FXUS63 KOAX 221643
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
1043 AM CST SAT JAN 22 2011
.UPDATE...
TWEAKED POPS AND SNOW ACCUMULATIONS THROUGH TONIGHT.
&&
.DISCUSSION...
SURFACE LOW AT 16Z HAD REACHED NORTH CENTRAL NEBRASKA AS UPPER-
LEVEL TROUGH DIVES ACROSS THE NRN ROCKIES. PRECIP IS ONGOING IN
CNTRL NEB AND WILL SPREAD EASTWARD THROUGH THE MORNING...REACHING
THE NWRN CWA BY 18Z AND ACROSS THE CWA BY 00Z. MAIN FORECAST
QUESTION WITH THIS SYSTEM IS NOT REALLY IF IT WILL SNOW...BUT
RATHER HOW MUCH. HIGHEST ACCUMULATION POTENTIAL IS FLIRTING WITH
THE 6 INCH WARNING CRITERIA IN A BAND FROM ROUGHLY KOFK TO KOMA TO
KRDK. HIGHEST SNOW ACCUMULATIONS ARE STILL UNCERTAIN...OF
COURSE...NOT ONLY IN AMOUNTS BUT IN HOW WIDESPREAD THOSE AMOUNTS
WOULD BE...AND BOTH OF THOSE WILL FACTOR INTO THE DECISION OF
WHETHER OR NOT TO UPGRADE PARTS OF THE CWA TO A WINTER STORM
WARNING. IN EITHER CASE...THE EVENT IS LIKELY TO STRADDLE THE LINE
BETWEEN HIGH-END ADVISORY AND LOW-END WARNING IN THAT BAND OF
HEAVIEST SNOW. WILL HOLD OFF ON THE DECISION FOR NOW TO GATHER
MORE INPUT FROM LATER MODEL RUNS AND TO SEE HOW THE SYSTEM EVOLVES
IN THE NEXT FEW HOURS.
UPDATED GRIDS/ZFP HAVE BEEN SENT.
&&
.PREV DISCUSSION... /ISSUED 356 AM CST SAT JAN 22 2011/
DISCUSSION...
THE PRIMARY FORECAST CONCERN IS SNOW THROUGH SUNDAY AND PROPER
CORRESPONDING HEADLINES.
RELATIVELY STRONG BUT FAST-MOVING SHORTWAVE WAS DIVING THROUGH
EASTERN MONTANA THIS MORNING AS PER WATER VAPOR LOOPS...AND WILL
ENTER NEBRASKA THIS AFTERNOON. ISENTROPIC UPGLIDE WILL BEGIN IN OUR
NORTHWEST CWA AND SPREAD QUICKLY SOUTHEAST THIS AFTERNOON. MODELS
ARE FAIRLY SIMILAR IN TRACK OF ASSOCIATED 850MB AND 700MB LOW
CENTERS MOVING NEAR OR THROUGH OUR WESTERN CWA. GFS IS A LITTLE
FASTER THAN NAM/ECMWF SOLUTIONS...AND APPEARS A BIT TOO FAST IN
MOVING SNOW OUT OF OUR CWA. HOWEVER GFS/ECMWF WERE MORE SIMILAR IN
AXIS OF BEST FRONTOGENETICAL FORCING THIS AFTERNOON AND TONIGHT FROM
NORTHEAST NEBRASKA AND DOWN THE MISSOURI RIVER VALLEY. AND 00Z RUNS
OF NAM/GFS/ECMWF/GEM/SREF WERE QUITE SIMILAR IN QPF AMOUNTS BETWEEN
THREE AND FOUR TENTHS OF LIQUID. BUT THE 06Z NAM HAS COME IN WITH
DOUBLE THAT QPF...PAINTING A STRIPE OF THREE-QUARTERS OF AN INCH OF
LIQUID FROM OMAHA INTO SOUTHWEST IOWA...AND A LARGE SWATH OF HALF
INCH QPF SURROUNDING THAT AREA. GIVEN 06Z RUNS HAVE BEEN SUSPECT
MUCH OF THE TIME...WILL CONTINUE TO SIDE WITH 00Z RUNS SHOWING ABOUT
A THIRD OF AN INCH OF QPF. GARCIA METHOD CALCULATIONS SUGGEST
MAXIMUM SNOW TOTALS OF 5 INCHES...WHICH IS IN LINE WITH HPC
FORECASTS AND A STRAIGHT 15 TO 1 RATIO OF ABOVE-MENTIONED AVERAGE
MODEL QPF.
SNOW AMOUNTS UP TO 5 INCHES PUTS US TOWARD THE UPPER END OF OUR
ADVISORY CRITERIA. EXPECT ABOUT A 12-HOUR SNOW IN ANY GIVEN
AREA...BUT IF SHORTWAVE SPEED IS SLOWER AND SNOW LINGERS...COULD
BOOST THOSE TOTALS SOME. AND IF OTHER MODELS TREND TOWARD 06Z
NAM...THEN ALL BETS ARE OFF. ALSO CONSIDERED WINDS AND POTENTIAL FOR
BLOWING/DRIFTING SNOW. SURFACE GRADIENT DOES TIGHTEN UP THIS
AFTERNOON AND EVENING AS SURFACE LOW DEEPENS TO OUR SOUTH. MODELS
SUGGEST SOME GUSTS OVER 20 MPH ARE LIKELY DURING THIS PERIOD...WHICH
SHOULD BE COINCIDENT WITH FALLING SNOW. THIS IS A LITTLE WORRISOME
FOR TRAVEL THIS AFTERNOON/EVENING. COMBINATION OF SNOW/WIND MAY
WARRANT WINTER STORM WARNING FOR SOME AREAS LATER THIS EVENING...
BUT WANT TO DEFER TO LATER SHIFTS FOR UPGRADE IF HIGHER SNOW AMOUNTS
BEGIN TO LOOK LIKELY.
SO WILL START WINTER WEATHER ADVISORY FOR NORTHEAST NEBRASKA AT NOON
THEN THE REST OF EASTERN NEBRASKA AND SOUTHWEST IOWA THIS EVENING.
SNOW SHOULD BE ENDING IN NORTHEAST NEBRASKA EARLY SUNDAY
MORNING...THEN EXIT OUR SOUTHEAST BY NOON.
TEMPERATURES TODAY SHOULD SURGE INTO THE 20S AHEAD OF SHORTWAVE AS
TEMPS ARE ALREADY IN THE TEENS OVER A GOOD PART OF OUR CWA AND
CENTRAL NEBRASKA. 00Z MODELS DIVERGE ON LOWS TONIGHT WITH GFS
PUTTING LOWS WELL BELOW ZERO FOR MUCH OF THE AREA. HOWEVER WITH
WINDS/CLOUDS LINGERING...CAN NOT SEE LOWS GOING BELOW THE SINGLE
DIGITS. HIGHS SUNDAY SHOULD HOLD IN THE TEENS.
HAVE TRIMMED SNOW CHANCES BACK SOME SUNDAY NIGHT AND MONDAY AS NEXT
SHORTWAVE DROPPING SOUTH HAS SHIFTED EAST WITH LATEST MODELS. DID
NOT CHANGE MUCH BEYOND MONDAY WITH PRIMARY FOCUS ON SHORTER TERM
SNOW POTENTIAL.
DERGAN
AVIATION...
TAF SITES KOFK/KOMA/KLNK
06Z TAFS
SAT LOOP SHOWS SC LAYER BREAKING UP ACROSS EAST CENTRAL NEBRASKA BUT
MORE SOLID BAND OF MVFR CIGS UPSTREAM EXPECTED TO MOVE BACK INTO THE
AREA THRU 12Z. STRONG WAVE DROPPING INTO THE AREA LATER TODAY
CURRENTLY OVER THE NORTHERN ROCKIES. IFR CIGS AND VSBYS EXPECTED TO
DEVELOP OR MOVE INTO THE AREA AFTER 18Z WITH SNOW DEVELOPING IN
ADVANCE OF THE WAVE AND CONTINUING THROUGH THE REMAINDER OF THE
FORECAST PERIOD.
FOBERT
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO NOON CST
SUNDAY FOR NEZ034-044-045-050>053-065>068-078-088>093.
WINTER WEATHER ADVISORY UNTIL 6 AM CST SUNDAY FOR NEZ011-012-
015>018-030>033-042-043.
IA...WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO NOON CST
SUNDAY FOR IAZ043-055-056-069-079-080-090-091.
&&
$$
MAYES