360 
FXUS63 KAPX 210553
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
153 AM EDT Sat Aug 21 2021

.UPDATE...
Issued at 915 PM EDT Fri Aug 20 2021

High pressure remains centered over the Great Lakes and the Ohio
Valley late this evening...maintaining our persistently clear and
quiet wx. Little will change overnight...but do expect areas of
fog will again develop into early Friday morning. Low temps
tonight will cool into the low to mid 60s.

&&

.NEAR TERM...(Through Tonight)
Issued at 335 PM EDT Fri Aug 20 2021

High pressure is over eastern lower MI and environs, drifting
east. The high reaches the eastern lakes overnight. Return flow
will develop tonight in the wake of the high, especially over/near
Lake MI and eastern upper MI. Presently, there is only a little cu
out there today (less so than yesterday), though there is plenty
of haze/smoke aloft.

Paltry cu will dissipate this evening, with limited cloud cover
otherwise. Overnight, some marine fog/stratus could reform again
(like this morning). This is most likely in the Straits area, and
adjoining parts of Lakes MI/Huron. Patchy fog will form elsewhere,
though not as much as the past couple of nights, given the
gradually tightening pressure gradient during the night.

Another muggy night ahead, with lows in the 60s, nearly 70f near
Lake MI.

&&

.SHORT TERM...(Saturday through Monday)
Issued at 230 PM EDT Fri Aug 20 2021

High Impact Weather Potential: Minimal, save for some small thunder 
potential late Saturday...

Pattern Synopsis/Forecast: 

Saturday morning...split flow aloft remains intact over the eastern 
US...with ridge axis more or less along the Ontario/Quebec border 
and troughing south of there, centered over the Mid-Atlantic 
states...with Henri getting absorbed into the overall flow as it 
makes a beeline for the New England coast. Shortwave troughing 
lifting through the Upper Midwest Saturday will lead to our next 
"best" potential for rain/storms Saturday night (naturally)...as 
another shortwave dives into the Pacific northwest. Additional 
shortwaves look to dip into the trough out west through the 
remainder of the period...which may bring additional shower/storm 
chances into the start of the next workweek. Though our shortwave 
from Saturday night may weaken it...somewhat anomalously strong 
ridging over eastern Canada this weekend may yet prove to block 
troughing associated with Henri (and the lower half of our recent 
split flow)...potentially leading to minimal changes in the 
downstream pattern into the long term portion of the forecast. 

Primary Forecast Concerns: Rain/storm potential Saturday 
evening/night...

Seeing as how we ended up with virtually no precip over the last 48 
hours, pretty much CWA-wide...am currently suspecting the trend of 
drier-than-expected will continue. This seems relatively reasonable, 
as the chance of even 0.01" of 24-hr QPF (rainfall totals) seems 
limited to maybe a 40-60% chance for much of Northern Lower, based 
on some probabilistic guidance. Slightly better potential exists 
across the UP/Eastern UP where better moisture should be located 
closer to better dynamics/forcing as the shortwave itself skirts us 
to the north, over what remains of ridging that will have been 
broken down/shunted southward...between the approaching shortwave 
and troughing associated with Henri to our southeast. That being 
said...there are some signals for a tiny bit of upper level 
divergence ahead of the shortwave/resultant surface cold front 
Saturday afternoon/evening...more or less co-located with the plume 
of higher moisture as it moves in from the west...which suggests 
that we can't completely write off Saturday as dry...especially with 
Pwat values approaching 1.8" again (which would be pretty much the 
max end of climatological norms for this time of year)...though the 
best moisture should (seemingly as usual) split around us...and many 
areas will remain dry and/or see very minimal precip. Still...with 
anomalously strong deep moisture passing through...wouldn't be out 
of the question for some areas to squeeze out a bit more QPF with 
any of the more vigorous showers/storms.

The third ingredient for precipitation, instability, seems to be 
lacking overall...as we may just barely get warm enough at the 
surface here in Northern Michigan Saturday afternoon to be able to 
finally overcome the cap (maybe) and generate some surface based 
instability for a change...though it may not be much. Most guidance 
seems to keep it under 1000 j/kg of surface-based CAPE...perhaps 
well under 1000 j/kg...though we'll see how much surface heating 
we're actually able to get in on. Worth noting that today, despite 
the smoke plume aloft...temperatures are still reaching into the mid 
to upper 80s inland...with some diurnal cu even beginning to develop 
across the area as of 2pm. Do believe we should be able to reach our 
full surface heating potential Saturday...especially as HRRR smoke 
guidance suggests that as winds become more southwesterly ahead of 
the front, less smoky air would be advected into the region...thus, 
bluer skies would be the norm. However...there are also some signals 
that the cap may ultimately remain in place in some parts of the 
area, despite surface heating, as it should be warm enough aloft to 
squash much development aside from general cumulus. It should be a 
little breezier Saturday as the pressure gradient tightens a tad in 
response to the approaching system...especially across northern 
sections of the CWA. Not sure if it will be strong enough to keep 
lake breezes from cropping up and lending additional sources of 
forcing to the equation...so we may have to keep half an eye on that 
as well.

As far as timing goes, looks like the best moisture (which seems to 
be dwindling, per the latest model runs) should begin to cross Lake 
Michigan perhaps as early as mid-afternoon...though mid-level 
moisture seems to diminish as it crosses the lake, with low-levels 
becoming more saturated with time. (As alluded to above...wouldn't 
be out of the question to see some diurnal pop-ups in the afternoon 
as well, ahead of the main line, which should move through later.) 
There is still some uncertainty in timing, however...with some 
guidance a bit quicker than others. It should be a rather slow 
progression across the CWA...perhaps with some of our sunrise side 
areas still experiencing the rain/clouds by sunrise (or later) 
Sunday, depending on how quickly the cold front departs in the 
morning. Behind this...looks like we should see some subsidence and 
a bit of cold advection...which should make for a much more pleasant 
Sunday than Saturday. 

Going into Monday, things become tricky again...as the niblet 
currently diving into the Pacific northwest as of 20/12z will have 
made it through the flow and be approaching the Great Lakes by 
Monday. Similar to Saturday's situation...looks like this system, 
too, may be a bit on the moisture-starved side...with the best 
forcing staying to our north...though there are still some timing 
and strength differences. Will be watching for this niblet to try to 
pick up the troughing/Henri to our east...and drag it on its way 
going into the long term.

.LONG TERM...(Monday night through Friday)
Issued at 230 PM EDT Fri Aug 20 2021

High Impact Weather Potential: Minimal attm...

As mentioned at the end of the short term...will be watching 
Monday's niblet of energy to attempt to drag Henri out of New 
England...with ridging holding on across the southern US...keeping 
much of the activity across the northern tier of the 
CONUS/international border. Some of these niblets of energy may be 
able to supply us with rain/storm chances in the coming 
days...though there is still enough uncertainty that some of the 
details...such as timing and strength of the niblets...will stay at 
low resolution for a while, until things become clearer in the 
coming days.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 152 AM EDT Sat Aug 21 2021

High pressure continues to sit over northern Michigan today ahead of 
an approaching cold front from the west. Ongoing patchy fog with 
clear skies will continue through the early AM hours before fog 
burns off shortly after sunrise. Mainly S/SSW winds are expected 
today before switching to N/NW behind the frontal passage around 
midnight for TAF sites except APN. Fair-weather cu may develop this 
afternoon before more widespread cloud cover moves in from the west 
this evening. Scattered showers and perhaps a few storms are 
possible ahead of the front this evening. 

&&

.MARINE...
Issued at 230 PM EDT Fri Aug 20 2021

High pressure will slowly move east, and a southerly breeze will
gradually increase on Saturday. Advisory-level winds/waves are a
possibility Sat afternoon on some of our Lake MI waters, as well
as on Whitefish Bay. An abrupt shift to a northerly breeze takes
places Sat night, as a weak cold front moves thru.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...NONE.
LM...NONE.
LS...NONE.
&&

$$

UPDATE...MR
NEAR TERM...JZ
SHORT TERM...FEF
LONG TERM...FEF
AVIATION...DJC
MARINE...JZ