Area Forecast Discussion

FXUS63 KMQT 171218

Area Forecast Discussion
National Weather Service Marquette MI
718 AM EST Sun Dec 17 2017

.SHORT TERM...(Today and tonight)
Issued at 417 AM EST SUN DEC 17 2017

WV imagery and RAP analysis indicated a wnw wind flow across the 
northern CONUS into the Upper Great Lakes with a shortwave trough 
upstream from southern Manitoba into the Northern Plains. At the sfc 
ridging from high pressure centered over eastern Ontario was keeping 
conditions dry over Upper Michigan into the early morning hours. 
Much cooler air advecting in from sfc high centered over Ontario has 
resulted in sub-zero min temps over eastern Upper Mi early this 
morning. Across the rest of the U.P weak warm advection and cloud 
cover has kept readings more generally in the teens to lower 20s. 

Today into Tonight, with marginal moisture to -10C for ice nuclei, 
and weak isentropic ascent, freezing drizzle could mix with snow 
over south central counties this morning and then spread into north 
central and eastern counties this afternoon and evening as 
isentropic ascent increases ahead of the approaching shortwave from 
the Northern Plains. Given how light pcpn is expected to be, impacts 
if any should be minimal. Even with considerable cloud cover, WAA 
will push high temps into the mid 20s to lower 30s today.

As the shortwave passes east later this evening, weakening 
isentropic ascent will allow any lingering light mixed pcpn to 
dissipate. There could be some breaks in cloud cover into west and 
north central Upper Mi later tonight with subsidence behind the 
shortwave.  Expect min temps to generally range from the teens 
inland to the lower 20s closer to the Great Lakes shorelines.

.LONG TERM...(Monday through Saturday)
Issued at 417 AM EST SUN DEC 17 2017

A couple shortwaves will move near the area Mon night into Tue 
night. As the first passes, a mix of rain and snow is forecast over 
northern portions of Upper MI, with the greatest rain chances being 
along the shorelines and snow chances over the higher terrain. 
Colder air moves in Tue, bringing an increase in lake effect precip 
and a quick change over to all snow. Light to occasionally moderate 
LES will then continue through Tue night. Gusty winds near Lake 
Superior will lead to blowing snow Tue and Tue night. Overall not 
expecting real significant impacts as snowfall amounts will not be 
that great. Will have to monitor things and refine precip amounts.

Lots of model disagreement/uncertainty for the last half of the 
week. Looks like we could get a quick possibly advisory level snow 
late Wed into early Thu as WAA forces snow ahead of Plains low. 
Evolution of that system is quite uncertain but at least models 
agree in moving it somewhere to our SE. Could be a good track for 
snowfall over all or portions of the area, but that will have to be 
monitored. Right now, doesn't look like a real strong system so 
should be a fairly common synoptic event for areas impacted.

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 704 AM EST SUN DEC 17 2017

MVFR conditions will continue for most of this forecast period at 
all sites as a moist south to southwest low level flow develops
across Upper Michigan. KIWD and KSAW could even see temporary IFR

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 417 AM EST SUN DEC 17 2017

Southwesterly winds will increase to 20 to 30 knots Monday over the 
west and north central portions of Lake Superior possibly reaching 
gales late Mon afternoon and evening before veering to northwesterly 
gales to 35-40 knots late Mon night into Tue night. With increasing 
wave heights and colder air temperatures, freezing spray is possible 
Tuesday night into Wednesday.

Upper Michigan...
Lake Superior...
Lake Michigan...