FXUS63 KOAX 222050
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
250 PM CST TUE DEC 22 2009
.SHORT TERM...TONIGHT THROUGH CHRISTMAS DAY.
SUMMARY...IMPENDING WINTER STORM IS THE OBVIOUS FORECAST CHALLENGE...
AND THE DURATION OF WINTRY WEATHER THAT IS EXPECTED TO LAST
THROUGH CHRISTMAS DAY. IMMEDIATE CONCERNS FOR TONIGHT AND TOMORROW
REVOLVE AROUND PRECIPITATION TYPE WITH ICING POTENTIAL ACROSS
SOUTHEASTERN 2/3 OF THE AREA. NORTHWEST 1/3 OF CWFA WILL LIKELY BE
ALL SNOW BY DAYBREAK WEDNESDAY WITH POTENTIALLY MORE THAN A FOOT
POSSIBLE. I80 CORRIDOR WILL SEE A WINTRY MIXTURE OF FREEZING RAIN
AND SLEET...THEN CHANGING OVER TO SNOW WITH POTENTIAL FOR SEVERAL
INCHES OF ACCUMULATION. FAR SOUTHEAST NEBRASKA AND SOUTHWEST IOWA
WILL HAVE THE POTENTIAL TO WARM UP ABOVE FREEZING...LIMITING THE
IMPACT IN THIS AREA...WITH LOWER AMOUNTS OF ICE...AND LOWER
AMOUNTS OF SNOWFALL. INCREASING WINDS THROUGH THURSDAY TO 25 TO 35
MPH MPH AND CONTINUING THROUGH FRIDAY WILL CREATES AREAS OF BLOWING
AND DRIFTING SNOW AND NEAR BLIZZARD CONDITIONS...MAKING FOR A
MISERABLE CHRISTMAS EVE AND CHRISTMAS HOLIDAY.
HEADLINES...REFERENCE THE SPECIFIC SUMMARY BELOW FOR THE DETAILS.
HOWEVER...WE WILL BE ISSUING A COMBINATION OF FREEZING RAIN AND
WINTER WEATHER ADVISORIES FOR TONIGHT. INITIALLY...PATCHY FREEZING
DRIZZLE IS EXPECTED...BUT AS MOISTURE BECOMES DEEPER...SHOULD
TRANSITION TO MEASURABLE FREEZING RAIN ALONG/SOUTH OF I80 TONIGHT.
WILL HAVE TO MONITOR THESE AREAS OVERNIGHT FOR POTENTIAL UPGRADE
TO AN ICE STORM WARNING...BUT WILL WAIT FOR THIS TO DEVELOP THROUGH
THE EVENING. I80 CORRIDOR WILL BE IN THE TRANSITION ZONE WITH A
MIXTURE OF FREEZING DRIZZLE...FREEZING RAIN AND SLEET. THIS INITIAL
HEADLINE WILL GO THROUGH 18Z. AT 18Z WEDNESDAY...WE WILL
TRANSITION NORTHEAST NEBRASKA INTO A WINTER STORM WARNING THAT
WILL CONTINUE THROUGH 00Z SATURDAY. IN THE I80 CORRIDOR...A WINTER
WEATHER ADVISORY WILL CONTINUE THROUGH 06Z...FOR A COMBINATION OF
SLEET... FREEZING RAIN AND SNOW. FOR THE SOUTHEAST ON WEDNESDAY...
TEMPS SHOULD WARM ENOUGH TO ALLOW FOR JUST RAIN...POSSIBLY MIXED
WITH SLEET. REGARDING THE WATCH...IN THE I80 CORRIDOR...THE WINTER
STORM WATCH WILL CONTINUE 06Z THU THROUGH 00Z SAT...WITH THE IDEA
THAT THIS WILL EVENTUALLY BE UPGRADED TO A WINTER STORM WARNING.
THE WINTER STORM WATCH IN THE FAR SOUTHEAST CWFA WILL RUN FROM 12Z
THU TO 00Z SAT.
SNOWFALL AMOUNTS...HIGHEST SNOWFALL AMOUNTS ARE FORECAST FOR
NORTHEAST NEBRASKA WHERE WE COULD SEE A FOOT OR MORE OF SNOW. THIS
IS THE LOCATION WHERE THE PRECIPITATION WILL BE SNOW THROUGH THE
WHOLE EVENT. IN THE I80 CORRIDOR...8 TO 10 INCHES SEEM LIKELY...AND
SOUTH OF THIS AREA...PERHAPS AROUND 6 TO 8INCHES.
ICE ACCUMULATION...ICE ACCUMULATION AMOUNTS FROM ONE TENTH TO ONE
QUARTER INCH WILL BE POSSIBLE IN SOME ALONG/SOUTH OF I80...BEGINNING
LATER TONIGHT THROUGH WEDNESDAY. THERE COULD ALSO BE SOME SLEET
MIXED IN WITH THIS TOO ESPECIALLY RIGHT ALONG I80. THERE IS SOME
POTENTIAL FOR A BIT MORE ICE SOUTH OF I80 ACROSS PORTIONS OF SOUTHEAST
NEBRASKA.
BRIEF SYNOPTIC OVERVIEW...12Z SUBJECTIVE UPPER AIR ANALYSIS REVEALED 3
INDIVIDUAL VORT MAXES ALONG WEST ER NORTH AMERICA. THE 2 VORT MAXES
IN THE WESTERN CONUS WILL LIKELY CONGEAL INTO A SINGLE SYSTEM
BRINGING THE FIRST WAVE OF PRECIPITATION INTO THE AREA SPREADING
FROM SOUTH TO NORTH LATE TONIGHT AND WEDNESDAY. DEFINITELY PREFER
A COMBINATION OF THE NAM/SREF/ECMWF. FEEL THAT THE GFS IS LIKELY
TOO DEEP AND TOO FAR NORTH...WITH TOO STRONG OF A BAROCLINIC
ZONE...AND RESULTANT TOO HIGH QPF. BY 12Z THUR...THE VORT MAX
CURRENTLY LOCATED IN WESTERN CANADA BEGINS TO DO A FUJIWARA
INTERACTION WITH THE SOUTHERN STREAM SYSTEM. THIS WILL RESULT IN
THE PROLONGED DURATION OF THE EVENT...WITH A SUBSTANTIAL INCREASE
IN WINDS THAT WILL LINGER THROUGH CHRISTMAS DAY.
UNCERTAINTIES...THE AMOUNT OF ICING ALONG/SOUTH OF I80 WILL BE VERY
NEAR OUR ICE STORM WARNING CRITERIA...AND WE MAY HAVE TO CONSIDER
UPGRADING SOME AREAS EARLIER THAN ANTICIPATED IF ACCUMULATIONS ARE
HEAVIER THAN FORECAST. ANOTHER UNCERTAINTY IN THIS AREA WILL BE
SURFACE TEMPERATURES. AN ICE STORM AT 31/32 WOULD NOT BE AS BAD AS
28/29. A COUPLE DEGREE TEMPERATURE DIFFERENCE CAN HAVE A VERY
LARGE IMPACT. THE I80 CORRIDOR STILL HAS A LOT OF UNCERTAINTY
BECAUSE OF THE MIXTURE OF SLEET AND FREEZING RAIN AND EVENTUAL
CHANGEOVER TO SNOW. THE UNCERTAINTY ACROSS NORTHEAST NEBRASKA
HINGES ON THE AMOUNT OF SNOW...AND WHETHER WE'VE GOT ENOUGH SNOW
IN THE FORECAST. AND FINALLY...UNCERTAINTIES REGARDING THE STRONG
WINDS WITH NEAR BLIZZARD CONDITIONS DURING THE CHRISTMAS HOLIDAY
PERIOD. MODEL UNCERTAINTIES ALSO STILL EXIST...WITH GFS STRONGER
WITH THE LOW AND FURTHER NORTH THAN OTHER MODELS...WHICH HAS A BIG
IMPACT ON NOT ONLY THE THE AMOUNTS OF SNOW...BUT WITH EVENTUAL
VISIBILITY REDUCTIONS. THERE COULD ALSO BE A CLAP OF THUNDER
ACROSS FAR SOUTHEAST NEBRASKA AND SOUTHWEST IOWA WEDNESDAY
AFTERNOON...ALTHOUGH THIS WASNT OFFICIALLY PUT INTO THE FORECAST.
.LONG TERM...FRIDAY NIGHT THROUGH TUESDAY. THE MAIN FORECAST
CONCERN IN THE LONG TERM WILL BE TEMPERATURES. ALTHOUGH MODELS
SHOW NO EXTENSIVE INTRUSION OF ARCTIC AIR BEHIND THE CHRISTMAS
WEEK STORM...NEW SNOW COVER FROM THE STORM WILL ALLOW MUCH COLDER
TEMPERATURES TO RETURN TO THE REGION DURING THE PERIOD. HAVE
TRENDED TEMPERATURES TOWARD A BLEND OF TODAYS HPC GUIDANCE AND
SURROUNDING OFFICES TEMPERATURES. SOUTHERN STREAM WAVE INDICATED
BY BOTH THE ECMWF AND GFS TOWARD THE END OF THE EXTENDED PERIOD
LOOKS LIKE IT WILL STAY SOUTH OF THE AREA...AT THIS TIME ANYWAY.
&&
.AVIATION...
TAF SITES KOFK/KOMA/KLNK
18Z TAFS
LIFR TO IFR CIGS/VIS SHOULD CONTINUE THROUGH THE TAF CYCLE AS
LOW-LEVEL CLOUDS/MOISTURE REMAIN IN PLACE. FIRST WAVE OF STORM
SYSTEM WILL APPROACH AROUND 06-12Z WED...BRINGING FZDZ AND FZRA TO
MUCH OF THE AREA THROUGH WED. KOFK MAY MIX WITH IP OR SN...WHILE
KLNK/KOMA ARE MORE LIKELY TO REMAIN FZRA/FZDZ THROUGH WED
MRNG...WITH A SMALLER MIXED PRECIP POTENTIAL. PRECIP AT KOFK SHOULD
SWITCH TO SN AROUND 15-18Z WED AND SHOULD REMAIN SN ONCE IT
SWITCHES. LIGHT NERLY WINDS WILL INCREASE WED MRNG TO AROUND
11-15KT WITH SOME HIGHER GUSTS TO AROUND 20KT.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO MIDNIGHT CST
WEDNESDAY NIGHT FOR NEZ034-045-051>053-065>068.
WINTER STORM WATCH FROM LATE WEDNESDAY NIGHT THROUGH FRIDAY
AFTERNOON FOR NEZ034-045-051>053-065>068-078-088>090-092.
WINTER WEATHER ADVISORY FROM NOON WEDNESDAY TO MIDNIGHT CST
WEDNESDAY NIGHT FOR NEZ078-088>090-092.
FREEZING RAIN ADVISORY FROM 6 PM THIS EVENING TO NOON CST
WEDNESDAY FOR NEZ078-088>093.
WINTER STORM WATCH FROM THURSDAY MORNING THROUGH FRIDAY
AFTERNOON FOR NEZ091-093.
WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO NOON CST
WEDNESDAY FOR NEZ011-012-015>018-030>033-042>044-050.
WINTER STORM WARNING FROM NOON WEDNESDAY TO 6 PM CST FRIDAY FOR
NEZ011-012-015>018-030>033-042>044-050.
IA...WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO MIDNIGHT CST
WEDNESDAY NIGHT FOR IAZ043-055-056-069.
WINTER STORM WATCH FROM LATE WEDNESDAY NIGHT THROUGH FRIDAY
AFTERNOON FOR IAZ043-055-056-069.
WINTER STORM WATCH FROM THURSDAY MORNING THROUGH FRIDAY
AFTERNOON FOR IAZ079-080-090-091.
WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO NOON CST
WEDNESDAY FOR IAZ079-080-090-091.
&&
$$
SHORT TERM...DEWALD/ZAPOTOCNY
LONG TERM...FOBERT
AVIATION...MAYES
