Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 042059
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
359 PM CDT SAT JUL 4 2015

.SYNOPSIS...
ISSUED AT 358 PM CDT SAT JUL 4 2015

LITTLE CHANGE IN THE SYNOPTIC UPPER LEVEL PATTERN OVER THE LAST 24
HOURS. REX BLOCK IN PLACE OVER THE EASTERN PACIFIC WITH A RIDGE
BUILDING OFF THE PACIFIC NORTHWEST COAST UP INTO ALASKA AND A
STATIONARY LOW WELL WEST OF THE CALIFORNIA COAST. JUST DOWNSTREAM
ANOTHER UPPER LEVEL LOW WAS DIGGING SOUTHEAST INTO NORTHERN
ALBERTA/SASKATCHEWAN AND FLATTENING THE SUBTROPICAL RIDGE TO THE
SOUTH OVER THE INTERMOUNTAIN WEST. NORTHWEST FLOW ALOFT OVER THE CWA
HAS SLOWLY BROKEN DOWN AS A SERIES OF MID-LEVEL PERTURBATIONS HAVE
MOVED THROUGH THE MEAN FLOW AND HEIGHTS BEGIN TO FALL IN ADVANCE OF
THE PROGRESSING NORTHWEST CANADIAN LOW. AT THE SURFACE A LEE SIDE
SURFACE TROUGH HAS BECOME ESTABLISHED ACROSS OVER THE CENTRAL HIGH
PLAINS IN RESPONSE TO INCREASING DPVA ALOFT. SOUTHERLY FLOW EAST OF
THE TROUGH HAS ALLOWED FOR THE POLEWARD FLUX OF LOW LEVEL
MOISTURE...WITH DEWPOINTS RUNNING 5F TO 10F HIGHER THAN THIS TIME
FRIDAY. SKIES WERE MOSTLY CLEAR WITH TEMPERATURES RUNNING IN THE MID
TO UPPER 80S. AS OF 20Z A CU FIELD HAS STARTED TO DEVELOP IN FAR
NORTHWEST NEBRASKA AS THETA-E POOLS IN A MOISTURE CONVERGENCE ZONE
ALONG THE LEE SIDE TROUGH...AN AREA THAT WILL NEED TO BE MONITORED
FOR DEEP CONVECTIVE INITIATION LATER THIS AFTERNOON AND EVENING.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 358 PM CDT SAT JUL 4 2015

THUNDERSTORM CHANCES AND THE POTENTIAL FOR SEVERE WEATHER LATER
TODAY AND TONIGHT ARE THE MAIN FORECAST CHALLENGES OF THE SHORT TERM
PERIOD. HI-RES MODELS HAVE COME INTO BETTER AGREEMENT THROUGH THE
DAY IN REGARDS TO THEIR CONVECTIVE TIMING AND EVOLUTION.
HOWEVER...SPATIAL COVERAGE AND POTENTIAL SEVERITY OF THE CONVECTION
STILL REMAIN IN QUESTION...ESPECIALLY GIVEN THE LACK OF WELL-DEFINED
UPPER LEVEL SUPPORT. CURRENT THINKING IS THAT ISOLATED TO SCATTERED
STORMS WILL FIRE IN THE VICINITY OF THE SURFACE TROUGH IN THE
PANHANDLE/SOUTHWEST SD LATER THIS AFTERNOON. THE LOCAL ATMOSPHERE
CONTINUES TO DESTABILIZE WITH LATEST MESOANALYSIS INDICATING CLOSE
TO 3000 J/KG OF MLCAPE AND A QUICKLY ERODING CAP PER LAPS PROXIMITY
SOUNDINGS. SHOULD STORMS FIRE...DEEP LAYER SHEAR PROFILES ARE
SUPPORTIVE OF SUPERCELLULAR STORM MODES WITH LARGE HAIL AND DAMAGING
WINDS POSSIBLE AS THE STORMS TRACK SOUTH AND SOUTHEAST. VEERING LOW
LEVEL WIND PROFILES WOULD SUGGEST THE THREAT FOR A TORNADO OR
TWO...BUT CONFIDENCE IN THIS THREAT IS QUITE LOW GIVEN THAT STORM
BASES WILL LIKELY BE AOA 750MB DURING PEAK HEATING...WITH STORMS
BECOMING ROOTED ABOVE THE BOUNDARY LAYER AFTER DARK. HI-RES MODELS
HAVE CONSISTENTLY SHOWN AN ORGANIZED AREA OF CONVECTION DROPPING
SOUTH THROUGH THE SANDHILLS THIS EVENING AND EARLY
OVERNIGHT...ESSENTIALLY FEEDING INTO THE WAA STREAM PROVIDED BY A
STRENGTHENING LLJ OVER WESTERN KANSAS.

PRECIPITATION CHANCES WANE AFTER MIDNIGHT. ATTENTION THEN TURNS TO
SUNDAY AS THE UPPER LEVEL LOW OVER NORTHWEST CANADA DROPS SOUTHEAST
AND DRIVES A STRONG COLD FRONT INTO THE NORTHERN PLAINS. MODEL
GUIDANCE HAS TRENDED SLOWER WITH THE PROGRESSION OF THE FRONT.
SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE IN NORTHWEST NEBRASKA BY
THE AFTERNOON HOURS. HEAVY RAINFALL POTENTIAL WILL HAVE TO BE
MONITORED AS PWATS INCREASE TO AROUND 1.5 INCHES IN THE VICINITY OF
THE FRONT. GIVEN THE SLOWER PROGRESSION OF THE SYSTEM...BEST CHANCES
FOR SHOWERS AND THUNDERSTORMS HAVE SHIFTED TOWARD LATER SUNDAY AND
INTO THE LONG TERM PERIOD. HIGHS SUNDAY WILL BE QUITE
HOT...ESPECIALLY IN FAR SOUTHWEST NEBRASKA WHERE A FEW SPOTS MAY HIT
100F AS VERY WARM MID-LEVEL AIR IS MIXED DOWN TO THE SURFACE.

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 358 PM CDT SAT JUL 4 2015

SUNDAY NIGHT THROUGH TUESDAY...THE MODELS ARE A BIT SLOWER AND
FARTHER NORTH WITH THE DYNAMICS FOR HEAVY RAIN SUNDAY NIGHT FAVORING
SOUTH DAKOTA. THE SFC WARM SECTOR HAS OPENED UP SENDING THE INVERTED
TROF INTO SD WHICH ANGLES SOUTHWEST INTO NORTHWEST NEB. THERE IS
STILL A GOOD CHANCE OF HEAVY THUNDERSTORM ACTIVITY ACROSS NRN NEB
BUT AREAS SOUTH OF NEBRASKA HIGHWAY 2 MAY JUST SEE SCATTERED STORM
COVERAGE. THE RIGHT ENTRANCE OR RIGHT REAR QUADRANT OF THE JET JUST
DOESNT SEEM TO FAVOR DECENT RAINFALL ACROSS SWRN NEB AND SEVERAL
MODELS SHOW A DONUT HOLE IN THE QPF TOTALS THROUGH 84 HOURS
FEATURING HEAVY RAINFALL ACROSS SD AND KS.

SPC IS EXAMINING THE LOW LEVEL JET SUNDAY EVENING ACROSS NCNTL NEB
AS A FORCE FOR SEVERE WEATHER. THIS JET STRENGTHENS AND BEGINS TO
VEER OFF EAST OF HIGHWAY 83 AT 03Z BUT CONTINUES TO EXPAND SOUTH
INTO SCNTL NEB BY 06Z. IT IS POSSIBLE SEVERE WEATHER COULD DEVELOP
ANYWHERE ALONG THE INTERFACE OF THE PACIFIC FRONT SAGGING SOUTH AND
THE LOW LEVEL JET VEERING OFF TO THE EAST BUT THE NAM IS OPENING UP
A DRY WARM SECTOR ACROSS THE SOUTH CUTTING OFF THE RAIN CHANCES.

THE SLOWER EVOLUTION OF THIS SYSTEM DOES PRESENT AN OPPORTUNITY FOR
ISOLATED ELEVATED POST FRONTAL SHOWERS AND THUNDERSTORMS MONDAY
ACROSS SOUTHWEST NEB. THE NAM WAS THE HEAVY HITTER IN THIS REGARD.

A FRESH BATCH OF PACIFIC HIGH PRESSURE WILL BUILD INTO THE FCST AREA
MONDAY AND THEN MOVE EAST INTO THE MIDWEST TUESDAY. HIGHS IN THE 70S
TO NEAR 80 ARE EXPECTED BOTH DAYS WITH LOWS IN THE 50S.

TUESDAY NIGHT THROUGH SATURDAY...AN INTERESTING DEVELOPMENT WILL
OCCUR. THE UPPER LEVEL RIDGE ACROSS THE WRN U.S. WILL DROP SOUTH
INTO MEXICO AND THEN VANISH ACROSS THE EASTERN PACIFIC. THEN AN
UPPER LEVEL RIDGE ACROSS THE WRN ATLANTIC WILL MIGRATE WEST INTO THE
MIDSOUTH BY NEXT SATURDAY. THIS WOULD SUPPORT A WEAKNESS IN THE
HEIGHTS ALOFT ALLOWING AN UPPER LEVEL LOW OFF THE WEST COAST TO MOVE
INTO THE WRN U.S.

A SERIES OF WEAK DISTURBANCES WILL TRANSIT THE CNTL AND SRN PLAINS
TUESDAY NIGHT THROUGH THURSDAY. THE UPPER LOW IN THE WEST WILL
PROVIDE MOISTURE SUPPORT ALOFT. MOISTURE IN THE LOWER LEVELS IS A
BIT LIMITED WITH SFC DEW POINTS IN THE 50S TO LOWER 60S. POPS ARE 20
TO 40 PERCENT AS THE GFS...GEF AND ECM SHOW A WEAKNESS IN THE QPF
ACROSS THE FCST AREA.

HIGH PRESSURE SHOULD CONTINUE HIGHS AROUND 80 WEDNESDAY WITH A
GRADUAL WARMING TREND THURSDAY THROUGH SATURDAY AS LOW PRESSURE
FORMS ON THE CNTL/NRN HIGH PLAINS. BY SATURDAY...A HEAT WAVE COULD
BE UNDERWAY WITH HIGHS IN THE 90S. ISOLATED POPS ARE IN PLACE FRIDAY
AND SATURDAY NIGHTS FOR NOCTURNALLY CONVECTION DRIVEN BY STEEPENING
LAPSE RATES.

THE MODELS ARE ACTUALLY IN VERY GOOD AGREEMENT. H700 MB TEMPERATURES
PEAK TOMORROW AT AROUND 15C...THEN FALL TO 5C TUESDAY AND GRADUALLY
RISE BACK TO 15C BY NEXT SATURDAY. THE H500MB FIELDS...850 MB WINDS
AND 500MB AGL DEW POINTS ARE IN SIMILAR AGREEMENT.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1222 PM CDT SAT JUL 4 2015

MAIN FORECAST CHALLENGE FOR THE 18Z TAF ISSUANCE IS THE THREAT FOR
ISOLATED/SCATTERED TSRA ACROSS WESTERN AND NORTH CENTRAL LATE THIS
AFTERNOON AND THROUGH THE EVENING HOURS. FORECASTER CONFIDENCE IS
STILL LOW IN THE SPATIAL COVERAGE AND MAGNITUDE OF THUNDERSTORM
ACTIVITY...BUT HAVE KEPT MENTION OF VCTS AT BOTH KLBF AND KVTN TO
HIGHLIGHT THE LATEST MODEL GUIDANCE TRENDS FOR POSSIBLE TIMING OF
TSRA NEAR THE TERMINALS. OTHERWISE VFRR CONDITIONS ARE EXPECTED TO
PREVAIL THROUGH THE NEXT 24 HOURS.

&&

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

$$

SYNOPSIS...MARTIN
SHORT TERM...MARTIN
LONG TERM...CDC
AVIATION...MARTIN





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