FXUS63 KOAX 220359
AFDOAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
959 PM CST MON DEC 21 2009

.UPDATE...
UPDATED GRIDS TO REMOVE MENTION OF ACCUMULATING PRECIPITATION IN
THE NORTH...AND CONFINED PATCHY FREEZING DRIZZLE MENTION TO NORTH
AND WEST AREAS.

&&

.DISCUSSION...
PRECIPITATION ASSOCIATED WITH CLIPPER SHORTWAVE WAS REMAINING TO
THE LEFT OF WAVE TRACK FROM SOUTHEAST SOUTH DAKOTA INTO CENTRAL
IOWA. THUS THE CHANCE FOR LIGHT SNOW OR FREEZING RAIN HAS
DIMINISHED GREATLY OVER THE NORTHERN AND NORTHEAST CWA. BAND OF
STRATUS SPILLING INTO CENTRAL AND NORTHEAST NEBRASKA ON BACK SIDE
OF SHORTWAVE AND ASSOCIATED SURFACE LOW WAS DRIVING VISIBILITIES
DOWN TO BELOW A MILE JUST WEST OF OUR CWA. SO A MENTION OF PATCHY
FOG IS WARRANTED THERE. LIFT FOR FREEZING DRIZZLE IS ON THE WANE
IN SUBSIDENCE REGION BEHIND SHORTWAVE...BUT KEPT MENTION FOR NOW
AS POSSIBILITY FOR LOW VISIBILITIES IN FREEZING FOG IS STILL THERE
WHICH WOULD HAVE A LESSER BUT SIMILAR IMPACT.

ALSO TOOK A QUICK LOOK AT INCOMING 00Z MODELS (NAM/GFS). IF
ANYTHING JUMPS OUT RIGHT AWAY IT IS THAT TEMPERATURE PROFILE WOULD
SUGGEST RAIN WILL MAKE IT FARTHER NORTHWEST INTO THE
CWA...ESPECIALLY INITIALLY WITH FIRST SURGE OF SIGNIFICANT
PRECIPITATION ON WEDNESDAY. WILL HAVE TO DO WAY MORE
INTERPRETATION TO GET A GOOD FIX ON WHAT WILL TRANSPIRE. MID SHIFT
WILL HAVE PLENTY OF TIME TO DO THAT.

DERGAN

&&

.PREV DISCUSSION... /ISSUED 429 PM CST MON DEC 21 2009/ 

SHORT TERM...TONIGHT THRU THURSDAY.
..POTENTIALLY CRIPPLING STORM TO AFFECT THE REGION THIS WEEK...

THE FORECAST CONCERNS IN THE SHORT TERM ARE NUMEROUS AND INVOLVE A
MAJOR WINTER STORM THAT WILL BEGIN TO AFFECT THE AREA TUESDAY
NIGHT AND CONTINUE INTO FRIDAY.

INITIALLY...A SHORTWAVE TROF TRACKING INTO IOWA TONIGHT WILL TAKE
THE BULK OF THE PRECIPITATION INTO MINNESOTA AND IOWA...THEN ON TO
SOUTHERN WI AND NORTHERN IL. FOR THE LOCAL AREA...MAINLY PATCHY
FREEZING DRIZZLE AND SOME FOG CAN BE EXPECTED WITH LOWS IN THE 20S TONIGHT.

TUESDAY...THE CLOSED LOW OVR THE PACIFIC NORTHWEST WILL BEGIN TO
DIVE SOUTHEAST TOWARDS FOUR CORNERS AREA. LITTLE IN THE WAY OF
LIFT IS AVAILABLE...THUS AGAIN...ANY PRECIPITATION SHOULD BE LIGHT
AND DUE TO THE COLD SURFACE TEMPERATURES AND LACK OF ICE IN THE
COLUMN...FREEZING DRIZZLE IS EXPECTED TO BE THE PREDOMINANT TYPE
OF PRECIP.

TUESDAY NIGHT...A WAVE OF ENERGY AHEAD OF THE MAIN LOW WILL BRING
LIFT AND INCREASING TRANSPORT OF DEEPER MOISTURE INTO THE REGION
ALONG WITH STRONG WAA. PRECIPITATION IS EXPECTED TO INCREASE
OVERNIGHT WITH MIXED PRECIPITATION AS THE WARMER AIR MOVES IN FROM
THE SOUTH. FOR THIS PACKAGE TRENDED TOWARD THE GFS/ECMWF FOR
TEMPERATURES. THIS PULLED THE WARMER AIR NORTHWARD ENOUGH TO
MENTION RAIN IN SOUTHEAST NEBRASKA AND SOUTHWEST IOWA. DUE TO THE
WARMER AIR WORKING INTO THE SOUTH...DECIDED TO ADJUST THE HEADLINE
FOR A LATER START OF THE WSW UNTIL WEDNESDAY NIGHT FOR SE NEB AND
SW IOWA. WITH OMAHA AND LINCOLN AREAS WILL ON THE EDGE AS TO THE
LOCATION OF THE SNOW/FREEZING RAIN AND RAIN...LEFT THEM IN THE
EARLIER WSW THAT STARTS TUESDAY NIGHT AT 06Z. OTHER HEADLINE
CHANGES WERE TO EXTEND THE WSWS UNTIL FRIDAY AS STRONG WINDS AND
SNOW ENDING WILL AFFECT THE FORECAST AREA. 

DURING THE DAY WEDNESDAY...THE FIRST WAVE OF LIFT AND WAA IS STILL
MOVING THROUGH WITH MIXED PRECIP FROM NORTH TO SOUTH FROM SNOW TO
SLEET AND FREEZING RAIN...TO RAIN IN THE SOUTH. THE SFC LOW IS
DEEPENING OVR TX WHILE THE MAIN STORM SYSTEM IS OVER ERN NEW MEXICO.

WEDNESDAY NIGHT...THE TROF OVR CANADA PHASES WITH THE TROF OVR THE
ROCKIES AND BECOMES NEGATIVELY TILTED. THIS ALLOW COPIUS AMOUNTS
OF MOISTURE AND WARM AIR TO BE DRAWN NORTHWARD FROM THE GULF ACRS
ARKANSAS AND MISSOURI...TOWARD NEBRASKA AND IOWA. LIFTED INDEX
VALUES LOWER TO BELOW ZERO OVER PARTS OF MISSOURI...WITH
THUNDERSTORMS...HEAVY RAIN...AND SEVERE WX FOR SRN MO.  LIFT
CONTINUES THRU THE DAY WITH A TIGHT BAROCLINIC ZONE ACROSS THE
CWA. DEPENDING ON EXACTLY WHERE THE SNOW/FREEZING RAIN/SNOW LINE
SETS UP...THERE COULD BE SIGNIFICANT AMOUNTS OF SNOW AND ICE
WEDNESDAY WITH RAIN IN SOUTHEAST NEBRASKA AND SOUTHWEST IOWA. AT
THIS TIME HAVE THE HEAVIER ICE ACCUMULATIONS JUST NORTH OF THE
LINCOLN AND OMAHA AREAS TOWARD COLUMBUS AND WEST POINT. THIS
HOWEVER MAY CHANGE SHOULD THE LOCATION OF THIS THERMAL GRADIENT
CHANGE AND THE STORM EVOLVES. HEAVY RAIN COULD ALSO IMPACT SOUTHEAST
NEBRASKA AND BRIEFED THE HYDROLOGIST ON THIS AS BOTH THE ECMWF AND
GFS WERE POINTING TO BTWN 1.5 AND 3 INCHES OF QPF FOR THE STORM.
SEVERAL INCHES OF SNOW REMAIN OVER THE REGION AND WILL INCREASE
RUNOFF.

ALTHOUGH THIS AREA OF LIFT MOVES THROUGH WEDNESDAY NIGHT...THE
STORM AND IT/S SFC LOW REALLY BEGINS TO DEEPEN THURSDAY AND MOVES
INTO MISSOURI...LIFTING NORTHWARD. THIS ALLOWS THE PRECIPITATION
TO CHANGE OVER TO HEAVY SNOW FROM NW TO SOUTHEAST...COMBINED WITH
STRENGTHENING NORTH AND NORTHWEST WINDS. THE DEFORMATION BAND SNOW
SHOULD REALLY ADD TO THE SNOW TOTALS THURSDAY.  WILL NEED TO
CONSIDER A BLIZZARD WATCH WITH 50KT H85 WINDS ON THE BACKSIDE OF
THE STORM. THE SNOW AND BLOWING SNOW WILL CONTINUE THURSDAY NIGHT
AND FRIDAY MORNING...WITH THE MORE SIGNIFICANT ACCUMULATING SNOW
TAPERING OFF FROM WEST TO EAST. INTIAL SNOW/ICE/RAIN TOTALS ARE
VERY PRELIMINARY. HAVE THE HEAVIEST AMOUNTS IN THE NORTHWEST WITH
10 TO 16 INCHES IN THE NORTHWEST TO 4 TO 8 INCHES IN THE
SOUTHEAST WITH SOME ICE ACCUMULATIONS IN EXCESS OF A QUARTER OF AN INCH.

LONG TERM...THURSDAY NIGHT THROUGH MONDAY.

THE MAIN FORECAST CONCERN IN THE LONG TERM IS THE CONTINUED MOVEMENT 
OF THE POTENTIAL WINTER STORM SYSTEM...WHICH WILL BEGIN TO EXIT THE 
REGION THROUGH FRIDAY INTO SATURDAY. LATEST MODEL SOLUTIONS HAVE 
COME INTO BETTER AGREEMENT REGARDING THE TIMING AND TRACK OF THE 
SURFACE LOW. AT 00Z FRIDAY...THE 12Z GFS AND ECMWF CONTINUE TO PLACE 
THE SURFACE LOW CENTER ALONG THE KANSAS/MISSOURI BORDER. THE LATEST 
RUN OF THE ECMWF HAS REVEALED MUCH BETTER AGREEMENT WITH THE 12Z GFS 
THAN THE PREVIOUS 00Z ISSUANCE...SLOWING THE MOVEMENT OF THE LOW OUT 
OF THE PLAINS. THIS SLOWER DEPARTURE WAS ABSENT FROM THE PREVIOUS 
ECMWF RUN...BUT EVIDENT IN THE 12Z GFS...AND IS FAVORED DUE TO THE 
LACK OF NEW ENERGY UPSTREAM OF THIS SYSTEM TO KICK IT OUT. THIS HAS 
ADDED GREATER CONFIDENCE TO THE MODEL SOLUTIONS. DUE TO THE PREVIOUS 
CONTINUITY OF THE ECMWF...AND BETTER AGREEMENT WITH THE GFS...HAVE 
SETTLED ON A COMPROMISE BETWEEN THE GFS AND ECMWF.

ACCORDING TO THE 12Z GFS...850 MB AND SURFACE TEMPERATURES AT 00Z 
FRIDAY ARE BELOW FREEZING ACROSS THE FORECAST AREA AND WARM AIR 
ADVECTION AND SOUTHERLY FLOW AHEAD OF THE STORM WILL PROVIDE 
SUFFICIENT MOISTURE.  THUS EXPECTING THE SNOW ON THURSDAY TO 
CONTINUE INTO FRIDAY MORNING AS FORECAST SOUNDINGS ACROSS THE AREA 
KEEP PROFILES BELOW FREEZING...ALONG WITH SUFFICIENT MOISTURE AND 
TEMPERATURES IN THE DENDRITIC LAYER CONDUCIVE TO SNOW DEVELOPMENT. 
BOTH THE 12Z GFS AND ECMWF ARE CONTINUING TO PREDICT STORM 
ACCUMULATED PRECIPITATION AMOUNTS NEAR 2.5 TO 3 INCHES BY 00Z 
SATURDAY ACROSS EASTERN NEBRASKA. IF THIS VERIFIES...IT WILL RESULT 
IN A SIGNIFICANT IMPACT REGARDLESS OF PRECIPITATION TYPE. HAVE ONLY 
ADJUSTED POPS SLIGHTLY FROM PREVIOUS FORECAST.  HAVE EXPANDED SLIGHT 
CHANCE POPS ACROSS THE EASTERN COUNTIES FRIDAY NIGHT INTO SATURDAY 
TO ACCOUNT FOR THE SLOWER DEPARTURE OF THE SYSTEM. 

AS THE STORM SYSTEM MOVES EASTWARD...MODEL SOLUTIONS CONTINUE TO 
PREDICT STRONG SURFACE WINDS ON THE BACK SIDE OF THE DEEPENING 
SURFACE LOW...WITH NORTH WINDS APPROACHING 40 KTS ACROSS THE REGION. 
THESE STRONG WINDS COULD LEAD TO VISIBILITY ISSUES DUE TO BLOWING 
SNOW...AND COULD ALSO LEAD TO EXTREMELY LOW WINDCHILL 
TEMPERATURES AS LOWS NEAR THE END OF THE WEEK ARE EXPECTED TO DROP 
INTO THE SINGLE DIGITS. OVERCAST CONDITIONS THURSDAY EVENING WILL 
KEEP LOWS IN THE TEENS...BUT LESSENING COVER ON FRIDAY AS THE SYSTEM 
HEADS EAST AND NORTHERLY FLOW SETS UP WILL CAUSE LOWS TO REACH THE 
SINGLE DIGITS FRIDAY NIGHT AND SATURDAY NIGHT. A RIDGE OF HIGH 
PRESSURE WILL BUILD IN BEHIND THE EXITING SYSTEM GIVING WAY TO 
CALMER WEATHER THROUGH MONDAY.

AVIATION...
TAF SITES KOFK/KOMA/KLNK 

18Z TAFS

LOWER CIGS HAD MOVED EAST OF THE MISSOURI RIVER AT 19Z WITH EXTENSIVE
MID LAYER ACROSS EAST HALF OF NEBRASKA IN ADVANCE OF MID LEVEL WAVE. 
FORECAST SOUNDINGS SUGGEST LIFR CIGS SHOULD RETURN TO ALL THREE 
SITES TONIGHT WITH SOME CHANCE OF -FZRA AFTER ABOUT 09Z. TEMPERATURES
FORECAST TO BE AROUND FREEZING TUE MORNING SO PRECIP TYPE BECOMES A 
PROBLEM. FOR NOW HAVE KEPT AS -ZR. 

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...WINTER STORM WATCH FROM LATE TUESDAY NIGHT THROUGH LATE THURSDAY 
     NIGHT FOR NEZ011-012-015>018-030>034-042>045-050>053-065-
     066-078-088.

     WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH FRIDAY MORNING 
     FOR NEZ067-068-089>093.

IA...WINTER STORM WATCH FROM LATE TUESDAY NIGHT THROUGH LATE THURSDAY 
     NIGHT FOR IAZ043-055-056-069.

     WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH FRIDAY MORNING 
     FOR IAZ079-080-090-091.

&&

$$

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