Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 230237

Area Forecast Discussion
National Weather Service La Crosse WI
930 PM CDT Sat Oct 22 2016

.SHORT TERM...(Tonight thru Sunday night)
Issued at 237 PM CDT Sat Oct 22 2016

Main fcst concerns this period: winds and temperatures on Sunday.

Data analysis at 18z had a weak pressure gradient over the area,
between a ridge axis from Jame`s Bay to western KY and low pressure
moving across SD. Deep, dry airmass and plenty of sunshine over the
Upper Midwest this afternoon. Temps under the sunshine this
afternoon back to near and above normal as weak low level warm
advection spreads across the region.

22.12z model runs initialized well. Solutions quite similar as the
shortwave near the MT/ND/Saskat border moves into northern MN
tonight then quickly into norhtern lower MI Sun, leaving NW flow
aloft over the Upper Midwest Sun night. Short-term fcst confidence
is good this cycle.

Shortwave moving into MN tonight develops low pressure near KMSP/
KSTP by 12z Sun. This low then moves quickly SE across the area Sun
morning as the shortwave tracks across northern WI. Sfc pressure
gradient tightens up by later Sun morning and for Sun afternoon.
This with mdt low level cold advection to steepen the lower level
lapse rates and provide subsidence. Models continue to indicate 25-
30kts of W-NW wind at 925mb for the late morning/afternoon, with
soundings showing mixing to near above that level by 18z. Winds much
of Sun afternoon looking to be NW 10-20 mph G20-30 mph and trended
winds in fcst grids up a bit. 925mb temps look to hold in the 10C to
14C range 12z-18z Sun, so now appears not much of a non-diurnal temp
trend for Sun. Low level cold advection continues Sun night as Can
high pressure quickly settles into the region under the NW flow
aloft. Low level cold advection continues Sun night with 925mb
temps in the 2C to 6C range by Mon morning. Trend of highs a
category or 2 above normal Sun, follow by near normal lows Sun
night looks good.

.LONG TERM...(Monday through Saturday)
Issued at 237 PM CDT Sat Oct 22 2016

For Monday and Monday night: main fcst concerns this period are
temperatures and increasing clouds Mon night.

Models in good agreement for hgts to rise across the region Mon/Mon
night as ridging slowly moves east across central NOAM. Fcst
confidence is good this period.

The sfc thru 850mb ridge axis drifts east across the region Mon, for
what should be a dry/mostly sunny day with light winds. Mixed 925mb
temps indicate highs near normal - mostly in the 50s. Moisture/
clouds ahead of the developing low and shortwave energy ejecting
into the central plains already starts to arrive Mon night. This
initial moisture and the QG/FN convergence/lift is above 700mb. Much
like last night, the question by later Mon night is will the
forcing/lift in the moistening layer above 700mb be enough to get
precip thru the drier sfc-700mb layer below it. May yet need some
small -SHRA chances or a sprinkle mention after midnight Mon night
but will leave it dry for now per the model consensus. Thickening
clouds by late evening/overnight Mon night - leaned toward warmer of
guidance lows, and may still be a category too low.

For Tuesday through Saturday (days 3 to 7): main fcst concerns this
period are SHRA/TSRA chances and rain amounts from Tue thru Wed.

Good agreement between the GFS and ECMWF of a lee cyclone developing
and moving east along the Interstate 80 corridor into Iowa and
Illinois through Wednesday. Decent moisture transport feeding into
strong frontogenesis in the lower to mid levels, along with
precipitable water values over 1 inch and strong lift indicate the
potential for a heavy rain axis somewhere in the area. Too early to
give an exact location, but models tend to favor an area along the
Minnesota/Iowa border, or perhaps a bit south of there, and then
east into Wisconsin. Potential remains for 1 to locally 3 inches
of rain much of the fcst area from Tue thru Wed. The expected
rain rates and dry trend since Sept 22 would indicate any runoff
issues with these rains would be minor.

The GFS and ECMWF diverge a bit following this system, as the 22.12Z
GFS slides another potent wave and precipitation to the north, while
the 22.12Z ECMWF keeps the the forecast area under northwest flow.
Regardless, both models favor mainly dry conditions, but confidence
is quite low given the differences.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 930 PM CDT Sat Oct 22 2016

RAP/HRRR/NAM12 Bufkit soundings all adamant that while the sfc winds
will stay light southeast overnight at KLSE, just off the sfc the
winds will be on the increase. This increase should act to prevent
any fog that develops over the main channel of the Mississippi from
spreading across KLSE - so will continue to keep it vsby restriction
free with just some scattered low cloud.

Cold front sweeps through in the morning, with winds increasing and
shifting to the northwest. GFS/NAM RH fields point to the potential
for mvfr cigs dropping southeast later Sunday afternoon. Going to
keep the trend of VFR for now, but something to be watched.




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