Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 211928

Area Forecast Discussion
National Weather Service Marquette MI
328 PM EDT Tue Mar 21 2017

.SHORT TERM...(Today and tonight)
Issued at 427 AM EDT TUE MAR 21 2017

The shortwave is currently just N of Lake Superior with a 1010mb SFC
low just ENE of Lake Superior. A cold front has moved through the
Keweenaw, prompting gusts of 40-45 mph just behind the front. This is
very similar to conditions that occurred for a very short period of
time upstream. 850mb should currently be AOA -10C, but will fall to
around -18C by 15Z today. GOES-16 does not show any low level LES
development over the big lake yet, but that will come over the next
2-4 hours. NW-NNW wind LES will then persist through much of
tonight. However, LES will really struggle due to very dry upstream
air. Not looking at significant snowfall at all, have 24 hour
snowfall amounts of 1-2" with potential for local amounts up to 3".

.LONG TERM...(Wednesday night through Tuesday)
Issued at 328 PM EDT TUE MAR 21 2017

The most sgnft challenge in the longer term remains the potential
for mixed pcpn/some freezing ra in the Thu ngt/Fri time period to
the n of a warm fnt associated with a srn branch closed lo fcst to
lift enewd fm the srn Rockies toward the OH River Valley this
weekend. Overall confidence is lo into this weekend because the fcst
wl depend on the interaction btwn this closed lo and hi pres
expanding into nw Ontario under a separate nrn branch flow that wl
prevail acrs srn Canada. Although Wed ngt wl be quite chilly under
passing sfc hi pres, overall temps into next week should run aoa
normal due mainly to warm overngt temps.

Wed ngt...The combination of incrsg hi clds sprilling over an aprchg
upr rdg axis and an incrsg sly flow on the wrn flank of the sfc hi
pres retreating toward the ern Great Lks wl limit the diurnal temp
fall. Expect the lowest temps over the interior e closer to the
departing hi and lighter winds/core of drier air with pwat holding
in the 0.10-0.25 inch range thru the ngt. Dropped min temps toward
the lo end of guidance in this area.

Thu...Some of the latest models are generating some lgt pcpn over
the area as the incrsg sly flow/waa btwn the departing hi and a nrn
branch lo pres tracking thru far nw Ontario results in quite a bit
of mid lvl moistening. But the acyc, dry llvl flow wl limit
pops/qpf. Given these limitations and passage of sharper deep lyr
qvector cnvgc to the n closer to the Ontario lo/associated shrtwv
track, suspect the drier 12Z NAM model is on the right track. But
the fcst wl include some lo chc pops over the w half for mainly some
aftn light ra.

Thu ngt into Sat...As a closed lo over the srn Rockies embedded in
the srn branch flow dominating the CONUS shifts slowly toward the
mid MS River Valley, guidance indicates an area of pcpn wl dvlp on
Thu ngt over Upr MI to the n of its accompanying warm fnt that wl
extend into the Lower Lks. There remain some differences as to how
far n the main, most persistent waa/mid lvl fgen pcpn band wl drift
on Thu ngt into Fri as well as the thermal profile/ptype/impact of
llvl evaporative cooling and then on how quickly expanding sfc hi
pres over scentral Canada under the large scale subsidence behind
the passing nrn branch shrtwv wl advect drier air into the Upr Lks
and push this pcpn band to the s on Fri into Sat. A consensus of
recent model runs show the most persistent waa pcpn band wl impact
mainly the scentral closer to the axis of sharper h85-7 fgen. Since
h85 temps are fcst to rise above 0C over the area and lingering llvl
dry air wl allow for evaporative cooling, there is the potential for
freezing ra/some ice accumulation before diminished evaporative
cooling with llvl moistening on Fri allows the pcpn to change to
mainly ra. Pcpn chcs wl then diminish on Fri ngt into Sat as the nrn
branch sfc hi pres expands into nw Ontario. Some of the guidance
indicates some lgt pcpn may linger on Sat over the ncentral with an
upslope ene wind on the srn flank of the Ontario hi pres.

Extended...Uncertainty lingers into Sun related to whether and how
far to the n the srn branch closed lo wl drift. The GFS remains the
most aggressive at lifting a stronger closed lo farther to the n and
causing more wdsprd mixed pcpn changing to ra over the area
following the passage of the hi pres and retreat of the core of the
dry air into Quebec. For next Mon/Tue, pcpn chcs wl linger as many
of the extended models show a disturbance tracking thru the Upr Lks.
But much uncertainty remains on the track/intensity of this feature
and the impact on the mslp field, so no changes were made to the
consensus fcst.

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 152 PM EDT TUE MAR 21 2017

At IWD and CMX, conditions have already improved as very dry air
upstream moves over Lk Superior and Upper Michigan. Both of those
sites will see cigs around 030 or higher this aftn along with
minimal vsby reductions as light snow comes to an end. Only a few
clouds will linger late this aftn into tonight as air remains dry
closer to approaching high pressure ridge.

At SAW, expect more persistent snow showers through late this aftn
before dry air eventually takes toll on ongoing lake effect.
Conditions will mostly be MVFR through the aftn, though brief IFR
vsby is possible during heavier snow showers. Clouds should scatter
out by early evening as the dry air moves in. Then later tonight
into Wed morning expect MVFR to lower VFR clouds and flurries to
return as winds turn out of the N off Lk Superior. Skies will
graudally clear out on Wed aftn though it may take some time as
onshore winds persist off Lk Superior.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 427 AM EDT TUE MAR 21 2017

Gales will gradually diminish into tonight, with no other gales
expected otherwise. Some isolated heavy freezing spray is expected
over far eastern Lake Superior today into tonight, but not enough to
warrant a warning.

Upper Michigan...
Lake Superior...
  Gale Warning until 2 AM EDT Wednesday for LSZ249>251-266-267.

  Gale Warning until 4 PM EDT this afternoon for LSZ243>248-264-

Lake Michigan...


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