323
FXUS63 KARX 252329
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
629 PM CDT TUE SEP 25 2018
SHORT TERM
(TONIGHT AND WEDNESDAY)
ISSUED AT 244 PM CDT TUE SEP 25 2018
MAIN SHORT-TERM FCST CONCERNS ARE EXITING SHRA THIS EVENING AND
COOLER TEMPERATURES AGAIN.
DATA ANALYSIS AT 18Z HAD THE COLD FRONT SLIPPING SE ACROSS THE
REGION, NEAR A KGRB-KPDC-KMCI LINE. MOIST, UNSTABLE AIRMASS AHEAD OF
THE THE FRONT. RISK OF A FEW SEVERE STORMS FROM FAR SOUTHERN WI TO
NORTHERN MO THIS AFTERNOON AS A VIGOROUS MID LEVEL SHORTWAVE SEEN IN
WV IMAGERY AIDS LIFT AND AN AREA OF SHRA/TSRA MOVING EAST-NE ACROSS
SW WI TO THE EAST 1/3 OF IA. AHEAD OF THE FRONT THIS AFTERNOON,
STILL KIND OF SUMMERY WITH TEMPS IN THE 70S-LOW 80S AND DEW
POINTS IN THE LOW-MID 60S. BEHIND THE FRONT IS AUTUMN WITH TEMPS
MOSTLY IN THE UPPER 40S TO LOWER 60S AND SOME NW WINDS.
MODEL RUNS OF 25.12Z INITIALIZED WELL. SOLUTIONS QUITE SIMILAR AS
THE MID LEVEL TROUGH AXIS ROTATES ACROSS AND EAST OF THE AREA
TONIGHT/WED. SHORT-TERM FCST CONFIDENCE IS GOOD THIS CYCLE.
FOR THE SHORT-TERM, PRESENT TIMING HAS THE SFC FRONT WELL EAST OF
THE FCST AREA BY 00Z, WITH THE FORCING/LIFT FROM THE SHORTWAVE
EXITING EAST AROUND 00Z. SOME LINGERING SHRA CHANCES ACROSS THE EAST
SIDE OF THE FCST AREA 00-03Z REASONABLE. THE FCST THEN TRENDS DRY
FOR THE REST OF TONIGHT/WED AS COOLER/DRY CAN HIGH PRESSURE BUILDS
IN BEHIND THE FRONT. CLOUDS DECREASE/CLEAR LATER THIS EVENING/
OVERNIGHT IN THE DEEPER SUBSIDENCE BEHIND THE MID LEVEL TROUGH AXIS
AND LOWER LEVEL ANTI-CYCLONIC FLOW SPREADING INTO THE AREA. WED
WOULD TREND AS A MOSTLY SUNNY DAY AS CAN HIGH PRESSURE SLIDES ACROSS
THE REGION, HOWEVER RATHER CONSISTENT MODEL SIGNAL FOR THE WEAK
SHORTWAVE IN WESTERN ND TO SPREAD A BATCH OF 925-850MB MOISTURE/
STRATO-CU CLOUDS SE ACROSS MUCH OF THE FCST AREA WED MORNING. ALL
MODELS KEEP THIS PROGRESSIVE, WITH A PARTLY SUNNY/MOSTLY CLOUDY
MORNING BECOMING A MOSTLY SUNNY AFTERNOON. COOLER AIR ALOFT WITH
SOME DIURNAL WARMING RESULTS IN DEEPER MIXING WED, FOR SOME
BRISK/GUSTY W TO NW WINDS FOR THE LATER MORNING/AFTERNOON HOURS.
BLEND OF GUIDANCE LOWS FROM THE UPPER 30S-MID 40S TONIGHT AND IN THE
MID 50S-LOWER 60S WED LOOK GOOD FOR NOW.
LONG TERM
(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 244 PM CDT TUE SEP 25 2018
FOLLOWING THE DRY DAY ON WEDNESDAY, ANOTHER COLD FRONT WILL SLIDE
THROUGH ON THURSDAY, PROVIDING ANOTHER SHOT OF COLD AIR AND RAIN
CHANCES. THE QUESTION WILL BECOME HOW FAR SOUTH INTO THE FORECAST
AREA THE RAIN EXTENDS. THE 25.12Z GFS AND NAM HAVE RAIN EXTENDING
ACROSS THE ENTIRE FORECAST AREA, WHILE THE 25.00Z ECMWF KEEPS THE
RAIN CONTAINED IN ONLY NORTHERN PORTIONS OF THE FORECAST AREA. ONE
THING MODELS ARE CONSISTENT ON IS ONLY A FEW HUNDRED J/KG AT MOST OF
MUCAPE IN THE AREA, SO NOT THINKING THERE WILL BE THUNDER.
SOME SHORTWAVE ENERGY WILL THEN MOVE ALONG THE FRONT AND LEAD TO A
BAND OF RAIN, BUT STILL QUESTIONS AS TO EXACTLY WHERE THIS WILL SET
UP. THE 25.12Z GFS KEEPS EVERYTHING SOUTH OF THE FORECAST AREA,
WHILE THE 25.00Z ECMWF IS FARTHER NORTH, GIVING NEARLY THE ENTIRE
AREA SOME LIGHT RAIN. THE GFS THEN BRINGS IN MORE RAIN CHANCES
SATURDAY AFTERNOON/EVENING AND SUNDAY WHILE THE ECMWF KEEPS THE AREA
DRY UNTIL MONDAY. BOTTOM LINE, GIVEN RECENT RUN TO RUN INCONSISTENCY
FOR ALL MODELS, FORECAST CONFIDENCE FOR FRIDAY THROUGH SUNDAY IS
RATHER LOW, BUT GENERALLY LOOKING COOL WITH OFF AND ON LIGHT RAIN
CHANCES. FRIDAY NIGHT DOES LOOK TO BE THE COLDEST NIGHT IN THE
PERIOD, WITH HIGH PRESSURE NEARLY OVERHEAD. AT THIS POINT, LOOKING
AT LOWS IN THE LOWER TO MID 30S, WITH SOME SPOTS DIPPING INTO THE
20S.
MODELS ARE ACTUALLY IN BETTER AGREEMENT THEN FOR THE BEGINNING OF
NEXT WEEK, BRINGING A WARM FRONT NORTHWARD THROUGH THE AREA, LEADING
TO MORE RAIN CHANCES. ALSO LOOKING AT A SLIGHT WARMUP GIVEN THE
STRONGER SOUTHERLY FLOW, WITH HIGHS GETTING BACK INTO THE LOWER TO
MID 60S.
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 629 PM CDT TUE SEP 25 2018
WITH THE SHOWERS NOW WELL EAST OF BOTH AIRPORTS, LOOKING AT WHEN
THE MVFR CLOUDS WILL MOVE OUT. OBSERVATIONS INDICATE THESE EXTEND
BACK INTO CENTRAL MINNESOTA, SO EXPECTING IT WILL BE THE MIDDLE OF
THE EVENING BEFORE SOLID VFR CONDITIONS MOVE IN. ANOTHER PERIOD OF
MVFR CEILINGS SHOULD OCCUR WEDNESDAY MORNING AS A SHORT WAVE
TROUGH, CURRENTLY OVER THE DAKOTAS, SWEEPS ACROSS THE REGION.
THESE SHOULD NOT LAST LONG WITH VFR CONDITIONS EXPECTED FOR THE
AFTERNOON.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
SHORT TERM...RRS
LONG TERM....CJA
AVIATION...04
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page