Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 290939
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
339 AM CST Tue Nov 29 2016

.SHORT TERM...(Today and tonight)
Issued at 339 AM CST Tue Nov 29 2016

main fcst concerns this period are clouds and temperatures.

06z data analysis had a 980mb sfc low thru 500mb low over SE ND,
with their broad circulations covering much of central & eastern
NOAM. Occluded front/trough extended east of the low across central
MN/northern WI. Lobe of vorticity rotating around the mid level low
and deeper 850-700mb moisture was rotating into/across the NW side
of the fcst area early this morning producing some -RA/-SN in areas
NW of KMCW-KRST-KEAU. More westerly flow south of the deep
circulation spreading low level cold advection across the area. Even
so, temps early this morning still well above the normal late Nov
highs.

Model runs of 29.00z initialized well and offer very similar
solutions as the mid level low centered near the MN/ND/SD border
early this morning slowly migrates to near KMSP/KSTP by 12z Wed.
Tightening consensus favors more northerly of the earlier runs with
the mid level low position late today and at 12z Wed. Short term fcst
is good this cycle.

For the short term, vort lobe and deeper moisture spreading the -RA/
-SN across the NW side of the fcst area early this morning set to
rotate NE of the fcst area by 12z. With loss of lift and some
shallow moisture over the area today behind it, today continues to
trend as a dry day over all but the far N end of the fcst area where
small -RA/-SN chances were lingered to blend with neighboring grids.
With the main/broad circulation remaining well NW of the fcst area
today, some of the drier low level air/clear/mostly clear skies over
central/southern IA poised to rotate NE across the S/E sides of the
fcst area. Given the snow-free ground, locations that see some
sunshine today looking at highs in the 45-50F range, with mostly 40-
45F elsewhere with skies remaining mostly cloudy to cloudy under the
strato-cu deck. Lower moisture/cloud shield spreads SE across the
entire fcst area tonight as the sfc-mid level low sinks to near the
Twin Cities. With the increase/deepening of the moisture column and
increase of cyclonic convergence/lift closer to the stacked low,
some mainly -SN chances to spread into the NW side of the fcst area
by late tonight. (Column has cooled enough with BL temps in the low-
mid 30s and cloud tops below -10C for ice in them.) Blend of model
lows mostly 30-35F tonight looks good with cloudy skies and
winds of 5-10mph to keep BL stirred.

.LONG TERM...(Wednesday through Monday)
Issued at 339 AM CST Tue Nov 29 2016

For Wed thru Thu night: main concerns this period are -RA/-SN
chances Wed thru at least Thu, cooler temperatures.

Model runs of 29.00z in good agreement swinging the mid level trough
axis across the area Wed then moving the main trough to the Can
maritimes by 12z Fri. Even as the main trough exits east Wed night
thru Thu night models lingering troughing over the region as
shortwave energy rotates around the N & W sides of the broader
eastern NOAM troughing. Some detail differences by Thu/Thu night but
fcst confidence thru this period is generally good.

This the busier fcst period this cycle. Deeper moisture and the
deeper/tighter cyclonic convergence rotates across the area Wed with
the passing mid level trough axis. Increasing -RA/-SN chances to
spread across the fcst area Wed, peaking during the afternoon with
the mid level trough axis overhead and model soundings showing
steeper lapse rates to around 800mb and perhaps even a little weak
instability. Model soundings showing plenty of colder air aloft and
ice in clouds for precip as snow Wed/Wed night, with precip type to
be determined by the BL temps. Highs Wed progged in the upper 30s to
lower 40s, with more of a -RA/-SN mix at higher terrain/ridge top
locations and more -RA in the valleys.  Left precip as -RA/-SN
Wed/Wed night to blend with neighboring grids but may well end up
more -SHRA/-SHSN Wed afternoon/early Wed evening. If precip does
end up more showery Wed afternoon, with higher precip rates, may end
up with more -SHSN and more minor snowfall in the valleys. Precip
chances then decrease thru Wed night/Thu morning as the trough axis
and its convergence move away and the column above 700mb gradually
dries out in the NW flow. Even as the mid level trough exits, plenty
of 850mb moisture/stratus clouds expected to remain over the area
thru Thu/Thu night. Model blend of Wed thru Thu night highs/lows
with a muted diurnal spread appears quite reasonable at this time.

For Fri thru Mon (days 4 to 7): main concerns this period are small
-RA/-SN chances Sun thru Mon.

29.00z medium range model runs in general agreement for some
troughing to remain over the region Fri/Fri night, but plenty of
detail differences on the shortwave energy in it. Loose signal for
weak ridging aloft to build across the region Sat/Sat night, ahead
of troughing moving into the central/northern plains by 12z Sun.
Beyond this, models at odds with the handling of this troughing as
it would move into/across the Upper Midwest Sun/Mon. GFS faster than
ECMWF/Can-GEM with this feature, especially by Mon. Lesser run-to-
run consistency among the models as well by Sun/Mon. Average fcst
confidence Fri/Sat, then below average for Sun/Mon.

Models would generally have high pressure building into the region
Fri/Sat for what would be dry/cooler weather. However, depending on
which model may be more correct with the details than the others,
cannot rule out some -SHRA/-SHSN Fri and perhaps even Sat. Left Fri
thru Sat night dry now per the model consensus. With models at odds
for Sun/Mon and poor run-to-run consistency, little confidence in
any one deterministic model in the day 6/7 time-frame. ECMWF would
spread a chance of accumulating snow into the area later Sun/Sun
night while GFS would hold off and spread a chance of mainly light
rain into the area Mon. Enough model differences that temps Sun/Mon
could vary by a category or 2 from the consensus in the fcst grids.
For now, small -RA/-SN chances Sun thru Mon and the consensus
highs/lows (still some 5-10F above normal) will have to do until
the model focus becomes clearer.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1100 PM CST Mon Nov 28 2016

Cigs/WX: Clear slot slipping across KLSE presently with VFR cigs
returning to KRST. Lower cigs are going to work into KRST over the
next few hours though as the low clouds rotate around a sfc low
currently over northern plains. With the clouds will come a few
flurries or -sn. Not expecting any vsby restriction at this time -
but trends will have to be monitored. Activity looks to be over
around 12z.

The MVFR cigs should hold tight across KRST, with models favoring
keeping KLSE VFR until later Tue night. After that, the TAF sites
could be stuck MVFR until Fri night.

&&

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

$$

SHORT TERM...RRS
LONG TERM...RRS
AVIATION...Rieck



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