Area Forecast Discussion

FXUS63 KMQT 061105

Area Forecast Discussion
National Weather Service Marquette MI
705 AM EDT Thu Aug 6 2020

.SHORT TERM...(Today and tonight)
Issued at 426 AM EDT THU AUG 6 2020

Aside from a few clouds off the western shores of Lake Superior, 
Upper Michigan skies remain clear. Temperatures are about 10 degrees 
warmer than this time yesterday, with only a few spots in the upper 
40s and widespread 50s elsewhere across the UP. Still a couple hours 
worth of cooling and could see places fall a couple more degrees, 
but nothing too crazy.

Today, the going trend of highs being a few degrees warmer than the 
day before will continue as all of Upper Michigan will climb into 
the upper 70s to low 80s. Light, westerly winds will become more 
from the SW assisting in the warm up as these lighter winds allow 
the development of another Lake Superior lake breeze this afternoon. 
CAMs continue to show the chance for afternoon diurnal showers and 
possible thunderstorms across the eastern half of Upper Michigan and 
have continued this trend in the fcst. Expanded PoP coverage 
slightly across the east, keeping fcst at scattered showers and 
isolated thunderstorms for most of Alger, Schoolcraft and Luce 
counties, extending eastward into Gaylord's cwa as well. With models 
ranging between 100 to 500 J/kg MUCAPE, and bulk shear only around 
20 knots, not expecting another more than some rumbles of thunder 
and brief gusty winds from any storm's death.

As shortwave ridging shifts east into the CWA tonight, diurnally-
driven cu will dissipate as clear skies will return. SW winds 
continue, but won't bring in the increased dewpoints just yet 
tonight, allowing temps to fall into the 50s across the interior and 
near 60 along the Lake Superior shoreline.

.LONG TERM...(Friday through Wednesday)
Issued at 444 AM EDT THU AUG 6 2020

Pattern across N America is in the process of deamplifying, leading 
to a lower amplitude pattern during this fcst period, particularly 
across the Lower 48. This lower amplitude pattern will feature the 
subtropical high stretching out across roughly the southern half of 
the U.S. while a relatively progressive flow regime takes hold to 
the n across the northern U.S. and southern Canada. For Upper MI, 
this change in the pattern will result in warming for the next 
several days. The combination of above normal temps and dwpts on the 
rise will make for a return of uncomfortable conditions this 
weekend. The warm/humid conditions will break for period during the 
first half of next week as the progressive nature of the flow sends 
a shortwave trof into eastern Canada with associated cold fropa 
across Upper MI late Sun night/Mon. Modest amplification of the 
pattern still looks to occur later next week as a trof develops into 
the western U.S. This will cause heights to build downstream, 
bringing a return of warm conditions/above normal temps and 
increasing dwpts. As for pcpn, the main focus for pcpn over the next 
7 days will occur over the weekend into Mon under a warm/more humid 
air mass and in association with cold fropa. In the wake of the 
front, it should be dry into the midweek period next week. Late next 
week, warming/increasing humidity and the potential of shortwaves 
ejecting downstream from the western trof should bring some 
potential of pcpn.  

Beginning Fri...weak troffing over the area today will have exited. 
In a more zonally oriented flow into the area, there are indications 
of a shortwave moving into northern MN during the aftn. Ahead of 
this wave, sharper theta-e advection is generally indicated to swing 
up thru northern MN and that will be the favored area for any 
convection. Farther e, fcst soundings indicate a bit of a cap to 
overcome in western Upper MI. So, it seems unlikely that there will 
be any pcpn over the w on Fri. 850mb temps are indicated to be a 
degree or two higher than today which should lead to highs on Fri 
being a few degrees higher than today. Expect highs into the lower 
80s for much of the area. Although dwpts will be rising, readings 
won't be too high yet (mid 50s to lwr 60s) to make conditions more 
uncomfortable. Gradient southerly wind will likely be strong enough 
to push warmth to the Lake Superior shore at most locations. 

It's possible the MN shortwave could lead to an organized cluster of 
storms evolving upstream and moving into the fcst area Fri night.
There is considerable spread in the guidance as would be expected 
with convection, but the overall theme is for some potential of 
convection to spread into at least portions of western Upper MI 
during the night, aided by modest low-level jet of around 25kt. 
Better chc of shra/tsra should occur on Sat in association with a 
second stronger shortwave. ECWMF has been very consistent with this 
Sat wave. Timing of this feature will probably work to hold temps 
back a bit from what was previously expected due to more cloud 
cover. Dwpts will be on the rise thru the 60s on Sat to make 
conditions more uncomfortable, but temps may be held back to the 
upper 70s/lower 80s. 

In the wake of the Sat shortwave, may end up with a dry period later 
Sat night and perhaps for much or all of Sun as fcst soundings show 
a healthy cap to overcome on Sun. With less cloud cover, Sun will be 
the most uncomfortable day of the weekend with dpwts in the 
mid/upper 60s and high temps in the 80s. 

After a misstep by the 00z/Aug 5 GFS/ECWMF runs jumping to a slower 
cold fropa, delayed until Tue, the 00z GFS/ECMWF/CMC/UKMET runs 
today are in quite good agreement showing cold fropa late Sun 
night/Mon. Expect shra/tsra to accompany fropa. Dry weather should 
then follow thru the midweek period. However, there are some hints 
that during late Tue into early Wed a shortwave will swing across 
northern Ontario within the trof heading for eastern Canada. This 
wave could generate some isold convection. Although temps won't fall 
too much after the Mon fropa (readings probably still a bit above 
normal), dwpts will at least fall back to somewhat more comfortable 

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 705 AM EDT THU AUG 6 2020

Similar conditions expected today at all TAF sites as seen the last 
few days, with VFR dominating. A diurnal cu field will develop later 
this morning. Another Lake Superior lake breeze will develop this
afternoon, but not expecting any impacts to SAW. Skies scatter 
out and clear tonight with calm winds expected. 

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 426 AM EDT THU AUG 6 2020

High pressure will persist over the Lower Great Lakes through 
tomorrow, as lack of pressure gradient over Superior will keep winds 
blo 20 knots. Southerly winds may increase up to 25 knots Friday 
night into Saturday before falling back below 20 knots through the 
rest of the fcst period. There will be some thunderstorms moving 
over the lake through the weekend and again on Tuesday next week, 
with some stronger winds associated with thunderstorms possible.

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


LONG TERM...Rolfson