Area Forecast Discussion

FXUS63 KMQT 222356

Area Forecast Discussion
National Weather Service Marquette MI
756 PM EDT Fri Oct 22 2021

.SHORT TERM...(This evening through Saturday)
Issued at 421 PM EDT FRI OCT 22 2021

Water vapor imagery and RAP analysis show an expansive mid-level low 
centered near southern James Bay. The northern Great Lakes are now 
firmly under the circulation of this low, but the deep cyclonic flow 
is weak. CAA regime into the fcst area ended last night, leaving 
850mb temps settled into the -3 to -5C range across Lake Superior. 
With Lake Superior sfc water temp roughly around 12C, but locally 
higher, sct lake effect -shra are occurring under nnw low-level 
flow. Last evening, Upper MI's first snowflakes of the season were 
observed at some locations. So, this season's first snowflakes 
occurred almost exactly 3 weeks later than last year (Oct 1, 2020). 
At the sfc, high pres centered over far northern Manitoba is ridging 
s into the Upper Mississippi Valley while low pres is located in 
central Quebec. Resulting weak pres gradient has led to a day of 
light winds across Upper MI. Temps are currently in the 40s F.  

Thru Sat, the mid-level low near southern James Bay will wobble 
slightly to the sw while 850mb temps generally hold in the -3 to -5C 
range. A weak shortwave extending w from the low across northern 
Ontario will pivot across the area tonight. As a result, there 
should be some uptick in lake effect pcpn coverage. Deep moisture 
profile upwards of 15kft or more will further aid the lake effect 
convection. Otherwise, nnw flow lake effect showers will continue 
into Sat. Moisture depth begins to fall on Sat from the w, so pcpn 
should end over at least the far w in the aftn. Since wetbulb zero 
heights tonight/Sat are similar to last night and today, the -shra 
will mix with or change to -shsn in similar locations to last night 
and this morning. Deeper convection could produce graupel, no matter 
the elevation. As has been the case, lake effect pcpn will continue 
to be more nmrs into n central Upper MI e of Marquette due to longer 
fetch and Lake Nipigon preconditioning. With lake induced 
equilibrium levels to 10-15kft and winds under 20kt thru the layer, 
conditions thru Sat morning remain somewhat supportive for the 
potential of waterspouts on Lake Superior, mainly on the e half of 
the lake. Low temps tonight will be similar to last night (upper 20s 
to upper 30s F), but if clouds scatter out long enough in the 
interior, temps will easily fall into the mid 20s. Highs on Sat will 
be similar to today, ranging thru the 40s, maybe reaching 50F s 

.LONG TERM...(Saturday night through Friday)
Issued at 301 PM EDT FRI OCT 22 2021

Blocking pattern across much of NOAM will continue through this 
weekend as an upper-level low remains btwn James Bay and the Great 
Lakes and anomalous ridging persists across central Canada northward 
into the Arctic. This low will begin to fill in by Sunday as a 
shrtwv ejects from the Rockies, spinning up a sfc low across the 
Central Plains into the Ohio River Valley by Monday. Further 
upstream, a strong trof will reach the Pac NW Sunday evening, 
"running into" the downstream ridging extending from north central 
CONUS northward through Canada. This strong trof will begin to shift 
this ridging eastward, as the low north of the Great Lakes combines 
with trof shifting through the Ohio River Valley Monday night.
Sfc high pressure dropping south from northern Canada will increase 
the pressure gradient for Monday as the sfc low tracks through the 
Ohio River Valley...which will bring stronger easterly winds across 
the area for Monday into Monday evening. By Tuesday evening, the 
ridge axis will begin to move over the western UP as southerly flow 
begins to increase. This will bring a warm up by the middle of the 
week, with high temps 5 to 10 degrees above normal as our normal 
high falls from 49 to 44 over the next 6 days. Model and ensemble 
spread increase on Wednesday, with confidence for the second half of 
the week quite low.

Saturday night, light NW flow with 850mb temps near -4C will lead to 
continued LER across parts of the Keweenaw and ern Upper Michigan. 
Inversion heights and saturation will range from near 8kft across 
the west to near 9kft across the east. Despite 850mb temps remaining 
near -4C through the day Sunday, saturation and inversion heights 
will decrease, falling to around 4kft by 18Z Sunday. As winds begin 
to veer from the NW to NE ahead of an approaching wave to our south, 
LER will begin to diminish in coverage through the morning hours, 
with only an isolated shower or two possible by late aftn on Sunday. 
Despite sfc temps remaining above or near freezing, higher inversion 
heights into the DGZ may allow for some wet snow or graupel to mix 

Heading into Monday, shrtwv and sfc low will pass to the south of 
Upper Michigan as the pressure gradient and easterly winds increase. 
While there could be some fgen rain along Lk Michigan, the UP is 
expected to remain dry with this system. Should be a raw feeling day 
with breezy conditions and highs in the 40s to potentially up to 50.

Ridging and sfc high pressure move overhead for Tuesday, with 
southerly winds bringing a warmer trend with highs 5 to 10 degrees 
abv normal. As the strong wave from the Pac NW reaches the central 
CONUS by Wednesday, associated sfc low develops across the Central 
Plains. Pcpn chances will then increase across the wern UP by 
Wednesday evening, before spreading over the UP into Thursday. Model 
spread increases by the middle of the week and with a blocking ridge 
across central Canada, inherent uncertainty exists for pcpn chances 
so chance PoPs will exist Thursday into the weekend.

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 742 PM EDT FRI OCT 22 2021

It's anticipated that all three terminals will be dominated by
primarily MVFR cigs, but KIWD and KCMX have been bouncing around
categories over the last 12 to 24 hours, and KSAW has been
reporting VFR conditions throughout the day. Given how close the
LER/S is to KSAW, didn't feel comfortable going VFR but an
amendment/update may be required if these trends continue to
indicate KSAW will remain free of the ongoing bands. More
confidence exists at KIWD and KCMX, with it worth noting that
there are indications KIWD could perhaps drop into lower
categories, so will monitor that as well. NW winds will remain 
fairly light (topping out to around 10 knots on Saturday) to calm
(overnight) through this TAF period.


.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 421 PM EDT FRI OCT 22 2021

With high pres ridge extending se toward the Upper Lakes, northerly 
winds on Lake Superior will remain under 20kt thru Sat night, but 
will be strongest across the e half of the lake. On Sun and Mon, 
high pres will build across northern Ontario as low pres moves e to 
the Upper Ohio River Valley. Increasing pres gradient btwn these 2 
features will probably lead to wind gusts increasing to at least 20-
25kt over portions of Lake Superior later Sun into Mon. Winds will 
then diminish to under 20kt into Tue morning as high pres ridge 
moves across Lake Superior. Some increase in winds will occur Wed as 
the ridge moves e and low pres moves across the central Plains. 

On another note, conditions will remain somewhat supportive for 
waterspout development on mainly the e half of Lake Superior 
into Sat morning.

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


SHORT TERM...Rolfson