Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 170525

Area Forecast Discussion
National Weather Service Marquette MI
125 AM EDT Mon Oct 17 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 night through Sunday)
Issued at 417 PM EDT SUN OCT 16 2016

Deep trof currently in the Gulf of Alaska and extending into western
N America is fcst to retreat from western N America in the coming
days. Initially, this trof is forcing ridging over the eastern CONUS
and warm, sw flow into the Upper Lakes. As the trof retreats and
heights rise over the western CONUS/western Canada, the last round
of energy coming off the Pacific into the western states will be
allowed to amplify into the central, then eastern CONUS by late this
week, downstream of the height rises over the w. As a result, the
initial warm pattern of the next few days, will trend down close to
normal mid and late week. Farther down the road, CPC, NAEFS outlooks
continue to favor overall above normal temps thru late month, and
CFSv2 runs have been consistently indicating that above normal temps
will dominate into early Nov. These outlooks don`t preclude some
periods of blo normal temps, but suggest that any cool periods will
be short lived. As for pcpn this week, after active weather thru Mon
night, consisting of basically 2 rounds of widespread pcpn, the
remainder of the week will feature periodic sct light pcpn
associated with the eventual eastern trof development.

Beginning Mon night, shortwave reaching the northern CA coast this
evening will reach the Upper Great Lakes Mon night with associated
sfc low tracking ne roughly across central Upper MI and far eastern
Lake Superior. 12hr 500mb height falls of 100-140m, fairly robust
deep layer forcing/isentropic ascent and low-mid level frontogenesis
should support widespread pcpn, mainly along/nw of sfc low track.
With precipitable water upwards of 1.3-1.5 inches avbl, 250-300pct
of normal, locally hvy rainfall will be a definite possibility.
MUCAPE of 500-1000j/kg are available for inflow into the pcpn area.
NAM is greater with the instability, up to 1500j/kg, and is farthest
n and w with the instability owing to its deeper/farther nw low
track. Its track has support from the ECMWF, but the ECMWF low is
not as deep. NCEP ARW and NMM represent the southern solutions as
they have the sfc low tracking across far northern Lake Michigan and
far eastern Upper MI. Deep layer shear over 55kt is much more than
sufficient for well organized storms and a svr risk. Even if storms
are elevated, which is most likely, shear is still more than
sufficient to support well organized storms and a svr risk if enough
instability is avbl at the level from which the inflow originates
for the elevated storms. There is some uncertainty in the elevated
instability component, but conditions warrant some potential of svr
storms, mainly for roughly the se 2/3rds of the fcst area. Large
hail should be the main svr risk. If the ARW/NMM are correct, svr
potential will be more limited to the se fcst area. May see a brief
burst of windy conditions in the wake of the low to the se of where
the sfc low actually tracks as trailing pres rise becomes
increasingly greater with time in its wake. Right now, it appears
lakeshore locations from near Munising eastward would be favored for
stronger winds. Unless the NAM solution is correct, not the high res
NAM which is weaker and se with low track, do not expect any
headline worthy winds.

Pcpn should be largely out of the area by 12z Tue as sfc low tracks
into northern Ontario to the ne of Lake Superior, and clouds should
gradually clear out from w to e thru the day. While incoming air
mass is cooler, it is not cool by Oct standards as 850mb temps at
mid day on Tue are 6-7C. This should support max temps generally
into the low/mid 60s.

Aforementioned trof moving out over the central CONUS midweek will
reach the Great Lakes Thu/Fri. Several weaker shortwaves may affect
the area as this trof approaches, then arrives in the Wed-Fri time
frame. At this point, none of these features appear strong enough to
support much pcpn. A consensus approach utilizing current/recent
model runs was used for pcpn. This results in nothing more than
schc/low chc pops Thu into Fri as an influx of colder air with time
becomes sufficient for a lake component to pcpn under nw flow.

There is some agreement for a shortwave to affect the area on Sat.
With mid level trof axis a bit farther e at that time, more
effective waa/isentropic ascent may allow for a more favorable
situation for some pcpn to spread across the area Fri night/Sat.
Some lake aided pcpn may linger into Sun as a cooler air mass
settles into the area.

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 124 AM EDT MON OCT 17 2016

A warm front will lift northward toward the area 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. IFR/LIFR
conditions will then persist through most of Monday with some
improvement possible late. Additional rainfall with a low pressure
system moving in Monday evening along with abundant low level
moisture will support IFR vsby.

.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 this morning for LSZ266-267.

Lake Michigan...


LONG TERM...Rolfson
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