873
FXUS63 KLBF 202028
AFDLBF
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
228 PM CST FRI NOV 20 2009
DISCUSSION
QUIET WEATHER IS EXPECTED THROUGH SATURDAY. THE POWERFUL PACIFIC
COLD ENTERING THE WRN U.S. THIS AFTN WILL WEAKEN AS IT MOVES
EAST AND IS EXPECTED TO DROP THROUGH THE FCST AREA SATURDAY NIGHT AND
BECOME STATIONARY ACROSS THE CNTL PLAINS SUNDAY MORNING. THIS FRONT
IS EXPECTED TO POOL MOISTURE ACROSS KANSAS AND NEBRASKA AND AID
RETURN MOISTURE FROM THE GULF OF MEXICO. THE NAM12 SUGGESTS STRATUS
AND FOG DEVELOPING ALONG AND EAST OF HIGHWAY 61 BEGINNING LATE
SATURDAY AND LASTING THROUGH SUNDAY AFTERNOON.
MONDAY THROUGH WEDNESDAY...THE HPC HAS LEANED STRONGLY ON THE
OPERATIONAL ECMWF. THEY BELIEVE THE MODEL HAS BEEN PERFORMING QUITE
WELL OVER THE LAST 10 DAYS AND IS THE BEST SOLN. THE GFS AND NAM12
HAVE BEEN RUNNING ABOUT 24HRS BEHIND THE ECMWF. MEANWHILE...GEM...
NOGAPS AND UKMET HAVE SUPPORTED THE ECMWF WHICH ALL SHOW A MAJOR
CYCLONE CROSSING THE CENTRAL PLAINS MONDAY THROUGH WEDNESDAY. THE
LATEST ECMWF MOVES THE STORM AT JUST 10 MPH WITH H85 WINDS INCREASING
TO NEAR 50KT. THATS DOWN FROM 65KT INDICATED IN THE 00Z ECMWF FROM
LAST NIGHT. BOTH THE ECMWF AND GFS ENSEMBLES ARE MUCH LESS
AMPLIFIED AND FEATURE A MORE OPEN WAVE SOLN.
THE ECMWF IS FCSTING ENERGY FROM A DEEP ALEUTIAN CYCLONE TO MOVE
THROUGH THE PAC NW SATURDAY NIGHT AND SOUTHEAST THROUGH WYOMING
AND INTO NRN KS MONDAY MORNING. THIS IS ATYPICAL OF CLASSIC SWRN U.S.
CUTOFF CYCLONE SYSTEMS BUT A POWERFUL PACIFIC COLD FRONT IS FCST TO
ENTER THE CNTL PLAINS MONDAY AND CHANGE RAIN TO SNOW AS THE SYSTEM
MOVES VERY SLOWLY EAST. THE 12Z ECMWF SUGGESTS A FULL BLOWN OCCLUDED
LOW AND TROWAL EVENT FOR SOUTHERN NEBRASKA. THIS IS ABOUT 100 MILES
SOUTH OF THE 00Z SOLN WHICH CARVED THE STORM THROUGH NRN NEBRASKA.
THE GEM IS VERY CLOSE TO THE 12Z ECMWF WHILE THE UKMET AND NOGAPS ARE
FARTHER SOUTH TRACKING THE STORM MORE THROUGH SRN NEB AND NORTHERN
KS. THUS IF LATER SOLNS CONTINUE TO TREND SOUTH...THE STORM COULD
MISS NEBRASKA ALL TOGETHER. STAYED TUNED.
THE OFFICIAL FCST CARRIES CHANCE 30 TO 40 PERCENT POP MONDAY
THROUGH TUESDAY NIGHT WITH RAIN CHANGING TO SNOW MONDAY NIGHT AND
CONTINUING THROUGH TUESDAY NIGHT. THIS CHANGEOVER MAY BE TOO QUICK
AND LATER FCSTS MAY HAVE TO DELAY THE CHANGEOVER UNTIL SOMETIME
TUESDAY. PRESUMABLY A RAIN SNOW LINE WILL DEVELOP NORTHWEST OF THE
SFC LOW ACROSS WHICH WILL MOVE VERY SLOWLY EAST MONDAY AND TUESDAY.
THE 12Z ECMWF IS FCSTING A 2 INCH BULLS EYE OF LIQUID PCPN JUST NORTH
OF THE H7 LOW CENTERED OVER KLBF. THE PREVIOUS 00Z RUN WAS CENTERED
OVER THE KONL-KOFK AREA AND THE 12Z RUN 24 HRS AGO WAS CENTERED
OVER KFSD. THUS THE FCST STORM TRACK WILL LIKELY CHANGE DURING THE
NEXT 72 HOURS AND THE ECMWF HAS BEEN TRENDING SOUTH. UNCERTAINTIES
WITH THIS POTENTIAL WEATHER EVENT WILL BE ADDRESSED IN THE HAZARDOUS
WEATHER OUTLOOK.
THURSDAY AND FRIDAY...PACIFIC HIGH PRESSURE WILL BUILD THROUGH THE
CENTRAL PLAINS THURSDAY IN THE WAKE OF THE STORM. LOW PRESSURE
TRACKING THROUGH THE NORTHERN PLAINS FRIDAY WILL TURN WINDS TO THE
WEST AND SOUTHWEST MODERATING TEMPERATURES.
AVIATION
VFR CIGS/VIS WILL CONTINUE THRU AT LEAST 00Z SUN. SOUTH WINDS MAY
GET ABOVE 12KTS AT KVTN TONIGHT...AND ALMOST CERTAINLY WILL FOR A
TIME ON SATURDAY AS A LOW PRESSURE TROUGH APPROACHES. AT KLBF...
THOSE WINDS ARE UNLIKELY UNTIL AFT 18Z SATURDAY DUE TO STRONGER
LOW-LEVEL STABILITY IN THE RIVER VALLEY. AFT 00Z SUN...NORTHWARD-
MOVING MOISTURE WILL INCREASE THE CHANCE OF MVFR OR LOWER CIGS AT
KLBF...BUT THE THE ACTUAL PROBABILITY WILL DEPEND ON THE TIMING OF
THE TROUGH PASSAGE.
LBF WATCHES/WARNINGS/ADVISORIES
NONE.
CDC/CS/TLK
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