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fxus63 kdtx 171958 
afddtx

Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
358 PM EDT Wed Jul 17 2019

Discussion...

For the remainder of the afternoon and evening... low-level cloud
cover will continue to erode as dry advection from persistent
northerly flow continues to work across Southeast Michigan. This will also bring
slight relief from the oppressive humidity as dew points diminish
from the upper-60s to lower-70s down into the low to mid-60s
overnight. Associated overnight temperatures to dip in the 60s
across the state, aided by the northerly flow and early night
radiational cooling.

Upper-level heights to gradually rise through the remainder of the
week as a flat, subtropical ridge settles across the Great Lakes,
which will usher in the hottest temperatures of the Summer season
thus far. Surface winds to veer from the northeast to the
south/southeast throughout Thursday morning into afternoon while a
low-level jet pivots from the Midwest into the Great Lakes Thursday
afternoon into early Friday morning. Low-level jet will aid in
ushering in warm and very moist conditions throughout the day,
marked by h850 temperatures at 17c Thursday morning to above 20c by
Thursday evening. This will translate to daytime high temperatures
peaking into the lower-90s for just about all of Southeast Michigan (pending
prior convection -- see paragraph below), with the exception for
communities located along the Lake Huron shoreline with slightly
muted temperature due to the marine influence. Dew points will also
return into the low to mid-70s, which will make it feel more like
the upper-90s to lower-100s during afternoon peak heating.

In addition to the increase in heat and humidity, the second weather
feature (and potential curveball) to note will be a possible
approaching mesoscale convective system system that is forecasted to initiated along the
leading edge of a low level jet and short-wave feature across
Minnesota/Wisconsin late tonight. Most cams from the 12z href cycle
have the mesoscale convective system propagating downstream across Michigan between 12z-20z,
although confidence remains low at this time regarding the evolution
of any potential convection, especially given that the ongoing
convection across Iowa has been poorly resolved by hi-res models and
may have impacts on future development. Most of the cams have the
system weakening and/or holding the strongest convection over SW mi,
away from the DTX cwa, along the leading edge of the
instability/higher Theta-E gradient. However, given that the
potential convection could approach and cross Southeast Michigan sometime in the
late morning/afternoon, it's possible that the system can hold
together as the boundary layer warms and instability rises. If the
latter holds true, strong to severe storms will be possible with any
thunderstorm development given the moderate bulk shear of 35
- 40 knots in place in addition to moderate low-level lapse rates.
The primary threat if the system holds up would be wind gusts in
excess of 50-60 mph. Storm Prediction Center has also included most of Southeast Michigan in a
marginal risk for severe weather to account for the potential storm
system. A secondary consideration to any rain/thunderstorms observed
during the late morning/early afternoon would be slightly moderated
temperatures (although still very muggy) for the early part of the
day, but temperatures should still have no problem warming up into at
least the upper-80s by the late afternoon/evening as waa ramps up.
At the very least the system will bring upper-level cloud debris
through the late morning and early afternoon.

Otherwise given high Theta-E and chance for redeveloping storms
along outflow boundaries, chance for pop-up showers/storms remain
possible for remainder of the afternoon and evening across southeast mi,
but a building eml may aid in limiting coverage. Additionally, heavy
downpours leading to localized flooding will be possible with any
thunderstorm development. Please see the hydrology section for more
details. Heat headlines will not be added this forecasting period
given the uncertainty to achieve heat advisory thresholds due to
possible morning/early afternoon thunderstorms.

Friday remains on track to be the warmest day of the Summer thus far
as h500 heights rise to 590 dam across Southeast Michigan and h850 temperatures
soar to around 23c. A strong cap in place should help inhibit any
widespread convection and will allow temperatures to rise into mid-
90s across all of southeast mi, and possibly the upper-90s over the urban
Metro region. With dew points projected to rise into the mid-70s,
heat indices will rise to between 105 - 110 degrees. Heat headlines
will be extremely likely on Friday...and not much relief is in store
overnight leading into Saturday as temperatures hold in the mid to
upper-70s.

Another extremely hot day is likely for Saturday as the same air
mass remains in place over the region. 850mb temps continue to hover
near 23c which should result in highs well into the 90s and heat
indices again over 100 degrees. Some relief may come in the form of
thunderstorm activity, as model guidance depicts a weak surface
trough over the Great Lakes and a convectively-enhanced shortwave
moving in from the Midwest. Soundings suggest a weaker cap compared
to Friday as well. Plenty of instability should be in place for
potential severe weather, but modest westerly flow of around or
below 30kt and lack of stronger forcing mechanism may prevent more
widespread severe activity. Certainly bears watching over the next
few forecast cycles.

A weak cold front will pass through Sunday and force the worst of
the heat east and south, but highs still look to remain a bit above
normal. A chance of showers and thunderstorms will come along with
this front, and another (stronger) cold front that will drop through
later in the day/evening. This second front will usher in much
cooler and drier Canadian air, leading to more seasonable
temperatures for the early to midweek period. Northwesterly flow
aloft and surface ridging will keep conditions on the quiet side
during this period as well.

&&

Marine...

Frontal boundary has moved into lower Michigan leaving lighter north
to northeast flow of around 10 knots or less across much of the
marine zones. The exception being across the Saginaw Bay where
slightly stronger 10-15 kt northeast flow is present due to the long
fetch of winds into the Bay. Thursday will see frequent gusts to
around 20 knots as winds flip out of the south across all marine
zones as gradient tightens. There will be potential for showers and
thunderstorms to move through the region during the first half of
the day bringing locally higher gusts and waves associated with any
thunderstorms moving over any local waters. Winds remain elevated
into Friday resulting from the pressure gradient between the low
pressure to the north in the Hudson Bay and high pressure across the
southeastern US.

&&

Hydrology...

There will be potential for a complex of thunderstorms to move into
Southeast Michigan during the first half of the day Thursday. High
moisture content will be moving in characterized by precipitable water values of
around 2.00 inches. Greater heavy rainfall threat will be towards
the Saginaw Valley, but any storms producing heavy rainfall over
urban areas will pose a flooding threat as well. If the complex of
storms does hold together and move into Southeast Michigan during
the first half of Thursday, rainfall amounts of 1-2" with locally
higher amounts will be possible. Potential also exists for activity
to redevelop later in the day, depending on how the early day
activity plays out. This activity would also pose a heavy rain
threat.

&&

Previous discussion...
issued at 153 PM EDT Wed Jul 17 2019

Aviation...

Deeper moisture has pushed east with the surface low this afternoon
as drier air is advected into the area under 5-10 knot north to NE flow.
Overall conditions will continue to improve VFR through the afternoon
for ptk and Metro area terminals while some pockets of MVFR remain
over Southeast Michigan within the scattered-broken diurnally enhanced cu. These
cloud ceilings will continue to lift from boundary layer growth
throughout the day. Expecting predominately VFR conditions with less
coverage in clouds north of I-69 for fnt and mbs, which will remain
through the remainder of today with only scattered low to mid clouds.
Mostly clear skies expected for the overnight period.

For dtw...while conditions continue to improve into VFR this
afternoon, a scattered-broken cu field will likely hover around or slightly
below the 5,000 ft threshold before clearing out between 00-02z.

Dtw threshold probabilities...

* moderate in ceilings at or below 5000 ft through this afternoon.



&&

DTX watches/warnings/advisories...
Michigan...Lakeshore flood advisory until 2 am EDT Thursday for miz048.

Lake Huron...none.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
&&

$$

Discussion...am/tf
marine.......aa
hydrology....aa

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