000
FXUS63 KARX 181958
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
250 PM CDT SAT MAY 18 2013

.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 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON) ISSUED
AT 1256 PM CDT SAT MAY 18 2013

A MOIST AIRMASS FLOWING INTO THE REGION THIS AFTERNOON WILL
PRODUCE SCATTERED TO BROKEN CUMULUS CLOUDS WITH BASES IN THE 2500
TO 3500 FT RANGE. SOUTH WINDS WILL INCREASE THIS AFTERNOON TO
AROUND 10 KTS AT KLSE AND TO AROUND 14 KTS AT KRST. CANNOT RULE
OUT AN ISOLATED SHOWER OR THUNDERSTORM THIS AFTERNOON...BUT THIS
LOOKS UNLIKELY GIVEN THE LACK OF FORCING. CHANCES FOR SHOWERS AND
STORMS INCREASE ACROSS THE REGION ON SUNDAY AS A LOW PRESSURE
SYSTEM DEEPENS OVER THE NORTHERN PLAINS. AT THIS TIME...THE
HIGHEST CHANCES FOR SHOWERS AND POSSIBLY A THUNDERSTORM APPEARS TO
BE AT KRST IN THE 10 TO 14Z TIMEFRAME...THEN ACROSS MUCH OF THE
AREA LATE SUNDAY AFTERNOON INTO SUNDAY EVENING. THE STORMS COULD
PRODUCE PERIODS OF HEAVY RAIN...GUSTY WINDS AND HAIL...ESPECIALLY
DURING THE LATE AFTERNOON AND EVENING ON SUNDAY.

&&

.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.
&&

$$

SHORT TERM...RIECK
LONG TERM....RIECK
AVIATION.....WETENKAMP
HYDROLOGY....RIECK