Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 201743

Area Forecast Discussion
National Weather Service Marquette MI
143 PM EDT Sat May 20 2017

.SHORT TERM...(Today and tonight)
Issued at 509 AM EDT SAT MAY 20 2017

Latest water vapor imagery shows a developing closed low and well-
defined shortwave over the KS/NE border lifting slowly northward
through the Central Plains. Deepening moisture and lift out ahead of
the closed low/shortwave was supporting showers early this morning
from MO into central IA and southern MN, but very dry low-level air
mass in place was breaking apart the leading edge of showers into
northern IL and southern WI.

Latest regional radar trends and very dry airmass in place across
much of the Upper Midwest and Great Lakes region as depicted by the
00z GRB and APX soundings support 00z models slower progression of
pcpn into Upper Mi today. Thus, only have low chc pops for rain just
reaching into the the Wi border counties by 18z. With increasing
upper diffluence ahead of shortwave and increasing 295-300k
isentropic ascent ahead of occluded front, especially from 21-03z,
expect very dry low-levels to finally moisten and allow rain to
spread northeastward across the rest of west and central Upper Mi.
Despite increasing q-vector convergence and upper diffluence ahead
of the approaching shortwave trough late evening into the overnight,
mid-level dry slotting and a transition to isentropic descent as
depicted by models will cause a general diminishing trend to showers
from late evening into the overnight hours.

With more sunshine expected in the morning hours, bumped up high
temps today into the mid to upper 50s across much of the cwa, except
around 50f over the Keweenaw in strengthening onshore easterly flow.
Followed CONSAll guidance tonight under expected clouds and steady
ese winds with min temps in the lower to mid 40s.

.LONG TERM...(Sunday through Friday)
Issued at 320 AM EDT SAT MAY 20 2017

An upr trof centered over the Great Lks wl dominate the upper air
pattern for at least the first half of the coming week. Although no
heavy pcpn appears likely during this time, a general cyc llvl flow
over the area should result in a good deal of cld cover and a chc of
some showers at times. Blo normal temps wl also prevail, especially
the daytime hi temps with the cld cover. After the deep upr trof
exits to the e at mid week, a passing sfc hi pres wl bring at least
a brief period of dry wx. There remains much uncertainly on the
track/timing of a rather strong disturbance that wl follow and bring
a return of shower chcs sometime later in the week.

Sun...Lingering rain on Sun mrng ahead of lo pres lifting nwd toward
the wrn cwa and its attendant occluded fnt to triple pt lo pres
moving thru Lower MI wl diminish to perhaps some drizzle with
vigorous dry slotting under jet surge region on the ern flank of
supporting shrtwv moving n thru MN. As the lo pres continues into
wrn Lk Sup/Ontario during the aftn and the occluded fnt shifts to
the n, a dvlpg wsw flow on the srn flank of the lo wl end any pcpn
over the scntrl with downsloping wind component. But upslope wind
component wl keep pcpn chcs going over at least the hier terrain of
the nw cwa. Although there could be some breaks in the cld cover
over the scentrl later in the day with the downsloping wind, more
lingering clds overthe rest of the cwa within the llvl cyc flow wl
hold max temps blo normal, especially over the wrn cwa.

Sun ngt into Mon ngt...Slow moving, closed lo is fcst to exit only
slowly to the ne, resulting in just a gradual weakening of the llvl
cyc wly flow over Upr MI. Although the absence of any large scale
forcing wl restrict pcpn chcs, the lingering moist cyc flow wl bring
a continued chc of mainly light showers to most of the cwa,
especially away fm the scentral, where the downsloping wind
component wl be a greater negative for pops. H85 temps falling into
the 2-4C range and the clds wl result in blo normal temps,
especially Mon daytime maxes with the cld cover.

Tue/Tue ngt...A shrtwv digging sewd thru the nrn Plains on Mon is
progged to move near Iowa by 12Z Tue and then Chicago by 12Z Wed,
resulting in a deepening upr trof centered over the Great Lks. Many
of the medium range models show a slowly deepening sfc lo pres
associated with this shrtwv moving toward Lower MI. Although the
sharper forcing/heavier pcpn accompanying the shrtwv are progged to
remain to the s of Upr MI, rather deep cyc flow and lingering mstr
over the cwa wl still result in plenty of clds and probably at least
some sct showers, with the hier pops over the se closer to the
sharper dpva/deep lyr qvector cnvgc. Since h85 temps wl remain arnd
2C, cool wx wl persist, especially the daytime hi temps on Tue under
the clds.

Wed thru Fri...As the deep upr trof axis/sfc lo pres drift slowly to
the e on Wed, trailing hi pres/acyc flow and axis of much drier air
wl bring clrg during the day. With h85 temps rising to within a
couple degrees of 6C, expect max temps to rebound aoa 60 over the
scentral farther fm Lk Sup moderation. Depending on how quickly
the sfc hi pres shifts to the e on Wed ngt, Thu mrng could be
chilly with lgt winds before a strengthening sly flow ahead of
the next shrtwv sliding e thru the Plains near the Cndn border
brings a return of moister, more seasonably warm air and shower
chcs late in the week. The longer range models show a great deal
of uncertainty on the timing/track of this disturbance, so the
fcst wl show only lo chc pops for Thu/Fri. &&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 139 PM EDT SAT MAY 20 2017

VFR conditions will prevail through this afternoon. Rain showers
will begin to lift north across the area as low pressure lifts north
towards the area. Conditions will fall to MVFR at all sites this
evening as the rain becomes more widespread, and as rain begins to
taper off overnight tonight conditions will lower to IFR. There may
even be a period of LIFR conditions at KSAW late tonight in a moist
upslope ese flow. A period of tsra may also be possible btwn 09z-
15z, as a disturbance lifts through the area. However, confidence
was not high enough to include mention in the TAF at this time.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 320 AM EDT SAT MAY 20 2017

Ene winds 10 to 20 kts this morning will increase up to 25 to 30 kts
over the w half of Lake Superior this afternoon as the pres gradient
ahead of lo pres approaching from the sw tightens sharply over that
area and where terrain influences will accentuate the ne flow. The
sharper pres gradient and strong winds up to 30 kts will overspread
the rest of the lake tonight. Not out of the question there could be
some gales over the far w where the funneling of the ene flow will
continue. As the lo pres passes into Ontario on Sun and drags a
trough across Lake Superior, expect the winds to diminish and shift
to the w-sw by Sun night. Winds under 20 kts should then be the rule
on Mon into Wed as a relatively flat pres gradient dominates the
Upper Lakes.

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


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