Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 271710
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1210 PM CDT THU AUG 27 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 346 AM CDT THU AUG 27 2015

AT 3 AM...A MESOSCALE CONVECTIVE COMPLEX WAS MOVING EAST ACROSS
SOUTH DAKOTA. THIS SYSTEM WAS NOT HANDLED WELL BY THE
DETERMINISTIC NAM...GFS...AND ECMWF. MEANWHILE BOTH THE ARW AND
NMM BRING THIS SYSTEM INTO SOUTHEAST MINNESOTA THIS AFTERNOON.
THIS SEEMS A BIT TOO MUCH OVER DONE CONSIDERING THE DRY DEW POINTS
OVER THE AREA. THE HRRR ALSO MOVES THIS SYSTEM EAST AND WEAKENS IT
ACROSS MINNESOTA. HOWEVER SOME LINGERING SHOWERS AND STORMS
CONTINUE ALONG A BAND OF 700 TO 500 MB FRONTOGENESIS. WITH SO MUCH
UNCERTAINTY...OPTED TO GO MORE OF A BLEND THAT SOME OF THE SHOWERS
AND STORMS WOULD MOVE INTO THE FAR WESTERN COUNTIES OF THE COUNTY
WARNING AREA THIS AFTERNOON. HOWEVER DID NOT INCLUDE ANY
PRECIPITATION INTO CLARK AND TAYLOR COUNTIES AT THIS TIME.

FOR TONIGHT...THE NAM...GFS...AND ECMWF TRACK THE SURFACE LOW
NEAR THE MINNESOTA AND IOWA BORDER. WITH MUCH OF THE 950 TO
500 MB FRONTOGENESIS REMAINING ACROSS SOUTHERN MINNESOTA AND
NORTHERN IOWA OVERNIGHT KEPT THE HIGHEST RAIN CHANCES MAINLY WEST
OF THE MISSISSIPPI RIVER. WILL HAVE TO WATCH HOW CYCLOGENESIS
TAKES PLACE ACROSS NEBRASKA TODAY. THERE IS SOME SUGGESTION IN THE
MESO MODELS THAT THE STRONGER WAVE COMING OUT OF THE CENTRAL AND
NORTHERN PLAINS WILL BE LOCATED MUCH FURTHER SOUTH AS THE SHORT
WAVE EJECTS NORTHEAST OUT OF UTAH THIS MORNING. IF THIS SCENARIO
COMES TRUE...WE MAY BE TOO FAR NORTH WITH THE RAINFALL TONIGHT AND
FRIDAY.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 346 AM CDT THU AUG 27 2015

FROM FRIDAY INTO FRIDAY NIGHT...THE 27.00Z DETERMINISTIC
GFS...NAM...AND ECMWF CONTINUE TO SHOW STRONG 950 TO 500 MB
FRONTOGENESIS AND 925 TO 850 MB MOISTURE TRANSPORT ALONG AND
NORTH OF THE INTERSTATE 90 CORRIDOR. THIS OCCURS AS A SHORT WAVE
TROUGH LIFTS EAST NORTHEAST OUT OF NEBRASKA. DESPITE THE LACK OF A
INSTABILITY...PRECIPITABLE WATER VALUES RANGE AROUND 1.6 INCHES
AND WARM CLOUD LAYER DEPTHS RANGING BETWEEN 4 AND 4.5 KM...THERE
WILL BE COALESCENCE OF THE RAIN DROPLETS...THUS...HEAVY RAIN LOOKS
POSSIBLE. BOTH THE NAM AND GFS SUGGEST A BAND OF 3 TO 4 INCHES.
MEANWHILE THE ECMWF LOOKS MORE REASONABLE CONSIDERING THE
INSTABILITY WITH A 1 TO 3 INCH BAND.

WHILE THERE IS GREAT AGREEMENT AMONGST THESE MODELS...THERE IS
SOME CONCERN THAT THE SHORT WAVE CURRENTLY DEVELOPING ACROSS
SOUTHEAST UTAH MAY CAUSE THE SURFACE LOW TO TAKE A MUCH FURTHER
SOUTH TRACK ACROSS IOWA. THE ARW...NMM...GEM...AND 11 OF THE 12
GFS MEMBERS WOULD SUGGEST THAT THIS COULD BE A POSSIBILITY. IF
THIS SCENARIO DID COME TRUE...THAN THE RAIN BAND WOULD HAVE TO BE
SHIFTED MUCH FURTHER SOUTH WHICH WOULD BE GREAT FOR THE ABNORMALLY
DRY AND MODERATE DROUGHT AREAS OF SOUTHWEST WISCONSIN AND
NORTHEAST IOWA.

FOR THE TIME BEING...STAY WITH THE MORE CONSISTENT GFS...NAM...
AND ECMWF AND WILL WATCH TO SEE HOW THE CYCLOGENESIS DEVELOPS
ACROSS THE CENTRAL PLAINS TODAY.

FROM TUESDAY THROUGH WEDNESDAY...THE MODELS CONTINUE TO SHOW THAT
A STRONG RIDGE OF HIGH PRESSURE WILL BE LOCATED ACROSS THE UPPER
MISSISSIPPI RIVER VALLEY. WITH 925 MB TEMPERATURES RUNNING AROUND
26 TO 27C...HIGH TEMPERATURES IN THE RIVER VALLEYS WILL LIKELY
CLIMB INTO THE LOWER 90S...AND INTO THE MID TO UPPER 80S. SINCE
THIS HAS BEEN A VERY CONSISTENT SIGNAL...RAISED THE MODEL
CONSENSUS HIGH TEMPERATURES ON BOTH DAYS BY 3 TO 5 DEGREES IN THE
RIVER VALLEYS AND 2 DEGREES ELSEWHERE.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1209 PM CDT THU AUG 27 2015

AN AREA OF SURFACE LOW PRESSURE CONTINUES TO DEVELOP OVER
SOUTHWEST NEBRASKA THIS MORNING. THE 27.12Z GUIDANCE HAS REMAINED
CONSISTENT WITH PREVIOUS SOLUTIONS OF MOVING THIS SURFACE LOW
NORTHEAST AND INTO NORTHWEST IOWA BY EARLY FRIDAY AFTERNOON. THIS
WILL OCCUR AS A SHORT WAVE TROUGH COMING ACROSS WYOMING MERGES
WITH ANOTHER SHORT WAVE TROUGH COMING OUT OF COLORADO TO FORM A
UNIFIED SYSTEM TO MOVE ACROSS THE REGION FRIDAY. THE FORCING AHEAD
OF THIS SYSTEM WILL START TO INCREASE LATE TONIGHT INTO FRIDAY
MORNING. A BAND OF LOW LEVEL FRONTOGENESIS WILL START TO TAKE
SHAPE ALONG THE IOWA/MINNESOTA BORDER NORTH OF THE EXPECTED
POSITION OF THE SURFACE WARM FRONT. THE ISENTROPIC UP GLIDE ON THE
300K SURFACE WILL INCREASE TO AROUND 4 UBAR/S ALONG AND SOUTH OF
THE WARM FRONT...BUT THE BEST FORCING WILL REMAIN TO THE WEST OF
THE AREA THROUGH 18Z FRIDAY AND SHOULD SPREAD IN FRIDAY AFTERNOON.
THE TIMING OF THE RAIN LOOKS TO BE A BIT SLOWER ON THE 27.12Z NAM
AND 27.15Z HRRR-CR...SO WILL SHOW A VCSH FOR SOME SPRINKLES OUT OF
A HIGH VFR DECK COMING IN LATE TONIGHT WITH PREDOMINANT SHOWERS
FOR KRST AROUND 28.11Z AND 28.14Z FOR KLSE. CONDITIONS SHOULD
INITIALLY BE VFR BUT GO DOWN TO MVFR AS THE HEAVIER RAINS START TO
MOVE TO SATURATE THE LOWER BOUNDARY LAYER. EXPECTING IFR
CONDITIONS TO DEVELOP BUT NOT UNTIL AFTER 18Z FRIDAY. THE
INSTABILITY WITH THIS SYSTEM LOOKS VERY LIMITED...BUT WITH THE
STRENGTH OF THE FORCING THERE PROBABLY WILL BE SOME EMBEDDED
STORMS WITH THE SHOWERS. HOWEVER...THE CONFIDENCE ON WHERE AND
WHEN THESE MAY OCCUR TO TOO LOW TO INCLUDE IN EITHER TAF AT THIS
TIME.

&&

.HYDROLOGY...TONIGHT THROUGH FRIDAY NIGHT
ISSUED AT 346 AM CDT THU AUG 27 2015

BOTH THE GFS AND NAM ARE SUGGESTING 3 TO 4 INCHES RAIN ALONG AND
NORTH OF THE INTERSTATE 90 CORRIDOR. MEANWHILE THE THE ECMWF HAS
1 TO 3 INCHES OF RAIN IN THIS SAME GENERAL LOCATION. CONSIDERING
THE AMOUNT OF INSTABILITY LOCATED AROUND THE AREA...THOUGHT THAT
THE ECMWF AMOUNTS SEEMED A BIT MORE REALISTIC...SO TRENDED THE
QPFS TOWARD IT. ELSEWHERE RAINFALL AMOUNTS LOOK TO BE LESS THAN
AN INCH.

HOWEVER AS STATED IN THE LONG TERM SECTION WILL HAVE TO
WATCH HOW THIS HEAVY RAINFALL BAND DEVELOPS TONIGHT...BECAUSE 11
OF 12 OF GFS FAMILY MEMBERS...GEM...ARW...AND NMM HAVE THE
HEAVIEST QPF BAND SOUTH OF THE INTERSTATE 90 CORRIDOR WHICH WOULD
BE GREAT FOR THE ABNORMALLY DRY AND DROUGHT AREAS OF NORTHEAST
IOWA AND SOUTHWEST WISCONSIN.

WITH HOURLY RAIN RATES LESS THAN AN INCH AN HOUR...NOT ANTICIPATING
ANY ISSUES WITH URBANIZED FLOODING. IN ADDITION...AREA RIVERS AND
STREAMS HAVE FLOWS CURRENTLY RUNNING ANYWHERE FROM 25 TO 50 PERCENT
OF CLIMATOLOGY. AS A RESULT...THIS RAIN SHOULD ONLY RESULT IN BANK
RISES.

&&

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

$$

SHORT TERM...BOYNE
LONG TERM...BOYNE
AVIATION...04
HYDROLOGY...BOYNE



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