FXUS63 KOAX 152104
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
304 PM CST SAT JAN 15 2011
.SHORT TERM...TONIGHT THROUGH TUESDAY
COMPLEX FORECAST THROUGH THE NEXT FEW DAYS AS SUBTLE FORCING BRINGS
CHANCES FOR LIGHT PRECIP...WITH TRICKY PRECIP TYPE ALSO A FACTOR.
SUBJECTIVE 12Z UPPER AIR ANALYSIS INDICATES DEEPENING TROUGH IN THE
ERN US...WITH VERY SUBTLE SHORTWAVES EMBEDDED IN NWRLY FLOW ACROSS
THE CENTRAL US. WARM NOSE PERSISTS OVER THE CWA...WITH 0C LINE AT
850MB CLOSE TO THE SD/NEB BORDER AS COLD AIR ADVECTS OUT OF THE
DAKOTAS. POOL OF VERY COLD 850MB AIR WAS NOTED IN CANADA/NRN HIGH
PLAINS...WITH 850MB TEMPS OF -19C AT KGGW AND -31C IN NERN
BC...THOUGH PACIFIC AIR ENCROACHING ON THE NRN ROCKIES WAS ALLOWING
TEMPS TO REMAIN ABOVE 0C THERE.
MAIN FORECAST CONCERNS ARE POTENTIAL FOR LIGHT PRECIP TONIGHT...THEN
AGAIN SUNDAY NIGHT INTO MONDAY...AND POSSIBLY FREEZING DRIZZLE
BETWEEN. SUBTLE WAVE MAY BRING VERY LIGHT PRECIP TO THE SRN CWA
TONIGHT...WITH A WEAK AND SHORT-LIVED PERIOD OF LIFT.
OVERALL...HAVE LOW CONFIDENCE IN PRECIP TONIGHT...INCLUDING
POTENTIAL FOR ACCUMULATION AS WELL AS PRECIP TYPE. HAVE LOWERED
POPS AS MOISTURE LOOKS TO REMAIN SHALLOW...AND THINK MOST AREAS WILL
STRUGGLE TO RECEIVE MEASURABLE PRECIP. DID KEEP PTYPE MENTION AS
ALL SNOW TONIGHT...LEANING TOWARD GFS SOUNDINGS...THOUGH COULD SEE A
BRIEF MIX WITH FZDZ AS MID LEVELS DRY OUT...AND IF NAM SOUNDINGS
WERE TO VERIFY...PRECIP WOULD BE ALL FZDZ. LOWERED TEMPS TONIGHT IN
THE NERN CWA...WHERE PRECIP IS LEAST LIKELY...BUT RAISED IN THE WRN
CWA UNDER CLOUDS AND RETURN FLOW BY LATE OVERNIGHT. WARM AIR
ADVECTION WILL CONTINUE FROM SUNDAY THROUGH EARLY MONDAY...AND HAVE
INDICATED LITTLE TEMPERATURE DROP-OFF ON SUNDAY NIGHT AS TEMPS
SHOULD BE STEADY OR RISING. WITH WARM AIR ADVECTION THROUGH THE DAY
SUNDAY...COULD SEE A POTENTIAL FOR DRIZZLE THROUGH THE DAY...AND
WITH SURFACE TEMPS BELOW FREEZING...IT WOULD FALL IN THE FORM OF
FREEZING DRIZZLE. THUS...CONTINUED MENTION THROUGH THE DAY ON
SUNDAY.
MORE SUBSTANTIAL WAVE IS PROGGED TO MOVE ACROSS THE DAKOTAS/MN/IA ON
SUNDAY NIGHT AND MONDAY. THINK MAIN PRECIP SHIELD WILL EXTEND FROM
WRN IA EASTWARD...JUST CLIPPING THE CWA...AS SYSTEM INTENSIFIES NEAR
THE MS RIVER VALLEY. HAVE LOWERED POPS A BIT IN THE WEST AND RAISED
IN THE EAST TO REFLECT THIS. PRECIP TYPE IS LIKELY TO BE AN ISSUE
AS STRONG WARM NOSE AROUND 850MB OVERSPREADS THE CWA WITH FALLING
SURFACE TEMPS. THOUGH THE HEAVIEST PRECIP WILL LIKELY BE
EAST...WHAT DOES FALL IN THE CWA COULD BE IN THE FORM OF FREEZING
RAIN FOR A GOOD PART OF THE EVENT...CHANGING TO SNOW IN THE
AFTERNOON AS DEEPER COLD AIR REACHES THE AREA. KEPT FZDZ MENTION IN
THE SRN CWA THROUGH MONDAY EVENING AS WELL...AS THE NOSE OF THE
COLDEST AIR PROGRESSES ACROSS THE CWA. BUMPED UP TEMPS ON MONDAY AS
WARM AIR CONTINUES TO SURGE IN AT LEAST THROUGH THE MORNING HOURS.
IN WAKE OF THE SURFACE LOW MOVING ACROSS SERN SD INTO IA...COLD AIR
IS PROGGED TO POUR INTO THE CWA MONDAY NIGHT AND TUESDAY. LIKELY
WILL SEE LITTLE WARMING ON TUESDAY AS COLD AIR ADVECTION AND GUSTY
NWRLY WINDS PERSIST THROUGH THE DAY...AND HAVE TRIED TO SQUEEZE DOWN
THE DIURNAL RANGE BETWEEN MONDAY NIGHT AND TUESDAY.
.LONG TERM...TUESDAY NIGHT THROUGH SATURDAY
THE LARGE-SCALE PATTERN CONTS TO BE WELL AGREED UPON BY THE GLOBAL
MODELS AND THEIR ENSEMBLES...BUT DETAILS OF INDIVIDUAL SHRTWV
TROFS AND THEIR ASSOCIATED SENSIBLE WX REMAIN IN QUESTION ATTM.
FOR THIS FORECAST WILL GENERALLY USE A BLEND OF THE 15/12Z EC AND
NAEFS.
PERIOD SHLD START OFF FAIRLY QUIET ON TUES NIGHT WITH SFC RIDGE AXIS
ALNG THE MO RIVER. WE HAVE COOLED LOWS A TOUCH ON TUES NIGHT...BUT
HESITATE TO GO AS COLD AS THE HPC DUE TO THE POTENTIAL FOR
CLDS...BUT GIVEN CLEAR SKIES AND THE AGREED UPON LIGHT WINDS...MAY
NEED TO ADJUST DOWNWARD IN THE FUTURE AND MEX SEEMS TOO WARM. THE
NEXT SHRTWV TROF IN THE PERSISTENT NW FLOW PATTERN WILL START TO
AFFECT THE FA ON WED. MODELS DO AGREE WELL ON THE SYSTEM DURING THAT
TIME PERIOD...BUT DIFFER ON THE LATITUDINAL TRACK. OPERATIONAL
GFS/EC WOULD TEND TO TAKE THE SYSTEM ACRS THE SRN FA...WHILE THE GEM
AND THE NAEFS WLD TAKE THE HIGHER PRECIP CHCS ACRS THE NRN FA. THE
END RESULT IS THAT WE INCREASED POPS ON WED AND WE DO EXPECT A
PERIOD OF -SN FOR PARTS OF THE AREA...BUT FORECASTING WHERE THE
HIGHEST ACCUMULATIONS WILL BE ARE DIFFICULT AT THIS RANGE. THIS
SYSTEM SHLD EXIT THE FA ON WED NIGHT BUT LINGERED SOME SCHC POPS IN
THE SE FA INTO THE EVNG HOURS. OTHERWISE QUIET WX IS EXPECTED UNTIL
LATER ON THURS. THEN THE MODELS GENERALLY AGREE ON A STG ARCTIC
CDFNT TO PLUNGE THRU THE FA. SOME OF THE COLDEST AIR OF THE SEASON
IS PROGGED TO DROP INTO THE NRN/CNTRL PLAINS...BUT HOW MUCH OF THIS
WILL AFFECT THE CWA IS YET TO BE SEEN. GFS IS FARTHER EAST WITH THE
UPPR LVL TROF AXIS KEEPING THE COLDEST AIR IN IA/MN...WHILE THE EC
SPILLS THE AIR RIGHT DOWN THRU THE HEART OF THE CWA. IF THE EC WERE
TO VERIFY...TMPS WLD BE WELL BELOW ZERO FROM THURS NIGHT THRU FRI
NIGHT. ENSEMBLE GUIDANCE INDCS SOME CAUTION HERE IN FORECASTING
EXTREME COLD...BUT WILL CERTAINLY DROP LOWS THURS NIGHT WITH MOST
AREAS SEEING TEMPERATURES LESS THAN -10 F. WE WILL ALSO DROP HIGHS
ON FRI...AND IF THE EC IS CORRECT...HIGHS WLD NOT CLIMB ABOVE ZERO
FOR THE FIRST TIME IN OMAHA SINCE JAN 1997. SFC RIDGE THEN STARTS TO
PUSH A LITTLE FARTHER EAST ON SAT ALLOWING A LITTLE
MODIFICATION...BUT STILL WELL BELOW NORMAL.
&&
.AVIATION...
TAF SITES KOFK/KOMA/KLNK
18Z TAFS
PRIMARILY MVFR CIGS EXPECTED THRU THE FCST PD AS SURFACE HIGH
PRESSURE SLIDES SLOWLY SOUTHEAST OF THE AREA TONIGHT AND SUNDAY.
SOME CHANCE OF LIGHT SNOW OR SLEET AFTER 06Z AS NEXT WEAK WAVE MOVES
INTO THE AREA BUT VSBYS ALSO EXPECTED TO REMAIN IN MVFR CATEGORY.
WINDS BECOME SOUTHERLY AFTER 12Z AT ALL 3 SITES ON BACKSIDE OF THE
HIGH.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&
$$
MAYES/BOUSTEAD/FOBERT