558 
FXUS63 KARX 111757
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1157 AM CST FRI JAN 11 2013

.SHORT TERM...
1157 AM CST FRI JAN 11 2013

VISIBILITY HAS REMAINED LOW AT A QUARTER MILE OR LESS ACROSS THE
REGION AND HAS NOT IMPROVED MUCH AT ALL THROUGH THE MORNING WITH
TEMPERATURES STICKING AROUND THE MID 30S. THE INCREASING WINDS
APPEAR TO HAVE ACTUALLY MADE CONDITIONS WORSE WITH CREATING AN
ADVECTION FOG THAT IS ERODING MORE OF THE SNOW PACK. THE WORST
VISIBILITIES ARE NORTH OF A WARM FRONT THAT IS CURRENTLY IN SOUTHERN
IOWA AND EXPECT THAT TO BE THE CASE THROUGH THIS AFTERNOON AND
EVENING. THEREFORE...HAVE EXTENDED THE DENSE FOG ADVISORY THROUGH
MIDNIGHT. THAT TIMING COULD END UP BEING TOO LONG...OR TOO SHORT
DEPENDING ON WHAT OCCURS THIS EVENING. THE 11.16Z TO 11.19Z RUNS
OF THE HRRR HAVE DONE A GOOD JOB OF SHOWING THE LOWER
VISIBILITIES...PARTICULARLY WITH THE HINTING AT SLIGHTLY BETTER
CONDITIONS IN THE COULEES...AND SHOWS AN IMPROVEMENT FROM THE
SOUTH THIS EVENING AS THE WARM FRONT LIFTS NORTH. CURRENT THINKING
IS THAT VISIBILITY WILL IMPROVE FROM THE SOUTH TO NORTH BETWEEN
6PM TO MIDNIGHT TONIGHT WHERE WE CAN CANCEL THE ADVISORY EARLY IN
THE SOUTH IF THE CONDITIONS DO IN FACT IMPROVE. THE WILD CARD IS
THAT ONCE THE WARM FRONT MOVES THROUGH THAT THE STRONGER SOUTHWEST
WINDS AND WARMER AIR COULD JUST MAKE THINGS WORSE AGAIN WITH THE
ERODING SNOW PACK. FOR NOW...HAVE TRENDED TOWARD THE HRRR SINCE
THE OBS ACROSS SOUTHERN IOWA DO IMPROVE SUBSTANTIALLY SOUTH OF THE
FRONT. SHOULD THE DENSE FOG CONTINUE INTO THE OVERNIGHT HOURS...IT
DEFINITELY WILL COME TO AN END ONCE THE POTENT COLD FRONT COMES
THROUGH AND INCREASES WINDS INTO THE 25 TO 40 MPH RANGE.

.LONG TERM...SUNDAY NIGHT THROUGH THURSDAY
300 AM CST FRI JAN 11 2013

THE GFS AND 11.00Z ECMWF AGREE THAT THE POLAR VORTEX WILL BE
MOVING SOUTH FROM OVER NUNAVUT TO NEAR HUDSONS BAY. THIS WILL PUSH
A COLD FRONT ACROSS THE UPPER MIDWEST DURING THE MIDDLE OF NEXT
WEEK. THE GFS KEEPS THE SURFACE LOW OFF TO THE NORTHEAST OVER
ONTARIO AND IS QUICKER TO BRING THE FRONT THROUGH ON TUESDAY
NIGHT. THE ECMWF AND 11.00Z GEM INDICATE THE SURFACE LOW WILL MOVE
ACROSS THE UPPER MIDWEST AND GREAT LAKES AND DO NOT BRING THE
FRONT THROUGH UNTIL WEDNESDAY OR WEDNESDAY NIGHT. FOR NOW...WILL
STAY WITH THE MODEL CONSENSUS AND CARRY A CHANCE OF SNOW FOR
TUESDAY NIGHT AND WEDNESDAY.

&&

.AVIATION...THROUGH 18Z SATURDAY
1157 AM CST FRI JAN 11 2013

LOW VISIBILITY AND CEILINGS WILL PERSIST AT RST AND LSE THROUGH
TONIGHT AS A WARM AND MOIST AIR MASS SITS ACROSS THE REGION.
THE COMBINATION OF THIS AIR MASS WITH A MELTING SNOW PACK HAS LED
TO WIDESPREAD DENSE FOG WITH VISIBILITIES DROPPING TO A QUARTER
MILE OR LESS THROUGHOUT THE REGION. SOME OF THE RIVER VALLEY
LOCATIONS HAVE BEEN SLIGHTLY HIGHER WITH THE VISIBILITY AT TIMES
BUT CEILINGS HAVE REMAINED LOW AT A FEW HUNDRED FEET. LITTLE
CHANGE IN THESE CONDITIONS ARE EXPECTED THROUGH TONIGHT AS A WARM
FRONT MOVES IN FROM THE SOUTH AS A LOW PRESSURE SYSTEM TRACKS
THROUGH THE PLAINS ON INTO MINNESOTA. THERE MAY BE SOME
IMPROVEMENTS THIS EVENING AFTER THE WARM FRONT MOVES THROUGH...BUT
THE WARMER AIR AND STRONGER WINDS MAY JUST LEAD TO MOVE SNOW MELT
AND CONTINUED LOW VISIBILITIES. LOW LEVEL WINDS WILL BE
STRENGTHENING AHEAD OF A COLD FRONT THAT WILL MOVE THROUGH
OVERNIGHT...WITH LOW LEVEL WIND SHEAR OCCURRING FROM SFC WINDS
AROUND 15KTS AND 2KFT WINDS STRENGTHENING TO 50-60KTS. AFTER THE
COLD FRONT MOVES THROUGH...VISIBILITY AND CEILINGS WILL IMPROVE TO
MVFR BUT WINDS WILL RAPIDLY INCREASE TO BEING OUT OF THE WEST-
SOUTHWEST AT 20-35KTS. THE BACK EDGE OF THE SYSTEM WILL THEN MOVE
THROUGH TOMORROW MORNING WITH SOME SNOW POSSIBLE THAT COULD BRING
VISIBILITY BACK DOWN TO IFR.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
1157 AM CST FRI JAN 11 2013

WI...DENSE FOG ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR WIZ017-029-
     032>034-041>044-053>055-061.

MN...DENSE FOG ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR MNZ079-086>088-
     094>096.

IA...DENSE FOG ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR IAZ008>011-018-
     019-029-030.


&&

$$

SHORT TERM...HALBACH
LONG TERM...04
AVIATION...HALBACH