Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 231711
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1211 PM CDT THU JUL 23 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 248 AM CDT THU JUL 23 2015

MAIN FORECAST CONCERNS ARE ON SHOWER AND THUNDERSTORM CHANCES FRIDAY
THROUGH SATURDAY MORNING WITH THE POTENTIAL FOR A FEW STRONG TO
SEVERE STORMS.

LATEST SURFACE OBSERVATIONS SHOWED MOSTLY CLEAR SKIES ACROSS THE
FORECAST AREA THIS MORNING WITH HIGH PRESSURE IN CONTROL. THE CLEAR
SKIES AND A LIGHT WIND LAYER FROM THE SURFACE THROUGH AROUND 10 KFT
HAS SET THE STAGE FOR PATCHY FOG ALONG RIVER VALLEYS AND CENTRAL
WISCONSIN CRANBERRY COUNTRY. THE FOG SHOULD QUICKLY DISSIPATE
THIS MORNING AFTER THE ONSET OF SURFACE HEATING. LOOKING AT
FORECAST  SOUNDINGS TODAY...WE SHOULD SEE A FEW CUMULUS CLOUDS
DEVELOP...OTHERWISE HIGH PRESSURE WILL CONTINUE TO DOMINATE THE
WEATHER PATTERN WITH DRY AND QUIET CONDITIONS. THE HIGH WILL START
TO SLIDE OFF TO THE EAST TONIGHT INTO FRIDAY MORNING AS A COLD
FRONT EDGES EAST ACROSS THE DAKOTAS. THE PRESSURE GRADIENT WILL
TIGHTEN ACROSS THE UPPER MISSISSIPPI RIVER VALLEY TONIGHT AND THIS
SHOULD CREATE UNFAVORABLE CONDITIONS FOR VALLEY FOG DEVELOPMENT
DESPITE MOSTLY CLEAR SKIES. FORECAST SOUNDINGS SHOW WINDS
INCREASING TO AROUND 20 TO 23 KTS AT 500-1000 FT TONIGHT HELPING
TO PROMOTE MIXING. PLAN ON A SEASONABLY WARM DAY TODAY WITH HIGHS
IN THE LOWER TO MID 80S. LOOK FOR LOWS TONIGHT IN THE LOWER TO MID
60S.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 248 AM CDT THU JUL 23 2015

A MOIST AND UNSTABLE AIRMASS WILL MOVE INTO THE REGION FRIDAY INTO
FRIDAY NIGHT AHEAD OF AN APPROACHING COLD FRONT. SHOWERS AND
THUNDERSTORMS LOOK TO DEVELOP OVER THE EASTERN DAKOTAS/WESTERN
MINNESOTA LATE THURSDAY NIGHT INTO FRIDAY MORNING THEN EDGE EAST
TOWARD THE FORECAST AREA FRIDAY MORNING. 0-1 KM MUCAPE VALUES LOOK
TO CLIMB INTO THE 2500 TO 3500 J/KG RANGE AHEAD OF THE FRONT. 0-3
KM BULK SHEAR VALUES ARE EXPECTED TO INCREASE TO 30 TO 35 KTS.
STORMS COULD BE ONGOING FRIDAY MORNING MAINLY WEST OF THE
MISSISSIPPI RIVER BUT WE COULD THEN SEE ADDITIONAL  DEVELOPMENT
ALONG THE COLD FRONT AS IT MOVES IN. THE BIG QUESTION FOR FRIDAY
IS WHAT IMPACT WILL THE FRIDAY MORNING STORMS HAVE ON THE
ATMOSPHERE AND WHETHER OR NOT IT WILL RECOVER FOR THE AFTERNOON
STORMS. THE LOW LEVEL JET WOULD SUGGEST THE STORMS WILL PERSIST
ACROSS PORTIONS OF SOUTHEAST  MINNESOTA...WESTERN WISCONSIN...AND
PERHAPS NORTHEAST IOWA THROUGH ABOUT MID MORNING ON FRIDAY BEFORE
WEAKENING. DEEP LAYER SHEAR THEN INCREASES FRIDAY AFTERNOON INTO
FRIDAY EVENING AS MID TO UPPER LEVEL WINDS INCREASE ACROSS THE
REGION. NOW...IF STORMS CAN REDEVELOP ALONG THE COLD FRONT FRIDAY
AFTERNOON INTO FRIDAY EVENING...SOME OF THESE STORMS COULD BECOME
SEVERE AND POTENTIALLY BE SUPERCELLS...WITH LARGE HAIL AND
DAMAGING WINDS. A LOT OF DETAILS TO BE WORKED OUT AS WE APPROACH
FRIDAY. KEEP A CLOSE EYE ON THE FORECAST AS WE DRAW CLOSER TO
FRIDAY AS DETAILS BECOME MORE CLEAR.

THE FRONT THEN PUSHES SOUTH OF THE FORECAST AREA BY LATE SATURDAY
MORNING LEADING TO A PLEASANT SATURDAY AFTERNOON AND SATURDAY
NIGHT AS WEAK HIGH PRESSURE MOVES IN. THE HIGH WON/T STICK AROUND
LONG AS IT LOOKS TO SLIDE EAST OF THE REGION ON SUNDAY WITH
MOISTURE RETURNING ON THE BACK SIDE OF THE HIGH. A SERIES OF WEAK
SHORTWAVES THEN LOOK TO INTERACT WITH THIS MOIST AND UNSTABLE
AIRMASS ON SUNDAY BRINGING CHANCES FOR SHOWERS AND STORMS TO THE
REGION. PLAN ON SEASONABLY WARM TEMPERATURES THROUGH THE WEEKEND
WITH HIGHS IN THE MID TO UPPER 80S. SHORTWAVES WILL CONTINUE TO
INTERACT WITH THE MOIST AND UNSTABLE AIRMASS MONDAY NIGHT THROUGH
TUESDAY NIGHT WITH MORE CHANCES FOR SHOWERS AND STORMS.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1211 PM CDT THU JUL 23 2015

SHORT WAVE TROUGH CURRENTLY COMING ACROSS MONTANA AND WYOMING IS
EXPECTED TO CONTINUE MOVING EAST/NORTHEAST THROUGH THE PERIOD OVER
THE TOP OF THE UPPER LEVEL RIDGE THAT IS IN PLACE OVER THE CENTRAL
PART OF THE COUNTRY. THE 23.12Z NAM SUGGESTS THE BEST FORCING FROM
THIS WAVE WILL REMAIN TO THE NORTH OF BOTH TAF SITES BUT THERE
COULD STILL BE SOME WEAK TO MODERATE PV ADVECTION IN THE 500-300
MB LAYER THAT COMES ACROSS AFTER 12Z. THE LOW LEVEL MOISTURE
TRANSPORT AXIS WILL BE THROUGH THE AREA AS IT IS PULLED NORTH
TOWARD THE SHORT WAVE TROUGH...BUT THE LOCAL AREA SHOULD STILL GET
INTO THE EASTERN AND CONVERGENT SIDE OF THIS AXIS AFTER 12Z.
EXPECTING A COMPLEX OF STORMS TO DEVELOP OVER THE DAKOTAS TODAY
AND THEN MOVE EAST WITH THE WAVE AND MOISTURE TRANSPORT. THE
QUESTION BECOMES HOW MUCH OF THIS COMPLEX WILL MAKE IT SOUTH TO
THE TAF SITES. THE 23.12Z CR-NAM NEST SHOWS A BROKEN LINE OF
WEAKENING CONVECTION GETTING INTO BOTH TAF SITES WHILE THE 23.12Z
HI-RES ARW AND NMM SHOW A LITTLE MORE AND STRONGER CONVECTION
COMING THROUGH. THE TIMING OF THE NMM IS PRETTY SIMILAR TO THE
CR-NAM NEST WHILE THE ARW IS A LITTLE QUICKER. FOR NOW...OVERALL
CONFIDENCE IS NOT THAT HIGH ON HOW FAR SOUTH THE CONVECTION WILL
GET...SO WILL START BY INTRODUCING A VCSH IN THE MIDDLE OF THE
MORNING WITH VFR CEILINGS. LATER FORECASTS MAY HAVE TO UPGRADE TO
INCLUDE THUNDER AND MVFR CEILINGS IF THE TRENDS SHOW THE
CONVECTIVE COMPLEX COULD COME THROUGH IMPACTING THE TAF SITES.

&&

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

$$

SHORT TERM...WETENKAMP
LONG TERM...WETENKAMP
AVIATION...04


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