FXUS63 KOAX 300931
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
331 AM CST THU DEC 30 2010
.DISCUSSION...
PRIMARY CONCERN THROUGH THE NEXT 36 HOURS ARE PRECIP TYPE AND
AMOUNTS...WITH DEVELOPING SYSTEM BEARING DOWN ON THE CENTRAL PLAINS.
SUBJECTIVE 00Z UPPER AIR ANALYSIS INDICATES DEEPENING UPPER TROUGH
IN THE WRN US...WITH 150M HT FALLS AT 500MB IN NRN AZ ASSOCIATED
WITH LEAD WAVE. 125KT JET STREAK WAS PUNCHING BEHIND THE
TROUGH...AND WEAK SHORTWAVE THAT HELPED PRODUCE DRIZZLE EARLIER WAS
OVER NEB. STRONG 850MB FLOW WAS FEEDING MOISTURE INTO THE CNTRL
PLAINS...AND TEMPS HAD NOSED ABOVE 0C INTO NRN SD/CNTRL MN. 08Z
MSAS ANALYSIS INDICATED DEEP /983MB/ LOW CENTERED IN WRN KS...WITH
STRONG WARM AIR ADVECTION AHEAD OF THE LOW...AND WITH INVERTED
TROUGH EXTENDING THROUGH CNTRL NEB INTO CNTRL SD.
CHALLENGING FORECAST CONTINUES TODAY THROUGH FRIDAY...WITH PROFILE
TEMPS AND SPEED OF SYSTEM IMPACTING PRECIP TYPE AND AMOUNTS. FOR
TODAY...TIMING OF INVERTED TROUGH/NOSE OF ARCTIC AIRMASS CONTINUES
TO SPEED UP IN SUCCESSIVE MODEL RUNS...NOW REACHING THE NWRN CWA BY
AROUND 15Z. WEAK EJECTING SHORTWAVE WILL ALLOW PRECIP TO DEVELOP
ALONG THE INVERTED TROUGH...MAINLY IMPACTING THE NWRN CWA. AS COLD
TEMPS SPILL INTO THE CWA...PRECIP TYPE WILL BECOME A CONCERN EVEN
THIS AFTERNOON...WITH RAIN MIXING WITH SLEET AND/OR FREEZING RAIN
BEFORE CHANGING TO SNOW. HAVE INCLUDED AN INCH OR SO OF SNOW/SLEET
ACCUMULATION THROUGH 00Z. MEANWHILE...SRN CWA WILL SEE DRY SLOTTING
AS THE FIRST SURFACE LOW /CURRENTLY IN WRN KS/ EJECTS ACROSS THE MO
RIVER VALLEY. VIS IS IMPROVING THIS MORNING...AND TEMPS HAVE BEEN
RISING ALL NIGHT. TEMP RISE WILL STALL IN THE AFTERNOON AS THE
ARCTIC AIRMASS SWEEPS IN...BUT WITH TEMPS ALREADY IN THE 50S...HIGHS
IN THE MID 50S ARE ASSURED. DID KEEP OUT FOG MENTION THOUGH...WITH
VIS RESTRICTED BUT MORE IN AN AVIATION SENSE.
CWA WILL SEE A LULL IN PRECIP FROM AROUND 00Z TO AROUND 06-09Z IN
THE WRN CWA...AND UNTIL AROUND 12Z IN THE ERN CWA...AS LEAD WAVE
EJECTS AND MAIN LOW APPROACHES. HAVE CUT BACK ON POPS IN THIS
TIME...AND WITHOUT THE HELP OF SATURATION DUE TO FALLING
PRECIP IN THE EVENING...TEMPS TONIGHT COULD REALLY TAKE A PLUNGE.
HAVE LOWERED MINS ACROSS THE CWA...ESPECIALLY IN THE
CENTRAL/NORTHEAST CWA WHERE PRECIP/SATURATION WILL TAKE THE
LONGEST TO ARRIVE. MEANWHILE...HAVE BUMPED UP HIGHS IN THE
SRN/SERN CWA TODAY AS TEMPS HAVE RISEN THROUGH THE NIGHT...WITH
READINGS IN THE 50S AT 08Z. MAIN UPPER LOW IS STILL PROGGED TO
MOVE FROM WRN KS THROUGH CENTRAL NEB TO ERN SD...WITH SECOND
SURFACE LOW MOVING ALONG THE FRONT FROM ERN KS THROUGH NWRN MO
INTO CENTRAL IA. THIS PLACES THE CWA ON THE COLD SIDE OF THE FRONT
BUT MAINLY ON THE WARM SIDE OF THE 500MB LOW. IN THE CENTRAL
CWA... PATTERN BRINGS A WARM NOSE AT AROUND 850-800MB AND A DEEP
COLD LAYER BENEATH...WITH DIFFICULTY IN MAINTAINING SATURATION AT
HIGHER LEVELS AS MID-LEVEL DRY SLOT MOVES THROUGH...AND LOOKS LIKE
A SLEET PROFILE. IN THE SERN CWA...WARM NOSE IS CLOSER TO
900-850MB WITH SFC TEMPS STILL BELOW FREEZING...THUS LOOKING MORE
LIKE A FREEZING RAIN EVENT THERE. ALL AREAS MAY SEE AT LEAST A
LIGHT SNOW ACCUMULATION AS WELL...BUT THINK DOMINANT PRECIP TYPE
IN THE NORTHWESTERN CWA WILL BE SNOW...IN THE CENTRAL AREAS WILL
BE SLEET...AND IN THE SOUTHEASTERN CWA WILL BE FREEZING RAIN.
DURATION OF PRECIP WILL BE ON THE SHORTER SIDE...WITH AROUND 6-12
HRS OF GOOD LIFT. TROWAL FEATURE SHOULD MISS THE CWA TO THE
NORTH...POINTING MORE INTO SD. WOULD NOT RULE OUT A LITTLE
CONVECTIVE ENHANCEMENT OF PRECIP AS SOUNDINGS INDICATE PRETTY
STEEP LAPSE RATES ABOVE THE WARM NOSE...BUT THAT IS CONTINGENT ON
SATURATION ABOVE THE WARM NOSE.
QUESTION...OF COURSE...IS WHETHER THE THREE AREAS DESCRIBED ABOVE
WILL SEE ENOUGH ACCUMULATION OF ANY PRECIP TYPE /6 INCHES OF
SNOW...0.5 INCHES OF SLEET...OR 0.25 INCHES OF FREEZING RAIN/ TO
NECESSITATE AN UPGRADE FROM WATCH TO WARNING...OR IF MIXING OF
PRECIP TYPES WILL BE ENOUGH TO LIMIT ACCUMULATIONS OF EACH TYPE AND
CREATE MORE OF AN ADVISORY EVENT. WITH LOW CONFIDENCE
REMAINING...AND WITH EVENT STILL IN 2ND TO 3RD PERIOD WHERE WATCH IS
IN EFFECT...WILL ALLOW DAY SHIFT TO WATCH EVOLUTION OF ARCTIC FRONT
AND UPPER LOW TODAY BEFORE MAKING A HEADLINE DECISION. REGARDING
THE WARNING IN THE NWRN CWA...HAVE CONCERNS THAT THE ERN AREAS MIGHT
NOT REACH WARNING CRITERIA OF ANY ONE PRECIP TYPE BECAUSE OF A MIX
BETWEEN SNOW AND SLEET...BUT WILL NOT CHANGE THE EXTENT OF THE
WARNING WITH THIS PACKAGE. HOWEVER...START TIME IS A CONCERN...WITH
WINTRY PRECIP THIS AFTERNOON...A LULL AROUND THE TIME THAT THE
WARNING STARTED...AND A SURGE OF PRECIP LATE THURSDAY NIGHT/FRIDAY
MORNING. NOT COMFORTABLE STARTING WARNING DURING A LULL...AND HAVE
MOVED TIMING UP TO INCLUDE THE AFTERNOON SNOW/SLEET POTENTIAL.
AMOUNTS ARE NOT EXPECTED TO BE SIGNIFICANT...BUT WILL LAY THE
FOUNDATION FOR WHAT FALLS TONIGHT.
WINDS ARE NOT EXPECTED TO BE STRONG WITH THIS SYSTEM...MAINLY AROUND
15-25 MPH...AS SFC LOW HOVERS NEARBY AND WITH 850MB LOW OVERHEAD
KEEPING WINDS CALMER OFF THE DECK. THAT SAID...SHOULD BE JUST
ENOUGH WIND TO PUSH WIND CHILLS INTO THE TEENS BELOW ZERO IN THE
NWRN CWA TONIGHT...WITH THE COLD WIND CHILLS SPREADING INTO AT LEAST
THE NWRN HALF OF THE CWA THROUGH THE DAY FRIDAY. WIND CHILLS COULD
REACH ADVISORY CRITERIA ON NEW YEARS EVE NIGHT AS WELL IN THE NRN
CWA. FOR NOW...GRIDS ARE MARGINAL AND OTHER CONCERNS ARE MORE
IMMEDIATE...BUT WILL MENTION IN THE HWO. DID TWEAK THE TEMPERATURE
GRIDS FRIDAY NIGHT THROUGH SUNDAY...MAINLY TO COOL TEMPERATURES.
&&
.AVIATION...
TAF SITES KOFK/KOMA/KLNK
06Z TAFS
WEAK WAVE LIFTING THRU ERN NEBR LATE WED EVENING SHIFTED MOST OF THE
DRIZZLE/LOWER CIGS AND VSBYS NE OF TAF SITES AND CIGS HAD IMPROVED
INTO MVFR CATEGORY AT TAF SITES AS OF 30/07Z...ALTHOUGH KOFK DROPPED
BACK DOWN A BIT AFTER 30/07Z. IN ADDITION...CLEARING AREA OF LOWER
CLOUDS HAD REACHED KBIE AT 30/08 AND COULD MOVE INTO KLNK THIS
MORNING A BIT EARLIER THAN PREV THINKING. CIGS/VSBYS A BIT TRICKIER
FARTHER NE AS BATTLE WILL EXIST BETWEEN THIS LOW CLOUD CLEARING AND
THE DIURNAL TRENDS FOR CIGS/VSBYS TO LOWER TOWARD SUNRISE. AS OF
30/07Z KEPT CIGS IN BOTH KOFK/KOMA WITH SOME LOWERING...BUT
CIGS/VSBYS SUBJECT TO REVISION AT ALL SITES. OTHERWISE...CDFNT WL
MOVE ACROSS TAF SITES THRU PD. A PD OF FZDZ COULD PREVAIL BEHIND
FNT THIS AFTN AT KOFK AND THIS EVENING AT KLNK/KOMA...BUT COVERAGE
AND EXACT TIMING MUCH IN DOUBT AND THUS NOT INCLUDED IN 06Z TAFS.
MORE SIGNIFICANT PCPN WL BE MOVING INTO ERN NEBR AFT 31/06Z.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...WINTER STORM WATCH FROM LATE TONIGHT THROUGH FRIDAY AFTERNOON
FOR NEZ015-032>034-042>045-050>053-065>068-078-088>093.
WINTER STORM WARNING FROM NOON TODAY TO 6 PM CST FRIDAY FOR
NEZ011-012-016>018-030-031.
IA...WINTER STORM WATCH FROM LATE TONIGHT THROUGH FRIDAY AFTERNOON
FOR IAZ043-055-056-069-079-080-090-091.
&&
$$
MAYES/CHERMOK