Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 231148
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
650 AM CDT MON MAR 23 2015

.SHORT TERM...(TODAY AND TONIGHT))
ISSUED AT 407 AM CDT MON MAR 23 2015

MAIN FCST CONCERNS THIS PERIOD...SNOW EXITING THIS MORNING...
TEMPERATURES.

DATA ANALYSIS AT 06Z HAD LOW PRESSURE OVER SOUTHWEST IA/NORTHWEST
MO...MOVING SLOWLY EAST-SOUTHEAST. WV/IR IMAGERY AND REGIONAL RADAR
REFLECTIVITY DEPICTED A SHORTWAVE MOVING EAST-SOUTHEAST ACROSS NORTH
CENTRAL IA. BROAD BAND OF LIGHT TO LOCALLY HEAVY SNOW MOVING EAST-
SOUTHEAST ACROSS SOUTHERN MN TO NORTHERN IL AHEAD/NORTH OF THE
SHORTWAVE EARLY THIS MORNING. SNOWFALL RATES OF 1 INCH OR MORE PER
HOUR RATHER COMMON IN THE HEAVIER PORTIONS OF THE SNOW BAND WITH
SNOW TOTALS OF 3 TO 8 INCHES COMMON ACROSS MUCH OF SOUTHEAST MN INTO
SOUTHWEST WI. TRAILING EDGE OF THE HEAVIER SNOW APPROACHING/CROSSING
I-35 AT 07Z.

NO BIG ISSUES NOTED WITH 23.00Z MODEL INITIALIZATIONS. GFS SHOWING
ITS USUAL 3-5F HIGH BIAS ON SFC DEW POINT NEAR/SOUTH OF THE IA/MO
SFC LOW. SOLUTIONS QUITE SIMILAR AS THE SHORTWAVE RESPONSIBLE FOR
THE SNOW MOVES QUICKLY SOUTHEAST OF THE REGION TODAY AND SHORTWAVE
RIDGING BUILDS ACROSS THE UPPER MIDWEST TONIGHT. TREND TENDS TO
FAVOR STRONGER OF THE EARLIER RUNS WITH THE SHORTWAVE RIDGING
TONIGHT...AHEAD OF THE NEXT STRONGER SHORTWAVE ENERGY DIGGING THRU
THE CENTRAL/NORTHERN ROCKIES. SHORT-TERM FCST CONFIDENCE IS GOOD
THIS CYCLE.

IN THE SHORT TERM...TODAY/TONIGHT CONTINUE TO SHAPE UP AS A QUIETER
WEATHER PERIOD. MID LEVEL LIFT/DIVERGENCE WITH THE SHORTWAVE AND
LOWER LEVEL THERMODYNAMIC FORCING/LIFT EXITS SOUTHEAST OF THE FCST
AREA BY 15Z. LINGERING 70-100 PERCENT -SN CHANCES ACROSS THE
SOUTHEAST 1/4 OF THE FCST AREA AT 12Z SUPPORTED BY DISTANCE-SPEED
TOOL ON RADAR REFLECTIVITY MOVING SOUTHEAST ACROSS THE REGION. DRY
FCST ACROSS THE FCST AREA AFTER 15Z ALSO APPEARS WELL TRENDED WITH
RAPID EXIT OF THE FORCING/LIFT. WILL LEAVE EXPIRATION OF REMAINING
HEADLINES AT 12Z...BUT MAY YET NEED TO EXTEND FOR AN HOUR OR TWO IN
THE COUNTIES OF FAR SOUTHWEST WI. WILL HANDLE THIS WITH AN UPDATE
BETWEEN 10-11Z...BASED ON RADAR TRENDS...IF NEEDED. IR CLOUD TOP
TEMPERATURES ACROSS WEST-CENTRAL/SOUTHWEST MN BEHIND THE SHORTWAVE
IN THE -17C TO -23C RANGE...COLD ENOUGH FOR ICE IN THE CLOUDS. ONCE
SNOW DIMINISHES...SFC OBS IN THESE AREAS REPORTING -SN. EVENING CREW
REMOVED MENTION OF -DZ/-FZDZ AND THIS CONTINUES TO LOOK GOOD. EVEN
AS THE SHORTWAVE PASSES AND HGTS START TO RISE BY MID MORNING...
PLENTY OF 925-700MB MOISTURE IN A COL AREAS ENDS UP STUCK OVER MUCH
OF NORTHERN MN TO NORTHERN IL TODAY. CLOUDS AND FRESH SNOW COVER TO
KEEP TEMPS DOWN TODAY ACROSS MUCH OF THE FCST AREA. SFC-500MB RIDGE
AXIS BUILDS ACROSS THE REGION TONIGHT. LOW/MID LEVEL SUBSIDENCE
SHOULD WORK TO CLEAR OUT THE LOWER CLOUDS...BUT HIGHER LEVEL
MOISTURE AHEAD OF THE SHORTWAVE ENERGY DIGGING THRU THE CENTRAL/
NORTHERN ROCKIES ALREADY INCREASES OVER MUCH OF THE REGION BY LATER
TONIGHT. COLDEST LOWS TONIGHT OVER THE EAST SIDE OF THE FCST AREA
WHERE APPEARS SKIES WILL BE CLEAR/MOSTLY CLEAR THE LONGEST. USED A
BLEND OF THE GUIDANCE HIGHS/LOWS FOR TODAY/TONIGHT.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 407 AM CDT MON MAR 23 2015

MAIN FCST CONCERNS FOR TUE THRU WED NIGHT...PRECIP CHANCES/RAIN/SNOW
AMOUNTS LATE TUE INTO WED MORNING...TEMPERATURES.

23.00Z MODELS OFFER REASONABLE AGREEMENT AS THE ROCKIES SHORTWAVE
ENERGY CROSSES THE CENTRAL/NORTHERN PLAINS TUE THEN HEADS TOWARD
SOUTHERN WI/LK MI BY WED MORNING. HOWEVER SPEED AND STRENGTH
DIFFERENCES TUE/TUE NIGHT AS THIS ENERGY MOVES EAST. OVERALL TREND BY
TUE NIGHT/WED MORNING IS SLOWER/STRONGER THAN EARLIER RUNS WITH BOTH
THIS ENERGY AND NORTHERN STREAM ENERGY DROPPING INTO ND. THE
STRONGER TREND CONTINUES WED/WED NIGHT AS THE SOUTHERN WAVE QUICKLY
EXITS THE REGION AND THE NORTHERN STREAM FEATURE/TROUGHING DROPS
INTO THE UPPER MIDWEST. FCST CONFIDENCE IN THE TUE THRU WED NIGHT
PERIOD IS AVERAGE.

SHORTWAVE ENERGY/TROUGH ADVANCING ACROSS THE PLAINS TUE QUICKLY
SPREADS INCREASING MOISTURE/CLOUDS INTO THE FCST AREA TUE
AFTERNOON. SLOWING TREND DELAYS THE ARRIVAL OF THE 925-700MB
SATURATION AND THE STRONGER LOWER LEVEL THERMODYNAMIC FORCING INTO
THE SOUTHWEST END OF THE FCST AREA INTO THE LATER AFTERNOON HOURS.
REDUCED -RA CHANCES IN THE 12Z-21Z TIME-FRAME TUE WITH THE MAIN
INCREASE OF -RA CHANCES ACROSS THE SOUTHWEST HALF OF THE FCST AREA
AFTER 21Z. DEEPEST/STRONGEST LIFT WITH THE PASSING SHORTWAVE TROUGH
SPREADS QUICKLY NORTHEAST ACROSS THE FCST AREA TUE NIGHT...EXITING
THE NORTH END OF THE FCST AREA WED MORNING. PW VALUES IN THE INFLOW
AIRMASS WITH THIS SYSTEM IN THE 0.75 INCH RANGE...WITH MODEL
CONSENSUS PRODUCING AROUND 1/2 INCH OF PRECIP ACROSS THE FCST AREA
FROM LATE TUE AFTERNOON INTO WED MORNING. SOME MODELS WITH MORE THAN
OTHERS AND VARIABILITY OF WHERE THE HEAVIEST PRECIP FALLS DUE TO
TIMING/STRENGTH DIFFERENCES OF THE SFC-500MB FEATURES. STAYED WITH
THE MODEL/ENSEMBLE CONSENSUS FOR NOW...WITH FCST GRIDS ALREADY
CARRYING 100 PERCENT PRECIP CHANCES TUE NIGHT. BIGGEST QUESTION TUE
NIGHT IS PRECIP TYPE. MODEL SOUNDINGS SHOWING A 0C TO +3C ELEVATED
WARM LAYER ACROSS MUCH OF THE FCST AREA TUE NIGHT...SOME MORE
ROBUST/FURTHER NORTH WITH THIS THAN OTHERS. WITH SFC TEMPS IN THE
30S MUCH OF TUE NIGHT...AND THE POTENTIAL ELEVATED WARM LAYER AS
FAR NORTH AS HWY 29 ACROSS WI...APPEARS BULK OF PRECIP WOULD FALL
AS RAIN...MIXED WITH SOME SLEET/SNOW ACROSS THE NORTH 1/3 OF THE
FCST AREA. LEFT PRECIP TUE NIGHT AS -RA OR -SN FOR NOW...PENDING A
TIGHTER CONSENSUS ON THE SFC-700MB THERMAL DETAILS. RAIN PLUS
MELTING OF THE SUN/SUN NIGHT SNOW TUE/TUE NIGHT HAS POTENTIAL TO
CREATE RISES ON AREA RIVERS... HOWEVER GROUND GENERALLY THAWED NOW
AND IN NEED OF SOME EARLY SPRING MOISTURE. MOST RAIN/RUNOFF LIKELY
TO JUST SOAK INTO THE SOIL...WITH ONLY MINOR WITHIN BANK RISES ON
THE AREA RIVERS.

MID LEVEL COOLING/TROUGH SINK ACROSS THE REGION WED/WED NIGHT...
WITH BITS OF SHORTWAVE ENERGY RIPPLING AROUND/THRU IT. NAM/GFS
SWING ANOTHER ROUND OF LOWER LEVEL LIFTING AND PV ADVECTION ACROSS
THE FCST AREA LATER WED/WED NIGHT. THIS WITH A COOLING COLUMN
PUTTING THE SQUEEZE ON LINGERING SFC-700MB MOISTURE OVER THE AREA.
SMALL -RA/- SN CHANCES LINGERING INTO WED AFTERNOON/NIGHT
REASONABLE FOR NOW. GIVEN THE DETAIL DIFFERENCES...FAVORED THE
MODEL/ENSEMBLE CONSENSUS FOR HIGHS/LOWS IN THE TUE THRU WED NIGHT
PERIOD.

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

MAIN FCST CONCERNS THIS PERIOD...TEMPERATURES...SMALL -RA/-SN
CHANCES THU/THU NIGHT AND AGAIN SAT NIGHT/SUN.

GOOD CONSENSUS AMONG 23.00Z MEDIUM RANGE MODELS FOR RATHER DEEP MID
LEVEL/LONGWAVE TROUGHING OVER THE UPPER MIDWEST THU/THU NIGHT WITH
THE TROUGH MOVING EAST AND NORTH FLOW ALOFT OVER THE REGION FRI.
REASONABLE CONSISTENCY FOR RISING HGT/SHORTWAVE RIDGING TO BUILD EAST
ACROSS THE REGION FRI NIGHT/SAT...AHEAD OF A STRONGER SHORTWAVE
TROUGH PROGGED TO BE DROPPING SOUTHEAST ACROSS CENTRAL CAN. ALMOST
BETTER CONSISTENCY WITH FEATURES FRI/SAT THAN WITH THE ONE TO IMPACT
THE REGION CENTERED ON TUE NIGHT. SURPRISINGLY GOOD BETWEEN MODEL
AND RUN-TO-RUN CONSISTENCY ON THE CENTRAL CAN SHORTWAVE TROUGH TO
DROP INTO THE REGION SAT NIGHT/SUN. DAY 4-7 FCST CONFIDENCE AVERAGE
THIS CYCLE.

WITH COLD MID LEVEL TROUGHING OVER THE AREA THU/THU NIGHT...AND SOME
925-700MB TROUGHING/MOISTURE TO ROTATE SOUTH ACROSS AREA...THE SMALL
-RA/-SN CHANCES OKAY FOR NOW. CAN HIGH PRESSURE/LOWER LEVEL ANTI-
CYCLONIC FLOW TO BUILD EAST/SOUTH ACROSS THE REGION FOR FRI THRU
SAT. FRI NIGHT TO BE ONE OF THE COLDER NIGHTS WITH THE SFC RIDGE
AXIS NEARBY/OVERHEAD AND 925MB TEMPS IN THE -8C TO -14C RANGE AND
SOME LINGERING SNOW COVER. STRONGER LOW LEVEL WARM ADVECTION RETURNS
LATE SAT/SAT NIGHT...AHEAD OF THE NEXT STRONGER SFC-700MB TROUGH/
COLD FRONT TO DROP ACROSS THE REGION. QUESTIONS CONCERNING HOW MUCH
MOISTURE MAY BE DRAWN NORTH AHEAD OF THIS TROUGH/FRONT BUT THE 15-30
PERCENT CONSENSUS -RA/-SN CHANCE...HIGHEST OVER THE NORTHEAST END OF
THE FCST AREA...REASONABLE AT THIS TIME. LOW LEVEL COLD ADVECTION
PROGGED TO RETURN ON SUNDAY BUT 925MB TEMPS AND DEEPER MIXING AT 00Z
MON WOULD STILL SUPPORT DAY 7 HIGHS IN THE MID 40S-LOW 50S. STAYED
WITH THE MODEL/ENSEMBLE CONSENSUS HIGHS/LOWS IN THE DAY 4-7 PERIOD.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 650 AM CDT MON MAR 23 2015

SNOW HAS QUICKLY EXITED EAST SOUTHEAST EARLY THIS MORNING...AND
EXPECT IT TO CLEAR KLSE BY 13Z OR SO.

CIGS ARE PROBLEMATIC TODAY. BAND OF LOW STRATUS HAS DEVELOPED TO THE
WEST...BEYOND THE BACK EDGE OF THE SNOWFALL. MOSTLY MVFR CIGS IN THE
WAKE OF THE SNOW...BUT SOME CONCERN THESE SUB 1 KFT CIGS COULD WORK
EAST TO KRST...PERHAPS KLSE. KRST HAS RECENTLY FALLEN BELOW 1 KFT AT
KRST...AND WILL PROBABLY STAY THERE THROUGH THE MORNING. CONFIDENCE
SHAKY FOR KLSE...SO WILL HOLD MVFR FOR NOW. HOW LONG THE CIGS HOLD
INTO THE EVENING IS ALSO A QUESTION MARK. EXPECT SOME BREAK INTO VFR
THOUGH LATER TONIGHT...BEFORE THE NEXT LOW PRESSURE SYSTEM TAKES AIM
ON THE REGION FOR TUE/TUE NIGHT. EXPECTING A ROUND OF RAIN TUE NIGHT.

&&

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

&&

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION.....RIECK


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