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Area Forecast Discussion (AFD)

Issued by Marquette, MI (MQT)

FXUS63 KMQT 171822

Area Forecast Discussion
National Weather Service Marquette MI
222 PM EDT Sat Aug 17 2019

.SHORT TERM...(Today and tonight)
Issued at 405 AM EDT SAT AUG 17 2019

Patchy fog has been dense at times across the west half of Upper 
Michigan early this morning, especially so across the Keweenaw 
Peninsula and central parts of the area. While surface winds 
remained light, fog has been intermittently dense likely due to the 
residual turbulent boundary layer winds. Once the sun comes up later 
this morning, visibilities could locally worsen before starting to 
improve through the mid-morning hours. Did opt to hang onto the 
inherited Special Weather Statement to draw attention to the fog and 
its associated hazards. 

Today, a mid-level shortwave will lift northeast across the Upper 
Great Lakes. The combination of increased sunshine today and warm 
air advection lifting into the region ahead of shortwave energy, 
will favor warmer temperatures UP-wide. Gradient winds will 
predominantly be out of the south-southwest today, between 5 and 10 
mph. These weaker gradient winds and increased sunshine will allow 
lake breezes to develop on both Lakes Michigan and Superior. Expect 
the south-southwest flow to keep the Lake Superior breeze confined 
close to the shoreline across the north-central. Over across the 
north end of Lake Michigan, the lake breeze boundaries will initially 
start off along the shoreline and then will gradually lift north 
throughout the day. Forecast soundings do show some weak capping 
aloft, but a few high-res models do show some isolated to scattered 
showers developing along the lake breeze boundaries, especially area 
with enhanced convergence due to terrain or interacting boundaries. 
Therefore, did introduce a few areas of isolated showers today. 

Tonight, once we lose isolated any ongoing showers or diurnally 
driven cumulus will dissipate. Tonight should remain quiet across 
the UP, with mild conditions as south winds persist overnight ahead 
of another approaching front from the west. Models have trended 
slower with this next wave coming in tonight, so did back off on the 
PoPs quite a bit. Some patchy fog is possible north of Lake Michigan 
tonight, but given the turbulent boundary layer winds expected do 
not think we will see and dense fog.

.LONG TERM...(Sunday night through Saturday)
Issued at 222 PM EDT SAT AUG 17 2019

A relatively benign forecast is expected through the extended 
period, with realistic precipitation chances relegated to Sunday 
night, Tuesday afternoon and evening, and late Friday afternoon into 
the weekend, with ample uncertainty in the evolution of next 
weekends forecast. Otherwise, quick moving high pressure passing to 
our south will bring warm and dry conditions Monday through Tuesday 
morning, and returning high pressure combined with a mid-level low 
spinning across northeastern Canada will bring cooler, drier 
northwesterly flow for Wednesday and Thursday. Return flow will 
begin to warm things back up again Friday. 

Sunday night, an exiting trough axis/embedded shortwave will allow 
for lingering showers and weak thunderstorms over the eastern Upper 
Peninsula, but these should exit by around or just after midnight. A 
little patchy fog can't be ruled out over the interior, but winds 
may remain just enough to keep the PBL well mixed. Surface high 
pressure will then move into the region, skirting across Wisconsin 
during the day Monday. Decent low level mixing is expected and a 
relatively dry airmass will lead to 25-30+ degree dew point spreads. 
The dry air could locally lead to relative humidities dipping below 
30 percent, but winds will be light for all locations except the 
Keweenaw Peninsula where some afternoon gusts are possible out of 
the SW. Fire weather concerns would thus be limited to the far 
northwestern UP on Monday, and even then only if enough dry air 
mixes to the surface. 

We will remain under moderate SW flow on Tuesday, and inland 
temperatures will reach the low to mid 80s ahead of a trough and 
associated cold front that should kick off a few showers and storms 
Tuesday afternoon. Could eek out enough instability for a marginally 
severe thunderstorm Tuesday afternoon/evening over the inland west. 

As high pressure builds from the Plains to the Upper Mississippi 
Valley Wednesday, a strengthening pressure gradient over the Upper 
Great Lakes will lead to gusty NW winds and could reach small craft 
advisory criteria on Lake Superior. Some models indicate a second 
wave embedded in the flow around the Canadian low that may lead to an 
isolated shower on Thursday over the east half, but better precip 
chances should hold off until later on Friday and especially 
Saturday after the high exits to the east.

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 140 PM EDT SAT AUG 17 2019

VFR today into tonight will prevail at all three terminals, with a
frontal boundary approaching early tomorrow ushering in
showers/reduced ceilings, along with an increase in winds.
Thunderstorms may be possible at KIWD as instability moves into
western Upper Michigan by tomorrow morning, with some uncertainty
remaining in whether or not lightning will make it to KCMX and
KSAW. Look for southerly winds by Sunday morning to shift and
start to become more westerly with the boundary's approach toward
the end of this TAF period.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 405 AM EDT SAT AUG 17 2019

Satellite trends show some area of stratus and perhaps some fog over 
the lake early this morning. However, no ship observations appear to 
have reported any fog this morning. Expect fog to persist across 
parts of the lake, but it should be on a the move throughout the 
day. Not totally out of the question there could be some locally 
dense fog out there this morning. 

Winds will remain between 15 and 20 knots for the most part of the 
weekend. A brief area of high pressure will track east across the 
region, reducing the winds somewhat Monday/Tuesday. Then, a cold 
front, followed be a sharply cooler air mass look to arrive late 
Tuesday and linger across the region into Thursday. This cooler air 
mass working over the relatively warmer waters of the lake will 
create an unstable conditions and the potential for northwest winds 
20 to 25 knots, and increased wave heights especially funneling into 
Whitefish Bay.

Upper Michigan...
Lake Superior...
  Dense Fog Advisory until 8 PM EDT this evening for LSZ266.

Lake Michigan...


SHORT TERM...Ritzman