Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 281206
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
706 AM EST Tue Feb 28 2017

.SHORT TERM...(Today and tonight)
Issued at 515 AM 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
supported a band of light snow from cntrl into ne MN. Another to the
south over srn WI combined with an area of strong 290K-295K
isentropic lift was bringing rain through ern WI along with a few
tsra. At the surface, low pressure was located over se Nebraska with
a warm front to the east into nrn IL and an inverted trough to the
ne to wrn Lake Superior. Although radar indicated some weak returns
over the west, with a 925-700mb dry layer through Upper Michigan,
pcpn will be slow to develop or reach the surface.

Today, short range models and radar trends suggest that the area of
rain over WI will slide mainly to the se of the cwa but may brush
the far south. The area of pcpn into wrn Lake Superior should
gradually advance into the west as the fgen forcing affects the
area. Confidence is lower that the broader area of weak to
moderate isentropic lift through the rest of the cwa will generate
much pcpn. However, at least some light amounts should develop by
mid morning. Pcpn typ also remains uncertain as the temps at or
near the sfc remain around or just below freezing. Although a
signficant warm layer is forecast to develop there may be enough
evaporative cooling to support mainly frozen pcpn. As sfc temps
gradually warm with WAA and daytime warming, mainly rain is
expected over all but the west where a mix of snow and rain will
remain possible. Colder air advancing eastward late in the
afternoon will change the pcpn back to snow over the west.

Tonight, the fgen band should support some additional light snow
over the west and into the east by late evening as the colder air
moves in. 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 will be possible in the higher terrain of north
central and far west Upper Michigan. Some fzdz may be possible late
as the inversion heights lower and mid level moisture departs.

.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
ncntrl.

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 12Z TAFS through 12Z Wednesday morning)
Issued at 702 AM EST TUE FEB 28 2017

Upslope southerly flow with low level moisture aided by Lake
Michigan has resulted in LIFR cigs at SAW with IFR fog which should
persist through the day. Low level dry air under a good deal of
mid/high clouds will result in VFR conditions at IWD/CMX early
this morning. But as mixed pcpn in advance of an approaching upper
level disturbance arrives this morning, predominant IFR
conditions are likely to develop and then prevail by the
afternoon. Expect gusty n winds to arrive late in the day/evening
following the cold fropa associated with the passing disturbance.
The pcpn will diminish nw- se through the evening with the arrival
of some mid level dry air behind the fropa.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 433 AM 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.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Gale Warning from 7 PM this evening to 1 PM EST Wednesday for
     LSZ265>267.

  Heavy Freezing Spray Warning from 1 AM to 1 PM EST Wednesday for
     LSZ263-264.

  Gale Warning from 4 PM this afternoon to 7 AM EST Wednesday for
     LSZ263-264.

Lake Michigan...
None.
&&

$$

SHORT TERM...JLB
LONG TERM...JLA
AVIATION...JLB
MARINE...JLA



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