Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 252356

Area Forecast Discussion
National Weather Service Marquette MI
756 PM EDT SUN SEP 25 2016

.SHORT TERM...(This evening through Monday)
Issued at 409 PM EDT SUN SEP 25 2016

12Z raobs/latest wv imagery and RAP analysis show hi amplitude
pattern dominating NAmerica featuring deep upr trofs in the plains
and over the Cndn Maritimes arnd an upr rdg over the Great Lks/NW
Ontario. Potent shrtwv lifting nnewd thru the Plains trof is moving
toward Lk Winnipeg with 12hr h5 hgt falls aprchg 100m. Mstr surge in
the warm conveyor belt ribbon ahead of this feature under h85 sw
winds up to 40 kts/sharp pres gradient btwn attendant sfc lo pres in
nrn Manitoba/attendant cold fnt in the plains and sfc hi pres over
Quebec and New England advected 12Z pwats up to about 1.75 inches
over INL/MPX, 250-300 pct of normal. Showers on the ern flank of
this mstr ribbon are impacting mainly the central zns despite drier,
stable airmass shown on the 12Z GRB/APX raobs closer to the sharp
upr rdg axis that has kept the far ern cwa dry. Dry slotting
following the warm conveyor belt has resulted in a band of partial
clrg fm the MN Arrowhead into far nw WI. Looking farther to the w,
there is a pronounced cool pool and plenty of lo clds over the nrn
Plains spreading into MN under the upr trof/behind cold fnt, with
12Z h85/7 temps at Bismarck, ND, down to 4/-2C. The 12Z h85/925 nw
winds at Bismarck were about 50/45 kts and are aiding the strong

There are a number of fcst concerns in the short term, mainly pops
and winds that wl accompany the passage of the warm conveyor belt
mstr ribbon/sfc cold fropa.

Late this aftn/tngt...Axis of deep mstr/deep lyr qvector cnvgc under
the warm conveyor belt are fcst to shift w-e acrs the cwa thru this
evng, exiting the far e arnd 06Z. Since the showers unstream have
become less wdsprd, wl fcst no hier than likely pops. Mucapes no
more than about 250 j/kg under this warm conveyor belt wl support no
more than isold TS. Dry slotting in the wake of the warm conveyor
belt/cold fropa wl diminish the pops as early as this evng over the
w and may actually bring some brief clrg as obsvd this aftn right
behind cold fropa over MN. But then more backwash mstr/lo clds wl
surge into the area later tngt in the strengthening cyc w flow
behind the fropa. The most wdsprd lo clds and some showers wl impact
mainly the hier terrain of the w with arrival of sharper trof
axis/some upslope wind component. h85 temps falling to about 4C wl
add a lk effect component to the pcpn as well.

Mon...Sharp, slowly veering wsw to wnw cyc flow under slow moving
trof axis/area of deep lyr qvector cnvgc associated with closed lo
driftng thru Ontario just n of Lk Sup wl bring nmrs/even wdsprd lk
enhanced showers to mainly the nw half of the cwa. Although no sharp
pres rise center that would aid an isallobaric component to the wind
is fcst to follow the trof axis, h925 winds up to 40 kts under the
thermal troffing wl support wind gusts aprchg advy criteria at
exposed locations over the Keweenaw Peninsula by later in the aftn.
As the winds veer a bit more toward the w over the ern cwa, waves
are fcst to build sufficiently to cause a hi swim risk in the
beaches of Alger County late in the day. Fortunately, the wx
conditions wl likely discourage swimmers.

.LONG TERM...(Monday night through Sunday)
Issued at 246 PM EDT SUN SEP 25 2016

Focus in the long term continues to be on a low pressure system that
will be occluding over or just N of far northern Lake Superior Mon
evening. The low will linger in the vicinity of the far northern
lake until Tue morning when it will start a slow move to eastern
Upper MI by 00Z Wed. The system moves S of the area Tue night, with
SFC and upper ridging moving in from the NW on Wed.

Main significant impacts will be strong winds near/over Lake
Superior and resulting high waves. Certainly will be seeing plenty
of rain, but not a worrying amount.

Models agree quite well with the track/strength/timing, but some run
to run variability still exists, so the wind forecast will continue
to need fine-tuning. Expect the strongest winds (at least in the
long term) on Monday evening with WNW gusts to 45mph along Lake
Superior over the western U.P. and over much of the Keweenaw. NW-N
winds will gust 35-40mph near Lake Superior for the rest of Mon
night through Tue. Winds will diminish Tue night into Wed.
Winds/waves will lead to dangerous swimming conditions on Lake
Superior, as well as beach erosion (especially along eastern Lake
Superior). No need for a beach hazards statement as temperatures
will be below criteria and it will be rainy.

Lake enhancement will occur as 850mb Temps will be 1-4C from Mon
into early Wed, which when combined with deep cyclonic flow and
upslope forcing will lead to lots of rain near Lake Superior and
more scattered showers well inland. Winds will favor WNW flow area
Mon night, NW-N flow areas Tue, N-NE flow areas Tue night, then
diminishing chances in north central Upper MI Wed morning as NE flow
remains while ridging increases. Should easily see over an inch of
rain Mon night and Tue over the higher terrain of the NW and a
quarter to half inch elsewhere near Lake Superior...under a quarter
inch south central. Tue night into Wed should add another quarter
inch or less of QPF...highest over the higher terrain of the north

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 755 PM EDT SUN SEP 25 2016

The arrival of some drying following cold fropa will lead to a
period of VFR conditions at KIWD/KCMX this evening, and IFR
conditions at KSAW will improve to VFR overnight. An increase in low-
level moisture will then bring a return of MVFR conditions at KIWD
late this evening, at KCMX before 06Z, and at KSAW toward sunrise.
Conditions may fall further to IFR at KIWD and perhaps at KCMX Mon
morning as shra increase in coverage. Winds will also become
increasingly gusty during Mon with the stronger winds at KCMX where
gusts will reach up to around 35kt in the aftn.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 409 PM EDT SUN SEP 25 2016

Sse winds that will gale force over portions of the e half of the
lake will diminish w to e this evening/tonight along with an
approaching cold front/weakening gradient. Maintained going gale
warning into late tonight for the far e section of the lake as
terrain enhancement may focus stronger winds in this area. A more
widespread w gale to 35-40 kts will develop over Lake Superior on
Mon under the tightening pres gradient/increasing instability behind
a lo pres trof passage. Opted to upgrade the gale watch to a warning
for this event.  With the slow approach of hi pres, these strong
winds will diminish later Tue into Wed. This hi pres will then bring
light winds to end the week.

Upper Michigan...
Lake Superior...
  Gale Warning until 4 AM EDT Monday for LSZ267.

  Gale Warning from 5 PM Monday to 5 AM EDT Tuesday for LSZ265-266.

  Gale Warning from 11 AM EDT /10 AM CDT/ Monday to 8 AM EDT /7 AM
     CDT/ Tuesday for LSZ162-240>242-263.

  Gale Warning from 2 PM Monday to 5 AM EDT Tuesday for LSZ243-244-

Lake Michigan...


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