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Area Forecast Discussion (AFD)

Issued by Marquette, MI (MQT)

FXUS63 KMQT 222348

Area Forecast Discussion
National Weather Service Marquette MI
748 PM EDT Thu Aug 22 2019

.SHORT TERM...(This evening through Friday)
Issued at 314 PM EDT THU AUG 22 2019

The coldest air of the season today has brought along cloudiness 
over most of the western and central Upper Peninsula, and with 850 
mb temperatures around 4C, some lake effect/enhanced rain showers 
aided by diurnally driven instability were able to form across north 
central portions of the area today. Temperatures have climbed into 
the 60s for much of the area, but rain cooled air made it quite 
chilly for this time of year earlier this afternoon with both MQT 
and KSAW in the mid 50s at 17Z. Isolated drizzle and sprinkles will 
continue to slowly push south this afternoon and should end with the 
loss of daytime heating this evening. 

Tonight, the story will be just how low temperatures can drop over 
the interior west. Model soundings continue to indicate deep 
subsidence and thus dry air aloft that will allow for efficient 
radiational cooling IF low clouds are able to clear out this evening 
and the boundary layer is able to fully decouple. If so, low 
temperatures well into the 30s are expected over the interior west, 
and a couple of the usual cold spots such as Baraga Plains, Amasa, 
or Stambaugh could briefly drop below freezing. But, a gander at the 
ModelCertainty tool shows lows in the 32-33 degree range along the 
Iron/Baraga County line are about the 25th percentile of all 
guidance and the 50th percentile of bias corrected guidance. Current 
dew points are in the mid to upper 40s, putting a notch in the 
column against widespread frost development. In all, patchy frost 
will be possible, but confidence is not high enough at this time to 
warrant an advisory product. An SPS will be issued to cover this 
threat instead. Patchy fog is also expected tonight across portions 
of the inland UP. 

Friday will remain seasonally cool and northerly flow will take on 
more of a northeasterly component. Temperatures during the day will 
top out in the low to mid 60s along Lake Superior and should reach 
the low 70s south, though it will be a struggle as some lake 
effect/diurnally driven clouds are again expected. Once again, some 
light shower activity similar to todays will be possible over the 
north central and perhaps the eastern UP as well.

.LONG TERM...(Friday night through Thursday)
Issued at 301 PM EDT THU AUG 22 2019

Upper air pattern consists of a 500 mb trough in the northern and 
central Rockies, a ridge over the plains into the upper Great Lakes 
and a trough in the lower Great Lakes region and New England 00z 
Sat. The ridge remains in the upper Great Lakes Fri night into Sat 
as the trough moves eastward to the northern plains. The trough then 
moves into the upper Great Lakes on Sun. Looks quiet and dry for 
this forecast with cooler than normal temperatures. Could even be 
some patchy frost Fri night in interior sections.

In the extended, the GFS and ECMWF show a 500 mb ridge across the 
southern half of the U.S. extending up into the ern U.S. with a 
trough in the northern and central plains 12z Mon. This trough has a 
cold front in MN 12z Mon. The trough moves into the Great Lakes 
region 12z Tue and a sfc cold front moves through the area then. 
More troughing then comes into the area on Wed into Thu. Another 
cold front moves through the area Wed night into Thu.

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 739 PM EDT THU AUG 22 2019

North-northeast winds will relax and become variable overnight. 
A few models continue to point towards the potential for fog 
development tonight over the western interior, which would be most 
likely at KIWD. But this is not a slam dunk as models hint there
could be a light se downsloping flow developing at KIWD later
tonight, so left mention out of TAF for now. Cloud development 
will return tomorrow morning at KSAW under conditions similar to 
today, but shallow expected cloud depth should prohibit showers.  
At this time, it appears ceiling heights would remain VFR but 
could approach MVFR thresholds briefly. 

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 314 PM EDT THU AUG 22 2019

Northerly winds generally less than 15 knots are expected tonight 
and much of tomorrow. The strongest winds are expected to return 
tomorrow afternoon and evening across the south half of the lake 
near the shorelines during the day, especially with some funneling 
into the Duluth Harbor and Whitefish Bay in the afternoon where some 
20 knot gusts are expected. Otherwise, high pressure will keep winds 
to speeds below 15 knots until Saturday night. As high pressure 
moves east of the region, southerly flow will start to ramp up 
across the lake, with winds 15 to 20 knots Saturday night through 
Monday. Sunday night, gusts could approach 25 knots over far eastern 
Lake Superior. Late in the day Monday through Monday night, south 
winds over much of the east half of the lake could gust upwards of 
25-30 knots ahead of an approaching front from the west.

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