Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 250551

Area Forecast Discussion
National Weather Service Marquette MI
1251 AM EST Tue Feb 25 2020

.SHORT TERM...(This evening through Tuesday)
Issued at 356 PM EST MON FEB 24 2020

Water vapor imagery and RAP analysis show a trof over central N
America with 2 branches of flow evident. The southern branch
features one shortwave over southern MO with a second dropping se
across the Rockies. To the n, a shortwave is moving into far
northern Ontario. Btwn these features, it`s been a quiet day across
the fcst area with much more sun than expected, except over the e
where bkn to ovc stratocu has developed with a definite spring-time
look (more sun closer to Lake Superior where it`s slightly more
stable from the marine layer and more cloud cover inland where there
is more instability from daytime heating). These clouds over the e
are also downstream from a low-level moisture band evident by cloud
cover streaking sse across northern Ontario to central Lake
Superior. With the sun, temps have risen into the lwr 40s
today across a good portion of the fcst area.

Diurnal heating and resulting increased mixed layer today has helped
to mix out at least some of the upstream moisture to the n of Lake
Superior, and this has some implications for the potential of any
-fzdz/flurries tonight under low-level winds veering from nw to ne.
Fcst soundings still indicate increasing low-level moisture tonight
due to added moisture from Lake Superior as 850mb temps ease down to
-8 to -10C during the night and due to nocturnal cooling of the
boundary layer. There is a fair amount of variation among the models
on whether temps in the moist layer will be low enough to support
ice nucleation (typically -10C is used as threshold). So, ptype
could be -shsn or -fzdz if pcpn develops. Since air mass is not cold
enough to support lake effect pcpn, pcpn would likely only be
upslope generated. For now, plan is to push back timing of any
potential pcpn to late tonight when low-level moisture will be
better. Will also confine pcpn mention to areas that have a more
direct upslope wind component over the far w and in Marquette/Baraga
Counties. Will also continue to mention ptype as -shsn/-fzdz though
given the mixing that has occurred today, not sure there will be
sufficient low-level saturation to yield -fzdz. Expect min temps
tonight in the 20s, but areas that have less clouds thru the night
will slip into the teens.

Slight cooling continues on Tue, but 850mb temps only fall roughly
another 1C. Will maintain mainly schc pops in the same areas as late
tonight. The slight cooling should tend to favor ptype becoming
mainly -shsn with time, if any pcpn does occur. Otherwise, expect
more cloud cover on Tue under the added moisture off the lake. Any
locations downwind of the lake that start the day with some sunshine
should see rapid stratocu expansion during the morning. Exception to
the cloud cover will be over the eastern fcst area as shorter fetch
under nne wind may cut down on low-level moisture off the lake to
diminish stratocu coverage. Will be cooler on Tue with highs in the
upper 20s to mid 30s, warmest south central.

.LONG TERM...(Tuesday night through Monday)
Issued at 334 PM EST MON FEB 24 2020

Previously it`s been said that the models are struggling with the
track and strength of the upcoming cross-country storm system. But
that`s not really fair to the rest of the models that aren`t the GFS;
the GFS has by far struggled to grasp the evolution more than any
other major modeling center`s output. Finally today it has settled
into the guidance envelope with the rest of the guidance in tracking
the main low well south of the area - so far so that even Milwaukee
is on the northern fringe of system snow now. The result for us up
here in the U.P. is no system snow is expected at all anywhere; any
snow we do see this week will be entirely lake-effect. It also
reduces the chance for significant NE flow upslope/lake enhanced
snow, instead shifting focus to the more traditional NW flow LES
belts, since we`ll be farther removed from the cyclonic flow around
the main low. The exception to that trend still looks like Tuesday
night into early Wednesday when there could still be a period of Ne
flow LES. The GFS is deeper with moisture and would support a couple
to maybe several inches - but again given its performance lately
have decided to stick with the NAM which depicts weaker lift in the
low levels and thus results in a little less snow. Still, some
scattered snow showers amounting to an inch or two is certainly
possible in this time frame.

Then comes the transition to NW flow LES Wed night through Friday.
This is when the GFS, EC, and other models remain in good agreement
about a secondary mid-level short wave merging into the upper level
low late Wednesday and shoving Arctic air southward over Lake
Superior. The combination of 850 mb temps in the -17 to -20 C range
and saturation to, at a minimum, 700 mb, should support plenty of
LES for the N to NW wind snow belts, with the heaviest snows
occurring late Wed night through Thurs night. The new version of the
NBM seems to struggle with lake-effect POPs compared to the previous
version, so needed to significantly increase POPs (to likely or in
some areas categorical) for this time frame. Now that this event is
getting a closer, we can talk a little bit about potential
accumulations. All in all this may end up just being a run of the
mill lake-effect event, except longer duration that some. Several
inches of fluffy snow is likely in the NW wind snow belts, but over
about a 48-hour period which will reduce the overall impact. Still,
along with some wind and with this fresh snow falling on top of the
now dense and smooth old snow, blowing snow will become a concern,
especially by Thursday.

This lake-effect snow could linger over the east as late as early
Saturday morning, but with diminishing intensity as drier air
filters in aloft ahead of ridging that will be building into the
Upper Great Lakes for the weekend. Speaking of that ridging, the
weekend still looks dry with temps warming back to near normal.
There are some indications that another storm system could be
brewing for early next week, but not going to cry wolf over that
this far out.

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1250 AM EST TUE FEB 25 2020

Stratus deck beginning to spread south across the area. MVFR cigs
reported at KCMX and IFR cigs at KSAW. Expect MVFR cigs to reach
into KIWD in a few hours with MVFR cigs continuing at KCMX and IFR
cigs continuing at KSAW into the overnight hours. MVFR cigs are
then likely to persist at most sites into Tue with maybe some
light lake effect snow showers or flurries developing.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 356 PM EST MON FEB 24 2020

Expect winds mostly blo 20kt across Lake Superior tonight. As low
pres slowly lifts across the Ohio Valley, Lower Great Lakes and into
Quebec Tue thru Thu, northerly winds will gradually increase,
reaching 20-30kt later Wed thru Thu and lingering into Fri. Over the
east half of Lake Superior, n to nw gales to 35kt are possible
Thu/Fri. Winds will then diminish from w to e in response to high
pres ridge arriving over the Upper Lakes on Sat.

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


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