Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 191740

Area Forecast Discussion
National Weather Service Marquette MI
140 PM EDT FRI AUG 19 2016

Issued at 1247 PM EDT FRI AUG 19 2016

A pair of MCV centers, one over the Door Peninsula and one near KLNL
as of 1630Z, have been the instigators of ongoing convection this
morning. The initial line of showers and storms produced fairly
uniform wind gusts to 30mph and has since pushed into the far
eastern CWA. A pocket of some clearing between the two MCVs should
allow for some boundary layer recovery across the south central this
afternoon. Expectation is that afternoon convection will be limited
to the vicinity of the western MCV as it tracks eastward across the
south-central while the approaching cold front keeps shower chances
across the remainder of the west and central. Have therefore pulled
back the thunder forecast to just a slight chance across all but the
south-central through this evening.

.SHORT TERM...(Today and tonight)
Issued at 430 AM EDT FRI AUG 19 2016

Latest Water Vapor satellite imagery shows a short wave digging into
the northern Rockies this morning which is amplifying the 5H pattern
from the earlier near-zonal flow over the northern U.S.  A weak
shortwave embedded in the flow continues to enhance some showers and
thunderstorm activity over the eastern U.P. this morning. A second
cluster of showers and thunderstorms continue over MN and WI in
association with surface trough/cold front.

The better forcing/moisture convergence associated with this second
cluster of convection along with improving upper level support
supports this convective activity reaching Upper Michigan this
morning. Timing and extend of this activity is the main question.
CAPES of around 1500 J/KG are focused over the south central U.P.
this afternoon along and ahead of the cold front working through the
region. With weak shear profiles over the area, generally 25 knots
or less, do not expect severe weather but there will be a possibility
for heavy rains as PWs of 1.5 inches or higher noted. With plenty of
sky cover today, afternoon highs will run a little cooler than
yesterday especially as the 850 MB thermal ridge shifts to the east.

As the cold front/surface trough stalls out just to the southeast of
Lake Superior, the deepening 5H trough over the northern plains will
result in a deepening surface low over the plains late tonight. This
low combined with improving upper level support will help expand
precipitation across Upper Michigan late tonight into Saturday. Lots
of cloud cover to help keep temps up, with overnight lows remain int
he upper 50s to mid 60s.

.LONG TERM...(Saturday through Thursday)
Issued at 421 AM EDT FRI AUG 19 2016

Still looking like the weekend will be wet for the Upper Great Lakes
Region. There are some model inconsistencies that could cause
significant changes, mainly to the winds for Saturday night into
Sunday, so that will need to be watched for further adjustment as
models hopefully come into better agreement.

Saturday through Sunday: With continued uncertainty in mind, the
cold front is expected to stall out across the central U.P. and
eastern U.P. for most of the day Saturday as the main upper level
500 mb trough axis slides from MN/Western Ontario into the western
U.P. Out ahead of the upper level trough, a surface low is expected
to develop/intensify over central to eastern WI and ride along the
front as it lifts northeastward. This low is expected to cross the
central U.P. by Saturday evening and then slide into southwest
Quebec by Sunday afternoon. The GFS/EC/UKMET have a similar
trek/strength while the NAM/GEM are much farther west with the
surface low and have the low much stronger. This added support from
the GEM is really in the wind fields only as the mid level low only
closes off briefly with the GEM and then fills in. The NAM maintains
a stronger mid level low for a longer period of time. PWATs are
still progged to be around 1.5 to 2 inches Saturday afternoon and
evening as the low pass through the area so moderate to heavy rain
would likely be the main threat. It looks like a dry slot will slide
into the eastern U.P. Saturday evening through Sunday, which would
act to limit the rain shower potential during that time period;
however, this may lead to more instability over those areas,
allowing for isolated to scattered thunderstorms Saturday afternoon
and evening. Behind the front/surface low , broad 500mb troughing
will slide into the Upper Great Lakes Region as well as a tighter
pressure gradient on the back side of the departing low. This
tighter gradient will allow strong, gusty north to northeast winds
to develop, creating a moderate to high risk swim risk by late
Saturday afternoon. The main 500mb trough axis will slide across the
U.P and moisture will continue to wrap back into the area on the
back side of the departing surface low late Saturday night into
Sunday morning, which will keep scattered rain showers in the
forecast. Temperatures will be more Fall-like as the low/cold front
continues east of the area along with the decreased heights
overhead. Sunday will continue to see gusty north to northeast winds
with the continued tight pressure gradient across the area, which
would support a continued moderate to high swim risk along Marquette
and Alger counties. The tight pressure gradient looks as if it may
also be strong enough for Gales over central and eastern Lake
Superior later Saturday night into Sunday, but the exact location
for the strongest gusts will be highly dependent on the low

Sunday night through Tuesday: Overall moisture looks to be fairly
limited through this time period along with a surface ridge in place
across the area. There may be a couple shortwaves that try to round
the base of the overall troughing across the area, but the limited
moisture and anticyclonic flow should limit any shower chances
through this time period.

Tuesday night through Wednesday night: Models are depicting a low
pressure system and 500mb trough sliding across central Canada to
northern Ontario during this time period. This would also allow a
cold front to slide through the area. Ahead of the front, southerly
flow will kick in, allowing temperatures to again warm to above
normal for Wednesday. Showers and thunderstorms are expected to
develop along and ahead of the front, with the best chances expected
Wednesday afternoon into Wednesday night.

Thursday through the extended: Broad troughing is progged to be in
place across the area; however, there looks to be very little
moisture to work with for precipitation. As timing of subtle
features is tough, at best, to pin down this far out, have decided
to stick with a consensus of the models.

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 140 PM EDT FRI AUG 19 2016

Isolated to scattered showers will affect all sites into the early
evening as a cold front approaches from the west. Then, expect a
period of dry and VFR conditions into the overnight hours at all
sites before a large shield of rain spreads NE across Upper MI late
tonight through Saturday afternoon. All sites should see at least an
extended period of IFR ceilings during this time, with NE upslope
flow at KSAW possibly leading to LIFR ceilings conditions Saturday

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 430 AM EDT FRI AUG 19 2016

Winds will remain at or below 15 knots today and through much of
tonight. The approaching surface low will increase northeasterly
winds over far western Lake Superior and this combined with local
terrain effects there may produce winds to around 20 knots during
the day. Where the surface low tracks will play a role in how strong
the winds do become Saturday evening through Sunday, with gusts
currently forecast to 25-30 knots over central and eastern Lake
Superior. High pressure builds into the region Sunday night, leaving
winds less than 15 knots through Tuesday.

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


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