Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 210311
AFDOAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
911 PM CST SAT DEC 20 2014

.UPDATE...
ISSUED AT 902 PM CST SAT DEC 20 2014

WE HAVE ISSUED A DENSE FOG ADVRY FOR PARTS OF THE WRN/SRN CWA FOR
TONIGHT. THE 01Z SFC ANALYSIS INDICATED A SFC TROF EXTNDG FM A LOW
OVER NORTHERN SD THRU CNTRL NEB AND INTO WRN KS. A WARM FRONT
EXTNDD FM SRN NEB THRU NE KS AND CNTRL MO. TO THE EAST OF THE SFC
TROUGH AND NORTH OF THE WARM FRONT IS WERE THE DENSE FOG WAS
DVLPG. THE FOG IS LIKELY TO BE MOST DENSE NEAR THE AREAS OF
OFK/BVN/OLU WHERE SFC TEMPERATURES ARE A BIT COOLER AND WINDS
OVERNIGHT ARE EXPECTED TO REMAIN LIGHTER. FARTHER SOUTH...THE WARM
FRONT IS EXPECTED TO TRY AND MOV A BIT NORTH OVERNIGHT AND
INCREASE THE TEMPERATURES AND MIXING OVER PARTS OF THE ERN/SRN
CWA. THIS MAY TEND TO REDUCE THE AMOUNT OF FOG LATE TONIGHT AND
WILL END THE ADVRY THERE FIRST.

EVENING UPPER AIR ANALYSIS INDICATED A WEAK SHEAR AXIS EXTNDD FM
THE SHRTWV TROF OVR ND SWD TO A SECONDARY SHRTWV OVER THE OK/TX
PANHANDLES. ALTHOUGH WEAK...SOME LARGE-SCALE FORCING FOR ASCENT IS
INDICATED ALONG THIS SHEAR AXIS PER SHRT RANGE MODELS. ALTHOUGH
CERTAINLY NOT STRONG ENOUGH TO PRODUCE RAIN...SOME DZ IS STILL
POSSIBLE...MAINLY OVER THE SRN 2/3RD OF THE FA OVERNIGHT.
TEMPERATURES WILL REMAIN ABOVE FREEZING THOUGH IN THIS AREA SO
LITTLE OVER-ALL IMPACT IS EXPECTED.

&&

.SHORT TERM...(TONIGHT THROUGH TUESDAY)
ISSUED AT 255 PM CST SAT DEC 20 2014

ANOTHER CHANCE OF DRIZZLE/FREEZING DRIZZLE TONIGHT...THEN RAIN OR
SNOW CHANCES SUNDAY NIGHT INTO MONDAY...ARE THE PRIMARY FORECAST
CONCERNS.

RELATIVELY ZONAL FLOW IN THE MIDDLE OF THE COUNTY WAS SEEN THIS
MORNING...BETWEEN AN EXITING SHORTWAVE TROUGH SWINGING INTO THE
GREAT LAKES AND ANOTHER WEAK TROUGH IN THE ROCKIES. EXITING TROUGH
PRODUCED ENOUGH LIFT OVERNIGHT TO PRODUCE AREAS OF DRIZZLE ACROSS
THE CWA WHERE TEMPERATURES HAD SLIPPED A COUPLE OF DEGREES BELOW
FREEZING. MINOR IMPACTS TO SIDEWALKS AND ELEVATED SURFACE WERE
SEEN...BUT NOT A HUGE TRAVEL HAZARD. EXPECT A REPEAT TO THE DRIZZLE
SCENARIO TONIGHT AS ROCKIES TROUGH DEEPENS IN THE HIGH
PLAINS...PUTTING OUR AREA UNDER CONTINUED WARM ADVECTION/LIFT OVER
SATURATED SURFACE LAYER. TEMPERATURES SHOULD HOLD NEAR OR ABOVE
FREEZING FOR THE MOST PART OVERNIGHT AS PERSISTENT LIGHT SOUTHERLY
FLOW PUSHES DEW POINTS TO OR ABOVE FREEZING.

EXPECT CLOUD COVER TO HANG TOUGH ACROSS THE CWA MUCH OF SUNDAY GIVEN
CONTINUED SOUTHERLY LOW LEVEL FLOW AND INFLUX OF MOISTURE.
HOWEVER WINDS WILL KICK UP A BIT MORE DURING THE AFTERNOON AND MAY
TURN A TAD WEST OF SOUTH AS LOW PRESSURE DEEPENS IN THE HIGH
PLAINS. THIS COULD SCOUR OUT CLOUDS IN A FEW AREAS...BUT PLAYING
IT PESSIMISTIC ON THE SHORTEST DAY OF THE YEAR APPEARS PRUDENT.
HIGHS SUNDAY WILL LIKELY RISE TO OR ABOVE 40 MOST AREAS.

MID LEVEL LOW PRESSURE AREA IS FORECAST TO DROP OUT OF CANADA INTO
EASTERN SOUTH DAKOTA SUNDAY NIGHT. BROAD ASCENT ON EAST SIDE OF
TROUGH AXIS COMBINED WITH BETTER FORCING ASSOCIATED WITH APPROACHING
UPPER LOW WILL LEAD TO INCREASING PRECIPITATION CHANCES ALONG
SURFACE TROUGH/WARM FRONT. EXPECT PRECIP SUNDAY EVENING TO DEVELOP
ALONG THAT SURFACE BOUNDARY IN NORTHEAST NEBRASKA THEN SPREAD/DEVELOP
SOUTHEAST AND EAST AS BOUNDARY ROTATES EAST THEN NORTHEAST. STRONG
WARM ADVECTION OVER SURFACE FRONT IS SHOWN BY ALL MODELS WITH 850
JET OVER 40KT RIDING ISENTROPES SOUTHWEST TO NORTHEAST ACROSS THE
CWA. HIGHEST PRECIPITATION CHANCES WILL SHIFT TO THE EASTERN HALF OF
THE CWA BY 12Z MONDAY...THEN GRADUALLY WORK EAST OF OUR AREA BY
NOON. IT APPEARS PRECIPITATION TYPE WILL REMAIN ALL RAIN THROUGH
THIS TIME AS SURFACE TEMPERATURES REMAIN ABOVE FREEZING UNTIL COLD
ADVECTION KICKS IN AFTER PRECIP ENDS. FORECAST SOUNDINGS ALSO SHOW
ABOVE-FREEZING AIR IN THE LOWEST 6000FT DURING PRECIPITATION.

SHOULD SEE A PRECIPITATION-FREE PERIOD FOR A TIME MONDAY BEFORE
UPPER LOW SWINGS ANOTHER SHORTWAVE INTO THE CWA LATER MONDAY
AFTERNOON AND OVERNIGHT. BY THIS TIME TEMPERATURES WILL BE COLD
ENOUGH FOR SNOW IN ALL AREAS. MOISTURE/LIFT WILL FAVOR NORTHEAST
NEBRASKA FOR HIGHEST POTENTIAL FOR ACCUMULATING SNOW WITH CHANCES
DIMINISHING TO NEAR ZERO AS WE HEAD TO THE KANSAS AND MISSOURI
BORDERS. AVERAGE QPF FROM MODEL OUTPUT SUGGESTS AN INCH OR TWO OF
SNOW IS POSSIBLE ALONG THE SOUTH DAKOTA BORDER DROPPING TO A HALF
INCH OR LESS ALONG INTERSTATE 80.

A FEW SNOW SHOWERS COULD LINGER INTO TUESDAY MORNING BEFORE
SHORTWAVE ROTATES FAR ENOUGH EAST. CLEARING SKIES AND STRONG
NORTHWEST WINDS WILL FOLLOW TUESDAY AFTERNOON. HAVE HIGHS THEN IN
THE 30S WITH WINDS GUSTING OVER 30.

.LONG TERM...(TUESDAY NIGHT THROUGH SATURDAY)
ISSUED AT 255 PM CST SAT DEC 20 2014

THE CHANCE FOR SNOW CHRISTMAS NIGHT INTO FRIDAY REMAINS THE PRIMARY
LONGER TERM FORECAST CONCERN.

UPPER TROUGH/LOW IN THE MIDDLE OF THE COUNTRY TUESDAY NIGHT WILL
GRADUALLY WORK EAST ON WEDNESDAY...THEN SWING THROUGH NEW ENGLAND
ON CHRISTMAS DAY. MEANWHILE ANOTHER TROUGH WILL BEGIN TO DEEPEN IN
THE WESTERN STATES...AND WILL EVENTUALLY MOVE INTO THE PLAINS LATE
IN THE WEEK.

MODELS...AT LEAST THE 12Z VERSIONS OF THE OPERATIONAL GFS AND
ECMWF...ARE IN BETTER AGREEMENT TODAY IN REGARDS TO STRENGTH AND
TIMING OF TROUGH SHIFTING INTO THE REGION THURSDAY NIGHT AND LIFTING
OUT ON SATURDAY. AHEAD OF IT...THE TRANSITION FROM NORTH OR
NORTHWEST TO SOUTHWEST FLOW ALOFT WILL OCCUR WEDNESDAY INTO
THURSDAY...WITH ASSOCIATED GRADUAL LOW LEVEL WARMING. SO
TEMPERATURES MAY GAIN A FEW DEGREES BOTH WEDNESDAY AND THURSDAY...BUT
INCREASING CLOUDS WILL CERTAINLY LIMIT AMOUNT OF WARMING. HAVE HIGHS
IN THE 30S EACH DAY.

EXPECT PRECIPITATION CHANCES TO INCREASE THURSDAY NIGHT AS
ISENTROPIC UPGLIDE COMMENCES ON EAST AND NORTH SIDE OF SURFACE LOW
EXPECTED TO TRACK ACROSS KANSAS INTO MISSOURI. TEMPERATURE PROFILES
IN PRECIP AREAS SUGGEST AN ALL SNOW EVENT...AND FAVORING NORTHEAST
NEBRASKA AT THIS TIME. PRECIP LOOKS TO MOVE OUT OF THE AREA BY
FRIDAY NIGHT...WITH AMOUNTS GENERALLY LOOKING LIKE A FEW INCHES AT
THE MAX. COOLER TEMPERATURES WILL FOLLOW WITH HIGHS FRIDAY AND
SATURDAY NEAR 30.

&&

.AVIATION...(00Z TAFS FOR KOFK...KLNK AND KOMA.)
ISSUED AT 531 PM CST SAT DEC 20 2014

LIFR CONDS AT KOFK/KOMA WILL CONT THROUGH THE OVERNIGHT HOURS.
AHEAD OF A RETREATING WARM FRONT TONIGHT WE MAY SEE SOME 1/4 TO
1/2 FG DEVELOP AT BOTH OF THESE LOCATIONS BY 06Z. IF THIS FG DVLPS
IT WOULD LIKELY PERSIST THRU THE NIGHT AT KOFK BUT MAY TEND TO
LIFT A BIT AT KOMA LATE TONIGHT AS MIXING INCREASES AS WARM FRONT
NEARS. WE WILL SEE MVFR CONDS GO TO IFR AT LNK...AND POSSIBLY LIFR
FOR A TIME THIS EVNG JUST AHEAD OF THE WARM FRONT BUT SOME
IMPROVEMENT IS LIKELY THERE OVERNIGHT. CONDITIONS AT ALL 3 SITES
SHOULD IMPROVE TO MVFR BY SUN AFT AS WINDS INCREASE ALLOWING FOR
VISBY TO IMPROVE AND CIGS TO LIFT.


&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...DENSE FOG ADVISORY UNTIL 6 AM CST SUNDAY FOR NEZ066>068-078-
     088>090-092.

     DENSE FOG ADVISORY UNTIL 10 AM CST SUNDAY FOR NEZ016-017-030>032-
     042>044-050-051-065.

IA...NONE.

&&

$$

UPDATE...BOUSTEAD
SHORT TERM...DERGAN
LONG TERM...DERGAN
AVIATION...BOUSTEAD



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