Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

FXUS63 KAPX 180136

Area Forecast Discussion
National Weather Service Gaylord MI
936 PM EDT Tue Sep 17 2019

Issued at 935 PM EDT Tue Sep 17 2019

Fog isn't coming on as gangbusters as last night, but we are
already seeing the beginnings of some fog. Eastern upper MI
(especially near Lake MI) is the one spot that struggled to mix 
out earlier today, so it is no surprise that ISQ/ERY are already
seeing fog. Patchy fog is also forming at other coastal locales
impacted by a marine layer, including SJX/OSC/MBL/LDM. Even the
oddball inland site (HTL) is seeing a touch of fog already.

The pressure gradient is slowly tightening, especially late in 
the overnight, which will help erode the fog quickly in the 
morning. In addition, we do have thicker cirrus advecting in from
the nw, blowoff from a small MCS near and north of Isle Royale. 
But even with the above, will need to hit fog a little harder in 
the grids and text products. No advisories, not yet anyways.


.NEAR TERM...(Through Tonight)
Issued at 301 PM EDT Tue Sep 17 2019

...Potential for some more fog and stratus tonight...

High impact weather potential: Minimal. May see some patchy dense 
fog by later tonight.

Pattern synopsis/forecast: Pattern change to a much milder one 
continues to unfold across the region this afternoon as stout mid 
level ridge axis builds into the western Great Lakes, all-the-while 
center of surface ridging pushes east into Ontario. This places 
northern Michigan in burgeoning warm air advection regime, with 
increasing southerly flow through the boundary layer. Overall 
subsidence also the result, with strongest moisture advection axis 
and lift via passing shortwave trough well off to our northwest. It 
took awhile, but August sun finally mixed out most of the abundant 
low level moisture (fog and stratus), although some stratus 
continues to linger in portions of eastern upper Michigan. 
Temperatures have responded nicely to that increasing sun and light 
southerly flow, with a good portions of the area punching well up 
into the 70s.

Just subtle eastward adjustment to the larger scale features as we 
head through tonight, with apex of mid level ridge centering itself 
right overhead by Wednesday morning, with just a very slow east 
movement of the surface high. Deep southerly flow and well above 
normal temperatures will be the result. 

Primary forecast concerns/challenges: Temperature trends and 
addressing the potential for more fog and low cloud development.

Details: Dry weather to prevail overnight as subsidence remains. Far 
bigger challenge addressing fog and low cloud potential...made a 
challenge by expected development of a weak (~20 knots) low level 
jet atop shrinking boundary layer. This is a bit higher than one 
would like to see for complete decoupling. Do believe winds will go 
light, and some of those more sheltered low lying areas will likely 
go calm for a time. Mixing has scoured out some of the near-surface 
moisture this afternoon, but dewpoints still remain a bit high, with 
some readings in the lower and even middle 60s. This does set the 
stage for more fog and stratus development, with focus across the Au 
Sable river valley and across eastern upper Michigan. Don't believe 
they will be nearly as extensive as last night, but very likely 
those more sheltered areas will see significant vis restrictions at 
times. A mild night, with expected lows ranging through the 50s 
several degrees above normal for this time of year.


.SHORT TERM...(Wednesday through Friday)
Issued at 301 PM EDT Tue Sep 17 2019

High impact weather potential: Thunderstorms possible Wednesday 
night through Thursday.

Pattern synopsis and forecast:

High pressure centered over the eastern Great Lakes will continue to 
dominate northern Michigan's weather. Any morning fog that remains 
will diminish quickly as the sun comes up. This high pressure will 
continue to bring mostly dry conditions, although a very weak cold 
front associated with a low pressure system over Hudson Bay will 
bring increased cloudiness and chances of some rain showers and 
possibly a rumble of thunder over eastern upper and parts of 
northwest lower Wednesday night through Thursday. Very weak 0-6km 
bulk shear, low lapse rates, dew points in the lower 50s...will not 
be favorable for severe thunderstorms. Any thunderstorms that do 
develop will be heavy rainers with up to about 600 J/Kg of very 
skinny CAPE. Winds will be southerly throughout the period and a bit 
breezy during the afternoon hours of Wednesday and Thursday as 
diurnal mixing maximizes. Temperatures will continue to trend above 
normal for this time of the year (10-15 degrees above) the mid 
to upper 70s with some locations reaching into the lower 80s.

.LONG TERM...(Friday night through Tuesday)
Issued at 301 PM EDT Tue Sep 17 2019

High Impact Weather Potential...minimal. 

Ridging begins an eastward movement, putting northern Michigan on 
the western periphery of the ridge. This will allow a few weak 
disturbances to bring chances of rain showers. The first chance will 
be Friday night into Saturday morning as a weak cold front 
associated with a low pressure system over Hudson Bay approaches the 
Great Lakes region, bringing slight chances of WAA precip. This 
pattern appears to remain throughout the long term period. 
Southwesterly winds will prevail until cold frontal passage...which 
will be at the beginning of next work week...when winds will veer to 
northwesterly. The northwesterly winds will usher in some colder 
temperatures (near normal), with daytime highs reaching into the 
upper 60s to low 70s.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 745 PM EDT Tue Sep 17 2019

Some fog again later tonight, not as much/bad as last night.

Low-level airmass remains unseasonably humid. Residual fog/ 
stratus is still hanging on over far northern Lake MI, including 
the ISQ area. PLN isn't too far away from there, and fog is likely
to develop there tonight. Have IFR fog at PLN and APN. Wait and
see for MBL/TVC, a tightening pressure gradient and increasing
high clouds make fog a little less likely there. Wherever fog does
form, it will quickly dissipate in the morning, with VFR
conditions for the rest of Wednesday.

Light southerly breezes.


Issued at 301 PM EDT Tue Sep 17 2019

South to southeast winds will increase some tonight and 
Wednesday, but still look to remain below advisory levels. Winds 
become southwest and remain a bit gusty on Thursday, with low end 
small craft advisory conditions possible on portions of northern 
Lake Michigan. Dry and mild weather will prevail through Wednesday, 
with just small chances for a few showers and possible thunderstorms 
across the northwest third of the area Wednesday night into Thursday.





National Weather Service Glossary of Abbreviations