Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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614
FXUS63 KDTX 291735
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
135 PM EDT Sat Apr 29 2017


.AVIATION...

Existing dry northeasterly flow will gradually given way to an
increasing surge of moisture over the next 24 hours.  Remainder of
the daylight period today largely defined with this drier profile,
some lingering higher based VFR stratus tucked beneath thicker high
cloud.  Probability for showers and subsequent reduction in ceiling
height will increase tonight, particularly at FNT/MBS where MVFR
conditions will be more likely.  Periodic showers areawide into
Sunday, with the highest coverage/intensity still focused at
FNT/MBS.  Elevated thunderstorms will be possible tonight and
Sunday, but the ill-defined timing and limited potential will
preclude any mention at this stage.  Firm northeast wind through
tonight, turning intermittently gusty /20 kts/ late today into the
evening.

For DTW...Satellite and observational trends favor a ceiling height
holding at or just below 5000 ft through the afternoon.  Any loss of
this ceiling likely of short duration, as renewed expansion of this
stratus occurs this evening/early tonight.  Low probability for
elevated thunderstorms tonight, limited coverage and uncertain
timing precludes a mention.  Firm northeast winds continue through
tonight.

//DTW THRESHOLD PROBABILITIES...

* Medium confidence in ceilings 5000 ft this afternoon and evening.
  High confidence overnight and Sunday.

* Low chance for thunderstorms late tonight and Sunday.

&&

.PREV DISCUSSION...
Issued at 326 AM EDT Sat Apr 29 2017

DISCUSSION...

Convective activity overnight has remained tied to the sfc front
down across the Ohio Valley. Some light showers did manage to brush
metro Detroit and points south overnight. A second region of showers
developed much higher up along the frontal slope across nrn and cntl
Lower Mi, aided by some upper jet support. While the mid
tropospheric frontal boundary will remain draped across Lower Mi
today, precip chances through at least mid afternoon look to be
rather low. Upper jet forcing will shift west of the forecast area
and the expansion of the Bermuda high across the eastern US will
actually lead to mid level height rises across the ern Great Lakes
(including Se Mi) during the day. The best chances for some showers
will thus remain focused near the Ohio border, closer to the low
level frontal boundary. Meanwhile, sfc high pressure will expand
across nrn Ontario today. This is already driving a back door cold
front across the forecast area, approaching the I-69 corridor as of
06Z. This front will push south of the state line this morning. Post
frontal lake-modified temps have dropped into the 40s. N-NE winds
will sustain cool conditions through the day. Diurnal heating should
at least boost temps back into the 50s away from Lake Huron this
afternoon.

The upper low will rotate from New Mexico into the Texas panhandle
today, sustaining the tropical moisture feed into the Mid Miss/Lower
Ohio Valley. This will support continued widespread convection in
this region. The latest hi res solutions, particularly the HRRR and
ARW, suggest a convectively induced mid level short wave will lift
out of this region and traverse Lower Mi tonight. Ample deep layer
moisture and decent elevated instability will be transported into
the area ahead of this feature, supporting high probabilities of
showers/thunderstorms. A deep warm cloud layer and 700mb dewpoints
approaching +5c combined with weak elevated instability will support
intense rainfall rates with any convection tonight.

The passage of any short wave feature by Sun morning will likely
support some decrease in areal coverage of convection. The
aforementioned upper low will rotate across the central plains on
Sunday. The deterministic model suite continue to suggest upper jet
dynamics will support good mid level fgen along the 850mb portion of
the front, which is expected to extend into the Saginaw Valley. This
may support some prolonged rainfall across the Tri Cities region and
will be something for later shifts to monitor in the event that a
flood watch may be needed. The upper low is forecast to make a push
to the northeast Sun night into Monday. This will bring the warm
conveyor across Se Mi Sun night, where the continued tropical
moisture feed will push precipitable water up to 1.6 inches. Good
upper level diffluence across the region and low to moderate
elevated instability will support widespread showers and
thunderstorms Sun night, with additional heavy rainfall possible.
With with surface low occluding well to the southwest, the warm
front is likely not going to lift North of the Mi/Oh state line on
Sunday. Potential showers and low clouds and a stronger easterly
flow is likely to lead to rather chilly temps over much of the
forecast area on Sunday.

The mid level dry slot is forecast to be overhead on Monday as the
upper low meanders its way across the western Great Lakes. The
potential for deep mixing suggests warm and breezy conditions
Monday. The upper low is then forecast to lift northeast of the
region on Tuesday, with the sfc occluded front passing across the
area Mon night. Much cooler air will filter into the area in the wake
of the front, supporting cool temps on Tuesday. Mean long wave
troughing is forecast to hold across the region through the end of
the work week, support continued cool conditions.

MARINE...

Conditions will be fairly unsettled through early next week as a
strong low pressure system slowly tracks through the area. Modestly
strong north to northeast winds will continue to generate large
waves over Saginaw Bay and off the tip of the thumb today. High
pressure center sliding through Ontario coupled with the area of low
pressure lifting through the plains will then turn winds to the east-
northeast late tonight and Sunday and allow for an increase in
speed. This will maintain Small Craft conditions in the current
advisory area, with additional advisories potentially needed for
other portions of the Lake Huron nearshore waters. Strong winds
gusting into the 25 to 30 knot range are then expected across all of
the Central Great Lakes on Monday in advance of a cold front before
they flip to west on Tuesday and finally decrease Tuesday night. A
wet and active pattern will develop late today, with periods of
heavy rain and thunderstorms possible late tonight through Monday
afternoon.

HYDROLOGY...

The chance for showers will remain low through the late afternoon
today, then begin to increase in the evening. Total rainfall through
800 PM is expected to remain near or under 0.25 inches. The chance
for rain then increases significantly tonight through Monday
afternoon, with periods of steadier rain expected, which may become
heavy at times. Total rainfall through Monday afternoon looks to
range between 1 and 3 inches, with the highest amounts expected over
the Saginaw Valley. Locally higher totals will be possible for areas
that experience thunderstorms Sunday into Monday, as storms will
bring brief periods of torrential rainfall. Rivers and streams will
see significant rises through the middle of the week, and ponding of
water may develop in low-lying areas and roadways. Flooding could
become a concern by Sunday and Monday, particularly over the Saginaw
Valley.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 4 PM EDT Sunday for LHZ443.

     Small Craft Advisory until 6 AM EDT Monday for LHZ421-422-441.

     Small Craft Advisory from 4 AM to 4 PM EDT Sunday for LHZ442.

Lake St Clair...NONE.
Michigan waters of Lake Erie...Small Craft Advisory until 4 PM EDT Sunday for LEZ444.

&&

$$

AVIATION.....MR
DISCUSSION...SC
MARINE.......HLO
HYDROLOGY....HLO


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