National Weather Service United States Department of Commerce

Forecast commentary -

Active forecast for the next week as a series of waves continues to eject out of the longwave trough
over the west coast and up through the Great Lakes region. Seemingly each time the main wave gets
ejected, it is quickly back filled by the next wave dropping into the trough. Thus each time it
looks like the pattern will break for a while, it quickly returns to a positively tilted trough.
Broad upper ridge over the se Contiguous U.S. will meander about through this process, largely
keeping the main baroclinic zone and upper level jet near or over the state. Models want to largely
keep se Michigan on the warm side of this baroclinic zone though some of the shortwaves will brush
us with cooler air on occasion. Overall temps look to hover a few degrees above normal through the
end of the month.

The flood watch will continue through this afternoon as the rain continues to fall. Most locations
to this point have received around 1.5 to 2 inches of rain. This has lead to several area rivers
reaching flood stage already with a few others forecast to reach flood stage over the next day or
so. A cold front over mid Michigan will drop through se Michigan by this afternoon bringing an end
to the rain but not before another 0.25 ( Saginaw valley ) to 1 inch ( Ohio border ) of rain falls.
A very healthy fetch of moisture seen on water vapor extends from the Gulf of Mexico up into
Michigan continuing to feed this dynamic pattern producing all the rain. In addition to the frontal
forcing in place, the next mid level shortwave riding along the front is entering southern Michigan
at press time which will bring another window of widespread moderate showers to the area. Once this
wave lifts through the front won't have much residency time left before exiting the area itself
around noon. All in all it still looks like a wide swath of 2-3 inches of total rainfall will occur
across the region with some locally higher amounts possible.

Strong area of high pressure will spread across the central Great Lakes this evening and overnight
bringing a stretch of dry and quiet weather. It will also be cooler as high temps top out in the
upper 30s Thursday. There is a slight chance of some light snow Thursday morning south of i94 as the
next shortwave riding up the frontal zone tries to bleed across the mi/oh border. With the dry air
in place with the strong surface high and northerly flow, it will be hard for anything to make it
this far north. Will leave a low PoP in for the moment to acknowledge the possibility.

Next opportunity for precip will come late Thursday night into Friday as the next system ejects out
of the trough through the region. As with this current system, there appears to be some phasing of
northern and southern stream waves which will lead to another feed of gulf moisture into the system
though not as moist as this current airmass. A warm front will lift up through the area early Friday
which model thermal profile want to favor a wintry mix north of the front before the warmer air
surges in turning it to all rain through the afternoon. After a short period of high pressure Friday
night, yet another system will lift through the region Saturday and Saturday night bringing mostly
rain once again.

. . posted at 335 AM EST Wed Feb 21 2018