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Area Forecast Discussion (AFD)

Issued by Marquette, MI (MQT)

FXUS63 KMQT 211715

Area Forecast Discussion
National Weather Service Marquette MI
115 PM EDT Wed Aug 21 2019

.SHORT TERM...(Today and tonight)
Issued at 417 AM EDT WED AUG 21 2019

A few isolated showers brought a quick-burst of rainfall to a few 
locations as the cold front continued to push eastward overnight. 
Otherwise, conditions remained dry, with lingering cloud cover in 
the vicinity of the front and some pockets of fog out west. 
Shortwave energy progged to pivot across the region throughout the 
day today is currently digging south towards the Arrowhead of 
Minnesota. Today the main weather hazards will come from the gusty 
northwest winds, as unfavorable conditions develop for small crafts 
along parts of the eastern Lake Superior shoreline and a moderate 
swim risk develops east of Marquette later this afternoon. 

As the above mentioned shortwave traverses the Upper Great Lakes 
region today, increasing cold air advection and subsidence behind 
the shortwave will allow for gusty northwest winds to develop, 
primarily west to east across the Upper Peninsula throughout the 
day. As the colder air moves in, this will favor mixing upwards of 7-
8kft and tapping into 25 to 30 knot winds aloft. While much of Upper 
Michigan will see gusty winds develop, the northwest half and east 
halves of Upper Michigan look to see the strongest winds gusts, 
upwards of 25 to 30 mph. A few BUFKIT soundings show momentum 
transport values exceeding 30 mph, so it's not out of the question 
that winds could gust slightly higher in spots. Otherwise, the rest 
of Upper Michigan stands to see 20 to 25 mph wind gusts today. The 
increasing cold air advection throughout the day will keep day-time 
highs down in the mid to upper 60s for much of the area. Localized 
warming, due to northwesterly downsloping winds, is expected across 
the south central and east, near Lake Michigan, where temperatures 
will climb into the low to mid 70s. While a very dry air mass will 
be moving into the region today, cooler temperatures will help keep 
RHs in the 40 to 45% range inland from Lake Superior, reducing fire 
weather concerns.  

As the sunsets tonight, diurnally-driven gusty winds will relax as 
mixing diminishes and the boundary layer decouples nicely. Given the 
dry airmass that will be in place tonight, overnight lows are 
expected to get rather chilly inland from Lake Superior. Overnight 
lows look to bottom out in the low 40s across much of the interior, 
with perhaps a few locations seeing upper 30s. Closer to Lake 
Superior, northerly flow will keep temperatures locally warmer, into 
the 50s.

.LONG TERM...(Thursday through Tuesday)
Issued at 452 AM EDT WED AUG 21 2019

The coming days will bring a preview of fall as cool air pushes into 
the Upper Great Lakes. Frost in the interior of Upper MI certainly 
not out of the question Thu night, depending on cloud cover, and 
possibly Fri night as well. This cool pattern will be the result of 
mid-level ridging over the Rockies linking up with a positive height 
anomaly centered nnw of Hudson Bay. The amplifying ridge will force 
a trof currently extending from northern Quebec to Saskatchewan to 
dig se across the Great Lakes region today thru Fri. Then, as 
troffing pushes across western Canada late this week, the ridge will 
shift across the Great Lakes region over the weekend, resulting in 
temps rising back above normal. During next week, mean troffing will 
shift from western Canada toward central N America. With indications 
of a building ridge over far western Canada into AK, inline with 
ensemble trends over the last few days, there will probably be one 
or two additional surges of cool fall-like air into the Northern 
Plains and Upper Great Lakes during the period from the middle of 
next week to Labor Day. As for pcpn, pattern for the next several 
days will not be favorable for any meaningful pcpn. If there is any 
pcpn, it would only be some sprinkles/isold -shra Thu under thermal 
trof and weakly cyclonic flow. As the western Canada trof gradually 
shifts e, a series of shortwaves will be tracking off the N Pacific 
and into the trof. It's likely that it won't be until Mon that one 
of those shortwaves will progress far enough downstream to bring the 
next chc of shra to the fcst area. 

Beginning Thu, a shortwave will be dropping se across Upper MI 
during the morning. Passage will be uneventful. However, with 850mb 
temps falling to around 4C and water temps in the lee of the 
Keweenaw up to 18C, there could be isold -shra or sprinkles into 
Marquette County during the morning. With daytime heating, a few 
sprinkles may develop elsewhere in the interior of the w half of 
Upper MI. Otherwise, with 850mb thermal trof moving over the area, 
expect considerable stratocu development. High temps will only be in 
the 60s. Under northerly winds, waves on Lake Superior wil be high 
enough to lead a mdt swim risk along the beaches of Alger County, 
especially thru the morning hrs. 

Skies should generally clear out Thu night. If so, it will be a 
chilly night, especially across the interior w under arriving sfc 
high pres ridge and precipitable water falling to around 0.45 
inches/50pct of normal which will enhance radiational cooling. 
Favored the low side of guidance there. Expect min temps in the 32 
to 35F range with frost development. If it is a clear night, would 
not be surprised to see a few of the traditional cold spots fall to 
30F or lower. Temps will range up to 50s F along Lake Superior from 
the Keweenaw eastward. 

Sfc high pres will be over the fcst area on Fri. With 850mb thermal 
trof still lingering, will likely see quite a bit of stratocu 
development, but coverage should be less than Thu given slight 
moderation. Cloud cover Fri should be greater inland from Lake 
Superior over the e under lower 850mb temps in that area. Max temps 
will be a little higher on Fri compared to Thu, especially over the 
w where some waa begins. In general, expect high temps in the mid 
60s to 70F. 

Model trends over the last 2 days are clearly for a slower 
progression of the mid-level trof from western Canada with sharp 
ridging lingering longer over the Great Lake region. Thus, the 
weekend looks to be dry and warmer. High temps Sat/Sun will return 
to the 70s under mostly sunny skies, and with dwpts not rising any 
higher than the 50s F, it will be a pleasant late summer weekend for 
Upper MI. Will turn a bit breezy on Sun under tightening pres 
gradient btwn high pres to the e and cold front moving out across 
the Plains.  

Progression of shortwaves thru the western trof will probably shift 
far enough e to push cold front toward Upper MI Mon with passage Mon 
night. Thus, chc of of shra/maybe thunder will return for Mon/Mon 
night. With the mean trof shifting toward central N America during 
next week, there should be additional opportunities for some pcpn, 
but right now, medium range guidance does not suggest anything 
significant or persistent.

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 115 PM EDT WED AUG 21 2019

VFR conditions will prevail across the region today into tonight. 
Northwest winds will be a little breezy through the afternoon. Some 
diurnal cumulus will dissipate later today leaving only a few 
passing high clouds through tonight. Can't completely rule out fog 
development at KIWD tonight, but it seems unlikely at this time. As 
winds shift to northerly tomorrow morning, a period of MVFR ceilings 
is expected to develop at KCMX and KSAW. It's also possible that 
KIWD would see these lower ceilings, but confidence is lower there.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 417 AM EDT WED AUG 21 2019

As cold air advection increases over the lake today, unstable 
conditions will develop and allow northwest winds to reach 15 to 25 
knots mainly across the east half. With winds aloft expected to be a 
bit stronger, it is not out of the higher platforms could gust to 30 
knots at times this afternoon. Tonight through Thursday, winds will 
become northerly and slacken in speed somewhat, between 10 and 20 
knots. The strongest winds are expected to be across the south half 
of the lake near the shorelines, especially funneling into the 
Duluth Harbor and Whitefish Bay. 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 wind 15 to 20 knots.

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


SHORT TERM...Ritzman
LONG TERM...Rolfson