Scientific Forecaster Discussion
fxus63 kdtx 190731
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
331 am EDT Thu Sep 19 2019
Modest convective activity ongoing within the upstream corridor of
instability draped from the northern Great Lakes into the eastern
Great Plains early this morning. This action will struggle to
survive into the daylight hours while any potentially organized
convection remains tied to the instability gradient over the Midwest
anyway. Thus, with southeasterly return flow continuing to dominate
locally, expect little change from yesterday aside from the
potential for a partial coverage of high cirrus debris originating
invof the upper MS River Valley early morning. Highs once again near
Low to mid 60s dewpoints over the lower Ohio Valley will
begin creeping into the area tonight into the weekend as the
prevailing pattern remains generally unchanged and light moisture
advection continues. This will place a rising a floor on overnight
lows each night while modest afternoon mugginess typical of late
September accompanies continued daytime highs in the 80s. Only item
of interest in the near term is potential for a weak mesoscale convective vortex to trigger
isolated/scattered showers or T-storms on Friday as low-level
instability builds. 4-km NAM and nmm are aggressive in their
depictions of this scenario, but analysis of forecast soundings
reveals Stout capping centered around 850mb and what appears to be
erroneous triggering of convective quantitative precipitation forecast. Nonetheless, there is a some
consensus among the various nwp, including the ECMWF, that a
convectively induced shortwave will propagate along the periphery of
the resident mid-level ridge potentially grazing the forecast area
Friday afternoon. A stronger outcome may therefore warrant an upward
revision to pops into the schc category, but maintained a dry
forecast for now. More likely scenario is simply a greater coverage
of lower-based diurnal cu than previous days, especially over
southern and eastern areas.
As the western US longwave trough runs its course and energy
releases into the central Continental U.S. And northwest Ontario, subsequent
deamplification of the downstream ridge will allow the instability
gradient to be forced through lower Michigan Sunday into Sunday
night warranting inclusion of showers/tstorms. High temps thereafter
settle closer to climatological average values.
Ridge of high pressure anchored over the mid Atlantic will maintain
benign marine weather through the end of the week. Southeast winds
will veer to the south today, prevailing from this direction to
finish the week.
issued at 1153 PM EDT Wed Sep 18 2019
A cold front in the Midwest sends only high clouds over lower
Michigan tonight as it reaches western Upper Michigan and dissipates
through Thursday. Dry/VFR conditions are also maintained by high
pressure centered over Quebec that continues to extend westward into
the central Great Lakes tonight. The high becomes centered over the
New England states and maintains control of aviation weather in Southeast
Michigan through Thursday evening.
Dtw threshold probabilities...
Lake St Clair...none.
Michigan waters of Lake Erie...none.