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Area Forecast Discussion (AFD)

Issued by Marquette, MI (MQT)

FXUS63 KMQT 230809

Area Forecast Discussion
National Weather Service Marquette MI
409 AM EDT Fri Aug 23 2019

.SHORT TERM...(Today and tonight)
Issued at 409 AM EDT FRI AUG 23 2019

Much of Upper Michigan saw cloud-free conditions during the 
overnight hours, allowing temperatures to tank into the upper 30s 
and low to mid 40s early this morning. Temperatures are expected to 
further cool a few more degrees until sunrise, so maintain mentions 
of frost across the interior west, and continued the inherited SPS 
to highlight the potential through early this morning. Near the 
Great Lakes, land-breezes and maritime influences helped keep 
temperatures in the 50s and 60s. Nighttime Microphysics satellite 
data does show some hints of patchy fog inland from the Great Lakes 
as well. 

Today, high pressure centered just north of Lake Superior will 
gradually drop south through this afternoon. Mid-level clouds 
southeast east of surface ridging have already started to work 
southeast over the tip of the Keweenaw and northeast parts of Upper 
Michigan. This cloud cover is expected to continue its southeastward 
progression throughout the day, with additional widespread diurnally 
driven cloud development as cold air aloft lingers over the area. 
There is a slight chance again for a few light rain showers, 
especially across the north central this morning, and then out east 
this afternoon. 

Temperatures will be trick today. Onshore flow along the Lake 
Superior shoreline will become reinforced this afternoon with an 
enhanced pressure gradient coming onshore with high pressure moving 
over Lake Superior. Lingering cold air advection aloft will also 
impact the east half of Upper Michigan during peak diurnal heating. 
Therefore, expect the north central and east parts of Upper Michigan 
near Lake Superior to be the cool spots today, with low to mid 60s. 
Across the south central and east near Lake Michigan, downsloping 
northerly winds will aid in boosting temperatures into the upper 60s 
to perhaps around 70 degrees. Out west, warm air advection will 
start to move in, which should help keep cloud cover more scattered 
and aid in afternoon highs climbing to near 70. As for winds today, 
the above mentioned enhanced pressure gradient this afternoon will 
allow for a window of breezy northeast to north winds across the 
central and east, respectively. Vertical shear profiles do not show 
much in the way of momentum to tap into with diurnal heating/mixing, 
so think wind gust will be more on the sporadic side opposed to 

Tonight high pressure will continue to exit Lake Superior and move 
eastward into Ontario. This will push any lingering mid-level 
moisture east of the region and allow for diurnal clouds to dissipate 
after sunset. This surface pattern will favor easterly, downsloping 
wind across eastern Upper Michigan, light and variable winds across 
the central, and southerly winds out west. Winds remaining light, 
skies clearing, and a strong subsidence inversion remaining in place 
we make for another cold night inland from the Great Lakes. The 
coldest spots look to be across the interior west, central, and far 
eastern Upper Michigan, where pre-dawn temperatures will range from 
the mid 30s to near 40 degrees. Not out of the question that we 
could see more patchy frost, especially closer to the surface ridge 
axis. With overnight lows expected to drop below the crossover 
temperature in spots, it is not out of the question that we could 
see patchy fog develop across the interior.

.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 06Z TAFS through 06Z Friday night)
Issued at 119 AM EDT FRI AUG 23 2019

Some patchy fog is expected at KIWD overnight and possibly at KSAW 
as well with occasional MVFR conditions. Diurnal cloud development 
will return tomorrow morning at KSAW under conditions similar to 
Thursday, but shallow cloud depth should prohibit any showers.  At 
this time, it appears ceiling heights would remain VFR but could 
briefly approach MVFR thresholds.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 409 AM EDT FRI AUG 23 2019

Northerly winds generally less than 15 knots are expected today as 
high pressure sinks south across the lake. Locally higher winds, up 
to 20 knots are expected to funnel into Whitefish Bay and the Duluth 
Harbor later this afternoon and evening. Otherwise, high pressure 
will keep winds to speeds below 15 knots through Saturday. Saturday 
night, high pressure continues to move east of the region and 
southerly flow starts to increase to between 15 to 20 knots. Sunday 
through Monday, the surface pressure gradient between the departing 
high and an advance cold front from the west will keep southerly 
flow between 15 and 25 knots over the lake. As the front starts to 
push east across the lake late Monday into Tuesday, across far 
eastern parts of the lake southerly flow may increase to 30 knots. 
As the front clears the lake Tuesday, the main area of low pressure 
will remain north of the lake keeping an enhanced pressure gradient 
across the lake through at least Wednesday. West-southwest to 
westerly winds between 20 and 30 knots will persist during this time 

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


SHORT TERM...Ritzman