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116
FXUS63 KDTX 220127
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
927 PM EDT WED SEP 21 2016

.UPDATE...

Radar/Satellite imagery indicates at least a couple short wave
featured across nrn Wisconsin. These impulses will track across
Upper Mi and the straits tonight into Thurs morning. This will
allow showers and a few thunderstorms to slowly extend from nrn
Wisconsin into northern Michigan, while the deeper convection
holds well west of the area within the quasi stationary convective
clusters across MN/IA/wrn Wi. There will remain a localized region
of mid level subsidence and associated drier mid level air across
Se Mi tonight well into Thursday. This should largely hold the
more organized showers and thunderstorms to the north and
northwest of the forecast area overnight and Thursday. Given how
far south some of the convection has developed in ern Wisconsin
this evening, it seems plausible that some stray showers/isolated
thunderstorms may impact the Saginaw Valley and tip of the thumb
overnight. This fully supports the low chance pop in the forecast
(along and north of a Saginaw to Sandusky line) overnight and
during the day Thursday. The only update to the forecast will be
to push the chances of rain back a few hours tonight based on
current trends and to lower forecast min temps a couple degrees
in the thumb where current temps are already nearing forecast
lows.

&&

.PREV DISCUSSION...
Issued at 657 PM EDT Wed SEP 21 2016

AVIATION...

Recent satellite data indicates localized subsidence across Lower
Mi, which is currently causing the convection across Wisconsin to
diminish as it moves east. Overnight, showers and thunderstorms are
expected to eventually expand east into the northern Great Lakes
along a frontal boundary, while some degree of subsidence holds
across Se Mi. The subsidence is expected to keep convection north of
the terminals through the night and well into Thursday. While MBS
will be closer to the better feed of moisture/instability along the
frontal boundary draped across the nrn Great Lakes, the
probabilities of TSRA at MBS are still rather low, too low to
include in the terminals attm. Satellite trends have shown enough
thinning/decrease in high clouds working into Se Mi to suggest some
periods of decent radiational cooling overnight. Given that sfc
dewpoints are well in the 60s, a chance of some MVFR type
visibilities in fog toward daybreak will be added to the TAFs.

For DTW...Metro Detroit will remain far enough removed from the
region of moisture and instability to the north and west to provide
little to no chance for TSRA through the TAF period. The thicker
cirrus will likely remain north of metro, so radiational cooling
potential may support a brief period of light fog early Thurs
morning.

//DTW Threshold Probabilities...

* None

PREV DISCUSSION...
Issued at 344 PM EDT Wed SEP 21 2016

DISCUSSION...

Energetic upper levels continue through mid week as a nearly zonal
140+ knot jet streaks across the US/Canada border. Weak southern
stream jet lifting northeast out of the developing west coast upper
level trough, will send a series of shortwaves through the plains
and into northern MI. The pattern has also resulted in a broad
surface developing over the central plains with a warm front taking
shape across the Central Great Lakes. This pattern will deviate very
little now through the end of the week as the strong Hudson Bay low
remains in place.

Area should remain dry through the rest of the evening and into the
overnight hours as subsidence in the wake of the early afternoon MCS
settles over southern MI. Hires HRRR and RAP advertise some
redevelopment this evening along I94 on the sinking outflow boundary
but confidence is low in the occuring. The current cap will make it
hard for anything to develop, even with a bit of late afternoon
heating. Radar trends through the day have shown the convection
struggling to advance much further west than Chicago away from the
stronger height falls. Without any forcing locally and no shortwaves
to speak of during the evening, think convection will struggle even
with peak heating as skies begin to clear out somewhat.

Tonight through Friday will focus on the warm frontal positioning
and shortwaves/MCSs that will ripple along the front for possible
showers and thunderstorms. Models have shifted north with the
positioning of the surface front which in turn refocuses the
developing isentropic forcing north. A brief shortwave ridge
rounding the base of the Hudson Bay low will allow the jet to arch
northward as well which will steer the approaching shortwaves
further north as well. All this leads to shifting the pops north
which really only leaves the Saginaw Valley and northern Thumb with
a short at precip through Thursday. Will highlight the period from
09-15Z Thursday for the best opportunity as the shortwave lifts
through northern lower aided by nocturnal low level jet and next
surge of theta e. The rest of the afternoon will likely dry out for
everyone again but with the front just to the north will leave a
slight chance for the extreme north.

The front will start to sag southward into mid MI Thursday night as
a strong trough rotates around the Hudson Bay low giving it a push.
It should passing through southeast MI by Friday afternoon which
will be the next chance for showers and thunderstorms. Should see a
good thermal gradient across southern MI on Friday with the front
draped across the region. This will mark the end of the current
stretch of 80 degree days as highs north of I69 will struggle to
reach 70 with strengthening northeast flow off Lake Huron. Timing of
the front will decide just how warm the Metro Detroit area can get
before cooling back off.

High pressure over Ontario will keep surface flow with an easterly
component locally over the weekend. Sharp NW/SE low-mid level theta-E
boundary across SE MI, and cannot totally rule out some light
showers Saturday with weak positive theta-E advection and PWAT
around 1.5 inches, but at this point expect most of the weekend to be
dry. Low predictability early next week with guidance indicating a
cutoff low taking shape somewhere to our west over the Northern
Plains/Upper Midwest, with meridionally-oriented moisture plume
ahead of it. Eastward progression of these features will determine
rain chances early next week, and not a whole lot of model consensus
at this point, so chance PoPs early next week will suffice for now.
Despite rather warm mid-level temps, easterly surface flow is
expected to keep temps in check near or slightly above normal.

MARINE...

A front will remain stalled over the northern Great Lakes tonight
through Thursday. An active pattern of showers and thunderstorms
will be the primary marine weather impact, mainly over northern Lake
Huron, while wind and waves remains light/low over other marine
areas. That will change Thursday night and Friday as the front
settles southward into Ohio and opens moderate northeast flow over
all areas. The long fetch of onshore, unstable flow over southern
Lake Huron and into Saginaw Bay will likely produce waves exceeding
SCA levels through Friday night before high pressure settles in
Saturday.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

UPDATE.......SC
AVIATION.....SC
DISCUSSION...DRK/DT
MARINE.......BT


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