Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 261023

Area Forecast Discussion
National Weather Service Marquette MI
523 AM EST Sun Feb 26 2017

.SHORT TERM...(Today and tonight)
Issued at 516 AM EST SUN FEB 26 2017

A lot of nuances to the forecast this morning. Suppose if some of
these little things come together just right there could be higher
impact weather over parts of the cwa into early this evening. Even
though this occurs within the next 12-15 hours, mesoscale details
are hard to pin down so covered the two possible tricky spots
(Keweenaw and eastern cwa) with Special Weather Statements at this
time highlighting potential for plowable snow of at least a few
inches if not a bit more if everything comes together ideally.

Split flow aloft this morning with northern stream affecting weather
across much of Conus. Troughing persent from Hudson Bay to Great
Lakes. Lead shoftwave and decaying h85 fgen is supporting light snow
and flurries over central cwa and heavier snow now heading over
western Lk Superior out of MN. Echoes off Thunder Bay Ontario radar
indicates moderate to heavy lake enhancement with first batch is
likely missing northern Keweenaw county as sfc winds are too much
SW, but area of snow over western Lk Superior is expected to slide
in this morning, especially over northwest cwa where at least a
couple inches of snow seems reasonable. Also will see increasing
snow downwind of Lk Michigan as this shortwave interacts with
another weaker shortwave lifting in from southwest across WI and
since there will be favorable thermal setup ahead of the waves with
SW winds and h85 temps lower than -10c flowing over northern Lk
Michigan. Increased qpf toward 0.10-0.15 into early aftn per latest
RAP, HRRR and GEM regional. SLRs should be 15-20:1 which gives snow
into early aftn of a few inches. SW winds could be quite gusty as
well with soundings showing gusts to 30 mph possible as mixing depth
increases. Added blowing snow but temps by that time will be upper
20s to near 30F so that may work against significant blowing snow
developing. Other areas could see a dusting of snow before this
first batch of snow exits early aftn.

Attn mid to late aftn is on second and what is appearing to be
stronger shortwave currently driving snow over eastern ND. Radar
indicates this snow is more convective looking which lines up with
steeper lapse rates noted on upstream 00z soundings at MPX/INL and
BIS. Fairly compact wave but strong q-vector convergence and signal
of h925 fgen point to sharper band of snow moving west to east
across most of cwa as sfc trough crosses the area. This period of
snow will be moderate to heavy but it also should be transient.
Areas closer to Lk Superior could see a quick inch or two out of
this second batch of snow this aftn. Given the strength if the
convergence band slows down where the snow would last more in the 3
to 4 hour duration compared to 1 to 2 hours, advisory amounts would
not be out of the question. Quiets down tonight behind both of these
smaller systems. Subsidence behind looks to drop lake effect chances
down so have lowered pops.

Overall not enough confidence to go with advisories, especially as
models are persistent in showing lower SLRs more in the 10-15:1
range with the initial snow this morning over the northwest. If it
was colder both aloft and at the sfc, think the lake enhanced snow
off Lk Michigan could be larger issue as well. SPS covers both these
areas for now. Dayshift will have to watch the sharp convergence
band of snow this aftn. Another SPS could be needed for that as well.

.LONG TERM...(Monday through Saturday)
Issued at 506 AM EST SUN FEB 26 2017

Models suggest that a progressive pattern will prevail through
next week as a mid/upper level trough over the west moves through
the north central CONUS and Great Lakes into the northeast by the
end of the week. A transition toward a more zonal pattern is
expected next weekend.

Monday and Monday night. Scattered snow showers will be possible
early over the Keweenaw early with wrly low level flow and 850 mb
temps climbing from around -14C. Otherwise,  WAA ahead of the next
trough will boost temps into the mid 30s under partly to mostly
cloudy skies.

Tuesday into Tuesday night, as southwest mid/upper level flow
develops ahead of a trough into the wrn CONUS, the models have been
consistent in bringing a shortwave, bands of fgen, moderate
WAA/isentropic ascent toward the nrn Great Lakes. Although the
forcing remains somewhat unorganized and confidence in the details
remains low, it should be strong enough to support QPF into the
0.10 to 0.25 inch range, greatest over the northwest half.
Precipitation type also remains uncertain. Wet-bulb zero heights
favor mainly snow over the northwest and a mix or mainly rain
changing to snow over the southeast half as highs climb into the
upper 30s in most areas. There be a mix with freezing rain of
freezing drizzle early as a warm layer aloft develops. In
addition, there may also be a period where ice nuclei are absent.
With temps marginal for snow, any accumulations to near an inch
should remain confined to the Keweenaw.

Wednesday, model trends and the more consistent ECMWF suggest that
the large area of precipitation associated with a shortwave and sfc
trough along the stronger baroclinic zone will remain to the south
of the cwa. Slowly backing northeast winds and 850 mb temps in the
-8C to -10C range may support some light snow showers or fzdz into
locations downstream of Lake Superior.

Thursday-Saturday, weak clipper shortwaves may affect the region in
the developing nw mid/upper level flow. Confidence is higher that
enough cold air will slide into the area for increasing nw flow LES
from late Thursday into Friday as 850 mb temps drop to around -21C
by Friday morning. A stronger Pacific shortwave and sfc moving
toward Manitoba will bring increasing WAA Saturday with a chance of
light snow along with moderating temps into the 30s.

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1238 AM EST SUN FEB 26 2017

As an aprchg lo pres trof moves closer early this mrng, some -shsn
wl impact mainly the wrn CMX/IWD sites, and cause lingering VFR
conditions to deteriorate to MVFR, at least temporarily. The VFR
conditions are likely to linger longer at SAW and thru 12Z farther
fm the band of forcing. Some -shsn wl continue at both IWD and CMX
much of the day, especially at CMX, where vsbys wl probably end up
in the IFR range a good portion of the time. The best chc for the
lower vsbys wl be under more focused shsn along a lo pres trof that
wl move w-e acrs Upr MI in the aftn. Expect at least a brief period
of lower IFR vsbys associated with the heavier sn showers that occur
along this trof that wl clr SAW arnd 27/00Z. The arrival of much
drier air behind this trof wl then bring a return of VFR conditions
this evng.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 515 AM EST SUN FEB 26 2017

Winds will remain 30 kts or less through the forecast period.
Strongest winds, with gales not of question, will be tonight
behind low pressure trough moving through region and late Tue
into Wed as northeast winds increase behind another low pressure
system crossing Great Lakes.


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


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