Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 211003
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
505 AM CDT MON JUL 21 2014

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 301 AM CDT MON JUL 21 2014

MAIN FORECAST CONCERN IS WITH THE RAIN CHANCES TONIGHT INTO
TUESDAY.

A WEAK COLD FRONT EXTENDED ACROSS NORTHERN MINNESOTA INTO NORTH
DAKOTA EARLY THIS MORNING. THIS FRONT IS NOT EXPECTED TO MOVE MUCH
TODAY AND THEN BECOME THE FOCUS FOR A MCS TO DEVELOP TONIGHT. A
SHORT WAVE TROUGH CURRENTLY OVER THE PACIFIC NORTHWEST AND ANOTHER
OVER NEVADA WILL MOVE EAST/NORTHEAST REACHING SOUTHERN
SASKATCHEWAN AND THE HIGH PLAINS RESPECTIVELY. THE COMBINED
FORCING FROM THESE WAVES WILL CAUSE STORMS TO DEVELOP ALONG THE
FRONT OVER NORTH DAKOTA TODAY AND THEN MOVE EAST TONIGHT. THE PATH
THAT THE MCS TAKES IS STILL SOMEWHAT IN QUESTION...BUT BETTER
AGREEMENT NOW BETWEEN THE 21.00Z HI-RES ARW...NMM...NAM AND 20.12Z
ECMWF THAT THE BULK OF THIS MCS SHOULD PROPAGATE EAST ACROSS
MINNESOTA TOWARD THE U.P. OF MICHIGAN. THE SHORT WAVE TROUGHS WILL
CONTINUE TO MOVE EAST/NORTHEAST TONIGHT CONCENTRATING THEIR LIFT
NORTH OF THE AREA. ALL THE MODELS SHOW THE LOW LEVEL JET
INTENSIFYING OVERNIGHT WITH THIS PASSING THROUGH THE AREA WITH THE
NOSE OF THE MOISTURE TRANSPORT ACROSS THE U.P. OF MICHIGAN. THE
FORWARD PROPAGATING CORFIDI VECTORS ALSO SUGGEST AN EASTWARD
MOVEMENT OF THE COMPLEX.

OF SOME CONCERN THOUGH...IS THE EASTERN AND CONVERGENT SIDE OF
THE MOISTURE TRANSPORT AXIS WILL BE OVER THE AREA. GOOD CAPE WILL
STILL RESIDE OVER THE FORECAST AREA TONIGHT WITH THE NAM SHOWING
BETWEEN 1500 AND 2500 J/KG OF ML CAPE FROM EAST TO WEST AT 09Z
TONIGHT. THIS IS LIKELY A LITTLE ON THE HIGH SIDE AS ALL THE
MODELS ARE PROBABLY TOO HIGH WITH AFTERNOON DEW POINTS AND THEN
KEEP THESE ANOMALOUSLY HIGH DEW POINTS THROUGH THE NIGHT. THE
MODELS SUGGEST DEW POINTS WILL JUMP 5 TO 7 DEGREES THIS AFTERNOON
OVER THE AREA FROM EVAPOTRANSPIRATION AND MIXING...PUSHING THEM
INTO THE UPPER 70S TO ALMOST 80 AND THEN MAINTAIN THESE HIGH DEW
POINTS. WOULD EXPECT LOWER TO MIDDLE 70S DEW POINTS TO BE MORE
REASONABLE CUTTING THE CAPE BACK TO MAYBE 1500 OR 2000 J/KG
OVERNIGHT. WITH THE MOISTURE TRANSPORT TROUGH THE CAPE
AXIS...COULD SEE SOME SCATTERED ACTIVITY DEVELOP.

AS FOR A SEVERE THREAT...FORECAST SOUNDINGS SHOW A STRONG CAP
DEVELOPS DURING THE DAY TODAY BETWEEN 850 AND 750 MB AND REMAINS
IN PLACE THROUGH THE NIGHT. WOULD THUS EXPECT THE ACTIVITY TONIGHT
TO BE ELEVATED BUT STILL PLENTY OF SHEAR IN PLACE. THE FORECAST
SOUNDING FOR LADYSMITH SUGGEST AROUND 50 KNOTS OF SHEAR ABOVE THE
CAP UP TO 6 KM WITH A PRETTY STRAIGHT HODOGRAPH. DAMAGING WINDS
AND HEAVY RAINS LOOK TO BE MAIN THREATS AS LIFTING ABOVE THE CAP
SHOWS A DEEP BUT SKINNY CAPE PROFILE WHICH SHOULD LIMIT THE HAIL
PRODUCTION. THE HEAVY RAIN THREAT IS ALSO INDICATED BY
PRECIPITABLE WATERS POSSIBLY APPROACHING 2 INCHES AND WARM CLOUD
DEPTHS OF 4.5 KM.

THE FRONT IS EXPECTED TO MOVE THROUGH THE AREA TUESDAY WITH SOME
UNCERTAINTY ON HOW MUCH CONVECTION MAY OR MAY NOT DEVELOP ALONG
IT. THE MAIN SHORT WAVE TROUGH WILL CONTINUE AWAY FROM THE AREA
INTO ONTARIO WITH SOME SUGGESTIONS BY THE NAM AND GFS OF A
TRAILING SHORT WAVE TROUGH THAT MAY NOT BE ABLE TO INTERACT WITH
THE FRONT UNTIL IT IS EAST OF THE AREA. ALSO...THE LARGE SCALE
WESTERLIES SHOULD ALLOW THE CAP TO REMAIN IN PLACE AHEAD OF THE
FRONT AND REALLY LIMIT THE AMOUNT OF ACTIVITY THAT DEVELOPS OVER
THE AREA.

OVERALL...HAVE LIMITED THE RAIN CHANCES TONIGHT TO AFTER 06Z AND
CONCENTRATED THE HIGHEST CHANCES TO ACROSS THE FAR NORTH WITH 60
TO 70 PERCENT CHANCES WITH THE REST OF THE AREA IN THE 20 TO 50
PERCENT RANGE. EXPECT THE REMAINS OF THE MCS TO MOVE OFF QUICKLY
TUESDAY MORNING AND DROPPED THE RAIN CHANCES BACK TO 30 TO 50
PERCENT EAST OF THE MISSISSIPPI RIVER. WILL SHOW SOME SMALL
CHANCES ACROSS THE ENTIRE AREA TUESDAY AFTERNOON...20 TO 40
PERCENT FROM WEST TO EAST...BUT CONFIDENCE OF ANYTHING DEVELOPING
ALONG THE FRONT IS LOW.

NO CHANGES PLANNED TO THE HEAT ADVISORY. THE FAR WESTERN SECTIONS
OF THE FORECAST AREA COULD SEE THE HEAT INDEX REACH 100 OR A
LITTLE OVER FOR A SHORT WHILE THIS AFTERNOON INTO THE EARLY
EVENING.

.LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 301 AM CDT MON JUL 21 2014

THE NEXT SIGNIFICANT CHANCE FOR RAIN COMES IN FOR THE END OF THE
WEEK INTO THE WEEKEND. THE UPPER LEVEL RIDGE THAT BUILDS OVER THE
ROCKIES EARLY THIS WEEK GETS FLATTENED BY AN UPPER LEVEL LOW
MOVING ACROSS CANADA. THIS ALLOWS A ZONAL TO NORTHWEST FLOW TO
DEVELOP OVER THE UPPER MIDWEST WITH SOME SHORT WAVE TROUGHS
EXPECTED TO PASS ACROSS THE REGION. THE FIRST OF THESE IS EXPECTED
TO BRING A ROUND OF RAIN FROM FRIDAY INTO SATURDAY AS A SURFACE
LOW MOVES SOUTHEAST FROM THE DAKOTAS TOWARD THE OHIO RIVER VALLEY.
THE NEXT CHANCE WILL BE SUNDAY WITH ANOTHER SHORT WAVE TROUGH.
HOWEVER...THE SURFACE LOW WITH THIS WAVE...MAY PASS BY THE AREA TO
THE NORTHEAST AND TAKE THE BEST CHANCES ACROSS THE GREAT LAKES AND
POINTS EAST.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 505 AM CDT MON JUL 21 2014

VFR CIGS IN THE 3-4 KFT RANGE WILL BREAK UP/EXIT EAST TOWARD 17-
18Z...LEAVING SCT SKIES FOR THE AFTERNOON HOURS. SOME MIXING WILL
RESULT IN GUSTINESS...BUT DON/T EXPECT MUCH MORE THAN 20-25 KTS FOR
GUSTS.

STORM COMPLEX DEVELOPS OVER THE NORTHERN PLAINS THIS
AFTERNOON...MOVING EAST/SOUTHEAST ACROSS THE UPPER MISSISSIPPI RIVER
VALLEY OVERNIGHT. LATEST MODEL TRENDS FAVOR KEEPING THE BULK OF THIS
MCS TO THE NORTH...OVER CENTRAL MN INTO NORTHWEST WI. THAT SAID...A
GOOD AMOUNT OF INSTABILITY AND A RIBBON OF LOW LEVEL MOISTURE
TRANSPORT WILL BE ACROSS THE TAF SITES. SOME INDICATIONS THAT SOME
CONVERGENCE AHEAD OF AN APPROACHING COLD FRONT COULD SPARK SHRA/TS
BEFORE 12Z AT KRST/KLSE. CONFIDENCE NOT HIGH IN HOW WIDESPREAD THIS
ACTIVITY WILL BE. CAN/T RULE OUT A MORE SOUTHEAST PUSH OF THE MCS
EITHER. WILL ADD VCSH TO THE FORECAST FOR NOW...WITH LATER FORECASTS
REFINING THE DETAILS.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...HEAT ADVISORY FROM 11 AM THIS MORNING TO 9 PM CDT THIS EVENING
     FOR MNZ079-086-087-094-095.

IA...HEAT ADVISORY FROM 11 AM THIS MORNING TO 9 PM CDT THIS EVENING
     FOR IAZ008-009-018-019.

&&

$$

SHORT TERM...04
LONG TERM....04
AVIATION.....RIECK


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