Scientific Forecaster Discussion
fxus63 kdtx 220348
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1148 PM EDT Sat Jul 21 2018
Moisture advection from the east during the course of the morning
will sustain at least some coverage of showers. Subtle cooling (sub
3k ft) will pose the risk of expansion/redevelopment of an MVFR
strato cu field during the morning. An upper wave now lifting across
Pennsylvania is forecast to advance into The Thumb region Sun
afternoon. This system will help drive additional showers into the
region. A push of cooler low level air from the northern during the
afternoon will result in enough cooling in the low levels to hold a
prevailing MVFR cloud base through the day sun.
For dtw...lingering instability over Lake Erie during the morning
may provide a stray thunderstorm in the vicinity. The chances of
this are very low, so no thunderstorms and rain mention will be warranted in the
terminal. The lack of much if any instability on Sunday will
further limit thunderstorms and rain potential.
Dtw threshold probabilities...
* moderate in ceilings at or below 5000 ft tonight and Sunday.
* Low in thunderstorms tonight and Sunday.
issued at 900 PM EDT Sat Jul 21 2018
A little better moisture influx already appears to be working into
southern Ontario and The Thumb region from the system now over the
Delmarva. This has resulted in an enhancement in showers from
generally Mt Clemens north into The Thumb region. Despite weak
instability with the lack of steep mid level lapse rates, there have
been a few lightning strikes within these showers. A forecast update
will be issued to increase shower coverage in this region this
evening as this moisture convergence is only going to slowly push
toward the northeast. The remainder of the forecast area (with the
exception of SW Lenawee county) has remained dry this evening with a
bit of a mid level dry slot overhead. In the update, shower coverage
will be reduced a bit in this region.
issued at 252 PM EDT Sat Jul 21 2018
Showers with a few embedded thunderstorms will remain prevalent into
early evening as low pressure settles southeast from southwest lower
Michigan into the Northern Ohio valley and moisture continues to
funnel northwest into the area within broad southeasterly flow
around this cyclonic circulation. While the chance of showers (and
isolated thunder) persists into the overnight hours, coverage and
generally intensity will decrease substantially with the loss of
diurnal late day heating. With the continued influx of moist low
level air during the overnight, low temperatures will remain mild in
the mid to upper 60s.
Shower chances will have to be increased to some degree on Sunday as
secondary low pressure wraps back west northwest towards the region
from the Delaware-Maryland-Virginia to near Lake Huron as the circulation of the
current low pressure center settles southeast of the Ohio River.
Model solutions remain widely divergent as to the exact amount of
moisture that will make it back this far west, but scattered shower
with isolated thunder seems a pretty good bet, particularly over the
northern half of the forecast area where lift/forcing from this
system will be strongest. Will also decrease temperatures given the
expectation of more overcast conditions.
Isolated showers will be possible again on Monday as this second low
stalls and dissipates in the vicinity. Temperatures will remain very
pleasant for late July given the mostly cloudy skies that should
remain in place with this system. Highs will range in the upper 70s
to lower 80s across the forecast area.
The extended forecast still remains in low confidence in chance of
precipitation terms. Weak ridging still looks to hang around,
however a trough axis is also forecasted to be close by. The area
is forecasted to stay mostly dry through the week, with only some
slight chances for showers. Tuesday through Thursday are expected
to be the warmest as highs warm up into the mid to upper 80s.
Broad low pressure will drift southeastward into the Northern Ohio
River Valley from tonight into Sunday. Unsettled conditions will
continue into tonight across most of the local waters with periodic
showers and isolated thunderstorms. However, coverage will decrease
with the loss of daytime heating. A second low pressure system will
track back northwest to near Lake Huron on Sunday, renewing the
chance of showers
Meanwhile, will cancel small craft advisories for the Lake Huron
nearshore waters with the afternoon update as gusts have dropped to
20 knots or less and waves remain below advisory criterion. There is
a chance that wind gusts and waves will warrant a Small Craft
Advisory over Western Lake Erie on Sunday. However, the forecast
remains just shy so will forgo an advisory at this time, especially
given the short duration of even marginal advisory conditions.
Lake St Clair...none.
Michigan waters of Lake Erie...none.