Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 210823
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
323 AM CDT MON APR 21 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 323 AM CDT MON APR 21 2014

THE MAIN FOCUS THROUGH TONIGHT IS ON THE TIMING OF THE COLD FRONT
PASSAGE AND THE CONVECTION THAT IS EXPECTED TO DEVELOP AHEAD OF IT
TODAY.

SHOWERS AND SOME THUNDERSTORMS CONTINUE ACROSS MUCH OF THE REGION
WHICH IS IN A BROAD CHANNEL OF LOW LEVEL MOISTURE TRANSPORT AHEAD
OF A SURFACE COLD FRONT. THE 21.07Z RAP ANALYSIS SHOWS THAT THE
HIGHEST 0-3KM MUCAPE OF A FEW HUNDRED J/KG IS ACROSS SOUTH
CENTRAL MINNESOTA AND NORTH CENTRAL IOWA WHERE DEW POINTS ARE IN
THE MID TO UPPER 50S AND TEMPERATURES ARE IN THE LOW 60S. 0-6KM
SHEAR IS ALSO WEAK AT 20-30KTS...SO ANY STORMS THAT HAVE
DEVELOPED ARE PULSEY AND COLLAPSE RATHER QUICKLY.

THE 21.00Z NAM/GFS/GEM/ECMWF AND 21.06Z RAP/HRRR/HOPWRF ARE ALL IN
VERY GOOD AGREEMENT WITH THE TIMING OF THE COLD FRONT COMING
THROUGH THE REGION TODAY. CURRENTLY...SURFACE OBS SHOW THAT THIS
FRONT IS IN WESTERN MINNESOTA/EASTERN NEBRASKA. GUIDANCE SUGGESTS
THAT THE FRONT WILL BE INTO NORTHEAST WISCONSIN/FAR SOUTHEAST
MINNESOTA/NORTHEAST IOWA AROUND NOON AND THEN CLEAR OF SOUTHWEST
WISCONSIN BY MID AFTERNOON. INSTABILITY WILL BUILD AHEAD OF THE
FRONT THOUGH THE 21.00Z NAM/GFS AND 21.06Z RAP LIKELY DEVELOP TOO
HIGH OF MUCAPE WITH THEM SHOWING SURFACE DEW POINTS CLIMBING UP TO
THE LOW 60S WHEN THEY WILL LIKELY BE MORE IN THE MID 50S. THERMAL
PROFILES SHOW THAT THIS INSTABILITY IS IN THE 0C TO -20C PORTION
OF THE SOUNDINGS...SO THERE COULD BE SOME SMALL HAIL THAT DEVELOPS
FROM THIS CONVECTION DESPITE 0-6KM SHEAR REMAINING WEAK AT
20-30KT.

ONCE THE FRONT COMES THROUGH...THERE IS A SOLID SLUG OF DRIER AIR
THAT WILL MOVE INTO THE REGION. TEMPERATURES MAY NOT MAKE TOO MUCH
OF AN INITIAL DROP SINCE THE FRONT IS COMING THROUGH DURING THE
MIDDLE OF THE DAY WITH THE DRIER AIR MASS BEHIND THE FRONT
ALLOWING FOR QUICKER WARMING UNDER SUNNY SKIES. TEMPERATURES WILL
PLUMMET TONIGHT WITH THE DRY AIR MASS IN PLACE AND NORTHWESTERLY
LOW LEVEL WINDS KICKING IN. COULD SEE SOME GUSTY WINDS AS WELL
WITH THIS DRY AIR IN THE AFTERNOON WITH SOME 35MPH GUSTS POSSIBLE
IN THE HIGHER TERRAIN OF SE MN/NE IA.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 323 AM CDT MON APR 21 2014

THE MAIN FOCUS IN THE EXTENDED IS ON A BROAD MID LEVEL TROUGH
CURRENTLY ALONG THE WEST COAST WHICH WILL PROPAGATE EAST ALONG THE
US/CANADIAN BORDER FROM THE MIDDLE TO END PORTION OF THE WEEK.
GUIDANCE HAS BEEN IN FAIRLY GOOD AGREEMENT ON THIS SYSTEM THOUGH
THERE ARE SOME MINOR DIFFERENCES THAT ARISE TOWARD THE LATER
PORTION OF THE SYSTEM. CONFIDENCE IS STILL FAIRLY HIGH THAT
PRECIPITATION WILL MOVE IN FROM THE WEST ON WEDNESDAY WITH THE
LEAD WARM AIR ADVECTION BAND FOLLOWED BY THE MAIN MOISTURE CHANNEL
AHEAD OF THE COLD FRONT ON THURSDAY. THERMAL PROFILES STILL DO NOT
SHOW MUCH IN THE WAY OF INSTABILITY BUT DO INCREASE PW VALUES UP
TO AROUND 1-1.50" EARLY ON THURSDAY. BASED ON THIS CONSISTENT
SIGNAL...HAVE UPPED PRECIPITATION CHANCES INTO THE 70-85 PERCENT
RANGE FOR MUCH OF THE REGION WITH TOTAL QPF VALUES EXPECTED TO BE
AROUND AN INCH.

GUIDANCE STARTS TO DEVIATE QUITE A BIT STARTING FRIDAY WITH THE
21.00Z GFS SHOWING A STRONG RIDGE OF HIGH PRESSURE EXTENDING FROM
HUDSON BAY THROUGH THE NORTHERN PLAINS WHILE THE 21.00Z ECMWF IS
WEAKER WITH THIS RIDGE AND KEEPS A LOW LEVEL THERMAL GRADIENT
ACROSS THE REGION ON INTO THE SOUTHERN GREAT LAKES. THE GFS
SOLUTION WOULD BE A COLDER/DRIER ONE FOR US WHILE THE ECMWF
SOLUTION WOULD MEAN A WETTER/SLIGHTLY WARMER SOLUTION THAT STILL
COULD BRING SOME P-TYPE ISSUES IN WITH IT. CURRENTLY...WPC IS
FAVORING THE GFS MORE THAN THE ECMWF BUT TIME WILL TELL. FOR
NOW...HAVE DONE A BLEND WITH SOME PRECIPITATION CHANCES IN THERE
FOR THE WEEKEND.


&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1114 PM CDT SUN APR 20 2014

SHOWERS AND EMBEDDED THUNDERSTORMS ACROSS NORTHERN IOWA...SITUATED
JUST NORTH OF A WARM FRONT ALONG US-20...ARE INCHING THEIR WAY
NORTHWARD TOWARDS THE TAF SITES. ITS POSSIBLE FOR THESE SHOWERS
TO AFFECT THE TAF SITES FROM NOW THROUGH 14-16Z WHEN A COLD FRONT
IS SLATED TO MOVE ACROSS. SINCE CONFIDENCE OF THESE SHOWERS
HANGING AT EITHER TAF SITE FOR MORE THAN 1 OR 2 HOURS IS LOW...
HAVE ONLY WENT WITH A VCSH. ALSO DID NOT INCLUDE THUNDER AS THE
AMOUNT OF LIGHTNING HAS DROPPED OFF QUITE A BIT WITH LOSS OF
INSTABILITY. THERE HAS BEEN SOME BR AROUND THE TAF SITES...ENOUGH
TO KNOCK LSE DOWN TO MVFR. MVFR VISIBILITIES SHOULD BE THE GENERAL
RULE UNTIL COLD FRONTAL PASSAGE. PLAN ON CEILINGS TO STAY VFR.
AFTER THE COLD FRONT PASSES...DRIER AIR COMES IN ON GUSTY
NORTHWEST WINDS TO ENSURE VFR CONDITIONS. THE WINDS COULD GUST
UPWARDS OF 25 KT. PLAN ON THE WIND GUSTS TO DIMINISH AROUND 01Z
WITH LOSS OF DAYTIME HEATING...BUT A 10-15 KT SUSTAINED WIND LOOKS
LIKELY TO PERSIST ASSOCIATED WITH COLD AIR FLOWING IN.


&&

.HYDROLOGY...
ISSUED AT 323 AM CDT MON APR 21 2014

ANYWHERE FROM A TENTH OF AN INCH TO AN INCH AND A HALF OF RAIN
FELL YESTERDAY ACROSS THE REGION WITH SOME ADDITIONAL RAIN FALLING
EARLY THIS MORNING FROM SHOWERS AND THUNDERSTORMS. THIS HAS LEAD
TO A SMALL CLIMB IN AREA RIVERS...PARTICULARLY IN NORTHEAST IOWA
WHERE SOME OF THE HEAVIEST RAIN HAS FALLEN. RAIN WILL COME TO AN
END FROM WEST TO EAST THIS MORNING AND EARLY AFTERNOON AS A COLD
FRONT PUSHES THROUGH. ANOTHER SYSTEM WILL COME IN AROUND MID WEEK
WHICH COULD DROP A WIDESPREAD AREA OF AN INCH OR MORE OF RAIN FROM
WEDNESDAY INTO THURSDAY. THIS WILL LIKELY LEAD TO A SECOND CREST
ON MANY AREA RIVERS.

&&

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

$$

SHORT TERM...HALBACH
LONG TERM...HALBACH
AVIATION...AJ
HYDROLOGY...HALBACH



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