Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 180843

Area Forecast Discussion
National Weather Service Marquette MI
443 AM EDT Tue Oct 18 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...(Wednesday through Monday)
Issued at 443 AM EDT TUE OCT 18 2016

Nam shows a 500 mb shortwave over WY and another over the Canadian
prairies 12z Wed. Both of these shortwaves move east and help dig a
deep trough over the central U.S. on Thu and Thu night. Looks pretty
quiet for this forecast period, but could still see some lake effect
pcpn starting on Thu as colder air comes into the area and across
Lake Superior. 850 mb temperatures fall to -3C to -5C on Thu and
with lake temperatures from 9C to 12C, this is enough lake-850 mb
delta-t for lake effect pcpn. Did add in some pops for this with low
chance pops in northwest and north lake effect pxpn belts for thu
and thu night. Did not make too many changes to the going forecast.

In the extended, GFS and ECMWF show a 500 mb ridge over the desert
sw with a deep trough over the central U.S. 12z Fri. This trough is
very deep with the GFS and broader with the ECMWF with 850 mb
temperatures down to -4C to -7C 12z Fri and this cold air remains
over Lake Superior through 12z Sat. A shortwave moves through Sat
night into Sun morning. A broad 500 mb ridge moves into the Rockies
with a trough over the ern U.S. 12z Mon. Temperatures look to be
below normal for the start of this forecast and then get to near
normal by the end of the forecast period.

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 125 AM EDT TUE OCT 18 2016

Lingering low level moisture along a warm front will keep lower
ceilings and visibility in place through tonight. A stronger low
pressure system will lift northeastward into the area and could
bring around of showers into the TAF sites, although it looks like
heaviest rain has moved east of the TAF sites. Conditions should
remain in the IFR to LIFR range through late tonight at all the TAF
sites although expect dry air to move on gusty w-nw winds late
tonight into Tue morning allowing for conditions to quickly improve
to VFR by late morning/early afternoon.

.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...
Lake Michigan...


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