Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 270437 AFDOAX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE OMAHA/VALLEY NE 1137 PM CDT TUE AUG 26 2014 .UPDATE... ISSUED AT 925 PM CDT TUE AUG 26 2014 MAIN CONCERN OVER THE NEXT 24 HOURS OF COURSE IS CONVECTIVE POTENTIAL AND IF/WHERE HEAVY RAINFALL WILL OCCUR. EVENING UPPER AIR ANALYSIS INDICATED BROAD SOUTHWEST FLOW ACROSS THE CNTRL PLAINS WITH A WELL-DEFINED SHORTWAVE TROUGH OVER ND...AND THE NEXT UPSTREAM ONE OVER THE 4-CORNERS AREA. BETWEEN THESE TWO SYSTEMS...THE LARGE-SCALE FORCING FOR ASCENT WAS NEGLIGIBLE. THE H85 ANALYSIS COMPARED WITH 24 HOURS AGO INDCS LESS ON A WELL- DEFINED FRONTAL BOUNDARY ACROSS NEB/IA...BUT THE PRESENCE OF GOOD MOISTURE ACRS THE KS/MO WITH H85 DEW POINTS >15 C. WE UPDATED EARLIER TO DELAY THE ONSET OF ANY PRECIP...AND GIVEN SHORT TERM TRENDS IT MAY BE WELL AFTER MIDNIGHT BEFORE CONVECTION INCREASES ACRS THE AREA. MODEL GUIDANCE INDCS THAT THERE WILL BE SOME INCREASE IN THE LOW-LEVEL JET AFTER 06Z LEADING TO BROAD ASCENT ON THE 305-310 SFC. THIS MAY LEAD TO SOME INCREASE IN CONVECTION AFTER 06Z...BUT WITHOUT A WELL-DEFINED BOUNDARY TO FOCUS MASS CONVERGENCE ON...IF AND WHERE A FOCUS HEAVY RAINFALL EVENT WOULD OCCUR IS UNCERTAIN. IT APPEARS THAT THE PROSPECTS OF HEAVY RAINFALL MAY ACTUALLY IMPROVE AS WE GET INTO WED MRNG AS THE AZ SHRTWV TROUGH EMERGES ONTO THE HIGH PLAINS AND CREATES A DYNAMICALLY INDUCED LOW-LEVEL JET THROUGH THE DAY ON WED ACTING ON THE 1.80 PWATS ACRS THE AREA. A BAND OF HEAVY THUNDERSTORMS APPEARS POSSIBLE TO MOVE FROM CNTRL INTO NE NEB THROUGH THE DAY ON WED AND HAVE INCREASED POPS IN THIS AREA FOR THIS TIME PERIOD. WE WILL KEEP THE FLASH FLOOD WATCH INTACT ATTM GIVEN THE UNCERTAINTY...BUT MAY CONCENTRATE ON THE RAINFALL POTENTIAL WED MRNG IN THE PRODUCT. OTHERWISE WILL UPDATE AGAIN A BIT LATER THIS EVENING TO DELAY THE ONSET OF POPS A BIT FARTHER INTO THE NIGHT AND FOR THE HIGHER POPS ON WED. OTHER ELEMENTS OF THE FORECAST APPEAR ON TRACK ATTM. && .SHORT TERM...(TONIGHT THROUGH FRIDAY) ISSUED AT 300 PM CDT TUE AUG 26 2014 DID NOT MAKE MANY CHANGES TO THE PREVIOUS FORECAST AND OVERALL THINKING HAS NOT CHANGED MUCH THE PAST FEW DAYS...WITH DECENT MODEL CONSISTENCY. TIMING OF TSTMS...RAIN AMOUNTS AND AXIS OF HEAVIEST RAIN LOCATION WILL CONTINUE TO PROVIDE THE MAIN FORECAST CHALLENGES. THE CONVECTION FORMED ABOUT AS EXPECTED LAST NIGHT... IN A GENERAL SENSE...BUT I DID NOT THINK WE WOULD SEE A MAX AMOUNT OF OVER 7 INCHES. THE AMOUNTS OVER 2.5 INCHES WERE IN A FAIRLY NARROW BAND. LARGE SCALE FEATURES FROM THE 12Z UPPER AIR PLOTS INCLUDED THE FOLLOWING. AT 300 MB...TWO MAIN JET SEGMENTS WERE NOTED. THE FIRST WAS DIGGING S/SW FROM WRN NV (80 KNOTS) AND THE OTHER WAS PUNCHING EWD ACROSS CNTRL MN (100 KNOTS). ONLY WEAK 12 HOUR HEIGHT FALLS WERE SEEN AT 500 MB...OVER CA AND OVER SWRN CO/NWRN NM. THE CLOSED LOW WHICH HAS BEEN OVER THE WRN UNITED STATES BECAME MORE ELONGATED AND SHIFTED A BIT S. WATER VAPOR SHOWED THE MAIN CHUNK OF ENERGY OVER SRN NV EARLY THIS AFTN. AT 700 MB...THE MOIST AXIS SEEMED TO HAVE THINNED A BIT OVER THE CNTRL PLAINS AND MOST OF THE HIGHER MOISTURE AT THIS LEVEL WAS LOCATED IN CO/AZ/NM. THE NEARLY STATIONARY LOW LEVEL FRONT WAS STILL DOWN ACROSS KS AND MO. COOL HIGH PRESSURE WAS OVER THE DKTS AND MN. TONIGHT...IT SEEMS THAT CONVECTION MAY GET GOING MAINLY AFTER 05Z. WILL KEEP SOME LOW POPS GOING THIS EVENING...THEN RAMP THEM UP VERY QUICKLY. LOW LEVEL JET TONIGHT SEEMS A BIT WEAKER...BUT MODEL POINT FORECAST SOUNDINGS AND PLAN VIEWS SHOW PRECIPITABLE WATER (PW) VALUES INCREASING TO OVER 2 INCHES TONIGHT. STRONGEST FORCING AND SUPPORT ARE IN THE SAME GENERAL AREA AS LAST NIGHT. WITH MORE SOIL MOISTURE NOW AND A SIMILAR QPF POTENTIAL POSSIBLE TONIGHT... DECIDED A FLASH FLOOD WATCH WAS APPROPRIATE. NOT ALL AREAS WILL SEE FLOODING...BUT THREAT IS HIGH ENOUGH TO INCLUDE HEADLINES. SOME PCPN SHOULD LINGER INTO MID MORNING WEDNESDAY...SO DECIDED TO RUN THE WATCH FROM 03Z WED TO 15Z WED. LOOK FOR LOWS TONIGHT IN THE 60S...COOLEST NRN ZONES AND WARMEST SRN ZONES. WEDNESDAY...STORMS SHOULD TEND TO WEAKEN THROUGH THE MORNING BUT MAY FIRE AGAIN BY LATE AFTERNOON. MODELS SUGGEST LOW PRESSURE WILL STRENGTHEN OVER ERN CO DURING THE DAY...THEN ATTEMPT TO LIFT NEWD WEDNESDAY NIGHT. THIS MAY SHIFT AXIS OF HEAVIEST RAIN FARTHER N ACROSS NERN NE IN THE EVENING AND THEN TO NRN IA/SRN MN FOR THE EARLY MORNING HOURS OF THU. UNSETTLED CONDS ARE LIKELY TO CONTINUE THU INTO THU NGT AS THE FRONTAL BOUNDARY LINGERS IN THE AREA WITH MID TROPOSPHERIC TROUGH NOT MOVING EAST OF OUR AREA UNTIL SAT. .LONG TERM...(FRIDAY NIGHT THROUGH TUESDAY) ISSUED AT 300 PM CDT TUE AUG 26 2014 THIS PERIOD GENERALLY LOOKS LESS ACTIVE...ESPECIALLY BY SAT...AND THE 12Z MODELS WERE IN PRETTY GOOD AGREEMENT WITH THE LARGE SCALE PATTERN ALOFT. WEAK RIDGING SHOULD BUILD INTO THE AREA FROM THE W ON SATURDAY...BUT THIS IS SHORT-LIVED. A STRONG TROUGH WILL BE DIGGING ACROSS THE ROCKIES OVER THE WEEKEND. IT APPEARS THIS SHOULD BECOME MORE BROAD AND MOVE A BIT FARTHER EAST TOWARD THE MIDLANDS BY TUESDAY. THE ECMWF...CANADIAN GEM AND THE 12Z GFS HAVE SOME DIFFERENCES WITH THE LOW LEVEL FEATURES AND ALSO WITH PCPN POTENTIAL. FOR NOW... GENERALLY USED A BLEND OF SOLUTIONS... WITH A BIT MORE WEIGHT GIVEN TO THE 12Z ECMWF. && .AVIATION...(06Z TAFS FOR KOFK...KLNK AND KOMA.) ISSUED AT 1129 PM CDT TUE AUG 26 2014 MAIN CHANGE FROM EARLIER DISCUSSION IS SOMEWHAT OF A DELAY IN CONVECTIVE INITIATION AND POSSIBLY A MORE PROLONGED TIME POTENTIAL OF OCCURRENCE. OTHERWISE FLIGHT CONDITIONS LOOK TO BE QUITE VARIABLE THROUGH ABOUT 18Z BEFORE BECOMING PREDOMINATLY VFR. SOME LIKELIHOOD OF MORE CONVECTION ACROSS THE AREA AGAIN AFTER 00Z AS SHORT WAVE ENERGY MOVES ACROSS THE REGION AHEAD OF UPPER LOW OVER THE SOUTHWEST CONUS. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...FLASH FLOOD WATCH UNTIL 10 AM CDT WEDNESDAY FOR NEZ042>045- 050>053-065. IA...FLASH FLOOD WATCH UNTIL 10 AM CDT WEDNESDAY FOR IAZ055-056-069. && $$ UPDATE... SHORT TERM...MILLER LONG TERM...MILLER AVIATION...FOBERT

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