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000
FXUS63 KARX 121111
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
611 AM CDT SUN MAY 12 2013

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 320 AM CDT SUN MAY 12 2013

MAIN FORECAST CONCERN IS ON FROST/FREEZE CONDITIONS TONIGHT.

CURRENTLY AS OF 08Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED RIDGING OVER THE WESTERN U.S. INTO ALBERTA WHILE ANOMALOUSLY
DEEP TROUGHING WAS PRESENT FROM HUDSON BAY INTO THE WESTERN GREAT
LAKES REGION. THE FORECAST AREA LIES ON THE BACK SIDE OF THE
TROUGHING...BUT STILL EAST OF THE INFLECTION POINT...WHICH RESULTS
IN NORTHWEST FLOW FROM THE SURFACE TO 500MB. THE FLOW CONTINUED TO
DRAG COLDER AIR SOUTHEAST WITH RAP 850MB TEMPS RANGING FROM -3C OVER
NORTHEAST IOWA TO -9C IN TAYLOR COUNTY WISCONSIN. DESPITE THE COLD
850MB TEMPS...READINGS ARE GENERALLY IN THE MID 30S TO AROUND 40...
STAYING UP BECAUSE OF THAT NORTHWEST WIND OF 5-10 KT AT THE SURFACE
KEEPING THE BOUNDARY LAYER MIXED. A LOT OF DRY AIR CONTINUES TO FLOW
IN TOO ON THE NORTHWEST WINDS FROM HIGH PRESSURE IN THE PLAINS.
DEWPOINTS ARE IN THE TEENS ACROSS MUCH OF THE DAKOTAS INTO MN AND
20S OVER WISCONSIN. COMBINATION OF THE WIND...TEMPERATURES AND DRY
AIR PRECLUDING ANY FROST DEVELOPMENT THUS FAR. THE AFOREMENTIONED
DRY AIR IS ALSO QUITE DEEP...REFLECTIVE FROM 00Z SOUNDINGS AT BIS...
ABR AND MPX HAVING PRECIPITABLE WATER VALUES OF 0.1-0.2 INCHES...OR
20-40 PERCENT OF NORMAL. THIS DRY AIR HAS HELPED CLEAR SKIES OUT
WEST OF WISCONSIN. SCT-BKN CLOUDS HAVE BEEN FLOWING ACROSS WISCONSIN
IN THE CYCLONIC FLOW IN THE UPPER TROUGH. FARTHER TO THE WEST UNDER
THE UPPER RIDGE...00Z SOUNDINGS FROM SAN FRANSISCO TO SALT LAKE CITY
AND NORTH TO GREAT FALLS MT ALL REPORTED 850MB TEMPS OF 20C OR
GREATER. THESE ARE 1.5-2.5 STANDARD DEVIATIONS ABOVE NORMAL.

BOTH THE UPPER RIDGE AND ANOMALOUSLY DEEP TROUGH ARE PROGGED TO
PROGRESS EASTWARD DURING THE NEXT 24 HOURS...PUSHED ALONG BY A
FAIRLY POTENT SHORTWAVE TROUGH APPROACHING THE PACIFIC NORTHWEST
COAST AT 12Z MONDAY. IT APPEARS THIS EVENING IS WHEN THE INFLECTION
POINT BETWEEN THE UPPER RIDGE AND DEEP TROUGH WILL REACH THE
FORECAST AREA. THIS MEANS TO PLAN ON THE SURFACE HIGH OVERHEAD AT
ABOUT THE SAME TIME.

TODAY...THE COMBINATION OF DRY AIR AND BEING FARTHER AWAY FROM THE
COLD POOL OF THE UPPER TROUGH WILL RESULT IN SUNNY SKIES. SINCE THE
AREA STAYS IN A GRADIENT AHEAD OF THE SURFACE HIGH AND WE HAVE FULL
SUN FOR DEEP MIXING...ANOTHER BREEZY DAY IS LIKELY...BUT NOT NEARLY
AS WINDY AS YESTERDAY. TEMPERATURES ARE DEFINITELY GOING TO STAY ON
THE COOL SIDE...THOUGH...WITH 850MB TEMPS HOLDING STEADY THROUGH
18Z. HIGHS SHOULD END UP VERY SIMILAR TO YESTERDAY.

TONIGHT...A REALLY GOOD RADIATIONAL COOLING SETUP IS FORECAST. WITH
THE SURFACE HIGH MOVING OVER THE AREA DURING THE EVENING...WINDS
WILL DECOUPLE EVERYWHERE. ADDITIONALLY...WE HAVE ALL OF THE DRY AIR
ACCOMPANYING THE SURFACE HIGH. THUS...TEMPERATURES SHOULD PLUMMET
DURING THE EVENING HOURS AFTER SUNSET. NOW...AFTER MIDNIGHT...THE
SURFACE RIDGE BEGINS TO PUSH EAST INTO CENTRAL WISCONSIN. THIS MEANS
A SOUTHERLY WARM ADVECTION FLOW WILL COMMENCE OVER WESTERN PORTIONS
OF THE FORECAST AREA. THEREFORE...OUR WISCONSIN COUNTIES CONTINUE TO
LOOK THE MOST FAVORABLE FOR THE COLDEST CONDITIONS...AND THE COLDEST
OVERALL OVER CENTRAL WISCONSIN. STAYED TOWARDS THE COLD SIDE OF
GUIDANCE FOR LOWS. GIVEN THE CONSISTENCY FOR TONIGHT TO BE COLD...
HAVE ISSUED FREEZE WARNINGS FOR THE PREVIOUS FREEZE WATCH AREA AND A
FEW EXTRA COUNTIES WHERE TEMPS ARE NOW FORECAST COLDER...WITH FROST
ADVISORIES FOR THE REST OF OUR WISCONSIN COUNTIES.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 320 AM CDT SUN MAY 12 2013

MONDAY THROUGH TUESDAY NIGHT...THE UPPER RIDGING OVER THE WESTERN
U.S. IS PROGGED TO CONTINUE TO GET PUSHED EASTWARD WHILE FLATTENING
WITH TIME. THIS IN RESPONSE TO THE POTENT SHORTWAVE OFF THE PACIFIC
NORTHWEST AT 12Z MONDAY TRACKING EASTWARD ALONG THE U.S./CANADIAN
BORDER. OVERALL MODELS ARE IN PRETTY GOOD AGREEMENT ON THE TRACK AND
SPEED OF THIS SHORTWAVE...WITH THE EXCEPTION OF THE 12.00Z NAM
WHICH BECOMES SLIGHTLY FASTER COME TUESDAY AND TUESDAY NIGHT. HAVE
DISCOUNTED THE NAM PROGRESSION AS AN OUTLIER FOR NOW. THE
PROGRESSIVE NATURE OF THE RIDGE AND SHORTWAVE RESULTS IN A VARIETY
OF ISSUES TO CONTEND WITH...

1. PRECIPITATION CHANCES AND TEMPERATURES MONDAY INTO MONDAY NIGHT.
A WARM FRONT AHEAD OF THE UPPER RIDGE AXIS IS FORECAST TO CROSS THE
AREA MONDAY NIGHT. PACIFIC MOISTURE MOVING THROUGH THE UPPER RIDGE
IN CONJUNCTION WITH ISENTROPIC LIFT AHEAD OF THIS WARM FRONT WILL
LIKELY TO LEAD TO EXTENSIVE MID AND HIGH CLOUDS. ADDITIONALLY...THE
LIFT APPEARS STRONG ENOUGH TO GENERATE PRECIPITATION FROM THESE
CLOUDS. THE BIG PROBLEM...THOUGH...IS LOW LEVEL DRY AIR LEFT OVER
FROM THE CURRENT CANADIAN HIGH PRESSURE AREA. OVERALL...12.00Z MODEL
GUIDANCE HAS BACKED OFF ON THE AMOUNT OF QPF POSSIBLE FROM THESE
CLOUDS...ESPECIALLY THE GFS...SUGGESTING THE DRY AIR MAY BE ABLE TO
ABSORB MUCH OF THE PRECIPITATION. HOWEVER...ALL GUIDANCE DOES
SUGGEST SOME LIGHT QPF POSSIBLE...THUS THE 20-40 PERCENT CHANCES
FROM THE PREVIOUS FORECAST STILL SEEMS REASONABLE. TIMING BETWEEN
18Z MONDAY TO 06Z TUESDAY ALSO STILL LOOKS GOOD. SHOULD SEE THE
CLOUDS AND PRECIPITATION PROGRESS EASTWARD THROUGH TIME DUE TO THE
PROGRESSION OF THE UPPER RIDGE. THE CLOUDS COMBINED WITH 850MB TEMPS
AT 18Z MONDAY OF 1C EAST TO 6C WEST ARE LIKELY TO KEEP TEMPERATURES
BELOW NORMAL...BUT NOT AS COLD AS TODAY.

2. HOW WARM TEMPERATURES WILL GET ON TUESDAY. THE SIGNAL OF A
CHINOOK WARM FRONT OFF THE ROCKIES...ACCOMPANYING THAT POTENT
SHORTWAVE...REMAINS FORECAST TO PUSH EAST THROUGH MUCH OF THE
FORECAST AREA DURING THE DAY TUESDAY. INCREDIBLY WARM 850MB TEMPS
FOR MID MAY ARE PROGGED TO FOLLOW IN ITS WAKE...WITH READINGS BY 00Z
OF 18-20C OVER CENTRAL WISCONSIN TO 22-24C WEST OF THE MISSISSIPPI
RIVER...OR 2 TO 3 STANDARD DEVIATIONS ABOVE NORMAL. SEEING THE
OBSERVED 850MB TEMPS UNDER THE UPPER RIDGE RIGHT NOW OVER THE
WESTERN U.S...THESE SEEM REASONABLE. THE QUESTION IS WITH A WARM
ADVECTION PATTERN THROUGH THE DAY...CAN WE MIX TO THESE 850MB TEMPS.
MODELS CONTINUE TO BE NOTORIOUSLY HIGH WITH SURFACE DEWPOINTS IN
THIS SITUATION...PREVENTING MODELS FROM MIXING ENOUGH. FOR
EXAMPLE...THE 12.00Z GFS/ECMWF/CANADIAN JUMP THEM OVER IOWA FROM
50-55 AT 12Z TO 60-65 AT 18Z...ALL LIKELY DUE TO EVAPOTRANSPORATION
THAT IS NOT THERE YET. ADDITIONALLY...A DOWNSLOPE FLOW FROM THE
ROCKIES USUALLY ENDS UP WITH DRIER DEWPOINTS...ESPECIALLY THIS TIME
OF YEAR. THUS...HAVE CONTINUED TO STAY TOWARDS THE WARM SIDE OF
GUIDANCE. ALTHOUGH THE 12.00Z NAM IS SLIGHTLY TOO PROGRESSIVE...ITS
TEMPERATURES SEEM REASONABLE. FOLLOWED MOS GUIDANCE MORE FOR
DEWPOINTS SINCE MOS HAS BEEN DOING MUCH BETTER IN THIS DEPARTMENT.

3. COLD FRONT CROSSING TUESDAY NIGHT AND POTENTIAL FOR PRECIPITATION
WITH IT. 12.00Z NAM AND GFS ARE JUST SLIGHTLY FARTHER SOUTH WITH THE
TRACK OF THE SHORTWAVE TRACKING ALONG THE CANADIAN BORDER...COMPARED
TO THE 12.00Z ECMWF/UKMET/CANADIAN. THIS DIFFERENCE RESULTS IN THE
NAM/GFS ADDING EXTRA FORCING TO THE LOW LEVEL FRONTOGENESIS ZONE ON
AND BEHIND THE COLD FRONT...AND THUS THE MODELS PRODUCE A BAND OF
PRECIPITATION OVER THE AREA. THE ECMWF/UKMET/CANADIAN ARE DRY. FEEL
THE LATTER MODEL GROUP IS MORE LIKELY TO OCCUR...BUT CONTINUED TO
HONOR THE NAM/GFS SCENARIO WITH A 20 PERCENT CHANCE JUST IN CASE.

WEDNESDAY INTO NEXT WEEKEND...
GOOD MODEL AGREEMENT EXISTS OF THE FLOW STARTING OFF AS ZONAL TO
BEGIN THIS PERIOD. ANY LOW LEVEL FRONTOGENETICAL FORCING BEHIND
TUESDAY NIGHTS COLD FRONT IS SOUTH OF THE AREA FOR WEDNESDAY...SO
WENT DRY DURING THIS TIME. THE ZONAL FLOW DOES NOT LAST LONG...WITH
A NEW TROUGH PROGGED TO COME INTO THE PACIFIC NORTHWEST THURSDAY
NIGHT. THIS CAUSES THE FLOW DOWNSTREAM TO BUCKLE...WITH THE 12.00Z
ECMWF/GFS/CANADIAN ALL SHOWING A SHORTWAVE TROUGH TRACKING ACROSS MN
AND WI THURSDAY INTO THURSDAY NIGHT. HAVE HONORED THE SHORTWAVE WITH
SOME SMALL CHANCES OF PRECIPITATION. WE COULD END UP WITH A DRY DAY
FRIDAY WITH SUBSIDENCE AND HIGH PRESSURE BUILDING IN. LOWERED
PRECIPITATION CHANCES FURTHER AND MAY BE ABLE TO COMPLETELY PULL
THEM WITH THE NEXT EXTENDED FORECAST UPDATE. THINGS LOOK TO PERHAPS
TO GET MORE ACTIVE FOR FRIDAY NIGHT INTO THE WEEKEND AS THE PACIFIC
NORTHWEST TROUGH BEGINS TO APPROACH THE PLAINS. SURPRISINGLY GOOD
MODEL AGREEMENT BETWEEN THE ECMWF AND GFS...ALONG WITH PREVIOUS
RUNS...OF A DEEPENING LOW DOWNSTREAM OVER NEBRASKA. AS ONE WOULD
EXPECT...A SURGE OF MOISTURE TRANSPORT OUT OF THE GULF OF MEXICO IS
AIMED DIRECTLY TOWARDS THE FORECAST AREA AHEAD OF THE LOW.
THUS...PRECIPITATION CHANCES INCREASE...ESPECIALLY ON SATURDAY WHERE
THE CONSENSUS EVEN RESULTS IN 50-60 PROBABILITIES. TEMPERATURES
SHOULD SLOWLY COOL THROUGH THE EXTENDED...BUT STILL STAY AT OR ABOVE
NORMAL WITH A FLOW GENERALLY OFF THE PACIFIC.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 611 AM CDT SUN MAY 12 2013

PLAN ON VFR CONDITIONS AT KLSE/KRST TODAY THROUGH TONIGHT AS HIGH
PRESSURE BUILDS INTO THE AREA. LOOK FOR BREEZY NORTHWEST WINDS
TODAY IN THE 12-20KT RANGE...TAPERING OFF AFTER SUNSET.

&&

.FIRE WEATHER...TUESDAY
ISSUED AT 320 AM CDT SUN MAY 12 2013

AFTER HAVING BREEZY...DRYING AND UNSEASONABLY COOL WEATHER THIS
WEEKEND...INCLUDING FROST/FREEZE CONDITIONS TONIGHT ACROSS
WISCONSIN...CONCERN CONTINUES TO INCREASE ABOUT CRITICAL FIRE
WEATHER CONDITIONS ON TUESDAY. MOST LOCATIONS SHOULD SEE HIGHS
CLIMB INTO THE 80S...WITH SOME WEST OF THE MISSISSIPPI RIVER
REACHING 90. DEWPOINT FORECASTS REMAIN TRICKY...BUT MINIMUM
RELATIVE HUMIDITY VALUES SHOULD HAVE NO PROBLEM FALLING INTO THE
30 TO 40 PERCENT RANGE. IT IS POSSIBLE LOCATIONS SAY ALONG AND
WEST OF US-52 COULD END UP DROPPING TOWARDS 25 PERCENT. COMBINED
WITH SOUTHWEST WINDS OF 15 TO 20 MPH AND HIGHER GUSTS...THE
SITUATION BEARS WATCHING.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...FROST ADVISORY FROM 1 AM TO 7 AM CDT MONDAY FOR WIZ032-041-054-
     061.

     FREEZE WARNING FROM 1 AM TO 7 AM CDT MONDAY FOR WIZ017-029-033-
     034-042>044-053-055.

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

$$

SHORT TERM...AJ
LONG TERM...AJ
AVIATION...DAS
FIRE WEATHER...AJ