Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 292006
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
306 PM CDT WED APR 29 2015

.SYNOPSIS...
ISSUED AT 304 PM CDT WED APR 29 2015

AS OF EARLY TUESDAY AFTERNOON THE UPPER AIR PATTERN OVER THE CENTRAL
CONUS WAS DEFINED BY AN AMPLIFIED PROGRESSIVE RIDGE. THE ADVECTION
OF A VERY DRY AND STABLE AIRMASS ALOFT WAS MITIGATING CLOUD COVER
OVER MOST OF THE CENTRAL AND NORTHERN PLAINS. AT THE SURFACE AN AREA
OF HIGH PRESSURE WAS SLOWLY MOVING SOUTHEAST INTO FAR EASTERN
NEBRASKA...BRINGING RELATIVELY LIGHT SOUTHERLY FLOW TO THE WESTERN
HALF OF THE STATE. TEMPERATURES WERE RIGHT AROUND NORMAL IN THE MID
TO UPPER 60S.

&&

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 304 PM CDT WED APR 29 2015

QUIET AND DRY CONDITIONS WILL HOLD FIRM THROUGH THE SHORT TERM
PERIOD. A LOW AMPLITUDE SHORTWAVE WILL TRACK ACROSS THE NORTHERN
ROCKIES AND INTO THE NORTHERN PLAINS. HEIGHT FALLS ALOFT WILL BEGIN
EARLY THURSDAY AND PROMOTE AN INCREASE IN SOUTHERLY FLOW AT THE
SURFACE. MOISTURE ADVECTION WILL BE WEAK WITH DEWPOINTS ONLY IN THE
MID TO UPPER 40S ALL THE WAY SOUTH TO THE WESTERN GULF COAST. WAA IN
THE MID LEVELS WILL BEGIN OVERNIGHT...AND DIURNAL MIXING UP TO 750MB
WILL RESULT IN HIGHS IN THE 70S AND LOW 80S. A COLD FRONT WILL BEGIN
TO ENTER NORTHWEST NEBRASKA BY MID AFTERNOON...BUT ANY ASSOCIATED
SHOWERS AND THUNDERSTORM ACTIVITY SHOULD STAY WEST OF THE CWA
THROUGH 00Z FRIDAY.

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 304 PM CDT WED APR 29 2015

THURSDAY NIGHT THROUGH SATURDAY...THE MOISTURE RICH NAM AND SREF
WERE GIVEN EXTRA WEIGHT FOR THIS FORECAST...2/3 WEIGHT.

THE NAM MODEL IS THE MOST AGGRESSIVE MODEL THURSDAY NIGHT. TWO
PLUMES OF SUBTROPICAL/PACIFIC MOISTURE MOVING ASHORE THIS
AFTERNOON THE WEST COAST WILL LIKELY POOL ACROSS THE NRN HIGH
PLAINS VIZ FRONTOGENESIS FROM 850MB TO 500MB PRODUCING A DEEP
MOISTURE LAYER WITH PWAT NEAR 1.0 INCH. ACCORDING TO THE VENERABLE
RAP MODEL...THIS PROCESS SHOULD BE UNDERWAY ACROSS ERN MT BY 00Z
THIS EVENING. THE GFS POOLS THE BEST MOISTURE NORTH AND WEST OF THE
FCST AREA. THE ECM AND GEM ARE CLOSER TO THE NAM AND SREF.

K INDICES SOAR TO 40C ALONG THE FRONT ACROSS WRN NEB THURSDAY
EVENING WHICH WOULD MOVE VERY SLOWLY EAST THURSDAY NIGHT. THE RESULT
IS THE POTENTIAL FOR A WEAKLY ORGANIZED MCS COMPRISED OF SLOWLY
MOVING SHOWERS AND THUNDERSTORMS. ODDLY...NONE OF THE MODELS
INDICATE HEAVY RAINFALL WHICH PROBABLY MEANS THUNDERSTORM COVERAGE
WILL BE ISOLATED TO SCATTERED AS SUGGESTED BY THE NAM REFLECTIVITY
PRODUCT.

GIVEN THE COLD AIR ALOFT...WET BULB HEIGHTS AROUND 8KFT...MODEST
ML-450MB BULK SHEAR 15-30KT AND ELEVATED CAPE NEAR 1000 J/KG...SMALL
HAIL IS QUITE POSSIBLE...MAINLY ALONG AND WEST OF HIGHWAY 61 UNTIL
MIDNIGHT THURSDAY. THE MODELS SHOW VERY DEEP SATURATION AND SLOW
STORM MOTION OF LESS THAN 10KT WHICH SUGGESTS THE HAIL COULD
REALLY ACCUMULATE.

POPS FOR THIS EVENT HAVE BEEN INCREASED 10 PERCENT TO 50 PERCENT
FROM THE PREVIOUS FORECAST.

ANOTHER OPPORTUNITY FOR STORM DEVELOPMENT ARISES FRIDAY AFTERNOON
ACROSS THE WRN SANDHILLS SOUTH AND EAST THROUGH SWRN AND SCNTL NEB.
THE NAM SHOWS A WEAK CAP...1000-1500 J/KG CAPE...K INDICES NEAR 40C
AND WEAK LIFT. THIS IS SUPPORTED BY THE SREF. POPS FOR THIS EVENT
ARE 30 PERCENT AND ACTIVITY WOULD LIKELY MOVE EAST OF THE FORECAST
AREA FRIDAY EVENING.

LASTLY...THE NAM...SREF AND THE GFS SHOW A DECENT DRYLINE BULGE
DEVELOPING ACROSS NRN NEB/SWRN SD SATURDAY AFTN. THIS COULD BE THE
BEGINNING OF A MORE ORGANIZED MCS WHICH WOULD PROPAGATE THROUGH
NCNTL NEB/ERN SD SATURDAY NIGHT. POPS SATURDAY ARE ISOLATED.

SATURDAY NIGHT THROUGH WEDNESDAY...THE MODELS ARE IN QUITE GOOD
AGREEMENT SHOWING AN UPPER LEVEL LOW FORMING OVER THE PACIFIC
NORTHWEST. A DISTURBANCE OFF THE COAST OF CALIFORNIA WILL BE SWEPT
EAST AROUND THE UPPER LOW AND INTO THE CENTRAL PLAINS SETTING UP AN
ACTIVE PERIOD OF RAIN CHANCES AND THUNDERSTORMS. THE PATTERN IS
BASICALLY A BLOCK WITH CENTERS OF MOISTURE CONVERGENCE ACROSS THE
NEBRASKA AND EAST INTO THE MIDWEST. HIGH PRESSURE ACROSS THE UPPER
MIDWEST AND THE SOUTHEAST U.S. PRODUCES MOISTURE CONVERGENCE IN AN
ARC FROM OKLAHOMA TO WISCONSIN. THE UPPER LOW ACROSS THE NORTHWEST
AND SWEPT FLOW OFF THE DESERT SOUTHWEST COMPLETES THE BLOCK.

SUNDAY WOULD BE THE WARMEST DAY WITH HIGHS IN THE 80S AHEAD OF A
COLD FRONT ASSOCIATED WITH CANADIAN HIGH PRESSURE BUILDING SLOWLY
THROUGH THE NRN PLAINS AND UPPER MIDWEST. THE HIGH REMAINS
STATIONARY AND SETS UP A STATIONARY FRONT ACROSS KANSAS. THE FRONT
WILL LIFT SLOWLY NORTH MONDAY THROUGH WEDNESDAY PROVIDING FOCUS FOR
SHOWERS AND THUNDERSTORMS. THE GULF WILL OPEN WIDE AND 50+F DEW
POINTS WILL SURGE NORTH THROUGH KANSAS. K INDICES OF 30+C COULD TAKE
UP RESIDENCE ACROSS WESTERN AND NORTH CENTRAL NEBRASKA MONDAY
THROUGH WEDNESDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1224 PM CDT WED APR 29 2015

VFR CONDITIONS WILL PREVAIL ACROSS ALL OF WESTERN AND NORTH
CENTRAL NEBRASKA THROUGH THE NEXT 24 HOURS. OUTSIDE OF A FEW MID
LEVEL CLOUDS THIS AFTERNOON SKIES WILL BE CLEAR THROUGH THE PERIOD.
WINDS WILL REMAIN SOUTH OR SOUTHEAST BETWEEN 5 AND 15 KTS.

&&

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

$$

SYNOPSIS...MARTIN
SHORT TERM...MARTIN/TAYLOR/SNIVELY
LONG TERM...CDC
AVIATION...MARTIN





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