Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 111750
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1250 PM CDT FRI JUL 11 2014

.UPDATE...
ISSUED AT 844 AM CDT FRI JUL 11 2014

FORECAST HAS BEEN UPDATED TO RAISE POPS CONSIDERABLY THROUGH THE
MORNING HOURS AS THE REMNANTS OF AN OVERNIGHT CONVECTIVE SYSTEM
TRACK TO THE EAST THROUGH THE REGION...PARTICULARLY IN SOUTHEAST
MINNESOTA AND WESTERN WISCONSIN. INSTABILITY REMAINS FAIRLY
WEAK...SO ANY THUNDERSTORMS SHOULD REMAIN FAIRLY ISOLATED. NOT
SURE HOW MUCH ACTIVITY WILL REDEVELOP IN THE AFTERNOON AS THIS
FEATURE MOVES OFF TO THE EAST BY THIS AFTERNOON. TEMPERATURES WILL
REMAIN DOWN DUE TO THE CLOUD COVER AND RAIN THIS MORNING...BUT
COULD MAKE A BRIEF REBOUND IN THE LATE AFTERNOON HOURS...SO HAVE
ADJUSTED THAT PART OF THE FORECAST AS WELL. UPDATES COMING
SHORTLY.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 255 AM CDT FRI JUL 11 2014

MAIN SHORT TERM CONCERN IS ON PRECIPITATION CHANCES TODAY.

CURRENTLY AS OF 08Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED RIDGING OVER THE CENTRAL U.S....A WEAK RIDGE OVER MICHIGAN...
A SHORTWAVE TROUGH CROSSING MN WITH THE CORE NEAR DULUTH...A WEAK
SHORTWAVE CROSSING NEBRASKA...AND A DEEP UPPER TROUGH OVER SOUTH
CENTRAL CANADA. DPVA AHEAD OF THE MN SHORTWAVE TROUGH COMBINED WITH
850MB MOISTURE TRANSPORT SEEN BY STRONGER 850MB WINDS ON RADARS FROM
EASTERN SOUTH DAKOTA INTO NORTHERN MN HAS SUPPORTED SHOWERS AND
STORMS NORTH OF MINNEAPOLIS. THE NEBRASKA SHORTWAVE AND ANOTHER NOSE
OF 850MB MOISTURE TRANSPORT HAS SUPPORTED OTHER SHORTWAVES AND
STORMS FROM NEBRASKA INTO SIOUX FALLS AREA. THE FORECAST AREA
MEANWHILE HAS ONLY SEEN A FEW LIGHT SHOWERS WEST OF THE MS RIVER
STEMMING FROM ACCAS CLOUDS ON THE EASTERN EXTENT OF THE MOISTURE
TRANSPORT ZONE. THE AIRMASS OVER THE REGION HAS CERTAINLY BECOME
WARMER AND MORE MOIST OVER THE PAST 24 HOURS. 850MB TEMPS HAVE
CLIMBED TO 12-15C ACCORDING TO 00Z SOUNDINGS WITH 20-25C READINGS IN
THE DAKOTAS. MEANWHILE...PRECIPITABLE WATER VALUES ARE UP TO 1-1.5
INCHES WITH A 2 INCH MAXIMA NEAR SIOUX FALLS PER RAP AND GOES
DERIVED.

THE FORECAST FOR TODAY IS RADICALLY DRIER THAN WHAT IT LOOKED LIKE
24 HOURS AGO. MUCH OF THIS IS A FUNCTION OF THE 850MB MOISTURE
TRANSPORT BEING INCORRECT. INSTEAD OF THE NOSE COMING RIGHT AT THE
FORECAST AREA...ITS IN NORTHERN MN AND NEAR SIOUX FALLS.
ADDITIONALLY...THE SHORTWAVE TRACKING ACROSS MN IS MOVING FASTER
THAN EARLIER PROJECTIONS.

RE-ANALYZING TODAYS FORECAST. IT APPEARS THE SHOWERS AND STORMS
TAKING PLACE NORTH OF MINNEAPOLIS WILL PROGRESS TO THE EAST THIS
MORNING WITH THE CORE OF THE SHORTWAVE TROUGH...PERHAPS CLIPPING
TAYLOR COUNTY. TO THE WEST...REGARDING THE SHOWERS AND STORMS
CROSSING NEBRASKA AND SIOUX FALLS...THESE MAY MAKE IT INTO NORTHEAST
IOWA LATE IN THE MORNING PER HRRR AND 11.00Z GFS PROGS. HOWEVER...
THE 850MB MOISTURE TRANSPORT NOSE SUPPORTING THEM IS PROGGED TO
DRAMATICALLY WEAKEN IN ALL MODELS...SO ITS POSSIBLE THEY DIE BEFORE
REACHING NORTHEAST IOWA. THIS LEAVES REALLY THE ONLY OTHER THREAT OF
PRECIPITATION FOR THE MORNING BEING THIS ACCAS WHICH COULD SHOWER
HERE AND THERE ACROSS MUCH OF THE FORECAST AREA DURING THE MORNING.
HEADING INTO THE AFTERNOON...DESPITE THE FACT THAT THE HIGHER
PRECIPITABLE WATER ZONE OVER SIOUX FALLS AREA IS PROGGED TO SHIFT
EAST INTO THE AREA...THERES NO FORCING TO DO ANYTHING WITH THAT
MOISTURE. SURFACE BOUNDARY WISE...A COLD FRONT LOOKS TO EXTEND
SOUTHWEST TO NORTHEAST ACROSS MN WHILE A WARM FRONT IS ACROSS
NEBRASKA...BOTH BEING WEST OF THE AREA. ADDITIONALLY...500MB HEIGHTS
ARE RISING IN THE WAKE OF THE SHORTWAVE TROUGH TO PROVIDE
SUBSIDENCE. 11.00Z NAM/GFS/REGIONAL CANADIAN ARE ALL DRY AND HAVE
TRENDED THE FORECAST EVEN MORE IN THAT DIRECTION. ONLY THE 11.00Z
HIRES ARW HAS SOME ISOLATED DIURNAL CONVECTION SO KEPT A 20 PERCENT
CHANCE IN CASE. WITH A DRIER FORECAST AND 850MB TEMPS BETWEEN 14-16C
TODAY...HAVE RAISED TEMPERATURES A FEW DEGREES. PLENTY OF MID CLOUD
WILL HAMPER HIGHS FROM REACHING FULL POTENTIAL...THOUGH.

FOR TONIGHT...THERE IS GOOD MODEL AGREEMENT FOR 850MB MOISTURE
TRANSPORT TO INCREASE ACROSS THE CENTRAL PLAINS INTO THE I-80
CORRIDOR ACROSS NEBRASKA AND IOWA. THE CAUSE FOR THE INCREASE IS
TIED TO A FAIRLY STRONG MONSOONAL SHORTWAVE SEEN ON WATER VAPOR
IMAGERY OVER LAS VEGAS...ROTATING UP AROUND THE CENTRAL PLAINS RIDGE
INTO SOUTH DAKOTA BY 12Z SATURDAY. GIVEN THE HIGH PRECIPITABLE WATER
AIRMASS IN PLACE...IT SEEMS ALL BUT CERTAIN SHOWERS AND
THUNDERSTORMS WILL FIRE ON THE NOSE OF THAT 850MB MOISTURE TRANSPORT
ZONE. SOME OF THESE STORMS COULD WORK INTO LOCATIONS SOUTH OF
INTERSTATE 90 AFTER MIDNIGHT...THOUGH BELIEVE THE GREATER FOCUS FOR
THEM WILL OCCUR SOUTH AND WEST OF THE AREA PRIOR TO 12Z SATURDAY.
ALSO CANNOT RULE OUT A FEW SHOWERS AND STORMS THROUGH THE NIGHT
CROSSING TAYLOR/CLARK COUNTIES FROM THE COLD FRONT OVER MN TRACKING
THROUGH THERE. WITH A HIGH PRECIPITABLE WATER AIRMASS IN PLACE AND
MID CLOUD SPREADING IN FROM THE SOUTHWEST...ANTICIPATING A WARM
NIGHT. IN FACT...HIGHER DEWPOINTS ADVECTING IN COULD RESULT IN SOME
FOG.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 255 AM CDT FRI JUL 11 2014

MAIN LONG TERM CONCERNS ARE ON SEVERE WEATHER POTENTIAL SATURDAY
AFTERNOON/EVENING AND THE UNSEASONABLY COLD AIR MONDAY INTO TUESDAY.

SATURDAYS FOCUS IS ENTIRELY ON THE CURRENT MONSOONAL SHORTWAVE NEAR
LAS VEGAS. MODEL CONSENSUS BRINGS THIS SHORTWAVE THROUGH OUR AREA AT
ABOUT THE TIME OF PEAK HEATING. 0-6KM...0-3KM AND 0-1KM SHEAR VALUES
ALL REALLY INCREASE THROUGH THE DAY IN RESPONSE TO THE SHORTWAVE...
TOPPING OUT AT 21Z AROUND 60 KTS...45 KT AND 20-25 KT RESPECTIVELY.
THIS IS PLENTY FOR ORGANIZED SEVERE CONVECTION. THE DEEPER SHEAR IS
ALSO NICELY CYCLONICALLY CURVED. MEANWHILE...THE ATMOSPHERE IS
JUICED UP PRECIPITABLE WATER WISE WITH VALUES OF 2 INCHES GETTING
ADVECTED INTO THE AREA. ALSO GOOD MODEL CONSENSUS EXISTS FOR 750-
2000 J/KG OF MLCAPE TO BUILD UP SOUTH OF I-90...LIMITED BY PLENTIFUL
CLOUD COVER...WITH EVEN HIGHER VALUES BUILDING UP IN A CAPPED
AIRMASS NEAR I-80. THUS...SEE SOME CHANCE FOR A SEVERE WEATHER EVENT
SATURDAY AFTERNOON. HAIL THREAT IS LIMITED BY THE HIGH PRECIPITABLE
WATER AND WARM CLOUD DEPTHS AROUND 4 KM. THESE PARAMETERS INCREASE
THE HEAVY RAIN AND FLASH FLOODING CONCERN...HOWEVER...THE STRONG
SHEAR SHOULD PROMOTE PROGRESSIVE CONVECTION. ADDITIONALLY...THE
RECENT DRY PERIOD WILL ALLOW SOILS TO ABSORB MORE WATER. THE STRONG
SHEAR DEFINITELY MAKES DAMAGING WINDS A CONCERN. CANNOT RULE OUT A
TORNADO EITHER GIVEN THE 0-1KM SHEAR AND A WARM FRONT LIKELY TO SIT
NEAR/SOUTH OF US-20. REALLY THE ONLY ISSUE WITH SATURDAY AMONGST THE
MODELS IS THE PLACEMENT OF AFTERNOON CONVECTION. THE 11.00Z
NAM/REGIONAL CANADIAN ARE ALONG/NORTH OF I-90...WHICH BOTH HAVE HAD
A NORTHWARD BIAS TO SEVERE CONVECTIVE EVENTS THIS YEAR. PREFER THE
FARTHER SOUTH 11.00Z GFS/ECMWF/HIRES ARW. MUCH OF THE CONVECTION
SHOULD PUSH SOUTHEAST OF THE AREA BY 03Z WITH THE PASSAGE OF THE
SHORTWAVE...FOLLOWED BY SIGNIFICANT DRYING OF PRECIPITABLE WATER OF
NEARLY 1 INCH BY 12Z SUNDAY.

ON SUNDAY...THE DEEP UPPER TROUGH OVER SOUTH CENTRAL CANADA IS
PROGGED TO BEGIN ITS DESCENT INTO OUR REGION. A COLD FRONT AHEAD OF
THE TROUGH SHOULD DROP SOUTH THROUGH THE AREA...AGAIN AT THE TIME OF
PEAK HEATING. 0-6KM SHEAR IS RUNNING 40-50 KT WITH 0-3KM AT 25-35KT.
HOWEVER...INSTABILITY LOOKS TO BE SEVERELY LACKING RESULTING FROM THE
SIGNIFICANT DRYING OF PRECIPITABLE WATER SATURDAY NIGHT. 11.00Z GFS
HAS THE GREATEST INSTABILITY AT 500-1000 J/KG OF MLCAPE...BUT THINK
ITS DEWPOINTS IN THE LOW 60S POOLING AROUND THE BOUNDARY ARE TOO
HIGH. FOR NOW HAVE CONTINUED SOME CHANCES OF PRECIPITATION FOR THE
FRONT...BUT BELIEVE THE DRIER 11.00Z ECMWF/CANADIAN/NAM WILL COME
TRUE. MUCH COOLER AND DRIER AIR SINKS SOUTH INTO THE AREA SUNDAY
NIGHT IN THE WAKE OF THE FRONT.

MONDAY AND TUESDAY STILL LOOK LIKE A TASTE OF FALL AS A SHOT OF
MODIFIED ARCTIC AIR COMES INTO THE REGION. AN UPPER LOW WITHIN THE
DEEP UPPER TROUGH IS PROGGED TO SLIDE ACROSS NORTHERN WI MONDAY
EVENING. COOL TEMPERATURES ALOFT...DAYTIME HEATING AND DPVA AHEAD OF
THE UPPER LOW SHOULD PROMOTE SHOWER DEVELOPMENT ACROSS MUCH OF THE
REGION MONDAY. THIS WILL BE ESPECIALLY TRUE OVER NORTHERN WI. HAVE
RAISED PRECIPITATION CHANCES AND FURTHER INCREASES MAY BE NECESSARY.
PRECIPITATION CHANCES CONTINUE INTO TUESDAY AS WELL WITH THE COLD
AIR ALOFT STILL AROUND. 850MB TEMPERATURES PLUMMET TO 4-6C ON MONDAY
ON A BREEZY NORTHWEST WIND AND HOLD THERE THROUGH TUESDAY. THESE ARE
2-2.5 STANDARD DEVIATIONS BELOW NORMAL SUGGESTING RECORDS ARE
POSSIBLE. SEE CLIMATE SECTION BELOW FOR MORE DETAILS.

THE WEATHER QUIETS DOWN THEN FOR WEDNESDAY AND THROUGH THE END OF
THE WEEK AS THE DEEP UPPER TROUGH GRADUALLY EJECTS OUT. PLENTIFUL
DRY CANADIAN AIR PLUNGES SOUTH THROUGH MUCH OF THE EASTERN U.S....
RESULTING IN A DRY FORECAST FOR WEDNESDAY AND BEYOND. TEMPERATURES
WILL GRADUALLY WARM EACH DAY AS THE SUN HELPS MODIFY THE COLD AIR.
WE SHOULD BE BACK CLOSE TO NORMAL BY NEXT WEEKEND.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1250 PM CDT FRI JUL 11 2014

A BAND OF LIGHT RAIN AND A FEW THUNDERSTORMS WILL MOVE THROUGH THE
TAF REGION EARLY THIS AFTERNOON. THESE SHOWERS LOOK LIKE THEY ARE
MAINLY EAST OF RST ALREADY...SO IT WILL MAINLY BE LSE THAT IS
UNDER THE THREAT OF SEEING SOME BRIEFLY LOWER CONDITIONS TO
MVFR/IFR. AFTER A PERIOD OF VFR THIS AFTERNOON...2-3KFT CLOUD
COVER SHOULD MOVE IN THIS EVENING AHEAD OF THE COLD FRONT AND
REMAIN STUCK OVER THE REGION INTO TOMORROW MORNING. WHILE SOME
SPOTTY RAIN SHOWERS/STORMS ARE POSSIBLE LATE THIS AFTERNOON INTO
TONIGHT...THE NEXT MAIN THREAT IS NOT EXPECTED TO ARRIVE UNTIL
TOMORROW AFTERNOON.

&&

.CLIMATE...
ISSUED AT 255 AM CDT FRI JUL 11 2014

RECORD COOL HIGH TEMPERATURES ARE POSSIBLE ON TUESDAY AS AN
UNSEASONABLY COLD AIRMASS SETTLES OVER THE UPPER MISSISSIPPI
RIVER VALLEY. FORECAST HIGH TEMPERATURES FOR TUESDAY ARE 65 AT
ROCHESTER AND 66 AT LA CROSSE. THESE TEMPERATURES WOULD BREAK THE
RECORD LOWEST HIGH TEMPERATURES FOR JULY 15TH. THE OLD RECORDS ARE
68 AT LA CROSSE SET BACK IN 1962 AND 67 AT ROCHESTER ALSO SET
BACK IN 1962.

&&

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

$$

UPDATE...HALBACH
SHORT TERM...AJ
LONG TERM....AJ
AVIATION...HALBACH
CLIMATE......AJ


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