Flooding in Nebraska, March 14 to 16, 2001

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA NE
312 PM CST WED MAR 14 2001

FORECAST CHALLENGES -- POTENTIAL WINTER STORM TONIGHT THROUGH
THURSDAY

SYNOPSIS -- MORNING UPPER-AIR ANALYSIS AND LATEST MOISTURE CHANNEL
IMAGERY SHOWS A COMPACT AND POTENT MID-LEVEL CIRCULATION CENTER
TRANSLATING SEWD INTO WY.  AT THE SURFACE, 19Z MSAS OBJECTIVE
ANALYSIS SHOWED A DEEPENING SURFACE LOW OVER N-CNTRL NEB WITH AN
ATTENDANT STATIONARY FRONT EXTENDING EWD ACROSS NERN NEB INTO SRN
IA.  A SECONDARY LOW WAS LOCATED OVER THE OK PNHDL WITH A WARM
FRONT EXTENDING NEWD INTO NERN KS AND NRN MO.

FORECAST -- PER PMDHMD AND MODEL INITIALIZATION WITH RESPECT TO THIS
MORNING'S OBSERVED 500MB HEIGHT FIELD, WE FAVOR A BLEND OF THE ETA
AND AVN SOLUTIONS.  12-HOUR DPROG/DT FROM BOTH THESE MODELS INDICATE
A SLOWER AND WEAKER MID-LEVEL SYSTEM WITH THE MAIN SURFACE LOW
FARTHER S OVER S CNTRL KS/NWRN OK.

IN THE SHORT TERM, CONVECTIVE POTENTIAL IS THE MAIN CONCERN.  12Z
SOUNDINGS FROM DRT NWD THROUGH OAX SHOWED VERY LIMITED LOW-LEVEL
MOISTURE AVAILABLE TO BE TAPPED BY THE APPROACHING SYSTEM.
MID-LEVEL LAPSE RATES ARE RATHER STEEP, ESPECIALLY IN AN AXIS FROM
HLC TO OAX, PER MID-CLOUD DEVELOPMENT ON LATEST VIS SATELLITE.
18Z MESOETA SBCAPE FORECASTS SUGGEST THAT ANY APPRECIABLE
INSTABILITY AND SUBSEQUENT CBL-BASED STORM DEVELOPMENT WILL REMAINED
CONFINED TO S-CNTRL KS ON S, WHICH AGREES WITH LATEST DAY 1
CONVECTIVE OUTLOOK.  NONETHELESS, SOME ELEVATED CONVECTION IS STILL
POSSIBLE THIS EVENING AND WE HAVE MADE MENTION OF THUNDER IN THE SRN
ZONES.

AS THE MID-LEVEL SYSTEM DIVES INTO KS TONIGHT, LARGE SCALE ASCENT
WILL INCREASE ALONG AND TO THE N OF THIS FEATURE.  PRECIPITATION
WILL INITIALLY BEGIN AS LIQUID BEFORE CHANGING OVER TO SNOW BY 06Z
OVER NERN NEB, 09-11Z OMA AND LNK, AND NOT UNTIL AFTER 12Z SERN
NEB/SWRN IA.  12Z QPF OUTPUT FROM THE ETA AND AVN SUGGEST 1 TO 3
INCHES POSSIBLE ACROSS THE NRN ZONES, WITH 2 TO 5 INCHES POSSIBLE
ACROSS MUCH OF THE REMAINDER OF THE AREA.  THE OTHER MAIN FACTOR
WILL BE WINDS.  SURFACE WINDS ARE FORECAST TO INCREASE TO 25 TO 35
MPH OVERNIGHT, CREATING AREAS OF BLOWING AND DRIFTING SNOW.  PER
COORDINATION WITH GID, LBF AND DMX, WE WILL ISSUE A WINTER WEATHER
ADVISORY TONIGHT INTO THURSDAY FOR PARTS OF NERN, E-CNTRL AND SERN
NEB.  ALTHOUGH SNOWFALL MAY BE ON THE LIGHT SIDE, ESPECIALLY IF THE
18Z MESOETA QPF VERIFIES, WE FEEL THAT THE STRONG WINDS WILL CREATE
TRAVEL PROBLEMS WITH ANY SNOW THAT FALLS.  ACROSS SERN NEB, THE
CHANGEOVER TO SNOW WILL NOT OCCUR UNTIL THURSDAY MORNING.  500-700MB
FRONTOGENESIS AND THE ASSOCIATED Q(SUB N)-VECTOR CONVERGENCE S OF
THIS FEATURE, IMPLY A RATHER STRONG AGEOSTROPHIC DIRECT THERMAL
CIRCULATION SETTING UP ACROSS FAR SERN NEB/SWRN IA IN THE POTENTIAL
DEFOMATION ZONE.  IF THIS VERIFIES, THIS WILL ENHANCE SNOWFALL RATES
ALONG AN AXIS THAT IS VERY CLOSE TO THE HPC 1838Z HIGH PROBABILITY
OF GREATER THAN 4 INCH ACCUMULATIONS.  PER COORDINATION WITH TOP,
EAX AND DMX, WE WILL ISSUE A WINTER STORM WATCH FOR FAR SERN
NEB/SWRN IA THURSDAY.  THE BIG UNCERTAINTY IS HOW MUCH SNOW WE CAN
GET TO STICK GIVEN THE EXPECTED SURFACE TEMPERATURES.

LIGHT SNOW SHOULD LINGER ACROSS THE FAR SERN ZONES INTO THURSDAY
EVENING.  WINDS WILL BEGIN TO DIMINISH AREAWIDE WITH DECREASING
CLOUDS FROM THE NW.  A SURFACE RIDGE AXIS WILL BUILD INTO THE AREA
THURSDAY NIGHT INTO FRIDAY WITH DAYTIME HIGHS SLIGHTLY BELOW
GUIDANCE DUE TO THE EXPECTED NEW SNOWCOVER, AND LOWS CLOSE TO MOS
VALUES.

IN THE EXTENDED, ANOTHER SYSTEM WILL AFFECT THE CENTRAL PLAINS THIS
WEEKEND WITH ANOTHER CHANCE OF RAIN OR SNOW.

THANKS TO GID, TOP, EAX, DMX, FSD AND LBF FOR COORDINATION!

.OMA...WINTER WEATHER ADVISORY TONIGHT THROUGH THURSDAY MORNING
        NEZ016-030>033-042>043-050
       WINTER WEATHER ADVISORY LATE TONIGHT THROUGH THURSADAY
        NEZ044>045-051>053-065>067-078-088 IAZ069-079
       WINTER STORM WATCH THURSDAY
        NEZ068-089>093 IAZ080-090>091

MEAD