FXUS63 KOAX 190937
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
337 AM CST SAT FEB 19 2011
.DISCUSSION...
CONVECTION STRENGTH/COVERAGE TONIGHT FOLLOWED BY FREEZING RAIN
THREAT LATE TONIGHT THROUGH MIDDAY SUNDAY PRIMARY FORECAST
CONCERN/FOCUS. IN GENERAL AND IN CONSENSUS MODELS HAVE SHIFTED SFC
LOW TRACK TRACK A BIT SOUTH FROM 24 HOURS AGO. 00Z ECMWF REMAINED
THE FARTHEST NORTH OF GFS/NAM/ECMWF TRIO AND WAS STILL PRETTY
CLOSE TO GFS ENSEMBLE MEAN. LEANED CLOSER TO THAT SOLUTION. NAM
WAS FARTHEST SOUTH WITH SFC LOW TRACK BUT QUICKLY LIFTED
PRECIPITATION NE THROUGH FORECAST AREA AND WAS NOT FAVORED. EVEN
WITH THE SLIGHTLY NW LOW TRACK OF ECMWF/GFS MEAN...SURFACE
TEMPERATURES COULD FALL TO FREEZING OR BELOW AS PRECIPITATION
STARTS N THRU WEST OF OFK LATE TONIGHT WHERE INVERTED SURFACE
TROUGH IS EXPECTED TO LIE. THEN TEMPERATURES WILL LIKELY STRUGGLE
TO CLIMB ABOVE FREEZING BEFORE FALLING AS LOW ENTERS SERN
NEBRASKA AND LOW LEVEL FLOW TURNS EVEN MORE NRLY IN NERN NEBR.
BUT BEFORE THEN...EARLY MORNING SATELLITE IMAGERY SHOWED A SUBSTANTIAL
PIECE OF ENERGY COMING ON SHORE INTO CENTRAL CALIFORNIA WITH MAIN
TROUGH AXIS STILL OFF SHORE. FOR TODAY AN INCREASE IN STRATO CU
FROM SOUTH TO NORTH IS EXPECTED TO REPLACE DEPARTING MID/HIGH
CLOUDS WITH NORTHERN ZONES POSSIBLY RECEIVING MORE SUNSHINE THAN
THE SOUTH. THUS BOOSTED TEMPS SLIGHTLY N. LEFT IN PATCHY AFTN
DRIZZLE SOUTH AS LOW LEVEL MOISTURE DEEPENS.
HOW THE WEST COAST ENERGY EVENTUALLY LIFTS ACROSS PLAINS WILL
INFLUENCE MID LEVEL CIRCULATION TRACK AND HEAVIER SNOW BAND...BUT
WITH GFS/ECMWF FORECASTING IT MOVING FM NCNTRL NEBRASKA INTO SERN
SD...HEAVIEST SNOW STILL APPEARS TO BE TO OUR N. HOWEVER...THE SYSTEM
WILL CAUSE SFC LOW PRESSURE TO DEEPEN TONIGHT OVR FAR NW KS/SW
NEBR VCNTY AND PULL UP 9-10 DEGREE C H85 DEWPOINTS INTO SERN
NEBRASKA CREATING NEGATIVE LIFTED INDICES AT THAT LEVEL OVER MUCH
OF THE AREA BY 12Z SUNDAY. IT WAS NOTED THAT THE 500 M MIXED LAYER
MOST UNSTABLE CAPE VALUES PER 00Z GFS/ECMWF WERE NOT NEARLY AS
UNSTABLE AS NAM AND ECMWF WAS GENERALLY LESS THAN 100 J/KG.
ALTHOUGH GFS WAS UP TO 500 J/KG...EVEN IT WAS MUCH LESS...AND
SHIFTED WEST OF...THE NAM. THAT SAID...STRONG LOW LEVEL JET WILL
BE IMPINGING ON SERN NEBRASKA AND MID LVL LAPSE RATES ARE FORECAST
TO BE STEEP ENOUGH TO MENTION SOME HAIL RISK IN HAZARDOUS WEATHER
OUTLOOK. WITH INSTABILITY SPREADING TOWARD FAR NRN ZONES...COULD
SEE SOME SLEET MIXED IN WITH PCPN FAR NW. HOWEVER...FOR THE TIME
BEING LIMITED PRECIP TYPE TO RAIN/FREEZING RAIN WITH TRANSITION TO
SNOW AS DEEPER COLD AIR STARTS MOVING SEWD AS SFC LOW TRACKS FM
SERN NEBR INTO SCNTRL IA BY 00Z. WITH QPF AMOUNTS PROBABLY OVER
1/4 INCH NERN ZONES...POSSIBLY ENHANCED BY TSTMS...AND SOME RISK
OF SFC TEMPERATURES REMAINING BELOW FREEZING...ISSUED A WINTER
STORM WATCH FAR NRN/NWRN COUNTIES TO REFLECT THE UNCERTAIN
TEMPERATURE THREAT. NOT SURE HOW STORM TOTAL QPF AMOUNTS...WHICH
COULD BE ON THE ORDER OF 1/4 TO 3/4 INCH...WILL AFFECT MINOR
ONGOING ICE JAM FLOODING. IF IT DOESN/T TEND TO FLUSH ICE
OUT...ADDED WATER COULD ENHANCE FLOODING. ON THE OTHER HAND IF IT
DOES HELP TO FLUSH ICE OUT IT COULD BE A SLIGHT IMPROVEMENT OR A
NET WASH. WOULD LEAN A BIT TOWARD FORMER BUT PROBABLY NOT ENOUGH
TO WARRANT FLOOD WATCH.
WITH SFC LOW TRACK PERHAPS JUST A BIT SE OF PREVIOUS THINKING
TRIMMED BACK HIGHS ALL BUT FAR SOUTHEAST ZONES. SOME 1 TO 2 INCH
SNOW ACCUMULATIONS POSSIBLE FAR NW SUNDAY AFTN/EVENING...BUT AT
THIS TIME KEPT AMOUNTS FARTHER S/SE 1 INCH OR LESS SUN NGT INTO
MONDAY. IT APPEARS UPPER LOW/TROUGH TRACK WILL KEEP INVERTED SFC
TROUGH AND PROLONGED PD OF LIGHTER SNOW JUST FAR ENOUGH NE OF
FORECAST AREA. LTL OR NO TEMPERATURE CHANGES MADE BEYOND SUNDAY
AND NO CHANGES BEYOND TUESDAY.
&&
.AVIATION...
TAF SITES KOFK/KOMA/KLNK
06Z TAFS
VFR CONDITIONS WILL BEGIN THE TAF PD WITH IFR CONDITIONS EXPECTED BY
LATER THIS AFTERNOON AS A STORM SYSTEM BEGINS TO APPROACH THE TAF
SITES. RAIN IS EXPECTED TO MOVE NORTH FROM KANSAS AND INTO NEBRASKA
AND COULD REACH AS FAR NORTH AS KLNK AND KOMA BY THE END OF THE TAF
PD. HAVE INCLUDED CB IN THE KLNK TAF AT THE END OF THE PD AS WELL AS
INSTABILITY INCREASES OVER THE REGION. WL LIKELY ADD THIS TO KOMA
AND KOFK IN 12Z TAFS.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...WINTER STORM WATCH FROM LATE TONIGHT THROUGH SUNDAY EVENING
FOR NEZ011-012-016-017.
IA...NONE.
&&
$$
CHERMOK/KERN