Area Forecast Discussion
Issued by NWS Hastings, NE

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000
FXUS63 KGID 210546
AFDGID

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HASTINGS NE
1246 AM CDT THU AUG 21 2014

.UPDATE...
ISSUED AT 1246 AM CDT THU AUG 21 2014

THE 18Z/00Z NAM HAVE THE BEST HANDLE BY FAR ON QPF THRU 05Z. A
NW-SE ORIENTED NARROW BAND OF SHWRS WITH EMBEDDED THUNDER HAS BEEN
LIFTING ENE AROUND 22 KTS THE PAST 3 HRS. THIS BAND SHOULD CONT
ACROSS S-CNTRL NEB THRU 5 AM. OTHER SCATTERED SHWRS WERE
DEVELOPING TO THE SW AND THE NAM HAS IT. SO UNTIL WE CAN GET A
BETTER GRASP ON WHAT DEVELOPS BEHIND THIS LINE...HAVE A 20 POP TO
COVER THIS.

THE FCST WAS UPDATED USING THE EXTRAPOLATION TOOL FOR POPS/WX/SKY.
ADDITIONAL ADJUSTMENTS MAY NEED TO BE MADE BEFORE DAWN DEPENDENT
ON RADAR TRENDS.

IT IS STILL WARM OUTSIDE. IT WAS STILL IN THE LOWER 80S S OF I-80
INTO N-CNTRL KS WHERE RAIN HAS NOT FALLEN. HOWEVER...LOW TEMPS
WERE LOWERED FROM THE TRI-CITIES S AND E TO ACCT FOR COOLING
EFFECTS OF THE RAIN.

&&

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 329 PM CDT WED AUG 20 2014

MAP ANALYSIS INDICATES UPPER TROPOSPHERIC RIDGING EXISTS OVER THE
CENTRAL CONUS...WITH TROUGHING OVER THE WESTERN AND EASTERN CONUS.
MAP ANALYSIS ALSO INDICATES A SUBTLE UPPER TROPOSPHERIC
PERTURBATION EXISTS OVER THE CENTRAL HIGH PLAINS. ENHANCED UPPER
TROPOSPHERIC FLOW EXTENDS FROM THE NORTHWESTERN CONUS...SOUTH
ALONG THE WESTERN CONUS COAST...THEN NORTHEAST INTO THE CENTRAL
CONUS...AND THEN BACK TO THE SOUTHEAST INTO THE OHIO RIVER VALLEY.
THAT BEING SAID...UPPER TROPOSPHERIC FLOW OVER OUR AREA IS NOT
OVERLY STRONG...ONLY MAXING OUT AT AROUND 50KTS NEAR 39000FT AGL
PER 12Z SOUNDING DATA FROM KLBF AND KOAX. WATER VAPOR IMAGERY ALSO
SHOWS THE AFOREMENTIONED UPPER TROPOSPHERIC RIDGE...TROUGHS...AND
PERTURBATION...AS WELL AS ENHANCED UPPER TROPOSPHERIC MOISTURE
EXTENDING FROM MEXICO INTO THE CENTRAL CONUS. TROPICAL MOISTURE IS
ALSO NOTED EXTENDING FROM TROPICAL STORM LOWELL IN THE
PACIFIC...INTO PORTIONS OF NORTHWESTERN MEXICO...BUT THIS TROPICAL
MOISTURE HAS YET TO MOVE INTO THE CONUS AND IS WELL AWAY FROM THE
CENTRAL PLAINS. AT THE SURFACE...AN AREA OF LOW BAROMETRIC
PRESSURE IS NOTED ACROSS WESTERN SOUTH DAKOTA...WITH A SURFACE
TROUGH ALSO NOTED EXTENDING SOUTH FROM THE LOW ACROSS PORTIONS OF
THE CENTRAL HIGH PLAINS. THE LOWER TROPOSPHERIC WIND FIELD ACROSS
OUR AREA REMAINS FROM THE SOUTH AS A RESULT.

GUIDANCE SUGGESTS THE UPPER TROPOSPHERIC PERTURBATION...CURRENTLY
OVER THE CENTRAL ROCKY MOUNTAIN RANGE...WILL MOVE NORTHEAST
THROUGH THE NEXT 24 HOURS...LIKELY POSITIONING ITSELF OVER SOUTH
DAKOTA BY 00Z THIS EVENING BEFORE MOVING EAST/SOUTHEAST OVER THE
UPPER MISSISSIPPI VALLEY AND EVENTUALLY THE GREAT LAKES REGION ON
THURSDAY. THE AREA OF LOW BAROMETRIC PRESSURE AT THE
SURFACE...CURRENTLY LOCATED ACROSS WESTERN SOUTH DAKOTA...IS
EXPECTED TO FOLLOW THE UPPER TROPOSPHERIC PERTURBATION BY MOVING
INTO CENTRAL SOUTH DAKOTA BY 00Z THIS EVENING...INTO EASTERN SOUTH
DAKOTA BY 12Z THURSDAY...AND INTO SOUTHWESTERN MINNESOTA BY 00Z
FRIDAY. THE ASSOCIATED SURFACE TROUGH SHOULD ALSO FOLLOW THE LOW
BY SLOWLY MOVING EAST ACROSS THE REGION SOMEWHAT...LIKELY WORKING
INTO OUR CWA THIS EVENING AND TONIGHT BEFORE STALLING OUT AND
BECOMING MORE OF A WARM FRONT ACROSS OUR AREA DURING THE DAY
THURSDAY. THE RESULTANT LOWER TROPOSPHERIC WIND FIELD ACROSS OUR
AREA SHOULD REMAIN FROM THE SOUTH FOR THE MOST PART THIS
EVENING...BUT LOCATIONS ACROSS OUR NORTH AND WEST COULD OBSERVE
MORE OF A NORTHEASTERLY LOWER TROPOSPHERIC WIND FIELD LATE TONIGHT
AND INTO THE DAY THURSDAY.

THERMAL ADVECTION AHEAD OF THE UPPER TROPOSPHERIC PERTURBATION
WILL CERTAINLY INCREASE ACROSS THE NORTHERN PLAINS...AND PERHAPS
PORTIONS OF THE CENTRAL PLAINS...THIS EVENING AND INTO
TONIGHT...BUT BASED ON THE ANTICIPATED PATH OF THE
PERTURBATION...IT CERTAINLY APPEARS AS THOUGH THE BULK OF THIS
THERMAL ADVECTION AND RESULTANT OMEGA WILL REMAIN NORTH OF OUR
AREA. AS A RESULT...THE VAST MAJORITY OF GUIDANCE SUGGESTS
PRECIPITATION WILL ALSO REMAIN TO OUR NORTH THROUGH 06Z TONIGHT.
THAT BEING SAID...A FEW SETS OF GUIDANCE DO SUGGEST THAT AFTERNOON
CONVECTION OVER THE CENTRAL HIGH PLAINS COULD MOVE EAST AND
SUSTAIN ITSELF LONG ENOUGH TO IMPACT WESTERN PORTIONS OF OUR CWA
21-03Z. GIVEN THIS...WENT AHEAD WITH 20-40% POPS ACROSS OUR
WESTERN CWA 21-03Z.

AFTER 03Z TONIGHT...GUIDANCE SUGGESTS THE AXIS OF A 35-45KT LOWER
TROPOSPHERIC JET STREAK...JUST ABOVE THE BOUNDARY LAYER...WILL
DEVELOP FROM CENTRAL KANSAS INTO SOUTH CENTRAL AND SOUTHEASTERN
NEBRASKA. AT THIS TIME IT APPEARS THERMAL ADVECTION ALONG THE AXIS
OF THIS JET STREAK WILL BE SUFFICIENT FOR PRECIPITATION
PRODUCTION ACROSS MUCH OF THE CWA. THIS IS A SOLUTION SUPPORTED BY
QPF FIELDS FROM THE NAM AND OPERATIONAL GFS. GIVEN THIS...WENT
AHEAD WITH 20-30% POPS ACROSS MUCH OF THE CWA 03-12Z.

SHOULD CONVECTION BE REALIZED ACROSS THE CWA TONIGHT...THEN THERE
COULD CERTAINLY BE SOME LINGERING CONVECTIVE ACTIVITY ACROSS THE
AREA AROUND SUNRISE THURSDAY. HOWEVER THIS ACTIVITY SHOULD QUICKLY
DISSIPATE AND DEPART TO THE EAST/NORTHEAST AND WITH AN OVERALL
LACK IN OMEGA...DRY CONDITIONS ARE EXPECTED FOR THE MOST PART
DURING THE DAY THURSDAY.

BY LATE THURSDAY AFTERNOON AND INTO THURSDAY EVENING
HOWEVER...DIABATIC HEATING AND A RESULTANT DECREASE IN CIN
VALUES...ALONG WITH AREAS OF LOCALLY ENHANCED CONVERGENCE ALONG
THE STRENGTHENING TROUGH / DEVELOPING WARM FRONT ACROSS THE
AREA...COULD PROMOTE ISOLATED THUNDERSTORM DEVELOPMENT ACROSS THE
AREA. GIVEN THIS...WENT AHEAD WITH ~20% POPS ACROSS MUCH OF THE
CWA STARTING AT 21Z THURSDAY.

WHILE THERE IS SOME QUESTION AS TO WHETHER THE HIGH PLAINS
CONVECTION CAN MAINTAIN INTENSITY AS IT MOVES EAST...AND WHETHER
IT ACTUALLY REACHES OUR CWA...THE NAM...OPERATIONAL GFS AND EC ALL
SUGGEST 1000-3000J/KG 0-1KM MLCAPE VALUES...ALONG WITH DEEP LAYER
BULK SHEAR VALUES OF 20-30KTS...WILL BE IN EXISTENCE ACROSS OUR
WESTERN CWA THROUGH AROUND 00Z THIS EVENING. GIVEN THIS...WOULD
FEEL MUCH BETTER HAVING AT LEAST SOME MENTION OF SEVERE WEATHER IN
THE FORECAST...AND WENT AHEAD WITH QUARTER SIZE HAIL AND 60MPH
WIND GUSTS IN THE HWO FOR LATE THIS AFTERNOON AND EVENING
PRIMARILY WEST OF HIGHWAY 281. DURING THE OVERNIGHT
HOURS...FORECAST PROXIMITY SOUNDINGS FROM ACROSS THE CWA...PER THE
NAM AND OPERATIONAL GFS...SUGGEST CONVECTIVE-AVAILABLE ENERGY WILL
BE LOWER WHEN COMPARED TO THIS AFTERNOON AND EVENING...UNDER
1000J/KG...BUT WILL GO AHEAD AND MAINTAIN A MENTION OF NICKEL SIZE
HAIL AND WIND GUSTS TO AROUND 50 MPH. FINALLY...THE
NAM...OPERATIONAL GFS AND EC ALL SUGGEST 0-1KM MLCAPE VALUES OF
1500-4000J/KG WILL BE IN EXISTENCE ACROSS THE AREA THURSDAY
AFTERNOON AND EVENING AND AS A RESULT...WENT AHEAD AND OUTLOOKED
SEVERE WEATHER FOR THURSDAY AFTERNOON AND EVENING AS WELL.


.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 329 PM CDT WED AUG 20 2014

THE PATTERN ALOFT CONTINUES TO INDICATE RIDGING TO THE EAST AND
TROUGHING OFF TO THE WEST OF THE OUTLOOK AREA DURING THE NEXT
SEVERAL DAYS. WE ARE ACTUALLY STUCK IN THIS PATTERN FOR MOST OF
THE LONG TERM...RESULTING IN SOUTHWESTERLY FLOW ALOFT UNTIL AT
LEAST TUESDAY...WITH SEVERAL PERTURBATIONS PASSING OVER THE CWA.
WE WILL FINALLY BREAK THIS PATTERN AS A TROUGH BEGINS TO PUSH
EASTWARD ACROSS THE CONUS AROUND TUESDAY. HIGH TEMPERATURES FOR
THE TRI- CITIES CONTINUE TO RANGE IN THE UPPER 80S AND LOWER 90S
UNTIL WE COOL DOWN SUNDAY THROUGH TUESDAY. IT SHOULD BE NOTED THAT
OUR NORTH CENTRAL KANSAS COUNTIES WILL LIKELY BE AROUND THE MID TO
UPPER 90S BEFORE THE COOL DOWN. HEAT INDICES COULD BE HAS HIGH AS
100 FRIDAY FOR A FEW OF OUR KANSAS COUNTIES.

IF SHOWERS/STORMS HAVE NOT ALREADY DEVELOPED BY THURSDAY
NIGHT...I DO EXPECTED THUNDERSTORMS TO DEVELOP AS THE LLJ
INCREASES...ESPECIALLY SOUTHERN AND EASTERN PARTS OF THE CWA.
THESE SHOWERS/STORMS SHOULD CONTINUE THROUGH THE MORNING HOURS
BEFORE THE LLJ DECREASES. THUNDERSTORMS WILL LIKELY INITIATE LATER
FRIDAY AFTERNOON ALONG A WEST-EAST ORIENTED WARM FRONT.
INSTABILITY OF 1000- 2000 J/KG OF MOST UNSTABLE CAPE AND 0-6 KM
SHEAR VALUES AROUND 30 KNOTS SHOULD HELP THUNDERSTORM DEVELOPMENT
ALONG THIS FRONTAL BOUNDARY AS PEAK HEATING BECOMES REALIZED.
THROUGH THE EVENING AND OVERNIGHT PERIOD THESE STORMS WILL BE
MAINTAINED BY THE LLJ AS THE ATMOSPHERE BECOMES DECOUPLED. OUR
BEST CHANCE FOR OVERALL PRECIPITATION ACROSS THE CWA DURING THE
LONG TERM WILL BE FRIDAY EVENING/OVERNIGHT. CURRENTLY...THIS WILL
ALSO BE OUR BEST CHANCE TO EXPERIENCE ANY STRONG TO SEVERE
THUNDERSTORMS DURING THE LONG TERM. THE MAIN THREAT WOULD BE
SEVERE WIND...BUT CANNOT RULE OUT SOME SEVERE HAIL AS WELL.
OVERALL...THERE WILL BE CHANCES FOR PRECIPITATION EVERYDAY THROUGH
THE EXTENDED. HPC IS CURRENTLY FORECASTING ANYWHERE FROM HALF AN
INCH TO ABOUT 2 INCHES FOR OUR CWA OVER THE NEXT 7 DAYS...WITH
HIGHER AMOUNTS TO OUR NORTH. I WOULD THINK THIS IS A GOOD BROAD
BRUSH START FOR QPF GIVEN THE MULTIPLE CHANCES OF RAINFALL WE ARE
EXPECTING TO GET OVER THE NEXT SEVERAL DAYS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1246 AM CDT THU AUG 21 2014

REST OF TONIGHT: VFR MID-LEVEL CEILINGS 10-12K FT. HOWEVER...THERE
IS A LOW PROBABILITY FOR IFR VISIBILITY AND G30 KTS IN BRIEF
+TSRA THRU 0630Z AT EAR AND 0730Z AT GRI. WINDS WILL BE S 7-12 KTS
EXCEPT AROUND TSTM ACTIVITY. LLWS. CONFIDENCE: MEDIUM

THU: VFR WITH SCT MID-LEVEL CLOUDS AROUND 15K FT. S-SSW WINDS
AROUND 10 KTS. THERE IS A SLIGHT CHANCE FOR A SHWR/TSTM...
ESPECIALLY AFTER 21Z. CONFIDENCE: MEDIUM

THU EVE: VFR WITH SCT MID-HIGH CLOUDS AT OR ABOVE 8K FT. WINDS
BECOME SE UNDER 10 KTS.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.
&&

$$

UPDATE...HALBLAUB
SHORT TERM...BRYANT
LONG TERM...GUERRERO
AVIATION...HALBLAUB



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