Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 141708

Area Forecast Discussion
National Weather Service Marquette MI
108 PM EDT Mon Aug 14 2017

.SHORT TERM...(Today and tonight)
Issued at 510 AM EDT MON AUG 14 2017

Water vapor imagery and RAP analysis show a blocky/omega pattern
across Canada with sharp/strong ridging across central Canada,
flanked by trofs along the W Coast and over eastern Canada. The
eastern trof extends sw into the Upper Mississippi Valley where a
well-defined shortwave is evident, centered over e central MN. To
the n, another shortwave is dropping s thru northern Ontario. Both
waves are generating showers and some thunder. KMQT radar has shown
some spotty -shra/sprinkles across western Upper MI/adjacent
northern WI and also over portions of Lake Superior overnight.

Both aforementioned shortwaves will more or less merge over the
western Great Lakes late this aftn/evening, providing forcing for at
least sct -shra today. Given the well-defined shortwave to the wsw
and its associated more organized shra area, highest pops into the
likely category will be painted over the far w around KIWD as that
area has the best potential of getting into a more persistent shra
regime. Elsewhere, expect daytime heating, which will be somewhat
limited by cloud cover, to lead to additional -shra development
though pcpn chance will be lower into the eastern fcst area than
over the w. Over the n central and e, lake breeze convergence should
provide the focus for -shra development. Some isold thunder is
possible today with consensus MLCAPES up to as much as 500j/kg. If
there is more sunshine than currently expected, thunder will have
greater coverage than isold.

With departure of shortwave tonight, expect -shra to end though shra
will hold on longest over the s central, perhaps past late evening.
With decreasing clouds and sfc high pres ridge arriving to drop
winds to calm/near calm, expect radiational fog to develop in the
interior, aided by today`s rainfall. The fog could become fairly
widespread. Over the w where clearing should occur earliest, temps
may fall to as low as the lower 40s in traditional cold spots.

.LONG TERM...(Tuesday through Sunday)
Issued at 404 AM EDT MON AUG 14 2017

Main issue this week is showers and thunderstorms moving through Wed
Night into Thu as a low pressure system crosses the Upper Great
Lakes. Could also be strong/gusty winds and potential small craft
conditions on both Lk Superior and Lk Michigan as the low pressure
system moves through. High pressure building back over the region
late this week into next weekend should result in generally quiet
weather with a warming trend.

Shortwave trough that brings potential for shra/tsra today will be
sliding east of area on Tue. High pressure builds in and will bring
dry weather into Tue night if not Wed morning. 00z models continue
to trend slower with arrival of shortwave trough and sfc low over
the middle Conus. Kept what blends gave for pops/sky on Wed, but if
slower trends continue, could see much of forecast area except far
west staying dry all day. SE winds may increase in the aftn but look
to become stronger during Wed evening as the sfc low moves to
western WI and sfc high slides toward New England.

Eventually the trough and sfc low should track across portions the
Upper Lakes late Wed night through Thu. Main slug of moisture
advection over forecast area occurs after midnight Wed night into
Thu morning and think that is when greatest chances of showers
should occur. Elevated instability seems sufficient enough to have
at least slight chances of thunder. As has been case a lot in recent
weeks though even with sufficient instability of possibly over 500
j/kg of MUCAPE, the overall shear remains weak so not expecting any
severe storms at this time. Temps kind of tricky as h85 temps remain
warm even after sfc low passes by to the east on Thu aftn. If there
is enough clearing after initial push of showers and storms move
though could see parts of forecast area seeing temps above 80
degrees. Stronger cold air advection does not occur until Thu night
and Fri. Breezy NW winds off Lk Superior behind the low along with
lingering 1000-850mb moisture spells low clouds and possible drizzle
and fog especially for northern forecast area closer to Lk Superior.
Not sure if we are looking at as dismal weather as occurred this
last Friday but there is at least some potential of that. For a
start, increased cloud cover and lowered temps near Lk Superior into
the low to mid 60s. Might be too optimistic, but for now kept temps
farther inland and near Lk Michigan in the low to mid 70s, close to
extended model blend.

Most areas will stay dry next weekend but cannot rule out small
chances of aftn/evening shra/tsra especially inland where highest
instability will build up each day. Temps in the low to mid 70s on
Sat should reach upper 70s to lower 80s on Sun as warmer air
begins to spill across the Upper Great Lakes with increasingly
zonal flow aloft.

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 107 PM EDT MON AUG 14 2017

Showers will be moving across portions of Upper MI, especially
around KIWD. Certainly possible that conditions could fall to MVFR
at times during periods of shra at KIWD this afternoon. As shra
depart tonight and clouds begin to clear out, radiational fog should
develop. KIWD is most likely to see denser fog with potential of
VLIFR conditions late. While KSAW is likely to fall to MVFR late.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 404 AM EDT MON AUG 14 2017

Winds less than 20 kts early this week with high pressure overhead,
then SE-E winds increase to 15-25 kts late Wed into Thu as low
pressure system crosses the Upper Great Lakes. Strongest winds, with
gusts to 30 kts possible, will be over western Lk Superior Wed aftn
into Wed evening then shifting to eastern Lk Superior late Wed night
into Thu morning. NW winds behind the low could then reach 20 kts
late Thu into Fri, strongest over east half of Lk Superior. Winds
diminish to 20 kts or less next weekend as high pressure builds back

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


SHORT TERM...Rolfson
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