Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 241126 AAA
AFDLBF

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE NORTH PLATTE NE
526 AM CST WED DEC 24 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 408 AM CST WED DEC 24 2014

SFC LOW PRESSURE ACROSS THE COLUMBIA BASIN WILL MIGRATE EAST
TODAY AND REDEVELOP ACROSS WRN NEB/NERN COLO BY 12Z THURSDAY. THE
MODELS DEVELOP A THERMAL RIDGE OUT AHEAD OF THE LOW. H850MB
TEMPERATURES RISE ABOVE ZERO THIS AFTERNOON WITH WEST NORTHWEST
WINDS AT 700MB AND BELOW. THE BANK OF STRATUS EAST OF HIGHWAY 83
IS EXPECTED TO MOVE VERY SLOWLY EAST AND EXIT THE FCST AREA 21Z-
00Z.

GIVEN THE SNOW COVER IN PLACE AND THE STRATUS HIGHS TODAY ARE
EXPECTED TO RISE INTO THE 30S. THIS A MARK DOWN FROM THE GUIDANCE
WHICH SUGGESTED NEAR 40 IN MANY AREAS. TONIGHT...THE THERMAL RIDGE
STRENGTHENS TO AROUND 8C AT 850MB AND MID LEVEL
CLOUDS...700MB-500MB...WILL BUILD INTO NRN AND WRN NEB 06Z-12Z
THURSDAY. THIS SHOULD LIMIT LOWS TO TEENS AND 20S.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 408 AM CST WED DEC 24 2014

THE PRIMARY FORECAST CONCERNS THROUGH THIS PERIOD ARE WITH SNOW
POTENTIAL THURSDAY NIGHT AND FRIDAY...THEN WITH THE RETURN OF COLDER
TEMPERATURES FOR MUCH OF THE NEXT WEEK.

MODELS BEGIN THE PERIOD IN DECENT AGREEMENT...BUT BEGIN TO DIVERGE
THURSDAY NIGHT AND FRIDAY WITH HOW THEY HANDLE THE NEXT SYSTEM
MOVING ON LAND FROM THE NORTHERN PACIFIC. THIS LEADS TO LOWERED
CONFIDENCE ON EXACTLY HOW THINGS WILL PLAY OUT LATER THIS WEEK.

THE CURRENT FORECAST HAS 30S TO LOW 40S FOR HIGHS THURSDAY...BUT
AM A BIT CONCERNED WITH THE FAR SOUTHEAST PART OF THE FORECAST
AREA AS THE FRONT WILL MOVE THROUGH AROUND MID AFTERNOON. IF THERE
IS ENOUGH SUNSHINE...WOULDN/T BE SURPRISED TO SEE TEMPERATURES
RISE INTO THE MID 40S OR EVEN A BIT HIGHER IN A FEW LOCATIONS.

THE SYSTEM IN QUESTION FOR LATER IN THE WEEK IS CURRENTLY STILL OVER
THE PACIFIC...OFF THE BRITISH COLUMBIA/WASHINGTON/OREGON COAST. THE
MODELS PUSH THIS SYSTEM ONSHORE OVER THE PACIFIC NORTHWEST BY 00Z
THURSDAY. THERE REMAINS DECENT MODEL AGREEMENT THROUGH THIS
POINT...WITH SOME DIFFERENCES THROUGH THE WEEKEND IN HOW THIS
SYSTEM WILL PROGRESS EAST AND WHAT THE IMPACT WILL BE LOCALLY.
THERE IS GOOD INDICATION THAT THE UPPER LOW WILL DIG ALMOST
STRAIGHT SOUTH INTO THE ARIZONA AND NORTHERN MEXICO THROUGH FRIDAY.
THE BIGGEST QUESTION IS WITH A WEAK SHORTWAVE TROUGH THAT EJECTS
NORTHEAST OUT OF THE MAIN LOW ACROSS THE CENTRAL PLAINS THURSDAY NIGHT
AND FRIDAY. THE ECMWF/GEM ARE FAIRLY SIMILAR IN TIMING AND ARE A
BIT WEAKER WITH THE PV ANOMALY MOVING UP ACROSS NEBRASKA. AS OF
LATE...THE MODELS HAVE BEEN TOO FAST WITH SYSTEMS MOVING ACROSS
THE AREA SO THE FORECAST WILL SIDE ON THE SLOWER ECMWF/GEM MODELS.

THE LIFT ASSOCIATED WITH THE SHORTWAVE TROUGH MOVING OVER THE
REGION ISN/T TERRIBLY IMPRESSIVE...BUT WITH DECENT MOISTURE BEING
PORTRAYED BY THE MODELS WITH PRECIPITABLE WATER VALUES EXCEEDING 125
PERCENT OF NORMAL HAVE DECENT CONFIDENCE THAT WON/T NEED EXTREMELY
STRONG LIFT TO ATTAIN PRECIPITATION PRODUCTION ACROSS THE AREA.
THERE IS A DECENT FRONTOGENETIC SIGNAL IN THE MODELS AS THE PV
ANOMALY MOVES BY...WHICH IS STRONGEST THURSDAY NIGHT AND OVER THE
NEBRASKA PANHANDLE INTO NORTH CENTRAL NEBRASKA. FORECAST SOUNDINGS
INDICATE THAT THE TEMPERATURES WILL EASILY DROP BELOW 0C PRIOR TO
ONSET OF PRECIPITATION AS THE COLD FRONT WILL MOVE THROUGH THE
AREA THROUGH THE DAY THURSDAY...SO AT THIS TIME HAVE NO CONCERNS
WITH PRECIPITATION TYPE AND HAVE ONLY SNOW IN THE FORECAST. A
SECOND WAVE OF ENERGY PULLS NORTHEAST FROM THE UPPER LOW ON
FRIDAY WHICH WILL EXTEND THE TIMING FOR SNOW CHANCES ACROSS THE
AREA AND WILL LIKELY DROP THE SNOW SOUTH INTO SOUTHERN NEBRASKA.
THE ECMWF/GEM ARE INDICATING SOME INTERACTION WITH A WEAK
SHORTWAVE TROUGH COMING OUT OF MONTANA FROM THE NORTHERN STREAM
WHICH MAY PROVIDE SOME EXTRA LIFT ACROSS THE AREA. THE STRONGEST
LIFT THROUGHOUT THIS EVENT IS NOT BEING SEEN THROUGH THE DENDRITIC
GROWTH ZONE SO NOT ANTICIPATING REAL HEIGHT SNOW TO LIQUID RATIOS
FROM THIS SNOW AND THE FORECAST HAS USED A RANGE OF 11:1 TO 14:1.
THIS GIVES GENERAL AMOUNTS OF 2 TO 4 INCHES ACROSS THE AREA. WILL
NEED TO KEEP AN EYE ON DETAILS OVER THE NEXT FEW FORECAST CYCLES
AS DETAILS BECOME MORE CLEAR.

ALTHOUGH CONFIDENCE IS NOT HIGH YET AT THIS POINT...THERE WERE
ENOUGH SIGNALS TO POINT TO THE NEED FOR INCREASING PRECIPITATION
CHANCES SO DID TREND UPWARD IN THE FORECAST FOR LATE THURSDAY
NIGHT THROUGH FRIDAY NIGHT.

STRONG SUBSIDENCE COMES INTO THE AREA BEHIND THE PASSING OF THE
PV ANOMALIES FRIDAY NIGHT SO LOOKING FOR CLEARING SKIES FOR
SATURDAY AND ALONG WITH THIS WILL BE DECENT COLD AIR ADVECTION.
THE COLDER AIR...WHICH IS INDICATING TO BE IN THE -3C TO -8C AT
850MB WOULD SUGGEST TEMPERATURES STAYING IN THE 20S FOR HIGHS
SATURDAY AND SUNDAY WITH LOWS IN THE SINGLE DIGITS AND TEENS FOR
SATURDAY NIGHT AND SUNDAY NIGHT.

THEN LOOKING INTO NEXT WEEK...MODELS ARE IN AGREEMENT WITH A MUCH
COLDER AIR MASS BEING PULLED SOUTH OUT OF CANADA AND INTO THE
CENTRAL PLAINS. THIS AIR MASS IS SUGGESTIVE OF 850MB TEMPERATURES
IN THE -20C TO -30C RANGE. IF THIS PANS OUT...WILL BE LOOKING FOR
THE COLDEST AIR OF THE SEASON...AS SOME OF THE STATISTICAL
GUIDANCE WOULD GIVE AREAS WHERE THERE IS SNOW COVER HIGHS AROUND
0F. THE FORECAST HAS BEEN TRENDED DOWNWARD IN TERMS OF
TEMPERATURES...BUT MAY BE WELL TOO WARM IF THIS COLDER AIR DOES
MAKE IT DOWN INTO THE REGION.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 525 AM CST WED DEC 24 2014

SATELLITE TIMING TOOLS SUGGEST THE AREA OF IFR CIGS NEAR KONL WILL
EXIT THE FCST AREA 22Z-01Z. THE FASTER TIME REPRESENTS EROSION
FROM SFC HEATING WHILE THE SLOWER TIME ASSUMES A STEADY STATE AND
NO DECAY. VFR IS EXPECTED ALL AREAS THEREAFTER.

&&

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

$$

SHORT TERM...CDC
LONG TERM...BROOKS
AVIATION...CDC





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