Area Forecast Discussion
Issued by NWS Marquette, MI
FXUS63 KMQT 181745
Area Forecast Discussion
National Weather Service Marquette MI
145 PM EDT THU AUG 18 2016
.SHORT TERM...(Today and tonight)
Issued at 459 AM EDT THU AUG 18 2016
High pressure over the eastern third of the U.S. continues to slowly
drift to the southeast while low pressure over central Canada pushes
into Hudson Bay. Zonal flow pattern continues over the northern U.S.
in the short term with the pattern beginning to amplify tonight as a
5H trough swings into the northern plains.
Clear skies and residual moisture from yesterday`s rains have
allowed some patchy fog to develop over the area this morning. This
fog will quickly lift after sunrise leaving skies mostly sunny.
Southerly winds will result in some warm air advection as well as
moisture advection through the day. Initially instability remains
similar to yesterday in the 500-1000 j/kg range, which will be
enough to trigger some showers and thunderstorms along the lake
breeze. Increasing instability is mainly focused over the far
western Upper Peninsula mainly in the evening as a short wave
approaches and with increasing moisture pooling along and ahead of a
cold front sliding into the area. The latest short-term models have
been delaying the onset of the heavier, more widespread
precipitation and have followed this convention for this forecast.
Thursday night, precipitation activity spreads from west to east
across the region as the cold front pushes through. With decent
Upper level support and with slow progress of the frontal boundary,
area should see widespread precipitation with a potential for heavy
precipitation in some areas. While there is a possibility that a few
storms along the Wisconsin border may approach severe limits, the
best chances for severe weather remains well to the south where
better instability to exists.
Afternoon highs will reach into the 80s in most locations as some
increase in sky cover offsets an increase in 850 mb temperatures.
Southerly flow off of Lake Michigan will help keep the eastern U.P.
a bit cooler but with higher dewpoints.
.LONG TERM...(Friday through Wednesday)
Issued at 401 AM EDT THU AUG 18 2016
Friday through Saturday: A strong cold front is progged to slide
into the western U.P. by Friday afternoon and then very slowly into
the far eastern U.P. by Friday evening. Aloft, at 500mb, there will
be a piece of shortwave energy that slides into the area for the day
Friday and again on Saturday. Along and ahead of the front showers
and thunderstorms will spread across the area from west to east
Friday and Friday night and again Saturday as a low pressure system
develops and rides northeastward along the front. There may be a few
strong thunderstorms Friday afternoon and evening as shear values
are progged to be around 20 to 30 knots with at least some portion
of the shear orthoganal to the front early Friday afternoon;
however, the shear quickly becomes parallel to the front from the
southwest with widespread cloud cover also being a limiting factor.
This increased cloud cover would tend to limit the overall amount of
instability. Saturday, shear will be around 20 to 30 knots as the
next wave slides through, but the shear is progged continue to be
parallel to the front with little to no instability. Overall, the
Friday through Saturday time period definitely looks to be wet.
Heavier rain may be an issue this weekend with the slower movement
of the front/approaching low, along with PWAT values progged to be
between 1.5 and 2.0 inches. Behind the front, 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 Saturday
Saturday night through Sunday: The main 500mb trough axis will slide
across the U.P and moisture will continue to wrap back into the U.P.
on the back side of the departing surface low through this time
period, which will keep scattered rain showers in the forecast.
Temperatures will be cooler 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 00Z NAM wraps the low up tightly across the area for
this time period, which could give gusts upwards of 40 mph or so
along theLake Superior shoreline; however, it is the only model that
has this solution so did not go that extreme at this point, but it
will need to be watched over the next couple days.
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.
Tuesday night through the Extended: Models are hinting at 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 aproach the area; however, there area some timing and
strength differences, as is typical this far out; therfore, have
used a consensus of the models for this time period. This would
possibly bring showers and thunderstorms into the U.P. during this
.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 144 PM EDT THU AUG 18 2016
VFR conditions are expected through this evening. Showers and a few
thunderstorms associated with a slow moving cold front will move
into IWD and CMX overnight and to SAW toward daybreak. There could
be a period with MVFR vsby with the rain showers. Although VCTS was
mentioned at IWD, closest to the higher instability, only showers
were included at CMX/SAW.
.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 459 AM EDT THU AUG 18 2016
Despite a slow moving cold front pushing through the region, winds
will remain at or below 15 knots until the weekend. High pressure
building in behind the front will boost the pressure gradient enough
to produce stronger N winds to 25-30 knots Saturday night into
Sunday, mainly over the east half of Lake Superior.