000
FXUS63 KARX 142012
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
312 PM CDT FRI MAR 14 2014

.SHORT TERM...(TONIGHT THROUGH SATURDAY NIGHT)
ISSUED AT 312 PM CDT FRI MAR 14 2014

THE MAIN FORECAST CONCERNS...SNOW CHANCES MAINLY SAT AFTERNOON/
EVENING...TEMPERATURES.

DATA ANALYSIS AT 18Z HAD LOW PRESSURE NEAR THE EAST END OF LK
SUPERIOR. ONE TROUGH/COLD FRONT EXTENDED THRU LK MI TO CENTRAL MO
WHILE THE SECOND COLD FRONT WITH THE COLDER AIR BEHIND IT STRETCHED
ACROSS LK SUPERIOR TO THE ND/SD BORDER. LOWER LEVEL MOISTURE/CLOUDS
WERE SPREADING SOUTHEAST ACROSS MN/WI/NORTHEAST IA BEHIND THE FIRST
FRONT...BEING HANDLED REASONABLY WELL BY THE MODELS. VIS IMAGERY
FROM 3/13 AND THIS MORNING SHOWING SOUTHWEST 1/4 OF MN AND ALL BUT
NORTHEAST 1/4 OF IA RELATIVELY FREE OF SNOW COVER.

NO LARGE ERRORS NOTED WITH 14.12Z MODEL INITIALIZATIONS. SOLUTIONS
CONTINUE TO CONVERGE TOWARD A TIGHTER/COMPROMISE CONSENSUS AS ONE
SHORTWAVE TROUGH EXITS THIS AFTERNOON AND ANOTHER A FAST MOVING
NORTHWEST FLOW SYSTEM DROPS ACROSS THE NORTHERN PLAINS TOWARD THE
MID MS VALLEY SAT/SAT NIGHT. NAM REMAINS THE WETTEST/FURTHEST NORTH
WITH THIS FEATURE SAT/SAT NIGHT AS FAR AS IMPACTS ON THE FCST AREA.
CHECK OF OBS VS. MODEL DATA AT 18Z SHOWED ALL WERE QUITE GOOD WITH
THE COLD FRONTS ACROSS THE REGION. A COMPROMISE OF THE MODELS LOOKED
BEST WITH THE LOWER CLOUDS/925MB RH SPREADING SOUTHEAST ACROSS THE
REGION BEHIND THE FIRST FRONT. PER WV IMAGERY ALL APPEARED
REASONABLE WITH THE SHORTWAVE DETAILS ACROSS NOAM/EASTERN PAC. WITH
NO ONE FAVORITE AND TIGHTENING COMMON CONSENSUS...FAVORED A MODEL/
ENSEMBLE COMPROMISE FOR TONIGHT THRU SAT NIGHT. SHORT-TERM FCST
CONFIDENCE IS AVERAGE TO GOOD THIS CYCLE.

IN THE SHORT TERM...LOWER CLOUDS/MOISTURE TO BE PROBLEMATIC AT LEAST
THIS EVENING WITH THE AREA REMAINING EAST OF THE SFC-925MB RIDGE
AXIS IN WEAK CYCLONIC FLOW. SOME SIGNAL FOR THE CLOUDS/MOISTURE TO
MOVE EAST OF THE AREA AFTER MIDNIGHT AS THE LOW LEVEL RIDGE AXIS
MOVES TO NEAR THE MS RIVER...BUT BY THEN...MID/HIGH LEVEL MOISTURE
AHEAD OF THE WAVE TO IMPACT THE AREA SAT/SAT NIGHT IS ALREADY
SPREADING EAST INTO THE AREA. RAISED CLOUD COVER FOR MUCH OF
TONIGHT...AND LOWS UNDER THE MORE PERSISTENT CLOUD COVER.

RATHER IMPRESSIVE 800-500MB FN/QG CONVERGENCE/ISENTROPIC LIFT SIGNAL
SPREADS ACROSS THE SOUTHWEST 2/3 OF THE FCST AREA SAT/SAT EVENING.
THIS ALONG WITH 500-300MB PV ADVECTION/FALLING HGTS AHEAD OF THE
SHORTWAVE AND TROUGH...AND DIVERGENCE ALOFT UNDER THE RIGHT ENTRANCE
REGION OF A 100+KT 300MB JET MAX OVER THE NORTHERN GREAT LAKES.
FORCING/LIFT SIGNAL RATHER SIMILAR AMONG THE MODELS...WITH THE
DIFFERENCE AMONG MODELS AND RESULTING QPF ACROSS THE AREA LOOKS TO BE
THE AMOUNT OF AVAILABLE MOISTURE AND SATURATING THE COLUMN BELOW
850MB FOR PRECIP TO REACH THE GROUND. NAM MOST ROBUST WITH THIS
WHILE ECMWF THE DRIEST. GIVEN THE STRENGTH OF THE FORCING/LIFT
SIGNAL...FAVORED A MIDDLE SOLUTION WERE SOME LIGHT PRECIP IS
PRODUCED ACROSS THE SOUTHWEST 1/2 TO 2/3 OF THE FCST AREA MAINLY
LATE SAT MORNING THRU SAT EVENING. TRENDED PRECIP CHANCE TO 50-70
PERCENT OVER THE SOUTH 1/2 OF THE FCST AREA SAT AFTERNOON/EVENING.
COLUMN COLD ENOUGH FOR ANY PRECIP TO FALL AS SNOW...BUT FOR THE FAR
SOUTH END OF THE FCST AREA SAT AFTERNOON WHERE BOUNDARY LAYER TEMPS
LOOK TO CLIMB INTO THE UPPER 30S. EXPECTED QPF WOULD PRODUCE 0.5 TO
1.5 INCHES OF -SN ACROSS THE SOUTH 2/3 OF THE FCST AREA. COLD
NORTHEAST LOW LEVEL FLOW/COLD ADVECTION SPREADS SOUTH ACROSS THE
AREA SAT NIGHT ALONG WITH DECREASING CLOUDS FROM NORTH TO SOUTH AS
CAN HIGH PRESSURE BUILDS IN. USED A BLEND OF THE GUIDANCE HIGHS/LOWS
FOR SAT/SAT NIGHT.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 312 PM CDT FRI MAR 14 2014

THE MAIN FORECAST CONCERNS FOR SUNDAY THROUGH MONDAY NIGHT...WARM
ADVECTION SNOW POTENTIAL LATE SUN NIGHT/MON...WINTRY MIX POTENTIAL
MON NIGHT...TEMPERATURES.

14.12Z MODELS IN GOOD AGREEMENT SUN/SUN NIGHT AS ONE TROUGH PASSES
EARLY SUN THEN HGTS FALL AGAIN ALREADY SUN NIGHT AHEAD OF THE NEXT
TROUGH/ENERGY MOVING ACROSS SOUTHERN CAN OR INTO THE PAC NORTHWEST.
DIFFERENCES SHOW UP BY LATER MON/MON NIGHT AS TROUGHING/ENERGY
CROSSING THE NORTHERN ROCKIES MON MOVES INTO THE CENTRAL/NORTHERN
PLAINS MON NIGHT. NO ONE MODEL WITH CLEARLY BETTER RUN-TO-RUN
CONSISTENCY IN THE MON/MON NIGHT PERIOD. FAVORED A MODEL/ENSEMBLE
CONSENSUS THIS PERIOD WITH FCST CONFIDENCE FOR SUN/SUN NIGHT
AVERAGE THEN TRENDING BELOW AVERAGE MON/MON NIGHT.

COOL/DRY CAN HIGH PRESSURE DRIFTS ACROSS THE REGION SUN WITH 850MB
TEMPS 1 TO 1.5 STANDARD DEVIATIONS BELOW NORMAL. STRONG 925-700MB
WARM ADVECTION BETWEEN THE RETREATING HIGH AND LOW PRESSURE MOVING
INTO THE NORTHERN PLAINS SPREADS INTO/ACROSS THE AREA LATER SUN
NIGHT/MON. DEEPER OF THE SFC-700MB SATURATION WITH THIS LOWER LEVEL
THERMO-DYNAMIC FORCING/WARM ADVECTION WING PROGGED OVER THE NORTH
END OF THE FCST AREA LATE SUN NIGHT INTO MON EVENING. LIMITED
20-30 PERCENT -SN CHANCES TO MAINLY THE NORTH HALF OF THE FCST
AREA CENTERED ON MON.

INCREASING LOWER LEVEL THERMO-DYNAMIC FORCING/LIFT WITH THE LOW/
TROUGH MOVING INTO THE CENTRAL/NORTHERN PLAINS BEGINS TO SPREAD INTO
THE FCST AREA MON NIGHT. STRONGER LOW LEVEL WARM ADVECTION SENDS
925-850MB TEMPS ABOVE 0C...WITH PRECIP CHANCES COMING IN MON
NIGHT AS A WINTRY MIX. ADDED -FZRA/SLEET TO FCST GRIDS FOR MON
NIGHT. FAVORING THE MODEL/ENSEMBLE CONSENSUS... USED A BLEND OF
THE GUIDANCE FOR HIGHS/LOWS SUN THRU MON NIGHT.

FOR TUESDAY THROUGH FRIDAY.../DAYS 4 TO 7/...

MAIN FORECAST CONCERN THIS PERIOD IS POTENTIAL FOR A SIGNIFICANT
WINTER STORM TO LIFT THRU THE MID/UPPER MS VALLEY TUE INTO WED.

14.00Z AND 14.12Z MEDIUM RANGE MODELS SLOWLY COMING INTO BETTER
AGREEMENT FOR A LONGWAVE TROUGH AND STRONGER SHORTWAVE TO MOVE
ACROSS THE CENTRAL CONUS IN THE TUE THRU WED TIMEFRAME. 14.00Z
MODELS FAVORED FASTER AND STRONGER OF EARLIER RUNS...WHILE 14.12Z
RUNS GENERALLY TRENDED WEAKER. BETWEEN MODEL AND RUN-TO-RUN
CONSISTENCY LEAVES QUITE A BIT TO BE DESIRED IN THE TUE-WED TIME-
FRAME. REASONABLE CONSENSUS AMONG THE 14.00Z MODELS/ENSEMBLE MEANS
FOR THE MAIN TROUGH TO MOVE INTO EASTERN NOAM THU/FRI WITH SLOWLY
RISING HGTS BUT NORTHWEST FLOW OVER THE REGION. 14.12Z GFS TRENDS
MORE PROGRESSIVE WITH THE SHORTWAVE RIDGING BUILDING OVER THE UPPER
MIDWEST BY FRI. FCST CONFIDENCE BELOW AVERAGE TUE-FRI GIVEN THE POOR
BETWEEN MODEL AND RUN-TO-RUN CONSISTENCY.

14.00Z/14.12Z MODEL DIFFERENCES FOR TUE/WED HAVE SIGNIFICANT IMPACTS
ON THE POTENTIAL WEATHER THESE PERIOD. FCST THESE PERIODS MESSY AT
BEST. LATEST GFS/ECMWF WOULD PASS THE BULK OF THE SYSTEM NORTH OF
THE FCST AREA TUE/TUE NIGHT...CAN-GEM/UKMET WOULD BRING IT SQUARELY
ACROSS THE FCST AREA WITH UKMET IMPACTS MORE TUE NIGHT/WED.
CONSIDERABLE TIMING/TRACK SPREAD AMONG 14.12Z GFS ENSEMBLE MEMBERS
WITH THE SFC LOW POSITION AT 00Z WED. GIVEN ALL THE VARIABILITY AND
BELOW AVERAGE CONFIDENCE IN ANY ONE DETERMINISTIC SOLUTION...FOR
NOW DID NOT STRAY FROM THE MODEL/ENSEMBLE CONSENSUS GRIDS FOR
TUE/WED. WITH LESSER CONSENSUS FOR RIDGING/HIGH PRESSURE LATER IN
THE WEEK...ALSO LEFT MODEL/ENSEMBLE CONSENSUS ALONE ON DAYS 6/7.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON) ISSUED
AT 1217 PM CDT FRI MAR 14 2014

FIRST FRONT IS THROUGH THE REGION WITH AN INCREASE IN NORTHWEST
WIND. SEVERAL GUSTS ABOVE 25 KTS OBSERVED...ESPECIALLY OVER HIGHER
TERRAIN AND OPEN AREAS...INCLUDING KRST. SECONDARY COLD FRONT
APPROACHING FROM THE NORTHWEST WILL ENHANCE THE GUSTINESS FOR A FEW
MORE HOURS JUST BEFORE SUNSET...WHEN DECOUPLING WILL ALLOW SPEEDS TO
SUBSIDE. UPSTREAM ACROSS MN THERE HAVE BEEN SOME LIGHT SPRINKLES AND
FLURRIES REPORTED. SOME OF THAT COULD SURVIVE TO REACH KRST...BUT IF
IT DOES IT WILL BE VERY LIGHT AND VERY BRIEF...NARY WORTH A MENTION.
ATTENTION THEN SHIFTS TO THE DISTURBANCE MOVING THROUGH THE REGION
FOR SATURDAY. BAND OF FRONTOGENESIS LOOKS TO FOCUS CHANCES FOR SNOW
FROM WNW- ESE. NAM/CANADIAN A BIT MORE ROBUST...AND THUS
FASTER/FURTHER NORTH COULD IMPACT THE TAF LOCATIONS AFTER 15Z SAT.
GFS/ECMWF A BIT WEAKER AND FURTHER SOUTH/SLOWER KEEPING MUCH OF THE
FOCUS JUST SOUTH OF THE TAF LOCATIONS. THIS POTENTIAL SNOW PERIOD IS
ON THE EDGE OF THE FORECAST. FOR NOW JUST ADDED LIGHT SNOW LATE IN
THE TAF PERIOD AND LATER ISSUANCES SHOULD BE ABLE TO ADD MORE DETAIL.

&&

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

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION.....MW