Area Forecast Discussion
Issued by NWS La Crosse, WI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KARX 022014
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
314 PM CDT THU JUL 2 2015

.SHORT TERM...(TONIGHT THRU FRIDAY NIGHT)
ISSUED AT 314 PM CDT THU JUL 2 2015

MAIN FCST CONCERNS THIS PERIOD...RADIATIONAL FOG POTENTIAL LATE
TONIGHT EARLY FRI MORNING...SMALL SHRA/TSRA CHANCE NORTH FRI
AFTERNOON...TEMPERATURES.

DATA ANALYSIS AT 18Z HAD HIGH PRESSURE CENTERED OVER NORTHERN LK MI
WITH RIDGING WESTWARD ACROSS WI/SOUTHERN MN. SKIES RANGED FROM SUNNY
OVER NORTHEAST WI NEAR THE CENTER OF THE HIGH...TO CLOUDY WITH A FEW
SHOWERS OVER WESTERN IA CLOSER TO THE EDGE OF THE HIGH AND UNDER
SOME SHORTWAVE ENERGY DROPPING SOUTHEAST NEAR THE MO RIVER. TEMPS
AGAIN ON THE COOL SIDE FOR EARLY JULY WITH MOST EARLY AFTERNOON
READINGS IN THE UPPER 60S TO MID 70S...SOME 5F TO 10F BELOW NORMAL.

02.12Z MODELS INITIALIZED WELL AND OFFER SIMILAR SOLUTIONS AS WEAK
SHORTWAVES RIPPLE THRU THE NORTHWEST FLOW ALOFT OVER THE UPPER
MIDWEST. ONE OF THESE WAVE TO PASS WEST/SOUTH OF THE FCST AREA
TONIGHT...ANOTHER TO DROP ACROSS LK SUPERIOR FRI/FRI EVENING WITH
ONE MORE INTO SD BY 12Z SAT. TREND GENERALLY FAVORS A COMPROMISE OF
THE EARLIER RUNS ON THE TIMING/STRENGTH OF THESE FEATURES. SHORT
TERM FCST CONFIDENCE IS ON THE GOOD SIDE THIS CYCLE.

FOR THE SHORT TERM...MOISTURE/FORCING/LIFT WITH SHORTWAVE ENERGY
PASSING SOUTHEAST ACROSS IA REMAINS WEST/SOUTH OF THE FCST AREA
TONIGHT. HIGH PRESSURE REMAINS OVER MOST OF THE UPPER MIDWEST WITH
THE RIDGE AXIS EAST-WEST NEAR THE MN/IA BORDER TO LOWER MI. ANOTHER
FAVORABLE NIGHT FOR RADIATIONAL VALLEY FOG ACROSS THE FCST AREA WITH
LIGHT WINDS AND CLEAR/MOSTLY CLEAR SKIES. BUFKIT SOUNDINGS
INDICATING WINDS LESS THAN 10KTS UP TO 500MB TONIGHT...QUITE
FAVORABLE FOR RADIATIONAL FOG FORMATION IN THE 06Z-13Z PERI0D. SFC
OBS SHOWING SFC DEW POINTS A FEW DEGREES HIGHER THAN THOSE OF WED AT
THIS TIME. PREVIOUS GRID-SET ALREADY HAD VALLEY FOG IN THE 07Z-13Z
PERIOD AND THIS LOOKS GOOD. SHORTWAVE DROPPING ACROSS LK SUPERIOR
FRI/FRI EVENING DRAGS A WEAK BOUNDARY INTO NORTHERN WI FRI AFTERNOON
THEN INTO THE NORTH END OF THE FCST AREA FRI EVENING. SOME MOISTURE
INCREASE AND MUCAPE OF AROUND 500 J/KG EXPECTED TO ACCOMPANY THIS
BOUNDARY ACROSS NORTHERN WI. QUESTION IS WILL THERE BE ENOUGH WEAK
CONVERGENCE ALONG THE SFC-850MB FRONT/TROUGH TO INITIATE SHRA/TSRA
ALONG THE BOUNDARY. WILL CONTINUE WITH A SMALL SHRA/TSRA CHANCE
ACROSS THE NORTH END OF THE FCST AREA LATER FRI AFTERNOON/FRI
EVENING. INSTABILITY ALL BUT GONE BY LATE FRI EVENING AND WITH
LITTLE FORCING/LIFT LEFT OVERNIGHT HOURS OF FRI NIGHT DRY EVEN AS
THE BOUNDARY CONTINUES TO SAG SOUTH INTO THE FCST AREA. FAVORED
COOLER OF GUIDANCE LOWS TONIGHT THEN USED A BLEND OF GUIDANCE
HIGHS/LOWS FOR FRI/FRI NIGHT.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 314 PM CDT THU JUL 2 2015

FOR SATURDAY THRU SUNDAY NIGHT...

MAIN FCST CONCERNS THIS PERIOD...SMALL SHRA/TSRA CHANCES
SAT...SHRA/TSRA CHANCES WITH STRONGER APPROACHING TROUGH/FRONT SUN
NIGHT...TEMPERATURES.

MODEL RUNS OF 02.12Z IN GOOD AGREEMENT FOR THE SD SHORTWAVE TROUGH
TO MOVE EAST SAT/SAT NIGHT. TREND WEAKENS IT AS IT IS PUSHED EAST
INTO THE RIDGING/RISING HGTS ALOFT OVER MN/WI IA...AHEAD OF STRONGER
TROUGHING MOVING INTO SOUTH-CENTRAL CAN. HGTS RISE YET SUN MORNING
BEFORE STARTING TO FALL LATER SUN/SUN NIGHT AS A PORTION OF THE
CANADIAN TROUGH DIGS INTO THE NORTHERN PLAINS. CONSISTENCY REMAINS
GOOD WITH THE SHORTWAVE PUSHED INTO THE RIDGING SAT/SAT NIGHT WHILE
TRENDS A BIT SLOWER WITH THE TROUGHING INTO THE NORTHERN PLAINS
SUN/SUN NIGHT. WITH A TIGHTENING MODEL CONSENSUS THRU THE PERIOD...
SAT THRU SUN NIGHT FCST CONFIDENCE IS ON THE GOOD SIDE AS WELL.

SFC/LOW LEVEL TROUGH FROM FRI NIGHT IS OVER THE NORTH HALF OF THE
FCST AREA SAT. INSTABILITY BUILDS ALONG THIS BOUNDARY FOR SAT
AFTERNOON...WITH POTENTIAL FOR 1000-1500 J/KG MUCAPE. GIVEN THE
BOUNDARY...SOME WEAK BUT INCREASING SOUTH FLOW/MOISTURE TRANSPORT
INTO THE BOUNDARY AND THE APPROACHING SHORTWAVE...EXPANDED A SMALL
SHRA/TSRA CHANCE ACROSS THE NORTH HALF OF THE FCST AREA SAT
AFTERNOON. MAY YET NEED TO EXTEND THIS SMALL CHANCE INTO SAT EVENING
BUT STRONGER TROUGH INTO THE NORTHERN PLAINS AND STRENGTHENING
SOUTHERLY FLOW SHOULD LIFT THE BOUNDARY NORTH OF THE FCST AREA BY
SAT EVENING. HGTS RISE SAT NIGHT/SUN. MAIN MOISTURE TRANSPORT IS
WEST/NORTH OF THE FCST AREA BY MID EVENING SAT THRU SUN...WITH LOWER
LEVEL ANTI-CYCLONIC FLOW OVER THE AREA. REMOVED SMALL SHRA/TSRA
CHANCES FROM SUNDAY. WITH THE SLOWING TREND OF THE APPROACHING MID
LEVEL TROUGH AND THE SFC TROUGH/FRONT ONLY INTO NORTH-CENTRAL MN TO
EASTERN SD AT 00Z MONDAY...LIMITED SMALL SUNDAY EVENING SHRA/TSRA
CHANCES TO THE NORTHWEST END OF THE FCST AREA. REDUCED SHRA/TSRA
CHANCES AFTER MIDNIGHT SUN NIGHT AS WELL...AND LIMITED THEM TO THE
NORTHWEST 2/3 OF THE FCST AREA.

USED A BLEND OF THE GUIDANCE HIGHS/LOWS FOR SAT AND SAT/SUN NIGHTS.
WITH A DRIER TREND FOR SUNDAY AHEAD OF THE APPROACHING TROUGH...
ALONG WITH THE INCREASING SOUTH WINDS FOR MIXING AND 925MB TEMPS IN
THE 22-24C RANGE...TRENDED TOWARD WARMER OF GUIDANCE HIGHS ON SUN.

FOR MONDAY THRU THURSDAY...DAYS 4 TO 7...

MAIN FCST CONCERNS THIS PERIOD...SHRA/TSRA CHANCES WITH PASSING
FRONT MON INTO TUE AND AGAIN THU...TEMPERATURES.

MEDIUM RANGE MODEL RUNS OF 02.00Z/02.12Z IN GOOD AGREEMENT MON ON A
TROUGH TO MOVE EAST ACROSS THE REGION/SOUTH-CENTRAL CAN. TREND IS A
BIT SLOWER THAN THE EARLIER RUNS. BY TUE TREND ND DECENT CONSENSUS
FAVORS MORE PROGRESSIVE OF THE EARLY RUNS WITH THE TROUGH AXIS/MAIN
ENERGY SHIFTING EAST OF THE REGION. AGREEMENT REMAINS GOOD FOR ZONAL
FLOW/WEAK SHORTWAVE RIDGING OVER THE UPPER MIDWEST BY LATE TUE AND
TUE NIGHT. DIFFERENCES BEGIN TO SHOW UP WED WITH 02.12Z MODELS NOW
BRINGING A SHORTWAVE ACROSS THE CENTRAL PLAINS TOWARD THE AREA WED.
TROUGHING DIFFERENCES OVER THE NORTHERN PLAINS/UPPER MIDWEST
CONTINUE INTO THU. FCST CONFIDENCE IS AVERAGE TO GOOD MON/TUE THEN
AVERAGE WED/THU.

TIGHTENING CONSENSUS FOR THE SFC TROUGH/FRONT WITH THE MID LEVEL
TROUGHING TO PUSH INTO/ACROSS THE FCST AREA MON AFTERNOON/EVENING.
PW VALUES PROGGED TO BE IN THE 1.5 TO 2 INCH RANGE AHEAD OF THE
FRONT MON WITH AT LEAST A MODEST ROUND OF LOWER LEVEL THERMO-DYNAMIC
FORCING/LIFT AHEAD OF/WITH THE FRONT. SHRA/TSRA CHANCES IN THE 60-75
PERCENT RANGE MON INTO MON EVENING APPEAR QUITE REASONABLE AT THIS
TIME. FRONTAL TIMING WOULD BE FAVORABLE FOR A SEVERE RISK WITH TSRA
MON AFTERNOON/EVENING...HOWEVER DETAILS OF CAPE AND SHEAR OVER THE
AREA ON MONDAY ARE FAR FROM CERTAIN. WITH THE MID TROUGH TRENDING
PROGRESSIVE TUE ANY LINGERING SHRA/TSRA CHANCE ON TUE LOOKS TO BE
EARLY TUE MORNING...WITH DRIER/COOLER/MORE STABLE CAN HIGH PRESSURE
BUILDING IN FOR MUCH OF TUE THRU WED. INCREASING SOUTHERLY FLOW
AHEAD OF THE NEXT SYSTEMS CROSSING THE CENTRAL/NORTHERN PLAINS
SPREADS INCREASING MOISTURE INTO THE AREA WED NIGHT/THU. DUE TO THE
LESSER CONFIDENCE BY WED-THU...WILL LEAVE THE CONSENSUS SHRA/TSRA
CHANCES WED NIGHT/THU AS IS FOR NOW.

MODEL/ENSEMBLE CONSENSUS OF HIGHS/LOWS FOR MON-THU OKAY FOR NOW.
HOWEVER...MONDAY HIGHS MAY BE TOO WARM DEPENDING ON TIMING/ COVERAGE
OF THE SHRA/TSRA INTO THE AREA...WHILE TUE NIGHT LOWS MAY BE TOO
WARM WITH THE COOLER/DRIER CAN HIGHS CENTERED OVER THE REGION.

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1222 PM CDT THU JUL 2 2015

HIGH PRESSURE PROVIDING LIGHT WINDS AND MAINLY CLEAR SKIES ACROSS
THE REGION. ONLY EXCEPTIONS ARE THE HIGH CIRRUS WITH THE BULK OF
IT PASSING JUST TO THE SOUTHWEST OF BOTH AIRFIELDS...AND THE VEIL
OF SMOKE FROM THE CANADIAN WILDFIRES. PRIMARY CONCERN IS THE
POTENTIAL FOR VALLEY FOG AGAIN TONIGHT AT KLSE. SOUNDINGS SHOW
DEEP REGION OF LIGHT WINDS...EXTENDING UP TO 20KFT. SIMILAR TO
THIS MORNING...DEEP LIGHT WINDS...COOL TEMPERATURES...AND HIGH
PRESSURE WITH CLEAR SKIES POINT TO FAVORABLE CONDITIONS FOR VALLEY
FOG. LIMITING FACTOR REMAINS THE RELATIVE LACK OF MOISTURE IN THE
BOUNDARY LAYER. BUT THIS WAS OVERCOME LAST NIGHT...AND FEEL THIS
SCENARIO WILL REPEAT. THUS HAVE GONE AHEAD AND ADDED A PERIOD OF
1/2SM FG FOR KLSE EARLY IN THE MORNING.

&&

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

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION.....MW



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.