Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 161945

Area Forecast Discussion
National Weather Service Marquette MI
345 PM EDT Sun Oct 16 2016

.SHORT TERM...(This evening through Monday)
Issued at 345 PM EDT SUN OCT 16 2016

Main focus in the short term will be an approaching warm front and
shortwave tonight and the associated showers and convection.
Temperatures will be well above normal through the short term as
well. Additionally, gusty winds will be possible overnight, with the
strongest gusts expected over eastern Lake Superior.

Tonight: The high pressure ridge that was in place most of the day
will continue to slide off to the east of the U.P. this evening. The
high pressure ridge and associated dry air should keep most of the
precipitation out of the area until or just after 06Z/17. Behind the
ridge, low pressure will slide from southern Saskatchewan eastward
into southern Manitoba late tonight. At the same time, a shortwave
will slide from the Plains states into the Upper Great Lakes region
as a warm front lifts northward toward the Upper Peninsula. The
tightening pressure gradient between the departing high and
approaching low will allow warm/moist southerly flow to increase
across the area. A 40kt to 50kt LLJ is also progged to form with
increased convergence occuring over northern WI by late evening and
then sliding northward into the U.P. overnight. This forcing, along
with increasing isentropic ascent into the area, on WAA, will set
the stage for widespread showers and some thunderstorms overnight.
MUCAPE values are progged to be up to 500 J/Kg, with this being in
the EML associated with the approaching warm front. Effective shear
values are progged to be around 20 to 30 knots in the convective
layer, so the overall potential for severe hail looks to be marginal
at this point; however, some small hail is not out of the question
later tonight, especially near the WI border. In addition to the
aforementioned shear/CAPE values 700-500mb lapse rate values are
progged to increase to around 7C/km as the shortwave slides through
the area. At this point SPC has areas near the WI border outlooked
for a marginal risk of severe thunderstorms late tonight with the
main risk being marginally severe hail. In addition to the shower
and thunderstorms tonight, breezy conditions will also be possible,
with the strongest winds expected across eastern Lake Superior.
925mb winds are progged to be between 30 and 40 knots over eastern
Lake Superior as the LLJ develops. Lake surface temps are running
around 12C while 925mb temps are progged to be around 7C. This will
allow some of the stronger winds to mix down to the surface, giving
an increased gale potential.

Monday: The aforementioned low pressure system will continue to
slowly drift across Manitoba through this time period as broad upper-
level troughing begins to slide across the Northern Plains. The warm
front is progged to slide into the U.P. or possibly just north of
the U.P. during the day as the first wave of showers and
thunderstorms continue to slide to the east and northeast.
Subsidence behind the first shortwave and associated mid level
drying will likely give a break in the showers and thunderstorms
through much of the day before a weak cold front slides
southeastward into the CWA by late afternoon. This cold front will
stall out as it slides into the western CWA; however, there will be
enough forcing and moisture that returns to the area late in the day
to create another round of showers and thunderstorms. CAPE values
are progged to be around 500-1000 J/kg, but a lot of this depends on
how far north the warm front lifts throughout the day. If it stalls
out across the U.P., increased cloud cover will likely limit
instability.  If the front lifts farther north, clouds may slide out
of the area enough for even more destabilization.

.LONG TERM...(Monday through Saturday)
Issued at 354 AM EDT SUN OCT 16 2016

Nam shows a 500 mb ridge over the southern plains and a broad trough
over the western U.S. 12z Mon with a shortwave moving into the upper
Great Lakes. Another shortwave ejects out of the broad trough and
moves into the upper Great Lakes Mon night. GFS and ECMWF show about
the same thing as well and will use a blend of them for this
forecast. Have likely pops in for most of Mon and Mon night for the
cwa. Bumped pops up a bit on Mon for the cold front that moves
through the area. Other than that, did not make too many changes to
the going forecast.

In the extended, GFS and ECMWF show a 500mb broad trough over the
Rockies 12z Wed with a ridge over the sern U.S. with a ridge on the
west coast. A trough moves into the northern plains 12z Thu with
850mb temperatures  dropping to -4C. This trough digs into the
central U.S. 12z Fri with 850 mb temperatures still remaining at -4C
over Lake Superior. With Lake Superior temperatures running from 9C
to 12C, this is enough lake-850 mb delta-t for lake effect pcpn. The
trough moves into the ern U.S. 12z Sat with a broad 500 mb ridge in
the western U.S. Temperatures will stay near normal to slightly
below normal for this forecast period.

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 141 PM EDT SUN OCT 16 2016

VFR conditions will linger through this afternoon into early this
evening. A warm front will lift northward toward the area by late
evening, bringing showers and a few thunderstorms to IWD first and
then to the rest of the TAF sites overnight. Ceilings will drop to
IFR overnight tonight at each TAF site with some visibility
restrictions due to rainfall. A low level jet will also develop
overnight which will introduce LLWS to all of the TAF sites with
shear values approaching 40 kts.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 345 PM EDT SUN OCT 16 2016

High pressure will continue to depart to the east this evening as
low pressure slowly approaches from the west. The pressure gradient
between the two will increase, which will lead to winds gusting
between 25 and 30 knots from the southeast over much of Lake
Superior. Expect the strongest se winds up to a gale force 35 kts
are expected to occur over eastern Lake Superior late tonight into
Monday morning; therefore the gale warning continues over eastern
Lake Superior. These strong winds will diminish through the day
Monday as the low pressure system and weaker gradient moves out of
the Upper Lakes. Another low pressure system will move northeast
near into Upper MI late Monday into Tuesday. This will allow strong
northwest winds to gust up to 30 kts to develop in its wake, mainly
over eastern Lake Superior, before weakening to about 20 kts or less
Tuesday night thru Thursday as high pressure approaches.

Upper Michigan...
Lake Superior...
  Gale Warning from 5 AM to 11 AM EDT Monday for LSZ266-267.

Lake Michigan...


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