Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 291100

Area Forecast Discussion
National Weather Service La Crosse WI
600 AM CDT Wed Mar 29 2017

.SHORT TERM...(Today through Thursday night)
Issued at 332 AM CDT Wed Mar 29 2017

Water vapor imagery early this morning shows a pronounced upper low
over New Mexico with with a plume of mid/upper moisture extending
to the north and east with increasing large scale ascent ahead of
the wave. This system will be our main weather maker over the
next 36-48 hours as it gradually lifts northeastward. 00Z MPX/GRB
soundings indicated quite a bit of dry air in place, but continued
mid/upper forcing will help to saturate the lower levels through
the day. By late morning showers should be increasing across
northeast Iowa, possibly encountering some resistance with
stubborn low-level dry air remaining. Rain will continue to
increase from the southwest through the afternoon, tied to
stronger 850- 700 mb warm advection. This warm advection along
with mid-level frontogenesis will help focus the precip through
the overnight hours into Thursday morning. The heaviest precip
totals are expected to be across far southwest WI and northeast IA
where an inch or a bit higher of rain is possible, with amounts
tapering to around a tenth of an inch over north central WI. The
29.00Z ECMWF remains more progressive with most of the precipitation
exiting to the east Thursday afternoon. However, the NAM/GFS hold
onto deformation zone precip longer into Thursday/Thursday night
with more of a pronounced TROWAL feature evident on 700 mb theta-e
fields. The NAM would even linger some precip into Friday in
western Wisconsin. Thus, will keep high precip chances going
through Thursday, especially over the southeast half of the area
decreasing to a mainly dry forecast on Friday.

There are still a few potential issues with precip type late this
evening through early Thursday, especially across central/north-
central WI. Surface temps should fall into the low to mid 30s
overnight tonight. NAM soundings in central WI suggest a period of
wet snow is possible especially north and east of I-94 overnight,
highly dependent on lower tropospheric temps and possibly precip
rate as well. However, NAM soundings in this area indicate some
potential for loss of ice overnight, which would lead to a liquid
scenario with surface temps critical. GFS soundings, on the other
hand, keep cloud ice through the night and show a rain/snow
scenario. With a rather deep nearly isothermal layer near 0C,
definitely a tricky forecast. All in all, it is possible there
could be some minor snow accumulations tonight mainly north/east
of I-94, but with warm ground temps and marginal air temps, it
will likely take high snow rates to create any travel issues.

.LONG TERM...(Friday through Tuesday)
Issued at 332 AM CDT Wed Mar 29 2017

Weak surface high pressure should bring a return to dry weather
Friday into Saturday, although Friday looks to be on the cloudy
side. Another southern stream upper low is expected to move from
the southern Rockies on Saturday eastward through early next week.
It is possible some light precipitation could spread north into
the area Saturday night into Sunday as a weak upper shortwave
ejects ahead of the main upper low, but at this time the higher
rain chances with this system look to be to the south. The
GFS/ECMWF then show a digging northern stream wave early next week
into the western CONUS, but there is poor model agreement and run
to run consistency in this pattern with the timing and
amplification of waves, so there is very low forecast confidence
for early next week. At this point, average to slightly above
average temps are favored.


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 600 AM CDT Wed Mar 29 2017

Cigs: increasing and lowering from the southwest today, ahead of a
low pressure system slated to bring rain (perhaps mixed with snow)
to the region this afternoon through Thu night. Models favoring a
swifting drop in cigs this afternoon, which matches fairly well with
current obs/satellite trends to the southwest. Expect mvfr/ifr by
00z. Low cigs will hang around through Thu night, and might not
clear until Friday night.

WX/vsby: low level warm air advection and a north-south
frontogenetic region will result in areas/bands of mostly rain
across the TAF sites from late afternoon through tonight. mvfr/ifr
vsbys will accompany the pcpn, which could mix with a few flakes of
snow later tonight (but no snow accumulation expected).

Winds: With the sfc low responsible for the clouds/rain keeping to
the south, winds will hold from an easterly direction through Thu,
with a little turn to north as the low passes. Tightening pressure
gradient will result in some increase in the winds through the day,
staying up tonight. Some gustiness also possible.




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