Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 201915

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
315 PM EDT Tue Jun 20 2017


The lead shortwave that has come onshore in British Columbia this
afternoon and trailing upper jet will be the dominant drivers of
weather over the region for the remainder of the week. Today`s
trough will exit east over the next 18 hours as the thermal trough
settles overhead for Wednesday. Gradually rising heights aloft will
force surface high pressure to translate into the area tonight into
Wednesday. The cool airmass featuring 850mb temperatures falling to
around 9C by Wed morning will support lows tonight a few degrees
lower than last night - low to mid 50s. Sheltered areas could dip
into the upper 40s. Positioned within the thermal trough, SE
Michigan will see appreciable boundary layer growth tomorrow with
dry adiabatic lapse rates supporting a mid 70s floor on high
temperatures/low 70s in the Thumb. Expect moderate building of
diurnal cu but not sufficient to substantially inhibit insolation,
so forecast highs will stay on the warmer side of guidance on the
expectation of overachieving potential.

Wednesday`s high pressure will be quickly replaced as dynamics
associated with the next system begin to manifest over the central
US and Great Lakes regions. Convection is forecast to develop along
the nose of the LLJ as a surge of higher theta-e air presses into
the area. Warm advection and lead fgen will likely support this
activity eastward through Wednesday night and into Thursday morning
supporting the inherited chance of rain during this period. Poor
lapse rates preclude any severe concern, although a few rumbles of
thunder cannot be ruled out. The surge of warmth and moisture will
favor substantially more humid conditions on Thursday with dewpoints
in the mid to upper 60s and 850mb temps rising toward the upper
teens. No complaints with guidance suggesting mid to upper 80s once
early-morning convection clears early Thursday. Weaker forcing
supports lower pops for the remainder of the daytime Thursday,
particularly given the capping evident on area forecast soundings.
This will still, however, mark the primary window for severe
potential during the forecast period. Timing of the arrival of
greater frontal forcing associated with the strengthening jet aloft
appears to the primary forecast consideration. There is at least
some indication that the mid-level frontal circulation will quickly
ramp up 00-06z Thursday evening in the presence of MLCAPE under 1000
j/kg. Shear associated with the emerging LLJ will be more than
sufficient to support organization, particularly if forcing arrives
slightly earlier during the latter portion of the diurnal heating

Persistent right entrance dynamics and a push from the deepening
upstream trough will result in a strong baroclinic zone setting up
from the Great Plains into northern Lower Michigan through Thursday
night. Attm, timing is progged to coincide with resurgence of a
nocturnal low-level jet oriented largely parallel to the boundary.
There is moderate to high confidence that a band of moderate to
heavy rain will set up somewhere over the LP Thursday night before
being ushered out on Friday by a progressive pattern aloft. Attm,
NWP consensus suggests an inch or more of rain will be possible
north of I-69 roughly collocated with the surface front and
coinciding with the track of the surface low. However, the solution
space does remain open to the possibility of a more progressive
fropa yielding a shorter-duration of heavier rain for any one
location Thurs night.

Confidence is fairly high regarding rain and thunderstorm chances
early in the day on Friday, as a cold front pushes in northwest to
southeast. This front will have the potential to produce a quick
quarter to a half inch of rain over the span of several hours, with
localized heavier amounts possible for areas that see thunderstorms,
as PW remains high ahead of the front (1.6 - 1.8 inches). Cooler
conditions will then settle in across Michigan and will remain in
the area as west to northwesterly flow dominates into early next
week. Expect daytime temperatures to peak in the low to mid-70s
during this time. On and off rain showers will be possible after the
front moves through Friday, although the signal looks very weak for
rain chances, thus PoPs will remain low through Saturday. The ECMWF
and GEM runs then develop and push an amplified trough through the
Great Lakes Sunday into Monday which will provide better chances for
rain throughout the day.



The upper level trough and shortwave will continue to move eastward
across the Great Lakes region.  This will bring a continued chance
for scattered showers and thunderstorms through this evening.
Southwesterly flow then turns more northwest behind the cold front.
High pressure then builds in behind the exiting trough, bringing
calmer and drier conditions to the region on Wednesday.

Additional shower and thunderstorm activity will once again be
possible on Thursday as developing low pressure system moves west
and pushes a warm front north through the central Great Lakes.  This
front will also bring in southerly flow to the area.



While there will be a continuing chance for showers this afternoon
and again the Thursday, the main hydro issue through the week will
be on Friday.  A boundary looks to setup across the area which will
provide several rounds of activity by the end of the week.  Rain
amounts from this will be dependent on where the boundary sets up.
Currently, models are projecting the heaviest rainfall amounts to be
across northern portions of the CWA.


Issued at 131 PM EDT Tue Jun 20 2017


Frontal boundary will continue to push into the area this afternoon
into the evening.  Diurnal cumulus have developed this afternoon and
so have some spotty shower activity over northern portions of the
area.  Best chances for showers (isolated thunder) will be northern
TAF sites as activity coming in from the west continues to hold
together. This activity will diminish later this evening as high
pressure starts to work into the area overnight and brings clearing
skies. Westerly/southwesterly winds continue to gust into the 20 mph
range ahead of the front before diminishing this evening.

For DTW...Broken ceilings around 5k feet will continue to work in
this afternoon.  Will maintain previous forecast which leaves the
area dry.  Better shower chances continue to be north of metro.
Decent pressure gradient will continue before the cold front passes
and allows the gradient to weaken later this evening.


* Very low for thunderstorms late afternoon into early evening.

* Medium in ceilings around 5000 feet this afternoon.


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



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