We will continue our string of nice days today and tomorrow with highs in the low 80s both days before the clouds begin to move in for the weekend and the chance of rain increases. Yesterday our high was 80° and the low 56°. Sunrise today was 6:54, sunset tonight will be 8:42.
-- Mainly dry weather continuing through Fri -- Latest GOES IR imagery reveals patchy cirrus over the CWA, with mainly clear skies otherwise. With weak low-level winds provided by a surface ridge axis positioned over the region, strong radiational cooling will continue through daybreak. Patchy fog can be expected this morning, particularly in low-lying areas and in places where the ground has been wetted from recent rainfall. Any fog should lift by 10 AM as boundary-layer mixing develops after sunrise. The persistent mid/upper-level cutoff low over New England will begin to lift northeastward today, resulting in modest midlevel height rises/warming over the Great Lakes region. Daytime heating, in conjunction with lingering boundary-layer moisture, should again yield MLCAPE of around 400-800 J/kg today. Cannot rule-out a few isolated showers today, mainly inland, but recent deterministic CAM guidance shows no compelling signal for showers today. -- Periods of rain this weekend -- A well-defined shortwave trough / vort max is currently evident in water-vapor imagery near southern Manitoba / ND. This feature will continue to dig southeastward today, then likely evolve into a compact, closed midlevel low tonight. At the surface, cyclogenesis will commence this afternoon, with a ~1008-mb surface low expected over central MN by midday Fri. Global ensemble (EPS and GEFS) means both indicate that this system will become nearly vertically stacked by Fri night, then move slowly southeastward, reaching the vicinity of northern OH by Mon afternoon. Showers and t-storms are possible on Sat, with greater coverage of precip expected on Sat night into Sun. Precip production will be aided by forcing for ascent in advance of the approaching deep-layer low amid PW approaching 1.5 inches by Sat night. Guidance continues to suggest that surface-based instability may be present on Sun, with MLCAPE of 500-1000 J/kg possible in the southern CWA, but weak effective bulk shear will limit storm organization. However, locally heavy rainfall is possible on Sun, given that forecast profiles exhibit deep moisture, a tall/skinny CAPE distribution, and a deep (~15 kft) warm-cloud layer--factors that support efficient warm-rain processes. Moreover, weak cloud-layer winds in the vicinity of the stacked low on Sun will favor slow storm motion, further contributing to a risk of locally heavy rain. -- Mon and beyond -- The EPS mean has trended a bit faster with the progression of the midlevel low/trough on Mon, but chance PoPs are certainly justified on Mon as this system gradually moves eastward. The deterministic ECMWF suggests that another shortwave trough may approach on Tue, but this scenario is uncertain.