Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 120819
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
319 AM CDT SAT JUL 12 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 319 AM CDT SAT JUL 12 2014

MAIN SHORT TERM CONCERN IS ON PRECIPITATION TRENDS THROUGH THE
EVENING AS WELL AS SEVERE WEATHER POTENTIAL.

CURRENTLY AS OF 08Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED A SUBTROPICAL HIGH OVER THE CENTRAL PLAINS AND A DEEP UPPER
TROUGHING COVERING MUCH OF CENTRAL CANADA. A SERIES OF MONSOONAL
SHORTWAVES WERE COMING AROUND THE WEST SIDE OF THE SUBTROPICAL
HIGH...ONE OVER SOUTH CENTRAL SOUTH DAKOTA AND A SECOND IN WYOMING. A
STREAM OF TROPICAL PACIFIC MOISTURE WAS ALSO EVIDENT AROUND THE
SUBTROPICAL HIGH. IN THE LOWER LEVELS...A PLUME OF 15-18C 850MB
DEWPOINTS STRETCHED FROM OKLAHOMA INTO SOUTH DAKOTA AND SOUTHERN
MINNESOTA PER 00Z RAOBS. ALL THIS MOISTURE EQUATES TO PRECIPITABLE
WATER VALUES OF AROUND 2 INCHES FROM SIOUX FALLS AREA SOUTHEAST INTO
CENTRAL ILLINOIS. A ZONE OF 850MB MOISTURE TRANSPORT AHEAD OF THE
MONSOONAL SHORTWAVES ACTING ON THIS MOISTURE...ALONG WITH LOW TO MID
LEVEL FRONTOGENESIS...HAS LED TO SHOWERS AND STORMS IN THAT
PRECIPITABLE WATER MAXIMUM. THIS PRECIPITATION HAS CAUSED THE
MAIN SURFACE WARM FRONT TO GET STUCK IN FAR SOUTHERN IOWA.

SOME OF THE GENERALITIES FOR TODAYS FORECAST. THE 2 MONSOONAL
SHORTWAVES WILL TRACK ACROSS THE FORECAST AREA...HELPING TO PULL THE
850MB MOISTURE TRANSPORT ZONE AND LOW TO MID LEVEL FRONTOGENESIS
NORTHWARD TOWARDS AND POSSIBLY INTO THE AREA. IN ADDITION...AN UPPER
JET STREAK ASSOCIATED WITH THE CENTRAL CANADA UPPER TROUGH IS
PROGGED TO ALIGN ITSELF FROM CENTRAL MN THROUGH LAKE SUPERIOR...
PLACING SOME IF NOT ALL OF THE FORECAST AREA IN THE FAVORABLE RIGHT
ENTRANCE REGION. INSTABILITY WISE...ALONG AND SOUTH OF THE WARM
FRONTAL BOUNDARY 1500-2500 J/KG OF MLCAPE SEEMS REASONABLE TO
DEVELOP THIS AFTERNOON...AS TEMPS CLIMB INTO THE 80S AND DEWPOINTS
HOVER IN THE MID 70S OR SO. PLENTIFUL PRECIPITABLE WATER AROUND AS
WELL AS NOTED IN THE CURRENT WEATHER DISCUSSION...RUNNING AROUND 2
INCHES. THUS...PLENTY OF MOISTURE EXISTS TO COMBINE WITH DYNAMIC AND
THERMODYNAMIC FORCING TO PRODUCE CONVECTION. 0-6KM AND 0-3KM SHEAR
VALUES REMAIN FAVORABLE FOR ORGANIZED SEVERE CONVECTION...ON THE
ORDER OF 40-50 KT AND 30-45 KT RESPECTIVELY. MUCH OF THIS SHEAR IS
CONFINED ABOVE 1 KM AS THE WINDS BELOW ARE FAIRLY LIGHT. STILL HAVE
CYCLONIC CURVATURE IN THE HODOGRAPH...THOUGH. BASED ON THE
AFOREMENTIONED PARAMETERS...DAMAGING WINDS AND HEAVY RAINS WOULD BE
THE MAIN CONCERNS...WITH SOME MARGINALLY SEVERE HAIL AND AN OUTSIDE
CHANCE OF A TORNADO. THE HIGHER SHEAR AND DRYING SOILS AS OF LATE
SHOULD HELP TO KEEP ANY FLOOD CONCERN LOCALIZED...IN AGREEMENT TOO
WITH THE DAY 1 EXCESSIVE RAINFALL OUTLOOK.

NOW...THE CRITICAL UNCERTAINTIES...

1. TIMING AND INTENSITY OF THE 2 MONSOONAL SHORTWAVES...WHICH
IMPACTS THE MOVEMENT OF THE 850MB MOISTURE TRANSPORT ZONE AND LOW TO
MID LEVEL FRONTOGENESIS. WHERE THAT MOISTURE TRANSPORT NOSE...F-GEN
ZONE...AND DPVA FROM THE SHORTWAVES WILL MODULATE WHERE THE
CONVECTION ENDS UP. MODELS ARE ALL OVER THE BOARD WITH THESE
SHORTWAVES...LEADING TO LOWERED CONFIDENCE.

2. HOW FAR NORTH THE WARM FRONT CAN MAKE IT WHICH IMPACTS THE ZONE
OF INSTABILITY AND THUS HOW FAR NORTH THROUGH THE FORECAST AREA A
SEVERE RISK EXISTS. ITEM NUMBER 1 ABOVE WILL IMPACT THE WARM FRONT.

DESPITE THE UNCERTAINTIES ABOVE...IT STILL APPEARS THROUGH THIS
EVENING LOCATIONS SOUTH OF I-90 STAND TO SEE THE HIGHEST CHANCE FOR
CONVECTION. ADDITIONALLY...SEVERE WEATHER IS GOING TO HAPPEN BETWEEN
I-80 AND I-90 AFTER 2 PM TODAY...CONSISTING OF SUPERCELLS AND BOW
SEGMENTS. PINNING DOWN THE LOCATION ANY FINER THAN THAT IS
PROBLEMATIC AT THIS TIME. LATER FORECAST UPDATES SHOULD BE ABLE TO
REFINE THE LOCATION AND TIMING.

HAVE ADJUSTED THE MORNING PORTION OF THE FORECAST TO FOLLOW TRENDS
IN THE HRRR...WHILE A MODEL CONSENSUS DOMINATES THE AFTERNOON AND
EVENING. NOTE THAT THERE COULD ALSO BE SOME SURFACE BASED CONVECTION
THAT FIRES OVER WEST CENTRAL WI THIS AFTERNOON ALONG A SOUTHEASTWARD
MOVING COLD FRONT. THE AFOREMENTIONED CONSENSUS JUST HAPPENS TO BE
SIMILAR TO THE 00Z NSSL WRF-ARW. HEADING INTO TONIGHT...THERE WILL
BE A NORTHWEST TO SOUTHEAST DRYING TREND AS THE SHORTWAVES PUSH OFF
TO THE EAST... USHERING IN SUBSIDENCE AND MUCH DRIER PRECIPITABLE
WATER VALUES.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 319 AM CDT SAT JUL 12 2014

A GRADUAL DESCENT OF THE DEEP UPPER TROUGH OVER CENTRAL CANADA INTO
THE FORECAST AREA REMAINS ON TRACK BETWEEN SUNDAY AND MONDAY...WITH
THE TROUGH SLOWLY PUSHING TO THE EAST ON TUESDAY. AS THIS
OCCURS...THERE ARE COUPLE OF ISSUES TO CONTEND WITH...

1. POTENTIAL FOR CONVECTION ON SUNDAY. A SURFACE COLD FRONT IS
PROGGED TO DROP THROUGH THE AREA...THOUGH THERE DOES NOT APPEAR TO
BE MUCH CONVERGENCE ON IT. THE 12.00Z ECMWF/NAM/REGIONAL
CANADIAN/HIRES ARW AND NMM ARE DRY...WHILE THE 12.00Z GFS HAS
REDUCED ITS QPF EVEN MORE. THE GFS STILL HAS TOO HIGH SURFACE
DEWPOINTS IN WHAT SHOULD BE A FAVORABLE MIXING REGIME...THUS PREFER
THE DRIER IDEA.

2. RAIN CHANCES MONDAY THROUGH TUESDAY. AN UPPER LOW WITHIN THE
TROUGH WILL SLIDE ACROSS NORTHERN WI MONDAY EVENING. DPVA FORCING
AHEAD OF THE UPPER LOW AND DAYTIME INSTABILITY SHOULD PROMOTE PLENTY
OF SHOWER ACTIVITY...ESPECIALLY ALONG AND NORTH OF HIGHWAY 29 CLOSER
TO THE UPPER LOW. SOME SHOWER ACTIVITY COULD CONTINUE INTO
TUESDAY...MAINLY IN WISCONSIN CLOSER TO THE UPPER TROUGH AXIS.

3. TEMPERATURES MONDAY AND TUESDAY. 850MB TEMP ANOMALIES PLUMMET TO
2 TO 2.5 STANDARD DEVIATIONS BELOW NORMAL DURING THIS PERIOD...OR
GENERALLY IN THE 4-7C RANGE. THESE READINGS GENERALLY SUPPORT HIGHS
IN THE 60S. HOWEVER...THERE ARE SOME MODEL SUGGESTIONS ON TUESDAY
THAT...DEPENDING ON HOW QUICK THE TROUGH PUSHES EAST...BOTH THE
850MB TEMP AND ACTUAL HIGH COULD BE A LITTLE WARMER. LOWS WILL BE
HELD UP SOMEWHAT BY BOTH CLOUDS AND A NORTHWESTERLY BREEZE. NEEDLESS
TO SAY...ITS GOING TO FEEL MORE LIKE FALL VERSUS SUMMER.

AFTER TUESDAY AND THROUGH THE END OF THE WEEK...EXPECT A LONG DRY
PERIOD AS SURFACE HIGH PRESSURE DOMINATES AND 500MB HEIGHTS RISE.
HOWEVER...THE 12.00Z GFS SHOWS DIURNALLY DRIVEN WIDESPREAD LIGHT
PRECIP WEDNESDAY...THURSDAY AND FRIDAY. THE MODEL APPEARS TO BE
SUFFERING FROM OVER-DOING EVAPOTRANSPIRATION...NOTED IN ITS SURFACE
DEWPOINT FIELD...AND THUS CONVECTS EASIER. THUS...HAVE IGNORED IT
AND STAYED WITH THE DRY ECMWF/CANADIAN.

TEMPERATURES WILL GRADUALLY WARM THROUGH THE WEEK...GETTING CLOSE TO
NORMAL FOR THE WEEKEND.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1143 PM CDT FRI JUL 11 2014

THE AREA OF MVFR CLOUDS HAS DISSIPATED OR LIFTED UP TO VFR
CEILINGS WITH THE BACK EDGE WORKING STEADILY EAST AND BY 06Z THE
CLOUDS SHOULD BE PAST KLSE. THIS INCREASES THE PROBABILITIES THAT
SOME FOG CAN FORM OVERNIGHT BUT AT THE SAME TIME...HIGH CLOUDS ARE
BEGINNING TO SPREAD IN FROM THE WEST...WHICH WOULD DECREASE THE
FOG PROBABILITIES. THE HIGH CLOUDS APPEAR TO BE DISSIPATING SOME
AS THEY COME INTO THE AREA AND IF THIS TREND CONTINUES...SOME FOG
COULD FORM SO HAVE HELD ONTO THIS IN BOTH FORECASTS. A WARM FRONT
SITS ACROSS SOUTHERN IOWA AND AS THE MOISTURE TRANSPORT INCREASES
INTO THIS OVERNIGHT SOME CONVECTION IS EXPECTED TO FORM ALONG THIS
BOUNDARY. THIS COMBINED WITH THE ONGOING ACTIVITY OVER NEBRASKA
AND SOUTH DAKOTA COULD DRIFT NORTHWARD INTO THE AREA EARLY
SATURDAY MORNING. THIS IS THE TREND THAT HAS BEEN SHOWN BY THE
LAST FEW RUNS OF THE HRRR AND HAVE INTRODUCED A VCSH FOR THIS BY
MID MORNING WITH A VFR CEILING. THE BETTER CHANCES FOR CONVECTION
WILL BE TIED TO THE SHORT WAVE TROUGH COMING ACROSS WYOMING AND
MONTANA. THE 12.00Z NAM SHOWS CONVECTION DEVELOPING AROUND MID DAY
OVER SOUTH DAKOTA AND NEBRASKA AND THEN MOVING EAST INTO THE AREA
LATE IN THE AFTERNOON INTO THE EVENING. BASED ON THIS
TIMING...HAVE PUSHED THE TIMING OF THE VCTS BACK A LITTLE AT BOTH
SITES BUT DID INTRODUCE A MVFR CEILING AT KRST.

&&

.HYDROLOGY...
ISSUED AT 319 AM CDT SAT JUL 12 2014

THERE IS A CONCERN FOR FLASH FLOODING THIS AFTERNOON INTO THIS
EVENING...PRIMARILY ACROSS NORTHEAST IOWA AND FAR SOUTHWEST
WISCONSIN. STORMS IN THIS REGION WILL BE CAPABLE OF PRODUCING VERY
HEAVY RAIN DUE TO A NEARLY TROPICAL AIRMASS IN PLACE. NO FLASH
FLOOD WATCH IS BEING ISSUED AT THIS TIME...THOUGH...BECAUSE OF

1. STRONG 0-3/0-6KM SHEAR WHICH SHOULD KEEP STORMS PROGRESSIVE
2. ANTECEDANT CONDITIONS HAVE DRIED OUT AND CAN TAKE MORE WATER

NEVERTHELESS...SINCE STORMS WILL HAVE HIGH RAINFALL RATES...THERE
COULD BE A NEED FOR A FLASH FLOOD WARNING OR TWO.

&&

.CLIMATE...
ISSUED AT 319 AM CDT SAT JUL 12 2014

RECORD COOL HIGH TEMPERATURES ARE POSSIBLE MONDAY AND TUESDAY AS AN
UNSEASONABLY COLD AIRMASS SETTLES OVER THE UPPER MISSISSIPPI RIVER
VALLEY.

FOR LA CROSSE...
MONDAY....FORECAST HIGH 69.  RECORD 65 IN 1994
TUESDAY...FORECAST HIGH 68.  RECORD 68 IN 1962

FOR ROCHESTER...
MONDAY....FORECAST HIGH 64.  RECORD 64 IN 1952
TUESDAY...FORECAST HIGH 67. RECORD 67 IN 1962

&&

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

$$

SHORT TERM...AJ
LONG TERM...AJ
AVIATION...04
HYDROLOGY...AJ
CLIMATE...AJ


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