Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 050248
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
948 PM CDT MON MAY 4 2015

.UPDATE...
ISSUED AT 948 PM CDT MON MAY 4 2015

HAVE MADE SOME CHANGES TO THE MORNING RAIN CHANCES...HAVE
INCREASED THEM NORTHWARD INTO THE I-90 CORRIDOR BUT SLIGHTLY
OFFSET HIGHER IN WI.

HAVE BEEN WATCHING RUN AFTER RUN OF THE HRRR AND RAP MODELS COME
IN THIS EVENING WITH CONSISTENT LIGHT PRECIPITATION FORECAST OVER
THE I-90 CORRIDOR BY SUNRISE. WHILE THIS ADDED TO THE
CONFIDENCE...WAS WAITING TO SEE ANOTHER MODEL PLATFORM INDICATE
THE SAME TO LEND MORE CONFIDENCE TO THE FORECAST. THE 05.00Z NAM
HAS NOW MADE THIS SAME CHANGE NORTHWARD. THIS IS IN RESPONSE TO
FAIRLY STRONG 600-800MB FRONTOGENESIS ROTATING NORTHEAST TONIGHT
FROM DES MOINES TO GREEN BAY ON THE NORTH SIDE OF THE SHORTWAVE
JUST EAST OF OMAHA PER RADAR. THE EASTERLY DRY FLOW BELOW 5-8KFT
WILL EVAPORATE SOME OF THE PRECIPITATION...BUT HAVE DECIDED TO
INCREASE TO MID-RANGE RAIN CHANCES /50 PERCENT/ IN THE EARLY
MORNING TO BEGIN A TREND.

UPDATE ISSUED AT 648 PM CDT MON MAY 4 2015

HAVE INCREASED THE RAIN CHANCES EARLY THIS EVENING ACROSS THE FAR
SOUTH BASED ON RADAR AND SURFACE OBSERVATIONS OF VERY LIGHT RAIN.
CLEARLY A NORTHERN EDGE TO THE DEFORMATION AREA IS SEEN ON THE
RADAR AT THIS TIME WITH PLENTY OF ECHO AND RAIN DEVELOPMENT AHEAD
OF THE SHORTWAVE TROUGH HEADING E-NE FROM NEBRASKA.

MODEL GUIDANCE DOES SHOW MID-LEVEL FRONTOGENESIS CURRENTLY
ASSOCIATED WITH THE RAIN BAND ACROSS IOWA SHIFTING NORTHEASTWARD
INTO THE FORECAST AREA TOWARD KGRB. INTERESTINGLY...THE RAP TAKES
THIS FEATURE TO I-90 BY MORNING AND LATEST RAP AND HRRR MODELS
ARE PRODUCING PRECIPITATION IN THAT CORRIDOR. 04.18Z NAM AND GFS WILL
HAVE NO PART OF IT WITH MUCH WEAKER FORCING. INTERESTING TO SEE NO
PRECIPITATION SPLASHING NORTH OF THE GFS RAIN SCHIELD...THIS DUE
TO NO CONVECTIVE INSTABILITY FOR THE MODEL TO DRIBBLE OUT ITS
SUMMER SPLASHES.

CURRENT FORECAST DOES HAVE RAIN CHANCES NORTH TO I-90 BY MORNING
/20 PERCENT/ AND WILL CONTINUE TO MONITOR/ADJUST THIS AS THE
EVENING PROGRESSES. CERTAINLY THE LOW-LEVEL DRY EASTERLY FLOW WILL
NEED TO BE OVERCOME BY STRONGER FORCING SUGGESTED IN THE RAP TO
GET RAINFALL TO I-90.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 339 PM CDT MON MAY 4 2015

AT 3 PM...A STATIONARY FRONT WAS LOCATED FROM CHICAGO TO KANSAS
CITY. NORTH OF THIS FRONT...DEW POINTS ARE IN THE 60S AS FAR NORTH
AS CENTRAL IOWA AND NORTHERN ILLINOIS. NORTH OF THIS AREA...NORTH
AND NORTHEAST WINDS HAVE LOWERED DEW POINTS INTO THE 30S AND 40S.

FOR TONIGHT AND TUESDAY MORNING...A SHORT WAVE TROUGH...CURRENTLY
LOCATED OVER NEBRASKA...WILL MOVE EAST NORTHEAST THROUGH
IOWA...AND SOUTHERN WISCONSIN ON TUESDAY. WHILE THE 925 AND 850 MB
MOISTURE TRANSPORT WILL BE WEAK...STRONG 900 TO 500 MB
FRONTOGENESIS WILL PRODUCE SHOWERS AND THUNDERSTORMS MAINLY SOUTH
OF INTERSTATE 90 FROM LATE THIS EVENING THROUGH TUESDAY MORNING.
WITH BOTH THE 0-3 KM AND 0-6 KM SHEAR BEING VERY WEAK AND MOST
UNSTABLE CAPE LESS THAN 500 J/KG...NOT ANTICIPATING ANY SEVERE
WEATHER.

ON TUESDAY AFTERNOON...SUBSIDENCE IN THE WAKE OF THE SHORT TROUGH
WILL DEVELOP ACROSS THE AREA. BOTH THE ARW AND NMM SUGGEST THAT
THE AREA WILL BECOME DRY. MEANWHILE MANY OF THE DETERMINISTIC RUNS
SUGGEST THAT SOME PRECIPITATION WILL LINGER INTO THE AFTERNOON. WAS
VERY TEMPTED TO LEAN TOWARD THE MESO MODELS. HOWEVER CONSENSUS WAS
MORE TOWARD THE DETERMINISTIC RUNS...SO WENT TOWARD THEM.

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 339 PM CDT MON MAY 4 2015

FROM TUESDAY NIGHT INTO WEDNESDAY...THE 04/12Z MODELS CONTINUE TO
SHOW THAT A SHORT WAVE RIDGE WILL MOVE AHEAD OF THE LONG WAVE
TROUGH. THIS WILL HELP THE WARM FRONT TO ADVANCE NORTHWARD ACROSS
THE AREA. WITH THE BEST 925 MB AND 850 MB MOISTURE ADVANCING
QUICKLY NORTH THROUGH THE AREA...NOT AS SEEING MUCH CONVERGENCE
OUTSIDE OF THE WARM FRONT ITSELF. AS A RESULT...THERE WILL BE THE
POTENTIAL FOR SOME DRY WEATHER IN THE WARM SECTOR OF THIS SYSTEM
ON WEDNESDAY MORNING AND POSSIBLY WEDNESDAY AFTERNOON. THIS IS HIGHLY
DEPENDENT ON THE LOCATION OF THE COLD FRONT. WITH WEAK 0-3 KM AND
0-6 KM SHEAR...NO SEVERE WEATHER IS ANTICIPATED WITH THE PASSAGE
OF THE WARM FRONT THROUGH THE REGION.

ON THURSDAY NIGHT AND FRIDAY...THE COLD FRONT WILL FINALLY MOVE
EAST THROUGH THE REGION. MOST UNSTABLE CAPES AHEAD OF THIS FRONT
WILL CLIMB INTO THE 1500 TO 2500 J/KG RANGE. WHILE THE 0-6 KM
SHEAR REMAINS WEAK...THE 0-3 KM SHEAR DOES CLIMB UP TO 30
KNOTS....SO MAY HAVE TO WATCH FOR THE POTENTIAL FOR SOME DAMAGING
WINDS.

ON SUNDAY NIGHT AND MONDAY...ANOTHER LOW PRESSURE SYSTEM WILL MOVE
THROUGH THE REGION. AT THIS TIME...IT LOOKS LIKE THE WARM SECTOR
WILL REMAIN SOUTHEAST OF THE AREA. THIS WILL GREATLY LIMIT THE
0-6 KM SHEAR AND INSTABILITY ACROSS THE REGION. THUS NOT
ANTICIPATING ANY SEVERE WEATHER AT THIS TIME.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 648 PM CDT MON MAY 4 2015

VFR CONDITIONS ARE FORECAST AT THE TAF SITES. A VIGOROUS WEATHER
SYSTEM MOVING THROUGH IOWA AND ILLINOIS WILL SPREAD RAIN INTO
AREAS SOUTH OF THE TAF AIRFIELDS. BY SUNRISE...THERE MAY BE SOME
LOWER CIGS IN THE HIGH MVFR CATEGORY WITH -SHRA. FOR NOW...THE
FORECAST HAS THE DRIER EASTERLY FLOW WINNING OUT AND THE CIGS
REMAINING VFR.


&&

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

$$

UPDATE...BAUMGARDT
SHORT TERM...BOYNE
LONG TERM...BOYNE
AVIATION...BAUMGARDT



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