AFOS product AFDMQT
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Product Timestamp: 2021-08-21 11:41 UTC

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FXUS63 KMQT 211141
AFDMQT

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

.SHORT TERM...(Today and tonight)
Issued at 458 AM EDT SAT AUG 21 2021

Water vapor imagery and RAP analysis show a vigorous, well-defined 
shortwave lifting ne into southern Manitoba. At the sfc, associated 
993mb sfc low pres is over far se Manitoba and tracking nne. 
Trailing cold front extends s across western MN with a prefrontal 
sfc trof from ne MN s across far western WI. Ahead of the trof, a 
sct-bkn line of convection (shra with some embedded isold thunder) 
has pushed out across western Lake Superior and extends s thru 
western WI. Another band of convection is farther w in the Duluth 
area along the sfc trof. Closer to home, it's been another warm 
night. Temps at 08z range from the middle 60s to the lwr 70s F, 
warmest w. A few of the traditional cool spots over the e half are 
around 60. 

The vigorous shortwave over southern Manitoba will continue lifting 
ne, reaching Hudson Bay tonight. With best forcing/height falls 
shifting ne with it, forcing will be diminishing with the cold front 
moving across the fcst area this aftn thru this evening. 
Nonetheless, expect convergence along the prefrontal trof and cold 
front to continue generating sct convection at times given the avbl 
instability/moisture. Speaking of which, models are actually in 
quite good agreement showing MLCAPE increasing to roughly 800-
1200j/kg this aftn across roughly the e half of Upper MI prior to 
fropa. Deep layer shear is fcst to be in the 25-30kt range, marginal 
for organized storms. So, at this point, still not expecting any svr 
storms today. With a narrow band of precipitable water around 2.0 
inches, roughly 200pct of normal, just ahead of the cold front and 
with warm cloud depths around 12kft, expect brief, hvy downpours 
with any of the storms that occur today. Prior to fropa, it will be 
very humid with dwpts well into the 60s to lwr 70s F. Dwpts will 
begin to fall w in the aftn. Highs should range from the upper 70s 
to mid 80s F. Expect breezy s winds gusting up to 25-30mph ahead of 
the cold front. Postfrontal westerly winds will likely gust to 
around 40mph on the Keweenaw based on potential momentum transfer 
from mixing. With incoming pres rises around 4mb/3hr providing an 
isallobaric wind component aligned with the gradient wind, would not 
be surprised if some gusts to around 45mph occur at times for a few 
hrs late aftn/early evening. The southerly winds up Lake MI in 
advance of the cold front today will build waves sufficiently high 
for a high swim risk along the Lake MI beaches of Schoolcraft County 
this aftn.  

Shra potential will continue over the eastern fcst area this evening 
until the cold front exits. In the wake of the front, high pres will 
build toward the Upper Lakes tonight, bringing cooler and drier air 
into the area. Temps tonight should slip down into the upper 40s 
over the interior w trending up to around 60F along Lake Superior.

.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 12Z TAFS through 12Z Sunday morning)
Issued at 740 AM EDT SAT AUG 21 2021

A cold front will sweep across west and central Upper MI today. Some 
shra and isold tsra will be possible until the front passes. There 
remains plenty of uncertainty in whether any of the terminals will 
be affected by pcpn, so only VCSH was included in the fcst for 
KIWD/KCMX/KSAW. Under a moist upslope sse wind off Lake MI, a low 
stratus deck has formed early this morning over central Upper MI, 
impacting KSAW. These low clouds/LIFR cigs will probably linger for 
a couple of hrs before the clouds mix out. Otherwise, there may be a 
period of MVFR cigs at all of the terminals around the time of fropa 
today. VFR conditions will then prevail at all terminals after fropa 
as drier air moves into the area. Winds will be gusty today to 20-
30kt. Strongest winds will occur at KCMX where wnw winds after fropa 
will gust to 35kt or so later this aftn.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 458 AM EDT SAT AUG 21 2021

A cold front will sweep across Lake Superior today thru early this 
evening. Ahead of the front, s winds will gust to 20-25kt at times. 
At high obs platforms, expect gusts to 30kt. After frontal passage, 
incoming pres rises from the w will give postfrontal w winds a 
boost. Until the axis of the pres rises passes, there will be the 
potential for some gale force gusts to around 35kt for a few hrs 
late aftn/early evening, particularly at higher obs platforms. The 
area from just w and n of the Keweenaw Peninsula toward Granite 
Island/Stannard Rock should be favored for the higher wind gusts. 
Winds will then diminish to under 20kt from w to e overnight thru 
Sun morning as high pres arrives. At the moment, it appears winds 
will remain generally under 20kt Mon thru Wed.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Beach Hazards Statement from noon EDT today through this evening 
     for MIZ014.

Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...Rolfson
LONG TERM...JAW
AVIATION...Rolfson
MARINE...Rolfson