000
FXUS63 KARX 181751
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1251 PM CDT TUE JUN 18 2013

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 337 AM CDT TUE JUN 18 2013

MAIN FORECAST CONCERNS THIS PACKAGE...SHRA/TSRA CHANCES EARLY THIS
MORNING/TODAY...TEMPERATURES THRU THE PERIOD.

06Z DATA ANALYSIS HAD HIGH PRESSURE OVER NORTHERN MN/LK SUPERIOR. A
WEAK TROUGH/COLD FRONT EXTENDED FROM THE MN/ND BORDER SOUTHEAST TO
A WEAK LOW OVER CENTRAL IL. SOME CLOUDS OVER MN/WI NORTH/EAST OF THE
FRONT BUT MAIN FEATURE EARLY THIS MORNING WAS A VIGOROUS MID LEVEL
SHORTWAVE SEEN IN WV IMAGERY OVER EASTERN SD/SOUTHWEST MN. THIS
FEATURE AND SOME WEAK INSTABILITY/CONVERGENCE NEAR THE TROUGH/FRONT
PRODUCING A GENERALLY INCREASING AREA OF SHRA/TSRA OVER WEST
CENTRAL INTO SOUTH-CENTRAL MN. ONE STRONG SUPER-CELL WAS LOCATED
SOUTH OF KRWF...JUST AHEAD OF THE SHORTWAVE. ON THE OTHER SIDE...
TEMPS NEAR THE CENTER OF THE HIGH OVER NORTHEAST MN/FAR NORTHEAST
WI WERE IN THE 30S/40S.

NO BIG ERRORS NOTED WITH 18.00Z MODEL INITIALIZATIONS. SOLUTIONS
QUITE SIMILAR FOR TODAY THRU WED...BUT THERE ARE SOME SMALL SCALE
DIFFERENCES WITH CONVECTION AS THE SHORTWAVE PASSES THIS MORNING.
DPROG/DT OF 500MB HGTS AT 18.00Z SHOWED THE MODEL RUNS OF 16.00Z AND
17.00Z VERIFIED REASONABLY WELL ACROSS NOAM HOWEVER ALL WERE TOO
WEAK...ESPECIALLY 16.00Z RUNS...WITH THE SHORTWAVE DROPPING ACROSS
THE DAKOTAS. TREND REMAINS CONSISTENT FOR THE VIGOROUS SHORTWAVE TO
PASS THIS MORNING AND SHORTWAVE RIDGING TO BE BUILDING IN FOR THE
AFTERNOON. HGTS CONTINUE TO RISE TONIGHT/WED AS THE EASTERN PAC MID
LEVEL LOW MOVES INTO THE NORTHWEST CONUS AND PUSHES THE RIDGING
AHEAD OF IT EASTWARD ACROSS THE CENTRAL/NORTHERN PLAINS. MODELS
REMAIN CONSISTENT TRYING TO SQUEEZE A SHORTWAVE EASTWARD ACROSS THE
CENTRAL PLAINS WED...THRU THE RIDGE AXIS...WITH PERHAPS A SLIGHT BIT
OF SLOWING WITH THIS FEATURE. CHECK OF OBS VS. MODEL DATA AT 06Z
SHOWED ALL TO BE REASONABLE WITH THE SFC MASS FIELDS OVER THE
CENTRAL CONUS. MODELS GENERALLY STRUGGLING ON THE CONVECTION AHEAD
OF THE SHORTWAVE...SOME OKAY WITH AMOUNTS...SOME OKAY WITH LOCATION/
COVERAGE. NO ONE CLEAR MODEL FAVORITE AND SIDED WITH A MODEL/
ENSEMBLE CONSENSUS. SHORT-TERM FCST GENERALLY GOOD THIS CYCLE.

SD/MN SHORTWAVE MOVES TO BETWEEN KDBQ-KDVN AT 18Z THEN TO NEAR THE
IN/IL BORDER BY 00Z WED. MAIN 500-300MB PV ADVECTION WITH THIS WAVE
AND SOME 300MB AGEOSTROPHIC MOTION/DIVERGENCE IN LEFT EXIT REGION
OF A 70-80KT JET MAX PASS OVER THE SOUTHWEST 1/3 TO 1/2 OF THE FCST
AREA CENTERED ON 12Z THIS MORNING. LOWER LEVEL THERMO-DYNAMIC FORCING
INDICATED TO BE WEAK WITH 25-850MB DOMINATED BY COLD ADVECTION ACROSS
THE AREA...NORTH/EAST OF THE COLD FRONT/SFC TROUGH. THUS BULK OF THE
FORCING/LIFT FOR THE SHRA/TSRA THIS MORNING IS MID/UPPER LEVEL.
DISTANCE-SPEED TOOL APPLIED TO CONVECTION WEST OF KMSP TRACKS IT
ACROSS THE SOUTHWEST END OF THE FCST AREA IN THE 12-16Z TIME-FRAME.
WITH THE JET-MAX ROUNDING THE BASE OF THE TROUGH THIS MORNING...
WILL LEAVE SOME 20-30 PERCENT SHRA/TSRA CHANCES OVER THE WEST END OF
THE FCST AREA BEFORE 12Z WITH POTENTIAL FOR ADDITIONAL CONVECTION
DEVELOPING EASTWARD. CARRIED 20-50 PERCENT SHRA/TSRA CHANCES ACROSS
ROUGHLY THE SOUTHWEST HALF OF THE FCST AREA THIS MORNING...TRENDING
QUICKLY DOWNWARD AFTER 18Z WITH PASSAGE OF THE SHORTWAVE/MID LEVEL
TROUGH AXIS.

QUIET WEATHER/CLEARING SPREAD SOUTH ACROSS THE FCST AREA FOR THIS
AFTERNOON. DRY WEATHER EXPECTED TONIGHT/WED AS THE MN/LK SUPERIOR
HIGH DRIFTS SOUTHEAST TO LOWER MI AND WEAK RIDGING EXTENDS WEST
INTO WI. A COOL NIGHT TONIGHT WITH CLEAR SKIES/LIGHT WINDS UNDER THE
HIGH/RIDGE AXIS. CLOSER TO THE CENTER OF THE HIGH...SFC DEW POINTS
LOOKING TO DROP INTO THE 40S ACROSS WI TONIGHT...ALLOWING FOR
STRONG RADIATIONAL COOLING. SOME MODIFICATION OF THE AIRMASS OVER
NORTHEAST MN/FAR NORTHEAST WI THIS MORNING EXPECTED TODAY...BUT
LOWS TONIGHT ALONG/NORTHEAST OF I-94 LOOKING TO DROP INTO THE LOW/
MID 40S...WITH PERHAPS SOME UPPER 30S IN THE NORMALLY COLDER/LOW
LAYING AREAS. LOW LEVEL WARM ADVECTION QUICKLY RETURNS WED. WITH
PLENTY OF SUNSHINE EXPECTED...STRONG DIURNAL WARMING WILL SEND WED
HIGHS BACK TO NEAR NORMAL EVEN AFTER THE CHILLY START. MAIN LOWER
LEVEL MOISTURE/INSTABILITY AXIS REMAIN WELL WEST OF THE AREA WED AND
LEFT RAIN CHANCES FOR WED NEAR ZERO.

.LONG TERM...(WEDNESDAY NIGHT THROUGH MONDAY)
ISSUED AT 337 AM CDT TUE JUN 18 2013

MAIN CONCERNS FOR THE LONG-TERM PERIOD ARE SHRA/TSRA CHANCES THRU
MOST OF THE PERIOD...INCREASING TEMPERATURES BY THE WEEKEND.

MODELS REMAIN QUITE SIMILAR WITH DECENT RUN-TO-RUN CONSISTENCY WED
NIGHT/THU AS THE AS THE WEAK RIDGE-CROSSING SHORTWAVE MOVES ACROSS
THE MID/UPPER MS VALLEY. LARGER SCALE CONSISTENCY REMAINS GOOD FOR
THU NIGHT INTO FRI...BUT SMALLER SCALE/DETAIL DIFFERENCES ON THE
INCREASE. CONTINUED TO FAVOR THE MODEL/ENSEMBLE CONSENSUS FOR THE
WED NIGHT-THU NIGHT PERIOD WITH FCST CONFIDENCE IN THIS PERIOD
AVERAGE.

HEAT/MOISTURE/INSTABILITY INCREASE ACROSS THE AREA WED NIGHT INTO
THU NIGHT. THIS ALONG WITH INCREASING 925-850MB WARM ADVECTION/
MOISTURE TRANSPORT AND PW VALUES INCREASING INTO THE 1.5 TO 1.75
INCH RANGE BY THU NIGHT. THEN THERE IS THE SHORTWAVE WHICH ALL
MODELS PUSH THRU THE RIDGE AND INTO/ACROSS THE REGION LATER WED
NIGHT AND THU. GIVEN THE MODEL DETAIL DIFFERENCES WITH MOISTURE AND
UNSTABLE LAYERS IN SOUNDINGS...AND WHERE MODELS MAY OR MAY NOT
INITIATE CONVECTIVE COMPLEXES TO MOVE ACROSS THE UPPER MIDWEST...
LEFT SHRA/TSRA CHANCES IN THE 20-30 PE RECENT RANGE FOR LATER WED
NIGHT/THU AND 20-40 PERCENT RANGE THU NIGHT FOR NOW.

MEDIUM RANGE MODEL RUNS OF 18.00Z IN REASONABLE AGREEMENT ON THE BIG
PICTURE OF WESTERN NOAM TROUGHING AND EASTERN NOAM RISING HGTS/
RIDGING FOR FRI THRU MON. THIS LEAVES THE AREA UNDER SOME FORM OF
SOUTHWEST FLOW ALOFT...AND A RATHER UNSETTLED WEATHER PERIOD FOR
THE DAY 4-7 PERIOD. DETAIL DIFFERENCES OF SHORTWAVES THRU THE FLOW...
WHERE OR WHERE NOT CONVECTIVE COMPLEXES MAY GENERATE AND MOVE AMONG
THE MODELS HAVE SIZABLE IMPACTS ON THE SENSIBLE WEATHER FOR THE
AREA DURING THIS TIME PERIOD. CONFIDENCE RATHER GOOD THAT RAIN WILL
OCCUR ON ONE OR MORE OF THE DAY 4-7 DAYS...BUT CONFIDENCE LOW ON
WHICH ONES THESE WILL ACTUALLY BE.

THE DEEP LAYERED SOUTH TO SOUTHWEST FLOW...WITH SOME FORM OF LOW
PRESSURE IN THE PLAINS...WILL CONTINUE TO ADVECT A MOIST/UNSTABLE
AIRMASS INTO THE UPPER MIDWEST THRU THE FRI-MON PERIOD. MODELS
INITIATE SEVERAL ROUNDS OF SHRA/TSRA DURING THIS TIME...BUT AGAIN
DETAIL DIFFERENCES OF WHERE SFC FRONTS/TROUGHS END UP AND WHEN
STRONGER SHORTWAVES IN THE FLOW PASS ACROSS THE AREA...IMPACT WHEN
AND WHERE THESE SHRA/TSRA WILL OCCUR. LEFT THE MODEL/ENSEMBLE
CONSENSUS SHRA/TSRA CHANCES MOSTLY IN THE 30-50 PERCENT RANGE FOR
FRI-MON AS IS...AS CONFIDENCE IN ANY ONE MODEL BEING MORE CORRECT
THAN THE OTHERS ON THE DETAILS IS LOW. THIS PERIOD WILL ALSO HAVE TO
BE WATCHED FOR REPEATED TSRA AND HEAVY RAINS AS PW VALUES LOOK TO
REMAIN IN THE 1.5 TO 1.75 INCH RANGE. MORE HYDRO DETAILS TO COME IN
THE FOLLOWING DAYS. PERSISTENT SOUTH/SOUTHWEST FLOW AND LOW LEVEL
WARM ADVECTION WILL PULL AN INCREASINGLY WARMER AIRMASS INTO THE
REGION. DEPENDING ON SHRA/TSRA AND CLOUD TRENDS ANY ONE DAY...AND HOW
DEEPLY THE AIRMASS MAY MIX...850MB TEMPS BY FRI WOULD SUPPORT HIGHS
OF AROUND 90 OR WARMER THRU THE WEEKEND INTO EARLY NEXT WEEK. AT
THIS TIME...WILL STAY CLOSE TO THE MODEL/ENSEMBLE CONSENSUS OF
HIGHS/LOWS FOR FRI-MON.

&&

.AVIATION...THROUGH 18Z WEDNESDAY
1251 PM CDT TUE JUN 18 2013

A FEW SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE THIS AFTERNOON
GENERALLY SOUTHEAST OF A DODGE CENTER MINNESOTA TO RICHLAND CENTER
LINE. OTHERWISE HIGH PRESSURE WILL PROVIDE VFR CONDITIONS AT THE
TAF SITES.

&&

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

&&

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION...BOYNE