Area Forecast Discussion
Issued by NWS North Platte, NE

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912
FXUS63 KLBF 151815
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
115 PM CDT FRI MAY 15 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 323 AM CDT FRI MAY 15 2015

TODAY AND TONIGHT... A WEAK COLD FRONT HAS DROPPED SOUTH TO JUST
NORTH OF INTERSTATE 80 PER SFC OBS AND RTMA ANALYSIS. EAST WINDS ARE
UNDERWAY IN THE PLATTE VALLEY. STRATUS NORTH OF THE FRONT ACROSS NRN
NEB COULD SPREAD SOUTH TO NEAR THEDFORD AND PERHAPS AS FAR SOUTH AS
BROKEN BOW BY MORNING. THE THUNDERSTORMS UNDERWAY ACROSS SWRN NEB
THIS MORNING SHOULD MOVE UP AND OVER THE FRONT PRODUCING RAIN COOLED
AIR WHICH WOULD KEEP THE FRONT IN OR NEAR THE PLATTE VALLEY UNTIL
AFTERNOON. THIS AFTERNOON...FRONT COULD BEGIN TO MOVE NORTH SLOWLY.
THE MODEL CONSENSUS SHOWS THE FRONT LIFTING RAPIDLY NORTH TONIGHT.

THE BEST GUESS ON THE SEVERE WEATHER IS A BIT OPTIMISTIC. STRONG
WINDS ALOFT...40 TO 50 KT AT 500 MB AND 60 KT AT 300 MB SHOULD MOVE
INTO SWRN NEB AROUND 18Z AND FIRE CONVECTION ON A WARM FRONT DRAPED
ACROSS THE SRN SANDHILLS BY 21Z...PERHAPS ALIGNED E-SE TOWARD
LEXINGTON. THE RAP SHOWS LARGE SCALE LIFT AT THE SAME TIME EMANATING
FROM A LONG WAVE TROF OVER THE SWRN U.S.

TORNADO PARAMETERS LOOK REASONABLY GOOD WITH NICELY CURVED
HODOGRAPHS NEAR THE FRONT FOR SEVERAL HOURS DURING THE AFTN. THIS
PRODUCES 0-3KM HELICITY OVER 400 M2/S2 AND WHEN COMBINED WITH THE
INSTABILITY THE ENERGY HELICITY INDEX IS OVER 4 ALONG THE FRONT.
THUS A TORNADO OR TWO COULD FORM. WINDS ALOFT ARE A BIT LINEAR AND
CONRAD CONTINUES TO SUGGEST SPLITTING DOMINANT RIGHT MOVING
SUPERCELLS.

NOTE THE RAP...THE FAVORED MODEL...MOVES THE FRONT VERY LITTLE TODAY
WHICH COULD ALLOW FOR SEVERE STORMS TO RIDE UP AND OVER THE FRONT
AND BECOME MORE OF A HAIL THREAT.

SPC SUGGESTED STORM ACTIVITY WOULD WEAKEN THIS EVENING AND IT IS
POSSIBLE THE LARGE SCALE LIFT AND UPPER LEVEL SUPPORT COULD DO THE
SAME CARRYING THE BULK OF THE STORM ACTION INTO NRN NEB BY 00Z AS
SUGGESTED BY THE MODEL CONSENSUS.

THE FORECAST USES A BLEND OF THE RAP...NAM...GEMREG...ARW AND NMM.
THE OTHER MODELS WERE TOO COARSE RESOLUTION TO CAPTURE THE SPIRIT OF
THE EVENT.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 323 AM CDT FRI MAY 15 2015

DETERMINISTIC MODELS AND ENSEMBLE MEANS CONTINUE TO ADVERTISE A
PERSISTENT UPPER LEVEL SYNOPTIC PATTERN THROUGH THE MIDDLE OF NEXT
WEEK. BLOCKY SETUP ALONG THE WEST COAST INTO THE CENTRAL ROCKIES
WITH A HIGH AMPLITUDE RIDGE OVER WESTERN CANADA OVER THE TOP OF A
BROAD TROUGH EXTENDING SOUTHWARD TOWARD THE BAJA OF CALIFORNIA.
RIDGE TO THE EAST WILL BEGIN TO FLATTEN INTO EARLY NEXT WEEK AS A
LOW BUILDS INTO SOUTHEAST CANADA. THE MEAN UPPER LEVEL FLOW OVER THE
CENTRAL PLAINS REMAINS OUT OF THE SOUTHWEST THROUGH THE LONG RANGE
PERIOD AND IN THE CROSSHAIRS OF SEVERAL SHORTWAVE PERTURBATIONS
ASSOCIATED WITH THE WESTERN CONUS TROUGH.

ANOTHER ROUND OF SEVERE WEATHER IS POSSIBLE AGAIN ON SATURDAY AS
STRONG PV MAX AND UPPER LEVEL JET STREAK EJECT NORTHEAST OUT OF THE
FOUR CORNERS REGION. LEE SIDE LOW AND ASSOCIATED PACIFIC FRONT MAKE
LITTLE EASTWARD PROGRESSION TOWARD THE EASTERN NEBRASKA PANHANDLE BY
THE BEGINNING OF THE PERIOD. SCATTERED ELEVATED STORMS LEFTOVER FROM
FRIDAY NIGHT SHOULD BE PUSHING NORTH AND EAST OF THE CWA DURING THE
MORNING HOURS...AIDED BY A VEERING LLJ. CONVECTIVE INITIATION IS
LIKELY ONCE AGAIN BY MID AFTERNOON IN AN INCREASINGLY UNSTABLE WARM
SECTOR EAST OF THE PACIFIC FRONT. MODELS ARE STRUGGLING WITH THEIR
HANDLING OF WARM SECTOR RECOVERY...AND ANY CLOUD COVER WILL HAVE A
SIGNIFICANT IMPACT ON THE DEGREE OF DESTABILIZATION. HOWEVER SEVERE
STORMS WILL STILL BE POSSIBLE GIVEN THE STRONG FORCING FOR ASCENT
AND FAVORABLE DEEP LAYER SHEAR. WIND PROFILES CONTINUE TO LOOK
FAIRLY UNIDIRECTIONAL THROUGH A DEEP LAYER SATURDAY...FAVORING
UPSCALE GROWTH AS THE THUNDERSTORM ACTIVITY EVOLVES THROUGH THE
AFTERNOON AND EVENING. LARGE HAIL...DAMAGING WINDS WILL BE THE
PRIMARY THREATS. LOCALLY HEAVY RAINFALL WILL ALSO NEED TO BE CLOSELY
WATCHED AS SOME AREAS MAY EXPERIENCE SEVERAL ROUNDS/TRAINING
THUNDERSTORMS.

SHOWER AND THUNDERSTORM CHANCES CONTINUE SUNDAY ACROSS THE NORTHERN
TIER OF THE CWA. LOW LEVEL MOISTURE WRAPS AROUND THE BACKSIDE OF THE
SFC LOW NOW OVER THE DAKOTAS AND BACK INTO NEBRASKA...UNDERNEATH
ANOMALOUSLY COLD AIR ALOFT ASSOCIATED WITH THE PASSING OF THE
UPPER LEVEL LOW. A TRANSITORY RIDGE MOVES OVER THE CENTRAL PLAINS
EARLY IN THE WEEK BRINGING A TEMPORARY PERIOD OF DRIER CONDITIONS.
THE MIDDLE OF THE WEEK LOOKS COOL AND WET AS ANOTHER UPPER LEVEL
SHORTWAVE TROUGH PIVOTS NORTHEAST THROUGH THE EASTERN ROCKIES.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 115 PM CDT FRI MAY 15 2015

MOST OF THE AREA BECOMING VFR AS SHOWERS LIFT INTO S DAKOTA. A FEW
POCKETS OF MVFR/IFR CIGS...MAINLY ACROSS NORTHERN NEBRASKA. THIS
EVENING THUNDERSTORMS ARE LIKELY TO DEVELOP AND LIFT NORTHEAST
ACROSS THE AREA. DEVELOPMENT NEAR KLBF AND ONLY INCLUDED VCTS FOR
NOW AND WILL AMEND AS DEVELOPMENT OCCURS. HIGHER CONFIDENCE OF
THUNDERSTORMS ACROSS NORTHERN NEBRASKA AND INCLUDED A TEMPO FOR
KVTN. ALSO GOING TO SEE INCREASING SOUTHEASTERLY WINDS FOR THE
AFTERNOON.

AFTER STORMS LIFT NORTH OVERNIGHT EXPECT A LULL IN THE ACTIVITY
INTO TOMORROW MORNING. HOWEVER SOME AREAS OF STRATUS COULD
DEVELOP AND IMPACT THE TERMINALS.

&&

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

&&

$$

SHORT TERM...CDC
LONG TERM...MARTIN
AVIATION...MASEK






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