000
FXUS63 KARX 180020
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
720 PM CDT FRI MAY 17 2013

.UPDATE...
ISSUED AT 643 PM CDT FRI MAY 17 2013

HAVE UPDATED THE FORECAST TO REMOVE THE THUNDER CHANCES IN WI AND
COUNTIES IMMEDIATELY ALONG THE MISSISSIPPI RIVER OVERNIGHT.

STATIONARY FRONTAL BOUNDARY CURRENTLY LIES JUST SW OF THE FORECAST
AREA FROM FAIRMONT MN TO WATERLOO AND THEN TO DAVENPORT IA. ALL
THE INSTABILITY IS ALONG THAT BOUNDARY AND ONLY SLIGHTLY EAST A
COUNTY OR TWO BEFORE STABILITY IS ENCOUNTERED. THE SURFACE
CONVERGENCE IS ALONG THE FRONT AND NO REAL FORCING IS GOING TO BE
IN PLAY OVERNIGHT. SO...HAVE LEFT ONLY AN ISOLATED THUNDER CHANCE
IN NERN IA AND SERN MN FOR THE NEXT HOURS.

AS DAYTIME HEATING DIMINISHES...WOULD EXPECT THE ACTIVITY OVER
SWRN/SC MN TO DIMINISH AS WELL. AT THIS TIME...THE STORMS ARE
REMAINING ON THE BOUNDARY AND DO NOT POSE A RISK TO THE AREA.
LITTLE IN THE WAY OF ADDITIONAL FORCING FOR DEVELOPMENT IS
EXPECTED IN THE NEAR TERM.

BIGGEST ISSUE TONIGHT MAY BE WIDESPREAD LOW CLOUD AND FOG AS THE
CURRENT SURFACE OBSERVATIONS INDICATE VERY LOW DEW POINT
DEPRESSIONS /3-7F/ FROM ABOUT I-90 AND NORTH. WITH ONLY THE CIRRUS
MOVING OVERHEAD DURING THE NEXT FEW HOURS FROM THE CURRENT UPSTREAM
CONVECTION...EXPECTED TO DISSIPATE...STRATUS/FOG WILL DEVELOP OVER/INTO THE
AREA BY LATE EVENING. SOME BOUNDARY LAYER WIND MAY HELP PREVENT
WIDESPREAD DENSE FOG...BUT WOULD THINK THE INVERSION AND BEING
NORTH OF THE STATIONARY BOUNDARY...WITH MOIST CONDITIONS
ALREADY...SPELL SOME FOG. CURRENTLY COLLABORATING THIS IDEA WITH
NEIGHBORING OFFICES.

HAVE HAD SOME RISES ON THE CEDAR BASIN STREAMS/RIVER WITH TODAYS 2
INCHES. HAVE ISSUED STATEMENTS ON THESE WITHIN BANK RISES.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 341 PM CDT FRI MAY 17 2013

LATEST SURFACE OBSERVATIONS PLACED A WARM FRONT EXTENDING FROM
BOOKINGS SOUTH DAKOTA...EXTENDING SOUTHEAST THROUGH SOUTHERN
MINNESOTA...TO NEAR FAIRMONT MINNESOTA...INTO EAST CENTRAL IOWA. THE
FRONT WAS NEARLY STATIONARY THIS AFTERNOON BUT WILL START TO SLOWLY
ADVANCE NORTHWARD TONIGHT. WATER VAPOR IMAGERY AND 500 MB RAP
ANALYSIS SHOWED AN ACTIVE PATTERN ACROSS THE CONUS. A VIGOROUS TROUGH
WAS DIVING INTO THE CENTRAL ROCKIES...PUSHING EAST. A SHORTWAVE WAS
MOVING ACROSS SOUTHERN MINNESOTA/NORTHERN THROUGH SOUTHERN WISCONSIN
AND WAS GENERATING A PERSISTENT BAND OF SHOWERS AND ISOLATED
THUNDERSTORMS. HEAVY RAIN HAS FALLEN ACROSS PORTIONS OF NORTH
CENTRAL IOWA INTO SOUTHEAST MINNESOTA.

KEEPING A VERY CLOSE WATCH ON THE WARM FRONT LATE THIS AFTERNOON INTO
THIS EVENING WITH ADDITIONAL SHOWER AND THUNDERSTORM DEVELOPMENT
EXPECTED ALONG IT. A CONVERGENT AREA WAS NOTED IN THE SURFACE WINDS
FIELDS OVER SOUTHWEST MINNESOTA...AND SHOWERS AND THUNDERSTORMS HAVE
DEVELOPED ACROSS THESE AREAS. ALL OF THE MESOSCALE MODEL GUIDANCE IS
SUGGESTING THAT THIS AREA OF SHOWERS AND STORMS WILL CONTINUE AND
DRIFT SOUTHEAST ALONG THE FRONT LATE THIS AFTERNOON INTO THIS
EVENING. A VERY UNSTABLE AIRMASS IS FEEDING INTO THE WARM FRONT.
WHERE THERE HAS BEEN SUN THIS AFTERNOON...SURFACE BASES CAPE VALUES
HAVE CLIMBED TO AROUND 2000 J/KG. A RATHER MOIST AIRMASS IN PLACE
OVER THE AREA WITH PRECIPITABLE WATER VALUES OF 1.2 TO 1.3 INCHES.
THE SHOWERS AND THUNDERSTORMS HAVE BEEN VERY EFFICIENT RAIN
PRODUCERS TODAY AND WITH THIS MOIST AIRMASS IN PLACE...ANY
ADDITIONAL SHOWERS AND STORMS WOULD ALSO BE EFFICIENT RAIN
PRODUCERS. 0-6 KM SHEAR IS RATHER WEAK SO THINKING THE MAIN SEVERE
WEATHER THREAT WITH ANY THUNDERSTORMS TONIGHT WOULD BE PERIODS OF
HEAVY RAINFALL. CANNOT RULE OUT AN ISOLATED STORM OR TWO WITH LARGE
HAIL. THE MAIN CONCERN FOR THIS ACTIVITY IS ACROSS PORTIONS OF
SOUTHEAST MINNESOTA INTO NORTHEAST IOWA.

A THUNDERSTORM COMPLEX WILL FIRE OVER WESTERN SOUTH DAKOTA AND RACE
EAST TONIGHT. INSTABILITY REALLY WANES LATE THIS EVENING...WITH 0-3
KM MUCAPE VALUES FALLING TO 300 J/KG ACROSS SOUTHEAST MINNESOTA AND
NORTHEAST IOWA MAINLY AFTER 6Z TONIGHT. THINKING THE THUNDERSTORMS
WILL REALLY START TO DIE OFF WHEN THEY APPROACH THE INTERSTATE 35
CORRIDOR. THE STRONGEST 850 MB MOISTURE TRANSPORT STAYS FOCUSED INTO
EASTERN SOUTH DAKOTA THROUGH THE LATE NIGHT HOURS SO A WEAKENING
TREND SEEMS REASONABLE AND THE MESOSCALE MODELS ARE ALSO IN LINE
WITH THIS.

EARLY SATURDAY MORNING...THE WARM FRONT IS EXPECTED TO SLOWLY LIFT
NORTH OF THE INTERSTATE 90 CORRIDOR. CLOUD COVER OVER CENTRAL AND
NORTHERN WISCONSIN MAY SLOW ITS ADVANCE TO THE NORTH WITH THE COOLER
AIR UNDER CLOUD COVER TO THE NORTH AND SOME SUNSHINE SOUTH OF THE
WARM FRONT. FORECAST MODELS HAVE BEEN GENERATING SOME LIGHT PRECIPITATION
ACROSS AREAS RIGHT ALONG AND EAST OF THE MISSISSIPPI RIVER LATE
SATURDAY MORNING INTO SATURDAY AFTERNOON. THERE REALLY ISN/T ANY
APPRECIABLE FORCING ALOFT TO WORK WITH BUT FORECAST SOUNDINGS SHOW
CAPE VALUES INCREASING TO AROUND 1500 J/KG ACROSS PORTIONS OF
SOUTHEAST MINNESOTA AND TO AROUND 300 J/KG OVER NORTH CENTRAL
WISCONSIN. HAVE EXTENDED SHOWER/THUNDERSTORM CHANCES A BIT FURTHER
SOUTH OVER THE PREVIOUS FORECAST TO ACCOUNT FOR THE INSTABILITY AND
SLOWER MOVEMENT OF THE WARM FRONT. IT WILL BE RATHER WARM ON
SATURDAY IN THE WAKE OF THE WARM FRONT WITH HIGHS CLIMBING INTO THE
LOWER TO MID 80S OVER NORTHEAST IOWA...SOUTHEAST MINNESOTA AND FAR
WESTERN WISCONSIN. IT WILL BE  A LITTLE COOLER ACROSS NORTH CENTRAL
WISCONSIN WHERE HIGHS WILL STRUGGLE TO GET OUT OF THE LOWER 70S.

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 341 PM CDT FRI MAY 17 2013

A VERY ACTIVE PATTERN IS IN STORE FOR THE REGION SUNDAY THROUGH
MONDAY WITH SEVERE WEATHER POSSIBLE. THUNDERSTORMS FIRING OVER THE
DAKOTAS INTO THE CENTRAL PLAINS AND MOVING EAST INTO THE FORECAST
AREA SUNDAY MORNING WILL HAVE AN IMPACT ON CONVECTION FOR SUNDAY
AFTERNOON.

A POTENT SHORTWAVE EJECTS OUT OF THE CENTRAL PLAINS SUNDAY AFTERNOON
AND LIFTS NORTH INTO THE UPPER MISSISSIPPI RIVER VALLEY...BECOMING
NEGATIVELY TILTED.  MEANWHILE...SURFACE LOW PRESSURE DEEPENS OVER
SOUTHEAST SOUTH DAKOTA...AND A SECONDARY WARM FRONT DEVELOPS OVER
NORTHERN IOWA AND LIFTS NORTH INTO SOUTHERN MINNESOTA EARLY SUNDAY
EVENING. 0-3KM MUCAPE VALUES INCREASE TO 1200-1500 J/KG LATE SUNDAY
AFTERNOON ACROSS NORTHERN IOWA/SOUTHERN MINNESOTA AND SOUTHWEST
WISCONSIN. 0-6 KM SHEAR INCREASES AS THE WAVE MOVES INTO THE
AREA...INCREASING TO 30 TO 45 KTS LATE SUNDAY AFTERNOON INTO SUNDAY
EVENING. MOST OF THIS SHEAR IS LOCATED IN THE 0-3 KM LAYER...OVERALL
RATHER IMPRESSIVE LOW LEVEL SHEAR PROFILES. LATEST THINKING IS THAT
THUNDERSTORMS WILL ERUPT OVER PORTIONS OF WESTERN IOWA SUNDAY
AFTERNOON WITH ADDITIONAL DEVELOP POSSIBLE TO THE NORTHEAST ACROSS
SOUTHEAST MINNESOTA AND NORTHEAST IOWA....AND POTENTIALLY INTO
SOUTHWEST WISCONSIN.  SHEAR PROFILES WOULD FAVOR SUPERCELL
STRUCTURES. SINCE MOST OF THE SHEAR IS LOCATED IN THE 0-3 KM
LAYER...THERE IS GROWING CONCERN FOR DAMAGING WINDS AND BOWING
STRUCTURES WITH THE STORMS. ISOLATED TORNADOES ARE ALSO POSSIBLE.
ALSO...THERE IS THE POTENTIAL FOR HEAVY RAINFALL...ESPECIALLY SUNDAY
EVENING AS 850 MB MOISTURE TRANSPORT INCREASES ACROSS NORTHERN
IOWA/SOUTHERN MINNESOTA AND SOUTHWEST WISCONSIN...FOCUSING INTO THE
WARM FRONT.

A BROAD UPPER TROUGH OVER THE UPPER MIDWEST WILL FINALLY CLOSE INTO
AN UPPER LOW ON MONDAY. SEVERAL PIECES OF ENERGY ROTATING AROUND THE
LOW WILL BRING ADDITIONAL CHANCE FOR SHOWERS AND THUNDERSTORMS TO
THE AREA. THINKING THE BULK OF THE INSTABILITY SHOULD BE SOUTHEAST
OF THE FORECAST AREA SO IT APPEARS THE GREATEST SEVERE THREAT SHOULD
BE SOUTHEAST OF THE AREA...BUT THIS WILL DEPEND ON HOW THE
CONVECTION PLAYS OUT SUNDAY NIGHT. THE UPPER LOW CONTINUES TO SPIN
OVER THE REGION THROUGH MIDWEEK WITH DAILY CHANCES FOR SHOWERS AND
POSSIBLE THUNDERSTORMS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 643 PM CDT FRI MAY 17 2013

CONTINUED THE IDEA IN THE TAFS OF AN IFR/LIFR CIG STRATUS
DEVELOPING OVERNIGHT. SURFACE OBSERVATIONS HAVE VERY LOW DEWPOINT-
TEMPERATURE SPREADS AND ANY AREAS NOT IN THE CLOUDS NOT WILL
LIKELY RADIATE AND FORM THE STRATUS. HAVE DECIDED TO LOWER
CONDITIONS AND HOLD THEM IFR LONGER IN THE MORNING WITH THIS
FORECAST. THIS APPEARS TO BE AN AFTERNOON MIX OUT OF THE
CLOUDS/FOG AND IMPROVING CONDITIONS TO MVFR AS THE FRONTAL
BOUNDARY THAT IS IN THE AREA LIFTS NORTHEAST.

CONFIDENCE ON THE LOW CIGS IS HIGH WITH MOIST CONDITIONS IN NEAR-
SURFACE LAYER...FRESH RAINFALL...SOME CLEARING WHERE IS NOT
CLOUDY...AND BEING LOCATED NORTH OF A STATIONARY BOUNDARY CAUSING
A TEMPERATURE INVERSION OVER THE TAF SITES THROUGH THE MORNING.

&&

.HYDROLOGY...THIS EVENING THROUGH MONDAY
ISSUED AT 341 PM CDT FRI MAY 17 2013

PERIODS OF SHOWERS AND THUNDERSTORMS ACROSS PORTIONS OF SOUTHEAST
MINNESOTA INTO NORTHEAST IOWA HAVE PRODUCED 2 TO NEARLY 2 1/2
INCHES OF RAINFALL SO FAR TODAY. SCATTERED THUNDERSTORMS ARE
EXPECTED LATE THIS AFTERNOON INTO EARLY THIS EVENING. THE STORMS
ARE SLOW MOVING AND WILL HAVE THE POTENTIAL TO PRODUCE PERIODS OF
HEAVY RAINFALL...WHICH COULD LEAD TO FLOODING...ESPECIALLY ACROSS
THOSE AREAS THAT HAVE ALREADY SEEN HEAVY RAINFALL.

THUNDERSTORMS ARE EXPECTED SUNDAY AFTERNOON THROUGH MONDAY. THE
STORMS COULD PRODUCE PERIODS OF HEAVY RAINFALL WHICH COULD LEAD TO
FLOODING. 1 TO 3 INCHES OF ADDITIONAL RAINFALL IS POSSIBLE FROM
SUNDAY INTO WEDNESDAY. A FLASH FLOOD WATCH MAY BE NEEDED IF
CONFIDENCE INCREASES ON WHERE THE HEAVIEST RAIN WILL FALL.

&&

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

$$

UPDATE...BAUMGARDT
SHORT TERM...WETENKAMP
LONG TERM...WETENKAMP
AVIATION...BAUMGARDT
HYDROLOGY...WETENKAMP