Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 212032
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
332 PM CDT THU MAY 21 2015

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 331 PM CDT THU MAY 21 2015

AT 20Z A SHORTWAVE RIDGE AXIS ALOFT WAS POSITIONED THROUGH THE
NEBRASKA PANHANDLE AND EASTERN COLORADO...DOWNSTREAM FROM A LONGWAVE
TROUGH BUILDING INTO THE WESTERN CONUS. AT THE SURFACE AN AREA OF
HIGH PRESSURE WAS SLOWLY DRIFTING SOUTHEAST INTO CENTRAL NEBRASKA.
SOUTHERLY FLOW IN THE WAKE OF THE DEPARTING HIGH WAS TRANSPORTING
LOW TO MID LEVEL MOISTURE BACK INTO THE AREA...EVIDENT BY AN
EXPANSIVE STRATUS DECK FROM FAR SOUTHWEST NEBRASKA INTO THE
PANHANDLE.  DRIER AIR TO THE EAST AND ALOFT HAS BEEN SLOWING THE
EASTWARD ADVANCEMENT OF STRATUS THIS AFTERNOON AND EVEN CREATING A
FEW BREAKS IN THE CLOUDS. TEMPERATURES WERE IN THE 60S IN AREAS
EXPERIENCING SUNSHINE...WITH COOLER TEMPS IN THE 50S UNDERNEATH THE
CLOUDS.

A LEAD PV MAX CURRENTLY ROUNDING THE BASE OF THE LONGWAVE TROUGH
EJECTS NORTHEAST FROM THE BAJA OF CALIFORNIA AND TOWARD THE CENTRAL
PLAINS TONIGHT. MOISTURE TRANSPORT INCREASES AS PWATS NEAR 1 INCH
LOCALLY. A BROAD AREA OF PRECIPITATION WILL DEVELOP OVER COLORADO
AND MOVE NORTHEAST INTO THE CWA OVERNIGHT. WIDESPREAD DEFINITE POPS
COVER MUCH OF SOUTHWEST NEBRASKA THROUGH THE MORNING HOURS FRIDAY.
MODEL COMPUTED LI/S ARE POSITIVE BOTH AT THE SFC AND 800MB THROUGH
00Z SATURDAY...SO LEFT ANY MENTION OF THUNDER OUT OF THE SHORT TERM
PERIOD. MODELS SHOW THE PRIMARY AREA OF RAINFALL ADVANCING INTO THE
CENTRAL AND NORTHERN SANDHILLS BY THE AFTERNOON. BEHIND THE MAIN
BAND OF RAIN...MODEL SOUNDINGS SHOW PERSISTENT LIGHT RAIN/DRIZZLE AS
THE LOW LEVELS REMAIN SATURATED IN THE PRESENCE OF MOIST
SOUTHEASTERLY FLOW.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 331 PM CDT THU MAY 21 2015

FRIDAY NIGHT THROUGH SUNDAY...WINDS ALOFT AT 300 MB INCREASE TO
AROUND 80 KT AS AN UPPER LEVEL LOW MOVES EAST INTO THE CNTL ROCKIES
FRIDAY NIGHT. THE MODELS SUGGEST A WEAK DISTURBANCE WOULD LIFT
NORTHEAST THROUGH SWRN NEB SPAWNING A CLUSTER OF TSTMS WHICH WEAKEN
ACROSS SCNTL NEB AFTER MIDNIGHT. IN THE WAKE OF THE DISTURBANCE DRY
AIR WILL MOVE IN ALOFT. THE NAM AND SREF...MET AND MAV GUIDANCE SHOW
FOG DEVELOPING WHICH MIXES OUT DURING THE DAY SATURDAY AND RETURNS
AGAIN SATURDAY NIGHT. THE FOG FORECAST FOLLOWS THE 40 PERCENT
PROBABILITY OF LESS THAN 1 MILE VISIBILITY INDICATED IN THE SREF.

ANOTHER PERHAPS MORE ROBUST ROUND OF TSTMS IS EXPECTED TO DEVELOP
ACROSS NERN COLO SATURDAY AFTERNOON WHICH LIFTS NORTH THROUGH THE
FCST AREA SATURDAY NIGHT. THE UPPER LOW WILL BE MOVING THROUGH
COLO/WY IN THE EVENING PROVIDING SUPPORT. THE MODELS SUGGEST STORM
COVERAGE WOULD GROW UPSCALE IN A LINEAR MULTICELL ENVIRONMENT
DEVELOPING EAST ACROSS THE FCST AREA. THE BEST FORCING WOULD BE
ACROSS THE WRN NEB CLOSER TO THE UPPER LOW. THE LOCATION OF A WARM
FRONT...NERN COLO OR SWRN NEB...WILL DICTATE THE POTENTIAL FOR
SEVERE WEATHER. SPC FORECASTS NORTHEAST COLO FOR IGNITION. THUS
STORMS LIFTING INTO THE FCST AREA WOULD LIKELY BE ELEVATED HAIL
MAKERS. THE NAM SUGGESTS SWRN NEB FOR SFC BASED SEVERE STORM
DEVELOPMENT. IN THAT CASE WIND DAMAGE WOULD BE INCLUDED IN THE
SEVERE WEATHER THREAT.

1/3 TO 3/4 OF AN INCH OF RAIN IS EXPECTED FRIDAY NIGHT THROUGH
SUNDAY WITH HIGHEST AMOUNTS ALONG AND WEST OF HIGHWAY 61 AND LEAST
RAINFALL ALONG HIGHWAY 281. LOCALLY HIGHER TOTALS SHOULD BE
EXPECTED...ESPECIALLY WEST.

RAIN CHANCES CONTINUE SUNDAY ALTHOUGH NOTHING ORGANIZED IS INDICATED
IN THE MODELS. LAPSE RATES STEEPEN AS TEMPS AT H700MB RISE AND THE
UPPER LEVELS REMAIN COLD WITH THE APPROACHING UPPER LOW. THIS COULD
SUPPORT DIURNAL TSTM DEVELOPMENT.

OTHERWISE...THE MODELS ARE TRENDING COOLER SATURDAY FOR HIGHS IN THE
60S. A WARM FRONT MAY CAPTURE SWRN NEB PRODUCING HIGHS NEAR 70 OR
WARMER BUT THAT IS THE GFS/NAM SOLN. THE ECM SHOWS 50S EVERYWHERE
WHILE THE NAM SHOWS 50S NORTHWEST AND 70S SOUTHWEST. THE GEM SHOWS
60S EVERYWHERE. GIVEN THE LIGHT QPF AND MOISTURE IN THE ECM
850-700MB DRIZZLE MAY DEVELOP SATURDAY.

THE TEMPERATURE FORECAST SUNDAY IS UNUSUAL AGAIN WITH THE ECM AND
GEM SHOWING 50S AND 60S WHILE THE NAM AND GFS SHOW 60S AND 70S. THE
WARMER MODELS PARTIALLY CLEAR SKY COVER IN THE FCST AREA WHILE THE
COOL ONES LOCK IN THE OVERCAST. THE FORECAST LEANS TOWARD THE COOLER
CLOUDY SOLNS FOR HIGHS IN THE 60S TO NEAR 70.

SUNDAY NIGHT THROUGH THURSDAY...A SECOND LOBE OF COLD AIR ALOFT WILL
REINFORCE THE UPPER LEVEL LOW SUNDAY NIGHT SLOWING THE FILLING
PROCESS. THE REAL CULPRIT IS AN ANOMALOUS AMPLIFICATION OF THE AN
UPPER LEVEL RIDGE OFF THE FL COAST TO 592 DM BY MONDAY MORNING
FORMING A BLOCK WHICH KEEPS HEIGHTS LOW ACROSS THE WRN U.S.. BY
MONDAY MORNING H500MB TEMPS HAVE COOLED TO -16C.

A PORTION OF THE UPPER LEVEL LOW LIFTS NORTH SUNDAY NIGHT WHICH
PRESUMABLY PRODUCES ADDITIONAL SCATTERED TSTMS GIVEN THE DIURNAL
HEATING CYCLE FOR IGNITION. THE BEST CHANCE FOR RAIN WOULD APPEAR
SUNDAY NIGHT AND MONDAY. THEREAFTER AN UPPER LEVEL DISTURBANCE
MOVING THROUGH THURSDAY PRESENTS AN OPPORTUNITY FOR ORGANIZED TSTM
DEVELOPMENT. OTHERWISE DIURNAL HEATING WOULD APPEAR TO BE THE ONLY
FORCING FOR TSTM DEVELOPMENT AND POPS ARE ISOLATED OR LOW END
CHANCE. THE GFS AND GEF SHOW A DISTURBANCE COMING ACROSS THE ROCKIES
TUESDAY BUT THE ECM SHOWS IT ACROSS TEXAS AND THE MIDSOUTH. THE GEM
HAS NOTHING.

SFC LOW PRESSURE SHOULD REDEVELOP ON THE NRN HIGH PLAINS TUESDAY AND
MIGRATE THROUGH THE NRN PLAINS WEDNESDAY AND THURSDAY. A GRADUAL
WARMING TREND SHOULD DEVELOP WITH HIGHS RISING INTO THE 70S. ODDLY
THE GEF IS FASTER AND PULLS A COLD FRONT THROUGH THURSDAY. THE
TEMPERATURE FORECAST IS A BLEND OF THE WARMER GFS/ECM AND COOLER
BIAS CORRECTED/GEF DATA FOR HIGHS IN THE 70S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1235 PM CDT THU MAY 21 2015

VFR CONDITIONS PREVAIL FOR MOST OF WESTERN AND NORTH CENTRAL
THROUGH THURSDAY EVENING. THE ONLY EXCEPTION IS FAR SOUTHWEST
NEBRASKA...INCLUDING KOGA AND KIML...WHERE A LOW STRATUS DECK IS
KEEPING CIGS NEAR MVFR LEVELS. THIS STRATUS DECK WILL ONLY
SLIGHTLY MOVE EAST DURING THE DAY...AND CONFIDENCE IS LOW THAT IT
WILL MAKE IT TO KLBF BEYOND JUST SCT SKY CONDITIONS OVER THE NEXT
6 TO 12 HOURS.

CONDITIONS BEGIN TO CHANGE OVERNIGHT AS PRECIPITATION ENTERS INTO
SOUTHWEST NEBRASKA. MVFR OR LOW CIGS ARE LIKELY BY FRIDAY MORNING
AT KLBF ALONG WITH -RA. VISBY AND CIGS MAY BE LOWER AT TIMES THAN
WHAT IS CURRENTLY INDICATED IN THE TAF...BUT CONFIDENCE IS TOO
LOW INCLUDE IN A GROUP AT THIS TIME. THE RAIN WILL ADVANCE
NORTHEAST DURING THE MORNING...POSSIBLY REACHING KVTN BY 18Z
FRIDAY.

&&

.HYDROLOGY...
ISSUED AT 331 PM CDT THU MAY 21 2015

LITTLE CHANGE HAS BEEN OBSERVED OVER THE LAST 12 HOURS ALONG THE
SOUTH PLATTE AND PLATTE RIVERS IN SOUTHWEST NEBRASKA AS OF THURSDAY
AFTERNOON. RIVER LEVELS WILL SLOWLY RECEDE THROUGH THE END OF THE
WEEK BEFORE HOLDING STEADY WITH MINOR FLUCTUATIONS OVER THE WEEKEND.
RECENT RAINFALL IN THE UPSTREAM SOUTH PLATTE RIVER BASIN WILL BRING
ADDITIONAL RIVER LEVEL RISES FOR THE FIRST HALF OF NEXT
WEEK...HOWEVER THE CRESTS WILL NOT BE HIGHER THAN WHAT WAS
EXPERIENCED LAST WEEKEND AND EARLIER THIS WEEK.

ADDITIONAL RAINFALL CHANCES OVER THE NEXT WEEK AND ABOVE NORMAL LATE
SEASON SNOW PACK IN THE UPPER REACHES OF THE RIVER BASIN WILL PROMOTE
ELEVATED FLOWS ALONG THE SOUTH PLATTE RIVER IN SOUTHWEST NEBRASKA
THROUGH AT LEAST THE END OF THE MONTH.

&&

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

$$

SHORT TERM...MARTIN
LONG TERM...CDC
AVIATION...MARTIN
HYDROLOGY...MARTIN





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