Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 222327 AAA
AFDLBF

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE NORTH PLATTE NE
527 PM CST SUN NOV 22 2009

.DISCUSSION...
A QUICK UPDATE FOR FOG DEVELOPMENT EAST OF KIML-KOGA-KVTN. THE RUC
AND 18Z NAM SOUNDINGS INDICATE A PRIME ENVIRONMENT FOR SHALLOW FOG
BEGINNING AROUND MIDNIGHT. KLXN IS CARRYING A DEWPT OF 36F AT 23Z...
KONL 35F. THIS SHALLOW MOISTURE SHOULD BE SWEPT WESTWARD OVERNIGHT
AND COMBINED WITH STRONG RADIATIONAL COOLING...FOG IS LIKELY.

.PREVIOUS DISCUSSION...
AS SPECULATED YESTERDAY...THE PACIFIC STORM CAME ASHORE IN TIME FOR
THE 12Z UA FLIGHT. THE NAM...GFS AND ECMWF WHERE INITIALIZED AND
PRODUCED VERY SIMILAR MODEL RESULTS FOR THE DEVELOPING CLOSED LOW
ACROSS THE CENTRAL PLAINS MONDAY. THUS FCST CONFIDENCE IS GOOD AND
POPS HAVE BEEN RAISED TO THE LIKELY CATEGORY ACROSS PARTS OF WESTERN
AND NCNTL NEB. THE PACIFIC FRONT ENTERING WRN WY THIS AFTN SHOULD BE
ACROSS WRN NEB BY 12Z MONDAY MORNING. DRY AIR AHEAD OF THE FRONT
WILL ALLOW TEMPERATURES TO RADIATE BELOW FREEZING TONIGHT IN TIME
FOR THE FRONTAL PASSAGE MONDAY MORNING IN THE WEST. THUS SNOW IS
LIKELY ACROSS WRN NEB MONDAY MORNING WITH RAIN CHANGING TO SNOW
ALONG AND AHEAD OF THE FRONT ACROSS NCNTL NEB MONDAY AFTERNOON. THE
FRONT SHOULD BE MOVING THROUGH EASTERN NEB MONDAY NIGHT WITH SNOW
ENDING IN THE WEST. ALL THREE MODELS TRACK THE H7 LOW THROUGH SRN
NEB WITH RAIN AND SNOW LIKELY RIGHT ALONG AND NORTH OF THIS TRACK.
THE NAM12 AND GFS BUFKIT SOUNDINGS SHOW ABOUT 3 TO PERHAPS 6 HOURS OF
DEEP LIFT TO 500 MB WHICH SHOULD SUPPORT MODERATE TO OCCASIONALLY
HEAVY SNOW WITH RATES NEAR 1 INCH PER HOUR AT TIMES. SINCE THE STORM
IS EXPECTED TO BEGIN DEEPENING AFTER 00Z TUESDAY...MONDAY EVENING
EAST OF HIGHWAY 83...FCST QPF IS GENERALLY LESS THAN 1/3 OF AN INCH.

THE SNOW SHOULD FALL DURING THE DAY ACROSS THE FCST AREA AND SNOWFALL
TOTALS SHOULD BE 3 INCHES OR LESS. 500M WINDS INCREASE TO 20 KTS AND
THIS SUPPORTS THE GUIDANCE OF 15 TO 25 MPH WINDS. THE OFFICIAL QPF
FCST USES A 3 WAY BLEND OF THE 12Z RUNS OF THE ECMWF...GFS AND NAM12
WHICH WERE VERY SIMILAR AND A 10 TO 1 RATIO FOR SNOW WHICH PRODUCED
UP TO 3 INCHES OF SNOW CENTERED OVER NWRN LINCOLN COUNTY STRETCHING
NORTH AND SOUTH FROM MULLEN TO HAYES CENTER. THIS IS CLOSE TO THE HPC
FCST OF 2 TO 4 INCHES OF SNOW ACROSS THE SAME LOCATION.

THE STORM INTENSIFICATION PROCESS WILL NEED TO BE WATCHED VERY
CLOSELY AS NEW MODEL DATA COME IN TONIGHT AND MONDAY. HEAVY RAIN
AND SNOW IS FCST TO DEVELOP ACROSS SCNTL AND ERN NEB MONDAY NIGHT
ONCE THE OCCLUSION PROCESS BEGINS AND IF THIS PROCESS BEGINS SOONER
THAN FCST...VERY HEAVY WET SNOW COULD DEVELOP ACROSS WRN AND NCNL NEB
ALONG AND WEST OF HIGHWAY 83.

AS THE STORM MOVES TOWARD THE UPPER MIDWEST...A SECONDARY REINFORCING
COLD FRONT IS EXPECTED TO MOVE THROUGH TUESDAY NIGHT PRODUCING SNOW
SHOWERS AND FLURRIES. THIS AIR MASS IS A HYBRID OF PACIFIC AND
CANADIAN HIGH PRESSURE WHICH SHOULD KEEP TEMPERATURES IN THE 40S
WEDNESDAY AND MOST OF THURSDAY. A SIGNIFICANT WARM UP IS FCST BY BOTH
THE ECMWF AND GFS FRIDAY WITH TEMPERATURES WARMING INTO THE 50S
FOLLOWED BY ANOTHER COLD FRONT SATURDAY. THIS HYBRID CANADIAN PACIFIC
HIGH SHOULD KEEP TEMPERATURES IN THE 40S SUNDAY.

&&

.AVIATION...
VISUAL FLIGHT RULES WILL CONTINUE FOR TERMINALS KLBF AND KVTN
THROUGH 18Z MONDAY. MODELS ARE IN BETTER AGREEMENT TODAY WITH
AVIATION FORECAST BASED ON RUC/NAM/GFS BLEND. THE VISIBLE SATELLITE
LOOP OVERLAYED WITH THE WX DEPICTION ANALYSIS AT 19Z SHOW IFR
CEILINGS OVER SOUTH CENTRAL NEB. SURFACE HIGH PRESSURE WAS RIDGING
INTO WESTERN NEBRASKA THAT WEAKENS TONIGHT AS AN AREA OF LOW
PRESSURE FURTHER DEVELOPS ON THE HIGH PLAINS. NORTHERLY WINDS WILL
SHIFT TO THE SOUTHEAST THAT WILL ALLOW DEEPER BOUNDARY LAYER
MOISTURE TO DEVELOP NORTHWEST. HOW FAR WEST THE STRATUS DEVELOPS
WILL AGAIN BE A CONCERN. FOR NOW THE WINDS WILL DROP OFF BY MIDNIGHT
WITH THE WESTWARD EXTENT TO THE STRATUS TO EXTEND NEAR A LINE FROM
KANW TO KLBF. THE KVTN TERMINAL IS EXPECTED TO STAY IN THE CLEAR FOR
VISUAL FLIGHT RULES UNTIL 18Z MONDAY. BEYOND CEILINGS ARE EXPECTED
TO LOWER THROUGHOUT TO MARGINAL VISUAL FLIGHT RULES THEN DETERIORATE
AS SNOW OR A MIXTURE OF RAIN AND SNOW DEVELOPS AND MOVES ACROSS
WESTERN NEBRASKA. THE MODELS HAVE PUSHED THE IMPACTS OF THIS SYSTEM
SOUTHWEST WHERE COLDER AIR GETTING DRAWN INTO THE SYSTEM. A MIXTURE
OF PRECIPITATION IS EXPECTED UNTIL EVENING WHEN THE PRECIPITATION
WILL TRANSITION TO ALL SNOW THAT COULD DROP VISIBILITIES BELOW 3
MILES. THE SYSTEM LIFTS OUT TUESDAY FOR CLEARING FROM WEST TO EAST
THROUGH THE MORNING ATTM. THE MODELS HAVE HAD A HARD TIME RESOLVING
THE STORM TRACK WITH SOME ADJUSTMENTS STILL POSSIBLE IN THE NEAR
TERM FORECASTS.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

CDC/TLK




  • National Weather Service
  • North Platte, NE Weather Forecast Office
  • 5250 E. Lee Bird Drive
  • North Platte, NE 69101-2473
  • 308-532-4936
  • Page Author: LBF Webmaster
  • Web Master's E-mail: w-lbf.webmaster@noaa.gov
  • Page last modified: Nov 10th, 2009 17:42 UTC
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