Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 281751
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1151 AM CST Mon Nov 28 2016

.SHORT TERM...(Today and tonight)
Issued at 351 AM CST Mon Nov 28 2016

Main fcst concerns this period: -RA/-DZ chances today/tonight,
TSRA potential this afternoon/evening, warm temperatures.

Data analysis at 06z had a broad 979mb low lifting north thru
eastern SD. Circulation around this low covered much of the central
CONUS and south-central Can. Main rain band around this low was
rotating into eastern & northern WI and central MN, already
exiting much of the fcst area. Some DZ lingered behind the main
rain band but even the back edge of this was approaching the MS
river as mid level drying (dry slot) was rotating around the SE
side of the mid level low across IA/S MN into western WI. Tight
pressure gradient around the low covered much of MN/IA/WI, with S
to SE winds of 15-25mph gusting 25-35mph quite common across the
region early this morning.

28.00z models initialized well. Solutions similar for today/tonight
with a mid level low to wobble around the MN/SD/ND border this
period, with rather good run-to-run consistency back to at least the
26.12z runs. Short-term fcst confidence is on the good side this
cycle.

For the short term: one of the first concerns early this morning is
the clearing under the dry slot working NE across IA toward the
area. Models struggling with this a bit, but as the sfc-850mb flow
back a bit thru 12-15z, the clearing is expected to rotate more into
south-central MN vs. continuing to spread NE. Will have to keep
an eye on the low clouds right away this morning. Main shortwave
over SW MN early this morning to continue rotating N today while
secondary over AZ/NM swings around the S side of the mid level
low/trough and into the mid MS valley by late in the day. The 2
progged to at least partly phase up with another round of stronger
PV advection and jet divergence aloft to move across the fcst area
this afternoon/evening. Any decrease of clouds early this morning
looks to fill back in by noon. After a respite from the precip
chances for most of the area this morning, carried 20-80% chances
this afternoon into this evening, highest across the east half of
the fcst area where the deeper moisture/higher PW airmass and
stronger/deeper of the forcing/lift are looking to come together.
Models have trended back on potential of some weak MUCAPE over the
area this afternoon into early this evening. Model sounding still
showing some weak CAPE in the 850-700mb layer as some mid level
cooling spreads in. Will continue with an isolated TSRA mention
across the SE end of the fcst area later this afternoon/early this
evening when the stronger/deeper of the lift would pass with the
secondary shortwave. Once the sfc-850mb trough/front and mid level
trough axis pass, -RA/-DZ chances diminish rather quickly after
midnight.

With a warm start this morning and brisk S-SE winds much of the day,
consensus highs in the mid 40s-low 50s appear quite reasonable under
cloudy skies. Modest low level cooling spreads in tonight on
westerly flow south of the sfc-mid level low, with lows only
looking to fall into the 30s across the area.

.LONG TERM...(Tuesday through Sunday)
Issued at 351 AM CST Mon Nov 28 2016

For Tuesday thru Wednesday night: main concerns this period are
cooling temperatures and deformation band -RA/-SN wrapping into the
area Wed/Wed night.

28.00z model runs in good agreement on the the sfc thru mid level
low/trough taking its time drifting east across the Upper Midwest/
great lakes Tue thru Wed night. Fcst confidence for the Tue-Wed
night period remains on the good side.

Deep/stacked cyclonic circulation centered NW/N of the area produces
an extended period of weak to mdt low level cold advection across
the area. Even with this, temps to remain above normal thru this
period due to plenty of cloud cover and SW to NW winds of 5 to 15
mph for boundary layer mixing. Even by Wed night, lows only looking
to be near the normal Nov 30th highs. Drying above 850mb and
broad/weak subsidence over the area Tue/Tue night, for a dry
period. Eventually as the sfc-mid level low move NE of the area
and the sfc-500mb flow becomes more NW, the deeper saturation in
the deformation band with its lift rotates SE into the fcst area
for Wed/Wed night. 20-40% mainly rain chances Wed and -RA/ -SN
chances Wed night quite reasonable for now.

For Thu thru Sun (days 4 to 7): main concerns this period include
small -RA/-SN chance Thu and again Sun.

Medium range models runs of 28.00z in reasonable agreement for some
form of troughing/NW flow aloft to remain over the north-central
CONUS/great lakes Thu/Fri. By Sat and especially by Sun, models
diverge with handling of troughing over the SW CONUS/CA Baja, with
these differences showing impacts into the mid/upper MS valley by
Sun/Sun night. Fcst confidence average to good Thu/Fri, decreasing
to below average by Sun.

Thu/Fri dominated by NW sfc-mid level flow, but not a lot of cold
air to tap into across the border in Canada. Sfc-850mb remains
cyclonic with plenty of lower level moisture looking to linger over
the region in this flow. Plenty of clouds Thu/Fri will temper
highs/lows as far as diurnal ranges. Small -RA/-SN Thu reasonable
and may yet need to extend these into Fri depending on the depth of
the moisture and if the lower level trough axis is still the area.
Sat would see weak high pressure over the region. Model differences
by Sun yield either broad sfc troughing over the great lakes
(GFS) or a significant sfc low/mild level trough/precip event
approaching from the south (ECMWF). Little if any confidence in
details to be making changes at the day 7 timeframe and stayed
with the model/ ensemble consensus for now, right or wrong as it
may end up. At least temperatures for Sat/Sun trending closer to
the early Dec normals appear reasonable.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1151 AM CST Mon Nov 28 2016

Main taf concerns are LIFR/IFR conditions at both RST/LSE taf sites
through this evening. Low pressure will remain nearly stationary
over the Northern Plains States through the taf period. This will
continue to advect low level moisture and the possibility of
preciptiation into the area. Latest surface analysis shows
surface front extending south of the low pressure system into
north central Iowa...with showers/isolated thunderstorms along the
surface front over south central Minnesota/north central Iowa.
Ceilings out ahead of the front are in the LIFR to MVFR range
across the area. As surface front slowly pushes west to east
across the area...ceilings should improve to the MVFR to VFR range
after 02z-03z Tuesday timeframe. Scattered showers/rain...
possibly an isolated thunderstorm...will accompany the surface
front and track over the taf sites through this evening. The low
pressure system will wrap MVFR ceilings back into the RST taf site
by 12z Tuesday. VFR conditions are expected to prevail after 03z
Tuesday at LSE taf site. Pressure gradient will relax this evening
and winds will diminish to 7 to 12 knots at both taf sites after
02z Tuesday.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION...DTJ



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