000
FXUS63 KARX 112021
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
321 PM CDT SAT MAY 11 2013

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 321 PM CDT SAT MAY 11 2013

FORECAST CHALLENGE IS ON LOW TEMPERATURES AND ANY FROST/FREEZE
CONCERNS OVERNIGHT.

UPPER-LEVEL TROUGH SWINGING THROUGH THE UPPER MIDWEST THIS AFTERNOON
INTO TONIGHT HELPING TO DRIVE SCATTERED RAIN/SLEET/SNOW SHOWERS
ACROSS MUCH OF THE FORECAST AREA. THIS ACTIVITY IS TIED TO A QUICKLY
ROTATING PV ANOMALY IN COMBINATION WITH STEEP LOW-LEVEL LAPSE RATES
AND DAYTIME INSTABILITY. ALL OF THIS WILL EXIT EAST OF THE AREA OR
SUBSIDE AROUND SUNSET...LEADING TO A DRY FORECAST TONIGHT.

LOW-LEVEL RIDGE AXIS EXPECTED TO REMAIN GENERALLY WEST OF I-35
THROUGH 12Z SUNDAY...WHICH KEEPS MUCH OF THE FORECAST IN A
WELL-MIXED ENVIRONMENT. WINDS WILL REMAIN 10 TO 15 MPH AND COMBINED
WITH DRY ATMOSPHERE...FROST FORMATION SHOULD BE LIMITED TO JUST
PATCHY WORDING. THE BEST CHANCE FOR FROST TO OCCUR WILL BE OUR FAR
WESTERN AREAS...AND THEN ALSO ANY SHELTERED LOW-LYING LOCATIONS.
LOOKING AT WHAT HAPPENED THIS MORNING UPSTREAM IN THE
DAKOTAS...MINIMUM TEMPERATURES WERE HELD ABOVE FREEZING ACROSS
EASTERN DAKOTAS...WHILE WEST OF THE RIDGE AXIS...TEMPERATURES WERE
IN THE UPPER 20S TO NEAR FREEZING. ALTHOUGH WE/RE STARTING COOLER
THAN THEY DID YESTERDAY...AIR MASS MODIFICATION ALSO WILL HELP KEEP
THINGS IN CHECK. IN COORDINATION WITH SURROUNDING OFFICES...HAVE
OPTED NOT TO ISSUE FROST ADVISORY SINCE MIXED BOUNDARY LAYER WINDS
AND DRY AIR SHOULD PRECLUDE WIDESPREAD FROST. IF WINDS DO DECOUPLE
MORE THAN EXPECTED TONIGHT...THEN THERE COULD BE A NEED FOR AN
ADVISORY IN THE FAR WEST...BUT AT THIS TIME...CONFIDENCE IN THAT
HAPPENING IS LOW.


.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 321 PM CDT SAT MAY 11 2013

FORECAST CHALLENGES INCLUDE FROST/FREEZE CONDITIONS SUNDAY
NIGHT...PRECIPITATION CHANCES MONDAY AFTERNOON...THEN WARM
CONDITIONS TUESDAY.

SUNDAY NIGHT: SURFACE HIGH PRESSURE SETTLES NEARLY OVERHEAD AND
COMBINED WITH A CONTINUED DRY AIR MASS AND LIGHT TO NEARLY CALM
SURFACE WINDS WILL PROVIDE EXCELLENT FROST OR FREEZE CONDITIONS. ALL
GUIDANCE SUPPORTS LOWS IN THE UPPER 20S ACROSS CENTRAL
WISCONSIN...TO LOWER TO UPPER 30S WEST OF THE MISSISSIPPI RIVER AS
THAT AREA WILL ALREADY HAVE SOUTHERLY RETURN FLOW. HAVE CONTINUED
MENTION OF AREAS/WIDESPREAD FROST CONDITIONS IN THE BOGGY...COLDER
SPOTS OF CENTRAL WISCONSIN AND THE CURRENT FREEZE WATCH PLACEMENT LOOKS
GOOD. COULD ENVISION A FROST ADVISORY FOR WISCONSIN BORDERING
COUNTIES...ALONG THE MISSISSIPPI RIVER. WILL LET SUBSEQUENT SHIFTS
EVALUATE THAT NEED.

MONDAY: AFTER A COLD START AND FROST/FREEZE CONDITIONS
SUBSIDE...WARM AIR ADVECTION KICKS IN EARNEST DURING THE DAY AS SEEN
BY THE 850 MB TEMPERATURE WARMING FROM NEAR 0C IN THE MORNING...THEN
BETWEEN 4 AND 8C BY MONDAY AFTERNOON. IN THE UPPER
LEVELS...AMPLIFIED PATTERN WITH STRONG RIDGING ACROSS THE NORTHERN
PLAINS WITH DEEP TROUGHING ACROSS THE EASTERN CONUS. AT THE
SURFACE...AN AREA OF LOW PRESSURE LOOKS TO SLIDE ACROSS CANADA WITH
A COLD FRONT EXTENDING INTO THE UPPER MIDWEST. THE COMBINATION OF
INCREASING WARM AIR ADVECTION AND DECENT ISENTROPIC LIFT ON THE
295K-305K SURFACES GIVES A CHANCE OF RAIN SHOWERS ACROSS WESTERN
INTO NORTH CENTRAL WISCONSIN. RUN-TO-RUN AND MODEL CONSISTENCY
REMAIN GOOD...SO HAVE OPTED TO INCREASE PRECIPITATION CHANCES FOR
THESE AREAS SLIGHTLY.

THE COLD FRONT STALLS/WASHES OUT MONDAY NIGHT...THEN AS ANOTHER WAVE
OF LOW PRESSURE DEVELOPS TO THE WEST...THIS WILL ACT TO LIFT
BOUNDARY AS A WARM FRONT THROUGH THE AREA ON TUESDAY. THIS SETS THE
STAGE FOR WHAT COULD BE THE WARMEST DAY OF THE YEAR SO FAR FOR PARTS
OF SOUTHERN MINNESOTA AND NORTHERN IOWA. SYNOPTIC SETUP FAVORABLE
FOR A WARM...DRY DAY AS SOUTHWESTERLY FLOW OFF THE CENTRAL HIGH
PLAINS ADVECTS A SLUG OF 20 TO 25C 850 MB AIR NORTHEASTWARD. AS
NOTED PREVIOUSLY...SURFACE DEWPOINTS MAY END UP OVERDONE BY MOST
OF THE GUIDANCE AND THIS LIMITS HOW DEEP THE LOWER-LEVELS WILL MIX
OUT. RIGHT NOW...HIGHS NEAR 90 TO LOWER 90S SEEM ON TRACK WEST OF
THE MISSISSIPPI RIVER...AND LOWER TO MID 80S ACROSS WISCONSIN.
INTERESTINGLY...11.12Z NAM AND 11.09Z SREF DO MIX OUT COMPLETELY
UP TO 700 MB...AND THIS PUTS OUT MID TO UPPER 90S ACROSS IOWA.
THIS IS ON HIGHER EXTREME...BUT GIVES AN IDEA OF WHAT IS POSSIBLE.
850 MB TEMPERATURE STANDARDIZED ANOMALIES ARE PEGGED AROUND
3.0...WHICH IS SIGNIFICANT. TUESDAY COULD APPROACH RECORD
HIGHS...ESPECIALLY AT ROCHESTER...94/2007...BUT AT THIS TIME LOOKS
TO FALL JUST UNDER. AT THE SAME TIME...THE AFOREMENTIONED WARM
FRONT LINGERS IN NORTH CENTRAL WISCONSIN WHERE SLIGHT RAIN SHOWER
CHANCES EXIST.

ANOTHER COLD FRONT QUICKLY ADVANCES THROUGH THE AREA TUESDAY NIGHT
INTO WEDNESDAY MORNING...BRINGING A CHANCE FOR SHOWERS AND
THUNDERSTORMS. BOTH THE 11.12Z ECMWF AND GFS SOLUTIONS STALL THIS
BOUNDARY ACROSS SOUTHERN IOWA INTO CENTRAL ILLINOIS MID-WEEK. THIS
KEEPS THE FORECAST AREA MOSTLY UNDER THE INFLUENCE OF SURFACE HIGH
PRESSURE AND GENERALLY DRY CONDITIONS LOOK TO PREVAIL.
HOWEVER...IF THIS BOUNDARY STALLS FURTHER NORTH...THEN COULD SEE
AN INCREASED CHANCE OF SHOWERS AND THUNDERSTORMS ACROSS IOWA AND
POSSIBLY SOUTHERN WISCONSIN. FOR NOW...20 TO 30 PERCENT
CHANCES...MAINLY IN THE SOUTH LOOK GOOD. THE REMAINDER OF THE WORK
WEEK INTO NEXT WEEKEND HAS LOWER CONFIDENCE...BUT BOTH 11.12Z
ECMWF AND GFS SHOW WESTERN CONUS UPPER LEVEL TROUGHING HELPING TO
DRIVE GULF OF MEXICO MOISTURE NORTHWARD WITH THE RESULT BEING A
MORE UNSETTLED PATTERN BY NEXT WEEKEND.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1234 PM CDT SAT MAY 11 2013

COLDER TEMPERATURES ALOFT COMBINED WITH SOME RESIDUAL LOW LEVEL
MOISTURE WILL RESULT IN ISOLATED TO WDLY SCT SHRA/SHPL THRU THE
EARLY AFTERNOON HOURS TODAY. GIVEN SPOTTY NATURE AND FAST MOVEMENT
OF THESE SHOWERS...ONLY INCLUDED VCSH IN TAFS. THIS MOISTURE WILL
EXIT LATER THIS AFTERNOON...WITH FURTHER DRYING/SUBSIDENCE AND HIGH
PRESSURE BUILDING PRODUCING SKC FOR TONIGHT/SUNDAY. PRESSURE
GRADIENT AND MIXING WILL RESULT IN CONTINUED STRONG/GUSTY NORTHWEST
WINDS INTO EARLY THIS EVENING. WITH LOSS OF DAYTIME HEATING AND
RELAXING OF THE GRADIENT...WINDS TONIGHT/SUN WILL MOSTLY BE IN THE
10-15KT RANGE.


&&

.FIRE WEATHER...TUESDAY
ISSUED AT 321 PM CDT SAT MAY 11 2013

TUESDAY STILL LOOKS TO BE ANOMALOUSLY WARM...WITH THE POTENTIAL FOR
RELATIVE HUMIDITIES TO FALL TO NEAR CRITICAL LEVELS...ESPECIALLY
ACROSS SOUTHERN MINNESOTA AND NORTHEAST IOWA. HIGHER CONFIDENCE
EXISTS THAT MAXIMUM TEMPERATURES WILL CLIMB INTO THE UPPER 80S AND
LOWER 90S ON TUESDAY...BUT WHAT REMAINS A BIT MORE UNCERTAIN ARE
SURFACE DEWPOINTS. THE FORECAST MODELS HAVE REALLY STRUGGLED WITH
THIS ELEMENT RECENTLY...AND GUIDANCE IS PROBABLY OVERDOING IT. AT
THIS TIME...MINIMUM RH VALUES ARE EXPECTED TO FALL INTO THE 30 TO
40 PERCENT RANGE BUT COULD EASILY DROP INTO THE 20 TO 30 PERCENT
RANGE IF LOWER DEWPOINTS ARE REALIZED. WINDS LOOK TO BE OUT OF THE
SOUTHWEST 15 TO 25 MPH.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...FREEZE WATCH FROM LATE SUNDAY NIGHT THROUGH MONDAY MORNING FOR
     WIZ017-029-034-042>044.

MN...NONE.
IA...NONE.
&&

$$

SHORT TERM...ZT
LONG TERM...ZT
AVIATION...RRS
FIRE WEATHER...ZT