Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 270752

Area Forecast Discussion
National Weather Service Marquette MI
352 AM EDT TUE SEP 27 2016

.SHORT TERM...(Today and tonight)
Issued at 315 AM EDT TUE SEP 27 2016

Upper air pattern consists of a 500 mb closed low north of Lake
Superior this morning. Nam takes the closed low south to southern
Lake Michigan by 12z Wed. Nam shows some 850-500 mb q-vector
convergence and deeper moisture remaining across the area through
this evening before the dynamics weaken and head south with the
upper low. Overall, did not make too many changes to the going
forecast. Interesting thing happened on Lake Superior though as the
western buoy dropped to 7C from 16C yesterday. The central and
eastern waters cooled about 2C from yesterday with the gale event.
With Lake Superior a bit cooler, this has helped to increase the
stability a bit and thinking is that the lake temperatures are
running from 12C to 15C and 850 mb temperatures will be around 4C,
so there is still enough lake-850 mb delta-t to get some lake
enhancement pcpn. Looked at thunder possibility and still looks like
there could be several hundred j/kg of cape to work with, so kept
isolated thunder mention in there. As for waterspouts, there is
still a small possibility even though the lake-850 mb delta-t has
decreased a bit from yesterday as the lake has cooled a bit. Enough
of a chance with the lighter winds in the east and in Lake Michigan
to keep a slight chance of waterspouts going.

.LONG TERM...(Wednesday through Monday)
Issued at 346 AM EDT TUE SEP 27 2016

Upper low and sfc low over the Great Lakes on Wed slides to the
western Ohio Valley by Thu morning. Cyclonic ne winds with the
weakening low along with low-level moisture and h85 temps 4-5c (Lk
Superior water temps averaging upper 50s to near 60 as they have
fallen some with stronger winds in last day) leading to delta t/s
near 10c should keep good deal of cloud cover and some light showers
around for most of cwa until later Wed aftn. Shower coverage may
increase late morning into the aftn helped along by daytime heating.
Continued to carry slight chance of waterspouts on Lk Michigan as
the upper low and sfc low centers are close by. Delta t/s around 15c
and convective cloud depth to 25 kft support the potential for upper
low or land breeze type waterspouts per the Szilagyi waterspout
nomagram. Parameters become less favorable by Wed aftn and there is
less low level convergence, so dropped waterspout mention for Wed
aftn. Does not appear to be enough instability to justify any
mention of tsra on Wed so removed that from the forecast.

High pressure building in Wed night and Thu should end the shower
potential and allow for decreasing clouds. Some indication that h85-
h8 RH decreases later Wed night. If that occurs could see potential
for fog/low stratus as only moisture left would be very shallow.
Introduced some patchy fog west inland. After highs in the 50s on
Wed the increased sunshine and h85 temps more at 6-7c should support
highs in the 60s on Thu. May even see upper 60s scntrl and near Lk
Michigan shore as the northeast winds provide some downslope at
locations such as MNM/ESC/ISQ.

Upper and sfc low pressure system will remain nearly stationary if
not drift north slightly by Fri. Fri should remain dry though over
Upper Michigan with increasing clouds. Highs again in the mid-upr
60s. Persistent NE winds will keep it cooler near the Lk Superior
shore. GFS and GEM becoming on board with recent ECMWF showing
system drifting farther north Fri night into Sat. Weekend that at
one time looked mainly dry with seasonably warm temps may be turning
wetter and cooler as the ECMWF has been showing for quite some time
now. Based on ECMWF and its trends over last few runs, bumped up
pops from consensus and put chance pops in for east on Fri night and
roughly the east half of cwa on Sat. Also increased cloud cover and
lowered max temps on Sat. This was one of the bigger changes to the
forecast this go around.

Trends from the ECMWF indicate upper low slowly moves toward New
England later Sun night into Mon. Should see improving weather
across Upper Michigan on Mon as upper level ridging becomes main
feature again. Ridge sharpens by Tue as deep troughing forms over
the western Conus. Sfc trough in the plains to scntrl Canada by this
time and departing ridge result in stronger south-southwest low-
level winds over the Upper Great Lakes. H85 temps Tue aftn show
quite contrast from cooler GFS (+7c) and warmer ECMWF (+14c).
Pattern fits the warmer ECMWF idea and would signal we could see
widespread highs in the 70s next Tue. Bumped up consensus highs
slightly but didn`t stray too far given the differences in the GFS
and ECMWF and since this is on the far edge of the forecast at this

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 121 AM EDT TUE SEP 27 2016

A slow moving low pres system will continue dominate the Upper Great
Lakes thru tonight. The resulting cyclonic upslope w to nw flow and
abundant moisture will lead to prevailing low MVFR cigs at KIWD/KCMX
thru this fcst period. IFR conditions are possible at times,
especially at KIWD as the flow veers more to the nw and increases
the overwater trajectory of the flow. At KSAW, the downslope nature
of the flow will allow for higher end MVFR cigs initially, but the
cig is still likely to drop into the lower MVFR range during the
early morning hrs as low pres now in northern Ontario sinks s and
draws closer. Gusty winds will also continue, more so at KIWD/KCMX,
and especially at the more exposed KCMX location, where gusts aoa
30kt are likely to continue thru the morning. However, winds will be
tending to diminish thru the day with the closer approach of the
Ontario low pres and a weakening pres gradient.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 315 AM EDT TUE SEP 27 2016

As low pressure over Ontario sinks slowly south and moves over Lake
Superior, the pressure gradient over the waters will continue to
slowly loosen and cause ongoing w gales to diminish under 30 kts
early this morning. There could be some waterspouts over the e half
of Lake Superior today into tonight under the slowly passing lo
pres. With the slow approach of trailing high pressure, the winds
will continue to slowly diminish into Wed. This high pressure will
then bring lighter e to ne winds under 20 kts to end the week.

Upper Michigan...
Lake Superior...
  Gale Warning until 5 AM EDT early this morning for LSZ243-244-

  Gale Warning until 11 AM EDT /10 AM CDT/ this morning for LSZ162-

  Gale Warning until 8 AM EDT /7 AM CDT/ this morning for

Lake Michigan...


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