Winter Storm Watch 3, NWS La Crosse, WI

Allamakee County, IA, Chickasaw County, IA, Floyd County, IA, Howard County, IA, Mitchell County, IA, Winneshiek County, IA, Dodge County, MN, Fillmore County, MN, Houston County, MN, Mower County, MN, Olmsted County, MN, Wabasha County, MN, Winona County, MN, Adams County, WI, Buffalo County, WI, Clark County, WI, Crawford County, WI, Jackson County, WI, Juneau County, WI, La Crosse County, WI, Monroe County, WI, Richland County, WI, Trempealeau County, WI, Vernon County, WI

Area Forecast Discussion
National Weather Service La Crosse WI
220 AM CST Fri Feb 7 2020

.SHORT TERM...(Today through Sunday)
Issued at 220 AM CST Fri Feb 7 2020

WINTER STORM SAT NIGHT/SUN:  Dynamic shortwave will carry quite a
punch as it moves across the area late Sat night through Sun - well
forecast by the variety of models. Main questions have not been if
it would snow, more on the track of the heavier snows (north-along-
or south of I-90) and just how much qpf there would be to work with.

500 mb shortwave trough tracks out of the PAC NW tonight, shifting
across the Dakotas Sat and then across the local forecast area
overnight Sat through Sun morning. Strong low level thermodynamics
with upglide on the 275:290 K sfcs lead the shortwave across the
region, strongest around 12z Sun. QG convergence is strong and deep
while a 300 mb jet max will add more lift in its left exit region.
Some frontogenetic support, but nothing that stands out (yet) that
would suggest where enhanced bands could develop. All in all, an
impressive amount of lift accompanies this shortwave - although
perhaps not quite as much as earlier model runs were suggesting.

As for QPF...EC sits around 6/10 or so while the NAM comes in closer
to 1 inch in its main band. Similar to the wet GFS of yesterday. The
GFS stays on the high end, although has shifted its heavier pcpn
line south of I-90. GEFS plumes continue to run mostly under the
operational GFS when it comes to the main qpf region, generally
suggesting 1/2 to a bit above. Will go this route. With DGZ still
less than 100 mb climatology or a bit above for snow ratios look
reasonable. The result is a swath of 6 to 8 inches centered around I-
90. Farther south, amounts look a bit less, but also has the
potential for a little icing later in the day Sunday with dry slot
promoting loss of ice in cloud. Doesn't look like much right now,
but its a trend worth monitoring.

Will issue a Winter Storm Watch for the entire area to cover the
impacts from the forecast snow.

LIGHT SNOW TODAY: weak upper level shortwave trough, currently
dropping south/southeast across the northern plains, still on track
to brush western portion of the forecast area today. Light snow
already evident across parts of southern MN in weak warm air
advective regime ahead of the shortwave. Could receive minor accums
in those areas today, dusting to a few tenths. To the west,
favorable lapse rates could lead to some flurries, although the
deeper saturation doesn/t work into southwest WI until tonight.
Drawback to the flurry potential. Will hold higher chances and
accums to the west/south with smaller chances/flurries elsewhere.

.LONG TERM...(Monday through Thursday)
Issued at 220 AM CST Fri Feb 7 2020

What a difference a run or two makes. What looked like a potentially
boisterous system for mid week could end up being much ado about
nothing...or at least a lot less. Certainly not unexpected
considering the flow. Anyway, EC remains fairly consistent with
lifting an upper level shortwave trough out of TX, across the
eastern Great Lakes Thu afternoon. No phasing with any northern flow
energy this go around though, so a bit weaker and also shifted a bit
more east. Could still get some accumulating snows across southern
portions of the forecast area, but not as much as some of its
previous runs suggested. Latest GFS favors a stronger, more southern
diving northern flow shortwave, which works to keep the trough to
the south well south. Some snow chances with the northern shortwave,
but no phasing. Snow would be a day before the EC, not as much
accums, and perhaps more across the north. Confidence obviously
rather low in the details with the shifts within and between the
models. Still could be an interesting period and need to keep an eye
on it. Will let blends provide the pcpn chances.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 956 PM CST Thu Feb 6 2020

VFR conditions at the moment will very slowly give way to MVFR
ceilings overspreading the area into the afternoon and evening -
just a little slower than earlier expected. Light snow also looks to
just clip RST for the coming day, with mainly VFR or MVFR
visibility, but a brief period of IFR possible during the mid to
late morning. Any accumulation will be mainly 1/2 inch or less.
Winds will remain light from the south overnight, shifting northwest
5-10 knots through the day Friday.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Watch from Sunday morning through Sunday afternoon
     for WIZ029-032>034-041>044-053>055.

MN...Winter Storm Watch from late Saturday night through Sunday
     afternoon for MNZ079-086>088-094>096.

IA...Winter Storm Watch from late Saturday night through Sunday
     afternoon for IAZ008>011-018-019.
&&

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...Lawrence

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