Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 241958

Area Forecast Discussion
National Weather Service Marquette MI
358 PM EDT Sun Sep 24 2017

.SHORT TERM...(This evening through Monday)
Issued at 219 PM EDT SUN SEP 24 2017

Upper air pattern consists of a deep 500 mb trough over the Rockies
and a strong 500 mb ridge over the ern U.S. The trough will move
into the northern and central plains 00z Tue while the ridge moves
to New England and the lower Great Lakes. Deeper moisture and
dynamics slowly move into the western cwa on Monday. Cool down will
begin starting on Monday, but temperatures will still remain above
normal and a few more records could be broken for Mon especially in
areas that do not have very long climate records like our office
here with 56 years of weather records. Temperatures look to be their
warmest in the morning, and then winds off Lake Superior will cool
things down in the afternoon as lake breezes set up. Will keep
slight chance pops late tonight in the far west and then slowly
bring in chance pops into the west half of the cwa late Mon
afternoon. Could be possible to see some lake breeze convection
break out Mon afternoon across the central cwa.

.LONG TERM...(Monday night through Sunday)
Issued at 357 PM EDT SUN SEP 24 2017

Cooler, more typical late Sept conditions will return this week.
Deep trof over the western CONUS is beginning to weaken, but strong
ridging remains over eastern N America with 500mb height anomalies
around 230m s of James Bay. Under the persistent deep sw flow into
the Upper Lakes, unseasonable, record breaking heat continues across
Upper MI. Over the next few days, the western trof will continue to
weaken while progressing downstream, reaching the Great Lakes
midweek. Upstream ridge building over western N America will result
in some amplification/slowing of the trof once it reaches the Great
Lakes. However, over the last 24hrs, much of the guidance is showing
a quicker downstream progression of the western ridge which would
force the trof out of the Great Lakes faster at the end of the week.
In any event, these large scale changes will lead to initial
unseasonable warm/humid conditions falling back to around normal by
mid week, then to briefly blo normal late week under trof
amplification thru the Great Lakes. Farther ahead, still looks like
a trend back to above normal temps will occur next week (1st week of
Oct) as there are indications that a western trof and eastern ridge
pattern will evolve. As for pcpn, potential of shra/tsra will
increase from w to e Mon/Tue as cold front shifts across the Upper
Lakes in response to progression of the western trof. Given days of
deep sw flow ahead of the trof, resulting in precipitable water of
at least 1.5 inches (200-250pct of normal) in the vcnty of the
front, potential will be there for mdt to hvy pcpn as front moves
across the area. A trend to dry weather should occur Wed behind the
front, then expect showery weather at times for Thu/Fri under mid
level troffing. At this point, the weekend looks like it should be

Beginning Mon night/ main energy in the western trof lifts
ne, reaching the Dakotas/MN Tue aftn, a sfc low pres wave is fcst to
lift up the frontal boundary that will be slowly moving into Upper
MI. While the front should drift into central Upper MI Mon
aftn/evening, it appears the front will then drift back to the w
with the approach of the sfc wave which will likely track nne across
far western Upper MI Tue morning. As a result, there will be some
focusing of convection across central Upper MI Mon evening in the
vcnty of the front before instability diminishes. Focus of more
widespread shra/embedded thunder will then shift back to the w
toward western Lake Superior overnight/Tue morning. This more
widespread shra activity may only brush western Upper MI given the
expected low track across that area. Given the high precipitable
water up around 1.6 inches (near record values for this time of
year), heavy rainfall is a possibility with any of the convection
during this time frame. As was the case yesterday, today`s model
runs show nothing particularly unusual for pcpn amounts though high
res models do show small streaks of hvy pcpn, indicating at least
localized hvy rainfall potential. At minimum, sct shra/thunder will
then accompany cold front across the area on Tue as sfc low pres
lifts into northern Ontario. Pcpn and progress of frontal boundary
will lead to cooler conditions Tue than Mon. Max temps should range
from the low/mid 60s w to mid/upper 70s e on Tue.

In the wake of fropa, cooler air will follow on Wed with a trend
toward dry weather. Max temps should be near seasonal late Sept
readings, in the upper 50s to mid 60s.

Thu/Fri, there is good agreement among the GFS/ECMWF/CMC for a
shortwave to drop se into the Upper Great Lakes Thu night/early Fri.
This is slightly faster than the consensus of guidance 24hrs ago.
Interestingly, the GFS and ECMWF have flipped on the strength of the
shortwave as now the ECMWF is strongest, similar to what the GFS had
been showing. The GFS is now weaker and was similar to the 00z CMC,
but the 12z CMC is now much stronger and similar to the ECMWF. There
is still not a lot of support from the CMC/GFS ensembles for the
strong solution, but there are more that are supportive compared to
the last 2 ensemble cycles, especially with the CMC ensembles. Fcst
will lean a little toward the stronger solution. If the ECMWF/CMC
solution is correct, a blustery, gale producing autumn sfc low pres
will drop se thru the northern and eastern parts of the Great Lakes.
Expect isold/sct -shra to develop Thu aftn as shortwave and
associated cold front approach. Ahead of the front, high temps
should be in the 60s. Isold/sct -shra should linger into at least
Fri morning under cyclonic flow. Cool air mass following fropa will
be marginally cold enough for a lake component to post frontal -shra
Fri morning. Fri will be the coolest day of the week as 850mb
thermal trof arrives. Expect highs in the lower 50s to lower 60s. If
the stronger shortwave solution of the ECMWF/CMC works out, max
temps on Fri won`t get out of the 40s in the higher terrain of the w
and n central.

The weekend looks dry with mid-level ridge and associated sfc high
pres passing across the Great Lakes. Next approaching shortwave may
be close enough to bring shra toward western Upper MI late on Sun.
Temps over the weekend will return to near normal for this time of

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1255 PM EDT SUN SEP 24 2017

VFR conditions are expected through the forecast period. A low level
jet developing above the nocturnal inversion will result in LLWS
late tonight at IWD and SAW.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 219 PM EDT SUN SEP 24 2017

Low to mid 60s dewpoints sliding across Lake Superior are expected
to linger into Tue bringing patchy to areas of fog across the lake.
Some of the fog could be locally dense at times. Expect winds to
generally be below 20 knots through the early part of the week under
a weak pressure gradient. However, as a cold front moves across Lake
Superior Tue night into Wed with colder air moving in, wind gusts
will increase to 20 to 30 knots. They will be in that range again
for Friday with cold air moving across the lake.

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


LONG TERM...Rolfson
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