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000
FXUS63 KARX 150809
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
309 AM CDT SAT JUN 15 2013

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 309 AM CDT SAT JUN 15 2013

MAIN FORECAST CONCERN IS FLASH FLOOD AND SEVERE WEATHER POTENTIAL
FOR LATER TODAY.

CURRENTLY AS OF 08Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED AN UPPER LOW OVER CENTRAL SASKATCHEWAN WITH TROUGHING
EXTENDING SOUTH INTO WESTERN NORTH DAKOTA...RIDGING FROM LOUISIANA
NORTHWARD INTO WESTERN ONTARIO...AND TROUGHING OVER SOUTHEAST CANADA
INTO NEW ENGLAND. ALSO OF NOTE WAS A SHORTWAVE TROUGH OVER WESTERN
KS INTO THE TX PANHANDLE. PLENTIFUL MOISTURE NOTED ON GOES DERIVED
PRECIPITABLE WATER IMAGERY WITHIN THE RIDGING...WITH VALUES OF
1.5-1.8 INCHES FROM THE SOUTHERN PLAINS INTO THE FORECAST AREA.
THESE OVER THE FORECAST AREA ARE ALMOST 180 PERCENT OF NORMAL. A
30-40 KT 850MB JET STREAMING FROM THE TX PANHANDLE INTO IOWA PER
PROFILER AND VWP DATA HAS HELPED BRING THAT MOISTURE TOWARDS US.
ACCOMPANYING THE MOISTURE HAS BEEN WARMER AIR...WITH 850MB TEMPS OF
21-27C ACROSS NEBRASKA AND KANSAS COMPARED TO 12-14C OVER THE
FORECAST AREA PER 00Z RAOBS. ADDITIONALLY...ON THE NOSE OF THIS LOW
LEVEL JET...CONVECTION ENCOMPASSES MUCH OF THE FORECAST AREA
SOUTHWARD INTO NORTHEAST MISSOURI. TO THE NORTHWEST...CLEARER SKIES
AND DRIER AIR IS PRESENT OVER THE DAKOTAS...BEHIND A COLD FRONT
SITUATED IN WESTERN MN.

MODELS ARE IN GOOD AGREEMENT FLATTENING THE RIDGE AXIS OVER
MINNESOTA TODAY...IN RESPONSE TO THE TROUGHING OVER WESTERN NORTH
DAKOTA TRAVERSING EAST INTO NORTHERN LAKE SUPERIOR. THIS TROUGHING
WILL EVENTUALLY HELP PUSH THE COLD FRONT OVER WESTERN MN THROUGH THE
FORECAST AREA...WHICH ACCORDING TO MODEL CONSENSUS OCCURS BETWEEN
00-06Z SUNDAY. ONCE THE FRONT PASSES...THE DRIER AIR SEEN OVER THE
DAKOTAS WILL FLOW IN AND END THE THREAT FOR PRECIPITATION. UNTIL
THEN...THE FORECAST IS SOMEWHAT PROBLEMATIC TRYING TO FIGURE OUT
CONVECTIVE EVOLUTION.

FOLLOWING THE TYPICAL CONVECTIVE CYCLE...THE CURRENT CONVECTION
BEING SUPPORTED BY THE NOCTURNAL ENHANCEMENT TO THE LOW LEVEL JET
SHOULD WEAKEN THROUGH THE MORNING. MODELS INDICATE THIS HAPPENING AS
WELL...WITH 850MB MOISTURE TRANSPORT DIMINISHING BY 15Z.
ADDITIONALLY...THIS 850MB MOISTURE TRANSPORT BECOMES ORIENTED MORE
WEST TO EAST...EVEN BY 12Z AS THE UPPER RIDGE AXIS BEGINS TO
FLATTEN. THERE COULD EASILY BE A 4-6 HOUR BREAK IN PRECIPITATION
OVER THE FORECAST AREA...SAY BETWEEN 14-19/20Z. THEN...DIURNAL
HEATING COMBINED WITH THE COLD FRONT MOVING THROUGH THE FORECAST
AREA SHOULD INITIATE NEW CONVECTION. IN ADDITION...THAT SHORTWAVE
TROUGH PRESENTLY OVER WESTERN KS INTO THE TX PANHANDLE LOOKS TO LIFT
INTO IA...HELPING TO REFOCUS AND INCREASE 850MB MOISTURE TRANSPORT
TOWARDS NORTHEAST IA...ALONG WITH BRINGING DPVA FOR FORCING WITH IT.
ANOTHER FORCING MECHANISM FOR CONVECTION THIS AFTERNOON IS AN UPPER
JET STREAK ON THE ORDER OF 85-115KT PASSING ACROSS THE NORTHERN HALF
OF MN INTO LAKE SUPERIOR AT 21Z AND 00Z. THIS JET STREAK WOULD PUT
UPPER LEVEL DIVERGENCE OVER THE AREA. 15.05Z HRRR AND 15.00Z HIRES
ARW/NMM MODELS PRETTY MUCH AGREE WITH THE SCENARIO WRITTEN HERE.
ANY CONVECTION SHOULD THEN SLOWLY SINK SOUTHEAST DURING THE
EVENING...AIDED BY A COMBINATION OF CONVECTIVE OUTFLOWS AND THE
PASSAGE OF THE COLD FRONT.

REGARDING SEVERE WEATHER POTENTIAL...CONVECTION THIS MORNING SHOULD
MOSTLY BE A HEAVY RAIN CONCERN GIVEN DEEP WARM CLOUD DEPTHS AND
TALL...SKINNY CAPE. THE AFTERNOON AND EARLY EVENING HOURS NEED SOME
WATCHING. FIRST OFF...INSTABILITY IS PLENTY. RAP MLCAPE PROGS AT 21Z
WITH ML DEWPOINTS OF 65-70F AND SURFACE TEMPS IN THE 82-87F RANGE
RESULT IN VALUES OF 2500 TO 4000 J/KG...HIGHEST ACROSS SOUTHERN
PORTIONS OF THE FORECAST AREA. THIS CAPE IS FAT TOO...REFLECTED BY
NCAPE VALUES CLIMBING TO 0.25-0.35...SUGGESTING RAPID THUNDERSTORM
GROWTH. THE TEMPERATURES FORECAST BY THE RAP ARE LIKELY TOO
HIGH...SINCE PLENTY OF CLOUDS SHOULD EXIST. MID 70S TO NEAR 80
SUGGESTED BY MOST GUIDANCE SEEM MORE REASONABLE. STILL...THIS
RESULTS IN 1500-3000 J/KG OF MLCAPE. BEST 0-6KM SHEAR LIES AROUND
THE FRONT...ON THE ORDER OF 40-50 KT...WITH THE BULK OF THIS SHEAR
RESULTING FROM A 50 KT WIND MAX AT 6 KM ASSOCIATED WITH THAT
SHORTWAVE TROUGH LIFTING NORTHEAST INTO IOWA. ADDITIONALLY...
FREEZING LEVELS ARE PROGGED LOWER THIS AFTERNOON...FROM 12000-13500
FT AGL NORTHWEST TO SOUTHEAST. THUS...THINKING THERE SHOULD BE
POTENTIAL FOR EITHER MULTICELLS OR SUPERCELLS CAPABLE OF PRODUCING
LARGE HAIL. THERE IS ALSO A DRY WEDGE OF AIR BETWEEN 600-800MB WHICH
COULD PROVE FAVORABLE FOR DAMAGING WINDS. LASTLY...ALTHOUGH FREEZING
LEVELS ARE LOWER...THE PLENTIFUL CAPE AND HIGH EQUILIBRIUM LEVELS
ALONG WITH STORM MOTIONS WHICH LOOK LIKE THEY MAY BE KIND OF SLOW
BRINGS UP A HEAVY RAIN CONCERN. THUS...THE FLASH FLOOD WATCH STILL
LOOKS GOOD.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 309 AM CDT SAT JUN 15 2013

SUNDAY THROUGH MONDAY NIGHT...
MAIN FOCUS IS ON THE UPPER LOW OVER CENTRAL SASKATCHEWAN...WHICH
MODELS REMAIN CONSISTENT IN DROPPING THROUGH THE FORECAST AREA
DURING THE DAY MONDAY AS A WEAKENING SHORTWAVE TROUGH. THE CURRENT
COLD FRONT PROGRESSING THROUGH THE FORECAST AREA THIS AFTERNOON AND
EVENING LOOKS TO SHUNT A LOT OF THE MOISTURE AWAY FROM THE AREA.
THIS IS REFLECTED BY PRECIPITABLE WATER VALUES OF 0.6-0.7 INCHES
DURING THE DAY SUNDAY. THUS...SUNDAY LOOKS DRY AND WITH 850MB TEMPS
RUNNING 13-15C...HIGHS SHOULD EASILY CLIMB INTO THE LOW 80S. THERE
IS A SURGE OF 700-850MB MOISTURE TRANSPORT FROM THE NORTHWEST SUNDAY
NIGHT...ASSOCIATED WITH THE SHORTWAVE TROUGH APPROACHING...BUT HARD
TO SAY IF IT IS GOING TO BE ENOUGH TO PRODUCE PRECIPITATION. THE
15.00Z GFS/CANADIAN/NAM ALL BRING SCATTERED SHOWERS AND
THUNDERSTORMS THROUGH THE FORECAST AREA BETWEEN 06Z MONDAY AND
MONDAY AFTERNOON...BUT THE 15.00Z ECMWF IS MOSTLY DRY AND HAS BEEN
FOR MANY RUNS. AFTER THE FRONT GOES THROUGH MONDAY...DRIER AND
COOLER AIR ASSOCIATED WITH CANADIAN HIGH PRESSURE INVADES THE AREA
MONDAY NIGHT...RESULTING IN A DRY NIGHT.

TUESDAY THROUGH FRIDAY NIGHT...
MODELS REMAIN CONSISTENT THROUGH THURSDAY ON SHOWING TROUGHING OVER
THE PACIFIC NORTHWEST...RIDGING FROM THE NORTHWEST TERRITORIES OF
CANADA INTO THE SOUTHERN PLAINS...AND TROUGHING OVER EASTERN CANADA
AND THE EASTERN GREAT LAKES. THIS KEEPS THE FORECAST AREA UNDER THE
INFLUENCE OF HIGH PRESSURE AND MAINLY DRY...OUTSIDE OF A SHORTWAVE
PROGGED TO DROP THROUGH NORTHWEST FLOW ON THURSDAY AND PERHAPS BRING
A FEW SHOWERS AND THUNDERSTORMS. IT SHOULD BE NOTED THAT THE 15.00Z
ECMWF IS SHOWING SOMETHING NEW...A SHORTWAVE DROPPING THROUGH
WESTERN PORTIONS OF THE FORECAST AREA ON TUESDAY AND PRODUCING
PRECIPITATION. SINCE THIS IS A NEW FEATURE...HAVE HELD ONTO A DRY
FORECAST. AS WE HEAD TOWARDS THE WEEKEND...THE 15.00Z ECMWF HAS
CHANGED FROM ITS PREVIOUS RUNS AND NOW HAS COME INTO MORE ALIGNMENT
WITH THE GFS. BASICALLY...THE PACIFIC NORTHWEST TROUGH IS SUGGESTED
TO EJECT EAST-NORTHEAST...SPLITTING THROUGH THE RIDGE IN PLACE. THIS
RESULTS IN A WARM ADVECTION PATTERN DOWNSTREAM TOWARDS THE FORECAST
AREA...BRINGING THE CONCERN FOR CONVECTION. GOOD MODEL AGREEMENT
RESULTS IN PRECIPITATION CHANCES IN AT LEAST 30-40 PERCENT RANGE FOR
FRIDAY...AND EVEN HIGHER FOR FRIDAY NIGHT. WE WILL HAVE TO WATCH HOW
THIS ALL EVOLVES TOWARDS THE END OF THE WEEK SINCE THE PATTERN WOULD
FAVOR SEVERE WEATHER AND HEAVY RAIN POTENTIAL.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1100 PM CDT FRI JUN 14 2013

CONVECTIVE COMPLEXES WERE ROLLING ACROSS IA WITH THE AID OF THE LOW
LEVEL JET...AND ONE WILL TRACK ACROSS THE TAF SITES FOR THE
OVERNIGHT HOURS. CIGS WILL DROP QUICKLY WITH THE ONSET OF THE
SHRA/TS...ALTHOUGH IT MAY TAKE A FEW HOURS TO FALL INTO THE MVFR
CATEGORY. EXPECT THE LOW CIGS TO HANG AROUND FOR THE BETTER PART OF
THE MORNING...WITH SOME IMPROVEMENT BY AFTERNOON.

AS FOR THE SHRA/TS...EXPECTING A BREAK FROM THE PCPN LATER SATURDAY
MORNING. CHANCES LOOK LIKE THEY WILL INCREASE FOR THE AFTERNOON AS
MODELS SUGGEST AN UPPER LEVEL SHORTWAVE WILL TRACK IN FROM THE
SOUTHWEST...INTERACTING WITH THE WARM FRONT THAT WILL STILL BE
WAVERING WEST-SOUTH ACROSS IOWA. THESE SHRA/TS SHOULD EXIT EARLY SAT
EVENING AS THE SHORTWAVE DEPARTS...WITH A CLEARING CLOUD TREND FOR
THE REST OF THE NIGHT.


&&

.HYDROLOGY...
ISSUED AT 309 AM CDT SAT JUN 15 2013

WIDESPREAD SHOWERS WITH EMBEDDED THUNDERSTORMS DEVELOPED EARLY THIS
MORNING ACROSS MUCH OF THE FORECAST AREA. HOWEVER...WITH LESS
INSTABILITY AVAILABLE COMPARED TO THE EVENING HOURS...THE MAJORITY
OF THE FORECAST AREA AS OF 08Z HAS SEEN LESS THAN 0.25 INCH OF
RAINFALL. THERE HAVE BEEN ISOLATED LOCATIONS OVER 1 INCH...INCLUDING
IN FLOYD COUNTY IA WHICH DOES NOT NEED THE RAIN. SO FAR MOST RIVERS
HAVE NOT RESPONDED TO THE RAIN.

PRECIPITATION IS ON THE WANE AS OF 08Z...AND WE MAY END UP WITH A
DECENT DRY PERIOD...SAY FROM 14-20Z. AFTER 20Z...MORE THUNDERSTORMS
ARE EXPECTED TO MOVE INTO THE FORECAST AREA...FROM AN APPROACHING
COLD FRONT COMING FROM THE WEST AND A SHORTWAVE LIFTING OUT OF
SOUTHWEST KS INTO IOWA. THESE WILL BE HEAVY RAIN PRODUCERS...WHICH
GIVEN THE ANTECEDENT MOIST SOILS COULD RESULT IN FLASH FLOODING.
THEREFORE THE FLASH FLOOD WATCH CONTINUES. THE FLASH FLOOD THREAT
SHOULD SUBSIDE DURING THE EVENING HOURS...MAYBE JUST SLIGHTLY AFTER
THE 00Z END TIME OF THE WATCH...AS THUNDERSTORMS WEAKEN AND DROP
SOUTHEAST.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...FLASH FLOOD WATCH THROUGH THIS EVENING FOR MNZ094-095.

IA...FLASH FLOOD WATCH THROUGH THIS EVENING FOR IAZ008>010-018-019-
     029-030.

&&

$$

SHORT TERM...AJ
LONG TERM...AJ
AVIATION......RIECK
HYDROLOGY...AJ