FXUS63 KOAX 240405
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
1005 PM CST WED FEB 23 2011
.UPDATE...
MINOR ADJUSTMENTS FOR WIND/SKY TONIGHT.
&&
.DISCUSSION...
EARLY EVENING SATELLITE SHOWED BAND OF LOW CLOUDS MOVING SOUTH
APPROACHING OMA AND OLU AT 04Z. WEST EDGE WAS THICKENING AS LOW
LEVEL FLOW WAS BECOMING MORE UPSLOPE ORIENTED...BUT HOLE ON EAST
EDGE WILL LIKELY DROP DOWN MO RIVER. 00Z NAM CONTINUED RATHER
OMINOUS WITH ITS QPF ON THURSDAY BUT WAS NOT FAVORED...AND QUICK
LOOK AT GFS SHOWED MUCH MORE MODEST AMOUNTS OUTSIDE OF SERN
NEBRASKA CORNER. STILL APPEARS TWO AREAS OF SNOW WILL SET UP...ONE
N OF H7 CIRC CENTER FM SCNTRL NEBRASKA NEWD ALONG I80 CORRIDOR AND
SECOND...PROBABLY HEAVIER ONE...FROM FAR SERN NEBRASKA INTO
ADJACENT PARTS OF KS/MO WHERE CURRENT ADVISORIES ARE IN PLACE.
RELATIVE FAST MOVEMENT OF SYSTEM AND WITH MUCH OF THE STEADIER/HEAVIER
SNOW FALLING DURING THE AFTN COULD LIMIT ACCUMULATIONS AND THUS
DID NOT ADJUST FORECAST FOR THURSDAY BASED ON LIMITED VIEWING OF
NEW DATA. CHERMOK
&&
.PREV DISCUSSION... /ISSUED 238 PM CST WED FEB 23 2011/
SHORT TERM...TONIGHT THROUGH SATURDAY.
SNOW CHANCES AND AMOUNTS ON THURSDAY...THEN CONTINUED PRECIP
CHANCES INTO SATURDAY...ARE THE PRIMARY FORECAST CONCERNS.
SURFACE TROUGH/FRONT WAS SLIPPING THROUGH THE CWA THIS AFTERNOON.
AHEAD OF THE TROUGH...TEMPERATURES HAVE WARMED WELL INTO THE 50S
WHERE SOUTHWEST LOW LEVEL FLOW PREVAILED..MAINLY OVER FAR SOUTHEAST
NEBRASKA AND SOUTHWEST IOWA. SUNSHINE AND NORTHWEST TO NORTH WINDS
PREVAILED OVER THE REST OF THE AREA...WITH TEMPERATURES WELL INTO
THE 40S. IN THE BIGGER PICTURE...UPPER TROUGH/WAVE WAS NOTED MOVING
ONTO THE SOUTHERN CALIFORNIA/NORTHERN BAJA COAST WITH STRONGER LOW
DROPPING SOUTH TOWARD SEATTLE. THIS LOW WILL HELP KICK SOUTHERN WAVE
INTO THE PLAINS LATER TONIGHT AND THURSDAY. MODELS ARE FAIRLY
SIMILAR IN SHOWING THIS...BUT DIFFER ON TRACK AND LOCATION OF
HIGHEST PRECIPITATION POTENTIAL AND AMOUNTS.
WHAT IS KNOWN IS THAT SURFACE PRESSURES WILL LOWER IN THE HIGH
PLAINS WITH THE APPROACH OF UPPER SYSTEM...THUS INDUCING ISENTROPIC
UPGLIDE THROUGH THE PLAINS OVER NORTH TO NORTHEAST SURFACE WINDS.
WHILE QPF VARIES BETWEEN MODELS...MIXING RATIOS AND WINDS ARE QUITE
SIMILAR ALONG THE 295K AND 300K THETA SURFACES. TRACK OF 700MB
LOW THROUGH SOUTHERN NEBRASKA IS SIMILAR AS WELL. DURATION OF
POTENTIAL SNOWFALL AND NORTHERN EXTENT IS A LITTLE DIFFERENT...
WITH NAM MORE BULLISH ON AMOUNTS/DURATION THAN FASTER GFS.
STILL...GIVEN MIXING RATIOS OF 2 G/KG EXPECTED THURSDAY
MORNING...AND 4 G/KG ADVECTING IN FROM CENTRAL KANSAS...COULD
EASILY SEE 3 OR 4 INCHES OF SNOW IN SOUTHEAST NEBRASKA FOR A 6 TO
12 HOUR SNOW EVENT BEGINNING THURSDAY MORNING. AFWA ENSEMBLE
FORECASTS SUGGEST A HIGH PROBABILITY OF AT LEAST 2 INCHES OF SNOW
IN THIS AREA...LEADING TO EVEN HIGHER CONFIDENCE. SURFACE
TEMPERATURES IN THE LOWER 30S WHERE MOST SNOW WILL FALL WILL HELP
TO LIMIT AMOUNTS SOMEWHAT...SO EXPECT 3 INCHES TO BE MAXIMUM
AMOUNTS. THIS IS RIGHT ON THE LOWER LIMIT OF OUR ADVISORY
CRITERIA...AND WINDS DO NOT LOOK TO BE A CONTRIBUTING FACTOR. BUT
AFTER COORDINATION WITH OFFICES TO OUR SOUTH AND WEST...WILL GO
AHEAD AND ISSUE A SNOW ADVISORY FOR SOUTHERN SECTIONS OF SOUTHEAST
NEBRASKA FOR THURSDAY.
NEXT CHANCE FOR PRECIPITATION WILL COME FROM UPPER TROUGH DROPPING
INTO THE NORTHERN PLAINS THROUGH SATURDAY. BROAD BUT WEAK MID LEVEL
DIFFLUENCE WILL BRING AN EXTENDED PERIOD OF SMALL SNOW CHANCES
BEGINNING IN OUR NORTHWEST THURSDAY NIGHT AND CONTINUING RIGHT
THROUGH SATURDAY. AMOUNTS WITH THIS SYSTEM WILL BE LIGHT WITH A
QUARTER TO HALF INCH OF SNOW EXPECTED IN ANY 6 HOUR PERIOD. OF
COURSE THIS COULD ADD UP TO A COUPLE OF INCHES WITH TIME...BUT NOT
ENOUGH TO CAUSE WIDESPREAD PROBLEMS. TEMPERATURES DURING THIS TIME
WILL BE HAMPERED BY CLOUDS AND EASTERLY LOW LEVEL FLOW...SO HIGHS IN
THE 20S AND LOWS IN THE TEENS SHOULD HOLD.
DERGAN
LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY.
LONG TERM PERIOD BEGINS WITH AN UPPER LOW OVER THE SOUTHWESTERN
STATES WITH SOUTHWESTERLY FLOW OVER THE MIDDLE OF THE COUNTRY. THIS
SHOULD PROVIDE FOR A RELATIVELY DRY START TO THE FORECAST...BUT
THINGS CHANGE QUICKLY AS THE UPPER LOW EJECTS INTO THE PLAINS. ECMWF
AND GFS ARE IN DECENT AGREEMENT IN MOVING THE MAIN LOW/TROUGH INTO
THE HIGH PLAINS BY SUNDAY AFTERNOON...THEN EAST OF THE MISSISSIPPI
RIVER BY SOMETIME MONDAY AFTERNOON. PRECIPITATION CHANCES WILL
INCREASE SUNDAY AS DIFFLUENT FLOW ALOFT PROVIDES LOW LEVEL LIFT
ACROSS A GOOD PART OF THE MIDDLE OF THE COUNTRY. THEN PRECIP CHANCES
DECREASE AGAIN MONDAY NIGHT AS SYSTEM EXITS TO THE EAST. RELATIVELY
FLAT FLOW TAKES OVER TUESDAY AND WEDNESDAY WHICH SUGGESTS AT LEAST
SOME WARMING WILL OCCUR...BUT COULD ALSO BRING A RIPPLE OR TWO OF
MID LEVEL ENERGY THAT COULD TRIGGER LIGHT PRECIP. FOR NOW THAT
PERIOD WILL REMAIN DRY IN THE OFFICIAL FORECAST.
AS UPPER LOW APPROACHES SUNDAY...SOUTHERLY LOW LEVEL FLOW WILL
DEVELOP...DRAWING MOISTURE NORTH AND PROVIDING FOR DECENT ISENTROPIC
UPGLIDE FROM KANSAS INTO NEBRASKA. MODELS SUGGEST 850 BAROCLINIC
ZONE WILL SET UP NEAR THE NEBRASKA/KANSAS BORDER WHERE HIGHEST PRECIP
CHANCES WILL BE PLACED. TEMPERATURE PROFILES SUGGESTS RAIN IS THE
MOST LIKELY PRECIP TYPE IN OUR SOUTH...WITH INCREASING CHANCES FOR
SNOW AS YOU HEAD NORTH THROUGH EASTERN NEBRASKA AND WESTERN IOWA.
SURFACE TEMPS WILL LIKELY SURGE INTO THE 30S MOST AREAS...SO
ACCUMULATING SNOW WILL BE TEMPERED SOMEWHAT. PRECIP CHANCES WILL
CONTINUE INTO SUNDAY NIGHT...THEN ONLY IN OUR SOUTHEAST ON MONDAY
AS SYSTEM EXITS TO THE EAST. GFS IS FASTER WITH THIS SYSTEM...SO
IT WOULD SUGGEST NO PRECIP ON MONDAY. WILL CONTINUE WITH AT LEAST
SMALL CHANCES FOR NOW.
DERGAN
AVIATION...
TAF SITES KOFK/KOMA/KLNK
18Z TAFS
GENERALLY VFR CONDITIONS EXPECTED THROUGH THURSDAY MORNING. HOWEVER
MVFR CIGS ARE POSSIBLE AFTER 12Z. COLD FRONT SWEEPING THROUGH
EASTERN NEBRASKA WEDNESDAY AFTERNOON WILL TURN WINDS TO THE
NORTHWEST WITH SPEEDS TO 15KTS. ONLY SCT-BKN MID LEVEL CLOUDS
EXPECTED THROUGH MUCH OF THE EVENING. THEN NORTH WINDS WILL
GRADUALLY DRAW MVFR CIGS SOUTH FROM THE NORTHERN PLAINS. SOME OF
THOSE MAY WORK INTO KOFK AREA AFTER 12Z. ALSO...INCREASING MID LEVEL
CLOUDS AHEAD OF LOW PRESSURE SYSTEM MOVING OUT OF THE ROCKIES COULD
LOWER CIGS TO MVFR IN THE KLNK AREA BEFORE 18Z THURSDAY. LIGHT
SNOW IS POSSIBLE AT ALL TAF SITES AFTER 18Z THURSDAY...WITH
ASSOCIATED MVFR/IFR CIGS AND VSBYS.
DERGAN
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...WINTER WEATHER ADVISORY FROM 9 AM TO 9 PM CST THURSDAY FOR
NEZ078-088>093.
IA...NONE.
&&
$$
DERGAN