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000
FXUS63 KARX 170807
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
307 AM CDT MON JUN 17 2013

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 307 AM CDT MON JUN 17 2013

CURRENTLY AS OF 08Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED AN UPPER LOW OFF THE PACIFIC NORTHWEST COAST...RIDGING
BUILDING FROM NEW MEXICO INTO BRITISH COLUMBIA...AND TROUGHING OVER
SOUTHEAST CANADA INTO THE EASTERN GREAT LAKES. WITHIN THE
WEST-NORTHWEST FLOW...TWO SHORTWAVES OF NOTE WERE NEAR FARGO NORTH
DAKOTA AND IN FAR SOUTHWEST SASKATCHEWAN. 700-850MB MOISTURE
TRANSPORT AHEAD OF THE FARGO SHORTWAVE HELPING TO SUPPORT SOME HIGH
BASED SHOWERS ALONG/NORTHEAST OF I-94. TALKING ABOUT HIGH BASED...
00Z MPX AND GRB SOUNDINGS BOTH DEPICTED MIXING UP TO 750MB...WITH
DEEP INVERTED-V APPEARANCE BELOW. THIS DEEP MIXING ALLOWED FOR
SHOWERS THAT MOVED THROUGH MPX AROUND RAOB RELEASE TIME TO PRODUCE
WIND GUSTS OF 30-50KT. THESE SHOWERS WERE MORE VIGOROUS THEN THOSE
OCCURRING NOW...PLUS THEY OCCURRED RIGHT AFTER PEAK HEATING WHEN
MIXING WAS AT ITS MAXIMUM...ALLOWING FOR THE STRONG GUST POTENTIAL.
OTHERWISE...SKIES ARE MOSTLY CLEAR OVER THE FORECAST AREA SOUTH OF A
COLD FRONT EXTENDING FROM NORTHERN MN INTO NORTHERN LOWER MI. 850MB
TEMPS AT 00Z AHEAD OF THE FRONT WERE 14-16C AT MPX...GRB AND
DVN...COMPARED TO 4C BEHIND THE FRONT UP AT PICKLE LAKE IN NORTHWEST
ONTARIO. ALTHOUGH DEEP MIXING EXISTED ON THAT MPX SOUNDING...THE
HIGHER MID LEVEL MOISTURE ALLOWED FOR THE PRECIPITABLE WATER TO JUMP
UP TO 0.93 INCHES AS OF 00Z...COMPARED TO 0.44 12 HOURS EARLIER.
THUS...THERE IS SOME MOISTURE AHEAD OF THE FARGO SHORTWAVE.

MODEL TRENDS FOR TODAY HAVE REALLY SHIFTED THE SHORTWAVE COMING INTO
THE FORECAST AREA NORTH COMPARED TO THE 16.00Z CYCLE. MODEL
CONSENSUS NOW SUGGESTS THAT THE SHORTWAVE NEAR FARGO ENDS UP
CROSSING CLARK COUNTY AT 00Z TUESDAY...COMPARED TO SAY LA CROSSE.
THIS HAS A BIG IMPACT ON PLACEMENT OF PRECIPITATION CHANCES.

WITH THE SHORTWAVE TRACKING FARTHER NORTH TODAY...THE COLD FRONT
ONLY DROPS SOUTH TO MAYBE THE I-94 CORRIDOR BY 00Z. COMBINATION OF
LOW LEVEL CONVERGENCE ON THE FRONT...LOW TO MID LEVEL FRONTOGENESIS
NORTH OF THE FRONT...THE APPROACH OF THE SHORTWAVE TO YIELD SOME
DPVA AND DAYTIME HEATING SHOULD PROVE FAVORABLE FOR NUMEROUS SHOWERS
ALONG/NORTH OF I-94. COULD EVEN SEE SOME ISOLATED/SCATTERED ACTIVITY
SOUTH OF THERE TOWARDS I-90 VERY LATE IN THE DAY AS THE FRONTAL
FORCING APPROACHES. DEEP MIXING AGAIN LOOKS LIKELY TODAY AHEAD OF
THE APPROACHING FRONT. NAM/RAP SOUNDINGS SHOW POTENTIAL OF 7500-9500
FT AGL FROM CLARK COUNTY SOUTHWARD...WHICH RESULTS IN HIGHS IN THE
LOW TO PERHAPS EVEN SOME MID 80S. THIS SHOULD ALLOW DEWPOINTS TO
FALL INTO THE LOW TO MID 50S. COMBINATION OF THE TWO RESULTS IN
0-1KM MLCAPES OF 400-700 J/KG IN THE AREA ALONG/NORTH OF THE FRONT.
ALTHOUGH THIS IS NOT MUCH...IT WILL BE ENOUGH TO BOTH ADD
THUNDERSTORMS AND MAKE THE SHOWERS MORE VIGOROUS. FREEZING LEVELS
ARE LOW...9500-1000 FT AGL AT 21Z WHICH COULD ALLOW FOR SOME
HAIL...BUT THE MINIMAL CAPE WHICH IS TALL AND SKINNY MAY KEEP ANY
HAIL SMALL. BIGGER CONCERN WILL LIKELY BE WIND GIVEN THE DEEP MIXING
YIELDING DEEP INVERTED-V LOOKS ON A SKEW-T. COULD SEE STRONG TO
SEVERE WIND GUSTS...JUST LIKE WHAT WENT THROUGH MINNEAPOLIS AROUND
00Z LAST EVENING.

THE VIGOROUS CONVECTIVE ACTIVITY WILL LIKELY DIMINISH QUICKLY AFTER
00Z AS LOSS OF HEATING KNOCKS DOWN CAPE. HOWEVER...
ISOLATED/SCATTERED SHOWER ACTIVITY MAY PERSIST THROUGH MUCH OF THE
NIGHT AS THE FRONT SLOWLY SINKS SOUTH...AIDED BY LOW TO MID LEVEL
FRONTOGENESIS PERSISTING ALONG/NORTH OF THE FRONT. ADDITIONALLY...
AFTER MIDNIGHT TONIGHT...ATTENTION TURNS TO THE SHORTWAVE OVER
SOUTHWEST SASKATCHEWAN. MODELS HAVE SPED UP THIS SHORTWAVE...PERHAPS
MOVING INTO FAR WESTERN PORTIONS OF THE FORECAST AREA BY 12Z TUESDAY
AS SUGGESTED BY THE 17.00Z GFS. 17.00Z NAM/UKMET ARE JUST SLIGHTLY
SLOWER. IN ANY EVENT...DPVA AND A LOWERING TROPOPAUSE WITH THIS
SHORTWAVE WILL LIKELY HELP STRENGTHEN THE LOW TO MID LEVEL
FRONTOGENESIS IN PLACE ALONG/NORTH OF THE FRONT. THUS...THIS
SHORTWAVE SHOULD HELP PROMOTE KEEPING ISOLATED/SCATTERED ACTIVITY
GOING.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 307 AM CDT MON JUN 17 2013

TUESDAY...ATTENTION IS ON THAT SHORTWAVE APPROACHING FAR WESTERN
PORTIONS OF THE FORECAST AREA AT 12Z. AGAIN...WITH MODELS SPEEDING
UP THE SHORTWAVE...THE WAVE PRETTY MUCH EXITS THE AREA BY
18Z...REACHING NORTHWEST INDIANA BY 00Z. MODELS HAVE COME INTO MUCH
BETTER CONSENSUS ON WHETHER THIS SHORTWAVE WILL PRODUCE
PRECIPITATION...WITH THE 17.00Z NAM/GFS/CANADIAN/UKMET/ECMWF AND
HIRES NMM/ARW ALL NOW DEPICTING SOME LIGHT PRECIPITATION. BELIEVE
THE REASON THE QPF IS LIGHT IS THAT THE MOISTURE TRANSPORT IS NOT
ALL THAT GREAT...AND THE AVAILABLE MOISTURE IS SOMEWHAT LIMITED.
HOWEVER...WITH ALL MODELS DEPICTING A FAIRLY STRONG SHORTWAVE PER
500MB PROGS...THE FORCING SHOULD BE ENOUGH TO SQUEEZE OUT SOME
SHOWERS AND POSSIBLY EVEN A THUNDERSTORM OR TWO ONCE DAYTIME HEATING
GETS GOING. THUS...HAVE ADDED 20-30 PERCENT CHANCES TO THE
FORECAST...HIGHEST TUESDAY MORNING. THESE CHANCES MAY NEED TO BE
INCREASED IN LATER FORECASTS. COMBINATION OF CLOUDS ACCOMPANYING THE
SHORTWAVE AND A NORTHEAST LOW LEVEL FLOW OUT OF HIGH PRESSURE IN
UPPER MICHIGAN WILL YIELD A COOLER DAY. HIGHS MOST LOCATIONS SHOULD
END UP IN THE LOW TO MID 70S.

TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...THE UPPER LOW OFF THE
PACIFIC NORTHWEST IS PROGGED TO MOVE INLAND DURING THIS
PERIOD...FORCING RIDGING TO INCREASE DOWNSTREAM OVER THE PLAINS.
THIS SETUP WOULD PLACE THE FORECAST AREA IN SUBSIDENCE EAST OF THE
RIDGE AXIS...FAVORABLE FOR HIGH PRESSURE AT THE SURFACE. THIS IS
TRUE ACCORDING TO MODELS...AND WOULD NORMALLY SUGGEST A DRY
FORECAST. HOWEVER...17.00Z NAM AND TO SOME DEGREE THE GFS THROW A
MONKEY WRENCH INTO THIS PLAN...AS THESE MODELS SHOW A NORTH TO SOUTH
ORIENTED SHORTWAVE BARRELING THROUGH THE RIDGE AND MOVING INTO THE
AREA WEDNESDAY NIGHT. BOTH MODELS END UP BRINGING LIGHT
PRECIPITATION INTO THE AREA. MEANWHILE...THE 17.00Z
ECMWF/CANADIAN/UKMET SHOW A MUCH WEAKER REFLECTION OF THIS SHORTWAVE
AS WELL AS SLOWER SPEED. AS A RESULT...THESE MODELS WOULD FAVOR THE
PREVIOUS DRY FORECAST. HAVE STAYED WITH THE DRY FORECAST FOR
NOW...BUT THIS SHORTWAVE WILL NEED SOME WATCHING. OTHERWISE...A COOL
NIGHT LOOKS ON TAP TUESDAY NIGHT WITH THE HIGH PRESSURE AREA IN
PLACE. SOME OF THE TYPICAL COLDER SPOTS COULD DROP INTO THE LOWER
40S. GRADUAL WARMING OF TEMPERATURES EXPECTED FOR HIGHS WEDNESDAY
AND WEDNESDAY NIGHT WITH THE HIGH PRESSURE AREA SLOWLY DRIFTING OFF
TO THE EAST...AS WELL AS AIRMASS MODIFICATION FROM DAYTIME HEATING
TAKING PLACE.

THURSDAY THROUGH THE WEEKEND...
SIMPLY STATED...MORE SUMMER-LIKE WITH INCREASING HUMIDITY...DEALING
WITH CAP CONCERNS AND POTENTIAL FOR MCSS.

17.00Z ECMWF/GFS/CANADIAN AND GFS ENSEMBLES CONTINUE TO SHOW GOOD
RUN-TO-RUN CONSISTENCY ON THE UPPER LEVEL PATTERN. THE TROUGHING
THAT HAS BEEN PERSISTENT IN SOUTHEAST CANADA IS PROGGED TO LIFT OUT
BEGINNING ON THURSDAY. MEANWHILE THE UPPER LOW IN THE PACIFIC
NORTHWEST SLOWLY EJECTS NORTHEAST INTO SOUTH CENTRAL CANADA ON
SUNDAY. THE MOTIONS OF THE TWO TROUGHS ALLOW FOR A FAIRLY
SUBSTANTIAL WARM/MOIST AIR ADVECTION TO TAKE PLACE ACROSS THE PLAINS
AND TOWARDS THE FORECAST AREA. AS A RESULT...THE POTENTIAL EXISTS
FOR MULTIPLE ROUNDS OF CONVECTION AS VARIOUS MCSS FORM. RUN-TO-RUN
MODEL CONSISTENCY AS WELL AS AGREEMENT ON THE MCS TRACKS IS FAIRLY
LOW...AND TO BE EXPECTED. THE ONLY WELL AGREED UPON MCS APPEARS TO
BE ON FRIDAY INTO SATURDAY WHERE AN MCS FORMS OVER THE DAKOTAS AND
TRACKS EAST INTO NORTHERN WI SAT MORNING. THUS...FOLLOWING A MODEL
CONSENSUS FOR PRECIPITATION CHANCES YIELDS 40-60 PERCENT CHANCES
ACROSS THE FORECAST AREA FOR SATURDAY...HIGHEST TOWARDS NORTHERN WI.
THERE ARE INDICATIONS TOO THAT CAPPING WILL BE AN ISSUE TO
CONTEND WITH AS 700MB TEMPS OVER 12C BEGIN ADVECTING TOWARDS THE
AREA FOR THE WEEKEND.

WE WILL DEFINITELY NEED TO WATCH FOR SEVERE WEATHER AND HEAVY RAIN
HEADING INTO THE WEEKEND...GIVEN THE MCS POTENTIAL AND WARM CLOUD
DEPTHS PROGGED IN THE 3500-4500 FT RANGE.

TEMPERATURES ARE EXTREMELY TRICKY AS THEY DEPEND ON HOW CONVECTION
EVOLVES...ESPECIALLY DAYTIME HIGHS. MODELS HAVE TRENDED WARMER FOR
THURSDAY THROUGH THE WEEKEND...SO HAVE FOLLOWED SUIT AND RAISED
HIGHS. HOWEVER...THESE MAY NEED FURTHER INCREASES IF SAY THE CURRENT
17.00Z ECMWF/GFS ARE CORRECT. THIS IS ESPECIALLY TRUE WHERE ON
SATURDAY THEY BOOST 850MB TEMPS UP TO 20-24C...OR 2 STANDARD
DEVIATIONS ABOVE NORMAL. HIGHS COULD EASILY CLIMB INTO THE LOW TO
POSSIBLY EVEN MID 90S IF THIS COMES TRUE. EVAPOTRANSPORATION AND
MOISTURE ADVECTION SHOULD HELP BOOST DEWPOINTS INTO THE 70S...WHICH
THIS LATENT HEATING WILL KEEP HIGHS FROM GETTING MUCH HIGHER THAN
THAT.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1105 PM CDT SUN JUN 16 2013

A WEST-EAST RUNNING SFC BOUNDARY WILL SLOWLY SINK SOUTHWARD ON
MONDAY...AIDED BY AN UPPER LEVEL SHORTWAVE SLIDING ACROSS THE UPPER
MISSISSIPPI RIVER VALLEY. THE BOUNDARY HOLDS MORE TO THE NORTH
THOUGH UNTIL LATER MONDAY NIGHT WHEN A SECONDARY...STRONGER PIECE OF
UPPER LEVEL ENERGY DIPS SOUTHEAST ACROSS THE REGION. INSTABILITY AND
WEAK MOISTURE TRANSPORT MAKES THE BOUNDARY A PRIME PLACE FOR SOME
SCATTERED SHRA/TS. ANY PCPN THAT DOES GET GOING WOULD HAVE THE
CHANCE FOR ENHANCED GUSTINESS...WITH A DRY NEAR SFC LAYER DEPICTED
IN BUFKIT SOUNDINGS FAVORING THE HIGHER GUST POTENTIAL.

EXPECT VFR CONDITIONS FOR MONDAY INTO MONDAY NIGHT...WITH PCPN
CHANCES LIKELY HOLDING OFF UNTIL MONDAY NIGHT - BETTER OVERNIGHT
INTO EARLY TUE MORNING. WILL PUSH THE VCSH SHOWER MENTION PAST
00Z...BUT CONFIDENCE FOR A SHRA/TS IS FOR THE OVERNIGHT HOURS.


&&

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

$$

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