Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 231945
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
345 PM EDT Sun Apr 23 2017

.SHORT TERM...(This evening through Monday)
Issued at 343 PM EDT SUN APR 23 2017

12Z raobs/latest wv imagery and RAP analysis show a confluent wnw
flow alf over the Upr Lks btwn nrn branch troffing centered over
Hudson Bay and a zonal srn branch flow dominating the CONUS. The
cold fnt which swung thru Upr MI late last ngt/early this mrng has
pushed into scentral WI and stalled, but the frontal bndry at h85-7
is still nearly ovhd and supporting a bkn band of rain/snow showers
over the wrn cwa. Sfc hi pres bldg into nw Ontario is extending a
sfc rdg axis over Lk Sup, and the llvl drying/sharper acyc flow
associated with this feature has brought some clrg to that portion
of the cwa. Very dry air is also located to the s of Upr MI even
over the stalled sfc fnt. Looking well upstream, a vigorous shrtwv
that caused 12hr h5 hgt falls of nearly 100m in the srn stream flow
is moving into the central Rockies.

Tngt...As the srn branch shrtwv now moving into the Rockies
aprchs the wrn Plains late, a sfc lo pres is fcst to deepen over
the ncentral Plains while the hi pres over northern Ontario drifts
slowly to the e. As the flow alf veers to the s in response to
the falling mslp to the w, the fntl bndry that stalls to the s wl
return to the n. The associated isentropic ascent best shown on
the 290-295K sfcs (h8-7) wl support some lgt pcpn generally in
the form of snow over mainly the nw half of the cwa away fm drier
llvl air over the e, but the steady shift to the n of the warm fnt
and influence of the llvl dry air wl limit pops/pcpn amnts. The
presence of a good deal of lingering clds over the w and incrsg
hi/mid clds over the e associated with the waa wl limit the
diurnal temp drop despite the llvl dry air.

Mon...The shrtwv/lo pres in the ncentral plains is fcst to drift ne
toward nw MN late in the day, lifting the sfc warm fnt and band of
waa pcpn to the n of Upr MI. The short range guidance shows quite a
bit of mid lvl drying in the warm sector. With the prospect of at
least some sunshine thru hi clds and h85 temps rising to arnd 5C,
temps should rise well into the 50s, especially in the downslope
areas influenced by the llvl se flow, where readings wl probably
reach the 60s. Tended toward the hier end of guidance for temps.
More clds/at least sct showers could arrive over the far w late in
the day as the lo pres/deeper mstr and stronger forcing ahead of the
shrtwv aprch.

.LONG TERM...(Monday through Saturday)
Issued at 343 AM EDT SUN APR 23 2017

...Active pattern with frequent chances for precipitation...

Active pattern continues this week with frequent chances for
precipitation. More chances for late season wintry precip too,
some of which could be high impact.

Cold front that settles across WI and lower MI will return north on
Mon as a warm front in response to sfc low crossing the northern
Plains. Could be a little light mixed rain/snow early on for Mon
over Keweenaw, but most areas will be dry on Mon. Lead shortwave in
broad upper level trough spreads area of h7-h5 q-vector convergence
and lift across Upper Great Lakes but with main sfc low passing just
west of here, majority of precip in the form of rain will affect
west forecast area. Temps on Tue will end up at or above normal in
the upper 50s to mid 60s as Upper Michigan ends up within warm
sector.

Round of heavier precip expected later Tue aftn into Tue night as
stronger shortwaves lift across northern Plains and central
Plains with associated wave of sfc low pressure lifting northeast
across the middle Mississippi River Valley to the Upper Great
Lakes. Despite the warm temperatures during the day, could see
fzra develop especially over far west Tue night as N-NE sfc winds
to the north of the sfc low bring in near freezing sfc temps
while temps aloft remain above freezing. NAM most aggressive with
this solution showing significant freezing rain/icing over far
west Upper Michigan vcnty of IWD. SREF probs over last two runs
also signal persistent/accumulating fzra over far west Upper
Michigan Tue night. Eventually, sufficient cooling occurs in low-
levels to change rain/freezing rain to snow late over western
forecast area though seems that recent model trends would support
better chances of that not occurring until daylight hours on Wed.
Tue night into Wed morning is the first of two main time frames
this week that focus will be on in terms of higher impact weather.

Precip gradually tapers off through day on Wed, but another wave of
low pressure results in more widespread precip later Wed into Thu.
Strong shortwave trough becomes negatively tilted as it lifts across
Upper Lakes and there is also coupled upper jet structure. Strong
forcing interacting with abundant moisture as pwats are over 1.25
inches which is at least 200 pct of normal. Main question is how far
west the system will track. Last few runs of GFS take it farther
east and only clip eastern forecast area with heavier precip,
staying in the form of rain. Canadian-NH is farther west with more
precip but also keeps ptype mainly rain. ECMWF farther west as well
but colder so it would result in more snow, at least over the west
half of forecast area. NAEFS ensembles point to farther west track
with more precip but warmer as well, so less snow. A lot of
solutions at this point which is no surprise since this wave is
still over the northern Pacific. Will have to continue to watch this
time frame as well as it could result in several inches of wet heavy
snow for parts of the forecast area. Turns colder on Thu behind the
departing system and there is enough lingering deep moisture and
cyclonic low-level flow to lead to leftover snow showers closer to
Lk Superior. High temps on Thu well below normal with mid 30s near
Lk Superior and only low 40s scntrl.

High pressure builds in behind the Wed-Thu system to bring dry
weather Fri into Sat. Some potential another wave could result in
more precip next weekend though. GFS last few runs is stronger and
farther north with upper level trough and has sfc low farther north
as well with widespread rain spreading over Upper Great Lakes as
early as Sat morning. Ensembles do support operational GFS idea so
may end up wetter. GEM and ECMWF also showing increasing chances for
precip as downright wet and active pattern marches on.
&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 122 PM EDT SUN APR 23 2017

As hi pres and drier llvl air expand into the Upr Lks this aftn,
expect any lingering pcpn near IWD to end, with improving conditions
at all the TAF sites thru early evng. Once the hi pres shifts to the
e later tngt/Mon, an incrsg se wind wl advect dry air into the area,
maintaining VFR wx.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 310 AM EDT SUN APR 23 2017

Winds look to stay at or below 30 knots through Tue night. Does look
like there could be a few gale gusts across central Lake Superior on
Mon. A northeast gale event looks likely on Wed into Wed evening on
Lake Superior as low pressure remains to the south. This looks like
the strongest winds for this period with winds slowly diminishing
Thu into Fri.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...KC
LONG TERM...JLA
AVIATION...KC
MARINE...07


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