the heavy rain chances.
Clouds will thin through the afternoon with dry air advection and
building mid level heights. Temps should have enough time to recover
reaching the mid 80s across the area.

Attention then turns to the subtropical ridge building from the
plains into the Great Lakes. A strong westerly jet racing across
southern Canada Wednesday night and Thursday will start pulling much
warmer air eastward into the region. Thursday appears to be the
transition day from the current warm airmass to the much hotter
airmass as the warm front on the lead edge of the eml lifts through
Michigan. 850mb temps already nearing 20c Thursday afternoon with 500mb
heights around 588dam will boost the temps to near 90. Dewpoints
look to climb from the 60s early in the day to near 70 by evening as
the front progresses northeast. Big question mark will be potential
mesoscale convective system developing over the Midwest Wednesday night on the lead edge of
the eml which should turn southeast following the instability gradient.
Based on suspected frontal position it would stay well west of here
but cloud debris in the early part of the day could dampen temps a
bit locally. Currently the forecast heat indices reach 95 to 105f
which would necessitate a heat advisory for at least part of the
area.

Friday and Saturday will be the hottest days of the week. Forecast
850mb temps reach near 23c resulting in high temps in the mid to
upper 90s across the area. With dewpoints in the 70s, heat indices
climb to over 100 both afternoons with little relief coming
overnight as min temps stay in the mid 70s Thursday night through
Saturday night. The possible catch for Friday temps will be the next
round of mesoscale convective system activity Thursday night initiating over northern Minnesota/WI
then tracking east-southeast through lower Michigan Friday. The strong westerlies
across northern Michigan and building cap across lower Michigan will hopefully
keep it north of US but a turn to the southeast will bear watching,
even if its just enhanced cloud cover.

Heat looks to break on Sunday as a pair of cold fronts drop through
the Great Lakes. Stronger of the two fronts looks to come later in
the evening so temps will still remain elevated in the mid/upper
80s. Temps will remain lower through the first part of the week as
mid level troughing builds over the region with surface high
pressure to the west providing northerly flow and drier air.

Marine...

A midlevel frontal boundary will remain draped across the region
heading into tonight, as the remnants of Barry lift northeastward
and result in an increasing coverage of showers and embedded
thunderstorms. A lingering pressure gradient across the region will
allow southwest winds to continue gusting around 20 knots the
remainder of the afternoon across Saginaw Bay and into the Central
Lake Huron basin, along with choppy 2-3 foot waves. As the remnants
of Barry move towards the Western Lake Erie Basin tonight, winds and
waves will temporarily weaken before becoming fresh northeasterly
Wednesday with gusts 15-20 knots across much of the Lake Huron basin
as the pressure gradient again tightens between high pressure
drifting east south of James Bay and the remnant low moving into the
mid-Atlantic. The flow will then become more southwesterly in
direction heading into Thursday, with frequent gusts around 20 knots
possible across much of the local waters.

Hydrology...

Late afternoon/evening thunderstorms on Tuesday produced a swath of
heavy rainfall across central and northern Washtenaw County, central
Wayne County and southwest Oakland County. 2 to 4 inches of rain
fell in these locations, with the highest amounts extending from
Ypsilanti into Canton Township. Weak low pressure will linger over
Metro Detroit and points south this morning. There is a chance for
some locally heavy showers and thunderstorms in this region this
morning. Confidence on additional flooding rains however is low.
There is the potential for the development of an organized
thunderstorm complex(s) thurs afternoon and thurs night across the
area. Given the high atmospheric moisture content, there is a risk
for locally intense rainfall if this convection is to develop as
forecast.

&&

DTX watches/warnings/advisories...
Michigan...none.
Lake Huron...none.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
&&

$$

Aviation.....SC
discussion...drk
marine.......SC
hydrology....SC

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