Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 172002

Area Forecast Discussion
National Weather Service Marquette MI
402 PM EDT Mon Oct 17 2016

.SHORT TERM...(This evening through Tuesday)
Issued at 402 PM EDT MON OCT 17 2016

Water vapor imagery continues to show a fairly potent shortwave
trough sliding into the Northern Plains this afternoon. Radar trends
are showing the early day convection continuing to slide to the east
of the Upper Great Lakes with a few showers developing across WI.
Cloud cover has been fairly extensive across the area and is
expected to continue this trend through tonight. The clouds over WI
are taking on more characteristics of convective cloud cover and
will need to be watched into the late afternoon early evening hours
for development. Temperatures under the breaks in the cloud cover
have jumped into the upper 60s and low 70s with dewpoints in the 60s.

Late this afternoon through Tonight: The aforementioned shortwave
sliding into the Northern Plains late this afternoon will slide
eastward to the U.P. by 06Z/18. At the same time, a surface low will
slide from the Central Plains into the Upper Great Lakes region. The
added dynamics will help to intensify the surface low as they phase-
up over eastern Lake Superior. Ahead of the surface low, the warm
front will become nearly stationary across Upper Michigan into
Wisconsin. The combination of these features will again focus
showers and thunderstorms across the U.P. by early evening. As the
shortwave slides into the area this evening, lapse rates are
expected to steepen to around 6C/km-7C/km on the warm side of the
front. This will help to push CAPE values as high as 500-1000 J/kg
across the south central and eastern portions of the U.P. As most of
these storms will be elevated on the warm nose into Upper Michigan,
the main threat will be large hail. Effective shear values are
progged to be around 40kts across the U.P. which would again support
larger hail production and storm organization. Overall wind
potential is expected to be marginal as these storms are again
expected to remain elevated with a fairly moist overall profile;
however, storm motion is expected to be around 40mph from the wsw
which could allow for a few stronger wind gusts. Additional
dynamical forcing will also slide in as the nose of the 850mb LLJ
moves into southern part of the U.P. by 00Z and then lifts slowly
north and eastward out of the area by 09Z. The U.P. will also be in
the left exit region of a 300mb 100kt+ jet also leading to
additional dynamical forcing. Most of the hi-res models have the
convection/precipitation reaching the WI/UP border around 00Z and
then lifting to the north and east of the area by 09Z with only a
few showers lingering on the back side of the low. In addition to
the shower and thunderstorm potential, winds may become gusty over
the Great Lakes as northwest flow kicks in on the back side of the
system. The best time for this would be from 06Z/18-13Z/18 and gusts
could reach gale force at times from the NW through that time
period. With some momentum transfer expected, with 925mb winds
progged to be as high as 40-45 knots have opted to issue a short-
lived gale warning for eastern Lake Superior from 07Z/18-13Z/18.

Tuesday: After a few lingering clouds in the morning, expect drier
air to filter in on the back side of the departing low pressure
system and ahead of a brief surface ridge. Skies will steadily clear
out throughout the day with sunshine sneaking out during the
afternoon hours. Daytime highs will be a bit cooler, but will remain
about 5 to 10 degrees above normal. Winds may be a bit gusty out of
the northwest in the morning, but the trend will be for lighter
winds moving in during the afternoon as the pressure gradient
decreases across the area.

.LONG TERM...(Tuesday night through Monday)
Issued at 330 PM EDT MON OCT 17 2016

WSW-SW flow aloft will keep temps at or above normal through middle
of this week. Trough aloft then is forecast to deepen over mid conus
late this week with cold air returning to Upper midwest and upper
Great Lakes Thu through Fri. Though main trough axis heads east Sun
into Mon, there are indications that troughing/NW flow will persist
over the Upper Great Lakes as additional shortwaves dive into back
side of the mean trough. Models are not consistent with each other
or individually run-to-run so there is uncertainty how weekend ends
up shaping up.

No large scale storm systems are on the horizon. Weak front works
through Wed aftn into Wed evening. Mid level moisture streaks in
ahead of front on Wed daytime but low-level moisture too dry to
support any showers. Eventually late in the week, cooler air aloft
(temps at 5kft as low as -6C/21F and as high as -3C/27F) pushing
across the warm waters of Lk Superior (observed water temps as low
as as 9C/48F and as high as 14C/58F) should support lake effect
precipitation as delta t/s climb to 12-20C. At the sfc by late this
week, high pressure will be from Manitoba to the central Plains
while lower pressure resides from Quebec to the lower Great Lakes.
Pressure pattern will favor NW low-level winds across Lk Superior
and the Upper Great Lakes Thu into Thu night which probably will end
up slightly cyclonic/convergent helping the lake effect along
somewhat, especially Thu night into Fri morning when there may be
weak upper level support and as core of colder air moves across.
Pops will be highest Thu night into Fri. Will continue to mention
mix of rain/snow for interior west Thu night and Fri night with h85
temps down blo -4c and 1000-850mb thicknesses falling blo 1300m.

Daytime high temps during this cool down will be lowest Thu and Fri
and probably into Sat as well with highs many areas staying in the
40s. Normal highs are around 50F to the lower 50s. Nighttime lows
near or blo freezing for interior west on Thu night then at more
inland areas on Fri night as the sfc ridge is nearby and pwat min
lowers to near 0.30 inches. Lowered min temps on Fri night over
consensus inland away from where any lake effect clouds may be
hanging on.

Shortwaves crossing the area as the upper trough either becomes re-
establishes or begins to depart could bring rain showers just about
anytime Sat-Mon. With no clear cut signal for stronger shortwave or
sfc trough, will just have slight chances or low chance pops for
these time frames.

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 135 PM EDT MON OCT 17 2016

Lingering low level moisture ahead of an approaching warm front will
keep lowered ceilings and visibility in place through tonight.  A
stronger low pressure system will lift northeastward into the area
late this evening into the overnight hours, bringing widespread rain
showers to each TAF site. There may be some thunderstorms as well,
with greatest likelihood of this happening at KSAW this evening.
Conditions will remain in the IFR to LIFR range through late tonight
at all the TAF sites, there may be a brief improvement late this
afternoon if the warm front lifts far enough north before stalling
out. Dry air will slide in behind the low pressure system on
Tuesday morning allowing for improving ceilings and visibility.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 330 PM EDT MON OCT 17 2016

Low pressure system lifts across Upper Michigan and Lk Superior
tonight while deepening. Expect winds less than 25 kts this evening
to quickly increase from the northwest to 30 kts overnight with
frequent gale force gusts to 40 kts over the eastern half of Lk
Superior. Period of strongest winds would be overnight tonight. A
gale warning has been issued for eastern Lk Superior. Winds diminish
less than 25 kts by Tue aftn and remain at 20 kts or less through the
rest of the week as pressure gradient becomes weaker.

Upper Michigan...
Lake Superior...
  Gale Warning from 3 AM to 9 AM EDT Tuesday for LSZ266-267.

Lake Michigan...


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