Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 261952
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
252 PM CDT SUN APR 26 2015

.SHORT TERM...(THIS EVENING THROUGH TUESDAY NIGHT)
ISSUED AT 252 PM CDT SUN APR 26 2015

AN EXPANSIVE AREA OF HIGH PRESSURE OVER ONTARIO WILL REMAIN NEARLY
STATIONARY THROUGH MONDAY. THIS WILL HELP TO CONTINUE THE CLEAR
SKIES AND PLEASANT EARLY SPRING WEATHER THROUGH MONDAY. IT WILL
IMPACT THE RELATIVE HUMIDITY AND FIRE CONCERNS AGAIN MONDAY AND
WILL ELABORATE ON THAT IN THE FIRE WEATHER SECTION.

THE HIGH WILL GET PUSHED OFF TO THE EAST MONDAY NIGHT INTO TUESDAY
AHEAD OF AN APPROACHING UPPER LEVEL TROUGH AND WEAK COLD FRONT.
THE UPPER LEVEL FLOW IS EXPECTED TO HAVE THE TROUGH COMING ACROSS
SOUTHERN CANADA AS AN UPPER LEVEL LOW MOVES EAST ACROSS THE
SOUTHERN PLAINS. AS THESE SYSTEMS APPROACH THE CENTRAL PART OF THE
CONTINENT...THE 26.12Z GFS AND 26.00Z ECMWF SUGGEST A PIECE OF
ENERGY WILL BREAK OFF FROM THE CANADIAN TROUGH AND DROP SOUTH
THROUGH THE MISSOURI RIVER VALLEY TO HELP AMPLIFY THE SOUTHERN
PLAINS UPPER LEVEL LOW. THE CANADIAN TROUGH SHOULD THEN CONTINUE
EAST WITH THE BULK OF THE ENERGY PASSING TO THE NORTH. WITH THIS
PATTERN...THE PV ADVECTION IN THE 500-300 MB LAYER IS EXPECTED
SPLIT THE REGION PASSING TO THE NORTH AND WEST WITH JUST THE
POSSIBILITY OF SOME VERY WEAK PV ADVECTION COMING ACROSS THE AREA
TUESDAY EVENING. THAT LOOKS TO ABOUT THE EXTENT OF THE FORCING
FROM THIS SYSTEM WITH THE FRONTOGENESIS IN THE 850-500 MB WITH THE
WEAK COLD FRONT SPLITTING SIMILAR TO THE SHORT WAVE TROUGHS AND
PASSING TO THE NORTH AND WEST. WHAT WEAK ISENTROPIC UP GLIDE THERE
IS ON THE 295K SURFACE LOOKS TO GO TO THE WEST OF THE AREA WITH NO
MOISTURE TRANSPORT INTO THE REGION. GIVEN THE PREVAILING LOW LEVEL
DRY AIR THAT WILL BE IN PLACE FROM THE SURFACE HIGH AND THE LACK
OF MOISTURE RETURN AND FORCING...DO NOT THINK THERE IS ENOUGH TO
SUPPORT MUCH OF A RAIN CHANCE AND REMOVED THE SMALL CHANCES THAT
WERE IN THE FORECAST FOR TUESDAY AFTERNOON AND NIGHT.

.LONG TERM...(WEDNESDAY THROUGH SUNDAY)
ISSUED AT 252 PM CDT SUN APR 26 2015

THE 26.12Z GFS AND ECMWF ARE TRYING TO SUGGEST SOMEWHAT OF A
PATTERN CHANGE FOR LATE IN THE WEEK INTO THE UPCOMING WEEKEND. THE
UPPER LEVEL RIDGE OVER THE CENTRAL PORTION OF THE CONTINENT IN THE
MIDDLE OF THE WEEK IS EXPECTED TO GET FLATTENED AS A SHORT WAVE
TROUGH MOVES ACROSS SOUTHERN CANADA. ONCE THIS HAPPENS...THE FLOW
IS THEN EXPECTED TO REMAIN ZONAL TO ALLOW SHORT WAVE TROUGHS
COMING IN OFF THE PACIFIC. WITH THIS PATTERN CHANGE...THE CHANCES
FOR RAIN WILL START TO RETURN TO THE REGION FROM FRIDAY THROUGH
SUNDAY AS THE WAVES COME THROUGH AND PUSH WEAK COLD FRONTS INTO
THE AREA. THE BEST CHANCES FOR RAIN MAY COME SUNDAY WHEN THE
MODELS SUGGEST A STRONGER SHORT WAVE TROUGH COULD APPROACH IN THE
ZONAL FLOW. FOR NOW...WILL KEEP THE CHANCES AROUND 20 PERCENT
UNTIL SUNDAY AND THEN GO UP TO 30 AND 40 PERCENT.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1210 PM CDT SUN APR 26 2015

A BROAD AREA OF HIGH PRESSURE CENTERED OVER HUDSONS BAY WITH RIDGING
SOUTH THRU THE UPPER MS VALLEY WILL REMAIN THE DOMINANT WEATHER
FEATURE FOR THE TAF SITES THRU TONIGHT AND MONDAY. CLEAR SKIES
EXPECTED THRU TONIGHT/MON UNDER THE INFLUENCE OF THIS HIGH...ALONG
WITH WEAKER PRESSURE GRADIENTS AND LIGHT WINDS. WINDS THE NEXT 24
HRS EXPECTED TO BE LESS THAN 10KT AND MAINLY FROM THE NORTHWEST TO
NORTHEAST.


&&

.FIRE WEATHER...
ISSUED AT 252 PM CDT SUN APR 26 2015

WITH THE HIGH REMAINING OVER ONTARIO...IT WILL MAINTAIN THE DRY
NORTH TO NORTHEAST FLOW OVER THE REGION THROUGH MONDAY. IN
ADDITION...A PRETTY DEEP MIXED LAYER SHOULD DEVELOP TO HELP MIX
DOWN DRIER AIR FROM ALOFT. THE COMBINATION OF THIS MIXING AND DRY
FLOW SHOULD AGAIN ALLOW SURFACE DEW POINTS TO DROP INTO THE MID
20S OVER CENTRAL WISCONSIN. COMBINED WITH TEMPERATURES IN MIDDLE
TO UPPER 60S...THE AFTERNOON RELATIVE HUMIDITY WILL DROP BELOW 30
PERCENT AND APPROACH 20 PERCENT ACROSS CENTRAL WISCONSIN.
FORTUNATELY...THE WINDS WILL BE ON THE LIGHT SIDE AND BE 10 MPH OR
LESS.

&&

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

$$

SHORT TERM...04
LONG TERM...04
AVIATION.......RRS
FIRE WEATHER...04


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