Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 032009
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
309 PM CDT WED JUN 3 2015

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 309 PM CDT WED JUN 3 2015

CURRENTLY AS OF 20Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED TROUGHING ALONG THE U.S. WEST COAST AND RIDGING OVER THE
CENTRAL AND SOUTHERN PLAINS. TOPPING THIS RIDGING WERE SHORTWAVES
OVER SOUTHERN MN AND THE KANSAS CITY AREA...WITH THE LATTER ONE
CONVECTIVELY INDUCED. THIS LATTER SHORTWAVE AND ITS CONVECTION HAS
HELPED BLOCK MOISTURE RETURN INTO THE FORECAST AREA...DESPITE A
GENERAL SOUTHERLY FLOW FROM THE WESTERN GULF OF MEXICO INTO MN.
THUS...THE SHORTWAVE OVER SOUTHERN MN DESPITE LOOKING QUITE STRONG
ON WATER VAPOR IS NOT PRODUCING AS MUCH CONVECTION AS IT COULD.
PLENTY OF CLOUD COVER ON VISIBLE IMAGERY OVER MN AND THE NORTHWEST
HALF OF THE FORECAST AREA IS ALSO LIMITING INSTABILITY FOR
CONVECTIVE DEVELOPMENT. NEVERTHELESS...THE SHORTWAVE ACTING ON
PRECIPITABLE WATER AROUND 1.5 INCHES HAS BEEN ABLE TO PRODUCE
NUMEROUS SHOWERS AND SOME THUNDERSTORMS...MAINLY NORTHWEST OF THE
FORECAST AREA WHERE THE BETTER DYNAMICS EXISTS. A DRY SLOT ON THE
SOUTH SIDE OF THE SHORTWAVE IS ALSO LIMITING SOME OF THE CONVECTIVE
ACTIVITY SOUTH OF I-90.

MODELS ARE SUGGESTING THAT THE UPPER RIDGING OVER THE CENTRAL AND
SOUTHERN PLAINS WILL TRY TO BUILD NORTHEAST DURING THE NEXT 24
HOURS. THIS IN TURN SHOULD HELP LIFT THE SHORTWAVE CURRENTLY IN
SOUTHERN MN NORTHEASTWARD...TAKING THE BULK OF THE PRECIPITATION
NORTH OF THE FORECAST AREA. HOWEVER...CANNOT RULE OUT SOME SHOWERS
AND A FEW THUNDERSTORMS CROSSING THE FORECAST AREA THROUGH THE EARLY
MORNING HOURS...RESULTING FROM SOME LOW LEVEL ISENTROPIC LIFT AND A
SURFACE COLD FRONT RUNNING INTO THIN UNCAPPED INSTABILITY / UPWARDS
OF 1000 J/KG MUCAPE AND LESS THAN 200 J/KG OF MLCAPE. SUBSIDENCE IN
THE WAKE OF THE SHORTWAVE LIFTING NORTHEAST SHOULD ALSO HELP TO
DIMINISH PRECIPITATION WEST TO EAST DURING THE NIGHT. ITS LOOKING
MORE LIKE THURSDAY MORNING WILL END UP DRY AS LOW LEVEL MOISTURE
TRANSPORT FORCING IS FOCUSING ON ACROSS NEBRASKA AND SOUTHERN
IOWA...JUST NORTH OF A WARM FRONTAL BOUNDARY SET UP JUST NORTH OF I-
70. ITS POSSIBLE SOME OF THIS CONVECTION MARCHES NORTHEASTWARD
TOWARD NORTHEAST IOWA DURING THE AFTERNOON AS THE UPPER RIDGE
BUILDS...BUT ITS EASILY JUST AS PLAUSIBLE THE OUTFLOWS KEEP THE
CONVECTION TO THE SOUTHWEST AS SUGGESTED BY THE 03.12Z ECMWF.
NOW...THERE IS A WEAK TROUGH PROGGED TO BE DRAPED ACROSS THE
FORECAST AREA DURING THE DAY...LEFT-OVER FROM THE COLD FRONT MOVING
THROUGH TONIGHT. HOWEVER...CONVERGENCE ALONG THE TROUGH LOOKS TOO
WEAK TO DEVELOP ANYTHING.

IN SUMMARY...OUTSIDE OF THIS EVENING...HAVE LOWERED PRECIPITATION
CHANCES AND THEY MAY EVEN NEED FURTHER LOWERING FOR THURSDAY.

COMBINATION OF CLOUDS AND SOUTHERLY FLOW INCREASING SURFACE
DEWPOINTS SHOULD KEEP LOW TEMPERATURES UP TONIGHT...AT LEAST 5
DEGREES ABOVE NORMAL. WE COULD GET STUCK WITH SOME
STRATUS/STRATOCUMULUS AROUND DURING THE MORNING...BUT THE STRONG
JUNE SUN SHOULD ALLOW FOR SOME SUN TO DEVELOP DURING THE
DAY...POSSIBLY RESTRICTED TOO BY BLOWOFF FROM CONVECTION TO OUR
SOUTHWEST. NEVERTHELESS...THAT MIXING PLUS 850MB TEMPS OF 14-16
SHOULD PUSH TEMPS INTO THE MID 70S TO LOW 80S.

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 309 PM CDT WED JUN 3 2015

MODELS WANT TO RETROGRADE THE UPPER RIDGE THAT WAS BUILDING INTO THE
REGION ON THURSDAY TO THE WEST FOR THURSDAY NIGHT AND FRIDAY. THIS
IS IN RESPONSE TO A TROUGH DROPPING THROUGH THE GREAT LAKES AS WELL
AS A SHORTWAVE COMING THROUGH NEBRASKA AND IOWA. THE COMBINATION OF
BOTH OF THESE FEATURES PUTTING OUR FORECAST AREA IN NORTHWEST FLOW
MAY MAKE IT HARD FOR CONVECTION TO MOVE IN.
ADDITIONALLY...CONVECTIVE OUTFLOWS FROM STORMS CROSSING
NEBRASKA...SOUTHERN IOWA AND NORTHERN MO MAY TEND TO WANT TO HOLD
THE CONVECTING NOSE OF THE MOISTURE TRANSPORT TO OUR SOUTHWEST. THE
03.12Z GFS/NAM/ECMWF HAVE ALL COME IN DRIER FOR THURSDAY NIGHT AND
FRIDAY...MAYBE NOT ALL THE WAY DRY BUT DEFINITELY ON THE DRYING
TREND WITH THE HEAVIER CONVECTION TO OUR SOUTHWEST. AS SUCH...HAVE
KNOCKED DOWN PRECIPITATION CHANCES AND IT IS POSSIBLE WE END UP
MAINLY DRY AS THE 03.12Z ECMWF SHOWS. HAVE CONSIDERED THE 03.12Z
CANADIAN AN OUTLIER AS IT IS TOO FAR NORTH WITH FIRING CONVECTION ON
THURSDAY...OVER SOUTH DAKOTA...COMPARED TO ALL OTHER GUIDANCE. WITH
THE POTENTIAL FOR A LITTLE MORE SUN THEN FOR FRIDAY...RAISED HIGHS
SLIGHTLY.

FRIDAY NIGHT AND MUCH OF SATURDAY LOOK DRY AS WELL AS THE AREA IS
UNDER THE INFLUENCE OF HIGH PRESSURE NOSING SOUTHWARD INTO THE
REGION. APPEARS RELATIVELY COOL AT THE TYPICAL COLD SPOTS IN
WI FRIDAY NIGHT AS PRECIPITABLE WATER FALLS TO 0.5-0.75 INCHES.

LATE SATURDAY AND ESPECIALLY SATURDAY NIGHT INTO SUNDAY...A
SHORTWAVE TROUGH IS PROGGED TO MAKE ITS WAY FROM THE MANITOBA/NORTH
DAKOTA AREA THROUGH THE FORECAST AREA. TIMING SEEMS TO BE FIRMING UP
AMONGST MOST MODELS THAT WE SHOULD SEE A WARM CONVEYOR BELT OF
SHOWERS AND SOME THUNDERSTORMS ACCOMPANY THE TROUGH.
THEREFORE...PRECIPITATION CHANCES DURING THIS TIME PERIOD HAVE BEEN
INCREASED. A CONSENSUS AMONGST GUIDANCE SEEMS TO SUGGEST RIGHT NOW
THAT 06-18Z SUNDAY WOULD BE THE MAIN TIME PERIOD FOR RAIN. THE
STRONGEST THERMODYNAMICAL ENHANCED CONVECTION BY LOW LEVEL JET...AND
THUS POSSIBLE SEVERE RISK...LOOKS TO BE ALONG I-80.

VERY GOOD MODEL AGREEMENT EXTENDS OUT INTO EARLY NEXT WEEK WITH A
FAIRLY DEEP TROUGH SETTLING IN OVER SOUTHEAST CANADA AND THE GREAT
LAKES. THIS PUTS THE FORECAST AREA IN STRONG NORTHWEST
FLOW...HELPING TO DRIVE DRIER AIR INTO THE REGION. STILL HAVE SOME
SMALL CHANCES OF PRECIPITATION FOR SUNDAY NIGHT AND MONDAY AHEAD OF
THE DEVELOPING DEEPER TROUGH. HOWEVER...AS THE 03.12Z ECMWF
SUGGESTS...ITS ENTIRELY POSSIBLE THIS PERIOD ENDS UP DRY TOO.
TYPICALLY THE NORTHWEST FLOW WOULD BE COOL...BUT 850MB TEMPS ARE
ONLY PROGGED TO DROP TO AS LOW AS MAYBE 12-14C MONDAY NIGHT BEFORE
CLIMBING BACK UP TO 14-18C BY WEDNESDAY AS THE UPPER TROUGH BEGINS
TO SHIFT EAST. THUS TEMPERATURES OVERALL SHOULD BE CLOSE TO NORMAL
MONDAY THROUGH WEDNESDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1236 PM CDT WED JUN 3 2015

SHORTWAVE OVER SOUTHWEST MN WILL CONTINUE TO LIFT NORTHEAST THIS
AFTERNOON. STRONGEST FORCING/LIFT FROM THIS FEATURE IS SET TO MOVE
ACROSS THE TAF SITES LATE THIS AFTERNOON THRU THIS EVENING. MIXED
SIGNAL AMONG ALL THE FCST MODELS HOW MUCH CONVECTION IS PRODUCED...
WHICH LOWERS FCST CONFIDENCE...AS THE FORCING/LIFT MOVES ACROSS THE
AREA. GIVEN THIS...AND MORE SCT COVERAGE EXPECTED...LEFT CONVECTION
MENTION IN TAFS AS A PERIOD OF VCTS/CB FOLLOWED BY A PERIOD OF VCSH
WITH CIGS MAINLY IN THE 3K-4K FT RANGE. SUBSIDENCE IN THE WAKE OF THE
BAND OF SCT CONVECTION AND BEHIND THE PASSING SHORTWAVE/TROUGH AXIS
LOOKS TO BREAK UP THE LOWER CLOUD DECKS...WITH SCT 2K-3K FT CLOUDS
DURING MUCH OF THE LATE EVENING THRU OVERNIGHT HOURS TONIGHT. PLENTY
OF MVFR/IFR CLOUDS IN NORTHERN MN/EASTERN SD BEHIND THE SFC LOW...
WITH THIS MOISTURE/CLOUDS EXPECTED TO ROTATE INTO THE KRST/KLSE
AREAS NEAR OR AFTER SUNRISE AS THE LOW LEVEL FLOW BECOMES MORE
NORTHWEST. DRYING/MIXING THEN LOOKS TO ERODE THESE CLOUDS FROM
NORTHWEST TO SOUTHEAST ACROSS THE AREA THRU THE LATE MORNING/EARLY
AFTERNOON HOURS OF THU.

THAT SAID...LATEST MESO MODELS AND RADAR TRENDS FAVOR PUSHING THE
CURRENT AREA OF SHRA/TS FROM SOUTHERN MN/IA EASTWARD. AS IT DOES
THOUGH...IT WILL START TO RUN OUT OF A FAVORABLE AIRMASS AND SHOULD
WEAKEN. COULD IMPACT KRST FOR A FEW HOURS...BUT LIKELY STAY WEST OF
KLSE.

IN THE AFTERNOON...INSTABILITY AXIS RE-ESTABLISHES ITSELF ACROSS THE
AREA...AND A SFC LOW AND UPPER LEVEL TROUGH SHOULD TAP INTO
THIS...FIRING ANOTHER AREA OF SHRA/TS. SOME MESO MODELS SUGGEST THE
MAIN MASS WOULD STAY ALONG/NORTH OF I-90...AND COULD IMPACT
KRST/KLSE.

COULD BE A PERIOD OF MVFR CIGS/VSBY WITH ANY THUNDERSTORM...BUT WITH
CONFIDENCE LOWER ON WHEN THIS WOULD BE MORE LIKELY...WILL NOT ADD TO
FORECAST. IN ADDITION...SOME HINTS THAT LOWER/MVFR CIGS WILL MOVE IN
OVERNIGHT AS THE SFC LOW MOVES IN. THIS MATCHES WITH LATEST
FOG/STRATUS IMAGERY AND SFC OBS. SOME MVFR VSBY TOO. UNCERTAIN THAT
IT WOULD REACH KRST BEFORE 12Z SO WILL NOT ADD...BUT THE POTENTIAL
WILL BE MONITORED.

&&

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

$$

SHORT TERM...AJ
LONG TERM...AJ
AVIATION...RIECK


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