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Area Forecast Discussion (AFD)

Issued by Marquette, MI (MQT)

FXUS63 KMQT 231800

Area Forecast Discussion
National Weather Service Marquette MI
200 PM EDT Mon Sep 23 2019

.SHORT TERM...(This evening through Tuesday)
Issued at 200 PM EDT MON SEP 23 2019

Upper air pattern consists of a 500 mb trough over the upper Great 
Lakes this morning with a shortwave over the Canadian Rockies. The 
shortwave moves into the northern plains on Tue. Shortwave ridging 
moves into the upper Great Lakes tonight. Showers will come to an 
end this afternoon, then will be quiet for the rest of the forecast 
period. Will be some patchy fog late tonight. Overall, did not make 
too many changes to the going forecast.

.LONG TERM...(Tuesday through Sunday)
Issued at 410 AM EDT MON SEP 23 2019

It's an active weather week ahead with multiple systems to watch. But 
first, Tuesday, which is likely the nicest day this week. There will 
probably be some fog around tomorrow morning, especially central and 
east where the majority of the rain falls today. But that'll mix out 
quickly after sunrise. With ridging overhead and 850 mb temps up to 
about 11-12 C it looks sunny and warm, with highs in the low to mid 
70s. There will be some decently dry air aloft and somewhat deep 
mixing which could drop dew points over the interior. Thankfully, 
however, last week's high dew points and today's rainfall means the 
ground vegetation should remain plenty wet to prevent fire weather 
concerns. The deep mixing to about 850 mb could also allow for some 
15-20 mph southerly gusts during the afternoon.

By Tuesday night a cold front will be approaching from the 
northwest, and a seasonably strong upper level jet will be diving 
into the Northern Plains and helping to spin up a secondary surface 
cyclone along the front in northern Ontario. Models deepen this low 
to about 990 mb Tuesday night and then down into the mid 980s 
Wednesday morning. The lack of a strong anticyclone to the south 
will keep isobars baggy and reduce the pressure gradient (and thus 
strong wind threat) somewhat - less than one might normally think 
with a 980s mb low this time of year, anyway. But it will still be 
enough for southerly gusts around 20 mph to continue overnight on 
land (maybe 25-30 mph in the downslope areas around MQT and Grand 
Marais) and 25-30 kt gusts on Lake Michigan and eastern Lake 
Superior. As that front marches in from the west, precip overspreads 
the area. Models all suggest about 1000 J/kg MUCAPE, so there could 
be some embedded elevated thunderstorms as well, but nothing strong 
or severe. 

The stronger forced frontal precip clears the area to the 
east by midday Wednesday, though with cold mid levels and plenty of 
lingering moisture, clouds and some light scattered wrap-around 
showers are likely through Wednesday night. There's a brief window 
for some lake-effect or at least lake-enhanced showers/drizzle over 
the west and keweenaw late Wednesday night/early Thursday morning. 
The GFS continues to be colder aloft (and thus more supportive of 
these showers) but if anything the deterministic run is a slight 
warm outlier to its ensemble so drew in some chance POPs in these 
areas. Mid-level height rises and drying bring all of that to an end 
Thursday morning. Still looking pretty cool Wednesday and Thursday 
behind the front. With the aforementioned clouds and showers around 
Wednesday, and therefore expecting less mixing, knocked high temps 
down about 2-4 F from NBM init. For Thursday the question is how 
much sunshine and how quickly? Even though the coolest air aloft 
passes overhead Thursday morning, more sunshine and deeper mixing 
may offset that so that Thursday's highs are similar to Wednesday's -
 upper 50s to around 60 for most.

No rest for the weary as the next system moves through Friday. 
Pretty good model consensus here for a decent rain region-wide but 
models have trended away from the more extreme, 1"+ solutions some 
had over the past few days. The major models all bring high pressure 
in for the weekend which at the moments looks dry and cool with 
temps right about where they should be for late September.

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1234 PM EDT MON SEP 23 2019

Conditions will continue to improve this afternoon at SAW as dry air 
moves in. Otherwise, VFR conditions are expected at all sites 
through the forecast period.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 200 PM EDT MON SEP 23 2019

Winds will generally stay in 10 to 20 knot range this afternoon 
today before going light tonight. Southerly winds increase to 15 to 
25 knots Tue night (greatest east half) ahead of incoming cold front 
and then up to 30 knots out of the west on Wed in the wake of the 
front. Winds will increase again to at least 30 knots on Fri as 
another frontal system moves through the area and could see some 
gale gusts then. Fri will be the strongest forecast winds for this 
forecast period on Lake Superior.

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