FXUS63 KOAX 241521
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
921 AM CST WED NOV 24 2010
.UPDATE...
HAVE REMOVED ADVISORY FOR EASTERN PARTS OF AREA ISSUED EARLIER
THIS MORNING AS TEMPERATURES HAVE WARMED INTO THE MID 30S.
&&
.PREV DISCUSSION... /ISSUED 312 AM CST WED NOV 24 2010/
DISCUSSION...
COMPLEX WEATHER FORECAST IS THE STORY...WITH DEPENDENCE ON SUBTLE
FEATURES LEADING TO LOW CONFIDENCE IN THIS CHALLENGING FORECAST WITH
SENSITIVE TIMING DUE TO HOLIDAY TRAVEL. SUBJECTIVE 00Z UPPER AIR
ANALYSIS INDICATES UPPER LOW CENTERED IN NRN ID/WRN MT. 125KT+
UPPER-LEVEL JET WAS PUNCHING BEHIND LOW AS WELL AS AHEAD...WITH LOW
STILL DIGGING/DEEPENING IN THE WRN US. 850MB MOISTURE WAS FAIRLY
WELL REMOVED FROM THE CWA...WITH SHARP GRADIENT FROM DRY AIRMASS TO
10-12C+ DEWPOINTS IN ERN TX/SRN OK/CNTRL AR...AS WELL AS SOME
SATURATION MOVING IN FROM THE PAC NW. STRONT 850MB WINDS WERE
HELPING ADVECT MOISTURE NWD THOUGH...WITH PROFILERS INDICATING
40-60KT WINDS IN THE CNTRL US. SURFACE LOW AT 08Z WAS CENTERED IN
NER CO...WITH STRONG PRESSURE GRADIENT ACROSS NEB INTO IA. LOW CIG
STRATUS WAS IN PLACE OVER CNTRL AND WRN NEB...BUT HAD NOT YET
PROGRESSED INTO THE CWA AT 08Z. AREA OF SHRA/TSRA WAS DEVELOPING
WELL S IN SRN MO...BUT AS OF 08Z...REGIONAL RADAR AND OBS WERE
PRECIP-FREE.
MAIN FORECAST CONCERNS LIE IN POTENTIAL FOR FREEZING DRIZZLE IN THE
NRN CWA TODAY AS WELL AS MEASURABLE OR NON-MEASURABLE PRECIP CHANCES
ELSEWHERE...FOLLOWED BY VERY COLD TEMPS TONIGHT. NOTHING SUBTLE
ABOUT THE UPPER-LEVEL FORCING TODAY AS A LARGE AND DEEP UPPER LOW
ROLLS EASTWARD ACROSS THE DAKOTAS...INDUCING LARGE-SCALE LIFT ACROSS
THE CNTRL PLAINS. 00Z REGIONAL RAOBS INDICATE A LONG WAY TO GO
BEFORE SATURATION REACHES ADEQUATE LEVELS FOR DZ...LET ALONE
SHRA...AND HAVE SLOWED TIMING OF PRECIP THIS MORNING SOMEWHAT.
BECAUSE OF THIS...ALSO HAVE PUSHED BACK START OF FREEZING RAIN
ADVISORY TO 12Z EVERYWHERE...AS SATURATION SEEMS TO BE SLOW TO REACH
THE NRN CWA...AND TEMPS ARE RISING TO NEAR OR ABOVE FREEZING IN THE
SRN CWA WHERE SATURATION IS MORE IMMINENT. BECAUSE SATURATION
REMAINS SHALLOW THROUGH THE DAY...EXPECT DZ/FZDZ TO BE THE
PREVAILING PRECIP TYPE ONCE SATURATION DOES OCCUR...BUT DID INCLUDE
LOW CHC POPS FOR POTENTIAL FOR MEASURABLE PRECIP...ESPECIALLY IN THE
ERN CWA WHERE DAYTIME MOISTURE ADVECTION AND ISENTROPIC LIFT ARE
STRONGEST. FINE LINE BETWEEN DZ AND FZDZ WILL SET UP WITH THE
SURFACE FREEZING LINE...WHICH IS EXPECTED TO SHIFT NORTHWARD UNDER
WARM AIR ADVECTION BEFORE STALLING AS COLD FRONT APPROACHES.
NORTHWARD PROGRESS OF THAT 32F LINE IS LOW IN CONFIDENCE...BUT DO
THINK THE I-80 CORRIDOR WILL BE CLEAR AND ALSO THINK THE NWRNMOST
CWA MAY NEVER GET ABOVE FREEZING TODAY. TIMING OF COLD FRONTAL
PASSAGE CONTINUES TO ACCELERATE...WITH CURRENT MODEL RUNS BARRELING
IT THROUGH THE CWA THIS AFTERNOON. EXPECT TEMPERATURES TO FALL
RAPIDLY BEHIND THE FRONT. COULD BE SOME PRECIP ALONG AND JUST
BEHIND THE FRONT AS WELL...AND AGAIN WITH SHALLOW
SATURATION...EXPECT MAINLY FZDZ BEHIND THE FRONT IF ANY PRECIP
FALLS...POSSIBLY MIXED WITH A FLURRY OR ICE PELLET AS THE COLD AIR
DEEPENS. WITH THIS POTENTIAL...CONTINUED TO INCLUDE THE NWRNMOST
CWA IN A FREEZING RAIN ADVISORY A LITTLE LATER...WITH POTENTIAL FOR
DAY SHIFT TO EXTEND IF POST-FRONTAL FZDZ IS BECOMING APPARENT. DAY
SHIFT MAY ALSO NEED TO CONSIDER CONVERSION TO A WINTER WEATHER
ADVISORY IN THE NORTH IF SNOW BECOMES THE MORE APPARENT PRECIP TYPE
BEHIND THE FRONT /ON TOP OF ICING EARLIER IN THE DAY/.
COLD AND DRY AIR MOVES IN RAPIDLY THIS EVENING BEHIND THE COLD
FRONT...WITH 850MB TEMPS OF -12 TO -16C DROPPING INTO THE CWA.
NWRLY WINDS WILL CONTINUE OVERNIGHT...PREVENTING A FULL DROP-OFF OF
TEMPS...BUT NONETHELESS BELIEVE COLD AIR ADVECTION WILL BE STRONG
ENOUGH TO PUSH TEMPS WELL INTO THE SINGLE DIGITS TO LOW TEENS ON
THANKSGIVING MORNING. IN FACT...WIND CHILLS MAY HIT THE -5 TO -15F
RANGE ALONG AND NORTH OF I-80 LATE TONIGHT/EARLY THURSDAY MORNING.
HAVE NUDGED TEMPS DOWNWARD JUST A BIT TONIGHT AND ALSO CUT
TEMPS ON THURSDAY...AS RECOVERY ON THURSDAY WILL BE LIMITED BY
WEAKENING WINDS AS A WEAK SURFACE RIDGE MOVES THROUGH. ANOTHER COLD
NIGHT IS EXPECTED THURSDAY NIGHT AS NEUTRAL TEMPERATURE ADVECTION
AND COLD AIRMASS PERSIST...ALONG WITH A BETTER POTENTIAL FOR
DECOUPLING WINDS AS SURFACE PRESSURE GRADIENT SLACKENS. RECOVERY
WILL BEGIN FRIDAY AND CARRY THROUGH THE WEEKEND...WITH MODERATING
TEMPS AND QUIET WEATHER.
AVIATION...
TAF SITES KOFK/KOMA/KLNK
06Z TAFS
COMPLEX AVIATION FORECAST WITH 24/06Z TAFS. INITIALLY STRONG SERLY
LOW LVL WINDS AHEAD OF LOW PRESSURE ALONG FRONT RANGE OF WY/CO COULD
CAUSE AREAS OF LLWS BEFORE THEY ADVECT ENOUGH MOISTURE NWD TO LOWER
CIGS AT TAF SITES LATER THIS MORNING. THESE CIGS SHOULD GENERALLY
BE IN THE MVFR CATEGORY BY 24/12Z...ALTHOUGH THEY COULD EVEN DROP
INTO IFR CATEGORY...SPCLY TWD KOFK...A FEW HRS AFTER THAT. IN
ADDITION...THIS LOW LVL INCREASE IN MOISTURE COULD ALSO CAUSE AREAS
OF DZ/FZDZ TO DVLP IN 24/12Z-24/15Z PD AND EVEN BRING A TSTM OR TWO
TO SERN NEBR/SWRN IA. HOWEVER....SFC TEMPS WILL BE CLIMBING TOWARD
OR PERHAPS JUST A BIT ABOVE FREEZING AT KOMA/KLNK...THUS WITH 06Z
TAF ISSUANCE FZDZ WAS JUST MENTIONED AT KOFK. ALSO IT WAS THOUGHT
THAT ANY TSTMS THIS MORNING WOULD REMAIN SE OF TAF SITES. MEANWHILE
A STRONG UPPER SYSTEM TRACKING ACROSS MT TDA WILL DRIVE AN ARCTIC
COLD FRONT ACROSS EASTERN NEBRASKA THIS AFTN. GUSTY NW SFC WINDS AND
MVFR CIGS ARE EXPECTED BEHIND THIS FRONT ALONG WITH POSSIBLY AN HR
OR TWO OF LGT FZDZ.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...FREEZING RAIN ADVISORY UNTIL 3 PM CST THIS AFTERNOON FOR NEZ011-
012-016-017-030-031.
IA...NONE.
&&
$$
FOBERT