182 
FXUS63 KARX 092058
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
258 PM CST TUE MAR 9 2010

.SHORT TERM...TONIGHT THROUGH FRIDAY

MAIN FORECAST CONCERNS ARE RAIN AND DENSE FOG THROUGH THE PERIOD.

LATEST WATER VAPOR SATELLITE IMAGERY INDICATING AN UPPER LEVEL
LOW OVER NEBRASKA AND KANSAS. FIRST SHORTWAVE TROUGH ROTATING
AROUND THE UPPER LEVEL LOW INTO NORTHERN IOWA. LATEST MOSAIC RADAR
INDICATING A BAND OF LIGHT RAIN FROM EASTERN SOUTH DAKOTA INTO
NORTHERN ILLINOIS. THIS IS IN RESPONSE TO ISENTROPIC LIFT AT 305K
SURFACE PER LATEST RUC.

THE 09.12Z GFS AND NAM ARE IN PRETTY GOOD AGREEMENT IN LIFTING AND
WEAKENING UPPER LEVEL LOW OVER KANSAS AND NEBRASKA NORTHWARD INTO THE
UPPER MIDWEST BY 00Z THURSDAY. BOTH MODELS ARE IN GOOD AGREEMENT
MOVING NEXT UPPER LEVEL LOW OVER THE SOUTHWEST U.S. INTO THE
CENTRAL PLAINS BY 12Z THURSDAY. MAIN DIFFERENCES ARE TIMING OF THE
WEAK SHORTWAVE TROUGHS ROTATING AROUND THE TWO UPPER LEVEL LOWS INTO
THE FORECAST AREA THROUGH FORECAST PERIOD. CONFIDENCE IN
PRECIPITATION CHANCES THROUGH FORECAST PERIOD IS HIGH...THOUGH TIMING
OF EACH INDIVIDUAL WAVES OF PRECIPITATION THROUGH PERIOD IS
MODERATE.

TONIGHT AND INTO WEDNESDAY...BAND OF LIGHT RAIN WILL CONTINUE TO
LIFT NORTHWARD INTO NORTHERN WISCONSIN AND CENTRAL MINNESOTA
TONIGHT. AS THIS BAND LIFTS NORTHWARD...A BREAK IN PRECIPITATION IS
EXPECTED OVER MUCH OF NORTHEAST IOWA AND SOUTHERN WISCONSIN THROUGH
06Z WEDNESDAY...AND OVER PORTIONS OF THE NORTHERN FORECAST AREA
AFTER 06Z WEDNESDAY. WITH SNOWPACK COVERING MUCH OF THE AREA AND
COMBINED WITH SNOW MELT AND THE RECENT LIGHT RAIN...DENSE FOG WILL BE
POSSIBLE ACROSS NORTHEAST IOWA AND SOUTHWEST WISCONSIN THIS
EVENING...AND POSSIBLY AFTER MIDNIGHT TONIGHT ACROSS PORTIONS OF THE
NORTHERN FORECAST AREA. AT THIS TIME...HAVE INTRODUCED AREAS OF FOG
ACROSS MUCH OF THE FORECAST AREA. WILL LET LATER SHIFTS MONITOR
VISIBILITY RESTRICTIONS AND IF NEEDED ANY DENSE FOG ADVISORIES FOR
TONIGHT. THE NEXT SHORTWAVE TROUGH OVER NORTHERN MISSOURI AFFECTS THE
SOUTHERN PART OF THE FORECAST AREA AFTER 06Z WEDNESDAY. THE 09.12Z
GFS AND NAM ARE INDICATING STRONG ISENTROPIC LIFT IN ASSOCIATION WITH
SHORTWAVE TROUGH...AND THIS WILL ALLOW FOR RAIN TO OVERSPREAD THE
SOUTHERN FORECAST AREA AFTER 06Z AND IMPROVE ANY REDUCTION IN
VISIBILITIES ACROSS THE SOUTHERN PARTS OF THE FORECAST AREA.

THE NEXT CONCERN IS THE UPPER LEVEL LOW OVER THE SOUTHWEST U.S.
EJECTING OUT INTO THE CENTRAL PLAINS WEDNESDAY NIGHT INTO THURSDAY.
THE 09.12Z GFS AND NAM ARE INDICATING STRONG WARM AIR ADVECTION
OVER FORECAST AREA AFTER 06Z THURSDAY...DECENT MOISTURE TRANSPORT AT
850-700MB LAYER AND A DEVELOPING LOW LEVEL JET OF NEAR 40
KNOTS AT 850MB IN ASSOCIATION WITH THE UPPER LEVEL LOW. CONFIDENCE
IS INCREASING CONSIDERABLY ON MUCH OF THE FORECAST AREA SEEING RAIN
AFTER 06Z THURSDAY AND CONTINUE THROUGH 00Z FRIDAY. THE 09.12Z GFS
AND NAM ARE INDICATING OF SOME INSTABILITY ALOFT WITH 0-6KM MOST
UNSTABLE CAPE OF 100-300 J/KG BETWEEN 06Z TO 18Z THURSDAY. HAVE
INTRODUCED ISOLATED THUNDER...MAINLY SOUTH OF INTERSTATE 90 FROM 12-
18Z THURSDAY.

THE UPPER LEVEL LOW OVER THE CENTRAL U.S. CUTS-OFF FROM FLOW AFTER
18Z THURSDAY AND BECOMES VERTICALLY STACK. THIS WILL ALLOW FOR
MOISTURE AND SHORTWAVE TROUGHS TO WRAP AROUND THE UPPER LEVEL LOW
INTO THE UPPER MIDWEST AND GREAT LAKES REGION THURSDAY NIGHT INTO
FRIDAY. MUCH OF THE FORECAST AREA WILL CONTINUE TO SEE LIGHT RAIN
ON AND OFF THURSDAY NIGHT INTO FRIDAY.

.LONG TERM...FRIDAY NIGHT THROUGH TUESDAY

MAIN FORECAST CONCERNS ARE PRECIPITATION CHANCES AND CLOUDS THROUGH
MONDAY. THE 09.00Z GFS AND ECMWF ARE IN PRETTY GOOD AGREEMENT WITH
SLOWLY MOVING UPPER LEVEL CLOSED LOW INTO THE NORTHEASTERN U.S.
THROUGH THE PERIOD AND BUILDING UPPER LEVEL SHORTWAVE RIDGE INTO THE
UPPER MIDWEST AND GREAT LAKES REGION MONDAY INTO TUESDAY. THE BIG
QUESTION IS HOW FAST THE UPPER LEVEL CLOSED LOW MOVES EAST INTO THE
EASTERN U.S...AS BOTH THE 09.00Z GFS AND ECMWF INDICATING A SLOWER
PROGRESSION OF THE UPPER LEVEL CLOSED LOW INTO THE EASTERN U.S. THIS
WILL ALLOW MOISTURE/SHORTWAVE TROUGHS TO WRAP AROUND THE
UPPER LEVEL CLOSED LOW INTO THE UPPER MIDWEST AND GREAT LAKES REGION
THROUGH 00Z MONDAY. THE 09.00Z GEFS IS ALSO INDICATING A SLOWER
PROGRESSION OF THE UPPER LEVEL CLOSED LOW. CONFIDENCE IS INCREASING
CLOUDS AND SMALL CHANCES OF PRECIPITATION WILL LINGER OVER THE
FORECAST AREA THROUGH SUNDAY. SUBSIDENCE UNDERNEATH UPPER LEVEL
SHORTWAVE RIDGE WILL ALLOW CLOUDS TO DIMINISH OVER THE FORECAST AREA
MONDAY INTO TUESDAY.

&&

.AVIATION...TONIGHT THROUGH WEDNESDAY MORNING

CURRENTLY WATCHING A BAND OF LIGHT-MODERATE RAINFALL LIFTING INTO
NORTHEAST IA/SOUTHEAST MN/FAR SOUTHWEST WI. THIS IS IN ADVANCE OF AN
AREA OF LOW PRESSURE MOVING NORTHEAST ACROSS EASTERN KS. AS
RELATIVELY WARMER AND DEFINITELY MORE MOIST AIR IS DRAWN ACROSS THE
MELTING SNOW PACK...WIDESPREAD IFR/POCKETS OF LIFR CONDITIONS
PERSISTED THROUGH THIS AFTERNOON. THE RAIN WILL CONTINUE TO LIFT
INTO THE AREA THROUGH THIS EVENING WITH PERHAPS A LULL IN THE RAIN
ACTIVITY BY MIDNIGHT AT THE KRST/KLSE TAF SITES AS THE MAIN RAIN
BAND LIFTS NORTH OF THE AREA. AS THE RAIN COMES TO AN END THOUGH...
LOOKS LIKE WE COULD SLIP WELL INTO/STAY IN LOWER IFR/LIFR CONDITIONS
THROUGH THE REST OF THE NIGHT INTO WEDNESDAY MORNING.

&&

.HYDROLOGY...

HYDRO CONCERNS WILL PERSIST THROUGH THE WEEK...AND LIKELY FOR A
WHILE...AS THE SNOW PACK CONTINUES TO MELT AND A COUPLE ROUNDS OF
RAIN ADDS ADDITIONAL RUNOFF INTO AREA CREEKS/STREAMS/RIVERS.
MAIN FOCUS IS ON TRIBUTARIES FLOWING INTO THE MISSISSIPPI...AND IN
PARTICULAR THE TREMPEALEAU...TURKEY...BLACK AND UPPER IOWA RIVERS.

TEMPERATURES ARE EXPECTED TO REMAIN ABOVE FREEZING THROUGH THE REST
OF THE WEEK...WHICH WILL CONTINUE THE DAILY SNOWMELT THROUGH THE
NIGHT. IN ADDITION...PERIODS OF RAIN ARE FORECAST THROUGH FRIDAY
NIGHT...WITH AMOUNTS FROM 1/2 TO 1 1/2 INCHES POSSIBLE. RIVER
MONITORING WILL BE NEEDED THROUGH THE WEEKEND.

ADDITIONALLY...THERE ARE STILL A FEW RIVERS WITH ICE ON
THEM...LEAVING THE THREAT OF ICE JAMS A POSSIBILITY.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...

WI...NONE.
MN...NONE.
IA...NONE.

&&

$$

SHORT/LONG TERM... DTJ
AVIATION.......... DAS
HYDROLOGY......... DTJ