Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 262234
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
634 PM EDT TUE JUL 26 2016


.AVIATION...

Winds will become west-southwesterly into Wednesday afternoon to
early evening as high pressure settles to the south. SCT diurnal
cumulus of 5-7kft will fade early this evening and reform midday
Wednesday. A weak frontal boundary will sag south into area late
Wednesday, provide a chance of TSRAS, first at KMBS by around 20z
with some activity settling south through rest of terminals into the
23z-00z time frame.

For DTW...VFR conditions are expected into Wednesday afternoon with
SW return flow behind exiting high pressure and approaching surface
front. This front will bring isolated to scattered convection near
terminal by the end of the forecast.

//DTW Threshold Probabilities...

* Low in thunderstorms affecting terminal by 23z-00z Wednesday.

&&

.PREV DISCUSSION...
Issued at 346 PM EDT Tue Jul 26 2016

DISCUSSION...

This evening and tonight. A sprawling surface ridge is now
entrenched over the southern Great Lakes. Local radar data and
surface observations show the lake breezes circulations have already
been on the move during the early afternoon which is indicative the
mean centroid of anticyclone has built into the Lake Erie basin.
Not much to talk about with a prototype summer evening weatherwise
with warm temperatures early this evening and low humidity. Light
and variable winds.

Wednesday. Pseudo split flow will be overhead of the Great Lakes
region with narrow separation between the two jet branches. The
Lower Peninsula could then be under the influence of entrance
dynamics from both jetlets. Large scale subsidence, while in place
early, will be break down in the afternoon both because of an
organized area of lowered heights advancing out of IL into MI and an
organizing weak synoptic frontal boundary dropping due southward
through northern Lower Michigan. Data suggests that lower level
theta e content and moisture ahead of this frontal boundary in
combination with steepening midlevel lapse rates will result in
approximately 1500 J/KG of MLCAPE for the far northern cwa during
the afternoon. Farther south, dry weather will hold as the residual
subsidence and dry midlevel air will be too difficult to overcome.
Models suggest some possible phasing of the jet streaks during the
afternoon which could support an isolated to possible scattered
coverage of showers and thunderstorms near Saginaw Bay. For the
POPs, instituted a diurnal curve to POPs ramp up and POPs ramp down
for Wednesday with chances beginning during the afternoon and ending
during the mid evening. With no respectiable potential vorticity
advection or organized height falls, the potential for widespread
severe weather will be low. However, the potential does exist for a
smaller scale Saginaw Bay influence on the local environmental wind
profile which could support better shear, storm organization and a
localized brief strong storm risk.

The flow will becoming increasingly more zonal for Thursday as a
mean trough over northeastern Canada and upper level ridge over the
southwestern US becomes phased and coupled. This will cause the
split flow to break down into a unified jet axis with better
cyclonic flow and right entrance region dynamics focusing over the
western Great Lakes. Steadily improving synoptic scale for ascent
will allow for some coalescing of disorganized shortwave energy. The
most favorable thing going for the setup will be some merging of
shortwave energy from the PACNW with higher midlevel PV rounding
northeastward from the Gulf of Mexico. The biggest trend in recent
models was to advertise more progressive solutions for the upper
level disturbance at the end of the week. It is now suggested that
best frontogenesis and shearing deformation support may pass south
of Lower Michigan through the Ohio River Valley taking a risk for
heavy rainfall with it. The forecast is reading a chance for showers
and thunderstorms for much of the cwa and that is the preferred
narrative. Too much noise in the data to be suggesting any details
on timing.

Broad upper trough overhead Fri/Sat will give way to rising heights
Sun into next week as another expansive ridge is progged to build
across much of the CONUS. PoPs continue to be a tough call Fri/Sat.
Surface high to our north looks to provide a feed of drier air, but
deeper moisture will not be far to the south. Notable trend in the
12Z ECMWF is to stray from the previously advertised strong upper
trough and now is more in line with the weaker, more disorganized
upper air pattern of the GFS. Taken at face value, the most recent
solutions do not offer much hope for rain chances, and none of the
latest GEFS members offer anything in the way of precipitation, but
long time horizon and run-to-run model inconsistencies argue for
keeping entry level PoPs Fri/Sat. Temps expected to be near normal
Fri/Sat before warming up again Sun into early next week.

MARINE...

Expansive area of high pressure will continue to provide favorable
marine conditions across the region as it drifts eastward. A weak
cold front is beginning to move into the northern Great Lakes and
will drop slowly southward reaching the southern Great Lakes
Wednesday night. The front will provide a chance of thunderstorms
Wednesday through Thursday before exiting into the Ohio Valley on
Thursday afternoon. A weak gradient through the period will result
in winds generally 15 knots or less. Southerly flow today will give
way to northwesterly flow Wednesday night which will veer to the
northeast on Thursday.

&&

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

$$

AVIATION.....DG
DISCUSSION...CB/DT
MARINE.......DRK


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