Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 241716 AFDOAX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE OMAHA/VALLEY NE 1216 PM CDT SUN AUG 24 2014 .UPDATE... ISSUED AT 1203 PM CDT SUN AUG 24 2014 SFC CDFNT IS THROUGH ABOUT HALF OF THE FA THIS MORNING AND WILL CONT TO MAKE SLOW PROGRESS TO THE SOUTHEAST THROUGH THE REST OF THE AFTN. WE HAD SOME CONVECTION EARLY IN SW IA BUT AS THE LOW- LEVEL JET WEAKENED AND BACKED THESE HAVE SINCE DISSIPATED. THE MAIN FORECAST CHALLENGE FOR THE AFTN/EVENING IS IF ANYTHING WILL TRY TO DEVELOP AGAIN. LITTLE IN THE WAY OF LARGE-SCALE SUPPORT FOR ASCENT THROUGH THE DAY TODAY. MODELS ALSO INDICATE SLIGHT MID- LEVEL HEIGHT RISES OVER THE NEXT 12 HOURS. THE FA DOES RESIDE IN THE RRE REGION OF A 60 KT H3 JET FROM NRN NEB INTO MN. THE ATMOSPHERE ALONG AND AHEAD OF THE COLD FRONT SHOULD BECOME MODERATE TO STRONGLY UNSTABLE LATER THIS AFTERNOON AS SEASONABLE STEEP MID LEVEL LAPSE RATES ARE JUXTAPOSED OVER A MOIST BOUNDARY LAYER. MODIFICATION OF 12Z KOAX SOUNDING...AS WELL AS POINT FORECAST SOUNDINGS FROM SHORT TERM GUIDANCE INDICATES THAT SOME CIN REMAINS THROUGH THE AFTERNOON HOURS THOUGH. GIVEN ABOVE FACTORS IT APPEARS THAT THE MOST LIKELY SCENARIO ATTM IS FOR VERY ISO CONVECTION TO DEVELOP NEAR THE FRONTAL ZONE IN AN AREA OF DEEP LOW-LEVEL MIXING OVER NE KS WITH SOME OF THIS ACTIVITY MOVING INTO SE NEB AND MAYBE SW IA LATE LATE THIS AFTN. OTHERWISE MOST OF THE AREA SHOULD BE DRY TODAY. WE MAY SEE A BIT OF AN UPTICK IN CONVECTION LATER THIS EVENING CLOSER TO THE H85 BOUNDARY /ALONG I80/ ONCE THE LOW-LEVEL JET DEVELOPS THIS EVENING BUT THIS TO IS LIKELY TO BE PRETTY ISOLATED. GOING FORECAST IN PRETTY GOOD SHAPE AND JUST UPDATED TO ADJUST TIMING OF POSSIBLE PRECIP A BIT. && .SHORT TERM...(TODAY THROUGH TUESDAY) ISSUED AT 309 AM CDT SUN AUG 24 2014 ...POTENTIAL FOR HEAVY RAIN MONDAY NIGHT THROUGH TUESDAY NIGHT... SEVERAL FORECAST CHALLENGES IN THE SHORT TERM INCLUDING SHARP TEMPERATURE CONTRASTS ACROSS THE FORECAST AREA AS A COOL FRONT MOVES INTO THE AREA...THEN STALLS. THERE WILL ALSO BE SEVERAL CHANCES OF THUNDERSTORMS...ESPECIALLY BY MONDAY NIGHT THROUGH TUESDAY NIGHT...WITH HEAVY RAIN POSSIBLE NORTH OF THE STALLED BOUNDARY OF SEVERAL INCHES IN THE NORTH HALF OF THE FORECAST AREA. UPPER CLOSED LOW REMAINS ACROSS THE NORTHERN ROCKIES THIS MORNING WITH ANOTHER LOBE MOVING THROUGH THE PLAINS TRIGGERING THUNDERSTORMS ACROSS EASTERN NEBRASKA. ACCAS FIELD ACROSS SOUTHWEST IOWA COULD ALSO BE GENERATING SPOTTY SHOWERS THERE...ALTHOUGH CLOUD BASES WERE QUITE AROUND 17000 FEET. MEANWHILE...A COLD FRONT IS POISED JUST WEST OF THE FORECAST AREA...WHICH WILL MOVE EASTWARD LATER TODAY...BUT COULD BE A TRIGGER FOR ADDITIONAL STORM DEVELOPMENT LATER TODAY AND TONIGHT. FOR EARLY THIS MORNING...THE BULK OF THE PRECIP COULD BE NORTH OF THE AREA BY 12Z...ALTHOUGH HRRR/NAM ARW/RAP INDICATE THERE COULD BE SPOTTY LINGERING ACTIVITY THROUGH ABOUT 15Z. WILL LIKELY MAKE SOME VERY LAST MINUTE POP ADJUSTMENTS BEFORE 4 AM TO ACCOUNT FOR VERY SPOTTY ACTIVITY ACROSS PRIMARILY EASTERN NEBRASKA THIS MORNING. WITH FRONT PUSHING IN LATER TODAY...ATMOSPHERE COULD BE CAPPED FOR MOST OF THE DAY...BUT COULD BEGIN TO SEE SPOTTY LATE AFTERNOON DEVELOPMENT ALONG/EAST OF THE MISSOURI RIVER...THAT COULD EXPAND THIS EVENING ACROSS WESTERN IOWA AS LOW LEVEL JET STRENGTHENS. HIGHS TODAY WILL AGAIN BE HOT AHEAD OF THE FRONT...RANGING FROM THE LOWER TO MID 90S...BUT COOLER LOWER 80S BEHIND IT. HEAT INDEX VALUES AHEAD OF THE FRONT WILL RANGE AROUND 100 THIS AFTERNOON BUT NOT WARM ENOUGH FOR A HEAT ADVISORY. THE THE FRONT STALLS IN SOUTHEAST NEBRASKA AND SOUTHWEST IOWA OVERNIGHT...AND COULD SEE ADDITIONAL SPOTTY ACTIVITY NEAR THE FRONT OVERNIGHT...BUT LIKELY NOT MUCH IN NORTHEAST/EAST CENTRAL NEBRASKA. THEN WE`LL BE WAITING FOR THE NEXT IMPULSE TO MOVE OFF THE HIGH PLAINS MONDAY. MOST OF MONDAY MORNING COULD ACTUALLY BE DRY...BUT CHANCES BEGIN TO INCREASE JUST SLIGHTLY MONDAY AFTERNOON. TEMPS AGAIN MONDAY COULD BE TRICKY...WITH MID 70S NORTH OF THE FRONT...BUT MID 90S FOR SOUTHEAST NEBRASKA. PRECIP CHANCES SUBSTANTIALLY INCREASE MONDAY NIGHT FOR THE NORTHERN FORECAST AREA NORTH OF THE STALLED SURFACE FRONT. PW VALUES INCREASE TO THE 90-97 30-YEAR CLIMATOLOGICAL PERCENTILE BASED ON NAEFS OUTPUT. LOCALLY HEAVY RAIN OF AN INCH OR TWO WILL BE POSSIBLE IN NORTHEAST NEBRASKA THROUGH DAYBREAK TUESDAY...AND THE AREA IS IN SLIGHT RISK FOR EXCESSIVE HEAVY RAINFALL. BELIEVE WE CAN HANDLE THE RAIN MONDAY NIGHT WITHOUT TOO MUCH TROUBLE...AND HAVE POPS RANGING FROM JUST SLIGHT CHANCE KS/NE BORDER INCREASING TO CATEGORICAL NORTH OF I80. THE SURFACE BOUNDARY REMAINS STALLED ON TUESDAY. WILL LIKELY SEE NUMEROUS SHOWERS NORTH OF THE FRONT ACROSS NORTHEAST NEBRASKA... TAPERING TO NOT MUCH OR ANY PRECIP SOUTH OF THE BOUNDARY. TEMPS AGAIN WILL VARY WIDELY NORTH TO SOUTH ACROSS THE FRONT...FROM THE MID 70S NEAR NE/SD BORDER TO MID 90S NEAR KS/NE BORDER REGION. .LONG TERM...(TUESDAY NIGHT THROUGH SATURDAY) ISSUED AT 309 AM CDT SUN AUG 24 2014 ANOTHER STRONG IMPULSE MOVES OFF THE HIGH PLAINS TUESDAY NIGHT. AGAIN...A RATHER LARGE AREA OF 90-97 PERCENT 30-YEAR CLIMATOLOGICAL PERCENTILE FOR PW REMAINS ACROSS THE MID MISSOURI RIVER VALLEY... RESULTING IN ANOTHER NIGHT OF CONVECTIVE RAINS...WITH HIGHEST AMOUNTS EXPECTED NORTH OF THE BOUNDARY ALONG/NORTH OF I80. THIS SECOND NIGHT OF HEAVY RAIN MAY BE COLOCATED WITH MANY AREAS THAT RECEIVED THE HEAVY RAIN MONDAY NIGHT...AND AGAIN THE AREA IS WITHIN A SLIGHT RISK OF EXCESSIVE HEAVY RAINFALL. TOO FAR OUT TO GO WITH ANY TYPE OF FLOOD WATCH...BUT WILL MONITOR CLOSELY IN LATER FORECASTS FOR POTENTIAL FLOODING BASED ON A COUPLE OF NIGHTS OF EXPECTED HEAVY RAIN. MODEL DIFFERENCES BEGIN TO DEVELOP BY THURSDAY AND BEYOND. THE GFS IS A BIT MORE PROGRESSIVE IN EJECTING THE FILLING MEAN TROUGH AND THE ECMWF IS SIGNIFICANTLY SLOWER. WILL STILL SEE NUMEROUS SHOWERS AND THUNDERSTORMS WEDNESDAY THROUGH WEDNESDAY NIGHT...AND THEN DIMINISHING BY THURSDAY/THURSDAY NIGHT. WILL MAINTAIN A DRY FORECAST FOR FRIDAY AND SATURDAY BASED ON PROGRESSIVE GFS MODEL...BUT TEMPS ALSO RETURN TO NORMAL BY THEN REBOUNDING TO THE MID 80S. WILL HAVE TO MONITOR THE ECMWF MODEL TO SEE IF SLOWER TRENDS CONTINUE. OVERALL SEVERE WEATHER THREAT THROUGH THE PERIOD SEEMS LOW...WITH MORE FOCUS ON HEAVY CONVECTIVE RAINS INSTEAD. && .AVIATION...(18Z TAFS FOR KOFK...KLNK AND KOMA.) ISSUED AT 1203 PM CDT SUN AUG 24 2014 VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD. THE CDFNT IS THRU KOFK/KLNK AND WILL BE THRU KOMA BY MID AFTN. SOME THREAT OF CONVECTION EXISTS AT KLNK/KOMA THIS EVENING/OVERNIGHT BUT THE THREAT IS EXPECTED TO BE TO ISOLATED TO INCLUDE IN THE TAFS ATTM. OTHERWISE JUST SCT- BKN MID LEVEL CLOUDS WITH LIGHT WINDS ARE EXPECTED. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...NONE. IA...NONE. && $$ UPDATE... SHORT TERM...DEWALD LONG TERM...DEWALD AVIATION...

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