Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 231120
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
620 AM CDT WED APR 23 2014

.SHORT TERM...(TONIGHT THROUGH WEDNESDAY NIGHT)
ISSUED AT 356 AM CDT WED APR 23 2014

MAIN FORECAST CONCERNS THIS PACKAGE...SHRA/TSRA CHANCES THRU THE
PERIOD...TEMPERATURES.

DATA ANALYSIS AT 06Z HAD CANADIAN HIGH PRESSURE CENTERED OVER
SOUTHWEST ONT...LK SUPERIOR AND NORTHERN WI. CLEAR SKIES...LIGHT
WINDS AND TEMPS IN THE 25F-40F RANGE ACROSS NORTHEAST MN/MUCH OF WI
UNDER THE RIDGE. NEXT TROUGH/SHORTWAVE ENERGY PASSING OVER THE
ROCKIES DEVELOPING A LEE LOW IN WY/EASTERN MT. MID/HIGH LEVEL
MOISTURE AHEAD OF THE TROUGH/ SFC LOW ALREADY SPREADING OVER IA/MN.
WARMER TEMPS ACROSS MUCH OF IA/SOUTHERN MN WITH SOME SOUTHEAST
BOUNDARY LAYER WINDS FOR MIXING AND UNDER THE INCREASING CLOUDS.

23.00Z MODEL RUNS INITIALIZED WELL AND OFFER INCREASINGLY SIMILAR
SOLUTIONS AS THE TROUGH OVER THE ROCKIES MOVES INTO THE CENTRAL/
NORTHERN PLAINS BY 12Z THU...AT LEAST WITH THE LARGER SCALE
FEATURES. STILL SOME DIFFERENCES WITH THE LEADING WARM ADVECTION/FN
CONVERGENCE PRECIP TODAY. CONSENSUS TREND TODAY/TONIGHT IS A SLIGHT
SLOWING OF THE SFC-MID LEVEL TROUGH BY 12Z THU. NO ONE MODEL LOOKING
TO HAVE BETTER RUN-TO-RUN CONSISTENCY THAN THE OTHERS THIS CYCLE.
CHECK OF OBS VS. MODEL DATA AT 06Z SHOWED ALL WERE QUITE GOOD WITH
THE HIGH OVER THE REGION AND THE 990MB LEE LOW OVER SOUTHEAST MT.
ALL APPEARED REASONABLE WITH THE SHORTWAVE DETAILS IN THE TROUGHING
CROSSING THE ROCKIES. ONCE AGAIN GENERALLY FAVORED THE MODEL/
ENSEMBLE CONSENSUS IN THE SHORT TERM WITH THE OVERALL TIGHTER
CONSENSUS IN THE LARGER SCALE FEATURES. SHORT-TERM FCST
CONFIDENCE GENERALLY REMAINS GOOD THIS CYCLE.

FOR THE SHORT TERM...MID LEVEL MOISTURE/CLOUDS AHEAD OF THE LEE LOW/
ROCKIES TROUGH WILL CONTINUE TO SPREAD EAST/NORTHEAST ACROSS THE
FCST AREA TODAY...BUT A BIT SLOWER THAN EARLIER THOUGHT. STRONGER OF
THE WARM ADVECTION/MOISTURE TRANSPORT/THETA-E CONVERGENCE CENTERED
AROUND 700MB...295-310K ISENTROPIC LIFT AND 850-500MB FN CONVERGENCE
NOW SLATED TO MOVE ACROSS THE AREA THIS AFTERNOON AND EVENING.
TRENDED -SHRA CHANCES DOWN THIS MORNING AND MORE INTO THE AFTERNOON/
EVENING FOR THE LEADING BAND OF WARM ADVECTION PRECIP. CAPE REMAINS
LIMITED AT BEST BUT CONTINUED AN ISOLATED TSRA MENTION THIS
AFTERNOON EVENING GIVEN THE STRENGTH OF THE 700-500MB FORCING/LIFT
SIGNAL AND SOME DIVERGENCE ALOFT AHEAD OF THE PROGRESSIVE TROUGH.
DEEPER/STRONGER DYNAMICS/LIFT/DIVERGENCE ALOFT WITH THE SFC LOW THRU
MID LEVEL TROUGH SPREAD INTO THE AREA LATER TONIGHT...ALONG WITH
INCREASING MOISTURE/WARM ADVECTION/ISENTROPIC LIFT IN THE SFC-850MB
LAYER. TREND OF SHRA/ISOLATED TSRA CHANCES TOWARD 100 PERCENT LATER
TONIGHT LOOKS GOOD. MODEL/ENSEMBLE CONSENSUS PRODUCES WIDESPREAD
1/4 TO 1/2 INCH OF PRECIP ACROSS MUCH OF THE FCST AREA LATER
TONIGHT. LOCALLY HIGHER AMOUNTS CERTAINLY POSSIBLE WITH ANY TSRA
GIVEN PW VALUES IN EXCESS OF AN INCH LATER TONIGHT...SOME 200
PERCENT OF NORMAL. BLEND OF GUIDANCE HIGHS/LOWS FOR TONIGHT LOOKED
GOOD. COOL HIGHS TODAY WITH MORE/INCREASE CLOUDS...COOLING
EAST/SOUTHEAST WINDS AND THE -SHRA THIS AFTERNOON LOOKING TO
PRODUCE EVAPORATIVE COOLING AS THE FALL THRU THE DRIER SFC-850MB
LAYER.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 356 AM CDT WED APR 23 2014

MAIN FORECAST CONCERNS FOR THURSDAY THROUGH FRIDAY NIGHT...SHRA/TSRA
CHANCES/RAIN AMOUNTS THU...LINGERING SHRA CHANCES THU NIGHT/FRI...
TEMPERATURES.

23.00Z MODEL RUNS CONTINUE TO COME INTO BETTER AGREEMENT AS THE
STRONG SFC-MID LEVEL LOW/TROUGH LIFTS INTO/ACROSS THE REGION THU/THU
NIGHT...THEN HGTS RISE FRI/FRI NIGHT. SOME SMALLER DIFFERENCES WITH
THE LOWER LEVEL FEATURES BY 00Z FRI...RELATED TO HANDLING OF THE
STRONGER SHORTWAVE ENERGY AS IT PASSES LATER THU/THU EVENING. EVEN
WITH THE MINOR DIFFERENCES BY THU NIGHT...FCST CONFIDENCE IN THE THU
THRU FRI NIGHT PERIOD IS GOOD.

DEEP/STRONG FORCING/LIFT AND HIGH PW AIRMASS THAT ARRIVE LATER
TONIGHT MOVE ACROSS THE FCST AREA THU...AHEAD OF/WITH THE SFC-500MB
TROUGH. WITH THE SLIGHT SLOWING TREND INDICATED AMONG THE
MODELS...THE STRONGEST/DEEPEST OF THIS IS NOW SLATED TO MOVE ACROSS
THE AREA THU MORNING AND TRENDED SHRA/ISOLATED TSRA CHANCES TOWARD
100 PERCENT THU MORNING. ANOTHER WIDESPREAD 1/4 TO 1/2 INCH OF
PRECIP EXPECTED WITH HIGHER AMOUNTS IN ANY TSRA. LOWER LEVEL
DRYING/DECREASE OF MOISTURE SPREADS EAST INTO THE AREA THU AFTERNOON
WITH PASSAGE OF THE SFC-850MB TROUGH. CONTINUED/ENHANCED THE
DOWNWARD TREND OF RAIN CHANCES IN THE WEST HALF OF THE FCST AREA
THRU THE AFTERNOON...WHILE AT LEAST EARLY IN THE AFTERNOON RAISING
PRECIP CHANCES EAST OF THE MS RIVER. NEARLY VERTICALLY STACKED
SYSTEM LIFTS INTO THE U.P. OF MI. DRIER SFC-700MB AIR SOUTH OF THIS
SYSTEM CONTINUES TO SPREAD ACROSS THE AREA THU NIGHT. PRECIP
CHANCES CONTINUE TO TREND DOWN THU EVENING WITH ANY LINGERING
-SHRA CHANCES LIMITED TO NEAR/NORTH OF HWY 29 ACROSS NORTH-CENTRAL
WI BY LATER THU NIGHT/FRI MORNING. STEEP SFC-800MB LAPSE RATES UNDER
THE MID LEVEL COLD POOL FRI AFTERNOON COMBINED WITH SOME LINGERING
LOWER LEVEL MOISTURE PRODUCE SOME WEAK INSTABILITY. SMALL DIURNALLY
DRIVEN -SHRA CHANCE FOR MUCH OF THE FCST AREA FRI AFTERNOON APPEARS
REASONABLE. DRIER/COOLER CAN HIGH PRESSURE NOSES IN FOR FRI NIGHT
AND LEFT THIS PERIOD DRY. FOLLOWED THE BLEND OF NUMERICAL GUIDANCE
HIGHS/LOWS FOR THU THRU FRI NIGHT. FRI HIGHS THE TRICKIEST...AS
MODELS DIFFER ON THE POTENTIAL OF A /BACKDOOR/ COLD FRONT THAT MAY
DROP SOUTH ACROSS MN/WI FRI AFTERNOON. IF ECMWF IS MORE CORRECT FRI
HIGH MAY BE 3-5F TOO COOL.

FOR SATURDAY THROUGH TUESDAY.../DAYS 4 TO 7/...

MAIN FORECAST CONCERNS THIS PERIOD...RAIN /POSSIBLY MIXED WITH
SNOW DURING THE LATE NIGHT/EARLY MORNING HOURS/ CHANCES MUCH OF
THE PERIOD...TEMPERATURES.

23.00Z MEDIUM RANGE MODELS SHOW A SLOWLY IMPROVING CONSENSUS IN THE
SAT THRU TUE PERIOD...MUCH OF WHICH LOOKS UNSETTLED AND CONTINUE
COOL/BELOW NORMAL TEMPS. WITH THE IMPROVING CONSENSUS AND TREND
TOWARD A COMPROMISE OF EARLIER RUNS...DAY 4-7 FCST CONFIDENCE IS
AVERAGE THIS CYCLE.

THE IMPROVING CONSENSUS SHOWS MID LEVEL SHORTWAVE RIDGING TO MOVE
ACROSS THE UPPER MIDWEST SAT WITH SFC HIGH PRESSURE OVER OR JUST
EAST OF THE REGION. CONTINUED TO TREND SAT DRY. CONSENSUS REMAINS
QUITE GOOD WITH THE MID LEVEL HGTS SUN/MON BUT LOWER LEVEL
DIFFERENCES BEGIN TO APPEAR/INCREASE. THIS AS A 500MB LOW MOVES
INTO THE CENTRAL PLAINS SUN/MON...APPEARING AS THE WESTERN SIDE OF
AN OMEGA BLOCK OVER CENTRAL/EASTERN NOAM. FLOW EAST OF THE SFC-
700MB LOW WITH THE MID LEVEL LOW SPREADS MOISTURE NORTHWARD INTO
THE UPPER MIDWEST FOR SAT NIGHT INTO TUE. BIGGER QUESTIONS ARE HOW
QUICKLY AND HOW FAR NORTH THIS MOISTURE...AND RESULTING PRECIP
CHANCES SPREAD THRU THE SAT NIGHT-TUE PERIOD. OVERALL TREND THE
PAST COUPLE DAYS IS STRONGER...FURTHER NORTH WITH THE
MOISTURE/LIFT AND PRECIP CHANCES. DUE TO THE LOWER LEVEL DETAIL
DIFFERENCES...GENERALLY SIDED WITH THE MODEL/ENSEMBLE PRECIP
CHANCES FOR SAT NIGHT THRU TUE. DEPENDING ON MODEL...APPEARS
COLUMN/SFC TEMPS MAY BE COLD ENOUGH FOR SOME -SN TO MIX IN DURING
THE LATE NIGHT/EARLY MORNING HOURS OF SUN-MON-TUE AND LEFT THIS IN
THE FCST GRIDS FOR NOW. FAVORING THE MODEL/ENSEMBLE
CONSENSUS...THE BLEND OF NUMERICAL GUIDANCE FOR HIGHS/LOWS IN THE
SAT-TUE PERIOD LOOK GOOD AT THIS TIME.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 620 AM CDT WED APR 23 2014

THE MAIN FOCUS AT THE TAF SITES IS ON THE RAIN CHANCES AND WHEN
CONDITIONS WILL DROP BELOW VFR. AN INITIAL BAND OF LIGHT RAIN
SHOWERS IS MOVING EAST ACROSS SOUTHERN MINNESOTA/NORTHERN IOWA
WITH ALL OBSERVATIONS ALONG IT SHOWING VFR CONDITIONS. THIS BAND
WILL INTENSIFY THIS AFTERNOON THOUGH CONDITIONS ARE STILL EXPECTED
TO STAY VFR. AFTER A BREAK THIS EVENING...THE HEAVIEST RAIN WILL
COME IN AFTER MIDNIGHT TOWARD DAYBREAK AS A LOW PRESSURE SYSTEM
APPROACHES FROM THE SOUTHWEST. MVFR CONDITIONS LOOK VERY LIKELY
WITH SOME IFR POSSIBLE...PARTICULARLY AT RST. RAIN WILL CONTINUE
THROUGH THE REST OF THE MORNING HOURS WITH THESE IFR/MVFR
CONDITIONS PERSISTING AS WELL.

&&

.HYDROLOGY...
ISSUED AT 356 AM CDT WED APR 23 2014

WIDESPREAD RAINFALLS OF 0.75 TO 1.50 INCH ARE EXPECTED TONIGHT
AND THURSDAY AND COULD RESULT IN SOME RUNOFF. THIS RUNOFF WOULD
KEEP AREA RIVER LEVELS ELEVATED INTO NEXT WEEK...BUT WITH THIS
RAIN FALL OVER A 12 TO 18 HOUR PERIOD...NO FLOODING IS EXPECTED
AT THIS TIME.

&&

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

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION...HALBACH
HYDROLOGY....RRS



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