FXUS63 KOAX 232111
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
311 PM CST WED DEC 23 2009
.SHORT TERM...TONIGHT THROUGH SATURDAY. LET ME START OFF BY SAYING
THAT EVEN THOUGH WE ARE ONE DAY CLOSER...SOME OF THE SPECIFIC DETAILS
REGARDING THE ONGOING WINTRY WEATHER REMAIN UNCLEAR.
THE FIRST ROUND...AS EXPECTED THIS FIRST ROUND OF PRECIPITATION
HAS PANNED ABOUT JUST AS EXPECTED. FREEZING RAIN DEVELOPED LAST
NIGHT AND MOVED INTO AREAS ALONG/SOUTH OF INTERSTATE 80...AND AS
THE BAD HAS MOVED INTO NORTHEAST NEBRASKA...SNOW HAS DEVELOPED
WHERE ITS COLD ENOUGH THROUGH THE ENTIRE COLUMN...WITH UP TO 3
INCHES ALREADY REPORTED. ALSO...SHOWERS WITH THUNDERSTORMS WERE
NOW MOVING INTO SOUTHEAST NEBRASKA AND WILL LIKELY STILL CLIP
SOUTHWEST IOWA...BUT TEMPERATURES ARE ABOVE FREEZING IN THIS AREA.
OTHERWISE...THE HORTEN BAND WILL CONTINUE TO SHIFT NORTH
TONIGHT...AND THERE WILL LIKELY BE A LULL IN THE PRECIPITATION FOR
OTHER AREAS UNTIL THE NEXT ROUND MOVES IN TOMORROW.
THE SECOND ROUND...THE INVERTED SURFACE TROUGH THAT EXISTS FROM
EASTERN OK THRU NWRN MO WILL REMAIN IN PLACE AS CYCLOGENESIS TAKES
PLACE TONIGHT...ALLOWING RAPID DEEPENING TO TAKE PLACE. THE NAM/GFS
ARE NOW IN VERY GOOD AGREEMENT REGARDING THE EVOLUTION...DEVELOPING
A 997SH LOW BY 12Z THURSDAY...DEEPENING TO AROUND 990SH BY 00Z FRI
AND MOVING TO SWRN MO...THEN DEEPENING EVEN MORE TO 987SH AND MOVING
DUE NORTH TO SCNTRL IA BY 12Z FRI...THEN EVEN RETROGRADING POSSIBLE
TO NORTHWEST IOWA. THIS IS CONJUNCTION WITH A NORTHERN AND SOUTHERN
STREAM UPPER SYSTEMS PHASING. THERE REMAINS SOME UNCERTAINTY HOW
FAR WEST THE SYSTEM DEVELOPS...WITH THE EC/GEM MODELS KEEPING THE
SURFACE LOW FURTHER EAST NEAR THE QUAD CITIES. BELIEVE THAT MAY BE
TOO FAR EAST...SINCE THE PHASING OFF THE TWO SYSTEMS SHOULD HELP
TO PULL THE SURFACE LOW FURTHER WEST.
FOR SENSIBLE WEATHER...WILL LIKELY SEE PRECIPITATION SPREAD INTO
THE FORECAST AREA FROM THE SOUTHEAST ON THURSDAY. HOWEVER...IN
SOUTHEAST NEBRASKA AND SOUTHWEST IOWA...THERMAL PROFILES STILL
SUGGEST THAT FREEZING RAIN WOULD BE LIKELY UNTIL MIDDAY...THUS
STILL A THREAT FOR ADDITIONAL SIGNIFICANT ICING ACCUMULATIONS FROM
FNB TO ICL FROM 6AM TO NOON BEFORE COLDER AIR ARRIVES. OTHERWISE...
THE COLD AIR SHOULD BE IN PLACE ELSEWHERE FOR ALL SNOW. ONCE THE
SNOW MOVES IN THROUGH THE DAY THURSDAY...FROM EAST TO WEST...THE
SNOW WILL CONTINUE THEN FOR THURSDAY NIGHT...FRIDAY...AND EVEN
FRIDAY NIGHT. DURING THIS TIME...WINDS WILL ALSO BE INCREASING TO
25 TO 35 MPH WITH GUSTS TO 40 TO 45 MPH. ALSO DURING THIS
TIME...SNOWFALL RATIOS WILL BE INCREASING...STARTING AROUND 10/12
TO 1...BUT INCREASING TO 14 TO 18 TO 1 THROUGH THE EVENT. THIS
WILL ALLOW THE SNOW TO BECOME DRIER WITH TIME...WHICH WILL ALSO
ALLOW MORE SIGNIFICANT VISIBILITY RESTRICTIONS.
HEADLINES...WITH THE COMBINATION OF A 48 HOUR DURATION EVENT...WITH
THE POSSIBILITY OF 6 TO 15 INCHES OF ADDITIONAL SNOW...ALONG WITH NEAR
BLIZZARD CONDITIONS DEVELOPING LATE THURSDAY AND FRIDAY...WE WILL
BE UPGRADING THE WINTER STORM WATCH TO A WINTER STORM WARNING
BEGINNING 6 AM THURSDAY...LINGERING THROUGH SATURDAY MORNING. AT
THIS TIME...HEAVIEST SNOWFALL APPEARS TO BE ORIENTED IN THE
MISSOURI RIVER VALLEY...WITH LESSER AMOUNTS FORECAST WEST/SOUTH OF
LINCOLN. THE EXISTING WINTER STORM WARNING WILL CONTINUE...FOR
SNOW THAT MOVES THROUGH THIS EVENING. WITHIN THIS EXISTING WINTER
STORM WARNING IN NORTHEAST NEBRASKA...THERE WILL ALSO LIKELY BE A
LULL IN THE PRECIP LATE TONIGHT AND EARLY THURSDAY. HOWEVER...FOR
SIMPLICITY...IT WAS BEST TO LEAVE THIS IN TACT...RATHER THAN
CANCELLING THE EXISTING WARNING...THEN ISSUING A NEW WARNING FOR
HEAVY SNOW THAT IS EXPECTED TO REDEVELOP.
UNCERTAINTIES...MODEL SOLUTIONS ARE STILL THE PRIMARY UNCERTAINTY...
WITH REGARDS TO HOW FAR WEST THE SURFACE LOW WILL MOVE. IF THE EC/GEM
VERIFIES WITH A FURTHER EAST TRACK...THE AXIS OF HEAVIEST SNOW WILL
SHIFT EAST. ANOTHER UNCERTAINTY WILL BE WHETHER OR NOT BLIZZARD
CRITERIA MIGHT EVENTUALLY BE MET LATE THURSDAY NIGHT THROUGH
FRIDAY. CERTAINLY EASTERN NEBRASKA HAS THE BEST POTENTIAL...WITH
SLIGHTLY LOWER WIND SPEEDS IN WESTERN IOWA DUE TO CLOSER PROXIMITY
TO THE SURFACE LOW. WITH INCREASED SNOW RATIOS...THE SNOW WILL
HAVE A GREATER ABILITY TO BLOW THUS HAVING A GREATER PROBABILITY
OF MEETING BLIZZARD CRITERIA. ALSO...VARYING SFC LOW POSITIONING
DURING THIS TIME WILL HAVE AN IMPACT ON COVERAGE AREA MAKING AREAL
PLACEMENT TOO DIFFICULT AT THIS TIME.
.LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY. LATE WEEK/WEEKEND
SYSTEM WILL STILL BE SPINNING IN THE WRN GT LAKES ON SAT NT AS IT
MOVES NEWD OUT OF THE AREA. HAVE ADDED A VERY LOW SCHC POP FOR LT
SNOW ON SAT NT IN THE ERN CWA...AND ALSO INCREASED CLOUDS...AS
MODELS INDICATE A WEAK WAVE ROTATING AROUND THE BACK EDGE OF THE
SLOW-MOVING UPPER LOW. FOR SUN THROUGH TUES...MADE FEW CHANGES TO
THE FORECAST AS HIGH PRESSURE AND UPPER-LEVEL RIDGING MOVE
THROUGH. KEPT TEMPS IN THAT PERIOD BELOW GUIDANCE WITH FRESH SNOW
COVER...PARTICULARLY IN THE NERN/NRN CWA WHERE THE HEAVIEST SNOW
IS EXPECTED IN THE NEXT FEW DAYS. IN WAKE OF UPPER RIDGE...MODELS
BEGIN TO DIG A SWRN TROUGH THAT IS THEN PROGGED TO EJECT OUT
ACROSS THE CONUS. GFS/ECMWF DIFFER SIGNIFICANTLY IN THE EVOLUTION
OF THAT LOW. THE GFS WAS MUCH FURTHER SOUTH AS AN ARCTIC HIGH
DEVELOPS IN ERN SD/WRN MN...KEEPING THE CWA LARGELY DRY OR WITH
JUST LIGHT PRECIP. MEANWHILE...THE 00Z ECMWF LIFTS THE TROUGH
RIGHT ACROSS THE PLAINS...BRINGING A SWATH OF SNOW TO THE MO RIVER
VALLEY. GEM HINTS AT SLOWER PATTERN PROGRESSION...ALSO KEEPING THE
CWA DRY THROUGH TUES. WITH SO MUCH UNCERTAINTY AMONG MODELS...KEPT
FORECAST DRY FOR NOW...WITH A SLIGHT INCREASE IN CLOUDS TUES-WED.
DID NUDGE TEMPS DOWNWARD ALSO TO BRING FORECAST CLOSER TO GUIDANCE.
&&
.AVIATION...
TAF SITES KOFK/KOMA/KLNK
18Z TAFS
IFR TO LIFR CONDITIONS WILL DOMINATE THROUGH THE TAF CYCLE...WITH
PRECIP TYPE AND TIMING THE MAIN CONCERNS. BAND OF MAINLY RA IS
WORKING THROUGH KLNK/KOMA. THAT PRECIP WILL DIMINISH THROUGH THE
AFTN AT KLNK/KOMA...WITH POSSIBLY SOME DZ/FZDZ LINGERING BUT LIKELY
A BREAK IN ANY PRECIP FROM LATE THIS EVNG INTO THE OVERNIGHT HRS.
SNOW SHOULD THEN PICK UP AT KOMA/KLNK IN THE EARLY MRNG. FOR
KOFK...SNOW WILL LIKELY LINGER...THOUGH BECOMING VERY LIGHT
OVERNIGHT FOR SEVERAL HRS BEFORE BECOMING HEAVIER TMRW MRNG. WINDS
AT ALL SITES WILL BACK TO NWLY BETWEEN 06-08Z...WITH SPEEDS AND
GUSTS INCREASING INTO TMRW.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...WINTER STORM WARNING FROM 6 AM THURSDAY TO 6 AM CST SATURDAY FOR
NEZ034-045-051>053-065>068-078-088>093.
WINTER STORM WARNING UNTIL 6 AM CST SATURDAY FOR NEZ011-012-
015>018-030>033-042>044-050.
WINTER WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR NEZ034.
IA...WINTER STORM WARNING FROM 6 AM THURSDAY TO 6 AM CST SATURDAY FOR
IAZ043-055-056-069-079-080-090-091.
WINTER WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR IAZ043.
&&
$$
SHORT TERM...DEWALD/ZAPOTOCNY
LONG TERM/AVIATION...MAYES
CONFERENCE CALL/MULTI MEDIA WEB BRIEFINGS...SMITH
