Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 012305
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
505 PM CST SUN FEB 1 2015

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 220 PM CST SUN FEB 1 2015

CONCERNS THROUGH MONDAY...
1. DIMINISHING SNOW/BLOWING SNOW THROUGH THE EVENING
2. NEED FOR WIND CHILL ADVISORY LATE TONIGHT/MONDAY MORNING
3. HIGHS MONDAY

CURRENTLY AS OF 20Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED RIDGING OVER THE WESTERN U.S....A SHORTWAVE TOPPING THE RIDGE
COMING INTO BRITISH COLUMBIA...A DEEP TROUGH OVER THE CENTRAL PLAINS
INTO SOUTHERN PORTIONS OF THE FORECAST AREA...AND A SHORTWAVE OVER
THE EASTERN DAKOTAS. MID-LEVEL FRONTOGENESIS ASSOCIATED ON THE NORTH
SIDE OF THE DEEP TROUGH CONTINUES TO BRING SNOW TO THE SOUTHEASTERN
2/3 OF THE FORECAST AREA. OVER THE NORTHWEST 1/3 AND THROUGH THE
REST OF MINNESOTA AND NORTHERN WI...DRIER AND COLDER AIR CONTINUES
TO ADVECT SOUTHWARD ON A BRISK NORTHERLY BREEZE. NUMEROUS SITES
NORTH OF I-94 REPORTING SURFACE DEWPOINTS BELOW ZERO...AND AS MUCH
AS 20 BELOW IN NORTHERN MN. TEMPERATURES TOO WERE IN THE SINGLE
DIGITS ABOVE AND BELOW ZERO NORTH OF I-94. CLEARING SKIES REFLECT
THE DRIER...COLDER AIR. MAIN 1004MB SURFACE LOW ASSOCIATED WITH THE
TROUGH WELL TO OUR SOUTHEAST...JUST EAST OF LINCOLN IL. HOWEVER...A
TIGHT PRESSURE GRADIENT EXISTS NORTH OF THIS LOW KEEPING THE BRISK
NORTH BREEZE GOING...WITH A 1034MB HIGH OVER THE DAKOTAS.

THE SNOW REMAINS ON TRACK TO DIMINISH NORTHWEST TO SOUTHEAST THROUGH
THE REST OF THIS AFTERNOON INTO EARLY THIS EVENING. BY 00Z...GOOD
MODEL AGREEMENT EXISTS FOR SNOW SOUTHEAST OF A LINE FROM OELWEIN TO
TOMAH...AND THEN OUT OF THE FORECAST AREA BY 03Z. ALTHOUGH SNOW IS
DIMINISHING...WINDS LOOK TO REMAIN BRISK THROUGH AT LEAST A GOOD
PORTION OF THE EVENING. 925MB WINDS AT 00Z RANGE FROM 25-35KT...
DROPPING TO 10-25KT AT 06Z. THESE GUSTY WINDS SHOULD KEEP
SOME BLOWING AND DRIFTING SNOW GOING AT EXPOSED LOCATIONS...EVEN
WHEN THE SNOW ENDS...THUS HAVE DECIDED TO HOLD OFF CANCEL ANY
HAZARDS AT THIS TIME. HOWEVER...ITS POSSIBLE SOME AREAS MAY
GET CANCELLED EARLY OVER THE NEXT FEW HOURS SEEING DODGE CENTER HAS
IMPROVED TO 10 MILE VISIBILITY ALREADY.

DURING THE OVERNIGHT HOURS...THE SHORTWAVE CURRENTLY IN THE EASTERN
DAKOTAS IS PROGGED TO CROSS THE FORECAST AREA. ALTHOUGH NO
PRECIPITATION PRODUCTION IS EXPECTED WITH THIS SHORTWAVE DUE TO
PLENTIFUL DRY AIR AROUND AND AHEAD OF IT...THE SHORTWAVE WILL HELP
TO BRING THE DAKOTAS SURFACE RIDGE INTO THE FORECAST
AREA...THUS DIMINISHING THE WINDS AND CLEARING THE SKIES OUT. WITH
THE FRESH SNOW COVER...TEMPERATURES COULD REALLY PLUMMET...AIDED TOO
BY 925MB TEMPS FALLING TO -16 TO -18C. WOULD NOT BE SURPRISED TO SEE
A FEW READINGS OF 10 BELOW...WHICH WOULD MOST LIKELY OCCUR NEAR
AUSTIN MN AND IN TAYLOR COUNTY WI. DESPITE THE COLD READINGS...WIND
CHILLS SHOULD STAY UP JUST ABOVE THE -20F THRESHOLD FOR AN ADVISORY.

A MUCH QUIETER BUT COLD DAY ON TAP FOR MONDAY AS THE SURFACE RIDGE
CROSSES THE FORECAST AREA. THE SURFACE RIDGE GRADUALLY CROSSES THE
FORECAST AREA...WITH MOSTLY SUNNY SKIES TO START. SHOULD SEE SOME
INCREASE IN CLOUDS IN THE AFTERNOON AS THE SHORTWAVE COMING INTO
BRITISH COLUMBIA DROPS DOWN INTO THE SIOUX FALLS AREA BY 00Z. 925MB
TEMPS DONT START WARMING UNTIL LATE IN THE DAY...AND WITH FRESH
SNOW...HIGHS ONLY LOOK TO TOP OUT IN THE LOW TO MID TEENS. ITS
POSSIBLE SOME LOCATIONS IN NORTHEAST IOWA ONLY REACH THE SINGLE
DIGITS ABOVE ZERO AS SUGGESTED BY THE 01.12Z ECMWF/CANADIAN.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 220 PM CST SUN FEB 1 2015

LONG TERM CONCERNS...
1. BRIEF LIGHT SNOW MAKER MONDAY EVENING FOR MAINLY NORTHEAST IOWA
2. ANOTHER LIGHT SNOW MAKER FOR TUESDAY AFTERNOON/EVENING...MAINLY
SOUTH OF I-90
3. POSSIBLE WIND CHILL ADVISORY FOR THURSDAY MORNING
4. POSSIBILITY FOR A BRIEF WARM UP...BUT BREEZY...FOR FRIDAY INTO
SATURDAY.

SHORTWAVE OVER BRITISH COLUMBIA IS PROGGED TO DIG INTO SOUTHEAST
IOWA AND NORTHEAST MO BY 06Z TUESDAY. THIS TRACK HAS TRENDED
SOUTHWEST SLIGHTLY OVER THE PAST FEW DAYS. DESPITE ITS POTENT
NATURE/LOOK...MODELS DO NOT PRODUCE MUCH QPF WITH IT DUE TO
DRY AIR IN PLACE FROM MONDAY...WITH THE GFS ENTIRELY DRY. GIVEN ITS
STRENGTH FEEL THE NEED TO INCLUDE A LOW PRECIPITATION CHANCE FOR
MONDAY EVENING...SIMILAR TO THE PREVIOUS FORECAST. HOWEVER...WITH
THE SOUTHWEST TREND IN THE GUIDANCE...SHIFTED THE CHANCES A LITTLE
MORE SOUTHWEST AS WELL. SHOULD ANY SNOW OCCUR...MAYBE A FEW TENTHS
ACCUMULATE.

AFTER A QUIET OVERNIGHT MONDAY NIGHT INTO TUESDAY MORNING...POSSIBLY
A BIT COOL WITH A SURFACE RIDGE CROSSING...ANOTHER SHORTWAVE TROUGH
COMING TROUGH NORTHWEST FLOW IS PROGGED TO AFFECT THE AREA TUESDAY
AFTERNOON AND EVENING. THIS SHORTWAVE...ALTHOUGH WEAKER
COMPARED TO THE PREVIOUS ONE...HAS A LITTLE MORE MOISTURE TO WORK
WITH AND A STRONGER MID LEVEL FRONTOGENESIS ZONE. AS SUCH...01.12Z
NAM/GFS/ECMWF/CANADIAN ALL DEVELOP PRECIPITATION...WITH SOME EVEN
SHOWING POTENTIAL TO EXCEED 0.10 OF QPF IN 6 HOURS. SOME
TRACK ISSUES AGAIN EXIST...WITH THE STRONGEST CONSENSUS FOR THE SNOW
TO MOVE THROUGH LOCATIONS SOUTH OF I-90. UNLESS THE SHORTWAVE
BECOMES STRONGER IN LATER RUNS...FEEL THE PLACEMENT OF THIS SNOW
SHOULD STAY PERSISTENT. THUS...DID RAISE PRECIPITATION CHANCES
TOWARDS 50 ACROSS NORTHEAST IA/FAR SOUTHWEST WI. MAY END UP
ACCUMULATING 1-2 INCHES. SOME CONCERN TOO FOR THE PRECIPITATION TO
END AS FREEZING DRIZZLE AS ICE IS LOST ALOFT...BUT ITS VERY
POSSIBLE THE PRECIPITATION ENDS TOO ONCE WE LOSE THE ICE.
THEREFORE...HAVE YET TO INTRODUCE THIS INTO THE FORECAST.
SOMETHING TO MONITOR.

A STRONG UPPER TROUGH DROPS INTO THE REGION ON WEDNESDAY. THERE
COULD BE A LITTLE LIGHT SNOW IN OUR SOUTH DURING THE AFTERNOON WITH
ANOTHER FRONTOGENESIS BAND SETTING UP ACROSS IOWA AND ILLINOIS.
HOWEVER...THE MORE SIGNIFICANT PART IS THE ARCTIC AIR ACCOMPANY THE
UPPER TROUGH. 925MB TEMPS PLUMMET FROM -10 TO -13C AT 12Z WEDNESDAY
TO -18 TO -20C AT 12Z THURSDAY. A SOMEWHAT BRISK NORTHERLY BREEZE IS
PROGGED WEDNESDAY AFTERNOON AND EVENING BEFORE DIMINISHING
OVERNIGHT. THIS DIMINISHING COULD KEEP US JUST OUT OF A WIND CHILL
ADVISORY NEED FOR THURSDAY MORNING...BUT TEMPERATURES WOULD TANK
INSTEAD...ESPECIALLY IF SKIES ARE CLEAR. STAYED ON THE COOLER SIDE
OF GUIDANCE FOR LOWS WEDNESDAY NIGHT GIVEN THIS REGIME AND
THINKING ARCTIC AIR COMING IN WILL CLEAR SKIES OUT.

THE UPPER TROUGH IS FAST MOVING SUCH THAT WEAK UPPER RIDGING COMES
IN BY THURSDAY AFTERNOON...WITH NORTHWEST FLOW PERSISTING BEYOND
INTO SUNDAY. THUS...AFTER THE COLD START THURSDAY MORNING WE WILL BE
ON THE WARMING TREND HEADING INTO FRIDAY AND SATURDAY. STILL A LOT
OF SPREAD AMONGST ECMWF GUIDANCE REGARDING THE HIGHS FRIDAY AND
SATURDAY...BUT GENERAL TREND SHOULD BRING HIGHS BACK TO NORMAL.
GFS/ECMWF 925MB WINDS ALSO INCREASE TO 20-40KT ON FRIDAY...THUS
SUGGESTING IT COULD BE A BIT BREEZY. SOMETHING WELL HAVE TO WATCH
HEADING INTO NEXT WEEKEND IS A FRONTOGENETIC ZONE DROPPING SOUTHWEST
THROUGH THE FORECAST AREA. ACTUAL POSITION AND TIMING HAS VARIED
SOMEWHAT...REQUIRING LOW CHANCES OF PRECIPITATION THROUGH THE
WEEKEND. NEVERTHELESS...COULD SEE A COUPLE INCHES OF SNOW
ACCUMULATION. COOLER AIR FOLLOWS IN THE WAKE OF THIS ZONE FOR
SUNDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 505 PM CST SUN FEB 1 2015

THE SNOW HAS SHIFTED EAST OF KRST/KLSE AT EARLY EVENING...WITH
LATEST OBS INDICATING THAT BLSN IS BECOMING LESS OF A CONCERN AT
KRST. CIGS HAVE ALREADY IMPROVED TO VFR AT THE TAF SITES TOO...AND
EXPECT VFR CONDITIONS TO PREVAIL TONIGHT THROUGH MONDAY.

WINDS WILL BE ON A DECREASING TREND THIS EVENING AS THE LOW EXITS
EAST...HIGH PRESSURE APPROACHES...AND THE PRESSURE GRADIENT
SLACKENS. VARIABLE WINDS IN THE MORNING WILL BECOME SOUTHERLY BY
18Z MONDAY.

UPPER LEVEL SHORTWAVE TROUGH SLATED TO SPIN ACROSS IOWA MONDAY
NIGHT...LIKELY BRINGING A LITTLE LIGHT SNOW. CURRENT TRACK WOULD
KEEP THE BULK OF ANY -SN SOUTHWEST OF KRST/KLSE...BUT WOULD BRING AT
LEAST SOME LOW/MID LEVEL CIGS. MVFR IS POSSIBLE.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...WINTER STORM WARNING UNTIL 9 PM CST THIS EVENING FOR WIZ054-061.

     WINTER WEATHER ADVISORY UNTIL 9 PM CST THIS EVENING FOR
     WIZ041>044-053-055.

MN...WINTER WEATHER ADVISORY UNTIL 9 PM CST THIS EVENING FOR
     MNZ086>088-094>096.

IA...WINTER STORM WARNING UNTIL 9 PM CST THIS EVENING FOR IAZ008>011-
     018-019-029-030.

&&

$$

SHORT TERM...AJ
LONG TERM...AJ
AVIATION...RIECK


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