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000
FXUS63 KARX 190545
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1245 AM CDT SUN MAY 19 2013

.UPDATE...
ISSUED AT 724 PM CDT SAT MAY 18 2013

HAVE BEEN WORKING TO GET A BETTER HANDLE ON THE THUNDERSTORM
CHANCES AROUND DAYBREAK MOVING IN FROM THE SOUTHWEST. THE
THUNDERSTORM CHANCES ARE CLOSELY TIED TO THE SHORTWAVE TROUGH
SHIFTING OUT OF KS/OK AND THE FOCUS OF CURRENT DEEP CONVECTION
THERE. THE STORMS/SHRAS WOULD BE ON THE LEADING EDGE OF A MOISTURE
SURGE OF 12G/KG MIXING RATIO ABOVE THE SURFACE ON THE 305K SURFACE
/850MB/...THUS CAPE WILL INCREASE TOO...PER 18.23Z RAP. SHOULD SEE
THE LINE OF CONVECTION ADVECT ACROSS IA ON THE NOSE OF THIS
MOISTURE AND LOW-LEVEL JET CONVERGENCE. HOWEVER...THE BEST
LOW-LEVEL JET CONVERGENCE IS FURTHER INTO IA AND IS WEAKER IN THE
LOCAL AREA PER THE RAP. PROBABLY WHY THE RAP HAS THE AREA DRY.

THE SPC SSEO HAS A PROBABILITY OF 70+ PERCENT CHANCE OF 40DBZ OR
HIGHER FROM THE 7 CONVECTION ALLOWING MODELS BY 12Z ALONG I-35.
THIS IS PROBABILITY IS DECREASING HOWEVER. 3 OF THE LATEST 4 HRRR
RUNS ALSO HAVE A TSRA/SHRA ALONG I-35 BY 09Z IN MN-IA. THE LATEST
RUN 18.21Z BRINGS THIS CONVECTIVE SYSTEM TO JUST WEST OF THE MISS
RIVER BY 12Z SUN. THERE ARE CONVECTIVE ELEMENTS OVER 50 DBZ WITH
ABOUT 1200 J/KG OF MUCAPE WHICH IS ELEVATED. THE WIND SHEAR IS
FAIRLY WEAK WITH ONLY 20-30 KTS OF FLOW AT 6 KM.

HAVE UPDATED THE FORECAST TO INCLUDE A HIGHER CHANCE OF TSRA WEST
OF THE MISS RIVER SUNDAY AROUND DAYBREAK. THE FORCING IS WEAKER
THAN FURTHER TO THE SOUTHWEST /IA/...BUT THIS MOISTURE SURGE
ISENTROPICALLY LIFTING IN THE OVERNIGHT HOURS USUALLY PRODUCES
SOME ELEVATED STORMS. WILL CONTINUE TO MONITOR...RAIN CHANCES MAY
NEED TO BE INCREASED FURTHER. WITH LIMITED WIND SHEAR...WOULD
THINK POSSIBLY AN ISOLATED SEVERE HAILER MAY BE ABOUT ALL THAT COULD
OCCUR. THE RAINFALL SHOULD BE PROGRESSIVE...BUT ANY RAIN ON THE
SERN MN AREA HAS TO BE FOLLOWED CLOSELY...SOILS JUST CANNOT TAKE
IT. A FLASH FLOOD WATCH MAY BE NEEDED THERE. SEE FACEBOOK POST FOR
30 DAY WATER EQUIVALENT THAT HAS FALLEN THERE...5-8 INCHES ABOVE
NORMAL.

&&

.SHORT TERM...(TONIGHT AND SUNDAY)
ISSUED AT 250 PM CDT SUN MAY 18 2013

MORNING MCS QUICKLY DIED OUT FOR THE AFTERNOON...WHILE A SFC
WARM FRONT HANGS ACROSS CENTRAL MN INTO NORTHERN WI. THE 850 MB JET
KICKS IN ACROSS SOUTHERN/CENTRAL PLAINS...AND EXPECT SOME CONVECTION
TO INITIATE. STEERING WINDS WOULD FAVOR A NORTH/NORTHEAST
MOVEMENT...LIKELY KEEPING IT JUST WEST OF THE FORECAST AREA THROUGH
12Z. THAT SAID...MESO ARW/HRRR SUGGEST IT COULD WORK INTO NORTHEAST
IA/SOUTHEAST MN BY 12Z. THINK THE POSITIONING OF THE VARIOUS WEATHER
ELEMENTS GIVES THIS SOLUTION SOME MERIT...AND WILL TREND SOME POPS
TOWARD THIS. ELSEWHERE...SOME INSTABILITY A LOFT PER BUFKIT
SOUNDINGS...BUT WITHOUT A KICKER TO TAP INTO IT...SHOULD BE A DRY
NIGHT.

FOR SUNDAY...UPPER LEVEL TROUGH HANGS WELL WEST WHILE ITS SFC LOW
WOBBLES OVER THE PLAIN STATES. THE SFC WARM FRONT STAYS NORTH WITH
THE COLD FRONT SOUTH OF THE SFC LOW...BUT SOME HINTS THAT ANOTHER
SFC BOUNDARY COULD EXTEND FROM THE LOW ACROSS EASTERN IOWA. THE LOW
LEVEL JET AND MOISTURE TRANSPORT FOCUS INTO EASTERN IA/EASTERN
MN/WESTERN WI BY 00Z MONDAY...PERSISTING THROUGH THE EVENING HOURS.
GFS/NAM SFC TDS PUSH UPPER 60S TO LOW 70S INTO THE FORECAST AREA BY
00Z MON...WHICH IS PROBABLY OVERDONE...ESP THE GFS. MID 60S SEEM
MORE REASONABLE...SO ASSOCIATED MODELED SBCAPE VALUES WILL ALSO BE
LESS AS A RESULT. MLCAPES AROUND 1200 J/KG LOOK GOOD. 0-6 KM SHEAR
IS NOT THAT IMPRESSIVE...MOSTLY 30 KTS. LOW LEVEL SHEAR IS MUCH
BETTER...30+ KTS IN THE 0-3 KM LAYER...WITH 15-25 KTS OF 0-1KM SHEAR
FROM 00-06Z SUNDAY EVENING. THE ATMOSPHERE WOULD BE SUPPORTIVE OF
SEVERE WEATHER...WITH A BETTER CHANCE FOR SUPERCELL DEVELOPMENT
SOUTHWEST...WHICH COULD MIGRATE INTO THE FORECAST AREA.
OVERALL...THINK THE THREATS WOULD FOCUS ON LARGE HAIL...DAMAGING
WINDS...AND FLASH FLOODING. CAN/T RULE OUT AN ISOLATED TORNADO WITH
THE STRONG NEAR SFC SHEAR AND POTENTIAL FOR ANY SMALLER SFC BOUNDARY
PROVIDING ENHANCED VORTICITY.

TIMING...LOCATION...AND INITIATION ARE ALL RATHER NEBULOUS
THOUGH...AND CONFIDENCE IS LOW IN THE WHERES AND WHENS OF THE
CONVECTION. IT IS HIGHER THAT THE BEST PCPN CHANCES WILL BE SUNDAY
NIGHT...WITH THE MAIN SEVERE THREAT IN THE EVENING.

SCENARIO COULD PLAY OUT LIKE THIS...MCSS OVER THE PLAINS TONIGHT
MAKE THEIR WAY TOWARD THE FORECAST AREA SUNDAY MORNING. THEY MAY OR
MAY NOT BRING RAIN TO WESTERN PORTIONS OF THE AREA...BUT WILL AT
LEAST BRING SOME CLOUDS FOR THE EARLY PART OF THE DAY. ATMOSPHERE
WILL NEED SOME TIME TO CLEAR/THIN CLOUDS...SO INSTABILITY WILL BE
BUILD LATER IN THE DAY. THIS WILL THEN INTERACT WITH SFC BOUNDARY
HANGING SOUTHEAST FROM THE SFC LOW AND AN UPPER LEVEL SHORTWAVE
TROUGH ROTATING OUT OF THE MEAN TROUGH TO SPARK SHOWERS/STORMS OVER
IOWA. SUPERCELL DEVELOPMENT IS PROBABLE...WITH SHEAR SUGGESTING A
TRANSITION TO LINE/BOWING SEGMENTS AS THE STORMS MOVE INTO THE
AREA...DAMAGING WINDS POSSIBLE AS THE STORMS ORIENT TO THE 0-3KM
SHEAR VECTOR. AGAIN THOUGH...CAN/T RULE OUT ISOLATED TORNADOES AS
LOW LEVEL SHEAR AND VARIOUS/POSSIBLE SFC BOUNDARIES WOULD SUPPORT
THIS. OF COURSE...THESE SEVERE THREATS ARE CONDITIONAL ON HOW
QUICKLY THE ATMOSPHERE CAN RELOAD...AND WHERE THE VARIOUS BOUNDARIES
WILL LIE.

FORECAST NEEDS MORE CLARITY...WHICH HOPEFULLY COMES WHEN WE GET A
BETTER HANDLE ON WHAT THE OVERNIGHT CONVECTION WILL DO.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 250 PM CDT SAT MAY 18 2013

A WET START TO THE WORK WEEK AS THE UPPER LEVEL LOW WOBBLES VERY
SLOWLY EASTWARD...WITH VARIOUS BITS OF ENERGY ROTATING AROUND IT.
THE SFC LOW TAKE AN EASTWARD TRACK ACROSS NORTHERN IA. PERSISTENT
INFLUX OF LOW LEVEL MOISTURE AHEAD OF AND WRAPPED AROUND THE LOW.
THIS MIX WILL KEEP THE AREA UNDER PERIODS OF SHOWERS AND
THUNDERSTORM.

WITH INSTABILTY RE-ESTABLISHING ITSELF MONDAY
AFTERNOON/EVENING...AND DECENT WIND SHEAR...ANOTHER SHOT FOR SEVERE
WEATHER WILL BE POSSIBLE. MUCH WILL DEPEND ON WHERE VARIOUS MESO
FEATURES RESIDE...ALA SURFACES BOUNDARIES...AND WHERE THE GREATER
INSTABILITY BUILDS.

SOME HOPE THAT THE SLOW MOVING SYSTEM FINALLY EXITS EAST THU NIGHT
WITH THE EC MERGING THE UPPER LEVEL LOW WITH A DEEPER/STRONGER LOW
OVER THE NEW ENGLAND STATES. THE GFS...HOWEVER...LINGERS THE LOW
LONGER...AND WOULD FIRE A FEW MORE SHOWERS/STORMS AROUND THE LOW/SFC
BOUNDARY THU NIGHT INTO EARLY FRI. HIGH PRESSURE TAKES OVER FOR
FRI/FRI NIGHT...PROMISING A DRY PERIOD. THAT SAID...THE EC IS
ALREADY BRINGING IN SOME QPF TO THE WEST SAT WITH WARM AIR
ADVECTION/SHORTWAVE INTERACTION ON THE BACKSIDE OF THE HIGH.

NOT MUCH CONFIDENCE WITH WHEN THE LOW WILL FINALLY EXIT EAST...AND
MODEL DIFFERENCES AREN/T HELPING WITH THE CLARITY. WILL HOLD WITH
THE CONSENSUS SOLUTION.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1245 AM CDT SUN MAY 19 2013

CONFIDENCE IS INCREASING THAT WEATHER WILL BE AROUND THE TAF SITES
IN THE MORNING HOURS AROUND 12Z. EXACTLY HOW THAT WILL AFFECT THE
AIRFIELDS IS STILL OF LOWER CONFIDENCE. WITH INCREASING
INSTABILITY MOVING IN AND SOME WEAK LIFT...THE CURRENT TSRA OVER
WRN IA WILL SHIFT INTO THE AREA AND WEAKEN AS IT MOVES TOWARD KLSE.
THUS...KRST HAS A BETTER CHANCE OF SEEING TSRA AT THE AIRFIELD
THAN KLSE.

THIS WILL BE A QUICK PERIOD OF WEATHER AND THEN A BREAK IS GOING
TO OCCUR UNTIL PROBABLY THE LATER AFTERNOON HOWEVER...THE TIMING
AND EXTENT OF THE WEATHER THIS AFTERNOON IS STILL VERY MUCH A
CHANGING FORECAST. IT APPEARS THE EVENING WILL BE OF GREATER
COVERAGE OF TSRA AND SHRA BUT THIS COULD BEGIN IN THE AFTERNOON.
PLENTY OF INSTABILITY IS IN PLACE....HIGHEST OF THE SEASON...BUT
THE EXACT TRIGGER FOR TSRA DEVELOPMENT IS IN QUESTION. SEVERE
WEATHER IS POSSIBLE WITH THE INSTABILITY IN PLACE AND LIFT
INCREASING THIS EVENING.

&&

.HYDROLOGY...SUNDAY AND INTO NEXT WEEK
ISSUED AT 250 PM CDT SAT MAY 18 2013

WITH CONSIDERABLE RAINFALL ACROSS PORTIONS OF SOUTHEAST MN AND
NORTHEAST IA YESTERDAY...SOILS ARE MOIST. 1 HR FFG IS FROM 1 1/2 TO
2 INCHES TO NEAR 2 INCHES FOR 3 HOURS. WHILE TODAY BROUGHT A PERIOD
OF DRYING...SHOWERS AND THUNDERSTORMS RETURN FOR SUNDAY INTO
WEDNESDAY. THERE IS THE POTENTIAL FOR 1 TO 3 INCHES OVER THIS
PERIOD. IF THIS FALLS IN A SHORT PERIOD...LOCALIZED FLASH FLOODING
WOULD OCCUR. A FLASH FLOOD WATCH MAY BE NECESSARY FOR PORTIONS OF
THE AREA. STREAMS...CREEKS...AND RIVERS HAVE RESPONDED TO THE RECENT
RAINFALL...MOSTLY WITHIN BANK RISES. HOWEVER...REPEATED ROUNDS OF
HEAVY RAIN COULD PUSH SOME OF THE MORE FLASHY BASINS ACROSS
SOUTHEAST MINNESOTA AND NORTHEAST IOWA TO NEAR FLOOD STAGE.

&&

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

$$

UPDATE...BAUMGARDT
SHORT TERM...RIECK
LONG TERM....RIECK
AVIATION...BAUMGARDT
HYDROLOGY....RIECK