Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 251644
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1244 PM EDT Sun Jun 25 2017


.AVIATION...

Corridor of isentropic ascent will pivot through the area during
peak heating. Most focused ascent will reside PTK north where
mention of -shra remains in the forecast. Given drier low-levels and
low rain intensity, expect nothing worse than brief MVFR with any
showers. Further south, VFR cu dominate. Low potential for showers
to move into the Detroit area given weaker forcing and downsloping
contributing to more dry air in the lowest levels. A passing shower
is possible but confidence is too low to warrant carrying in the TAF.

For DTW...Cigs aob 5kft will be possible but downsloping within
westerly flow makes the forecast difficult given borderline upstream
obs. For now will carry a borderline BKN050 pending evidence for
sustained 060 or higher.

//DTW THRESHOLD PROBABILITIES...

* Low for cigs aob 5kft

* Low for winds reaching crosswind thresholds from 270 degrees

&&

.PREV DISCUSSION...
Issued at 353 AM EDT Sun Jun 25 2017

DISCUSSION...

Closed mid level circulation pivoting through the existing larger
scale broad troughing on pace to translate across central lower Mi
during the latter half of the morning.  The corresponding uptick in
in cyclonic vorticity advection with some weak surface troughing
will maintain a window for shower development during this time.
Inability of the attendant cold pool to better capitalize on diurnal
destabilization given the early day timing remains a negative for
seeing greater coverage, supporting simply a low end pop.  A period
of weak deep layer cold air advection trailing this system will
effectively leave colder/drier conditions in place for peak heating
relative to yesterday. Afternoon highs expected to arrive a good 5-7
degrees colder...or near 70 degrees.  Lingering pocket of cold mid
level air in conjunction with daytime heating will establish
sufficiently steep lapse rates to support some scattered instability
showers/isolated thunderstorms. Greater focus once again across the
Tri-cities and northern thumb, where mucape spikes to around 1000
j/kg beneath the coldest 500 mb temperatures and where residual cva
still exists.  Small hail again a possibility within any better
cores given the low freezing levels. Rapid reduction in coverage
upon the loss of diurnal support by late this evening.

Additional shortwave energy now evident on water vapor digging
southeast into northern Minnesota will lift into region overnight.
Development of a weak surface low and attendant trough within the
lowering height field may support some light shower production into
the early morning period, but generally unfavorable thermodynamics
given the timing will preclude a greater response.  However,
trailing stronger circulation currently timed to arrive at the back
end of the peak heating cycle on Monday.  Some question yet as to
the placement of the best forcing with this feature, but established
cold mid level temperatures and the likelihood for a period of
greater cva once again presents a solid opportunity for the diurnal
expansion of showers/isolated thunder late Monday.  An already
cooler resident air mass takes one final step down on Monday, as
temperatures largely hold in the mid and upper 60s.

Air mass modification commences beginning Tuesday upon the gradual
eastward exit of the mid level trough, prompting a corresponding
increase in upper heights.  Assuming one final weak perturbation is
not embedded within the residual northwesterly flow, simply looking
at typical late day diurnal cu growth with temperatures peaking in
the low-mid 70s.  Benign conditions into Wednesday under weak
shortwave ridging, with the thermal recovery now augmented by
emerging low level southwest flow.  Wednesday night into Thursday
the next period to monitor, as potential shortwave energy lifting
through the deepening upstream corridor of warm/moist advection and
backed by low level jet support may yield an expanding corridor of
convection/MCS that ultimately becomes elevated and funnels into
lower Michigan.

MARINE...

An increase in winds is expected today as the pressure gradient
tightens between a trough of low pressure tracking through northern
Lake Huron and high pressure building into the Plains and Tennessee
Valley. The strongest winds will be located over Lake St Clair and
Western Lake Erie, where gusts should reach about 25 knots. A Small
Craft Advisory remains in effect for these lakes today. Another
round of gusty winds looks to develop Monday as another area of low
pressure tracks through northern Michigan. This could again
necessitate Small Craft Advisories. Offshore westerly flow will
limit wave growth each day. There is also a slight chance for
thunderstorms today and Monday as the airmass remains unstable. High
pressure expanding into the Great Lakes will then bring southerly
flow and dry weather from late Monday night into Wednesday evening.

HYDROLOGY...

Scattered rain showers and a few thunderstorms are expected once
again this afternoon, with greatest coverage north of Flint. Showers
and storms that do develop will move slowly, and a few locations may
receive more than one-quarter of an inch of rain. Additional showers
are expected over the Saginaw Valley and Thumb overnight, with
activity becoming more widespread on Monday as low pressure tracks
across the area. Rainfall may again exceed one-quarter of an inch on
Monday within thunderstorms. Dry weather is expected from Monday
night into Wednesday evening.

The Tittabawassee River crested Saturday evening, and flood waters
are expected to slowly recede today through Monday morning. Waters
will meanwhile continue to rise on the Saginaw River today and
Monday, with the crest expected to be reached late Monday night.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...Small Craft Advisory until 8 PM EDT this evening for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 8 PM EDT this evening for LEZ444.

&&

$$

AVIATION.....JVC
DISCUSSION...MR
MARINE.......HLO
HYDROLOGY....HLO


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