Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 152045
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
245 PM CST Sun Jan 15 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 244 PM CST Sun Jan 15 2017

The 15.12Z models have come in with solutions very similar to the
previous runs. This has lent some confidence to the forecast and
helps reinforce the idea that we are going to get a real mess of
weather types.

The upper level low has started to lift northeast and was
crossing the Rio Grande early this afternoon. The low will
continue to lift northeast as a closed low through Monday then
start to open up as a northern stream short wave trough comes in
behind it. This northern stream wave will act as the kicker as it
drops into the Upper Midwest Tuesday and then quickly moves east
Tuesday night. The period of strongest forcing looks to be
centered on late Monday afternoon into the early evening. The pv
advection in the 500-300 mb layer looks to be moderate in
strength during this time period with moderate to weak qg
convergence in the 1000-300 mb layer. The isentropic up glide
ahead of the system looks to be generally in the 2 to 3 ubar/s
range but more importantly, the moisture transport on this surface
is right into the forecast area. This could lead to some higher
precipitation rates at times with a solid quarter inch of qpf
amounts expected Monday afternoon across northeast Iowa into
southwest Wisconsin and again Monday evening across much of
western Wisconsin. Some concern that these amounts could be even
higher, especially Monday afternoon.

So while the signals remain that there will be precipitation with
this system, still lots of concerns on what type that will be.
Initially, the system looks to come in with ice aloft, but this is
gradually lost from south to north from late Monday afternoon
through Monday night. Even before this occurs, temperatures aloft
will be warming from early Monday morning right into early Monday
evening. This will work to create the mess of precipitation types
from snow to sleet to freezing rain. Even where air temperatures
do get above 32 Monday, freezing rain will still be a concern.
Surface dew points will initially be low enough to allow for the
surface wet bulb temperature to go below freezing. Also, road
temperatures will be a concern. With the sunshine today, these
have warmed into the lower to middle 30s, so it will be
interesting to see how much they cool overnight, but with air
temperatures expected to fall into the teens, would expect these
to drop below freezing and then may stay there through Monday.
With all this going on, the ice accumulation looks to be the
biggest concern. Most areas are expected to get some, even if it
is just a glazing, with amounts of 1 to 2 tenths of an inch
possible along and south of Interstate 90. With the onset of the
precipitation expected to be late tonight across northeast Iowa
and southwest Wisconsin and the concerns about the warm air aloft
leading to some icing, we opted to start the winter weather
advisory late tonight for those areas. The precipitation should
then reach the Interstate 90 corridor just in time for the morning
commute with the advisory starting at 6 a.m. for that area. After
that, the precipitation may really battle the dry air and be slow
to advance north so will only add in the row of counties from
Wabasha over to Jackson starting at Noon. Expect that a advisory
will be needed farther north, but given the slower arrival of the
precipitation, still have some time before the advisory is needed.

This mess of precipitation types will start to end Tuesday as the
system pulls away from the area. With the northern stream short
wave trough dropping in, the remains of the other low should get
kicked east pretty quick. The precipitation chancez will really
wind down Tuesday morning with most of it expected to be done by
the afternoon.

.LONG TERM...(Wednesday night through Sunday)
Issued at 244 PM CST Sun Jan 15 2017

The GFS and ECMWF remain consistent on warming into next weekend as
an upper level ridge axis will slide through Thursday night/Friday
morning with 850 hPa temperatures reaching the 6 to 10 C range.
Highs will be in the 40s for much of the region through Sunday.
Models are showing the next precipitation chances for the region on
Friday into Saturday, and again on Sunday, pushing a shortwave trough
through the area from the southwest on Friday/Saturday and then
cutting off a low over the south-central US and bringing it north on
Sunday. Differences in timing exist, with the the past few runs of
the ECMWF being a bit faster than corresponding GFS runs in both
cases. The warm temperatures indicate a mostly/all liquid
precipitation type, especially during the day, but still too far out
and too many timing differences to get rid of the mentions of snow.

It is also worth mentioning potential hydro issues from ice jams and
runoff, but these will depend on how much precipitation falls in the
coming days and how warm it actually gets.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday noon)
Issued at 1132 AM CST Sun Jan 15 2017

Good VFR conditions to continue this afternoon/evening as dry high
pressure holds over the area. Mid/high clouds then increase/
thicken later this evening/overnight. May see some MVFR BR at the
TAF sites later tonight, but the increasing mid/high clouds
looking to limit this and left out of TAFs for now. Bigger
concerns is the wintry mix of precip (starting as -SN) and
MVFR/IFR cigs/vsbys to spread northward into the TAF sites Mon
morning. This mix and lowering cigs/vsbys looking to reach the KRST
area around 13z and KLSE area around 14z. A wintry mix of precip
and the lower cigs/vsbys then continue across the area thru Mon
afternoon into Tue morning.


&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from 3 AM Monday to noon CST Tuesday for
     WIZ054-055-061.

     Winter Weather Advisory from 6 AM Monday to noon CST Tuesday for
     WIZ041>044-053.

     Winter Weather Advisory from noon Monday to noon CST Tuesday for
     WIZ032>034.

MN...Winter Weather Advisory from 6 AM Monday to noon CST Tuesday for
     MNZ086>088-094>096.

IA...Winter Weather Advisory from 3 AM Monday to noon CST Tuesday for
     IAZ008>011-018-019-029-030.

&&

$$

SHORT TERM...04
LONG TERM...CA
AVIATION...DAS



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