Area Forecast Discussion
Issued by NWS La Crosse, WI

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
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 150423
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1120 PM CDT SUN SEP 14 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 336 PM CDT SUN SEP 14 2014

CURRENTLY AS OF 20Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED RIDGING ALONG THE WEST COAST OF THE U.S. INTO BRITISH
CLIMB...WHILE DEEP TROUGHING ENCOMPASSED MUCH OF CENTRAL CANADA
INTO THE NORTHERN TIER OF THE CENTRAL U.S.. WITHIN THIS DEEP
TROUGH...THE TWO SHORTWAVE TROUGHS OF INTEREST WERE OVER LAKE
SUPERIOR AND IN SOUTHWEST SASKATCHEWAN. THE LAKE SUPERIOR
SHORTWAVE TROUGH WAS DRAGGING A COLD FRONT THROUGH THE FORECAST
AREA TODAY...BUT WITH LITTLE FAN FARE AS THE FRONT HAS BEEN
MOISTURE STARVED. 12Z SOUNDINGS FROM MPX AND ESPECIALLY GRB
REFLECT THE LACK OF MOISTURE. ADDITIONALLY...THE FRONT HAS BEEN
BASICALLY TURNING INTO A WIND SHIFT WITH 925MB TEMPS RUNNING
AROUND 10C ACROSS THE FORECAST AREA PER LATEST RAP ANALYSIS. THESE
TEMPS...BEING 2-4C WARMER THAN YESTERDAY...COMBINED WITH FULL SUN
HAS ALLOWED READINGS TO CLIMB INTO THE 60S. FARTHER TO THE
WEST...A SECONDARY COLD FRONT WAS DROPPING THROUGH NORTHWEST MN
WITH TEMPERATURES IN THE 50S AND SOME STRATUS IN ITS WAKE. AHEAD
OF THE FRONT...A STREAM OF MID CLOUDS WERE EXPANDING ACROSS
NORTHERN SOUTH DAKOTA INTO SOUTHERN MN...ASSOCIATED WITH MID-LEVEL
FRONTOGENESIS DOWNSTREAM OF THE SASKATCHEWAN SHORTWAVE. A 100 KT
JET STREAK FROM CENTRAL MN INTO UPPER MI AT 250MB IS ALSO
SUPPORTING THE MID CLOUDS.

MODELS ARE IN GOOD AGREEMENT TAKING THE SHORTWAVE OVER SOUTHWEST
SASKATCHEWAN THROUGH SOUTHWEST MN MONDAY MORNING AND ACROSS THE
FORECAST AREA MONDAY AFTERNOON. ADDITIONALLY...MODELS CONTINUE TO
SUGGEST THE SHORTWAVE WILL STRENGTHEN AS IT APPROACHES THE FORECAST
AREA...WHICH IN TURN INDUCES AN INCREASE IN THE UPPER JET STREAK
DOWNSTREAM AS WELL AS THE MID LEVEL FRONTOGENESIS. IN FACT...BY 12Z
MONDAY...THE SOUTHERN PORTION OF THE FORECAST AREA LIES IN A VERY
FAVORABLE DYNAMIC SITUATION...WITH A RIGHT ENTRANCE REGION OF THE
UPPER JET...DPVA AHEAD OF THE SHORTWAVE AND A FAIRLY STRONG COUPLET
OF MID LEVEL FRONTOGENESIS AND FRONTOLYSIS.

THE OVERALL BIG PROBLEM FOR PRECIPITATION IS MOISTURE. MOISTURE
TRANSPORT AHEAD OF THE SHORTWAVE WILL HELP PULL HIGHER PRECIPITABLE
WATER FROM THE SOUTHERN PLAINS TOWARDS THE REGION TONIGHT.
HOWEVER...CONVECTION SHOULD BREAK OUT ON THE NOSE OF THIS TRANSPORT
ACROSS NORTHERN MO...PUTTING A WALL UP ON THE MOISTURE RETURN.
STILL...PRECIPITABLE WATER SHOULD CLIMB UP TO ABOUT 1 INCH WHICH
WITH THE FORCING SHOULD BE ABLE TO SQUEEZE OUT SOME RAIN. DRY SUB-
CLOUD AIR MAY HINDER AMOUNTS TO SOME DEGREE.

TIMING WISE...SOME LIGHT RAIN COULD BREAK OUT AS EARLY AS THIS
EVENING...BUT THE BETTER CHANCE FOR RAIN COMES AFTER MIDNIGHT INTO
MONDAY MORNING. LOCATIONS AROUND AND SOUTH OF I-90 APPEAR TO HAVE
THE BEST CHANCE TO SEE RAIN. PRECIPITATION WILL DIMINISH RAPIDLY
MONDAY AFTERNOON AS THE SHORTWAVE MOVES THROUGH...WITH SKIES
CLEARING TOO.

REGARDING TEMPERATURES. THE SECONDARY COLD FRONT LOOKS TO PUSH
THROUGH THE FORECAST AREA TONIGHT...SENDING READINGS DOWN INTO THE
40S TO NEAR 50. IF THE CLOUDS STAYED IN ALL DAY MONDAY...HIGHS WOULD
STRUGGLE TO GET ABOVE THE MID 50S. HOWEVER...CONFIDENCE IS HIGH FOR
SUNSHINE IN THE AFTERNOON...WHICH SHOULD MUCH OF THE FORECAST AREA
CLIMB INTO THE UPPER 50S TO LOW 60S.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 336 PM CDT SUN SEP 14 2014

FROM LATE MONDAY NIGHT AND TUESDAY MORNING...CANADIAN HIGH
PRESSURE WILL BUILD ACROSS THE AREA. THIS HIGH WILL PROVIDE CLEAR
SKIES ACROSS THE AREA. WITH THE CENTER OF THIS HIGH PASSING TO
SOUTHWEST...THERE WILL BE A SHALLOW LAYER OF LIGHT WINDS BELOW 950
MB. MEANWHILE THE WINDS WILL BE IN THE 10 TO 15 KNOT RANGE BETWEEN
950 AND 800 MB. THESE WINDS MAY HINDER THE DEVELOPMENT OF FOG AND
FROST. HOWEVER IS A STRONG SHALLOW NOCTURNAL INVERSION CAN
DEVELOPMENT CANNOT RULE OUT EITHER FROM OCCURRING...SO INCLUDED A
MENTION OF PATCHY VALLEY FOG IN THE MISSISSIPPI TRIBUTARIES AND IN
CENTRAL WISCONSIN. IN ADDITION WITH TEMPERATURES IN THE MID 30S
ACROSS PARTS OF WESTERN WISCONSIN... THERE MAY BE PATCHY FROST
TOO.

FROM LATE TUESDAY NIGHT AND WEDNESDAY MORNING...THERE WILL BE A
DEEPER LAYER OF LIGHT WINDS /UP TO 800 MB/. THE NAM CONTINUES TO
PRODUCE A VERY SHALLOW SATURATED LAYER. MEANWHILE THE GFS DOES NOT
PRODUCE THIS. WITH THE LIGHT WINDS AND COOL TEMPERATURES OVER THE
WARM RIVER WATERS...EXPECT THAT THERE WILL PATCHY TO AREAS OF FOG
IN THE RIVER VALLEYS AND OVER THE CRANBERRY BOGS OF CENTRAL
WISCONSIN. DUE TO THIS INCLUDED...IT IN THE FORECAST GRIDS.

ON WEDNESDAY...A BACK DOOR COLD FRONT MOVES THROUGH THE FORECAST
AREA. THE GEM PRODUCES SOME LIGHT PRECIPITATION ALONG AND NORTH OF
INTERSTATE 94. MEANWHILE THE ECMWF AND GFS KEEPS THE AREA DRY.
WITH THE BUFKIT SOUNDINGS SHOWING ONLY ABOUT 50 MB OF MOISTURE
BETWEEN 800 AND 850 MB...KEPT THE FORECAST DRY.

FROM LATE WEDNESDAY NIGHT THROUGH THURSDAY MORNING...IT LOOKS LIKE
THERE WILL BE YET ANOTHER NIGHT FOR THE POTENTIAL OF VALLEY FOG AS
THE LIGHT WINDS ASCEND UP TO 700 MB. HOWEVER WITH THE WINDS
INCREASING INTO THE 10 TO 15 KNOTS LATE IN THE NIGHT...WE MAY END
UP WITH FOG DEVELOPING EARLIER IN THE NIGHT AND THEN BECOMING A
LAYER OF STRATUS AS THE LOW LEVEL WINDS INCREASE. DUE TO THIS
UNCERTAINTY...KEPT THE MENTION OF FOG OUT OF THE FORECAST GRIDS
FOR NOW.

FRIDAY INTO FRIDAY EVENING IS STARTING TO LOOK MORE INTERESTING AS
BOTH MODELS ARE STARTING TO CONVERGE ON A SOLUTION. A WARM FRONT
MOVES THROUGH THE AREA DURING THE MORNING AND THEN A COLD FRONT
MOVES INTO THE AREA ON FRIDAY EVENING. AS THE AREA MOVES INTO THE
WARM SECTOR OF THIS SYSTEM...THE ML CAPES CLIMB INTO THE 1500 TO
2500 J/KG RANGE. IN ADDITION...THE 0-6 KM SHEAR CLIMBS ABOVE 40
KNOTS. THIS COULD POTENTIALLY RESULT IN THE DEVELOPMENT OF SUPER
CELL THUNDERSTORMS WITH LARGE HAIL AND DAMAGING WINDS BEING THE
PRIMARY THREATS.

ON SATURDAY...THE 14.00Z MODELS SHOW A SURFACE LOW MOVING THROUGH
THE AREA. THIS KEEPS THE 0 TO 6 KM SHEAR ABOVE 45 KNOTS. WITH ML
CAPES IN THE 1000 TO 1500 J/KG...THERE COULD BE THE POTENTIAL FOR
SUPER CELL THUNDERSTORMS ACROSS NORTHEAST IOWA...AND SOUTHWEST AND
CENTRAL WISCONSIN. WITH 0-1 KM CAPES OVER 150 J/KG...LCL HEIGHTS
LESS THAN 2K FEET...AND 0-1 KM HELICITY OVER 100 M2/S2 ALONG THE
WARM FRONT WHICH IS LOCATED NEAR THE INTERSTATE 90 CORRIDOR IN
WISCONSIN...COULD NOT RULE THE POSSIBILITY OF ISOLATED TORNADOES
TO GO ALONG WITH THE THREAT FOR LARGE HAIL AND DAMAGING WINDS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1120 PM CDT SUN SEP 14 2014

NARROW BAND OF SHOWERS CONTINUES ACROSS SOUTHERN MN/WESTERN WI...IN
A REGION OF ELEVATED FRONTOGENETIC FORCING. PCPN IS FALLING OUT OF
MID LEVEL CLOUDS WITH NO VSBY RESTRICTIONS. AS AN UPPER LEVEL
SHORTWAVE STARTS TO PUSH IN FROM THE NORTHERN PLAINS OVERNIGHT...THE
PCPN WILL BECOME MORE WIDESPREAD AND START TO SINK SOUTH. LOW LEVEL
RH INCREASES...PER BUFKIT SOUNDINGS...AND CONDITIONS LOOK FAVORABLE
FOR A DROP INTO MVFR CIGS FOR A FEW HOURS.

MESO MODELS TAKE THIS SYSTEM ACROSS THE REGION DURING THE
AFTERNOON...EXITING BY EARLY EVENING. PCPN SHOULD FOLLOW SUIT...BUT
A BIT EARLIER...MOVING EAST/SOUTHEAST OF THE TAF SITES BETWEEN 15-
18Z. SUBSIDENCE POST THE SHORTWAVE...ALONG WITH A SFC HIGH
INFLUENCING FROM THE CENTRAL PLAINS...SHOULD CLEAR SKIES LATER MON
AFTERNOON.

SEE A POTENTIAL FOR RIVER VALLEY FOG AT KLSE FOR TUE MORNING. WITH
EARLY MORNING PCPN...CLEARING SKIES...AND THEN A LIGHT WIND FIELD
MONDAY NIGHT...THE SETUP LOOKS GOOD. BIGGEST QUESTION MARK AT THIS
TIME WOULD APPEAR TO BE THE DEPTH OF THE LIGHT WIND LAYER. 00Z NAM
BUFKIT SOUNDINGS ARE SHALLOW FOR THE EVENING HOURS...BUT QUICKLY
DEEPENS OVERNIGHT. COULD BE ENOUGH FOR SUB 1SM VSBY FOG - PERHAPS
1/4SM.


&&

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

$$

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



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