Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 261729
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1129 AM CST THU FEB 26 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 345 AM CST THU FEB 26 2015

MAIN FCST CONCERNS THIS PERIOD...COLD TEMPERATURES AND WIND CHILLS.

06Z DATA ANALYSIS HAD THE NEXT IN THE SEEMINGLY ENDLESS PARADE OF
ARCTIC HIGHS BUILDING INTO THE UPPER MIDWEST. CENTER OF THE HIGH WAS
STILL IN SOUTHERN SASKAT BUT ITS INFLUENCE WAS AS FAR SOUTH AS THE
TX PANHANDLE AND EAST AS MUCH OF ONTARIO. SYSTEM THAT BROUGHT SNOW
TO THE AREA WAS ALREADY WELL INTO THE OH VALLEY WITH CLOUDS BEHIND
IT MAINLY LIMITED TO SOUTHEAST WI/IA. TEMPS ALREADY WELL BELOW ZERO
AGAIN ACROSS THE NORTH 1/3 OF THE REGION AS THE HIGH BUILDS IN. WIND
CHILLS NORTHWEST OF A KGRB-KLSE-KDSM LINE MOSTLY -10 TO -25 EARLY
THIS MORNING AS WINDS EAST/SOUTH OF THIS HIGH MOSTLY ONLY 5-10MPH.

NO PROBLEMS NOTED WITH 26.00Z MODEL INITIALIZATIONS. SOLUTIONS VERY
SIMILAR OFFER A TIGHT CONSENSUS AND GOOD RUN-TO-RUN CONSISTENCY
TODAY AS SOME SHORTWAVE ENERGY AND RATHER SHARP MID LEVEL TROUGHING
SWING ACROSS THE AREA THEN WEAK SHORTWAVE RIDGING BUILDS IN TONIGHT.
SHORT-TERM FCST CONFIDENCE REMAINS GOOD THIS CYCLE.

IN THE SHORT TERM...EVEN AS THE MID LEVEL TROUGHING/SHORTWAVE ENERGY
SWINGS ACROSS THE AREA TODAY...QUIET/DRY...AND COLD...WEATHER
EXPECTED. THIS AS THE LARGE ARCTIC HIGH DRIFTS SOUTHEAST TO BE
CENTERED OVER ND BY THIS EVENING...THEN CENTERED OVER WESTERN IA BY
FRI MORNING. 925MB TEMPS IN THE -18C TO -22C RANGE AT 12Z THIS
MORNING ARE PROGGED TO STILL BE IN THE -18C TO -20C RANGE AT 12Z
FRI. WITH THE CENTER OF THE HIGH OVER WESTERN IA AT 12Z FRI...SFC
PRESSURE GRADIENT RELAXES EVEN FURTHER. WINDS EARLY THIS MORNING
ALREADY MOSTLY 5-10 MPH. WITH EVEN A WEAKER GRADIENT OVER THE AREA
TONIGHT...WINDS LIKELY TO DECOUPLE/BECOME LIGHT/CALM AT MANY
LOCATIONS. WITH MOSTLY CLEAR/CLEAR SKIES UNDER THE HIGH AND SOME
FRESH SNOW COVER FROM WED...FAVORABLE SET-UP FOR STRONG RADIATIONAL
COOLING TONIGHT AND LOWS MOSTLY IN THE -10F TO -20F RANGE ONCE
AGAIN. APPEARS A WIND CHILL ADVISORY WILL BE NEEDED FOR PARTS OR ALL
OF THE AREA LATE TONIGHT INTO FRI MORNING. HOWEVER THIS WILL BE
PROBLEMATIC WITH LIGHT/VARIABLE OR WINDS LIKELY GOING CALM IN LOW
LAYING/RIVER VALLEY LOCATIONS. WITH A WIND CHILL ADVISORY ALREADY IN
EFFECT FOR PARTS OF THE FCST AREA...WILL DEFER ANY ADDITIONAL NEEDED
HEADLINES TO THE DAY CREW TO AVOID ANY DOUBLE HEADLINE CONFUSION.
USED A BLEND OF THE GUIDANCE HIGHS TODAY THEN CONTINUED TO TREND
TOWARD COLDER OF GUIDANCE LOWS TONIGHT.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 345 AM CST THU FEB 26 2015

MAIN FCST CONCERNS FOR FRI THRU SAT NIGHT...SNOW CHANCES SAT
NIGHT...TEMPERATURE TREND THRU THE PERIOD.

26.00Z MODELS REMAIN IN GOOD AGREEMENT FOR A 500MB PATTERN SHIFT
FROM NORTHWEST TO WEST FLOW OVER THE UPPER MIDWEST FRI/FRI NIGHT.
SHORTWAVE ENERGY DURING THIS PERIOD REMAINS CHANNELED SOUTH OF THE
FCST AREA. PATTERN TRANSITION CONTINUES SAT/SAT NIGHT WITH STRONG
TROUGHING OVER THE CENTRAL ROCKIES/CA. TREND ALSO CONTINUES FOR A
STRONGER NORTHERN STREAM SHORTWAVE TO DROP INTO THE NORTHERN PLAINS
SAT NIGHT...BUT LATEST MODEL SUITE TRENDS TOWARD MORE PHASING WITH
THIS TROUGH AND SOME SOUTHERN STREAM ENERGY COMING OUT OF THE
WESTERN CONUS TROUGHING. GIVEN A RATHER TIGHT MODEL CONSENSUS THRU
SAT NIGHT...FCST CONFIDENCE FOR FRI THRU SAT NIGHT IS GOOD.

THE UPPER MIDWEST REMAINS DOMINATED BY COLD...ARCTIC HIGH PRESSURE
FRI/FRI NIGHT. SOME MODERATION OF TEMPERATURES FRI/FRI NIGHT AS THE
COLDEST CORE OF LOW LEVEL AIR SHIFTS SOUTHEAST OF THE AREA AND THE
SFC-700MB FLOW SLOWLY SWINGS TO THE WEST AND SOUTHWEST. TEMPS STILL
LOOKING TO BE AROUND 20 DEGREES BELOW NORMAL FRI/FRI NIGHT. TEMPS
START A MORE ROBUST RECOVERY SAT AS SFC-700MB FLOW BECOMES MORE
SOUTHWESTERLY AND INCREASES...FOR BOTH INCREASING LOW LEVEL WARM
ADVECTION AND MORE LOW LEVEL MIXING. WARMING SAT LOOKS TEMPERED BY
INCREASING CLOUDS SAT AFTERNOON. MODEL TREND OF MORE PHASING OF THE
NORTHERN SOUTHERN STREAMS LATER SAT/SAT NIGHT CONTINUES TO SHIFT A
POTENTIAL ROUND OF SNOW BACK NORTHWARD ACROSS THE FCST AREA AND
NEARBY PARTS OF IA/WI/MN. THE STRONGER PHASING ALLOWS FOR A MORE
NORTHERLY TRACK OF THE SOUTHERN STREAM ENERGY ACROSS THE AREA...AND
MORE DIVERGENCE ALOFT AHEAD OF THE WAVE. MORE SFC/LOW LEVEL
REFLECTION OF THE WAVE...MORE SOUTHERLY LOW LEVEL FLOW/MOISTURE AND
THERMO-DYNAMIC FORCING INDICATED AS WELL. RETURNING MOISTURE
CONTINUES TO LOOK LIKE THE LIMITING FACTOR....BUT TIGHTENING MODEL
CONSENSUS AND TREND WOULD NOW SPREAD 1 TO 2 PERHAPS UP TO 3 INCHES
OF SNOW ACROSS MAINLY THE SOUTH HALF OF THE FCST AREA SAT NIGHT. FOR
NOW...RAISED SNOW CHANCES ACROSS THE SOUTH 1/2 TO 2/3 OF THE FCST
AREA INTO THE 40-60 PERCENT RANGE FOR SAT NIGHT...WHICH BLENDS QUITE
WELL WITH THE NEIGHBORS. USED A BLEND OF THE GUIDANCE HIGHS/LOWS FOR
FRI THRU SAT NIGHT.

FOR SUNDAY THRU WEDNESDAY...DAYS 4 TO 7...

MAIN FCST CONCERNS THIS PERIOD...SNOW CHANCES MON NIGHT INTO WED...
TEMPERATURES THRU THE PERIOD.

26.00Z MEDIUM RANGE MODELS IN GOOD AGREEMENT SUN AS THE PHASING
NORTHERN/SOUTHERN STREAM ENERGY FROM SAT NIGHT MOVES ACROSS THE
REGION. TREND FAVORS FASTER OF EARLIER MODELS WITH THIS TROUGH. GOOD
SIGNAL/CONSENSUS CONTINUES SUN NIGHT/MON FOR RISING HGTS/SHORTWAVE
RIDGING TO BUILD ACROSS THE REGION AND A DEEP LONGWAVE TROUGH TO
DEVELOP OVER THE WESTERN CONUS. TIGHTENING CONSENSUS FOR A STRONGER
PIECE OF ENERGY EJECT OUT OF THE WESTERN TROUGHING AND TOWARD/ACROSS
THE UPPER MIDWEST MON NIGHT/TUE. GENERAL BETWEEN MODEL AGREEMENT FOR
THE REGION TO REMAIN UNDER SOUTHWEST FLOW ALOFT TUE NIGHT INTO
WED...AHEAD OF MORE NORTHERN STREAM ENERGY DROPPING INTO THE
LONGWAVE TROUGH/NORTHERN PLAINS. WITH A REASONABLE MODEL CONSENSUS
IN THE SUN THRU WED PERIOD...DAY 4-7 FCST CONFIDENCE IS ABOVE
AVERAGE THIS CYCLE.

FASTER TREND OF MODELS PUSHES THE FORCING/LIFT/MOISTURE FROM SAT
NIGHT OUT MORE QUICKLY ON SUN...WITH ONLY SMALL LINGERING -SN
CHANCES...MAINLY IN THE MORNING. HIGH PRESSURE BUILDS IN FOR LATER
SUN INTO MON UNDER THE RISING HGTS/SHORTWAVE RIDGING. THIS ONE OF
MODIFIED PACIFIC/CAN ORIGIN AND DRIFTS ACROSS THE CENTRAL/NORTHERN
PLAINS INTO THE REGION...AND UNDER THE DEVELOPING SOUTHWEST FLOW
ALOFT. TEMPS CLOSER TO NORMAL FOR SUN-MON LOOK GOOD. SHORTWAVE
ENERGY PROGGED TO EJECT OUT OF THE WESTERN TROUGH MON NIGHT/TUE
SENDS A ROUND OF INCREASING LOWER LEVEL THERMO-DYNAMICS FORCING AND
MOISTURE ACROSS THE FCST AREA. POTENTIAL OF PW VALUES OF 1/2 INCH IN
THE SOUTHERLY FLOW COMING NORTH WITH THIS SHORTWAVE. CONSENSUS SNOW
CHANCES TRENDING TOWARD 40-60 PERCENT FOR MUCH OF THE FCST AREA MON
NIGHT/TUE LOOK GOOD AT THIS TIME. TRENDS OF THIS SYSTEM WILL HAVE TO
BE WATCHED THE NEXT FEW CYCLES FOR POTENTIAL SIGNIFICANT SNOWFALL
SOMEWHERE ACROSS THE UPPER MIDWEST EARLY NEXT WEEK. DIMINISHING SNOW
CHANCES TUE NIGHT/WED AS THE LOW LEVEL TROUGH/FORCING EXITS EAST AND
LOW LEVEL COLD ADVECTION/NEXT CAN/ARCTIC HIGH BUILDS INTO THE NORTH-
CENTRAL CONUS. MODEL/ENSEMBLE CONSENSUS OF HIGHS/LOWS FOR SUN-WED
APPEARS WELL TRENDED EARLY THIS MORNING.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1129 AM CST THU FEB 26 2015

HIGH PRESSURE WILL BUILD INTO WESTERN IOWA THIS AFTERNOON INTO
TONIGHT AND PROVIDE VFR CONDITIONS AT BOTH RST AND LSE TAF SITES
THROUGH THE TAF PERIOD. DAYTIME HEATING WILL ALLOW FOR
DEVELOPMENT OF SCATTERED CUMULUS CLOUDS ACROSS THE AREA THIS
AFTERNOON. CLOUD HEIGHTS ARE EXPECTED TO BE IN THE 2500-3500 FEET
RANGE. INTRODUCED SCATTERED CLOUDS AT BOTH TAF SITES FOR THIS
AFTERNOON. NORTHWEST WINDS WILL DIMINISH TO AROUND 5 KNOTS OR
LESS AFTER 02Z FRIDAY AT BOTH TAF SITES.

&&

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

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION...DTJ


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