725 
FXUS63 KMQT 210728
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
328 AM EDT Sat Aug 21 2021

.SHORT TERM...(This evening through Saturday)
Issued at 327 PM EDT FRI AUG 20 2021

Currently, we are looking almost like a complete repeat of 
yesterday. Satellite imagery shows diurnal cu popping up in the U.P. 
this afternoon as a dry high pressure ridge slowly makes its way 
eastward. Some areas in the elevated terrain near Lake Superior (and 
near southern Houghton County) are already around 90F! The only 
saving graces right now is that RHs are around 40% in those areas 
this afternoon and there is a light south/southwesterly breeze 
across most of the area. Some light haze can still be seen across 
the area, particularly in the east (as seen in the vertically 
integrated smoke product in the HRRR smoke model).  This haze should 
slowly leave the area tonight as a cold front approaches from the 
west. 

Tonight, expect temperatures to bottom out near the 60s across the 
area, as some cloud cover associated with the cold front should 
start rolling into the western CWA late. As the front approaches, 
expect southerly winds to pick up from west to east. These winds 
should bring some breezy conditions across the area ahead of the 
cold front tonight and Saturday. Not expecting the rainfall 
associated with the cold front to arrive in the far west until late 
tonight. Given that only the NAM12km was showing some CAPE along the 
frontal boundary during the overnight and early morning hours, 
decided to cap thunder chances to slight until late Saturday 
morning. 

As the front progs eastward throughout the day Saturday, expect 
cooler temperatures (mainly upper 70s) in the west behind the front, 
whereas the far east (near Newberry) could see still see 
temperatures approach the mid-80s.  Could still see some pockets of 
low 80s along the downslope areas near Lake Superior, as the 
downslope of southerly winds could raise temperatures to get over 
80. Also, could see the low-80s in the south central too Saturday, 
as the front isn't expected to arrive until the afternoon. 
Thunderstorm chances improve throughout the day Saturday, as some 
diurnal heating ahead of the cold front should increase instability 
in central and eastern Upper MI. Not expecting severe wx, as the 
front should be dying as it moves east; while MUCAPEs look modest 
(around 1000-1500 J/kg) and bulk shear looks marginal for severe wx 
(around 30 knots at most spots near the frontal boundary), because 
the front is dying, the forcing mechanism to produce convection 
should weaken with time. Therefore, while I think convection is a 
definite possibility, I'm doubtful that the modest instability and 
marginal bulk shear will be enough to overcome the loss of forcing 
in the cold front to produce severe wx. The better forcing for 
convection is expected north of us in northern Ontario, as the low 
associated with this cold front lifts northeast towards Hudson Bay. 
Thinking we will see more breezy conditions behind the cold front 
Saturday, particularly in the Keweenaw Peninsula, as significant 
height rises and temperature advection is expected; the Keweenaw 
could see some wind gusts over 35 mph late tomorrow afternoon! The 
wind direction behind the front is expected to be westerly.

.LONG TERM...(Sunday through Friday)
Issued at 327 AM EDT SAT AUG 21 2021

Through the extended fcst period, models indicate mean troughing 
over western Canada, and at times over the western CONUS, as a 
series of shortwaves eject eastward across the northern CONUS and 
Upper Great Lakes region in a progressive flow through next week. 
Based on dynamics and available moisture, it looks like the more 
promising chances for widespread showers would not be until mid to 
late next week. Temperatures will fluctuate from near to above 
normal through much of the period.  

Beginning Saturday night into Sunday, models indicate any remaining 
showers ending in the evening over the eastern portion of the cwa, 
then dry, cooler and less humid conditions thereafter into Sunday as 
sfc high pressure builds in quickly from the west behind Saturday's 
shortwave/cold front. Min temps Sat night will fall back into the 
more comfortable 50s for most locations. Sunday's max temps will be 
closer to seasonal normals with highs in the 70s and dew points in 
the upper 40s to mid 50s. Waves generated from fairly gusty nw-n 
winds behind the front will likely warrant a high swim risk for 
Alger County on Sunday.   

The next shortwave moving across the Northern Plains on Sunday will 
weaken as it lifts into northern Ontario by Monday morning. Models 
show a weaker pcpn signal with this weakening wave compared to the 
wave on Saturday. Even though GFS soundings indicate MLCAPE values 
increasing to 500-1000j/kg Mon ahead of the front, warm nose of 
nearly 17C temps aloft and fairly significant CIN may prohibit 
convective development on Mon across much of the area. In the end, 
the better chc of pcpn with this wave looks to be late Sun 
night/early Mon over the w in association with an approaching, but 
weakening 30 kt low-level jet. Otherwise, nothing more than low 
chc/schc pops are warranted late Sun night/Mon. Max temps will rise 
back into the lower to mid 80s most locations on Monday and Tuesday. 

Latest models indicating perhaps a better signal for showers/t-
storms with the next shortwave due in late Tue into Wed. Trends 
indicate better shortwave dynamics and stronger WAA/moisture 
transport ahead of the system. With MUCAPE values approaching 1000-
1500 j/kg and deep layer shear 40-50 knots there certainly could be 
some strong to marginally severe storms associated with this system. 
High pressure building in behind this system should result in dry 
and cooler conditions on Thursday. 

Models certainly differ on the timing/strength details but there 
does appear to be a pretty consistent signal that a broader, deeper 
trough will dig in from the Northern Plains late next week/weekend 
bringing more opportunities for rainfall.
&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 135 AM EDT SAT AUG 21 2021

With the precip and its front inching closer to Upper Michigan, 
timing looks fairly on track to the previous TAF issuance. Lightning 
remains embedded, albeit has certainly dropped off after sunset. 
But, with enough instability lingering around, have left VCTS 
mention, but went with predominately rain at KIWD and KCMX. With it 
still a bit too far out timing wise for KSAW, have also left just 
VCTS mention, leaving time for the next TAF issuance to determine if 
TSRA or simply RA is warranted. Current indications for KSAW lean 
toward the former, particularly with a diurnally-driven assist 
possible. 

Winds remain a high-impact for aviation interests, especially 
overnight with LLWS expected. Gusty southerly winds overnight will 
yield to a more westerly component with the fropa, remaining 
elevated through the end of this TAF period, especially at KCMX.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 327 PM EDT FRI AUG 20 2021

Winds should remain 20 knots or less until this evening. As a cold 
front approaches the lake tonight, expect southerly winds to 
increase to 20 to 30 knots ahead of the cold front. As the cold 
front moves through Saturday, expect the southerly winds to weaken 
ahead of the front and for the westerly winds behind the front to 
strengthen to 20 to 30 knots. Some westerly gale force gusts up to 
35 knots are possible behind the cold front in the western and 
central lake Saturday afternoon and evening. As the winds become 
northwesterly Saturday evening, expect wind speeds to diminish; by 
Sunday morning the winds should be 20 knots or less. The winds 
should remain around 20 knots or less for the remainder of next 
week.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...TAP
LONG TERM...JAW
AVIATION...lg
MARINE...TAP