Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 061143
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
543 AM CST SAT FEB 6 2016

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 315 AM CST SAT FEB 6 2016

WATER VAPOR SATELLITE THIS MORNING SHOWS THE NEXT SYSTEM JUST
MOVING ONTO THE WASHINGTON AND BRITISH COLUMBIA SHORE FROM THE
PACIFIC. THE 06.00Z GUIDANCE HAS COME INTO MUCH BETTER AGREEMENT
ON THE HANDLING OF THIS SYSTEM AND SHOWS GOOD CLUSTERING WITH IT
THROUGH SUNDAY. ONCE THE SHORT WAVE TROUGH CROSSES THE CANADIAN
ROCKIES...IT WILL START TO INTENSIFY WITH AN UPPER LEVEL LOW
FORMING LATE THIS AFTERNOON TO THE SOUTHWEST OF LAKE WINNIPEG.
THIS LOW THEN MOVES SOUTHEAST INTO NORTHERN WISCONSIN BY 08.00Z
AND THEN MOVES EAST OF LAKE MICHIGAN MONDAY. THERE ARE THREE
CONCERNS WITH THIS SYSTEM.

THE FIRST IS WHETHER ANY LIGHT SNOW WILL DEVELOP ACROSS THE
NORTHERN SECTIONS OF THE FORECAST AREA TONIGHT IN THE WARM AIR
ADVECTION ZONE AHEAD OF THE SURFACE LOW. THE MODELS HAVE BEEN
WAVERING ON HOW FAR SOUTH THE LIGHT SNOW WILL GET IN THIS AREA OF
WARM AIR ADVECTION. THE ISENTROPIC UP GLIDE IS NOT THAT
IMPRESSIVE OVER NORTHERN WISCONSIN AND IS ON THE ORDER OF 1 TO 1.5
UBAR/S ON THE 280K SURFACE AND THE BECOMES STRONGER OVER LAKE
SUPERIOR INTO CANADA. THERE IS ONLY SOME WEAK FRONTOGENESIS IN THE
850-700 MB LAYER WITH THIS AGAIN BECOMING MUCH MORE FAVORABLE
FARTHER TO THE NORTH. WILL SHOW JUST A VERY SMALL CHANCE FOR SOME
LIGHT SNOW LATE THIS EVENING ACROSS THE NORTH...BUT WOULD NOT BE
SURPRISED IF THIS IS NOTHING MORE THAN FLURRIES.

THE SECOND CONCERN THEN IS WITH THE PRECIPITATION CHANCES SUNDAY
INTO MONDAY NIGHT. THE FORCING LOOKS MUCH BETTER IN THIS TIME
PERIOD...ESPECIALLY SUNDAY AFTERNOON AND NIGHT. AS THE UPPER LEVEL
LOW MOVES BY...A SHORT WAVE TROUGH WILL ROTATE UNDERNEATH THE LOW
AND COME ACROSS THE REGION WITH STRONG PV ADVECTION IN THE 500-300
MB LAYER. THE QG CONVERGENCE WITH THIS WAVE LOOKS A LITTLE
DISJOINTED AND MAINLY WEAK IN THE 850-500 MB LAYER. THERE WILL BE
A BAND OF WEAK FRONTOGENESIS THAT MOVES THROUGH SUNDAY NIGHT IN
THE 850-500 MB LAYER ALONG WITH A BAND OF 1 TO 2 UBAR/S OF UP
GLIDE ON THE 280K SURFACE. THIS LOOKS TO BE ENOUGH FORCING TO
GENERATE SOME LIGHT SNOW FROM SUNDAY AFTERNOON THROUGH SUNDAY
NIGHT WITH SOME LINGERING LIGHT SNOW MONDAY AND MONDAY NIGHT ON
THE BACK SIDE OF THE SYSTEM IN THE CYCLONIC FLOW.

THE THIRD CONCERN IS WITH THE WINDS AND THE BLOWING SNOW
POTENTIAL. A TIGHT PRESSURE GRADIENT WILL BE IN PLACE ON THE BACK
SIDE OF THE SURFACE LOW AS IT GOES PAST THE AREA SUNDAY NIGHT INTO
MONDAY. A DECENT TROPOPAUSE FOLD WILL MOVE OVER THE AREA WITH THE
1.5 PV INTRUSION GETTING DOWN TO ABOUT 600 MB OR SO. LOOKING AT
THE BUFKIT SOUNDINGS FOR THE WESTERN SECTIONS OF THE FORECAST
AREA...THERE WILL BE SOME GOOD WINDS AVAILABLE IN THE MIXED LAYER
WITH THESE TOPPING OUT AROUND 40 KNOTS OR SO AT THE TOP OF THIS
MIXED LAYER. THE AXIS OF STRONGEST WINDS...50+ KNOTS...LOOKS TO
REMAIN TO THE WEST OF THE FORECAST AREA...FROM WESTERN MINNESOTA
DOWN INTO IOWA...POSSIBLY JUST TOUCHING THE FAR SOUTHWEST PART OF
THE FORECAST AREA SUNDAY AFTERNOON. THE BEST OVERALL SUBSIDENCE
LOOKS TO STAY TO THE WEST WITH THE AXIS OF COLD AIR ADVECTION
LINING UP NICELY WITH THE AXIS OF STRONGER WINDS AT 850 MB. LAPSE
RATES INITIALLY START OUT BEING FAVORABLE FOR STRONG WINDS SUNDAY
AFTERNOON BUT THE 06.00Z NAM REALLY SHOWS THESE FAVORABLE LAPSE
RATES BEING PUSHED TO THE WEST SUNDAY NIGHT INTO MONDAY. LOOKING
AT THE BUFKIT SOUNDING FOR KRST...CONCERNED THAT THERE IS NO REAL
SIGNAL FOR SUBSIDENCE IN THE MIXED LAYER. IN FACT...THERE IS
UPWARD MOTION INDICATED SUNDAY AFTERNOON INTO THE EVENING BEFORE
BECOMING NEUTRAL TO SLIGHTLY SUBSIDENT OVERNIGHT SUNDAY INTO
MONDAY. THE SOUNDING FOR KMCW IS MUCH DIFFERENT WITH SUBSIDENCE
FOR MUCH OF SUNDAY AFTERNOON INTO MONDAY WITH THIS BEING THE
STRONGEST LATE SUNDAY NIGHT INTO MONDAY MORNING. NO DOUBT IT IS
GOING TO BE WINDY AND GUSTY...BUT EXPECTING THE CORRIDOR OF
STRONGEST WINDS TO MISS THE AREA OR JUST BRUSH THE FAR SOUTHWEST
SECTIONS. THESE WINDS WILL BE STRONG ENOUGH TO CREATE SOME BLOWING
AND DRIFTING SNOW AND THE QUESTION BECOMES HOW BAD WILL CONDITIONS
GET. THE STRONGEST WINDS WILL BE DISPLACED FROM THE AXIS OF
GREATEST SNOW FALL WITH THIS SYSTEM. NEW SNOWFALL WHERE THE WINDS
WILL BE THE STRONGEST CURRENTLY LOOKS TO BE IN THE 1 TO 1.5 INCH
RANGE...BUT THIS SHOULD BE A LIGHTER AND FLUFFY SNOW WITH RATIOS
OF 13-17 TO 1 EXPECTED. SOME UNCERTAINTY ON THE STATE OF THE
SNOWPACK AND THE AVAILABILITY OF IT TO BE PICKED UP AND MOVED. THE
SNOW WITH THE LAST STORM HAD LOWER RATIOS SO THERE WAS MORE
MOISTURE IN THE SNOW TO BEGIN WITH. A HARD GLAZE HAD DEVELOPED
LOCALLY ON THE TOP OF THE SNOW...BUT UNCERTAIN HOW FAR WEST THIS
EXTENDS. THE EXPERIMENTAL BLOWING SNOW GRIDS SHOW VERY LITTLE
SIGNAL FOR VISIBILITIES DROPPING TO A HALF MILE OR LESS WITH JUST
A SMALL PROBABILITY ACROSS THE FAR SOUTHWEST PART OF THE FORECAST
AREA. THE HIGHEST PROBABILITIES LIE TO THE WEST OF INTERSTATE 35.
PUTTING IT ALL TOGETHER...CAN SEE WHERE SOME BLOWING SNOW WILL BE
POSSIBLE FOR AREAS GENERALLY ALONG AND WEST OF U.S. HIGHWAY 52 AND
COULD NOT RULE OUT SOME BRIEF WHITEOUTS. THE BEST POTENTIAL FOR A
GROUND BLIZZARD LOOKS TO BE TO THE WEST OF THE AREA SO NO PLANS TO
ISSUE A BLIZZARD WATCH. A WINTER WEATHER ADVISORY WILL MOST LIKELY
BE NEEDED TO COVER THIS SCENARIO.

.LONG TERM...(MONDAY NIGHT THROUGH FRIDAY)
ISSUED AT 315 AM CST SAT FEB 6 2016

THERE COULD STILL BE A BIT OF LINGERING LIGHT SNOW OVER THE FAR
EASTERN SECTIONS OF THE AREA MONDAY NIGHT WITH THIS EXPECTED TO
END BY TUESDAY AS THE LOW LEVEL CYCLONIC FLOW RELAXES. THE NEXT
CHANCE FOR ANY LIGHT SNOW LOOKS TO COME IN THURSDAY NIGHT INTO
FRIDAY. A WEAK SHORT WAVE TROUGH IS EXPECTED TO ROTATE ACROSS THE
UPPER GREAT LAKES PUSHING A SURFACE LOW ACROSS SOUTHERN ONTARIO.
THE TRAILING COLD FRONT SHOULD THEN COME ACROSS THE AREA AND COULD
PRODUCE A LITTLE BIT OF LIGHT SNOW.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 542 AM CST SAT FEB 6 2016

A WEAK TROUGH PRODUCED WILL CAUSE A TEMPORARY SHIFT IN THE WINDS
TO WEST THROUGH MID MORNING...AND THEN THE WINDS WILL ONCE AGAIN
SHIFT TO THE SOUTHWEST FROM LATE MORNING INTO SUNDAY MORNING. WIND
SPEEDS THROUGH THIS TIME PERIOD WILL RANGE FROM 10 TO 15 KNOTS. IFR
CEILINGS AND MVRF VISIBILITIES WILL PERSIST AT THE TAF SITES
THROUGH MUCH OF THE MORNING...AND THEN BECOME VFR AT KRST AROUND
06.15Z AND KLSE AROUND 06.18Z.

&&

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

$$

SHORT TERM...04
LONG TERM...04
AVIATION...BOYNE


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