Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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223
FXUS63 KDTX 290458
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1158 PM EST Mon Nov 28 2016


.AVIATION...

Excruciating mix of VFR to IFR ceilings have existed this evening
with height of widespread precipitation lifting northward through
the cwa. Pockets of moderate rainfall have developed over the past
hour, but back edge of the precipitation and dryslot is already
lifting into the far southern cwa. The NAM remains adamant that
ceiling heights will tank into IFR while the HRRR has backed off
considerably suggesting MVFR. Rolled back mention for
precipitation the remainder of the night based on trends and
shifted to -DZ. Deep, but not particularly strong or active,
subsidence will build into southeastern Michigan for Tuesday.
Potential does exist for some MVFR ceilings with moisture trapped
below inversion, however, clouds Tuesday may be more scattered in
nature.

For DTW...MVFR and IFR conditions have been slow to develop.
With back edge of the rain already lifting into the area, rolled
back the mention and shifted to -DZ. Cold front passage is timed
at DTW around 14Z with a minor change in wind direction from about
190 to 210. VFR cigs to develop by mid morning with return to MVFR
likely Tuesday evening.

//DTW Threshold Probabilities...

* High for ceilings AOB 5000 feet into Tuesday morning.

&&

.PREV DISCUSSION...
Issued at 935 PM EST Mon Nov 28 2016

UPDATE...

Forecast remains on track. Updated to refresh wording as the lead
edge of the main precipitation activity is now lifting into the
cwa. Nose of incredible low level jet, 60 knots on KDTX vad at 4.0
kft agl and 65 knots on KIWX vad at 4.0 kft agl, is now lifting
northward into the state from the south. Nam forecast has
925-850mb winds of 65 knots at 03Z just south of Toledo. As a
result, expecting top end ageostrophic response at exit region of
low level jet. Already seeing east to west orientated fine line
structures emanating due northward; gravity wave packets symptomatic
of the mass adjustment. Best of forcing appears tied to the anchor
point to the anticyclonic bifurcation of this low level jet axis
that is now near Indianapolis; forecasted to track towards far
western shoreline of Lake Erie. With a leaf like orientation of
the Z echoes to the north of this point still expecting some
isolated, brief heavy rainfall potential from 4-6Z for the south
half of the cwa. All observational evidence suggests a very
stable layer in place between 900-2000 ft agl, but will be
monitoring winds at the surface this evening with the low level
jet in close proximity.

PREV DISCUSSION...
Issued at 311 PM EST Mon Nov 28 2016

DISCUSSION...

Lead batch of showers with initial moisture surge this morning
shriveled up and dissipated, as there was a lot of dry air in the
low levels to overcome, as 12z dtx sounding checked in with a 44 C
dew pt depression at 850 mb. Plenty of moisture over the Western
Ohio Valley however, as ILX sounding indicated a 7 C dew pt at 850
mb. Should be no problem to generate widespread showers this
evening/tonight as upper wave/cold pool (-26 C at 500 mb) ejecting
out of the southern Plains will slide into Southern Lower Michigan
by morning. Excellent dynamics/negatively tilted trough axis,
coupled with modest instability (sfc-850 MB going slightly negative)
supports isolated mention of thunderstorms, as thunderstorms have
also been reported upstream over Illinois, although the steep
level lapse rate (8 C/KM) arrive toward 12z, and that is
associated with the mid level dry slot, and it is likely
precipitation activity will have ended by then. Ridiculously
strong low level wind shear, as 0-1 KM bulk shear of 50+ knots
lifts through overnight, drawing concern for damaging winds and
and even non-zero tornado threat (see 17z HRRR STP fields 3-7 AM),
but near surface environment likely too stable to allow this to
happen, along with the overall limited cape/instability.

Good drying/subsidence to take place tomorrow with PW values
slipping back below half an inch, although low level moisture (2-3
kft)/clouds will likely take some time to scour out, which could
impact maxes slightly, otherwise 925 mb temps around 10 C (per 12z
nam) suggests maxes approaching 60 degrees.

Weak wave/850-700 mb Theta-E to lift through Tuesday evening, and
mid level lapse rates appear steep enough to possibility generate a
few high based showers. Despite the near zero showalter index
progged, left mention of thunder out, as soundings still indicated a
lot of dry air down low and significant cap.

Massive Upper Level Low/Trough centered over Red River Valley
will slowly wobble off to the East-Southeast, translating through
Great Lakes Region during Wednesday-Thursday Time Frame. Upper
level PV train/trough axis over Four Corners region tomorrow,
tracking through Ohio Valley on Wednesday, with cyclogensis taking
place over Eastern Ohio Valley, into the Eastern Great Lakes by
Wednesday Evening. Looks reasonable shot of rain shield clipping
southeast Michigan in this time frame, per 12z Euro.

The beginning of December will start off with longwave troughing
over the region through the end of the week before ridging builds
back in.  Periods of showers will still be possible as the low
pressure system continues to push off towards the New England area.
Drier conditions come back for the the majority of the weekend
before more unsettled weather moves back in by the end of the
weekend. Temperatures will remain consistent through the extended
period with highs hovering around 40 degrees and lows around 30
degrees.

MARINE...

Southeast winds will continue to increase into tonight as a warm
front approaches from the south. This will lead to a period of gale
force winds throughout the Lake Huron basin, as well as the Michigan
waters of Lake Erie. Peak gusts during the overnight period will
climb to between 40 to 45 knots across northern and central sections
of Lake Huron. The long southeast fetch will also support extensive
wave growth, with waves potential peaking near 20 feet. Small Craft
Advisories will transition to Gale Warnings this evening. Winds and
waves are projected to improve Tuesday night into Wednesday as
direction shifts to the southwest and milder air and more stable
conditions overspread the region.

HYDROLOGY...

Rain will overspread the area late this afternoon and continue into
tonight as abundant gulf moisture lifts north into area in advance
of approaching warm front. This rain will come to an end early
Tuesday morning as the warm front progresses north of the region.
Total rainfall amounts of one half to three quarters of an inch are
expected across the region during this time frame. While this is an
above normal amount of rainfall for this time of year, flooding is
not anticipated.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning until 4 PM EST Tuesday FOR LHZ363-421-422-441-462.

     Gale Warning until 10 AM EST Tuesday FOR LHZ361-362-442-443-463-464.

Lake St Clair...Small Craft Advisory until 10 AM EST Tuesday FOR LCZ460.

Michigan waters of Lake Erie...Gale Warning until 7 AM EST Tuesday FOR LEZ444.

&&

$$

AVIATION.....CB
UPDATE.......CB
DISCUSSION...SF/SS
MARINE.......DG
HYDROLOGY....DG


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