Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 111141

Area Forecast Discussion
National Weather Service Marquette MI
741 AM EDT Fri Aug 11 2017

.SHORT TERM...(Today and tonight)
Issued at 450 AM EDT FRI AUG 11 2017

Only significant impacts in the short term are due to high swim risk
in Marquette and Alger Counties today.

As the SFC low currently over eastern Upper MI moves east, NW winds
will become gusty across much of the area, which will lead to
increased waves and high swim risk today. A Beach Hazard Statement
was issued.

Otherwise, just timing out the ending of precip from E to W through
tonight. Precip will be confined to N-central and eastern Upper MI
by late morning today, then just to eastern Upper MI by midnight

.LONG TERM...(Saturday through Thursday)
Issued at 357 AM EDT FRI AUG 11 2017

Overall, the prevailing pattern this summer has featured
ridging/positive height anomalies over western N America, western
Canada in particular, and troffing/negative height anomalies over
eastern N America. When departures from this pattern have occurred,
they have generally been short-lived. The current pattern across N
America reflects the prevailing summer pattern. Longer range
guidance has been suggesting a change in the pattern for well over a
week, and recent days medium range model runs support that change
which will be getting underway today. Positive height anomalies
currently over western Canada will build while shifting to n central
Canada this weekend. This area of positive height anomalies will
then gradually settle into the Hudson Bay vcnty and eastern Canada
during next week. Initially, the shifting of positive height
anomalies to n central Canada will aid in maintaining troffing over
eastern Canada into the Great Lakes thru the weekend. Then, gradual
progression of the positive height anomalies will push the eastern
trof out next week, leading to a more zonally oriented flow across
the northern CONUS. For Upper MI, these changes will mean temps near
normal this weekend will trend to modestly above normal next week.
Looking farther ahead, there are suggestions that the shifting of
positive height anomalies to eastern Canada next week may be a new
pattern that persists out thru the end of the month per CFSv2
ensemble means. So, late Aug may end up on the warm side. As for
pcpn over the next 7 days, drier conditions will be setting in thru
the first half of next week with any minimal pcpn chances tied to
shortwaves that may brush the Upper Lakes as the eastern trof
departs. A shortwave trof tracking eastward in the more zonally
oriented flow developing mid week will then bring the next potential
of more organized pcpn Wed/Thu.

Beginning this weekend, slow moving shortwave that brought the
shra/tsra over the last couple of days may still be close enough
keep some shra lingering over the far eastern fcst area Sat morning.
If so, those shra will end during the morning. Attention, then turns
to a weak shortwave dropping sse toward Lake Superior Sat aftn and
passing across the area Sat night. Aided by diurnal heating, sct
shra/tsra will probably develop n of Lake Superior Sat aftn. Being
diurnally driven, this convection should have difficulty surviving
the trip across the cool marine layer late Sat aftn/evening. Setting
of the sun/weakening instability over land will then further
diminish prospect for convection to reach or develop over Upper MI
as the shortwave arrives Sat night. For now, fcst will reflect dry
weather, except for Isle Royale, but not totally out of the question
that there could be isold shra Sat night. On Sun, with the fcst area
btwn a shortwave moving across the Upper Mississippi Valley and
another dropping thru northern Ontario, should be able to slip in
another dry day with convection to the s and sw of Upper MI and also
to the n in Ontario.

On Mon, as the eastern trof begins to exit out of the Upper Lakes,
one last weak shortwave will pass across the area. Coinciding with
peak heating, there may be isold shra/tsra Mon aftn along lake
breezes, probably only over the e half of Upper MI where lake
breezes from Lake MI and Lake Superior converge.

Tue looks dry with shortwave ridging pushing into the area, then
medium range models are in reasonable agreement and show run-to-run
consistency with a shortwave trof moving along the U.S./Canadian
border toward the Upper Lakes for Wed/Thu. Utilized a consensus fcst
which results in chc pops late Wed into Thu.

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 739 AM EDT FRI AUG 11 2017

Conditions will improve at all sites from W to E as low pressure
moves out and high pressure moves in.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 450 AM EDT FRI AUG 11 2017

As a low pressure system over eastern Upper Michigan exits the
region, wNW winds will gust up to 25 kts over central and eastern
Lake Superior today into early tonight. Winds will then remain below
20 kts Sat through the end of the forecast period.

Upper Michigan...
  Beach Hazards Statement through this evening for MIZ005-006.

Lake Superior...
Lake Michigan...


LONG TERM...Rolfson
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