Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 211735
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1235 PM CDT THU AUG 21 2014

.UPDATE...
ISSUED AT 733 AM CDT THU AUG 21 2014

THE LINE OF STORMS THAT WAS HEADING AT SOUTHEAST MN AND NORTHEAST
IOWA WEAKENED CONSIDERABLY AS IT MOVED IN. THERE WAS A GUST OF 38
MPH AT DODGE CENTER BUT THAT WAS THE MOST THAT OCCURRED. MUCAPE
VALUES NOW ONLY AROUND 1000 J/KG...COMBINED WITH THE 850MB
MOISTURE TRANSPORT VECTORS NOW ALIGNED MORE WEST-EAST WITH THE
NOSE CENTERED IN CENTRAL IA...ARE LIKELY REASONS WHY THE
CONVECTION WEAKENED. HOWEVER...THERE IS STILL A DECENT
SHORTWAVE COMING THROUGH ON WATER VAPOR AND INSTABILITY
AROUND...THUS EXPECT CONTINUED CONVECTION.

CANCELLED THE SEVERE THUNDERSTORM WATCH FOR SOUTHEAST MN INTO
VERNON COUNTY WITH NO SEVERE WEATHER EXPECTED THERE NOW. GIVEN
THAT NORTHEAST IOWA AND FAR SOUTHWEST WI ARE CLOSER TO THE NOSE OF
THE 850MB MOISTURE TRANSPORT...HAVE KEPT THE WATCH GOING THERE FOR
THE TIME BEING. THIS IS THE AREA THE CONVECTION IS STRONGEST.
HOWEVER...SHOULD THE CONVECTION WEAKEN OVER THE NEXT HOUR...WILL
LIKELY DROP THE REST OF THE WATCH THEN.

UPDATE ISSUED AT 535 AM CDT THU AUG 21 2014

A LINE OF STRONG TO SEVERE STORMS WAS APPROACHING THE INTERSTATE
35 CORRIDOR AT 530 AM THIS MORNING. THESE STORMS HAVE HAD A
HISTORY OF PRODUCING QUARTER SIZE HAIL AND WIND GUSTS OF 55 TO 60
MPH. THE LINE IS EXPECTED TO HOLD TOGETHER AS IT PUSHES INTO
SOUTHEAST MINNESOTA/NORTHEAST IOWA THIS MORNING. IN FACT...THE
REAR INFLOW JET IS BECOMING MORE APPARENT WITH THE LINE STARTING
TO SHOW A BOWING STRUCTURE. THE MAIN HAZARDS FROM THIS LINE OF
STORMS WILL BE DAMAGING WINDS AS IS PUSHES INTO THE FORECAST AREA.
THE LINE SHOULD HOLD TOGETHER AS IT APPROACHES THE MISSISSIPPI
RIVER AROUND 730 AM THIS MORNING AND COULD HOLD TOGETHER INTO
SOUTHWEST WISCONSIN. ALSO...THE STORMS ARE PRODUCING HEAVY
RAINFALL WHICH COULD LEAD TO LOCALIZED FLOODING ESPECIALLY IN
URBAN AREAS.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 344 AM CDT THU AUG 21 2014

MAIN FORECAST CONCERNS THIS MORNING ARE ON STRONG TO POSSIBLY SEVERE
STORMS MOVING ACROSS THE AREA. FOCUS THEN TURNS TO ANOTHER ROUND OF
STRONG TO SEVERE STORMS LATE THIS AFTERNOON INTO THIS EVENING.

LATEST RADAR SHOWED AN EXPANSIVE AREA OF THUNDERSTORMS OVER MUCH OF
WESTERN MINNESOTA MOVING WEST. THIS ACTIVITY IS EXPECTED TO PUSH
INTO SOUTHEAST MINNESOTA AND POSSIBLY SOUTHEAST MINNESOTA IN THE 5
AM TO 6 AM TIMEFRAME. THE ACTIVITY COULD GROW UPSCALE INTO A
SQUALL LINE WITH THE POTENTIAL FOR DAMAGING WINDS. HOWEVER IT IS
STRUGGLING TO ORGANIZE THIS MORNING WITH MORE OF A THREAT FOR
HEAVY RAINFALL WHICH COULD POTENTIALLY LEAD TO FLASH FLOODING
CONCERNS. WHILE MOST AREAS COULD TAKE SOME RAIN WITH 1 HOUR FLASH
FLOOD GUIDANCE RUNNING IN THE 2 TO 2.5 INCH RANGE...URBAN AREAS
AND AREAS THAT HAVE RECENTLY RECEIVED HEAVY RAINFALL WOULD HAVE
AN ENHANCED RISK OF EXPERIENCING  FLASH FLOODING CONCERNS. WITH
PRECIPITABLE WATER VALUES RUNNING RIGHT AROUND 2 INCHES AND WARM
CLOUD DEPTHS OF 4.0 KM...THE STORMS WILL BE VERY EFFICIENT RAIN
PRODUCERS. THERE IS MORE THAN ENOUGH MUCAPE TO WORK WITH AHEAD OF
THE DEVELOPING MESOSCALE CONVECTIVE COMPLEX WITH MUCAPE VALUES
RUNNING RIGHT AROUND 2000 J/KG OVER SOUTHEAST
MINNESOTA...NORTHEAST IOWA...AND FAR SOUTHWEST  WISCONSIN. IN
ADDITION...1 TO 7 KM BULK SHEAR VALUES ARE HOVERING RIGHT AROUND
30S KTS THIS MORNING AND THE 0-3 KM SHEAR VECTOR IS ORIENTED
NEARLY PERPENDICULAR TO THE LINE OF STORMS MOVING IN THIS MORNING.
CONSIDERING ALL OF THIS...SOME OF THE STORMS WILL BE CAPABLE OF
DAMAGING WIND GUSTS AND HEAVY RAINFALL.

AFTER THE FIRST ROUND OF STORMS THIS MORNING...ANOTHER ROUND OF
STORMS ARE EXPECTED THIS AFTERNOON INTO EARLY THIS EVENING AS A
SHORTWAVE TROUGH MOVES THROUGH. 0-1KM MUCAPE VALUES ARE EXPECTED
TO CLIMB INTO THE 1700 TO 2500 J/KG RANGE WITH 0-6 KM BULK SHEAR
VALUES INCREASING INTO THE 30 TO 35 KT RANGE. ALSO...A FRONTAL
BOUNDARY WILL BE STALLED OVER THE AREA...ESSENTIALLY A WARM FRONT
THAT HAS BEEN REINFORCED BY THE MORNING CONVECTION. LATEST
THINKING IS THAT STORMS WILL FIRE OVER CENTRAL INTO EAST CENTRAL
MINNESOTA DURING THE AFTERNOON HOURS THEN RACE SOUTHEAST INTO
LOCATIONS ALONG AND EAST OF THE MISSISSIPPI RIVER. THE MAIN
HAZARDS FROM THESE STORMS APPEAR TO BE DAMAGING WIND GUSTS AND
HEAVY RAINFALL. CANNOT RULE OUT ISOLATED LARGE HAIL AS WELL. WILL
HAVE TO KEEP A CLOSE EYE ON THE POTENTIAL FOR AN ISOLATED TORNADO
NEAR THE BOUNDARY LATE THIS AFTERNOON INTO THIS EVENING.
HOWEVER...THE TORNADO THREAT APPEARS LOW AT THIS TIME GIVEN WEAK
0-1 KM SHEAR. THE STORMS WILL TAPER OFF LATE THIS EVENING INTO THE
OVERNIGHT HOURS AS THE BOUNDARY SLIPS SOUTH OF THE FORECAST AREA.
WARM AND MUGGY CONDITIONS ARE EXPECTED TODAY WITH HIGHS CLIMBING
INTO THE MID TO UPPER 80S ALONG AND WEST OF THE MISSISSIPPI RIVER.
THESE TEMPERATURE COMBINED WITH DEW POINTS IN THE LOWER 70S WILL
PRODUCE HEAT INDEX VALUES OF 95 TO 98 DURING THE AFTERNOON HOURS.

A LATE ADDITION...ADDED AREAS OF FOG TO THE NORTHWEST HALF OF THE
AREA. RECENT RAIN...HIGH DEWPOINTS...SKIES CLEARING OUT AND
DIMINISHING WINDS THROUGH THE NIGHT WILL LIKELY CAUSE FOG TO FORM.
THERE COULD EVEN BE SOME DENSE FOG.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 344 AM CDT THU AUG 21 2014

THE WARM FRONT STARTS TO EDGE BACK TO THE NORTH LATE FRIDAY
AFTERNOON INTO FRIDAY NIGHT. SHOWERS AND THUNDERSTORMS ARE POSSIBLE
ALONG THE FRONT FRIDAY NIGHT MAINLY SOUTHWEST OF THE INTERSTATE
94 CORRIDOR. THE HIGHER CHANCES FOR THIS ACTIVITY WILL BE SOUTH OF
INTERSTATE 90. THE WARM FRONT THEN LIFTS NORTH ACROSS THE REGION
ON SATURDAY BRINING THE STEAMY AIRMASS BACK INTO THE AREA. A FEW
SHOWERS AND STORMS ARE POSSIBLE ALONG THE FRONT AS IT MOVES THOUGH
BUT GIVEN THE STRENGTH OF THE RIDGE BUILDING IN WE MAY NOT SEE
MUCH PRECIPITATION. AN UPPER TROUGH OVER THE NORTHWEST  CONUS
THEN MAKES ITS WAY EAST LATE SATURDAY INTO SUNDAY AS THE RIDGE
OVER THE MISSISSIPPI RIVER VALLEY EXTENDING  INTO THE WESTERN
GREAT LAKES STARTS TO EDGE EAST. A FEW SHORTWAVES TRACK OVER
MINNESOTA AND WESTERN IOWA SATURDAY NIGHT THROUGH SUNDAY  GENERATING
SHOWERS AND THUNDERSTORMS BUT THESE LOOK TO STAY WEST OF THE
FORECAST AREA. THE ECMWF IS DRY DURING THIS TIMEFRAME WHILE THE
GFS BRINGS THESE WAVE A LITTLE FURTHER EAST PRODUCING
PRECIPITATION OVER THE FORECAST AREA. HAVE INCORPORATED A BLEND OF
THE TWO BUT WOULD BE SUPPRESSED TO STAY DRY THROUGH MUCH OF THE
DAY ON SUNDAY AS WELL. HAVE WARMED TEMPERATURES ON SUNDAY ACROSS
THE ENTIRE FORECAST AREA. HIGHS LOOK TO RANGE FROM THE MID 80S
OVER NORTH CENTRAL WISCONSIN TO THE LOWER TO MID 80S OVER
SOUTHWEST WISCONSIN INTO PORTIONS OF NORTHEAST IOWA. THESE
TEMPERATURES COMBINED WITH DEW POINTS IN THE LOWER 70S WILL
PRODUCE HEAT INDEX VALUES OF 95 TO 102 AND A HEAT ADVISORY MAY BE
NEEDED...ESPECIALLY OVER SOUTHWEST INTO CENTRAL WISCONSIN. UPPER
RIDGE FINALLY PUSHES EAST AND STARTS TO BREAK DOWN EARLY NEXT WEEK
AS SOUTHWEST FLOW ALOFT SETS UP OVER THE UPPER MISSISSIPPI RIVER
VALLEY. THIS WILL SET THE STAGE FOR AN ACTIVE PATTERN GOING INTO
THE EARLY PART OF NEXT WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1235 PM CDT THU AUG 21 2014

FIRST COMPLEX OF SHRA/TSRA AND LCL MVFR/IFR CIGS/VSBYS MOVING
SOUTH/EAST OF THE TAF SITES...BUT TOOK A WHILE TO DO SO. MUCH OF THE
EARLY/MID AFTERNOON NOW LOOKS TO BE VFR AS THE DELAYED EXIT OF THE
FIRST ROUND OF CONVECTION HAS LOWERED CONFIDENCE IN THE EVOLUTION/
REDEVELOPMENT OF CONVECTION FOR LATER THIS AFTERNOON/EVENING...WHICH
DEPENDS ON WHERE A SFC WARM FRONT ENDS UP. SFC PRESSURE TROUGH HAS
JUMPED NORTH OF THE TAF SITES TO NEAR KMSP AND NORTH OF KLSE...WHILE
WEAK CONVECTIVE OUTFLOW AND BOUNDARY LAYER COOLING WITH CLOUDS/RA
HAS KEPT ANOTHER BOUNDARY IN CENTRAL/SOUTHERN IA. DEW POINT
DISCONTINUITY IS ACROSS THE NORTHERN TROUGH/BOUNDARY. BETTER LOWER
LEVEL MOISTURE TRANSPORT/THETA-E CONVERGENCE IS STILL ALIGNED ALONG/
NORTHEAST OF THE MS RIVER LATER THIS AFTERNOON/EVENING. WILL
CONTINUE WITH THE VCTS/CB MENTIONS AT KRST/KLSE IN THE 21-01/02Z
TIME FRAME FOR NOW UNTIL A CLEARER SIGNAL IS SEEN. ONCE THIS
CONVECTION WOULD SLIDE EAST/SOUTH OF THE AREA...ATTENTION FOR
TONIGHT/EARLY FRI MORNING TURNS TO BR/FG. WEAK SFC PRESSURE
GRADIENTS OVER THE AREA TONIGHT AS A WEAK SFC LOW SLIDES INTO THE
AREA. THIS ALONG WITH THE RECENT RAINS/RADIATIONAL COOLING SETS THE
AREA UP FOR BR/FG...ESPECIALLY IN THE 09-13/14Z PERIOD. GIVEN THE
WEAK GRADIENT AND IT IS NOW LATE AUG...BR/FG WILL BE SLOWER TO BURN
OFF IN THE MORNING...WITH SOME 4-6SM HZ EXPECTED TO LINGER THRU MUCH
OF THE MORNING.

&&

.HYDROLOGY...TODAY INTO TONIGHT
ISSUED AT 344 AM CDT THU AUG 21 2014

THUNDERSTORMS WILL MOVE ACROSS THE FORECAST AREA THIS MORNING AND
ARE EXPECTED TO PRODUCE HEAVY DOWNPOURS AT TIMES. RAINFALL AMOUNTS
OF 1 TO 2 INCHES ARE EXPECTED WITH LOCALLY HIGHER AMOUNTS
POSSIBLE WHICH COULD LEAD TO LOCALIZED FLOODING. 1 HOUR FLASH
FLOOD GUIDANCE RANGES FROM 1.5 TO 2.5 INCHES ACROSS THE AREA SO
THE SOILS CAN TAKE SOME RAINFALL. THE MAIN CONCERN INITIALLY WILL
BE OVER URBAN AREAS AND IF ANY OF THE STORMS WOULD HAPPEN TO TRAIN
THERE COULD BE A FLASH FLOOD THREAT THIS MORNING. ANOTHER ROUND OF
STORMS IS EXPECTED THIS AFTERNOON INTO THIS EVENING. THESE STORMS
WILL ALSO BE CAPABLE OF PRODUCING HEAVY DOWNPOURS. DEPENDING ON
HOW MUCH RAIN FALLS OUT OF THE MORNING ACTIVITY...THE AFTERNOON
AND EVENING STORMS COULD BRING A THREAT FOR FLASH FLOODING.

&&

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

$$

UPDATE.......AJ
SHORT TERM...WETENKAMP
LONG TERM....WETENKAMP
AVIATION.....RRS
HYDROLOGY....WETENKAMP


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