Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 191718
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
118 PM EDT Wed Apr 19 2017

.SHORT TERM...(Today and tonight)
Issued at 459 AM EDT WED APR 19 2017

Main focus is on tonight when rain and snow will move in.

Shortwave energy and SFC low are currently over the inter-mountain
west, but will move into WI by 12Z Thu. Precip (mostly rain) will
move in from the SW after 00Z this evening, covering most of the
area by 12Z Thu. The precip out ahead of the system will be healthy,
with amounts of a quarter to one inch, highest south-central. While
there remains uncertainty with QPF amounts, the most uncertainty is
with ptype over the NW portions of Upper MI. Wet-bulb and dynamic
cooling will bring thermal profiles right on the edge of rain or
snow over mainly the higher terrain of the NW, with the most likely
scenario being a rain/snow mix and periodically switching back and
forth. However, with conditions being borderline, relatively small
changes with the system could change ptype and snowfall amounts. At
this time, generally only expecting an inch or less of accumulation
over the favored areas through 12Z Thu. Stay tuned to updates from
the next shift or two as things could change some.

.LONG TERM...(Thursday through Tuesday)
Issued at 418 AM EDT WED APR 19 2017

A split upper flow wl dominate the wx pattern across NAmerica during
the medium/extended range. Recent model runs have trended farther
north with the track of the next southern branch shrtwv/sfc low pres
to impact Upr MI tonight into Thu, bringing the potential for some
moderate wet snow to mainly the higher terrain of the ncentral/nw
cwa. Hudson Bay hi pres expanding into the area in the wake of this
disturbance wl then bring a period of dry wx for at least Fri and
Sat. Although a cold front associated with a northern branch shrtwv
may pass Upper MI Sat night or early Sun, accompanying pcpn should
be on the light side. The next disturbance to impact the area will
likely arrive late Mon into Tue. Expect temps to run at or blo
normal during the medium/extended range.

Thu and Thu night...GFS/NAM and regional CMC all coming into better
agreement on track of Plains shortwave and associated sfc low for
Thu into Thu evening taking the sfc low across northern Lake Mi into
eastern Upper Mi by early Thu evening.  Models show a significant
amount of qpf over much of Upr MI under large scale dpva and
diffluent upper flow ahead of the shortwave that wl result in 12hr
h5 height falls of 120-140m along the projected track of the
associated h85 low track. An upslope, strengthening cyclonic e-ne
flow wl enhance pcpn rates over the higher terrain of ncentral
counties, particularly Baraga and western Marquette counties and
over the Keweenaw Peninsula. The forecast thermal profiles suggest
the pcpn wl begin as ra but then mix with or change to sn over at
least the higher terrain of the nw half by sometime on Thu morning
as the vigorous uvv results in sufficient dynamic cooling thru a
deep enough layer. Models including SREF products and WPC snow
accumulation progs seem to be pegging Huron Mountains and even the
Keweenaw Peninsula as areas with greatest potential for significant
snowfall with upslope ene to ne flow and mid-level fgen as driving
forces.  However, there are concerns looking at the NAM and GFS bufr
soundings that the model QPF may be overforecast as both models have
drier air working into the area by 12Z Thu and the depth of moisture
does not reach to the -10C isotherm. At this point, do not feel
comfortable issuing a winter weather advisory given considerable
model uncertainty regarding marginal thermal profiles and
possibility of drying mid-levels on Thu. Feel inclined to keep SPS
going with a mention of a potential for moderate wet snow at times
into the Keweenaw and possibly Baraga and western Marquette
counties.

Expect the pcpn to diminish w-e on Thu night as the
shortwave/dynamic support exit to the e. But clouds and some lighter
sn wl persist thru the night especially over the northern tier with
lingering cyclonic upslope northerly flow.

Fri thru Sat...Hudson Bay high pres bldg into the Upr Lakes in the
wake of the departing low pres will bring a drying trend to Upr MI
on Fri, with some clrg as the llvl flow becomes more anticyclonic.
There could be some lingering -shsn/shra mainly east of MQT in the
morning where cyclonic nw will hang on a bit longer. Lingering clds
and llvl n winds off Lk Superior wl hold down the rise in max temps,
especially near the lake. The combination of light winds/clrg skies
and pwat falling under 0.25 inch in the subsidence behind the shrtwv
wl allow temps on Fri night to fall into the chilly 20s over the
interior. A good deal of sunshine and h85 temps rebounding to near
4C on Sat will allow max temps to rebound as high as the low 60s
over the western interior away fm the cooling influence of the lakes.

Late Weekend...The medium range guidance indicates a shortwave in
the nrn branch flow wl push thru Ontario and drag a cold front
across the Upr Lakes on Sat night/Sun morning. Although there are
timing differences, all the models generally show an absence of
moisture inflow that wl diminish the potential for any significant
pcpn, especially since the sharper forcing ahead of the shortwave wl
remain to the n. Even if there is a return of at least some sunshine
with trailing high pres on Sun, a north wind off Lk Superior and h85
temps falling as low as -8C wl result in blo normal temps.

Early next week...Models coming into better agreement, particularly
the 00Z GFS and ECMWF, on timing of the next shortwave/low pres that
is fcst to approach fm the w with the next best chance of pcpn
appearing to be Mon night into Tue.
&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 118 PM EDT WED APR 19 2017

Conditions have slowly improved from IFR to MVFR this afternoon.
Ceilings will continue to improve through the afternoon and early
evening hours. However, have included mentions of scattered low
clouds to hint towards the possibility that they may linger longer
than anticipated. A system from the southwest will impact all
terminals beginning in the west first, impacting KIWD/KCMX, and then
eventually lifting northeast and impacting KSAW. Fairly widespread
precipitation is expected, with rain most likely late tonight
through the morning hours at KSAW, and a rain/snow mix at KIWD/KCMX.
Eventually rain/snow will transition over to all snow at KCMX, with
confidence less likely in this transition at KIWD/KSAW within this
TAF period. Ceilings are expected to drop as well upon the arrival
of precipitation, and especially once colder air aloft begins to
drop south across towards the very end of this TAF period. North
winds will veer around to the east, with gusty winds expected
through the morning and afternoon hours on Thursday.
&&

.MARINE..

E to NE gales to 35-40kts are expected late tonight into Thu
afternoon as a system moves south of the area. N winds to 30kts will
linger behind the system through Fri morning. Winds will then drop
below 25 knots until Mon night into Tue when SE-E winds up to 30kts
are possible.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Gale Warning from 8 AM to 6 PM EDT Thursday for LSZ250-251-266-
     267.

  Gale Warning from 6 AM EDT /5 AM CDT/ to 3 PM EDT /2 PM CDT/
     Thursday for LSZ162-263.

  Gale Warning from 8 AM to 4 PM EDT Thursday for LSZ244>248-264-
     265.

Lake Michigan...
  Gale Warning from 5 AM to 2 PM EDT Thursday for LMZ248-250.

  Gale Warning from 5 AM to 1 PM EDT Thursday for LMZ221.

&&

$$

SHORT TERM...Titus
LONG TERM...Voss
AVIATION...Ritzman
MARINE...Titus



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