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Area Forecast Discussion (AFD)

Issued by Marquette, MI (MQT)

FXUS63 KMQT 221901

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

.SHORT TERM...(Today and tonight)
Issued at 417 AM EDT THU AUG 22 2019


Chilly predawn temperatures were observed inland from Lake Superior, 
as lows dropped into the 40s for many locations. Closer to the big 
lake, northerly flow coming onshore kept lows in the 50s and 
lower 60s for most locations. Satellite trends this morning show mid-
level clouds spreading to the southeast as another shortwave digs 
south towards the region. However, much of the Upper Peninsula 
remained cloud-free this morning, outside of the west. 

Today will be cooler compared to yesterday, with predominately 
northerly wind across the area. Clouds currently off to our north 
and west will gradually work into the area, and increase in 
coverage as diurnal heat and cold air aloft favor the development of 
stratocu later today. Cloud cover looks more widespread across the 
west half of Upper Michigan, where diurnal heating will allow for 
local destabilization within the boundary layer. The destabilization 
across the west and central this afternoon does look to favor the 
development of diurnally driven rain showers. Confidence isn't high 
in regards to how widespread these rain showers will get, but given 
the cold air aloft and a narrow pocket of unstable air towards the 
top of the boundary layer, certainly looks like a day for convective 
rain showers. Out east, northerly flow off of Lake Superior 
funneling down into Lake Michigan should keep conditions 
more stable, with less clouds. These stable conditions will inhibit 
the development of afternoon showers. However, out east, winds off 
of Lake Superior, and remnant stronger winds aloft will make for 
gustier winds at times late this morning and afternoon. The 
lingering dry conditions across the area, but cooler temperature are 
expected to keep RHs in the 40-55% range, locally driest across the 
southern parts of Upper Michigan across the south central and east, 
where downsloping northerly winds help dry things out further.

Tonight, high pressure starts to drop south into the western parts 
of Upper Michigan. This increased subsidence and locally veering of 
the winds across the interior parts of Upper Michigan does look like 
it will favor clearing skies. Given the already dry air mass 
expected to be in place, with ample radiational cooling and 
decoupling of the nocturnal boundary layer, overnight lows look to 
tank into the low 30s to around 40 inland from the Great Lakes. The 
areas across the interior west certainly look to be the cold spots 
Friday morning, meaning we could see some early-season frost 
develop. Using the Model Certainty Tool this morning, it appears 
that the current forecast lows fall right around the 25th 
percentile, so towards the lower end of the distribution among the 
model guidance. That being said, will let the day shift re-evaluate 
later today as to whether or not a frost advisory will be needed.

.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 18Z TAFS through 18Z Friday afternoon)
Issued at 125 PM EDT THU AUG 22 2019

Onshore flow continues to bring clouds to all TAF sites, but 
ceilings have remained well within VFR range. A few lingering light 
rain showers may affect KSAW this afternoon but that threat should 
end after 19Z. North winds will relax and become variable overnight. 
A few models continue to point towards the potential for fog 
development tonight, which would be most likely at KIWD but possible 
at KSAW as well. With relatively dry air remaining in place aloft, 
this is not a slam dunk but worth mentioning in the TAF given fog 
development occurred the last two nights at KIWD. Cloud development 
will return tomorrow morning at KSAW under conditions similar to 
today, and another brief shower will be possible there. At this 
time, it appears ceiling heights would remain VFR but could approach 
MVFR thresholds.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 417 AM EDT THU AUG 22 2019

Northerly winds between 10 and 20 knots are expected today. The 
strongest winds are expected to be 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. High 
pressure then takes over for the end of the week into the first 
half of the weekend, reducing winds to speeds below 15 knots. 
Towards the end of the weekend, high pressure moves east of the 
region, and southerly flow will start to ramp up across the lake, 
with winds 15 to 20 knots Saturday night through Monday. Late in the 
day Monday through Monday night, south winds over the east half of 
the lake could gust upwards of 30 knots ahead of an approaching 
front from the west.

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


SHORT TERM...Ritzman