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Area Forecast Discussion (AFD)

Issued by Marquette, MI (MQT)

FXUS63 KMQT 251830

Area Forecast Discussion
National Weather Service Marquette MI
230 PM EDT Sun Aug 25 2019

.SHORT TERM...(This evening through Monday)
Issued at 230 PM EDT SUN AUG 25 2019

Upper air pattern consists of a 500 mb ridge across the upper Great 
Lakes with a shortwave over the plains this morning. This shortwave 
heads east and affects the upper Great Lakes on Mon. Nam shows some 
850-500 mb q-vector convergence and deeper moisture on Mon. Dry for 
tonight, then pops move into the area on Mon. Overall, did not make 
too many changes to the going forecast except slowed down the 
progression of pops eastward tonight into Mon.

.LONG TERM...(Monday through Saturday)
Issued at 407 AM EDT SUN AUG 25 2019

The main focus of the long-term period remains the impressive system 
(by August standards) that will slowly move across the Upper Great 
Lakes tomorrow through Wednesday, bringing with it a round of heavy 
rain tomorrow afternoon and night and gusty winds, both tomorrow 
night and then again Tuesday into Wednesday. Another much weaker 
short wave may keep showers in the forecast through the end of the 
week, but at the moment Labor Day Weekend is looking dry.

By tomorrow morning, a fairly strong upper-level jet will be aimed 
into the Northern Plains, energizing a short wave that will dig into 
Minnesota by tomorrow afternoon. In the low to mid levels, strong 
southerly moisture transport overcomes the bone dry air mass we've 
had aloft the past few days. Just how quickly remains a question, 
however. Models this morning continue to slow down precip arrival, 
with most of the daylight hours being dry for generally the eastern 
half of the U.P., and showers only moving into the west in the 
afternoon. Once they do move in, however, they will be capable of 
producing locally heavy rain given PWATs up around 1.75" and at 
least a little bit of elevated CAPE. Have just a slight chance of 
thunder in for tomorrow afternoon and night as well but this would 
be an isolated rumble or two with any elevated convection, not any 
sort of strong or severe surface-based storms. As the system's 35-50 
knot LLJ moves overhead, will see gusty winds as well, even into the 
overnight, with 20-30 mph southerly gusts likely on land and gusts 
perhaps approaching gale force over the eastern arm of Lake Superior 
for a brief period.

Models diverge slightly Tuesday into Wednesday on the exact track 
and strength of the surface low, but the sensible weather is about 
the same for most. The GFS (and CMC) keep a strong low close by, 
near or just north of Thunder Bay, while the EC and NAM drive it 
farther north into northwestern Ontario. With the GFS solution, 
westerly gales would be a good bet Wednesday over much of Superior. 
The EC and NAM are less impressive but even they could still support 
marginal gale gusts, especially on the western arm. Back on land, 
with cool air aloft and some surface heating, could be a few 
scattered showers in the cyclonic curvature and perhaps an isolated 
low-topped thunderstorm or two on Tuesday. With the parent upper low 
taking its time moving out Wednesday, the clouds and showers 
continue, though without the thunder chance. Could still be cool 
enough for some lake-effect rain showers/enhancement to any synoptic 
showers, but at the moment the surface wind field (W or even WSW) 
would really only favor the Keweenaw. Knocked highs down a few 
degrees Wed. over NBM init given the unusually cool air aloft and 
clouds and showers around. Right now have everyone reaching at least 
60 though over the west that may end up being a struggle.

A ridge builds over the intermountain west Thursday and finally 
kicks this upper low out, leading to a nice and hopefully dry day 
Thursday. Models continue to resolve a much weaker short wave late 
Thursday night or Friday so have introduced slight chance POPs then. 
But the first look at Labor Day is dry and cool with high pressure 
in control.

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1233 PM EDT SUN AUG 25 2019

VFR conditions are expected through the forecast period for all 
sites. However, there is a hint that an MVFR could deck could sneak 
into KSAW towards the end of the period. Winds could be gusty at all 
sites Mon morning. Rain will be moving into IWD towards the end of 
the forecast period.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 230 PM EDT SUN AUG 25 2019

The wind will remain at or below 20 knots into Mon afternoon and 
then increase to 20 to 30 knots Monday night. There could be some 
southeast gale gusts to 35 knots Mon night across central and 
eastern Lake Superior. 20 to 30 knot winds will then persist across 
all of Lake Superior Tue through Wed with a cold front moving 
through the area. Winds then diminish to 15 to 25 knots Thu into Fri.

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