Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 211725
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1225 PM 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 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1225 PM CDT MON JUL 21 2014

GOOD VFR CONDITIONS WILL PREVAIL THIS AFTERNOON AND EVENING AS
DIURNAL WARMING INCREASES THE MIXING DEPTH...WITH ANY CUMULUS IN THE
4K-5K FT RANGE. INCREASED MIXING SHOULD KEEP THE BOUNDARY LAYER HAZE
TO A MINIMUM AS WELL. THE DEEPER MIXING AND MDT PRESSURE GRADIENT
ACROSS THE AREA WILL RESULT IN SOME WIND GUSTS IN THE 20KT RANGE AT
BOTH KRST/KLSE THIS AFTERNOON.

A STORM COMPLEX IS STILL EXPECTED TO DEVELOP OVER EASTERN ND/
NORTHERN MN THIS EVENING. BULK OF THE FORCING TAKES THIS COMPLEX
EAST-SOUTHEAST ACROSS MN/NORTHERN WI OVERNIGHT/EARLY TUE MORNING. A
COUPLE OF MODEL SOLUTIONS BRING THIS COMPLEX SOUTHEAST DOWN THE MS
RIVER OVERNIGHT...AND INTO THE KLSE/KRST AREAS IN THE 09Z-12Z TIME
FRAME. THIS LOOKS RATHER UNLIKELY WITH VERY WARM TEMPERATURES AROUND
700MB CAPPING THE AIRMASS OVER SOUTHEAST MN/SOUTHWEST WI TONIGHT AND
THE MAIN FORCING OVER NORTHERN WISCONSIN. LEFT THE KRST TAF DRY LATE
TONIGHT AND ONLY CARRIED A 10-13Z VCSH MENTION AT KLSE. GRADIENT
WINDS OF 10-15KTS TONIGHT SHOULD KEEP LATE NIGHT BR TO A MINIMUM. A
COLD FRONT DROPS ACROSS THE AREA TUE...AROUND 15Z AT KRST AND 18Z AT
KLSE. FRONT WILL BRING A SWITCH TO NORTHWEST WINDS AND A DRIER LOW
LEVEL AIRMASS TO THE TAF SITES LATER TUE MORNING/TUE AFTERNOON.

&&

.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.....RRS



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