Scientific Forecaster Discussion
fxus63 kdtx 252245
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
645 PM EDT Mon Sep 25 2017
Other than patchy MVFR fog late tonight, expect VFR conditions with
mainly clear skies as strong ridge of high pressure holds sway.
Light variable winds will become south southwest on Tuesday and may
approach 10 knots during peak afternoon mixing. Any diurnal cumulus
will most likely be trivial.
//Dtw threshold probabilities...
issued at 352 PM EDT Mon Sep 25 2017
Dominant upper level ridging remains in place over eastern North
America and continues to support unseasonably hot weather across
southeastern Michigan. This airmass is expected to persist for
another 48 hours.
Through the early afternoon, observational trends, including 24 hour
departures, suggests high temperatures for today topping out around
the 90 degree mark. Daily records are yet again in jeopardy at dtw,
fnt and mbs. Low level moisture and high surface dewpoints have been
able to make the turn within the large upper level ridge and has
flooded back northward into lower Michigan. This is obvious in the
surface obs with dewpoints in the 60s for many areas of southeastern
Michigan. The return of this moisture has actually led to some
cumulus development. Bulk of hi-resolution explicit convection
models suggests some lower end potential for convective development
across northern portions of the cwa, near Saginaw Bay during the
late afternoon. 0.5z kdtx reflectivity and northern edge of cumulus
in satellite imagery places a mesoscale convergence zone over the
northern edge of the cwa. The one item that will be monitored during
the remainder of the afternoon is the arrival of a tounge of 600-
500mb equivalent potential temperature from the southwest during the
19-22z time window. The introduction of this midlevel moisture could
cool the 12.5 to 16.0 kft agl layer, allowing for convection to
initiate. Again, the potential for a thunderstorm exists north of I
69 near the Tri Cities conditional to convective initiation. No
severe weather is expected.
Right entrance region dynamics will push across portions of northern
Ontario tonight. Locally, the response of this occurring will be for
a shortwave ridging component to amplify the mid to upper level
ridge axis back over the Great Lakes region. Low cloud fraction is
anticipated across southeastern Michigan. A little interesting that
850mb temperatures are expected to be 1 to 1.5 degrees warmer
tomorrow. With the approach of increasing gradient southwesterly
flow ahead of the approaching cold front and increase in
compressional warming, wanted to make sure the forecast had 90
degree readings for many area.
Upper level jet core is shown to push directly into sections of
lower Michigan already by Tuesday evening which will finally allow a
cold front to push across the region. A very stable consensus in nwp
continues for a dry front across Michigan during the day on
Wednesday. The support for a dry front includes a late morning
timing, extremely unfavorable positioning of southeastern Michigan to
a straight anticyclonic shear side of the upper level jet axis, and
the propensity for the front to become increasingly more parallel to
the mean flow. Daytime highs on Wednesday are expected to be some 10
to 15 degrees below what we have seen here on this run.
Cold advection will be complete by Thursday morning as the thermal
trough pivots through the region. Surface ridging will bring dry
conditions on Thursday as highs top out near normal in the upper
60s. A shortwave pivoting southeastward through the upper level
trough will drop an area of low pressure through the region on
Friday. This low will bring a chance of showers along with a
reinforcing shot of cooler air as 850 mb temps approach 0 c Friday
night into early Saturday. Surface high pressure then builds into
the region for the weekend as upper level ridging moves eastward
over the Great Lakes. This will bring pleasant, dry weather for both
Saturday and Sunday as highs slowly warm through the 60s each day
while lows fall into the 40s.
Record early fall warmth will continue today through Tuesday. The
warm air and light southerly wind will produce ideal marine
conditions during this time. A cold front crossing the central Great
Lakes Tuesday night and Wednesday will then bring temperatures back
down toward normal along with a low chance of showers and
thunderstorms. Winds behind the front will become northwest at light
to moderate speed, although a few gusts near 30 knots will be
possible over the open waters of Central Lake Huron. The part of the
forecast to monitor will be the associated higher wave pattern
remaining far enough offshore to avoid the need for small craft
advisories over Southern Lake Huron. Another low pressure system and
cold front due Friday will bring a reinforcement of colder air and
unstable marine conditions for the weekend.
Lake St Clair...none.
Michigan waters of Lake Erie...none.