Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 282055

Area Forecast Discussion
National Weather Service Marquette MI
355 PM EST Tue Feb 28 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 355 PM EST TUE FEB 28 2017

WV imagery and RAP analysis indicated a mid/upper level trough over
the wrn CONUS with several weak shortwaves embedded in the wsw flow
toward the nrn Great Lakes. A shortwave and area of 850-700 mb fgen
is supporting a band of light snow from cntrl mn into western Lake
Superior. Another shortwave to the se and assoc isentropic ascent
was producing shra and a few tsra over central Lower Mi. Over Upper
Mi, a trough/cold front has moved through wrn Upper Mi into ncntrl
Upper Mi, and this trough/front will continue to progress e through
the rest of Upper Mi this evening.

Tonight, the fgen band should support some light snow over the west
and into the east overnight as the colder air moves in. Dry air in
mid-levels in ice nucleation region could also support some frdz
this evening in the west and especially ncntrl Upper Mi where
upslope nne flow will enhance lift. A strengthening gradient between
low pres into lower Michigan and high pres over nrn Ontario will
result in a stiff nne wind into the region. 850 temps in the -4C to
-8C will be marginal for lake enhanced snow but with strong upslope
flow some light accumulations of 1 to possibly 2 inches can be
expected in the higher terrain of north central and far west Upper

On Wed, shortwave now in the base of wrn conus trough will be
lifting ne into Lower Mi late tonight and then another shortwave
from the Central Rockies associated with the mid-level trough axis
will follow later in the day on Wed strenghtening the associated sfc
low moving through Lower Mi. Mid-level q-vector convergence and fgen
associated with the shortwave and the deepening sfc low track could
support an inch or two of light snow to southeast portion of the
cwa. Some light lake effect could linger over north central cwa with
NNE winds and shallow moisture to near 2kft with temps of -11c to -
12c. Otherwise expect only a dusting of system elsewhere.

.LONG TERM...(Wednesday through Monday)
Issued at 433 AM EST TUE FEB 28 2017

Shortwave entering the base of the trough over the western Conus
this morning should be crossing Neb and Iowa on Wed morning. H7-H5 q-
vector convergence with the wave along with ribbon of deeper h85-h7
moisture combine to bring chance of light snow of an inch or two to
south and east cwa to the northwest of 990-995mb sfc low crossing
central Great Lakes. Also will see chances of light snow showers
due to lake effect over north central cwa with NNE winds and
shallow moisture at least to H9 extending to temps of -11c to
-13c. Weak lake effect could persist through Wed night mostly
across north central cwa. Even though instability is marginal, all
the cloud layer within dgz could allow for very fluffy snow and
may even see some light accums Wed into Wed night for west and

Weak shortwave swings through late Wed night into Thu morning within
deepening trough aloft. Lake effect may increase some where it will
already be ongoing, mainly north central cwa and also over far
west cwa where northerly winds are favorable for lake effect. Also
if the shortwave has enough lift and moisture could see period of
lgt snow or flurries for most of the cwa even away fm Lk
Superior. Behind the mid level shortwave, reinforcing sfc cold
front moves through Thu evening. H85 temps down to -15c by 00z Fri
fall further to around -20c 12z on Fri. Expect lake effect to
increase Thu evening into Fri morning for the NW wind snow belts.
Forecast soundings show inversions up to 5kft over the west and to
8kft at the end of fetch over eastern Lk Superior into eastern
Alger county and northern Luce county. Since it is getting colder,
dgz is pushed closer to the ground and possibly may be out of
cloud layer, so snowflakes may get smaller and be better at
reducing visibility instead of producing much accumulation.
Likely snow showers for sure, but probably looking at 1-3" or
2-4"/12 hr type snows in this setup, with isolated higher amounts
if there is stronger convergence which would bring dgz more into
play and lead to higher slr/s. Blsn should not become too
significant since 925mb winds only reach around 20 kts later Thu
night into Fri.

Large high pressure ridge axis crosses area Fri into Fri evening
switching winds to S/SE and ending lake effect off Lk Superior.
Though cold enough for lake effect off Lk Michigan with that low-
level flow into cntrl cwa also seems too dry in low-levels to hit
that up at this point. Ridge is followed by rising heights aloft and
gradual warm front passage late Sat into Sun. Could be some light
snow as the warm front approaches but due to stronge ridge aloft and
more of a focused shortwave tracking south of Upper Michigan, last
couple runs of the models have backed off of the chances. If there
would be some snow it would occur late Fri night through midday Sat.
Rest of weekend into early next week looks potentially active but
the pattern is muddled. Ridge aloft slides across later Sat into Sun
but ECMWF continues to hint at small precip chances developing Sun
along tighter gradient of sfc-h85 temps and as it shows shortwave
cutting beneath ridge. If this light precip would come in earlier in
the day could have fzra issues as it looks warm enough aloft but sfc
temps could still be blo freezing. Pretty low chance at this point
though and just went with chance of rain/snow this far out.

Still looks like stronger low pressure system could impact the Great
Lakes next Mon into Tue. Recent runs of GFS and ECMWF trended north
which would lead to more rain on Mon then changing over to snow by
Tue, but maybe not as heavy as it looked before as the strongest
height falls will be tracking north of Upper Lakes. Overall even
though there is general agreement a storm may be there, there is a
lot of variability seen in recent ensembles from NAEFS and the
ECMWF. One thing that was apparent is the very progressive solution
from the Canadian is not supported by majority of its own ensembles
that have stronger low back across Upper Lakes similar to GFS and
ECMWF. System that helps spin up this low is still over northern
Canada so a long ways to go before getting to the details.

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1241 PM EST TUE FEB 28 2017

Moist upslope southerly flow contributing to LIFR conditions at
SAW will shift north-northeast this afternoon in the wake of a
cold frontal passage. Developing upslope north-northeast winds at
IWD and SAW will maintain LIFR to IFR conditions through much of
tonight before drier air moves in on Wednesday to allow
improvement to MVFR. Improvement from IFR/LIFR to MVFR will occur
quicker at CMX (possibly by late evening) given that nne flow is
more a downslope direction. Light enhanced lake effect snow could
also develop at IWD this afternoon and this evening at SAW as
colder air works in behind the front.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 355 PM EST TUE FEB 28 2017

Light winds less than 20 kts to start the day but winds ramp up
quickly this aftn to 30-35 kts as low pressure system moves toward
western Great Lakes. As the low crosses the central and lower Great
Lakes into Wed and a high pressure ridge moves across northern
Ontario, expect NE gales 35-40 kts over much of the lake Tonight
with gales continuing over eastern sections on Wed morning. Winds
will then remain below 30 knots through the rest of the forecast
period. Heavy freezing spray is expected tonight into Wed,
especially for north central portions of the lake.

Upper Michigan...
Lake Superior...
  Gale Warning from 7 PM this evening to 1 PM EST Wednesday for

  Heavy Freezing Spray Warning from 1 AM to 1 PM EST Wednesday for

  Gale Warning until 7 AM EST Wednesday for LSZ263-264.

Lake Michigan...
  Dense Fog Advisory until 1 AM EST Thursday for LMZ248-250.



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