Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 221926

Area Forecast Discussion
National Weather Service Marquette MI
326 PM EDT Sat Apr 22 2017

.SHORT TERM...(This evening through Sunday)
Issued at 324 PM EDT SAT APR 22 2017

12Z raobs/latest wv imagery and RAP analysis show a split flow
dominating the wx pattern over NAmerica. Upr MI is on the srn flank
of a nrn branch flat upr trof centered near Hudson Bay. A shrtwv
embedded in this flow is tracking acrs far nrn Ontario, with
attendant sfc cold fnt stretching fm sfc lo pres aprchg srn James
Bay into nrn MN. Due to the warmth/dryness of the airmass ahead of
this bndry per local 12Z raobs that has supported max temps into the
60s/rh falling as lo as about 20 pct over the cwa, there is an
absence of pcpn and even much cld cover ahead of the slowly aprchg
cold fnt. But on the cold side, there is a solid ovc and some light
ra that changes to sn under a band of h7 fgen and with an influx of
much colder air ahead of 12Z h85 temps as lo as -15C at The Pas

Tngt...Lingering dry air associated with sfc hi pres retreating
slowly to the se wl bring dry wx early in the evng, but then
incoming cold fnt associated with the disturbance in the nrn branch
tracking thru Ontario wl reach the Keweenaw by 03Z and then the far
scentral arnd 12Z Sun. The band of pcpn under axis of h7 fgen on the
cold side of the fnt wl arrive over the far nw cwa toward midngt and
influence mainly the nrn tier with an upslope nly flow in the wake
of the fropa. Although the pcpn, which wl start as ra but then mix
with sn as colder air follows, wl be relatively light with an
absence of sgnft mstr inflow and passage of sharper dynamic forcing
to the n closer to the shrtwv track, there could be some wet sn
accum over the hier terrain of nw Upr MI as min temps dip to 32.

Sun...Hi pres bldg into nw Ontario under larger scale subsidence
following the exiting shrtwv is fcst to extend a sfc rdg axis into
the Upr Lks. Although the arrival of this rdg axis/some drier llvl
air and acyc flow as well as weakening fgen wl tend to diminish any
pcpn over mainly the nrn tier persisting in the mrng, a good deal of
mid lvl mstr/cld cover wl linger near an h85-7 fntl bndry that
remains near the area to the n of the sfc fnt that wl stall in WI.
The best chc for some partial clrg in the aftn wl be over the ne
cwa, which wl be more influenced by deeper drying. Did retain some
lo chc pops thru the aftn over the w, where the drying wl be less
emphatic. H85 temps falling as lo as arnd -6C over the Keweenaw and
llvl nly flow off Lk Sup wl cause much cooler wx for the cwa, with
hi temps holding in the 30s near Lk Sup.

.LONG TERM...(Sunday through Friday)
Issued at 406 AM EDT SAT APR 22 2017

Nam shows a closed 500 mb low near Paducah, KY 12z Sun with a trough
over the upper Great Lakes. This trough moves east with another
trough moving into the Pacific NW 12z Mon. This trough moves into
the Rockies Mon night. Nam shows some 850-500 mb q-vector
convergence and deeper moisture over the area 12z Sun that remains
into 12z Tue. Frontal zone gets hung up over the area and remains
through Mon night. Moisture still remains limited until Mon night,
so will keep low chance pops in. Overall, did not make too many
changes to the going forecast.

In the extended, GFS and ECMWF show a broad 500 mb trough across the
Rockies into the plains 12z Tue. This trough moves into the upper
Great Lakes 12z Wed with some colder air moving in behind this
trough for Wed into Thu. A 500 mb trough over the Rockies on Thu
will strengthen and move into the northern plains 12z Fri. This
trough remains into Sat. Still looks unsettled for this period with
temperatures being the warmest on Tue and then going below normal
for Wed through Sat.

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 136 PM EDT SAT APR 22 2017

A gusty wsw wind will prevail at the TAF sites this aftn under
the tightening pres gradient btwn hi pres in the Lower Lakes and an
aprchg cold fnt in Ontario. Since this flow wl be tapping very dry
air, VFR conditions wl also predominate. A cold front will drop s
across the area tonight, passing CMX late this evening and IWD/SAW
overnight. Lo clds/IFR and even some LIFR cigs along with some ra
changing to sn wl impact the sites following the fropa and into Sun
mrng before the arrival of somewhat drier near sfc air allows for an
improvement later in the fcst period.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 407 AM EDT SAT APR 22 2017

Winds light today ahead of a strong cold front that moves in late
tonight. NE winds behind the front will increase to 15-25 kts Sun
into Sun night with strongest winds over western Lk Superior due to
funneling flow between Keweenaw Peninsula and MN shoreline. E winds
will then increase up to 25 to 30 kts Mon into Tue as low pres moves
from the ncentral Plains across the Upper Lakes. Where the winds are
stronger over portions of the ncentral and e parts of the Lake, not
out of the question there could be a gale at least a part of this
time depending on the strength of the low pres. Expect a wind shift
to the N-NE up to 25-30 kts on Wed following the exiting low pres/
attendant cold frontal passage.

Upper Michigan...
Lake Superior...
Lake Michigan...


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