FXUS63 KOAX 211543
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
1043 AM CDT TUE SEP 21 2010
.UPDATE...
WILL BE UPDATING TO LOWER AFTERNOON POPS
&&
.DISCUSSION...
WELL DEFINED SHRTWV TROF ON WV AND MRNG UPPR AIR ANLYS WAS SLIDING
EWD THRU KS ATTM. THIS WAS LEADING TO LARGE-SCALE SUPPORT FOR
ASCENT ACRS ERN NEB...AND WITH A NEARLY UNCAPPED ATMOSPHERE
/LIFTING A PARCEL FM AROUND 775 MB PER 12Z OAX SOUNDING/ HAD LED
TO A SIG INCREASE IN SHOWER AND THUNDERSTORM ACTIVITY THIS MRNG.
EARLIER INCREASED POPS INTO THE LIKELY RANGE FOR THIS ACTIVITY.
LATEST SHRT TERM MODELS INDC THIS SHRTWV AND ASSOCIATED UVV WL
CONT EWD THRU THE AFTN LEAVING ERN NEB IN NEUTRAL TO WEAK
SUBSIDENCE DURING PEAK HEATING. THUS ANY REDEVELOPMENT OF ACTIVITY
DURING THE AFTN IS IN QUESTION ONCE MRNG ELEVATED STORMS SHIFT
EWD. 15Z SFC ANLYS INDCD CDFNT FM ARND ATLANTIC SWWD THRU FBY.
THIS FNT IS EXPECTED TO ONLY SLOWLY SHIFT SWD THRU AROUND 18Z AND
THEN BECOME STATIONARY. LOW LEVEL FLOW WL TEND TO BACK THIS AFTN
AS UPPR LVL SHORT-WAVE RIDGE STARTS TO MOV OVR THE FA LEADING TO
WEAKER CONVERGENCE ALONG THE BOUNDARY ALSO LIMITING PROSPECTS FOR
RENEWED CONVECTIVE DEVELOPMENT. NEVERTHELESS...12Z KOAX SOUNDING DOES
INDC A GENERALLY UNCAPPED SFB-BASED ENVIRONMENT GIVEN TMPS IN THE
MID 80S AND DEW POINTS IN THE MID 60S WHICH DOES SEEM POSSIBLE
OVER SE NEB/SW IA THIS AFTN. IN ADDITION...MODELS INDC THE
DEVELOPMENT OF LOW TO MID LVL WAA AS THE FLOW BACK THIS AFTN. THUS
WL MAINTAIN A CHC POP FOR THIS AFTN IN THIS AREA...BUT EXPECTED
COVERAGE TO BE FAIRLY LIMITED AND DROPPED POPS BACK.
OTHERWISE...DO EXPECT SOME CLEARING ONCE MRNG ACTIVITY SHIFTS EWD
AND SO NO CHANGES TO GOING TMPS ATTM.
BOUSTEAD
&&
.PREV DISCUSSION... /ISSUED 340 AM CDT TUE SEP 21 2010/
DISCUSSION...
UNSETTLED WEATHER...AND TEMPERATURES THE PRIMARY CONCERNS OVER THE
NEXT FEW DAYS.
AFTER A HOT AND WINDY MONDAY...THE COLD FRONT IS MAKING IT/S WAY
SOUTHWARD ACROSS THE FORECAST AREA. AT 08Z...THE SFC WINDS WERE FM
THE NORTH A KOLU/KOFK/KLCG WITH SOUTH WINDS AHEAD OF THE FRONT.
THUNDERSTORMS WERE NOTED AHEAD OF AND ALONG THE COLD FRONT WITH
SHOWERS TRAILING FARTHER WEST. 90M HT FALLS WERE NOTED WITH THE
SHORTWAVE TROF THAT WAS TRACKING ACRS THE NRN PLAINS AND THIS WAVE
IS ALREADY MOVING INTO THE GREAT LAKES...WITH A WEAKENING PUSH OF
THE FRONT. WILL NEED TO DECIDE HOW TO HANDLE CONVECTION.
CONVECTION HAS BEEN DEVELOPING SOUTH INTO THE MO VALLEY AS THE
SHORTWAVE TROF SHIFTS EAST AND HAS PRODUCED SOME DIME-SIZED HAIL
WITH SOME OF THE STORMS. H85 THETA-E ADV IS EXPECTED TO INCREASE
LATER THIS MORNING AND CONTINUE THIS AFTERNOON CENTRAL AND SOUTH
WITH POOLING OF H7 MOISTURE AND H85 DEWPOINTS AROUND 14 DEG C
RANGE. THE WATER VAPOR STLT IMAGERY SHOWS A PLUME OF MID LEVEL
MOISTURE ATTENDING THE MID LEVEL TROF STREAMING FM MEXICO ACRS NM
INTO KS AND NEB. WILL ADJUST POPS BASED ON TRENDS...BUT EXPECT TO
KEEP SOME LIKELY POPS IN THE AREA TODAY WITH THE SFC FRONT AND
THEN HAVE THE HIGHER POPS IN THE SOUTHEAST BEFORE TRENDING
DOWNWARD TONIGHT AS THE FORCING WEAKENS. SFC TEMPS HAVE DROPPED
INTO THE 50S NEAR ONL...BUT REMAIN IN THE 70S SOUTH OF THE FNT.
MOST TEMPS SHOULD REMAIN IN THE 70S...HOWEVER IN THE SOUTH...SOME
SPOTS MAY RISE INTO THE 80S BEFORE FROPA. WITH HIGH DEWPOINTS AND
WEAK FLOW SHOULD SEE SOME FOG IN THE MORNING.
WEDNESDAY AHEAD OF THE NEXT APPROACHING TROF...THE SFC FRONT WILL
LIFT NORTH AS A WARM FRONT. UVV AHEAD OF THE LEAD WAVE
WITH CONTINUED THETA-E ADVECTION SHOULD SPARK ADDITIONAL
THUNDERSTORM DEVELOPMENT. THE ORGANIZED THUNDERSTORMS WILL BE OVER
NORTHERN NEB INTO SOUTH DAKOTA AND IOWA. SEVERE STORMS MAY DEVELOP
AS MODERATE INSTABILITY IS EXPECTED ALONG WITH STORMS BEING ON THE
GRADIENT OF THE STRONGER DEEP LAYER SHEAR. DUE TO TRAINING OF
STORMS...WILL NEED TO MONITOR FOR LOCALLY HEAVY RAINS. THERE ARE
SOME DIFFERENCES FOR WED NIGHT AS THE ECMWF/NAM HOLD OFF ON THE
RAIN WHILE THE GFS BRINGS THE PRECIP FARTHER SOUTHEAST. FOR NOW
WILL KEEP THE HIGHEST POPS IN THE NORTH WED NIGHT AND THEN BRING
THEM SOUTH THURSDAY AHEAD OF THE SHORT WAVE TROF...MORE IN LINE
WITH THE ECWMF/NAM. THURSDAY NIGHT...THIS WAVE MOVES EAST WITH THE
TRAILING COLD FRONT AND HIGH PRES BUILDS IN OVERNIGHT.
FRIDAY THROUGH TUESDAY IS STILL LOOKING MAINLY DRY. THERE MAY BE
SOME ISO SHOWERS FRI NIGHT AND SAT. LOWS IN THE 40S AND 50S WITH
HIGHS IN THE 70S.
AVIATION...
06Z TAFS
MAINLY VFR CONDITIONS ARE EXPECTED THROUGH 06Z WEDNESDAY. A COLD
FRONT DRIFTING SOUTHEAST THROUGH EASTERN NEBRASKA WILL TRIGGER
SHOWERS THROUGH TUESDAY. CIGS BETWEEN FL050 AND FL100 ARE LIKELY
WITH AREAS OF VSBYS NEAR 3SM IN THE RAIN. LOWER CIGS NEAR FL030 MAY
DEVELOP THROUGH 18Z BEHIND THE FRONT. CHANCES FOR RAIN DECREASE
MARKEDLY AFTER 00Z WEDNESDAY WITH WEAK NORTHEAST OR EAST SURFACE
WINDS. MVFR/IFR CIGS ARE POSSIBLE AT ALL TAF SITES AFTER 06Z.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&
$$