FXUS63 KLBF 270811
AFDLBF
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
211 AM CST FRI NOV 27 2009
.DISCUSSION...
THE SFC WARM FRONT APPEARS TO HAVE PUSHED EAST OF THE FCST AREA WITH
WEST WINDS APPROACHING KOFK. MEANWHILE A SUBSTANTIAL AREA OF HIGH
CLOUDS ACROSS THE NORTHERN PLAINS IS ATTEMPTING TO BUILD SOUTH INTO
NEBRASKA BUT SUBSIDENCE IS DRYING OUT THE ATM. ALL OF THE MODELS
INDICATE GENERALLY CLEAR SKIES TODAY THE AN UPPER LEVEL RIDGE
AMPLIFIES THROUGH THE CNTL PLAINS. WEST WINDS FROM THE SFC TO 700 MB
SHOULD SUPPORT VERTICAL MIXING TO AT LEAST 800 MB. THE FCST HIGHS IN
THE MID AND UPPER 60S THIS AFTERNOON ARE ON THE WARM SIDE OF THE
GUIDANCE ENVELOP.
THE NEXT PACIFIC COLD FRONT IS COMING ON SHORE THIS MORNING. THE GFS
AND NAM ARE SLIGHTLY FASTER WITH THE TIMING OF THE FRONTAL PASSAGE
WHICH WILL BE QUITE DIFFUSE AT THE SURFACE. THIS IS IN BETTER
AGREEMENT WITH THE ECMWF. THUS ISOLATED SHOWERS COULD BE ENTERING
NORTHWEST NEBRASKA LATE SATURDAY AFTERNOON WHICH WILL CHANGE TO SNOW
SHOWERS SATURDAY NIGHT. NO SIGNIFICANT SNOW ACCUMULATION IS EXPECTED
AS LIQUID AMOUNTS WILL BE TRACE TO A FEW HUNDREDTHS. SKIES SHOULD BE
CLEARING OUT SUNDAY MORNING WITH THE FASTER FRONTAL ARRIVAL SATURDAY
EVENING.
PACIFIC HIGH PRESSURE WILL CONTINUE TO BUILD THROUGH THE REGION
SUNDAY AND SETTLE OVER KS MONDAY MORNING. LOW PRESSURE WILL BE MOVING
THROUGH SRN CANADA MONDAY AND TUESDAY PRODUCING ANOTHER ROUND OF
WESTERLY DOWN-SLOPE WINDS AND WARMING. HIGHS MONDAY AND TUESDAY ARE
CONSERVATIVELY MARKED IN THE UPPER 40S TO LOWER 50S. GENERALLY
CLEAR SKIES ARE EXPECTED THESE DAYS SO THERE MAY BE AN FUTURE
OPPORTUNITY TO RAISE THESE FCST HIGHS.
WEDNESDAY AND THURSDAY...UNCERTAINTY ABOUNDS WITH THE 12Z AND 00Z
RUNS OF THE ECMWF AND GFS INCLUDING THEIR ENSEMBLES. DIFFERENCES IN
THE POSITION...INTENSITY OR OUTRIGHT ABSENCE OF KEY CIRCULATIONS AT
HIGH LATITUDES AS DEPICTED IN BOTH MODELS SUGGEST A PROTRACTED COLD
SPELL MAY NOT DEVELOP AS ADVERTISED. THE MODELS CONTINUE TO SHOW
THE VERY DEEP ALEUTIAN LOW RETROGRADING INTO SIBERIA BUT THE GFS...
GFS ENSEMBLE AND EURO ENSEMBLE DONT SHOW A PERSISTENT HIGH AMPLITUDE
RIDGE DEVELOPING ACROSS ALASKA.
INSTEAD...THE 18Z/00Z GFS...12Z GFS ENSEMBLE AND THE 12Z ECMWF
ENSEMBLE INDICATE A FLATTER RIDGE BUILDING INTO ALASKA AND THE BULK
OF THE COLD AIR TRACKING THROUGH THE UPPER MIDWEST AND GRT LAKES
REGION SPARING THE WRN HIGH PLAINS OF A DIRECT COLD SHOT.
MEANWHILE THE 12Z AND 00Z ECMWF OPERATIONALS CONTINUE TO SHOW A DEEP
PROTRACTED COLD SPELL DEVELOPING ACROSS THE LOWER 48 AS A HYBRID
PACIFIC ARCTIC HIGH PRESSURE SYSTEM DRIVES SOUTH THROUGH THE HIGH
PLAINS WEDNESDAY AND THURSDAY. LIGHT SNOW OR FLURRIES WOULD APPEAR
LIKELY IN THIS STRONG COLD AIR ADVECTION PATTERN. THE KEY H10-5
THICKNESSES AT KLBF ARE 539 DM BOTH MODELS AT 00Z THURSDAY AND 532 DM
IN THE GFS VS 512 DM IN THE ECMWF FRIDAY MORNING. THIS IS A VERY
LARGE SPREAD IN THE INTENSITY OF THE COLD AIR ADVECTION. THE BEST
MINDS AT NCEP SUGGESTED IT MIGHT BE MORE REALISTIC TO EXPECT WAVES OF
COLD AIR MOVING THROUGH THE CONUS PUNCTUATED BY A WARM UP AS
SUGGESTED BY THE GFS. THIS IS A MUCH MORE COMPLICATED FCST AS LARGE
TEMPERATURE VARIATIONS COULD DEVELOP. NO CHANGES HAVE BEEN MADE TO
THE TEMPERATURE FCST WEDNESDAY AND THURSDAY WHICH FCST HIGHS IN THE
LOWER 30S. LATER FCSTS WILL CERTAINLY CLARIFY THIS FCST.
&&
.AVIATION...
VFR CONDITIONS WILL CONTINUE THROUGH NEXT 24 HRS WITH WEST WINDS AT
15 TO 15 MPH.
&&
.FIRE WEATHER...
MINIMUM RELATIVE HUMIDITIES WILL FALL TO AROUND 20 PERCENT THIS
AFTERNOON OVER WESTERN NEBRASKA WEST OF US HIGHWAY 83. WINDS AND
MINIMUM RELATIVE HUMIDITIES WILL BE BELOW CRITERIA FOR RED FLAG
CONSIDERATIONS.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
CDC/MP
