Area Forecast Discussion
Issued by NWS Marquette, MI
FXUS63 KMQT 170832
Area Forecast Discussion
National Weather Service Marquette MI
432 AM EDT Mon Oct 17 2016
Issued at 432 AM EDT MON OCT 17 2016
00Z raobs/latest wv imagery and RAP analysis show a potent shrtwv
lifting newd thru the nrn plains toward Lk Winnipeg, accompanied by
12hr h5 hgt falls aprchg 100m. Strong llj with h85 s winds up to
50kts over MN and vigorous theta-e advctn/isentropic ascent/steep
mid lvl lapse rates shown on the 00Z MPX raob in advance of this
feature and warm fnt moving thru the Upr Midwest is causing an area
of showers/TS over the wrn Great Lks into wrn Upr MI. A few of the
storms turned strong, producing marginally svr hail at Rockland in
Ontonagon County. There is a break in the pcpn over the nrn Plains
under the influence of drier mid lvl air depicted at h7, but another
shrtwv lifting into the nrn Rockies is causing an area of colder cld
tops/pcpn to aprch the nw Plains.
Main fcst concerns in the short term focus on pop/convective trends
tday associated with vigorous waa ahead of shrtwv lifting into
scentral Canada. As the shrtwv now aprchg the nrn Rockies aprchs
tngt, focus wl shift to pops/convection associated with that feature.
Today...Band of showers/TS under llj/axis of deep lyr qvector cnvgc/
mucapes up to about 1000-1200 j/kg wl move e acrs the area this mrng
with this dynamic forcing before arrival of mid lvl drying/
stabilization in the wake of the sharper forcing results in
diminishing pops w-e thru the day. Considering the instability and
effective lyr shear within the elevated convection, not out of the
question some of the storms this mrng could cause some svr hail. The
best chc for some lingering showers/TS thru the day wl be over the
scentral, where the aprchg warm fnt is fcst to stall out. H85 temps
are fcst to peak arnd 15C over the far scentral, but plenty of
lingering lo clds wl hold down max temps. Still, max temps arnd 70
with dewpts over 60 wl make the day feel warm and humid.
.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.
Gale Warning until 11 AM EDT this morning for LSZ266-267.
Gale Warning until 5 AM EDT /4 AM CDT/ early this morning for
Gale Warning until 11 AM EDT this morning for LSZ264.
Gale Warning until 8 AM EDT this morning for LSZ263.