848 FXUS64 KLUB 131730 AFDLUB AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LUBBOCK TX 1230 PM CDT TUE AUG 13 2013 .UPDATE... LATE MORNING SFC ANALYSIS SHOWS A WEAK OUTFLOW BOUNDARY THAT HAD MOVED TO THE SRN EDGE OF THE FCST AREA EARLIER HAD NOW BEGUN TO DISSIPATE WITH LIGHT SOUTH WINDS BEGINNING TO OVERTAKE THE SRN SOUTH PLAINS. MEANWHILE...ANOTHER WEAK BOUNDARY WAS BEGINNING TO SHARPEN ACROSS THE NRN PANHANDLE...AND IT IS THIS BOUNDARY THAT THE NAM AND RAP SEEM TO BE KEYING ON FOR AFTN THUNDERSTORM DEVELOPMENT. 12Z MODEL RUN WANTS TO SHIFT THIS BOUNDARY A BIT FURTHER SWD THAN PREVIOUS FCST AND AS A RESULT HAVE SHIFTED AXIS OF HIGHER POPS FOR THE 18Z-00Z TIME FRAME SWD AS WELL. OTHER CHANGES TO AFTN WERE EVEN MORE MINOR...MAINLY ADJUSTING FOR TRENDS IN DEW POINT AND WIND. HAVE LEFT EVENING FCST ALONE FOR NOW. MAY ALSO NEED TO SHIFT HIGHER POPS SWD THERE...BUT WOULD LIKE TO SEE THE WHITES OF ITS EYES IN RELATION TO EXPECTED INITIATION ZONE BEFORE MAKING CHANGES. SECONDARY PRECIP MAY COME WITH HIGH TERRAIN STORMS FROM NERN NM SURGING SEWD INTO MOIST UPSLOPE FLOW AIDED BY ABOUT 30 KT FLOW AT 500 MB. ATTM HIGH CHANCE TO LIKELY POPS FAVORING NRN ZONES STILL APPROPRIATE WITH REEVALUATION FOR THE AFTN PACKAGE. && .AVIATION... WEAK SFC BOUNDARY SHOULD FOCUS SCATTERED CONVECTION LATE AFTN EARLY EVENING PROBABLY IN A BAND NEAR BOTH TERMINALS...POSSIBLY BETWEEN THE TWO...BUT PROBABLY HIGH ENOUGH CONFIDENCE TO INSERT A TEMPO MENTION. NAM MODEL SEEMS TO BE OVERPLAYING POTENTIAL FOR MVFR CIGS LATE TONIGHT. THIS IS A BIAS OF THAT MODEL AND FOR NOW WILL LEAN TOWARD THE MORE OPTIMISTIC GFS. && .PREV DISCUSSION... /ISSUED 639 AM CDT TUE AUG 13 2013/ AVIATION... A COLD FRONT MOVING THROUGH THE AREA WILL BRING A N-NE WIND SHIFT TO KLBB BY ABOUT 13Z...FOLLOWED BY PREVAILING E-NE WINDS AT BOTH TERMINALS THROUGH THE REMAINDER OF THE FCST. SCATTERED SHOWERS AND THUNDERSTORMS MAY AFFECT EITHER/BOTH TERMINALS THIS AFTERNOON AND EVENING AND WE HAVE A PROB30 MENTION AT BOTH. THE SHOWER ACTIVITY MAY CONTINUE OVERNIGHT BUT WITH LOW CONFIDENCE IN THE PARTICULARS. ALSO...THERE IS SOME INDICATION THAT LOW CEILINGS NEAR OR BELOW 2000 FT MAY DEVELOP AT EITHER TERMINAL...MORE LIKELY AT KCDS. WE WILL LEAVE MENTION OUT OF TAF FOR NOW UNTIL THERE IS A STRONGER INDICATION. PREV DISCUSSION... /ISSUED 419 AM CDT TUE AUG 13 2013/ SHORT TERM... INITIAL OUTFLOW BOUNDARY MOVED THROUGH MOST OF THE AREA LAST NIGHT WITH WEAK EASTERLY WINDS NOTED ACROSS ALL BUT THE SW SPLNS...WHERE WINDS REMAINED SOUTHERLY. WE/VE SEEN SOME MORNING SHOWER ACTIVITY CROP UP JUST WEST OF THE STATE LINE AS WE CONTINUE TO SEE SOME WEAK UPPER-AIR RIPPLES ROTATE AROUND A VERY FLAT RIDGE CENTERED OVER SW TX. FARTHER TO THE NORTH...A W-E BAND OF MORE WIDESPREAD SHOWERS AND THUNDERSTORMS STRETCHED ACROSS THE NRN TX PANHANDLE WITH A WELL-DEFINED OUTFLOW/COLD FRONT BOUNDARY MOVING SOUTH...APPROACHING KAMA AT 3 AM. THIS BOUNDARY SHOULD MOVE INTO OUR NRN ZONES EARLY THIS MORNING...AND POSSIBLY FARTHER SOUTH BEFORE LOSING MOMENTUM. SURFACE WINDS WILL BECOME FAIRLY LIGHT ACROSS THE AREA TODAY...LIKELY WITH A SMALL NORTH TO EAST COMPONENT. THIS SHOULD MAINTAIN HEALTHY MOISTURE IN PLACE IN THE LOW-LEVELS. ALOFT...WATER VAPOR IMAGERY THIS MORNING SHOWS A SHORTWAVE LIFTING NORTH ACROSS THE GREAT BASIN...ANOTHER SWINGING SOUTH THROUGH THE DAKOTAS...WITH CONVOLUTED FLOW IN-BETWEEN THESE TWO SYSTEMS FROM THE SRN ROCKIES INTO THE HIGH PLAINS. AN UPPER-LVL JET WILL ADVANCE INTO SRN CO/KS TODAY...WITH A BELT OF 30+ KT MID-LVL WINDS DEVELOPING ACROSS NE NM TO WRN OKLA THIS AFTERNOON...AND SPREADING INTO THE NRN SPLNS TO RED RIVER VALLEY TONIGHT. LIFT WITH THE JET WILL COUPLE WITH LOW-LVL LIFT IN THE FRONT/OUTFLOW ZONE AND A MODERATELY UNSTABLE AIRMASS TO SUPPORT CONVECTIVE CHANCES THROUGH THE DAY AND ON INTO THE NIGHT. HIGH-RES GUIDANCE SUGGESTS THAT THE ACTIVITY IN THE PANHANDLE WILL SAG SOUTH INTO OUR NRN ZONES THIS MORNING AND WEAKEN. THEN THIS AFTERNOON...WE SHOULD SEE SCATTERED CONVECTIVE DEVELOPMENT PRIMARILY ACROSS THE NW PORTIONS OF THE SPLNS AND SWRN TX PANHANDLE...ALTHOUGH WE CAN/T RULE OUT DEVELOPMENT ALMOST ANYWHERE. STORMS WILL GENERALLY MOVE EAST AND WILL TAP INTO MLCAPES RUNNING 1000 TO 2000 J/KG AND 0-6 KM BULK SHEAR OF 30 KTS SOUTH TO 40+ KT NORTH. THIS ENVIRONMENT WILL SUPPORT SOME SEVERE STORM POTENTIAL /MAINLY DAMAGING WIND GUSTS/ THIS THREAT WILL BE HIGHER ACROSS THE NRN ZONES WHERE THE SHEAR WILL BE GREATER...BUT WE WILL HAVE TO MONITOR JUST WHERE THE OUTFLOW BOUNDARY ACTUALLY SETS UP TO ENHANCE LOW-LVL CONVERGENCE AND LIFT. ALSO...STORM CELLS POSSIBLY TRAINING ON THE COLD SIDE OF THE BOUNDARY COULD LEAD TO SOME LOCALLY HEAVY RAIN POTENTIAL THIS EVENING. AS WE HEAD INTO THE OVERNIGHT HOURS...THE FORECAST CONFIDENCE DECREASES AS BEST UPPER-LEVEL LIFT WILL REMAIN POSITIONED ACROSS THE NORTH...BUT BEST LOW-LVL FOCUS WILL KEEP SHIFTING SOUTH...WITH THE FRONT MOVING ON INTO THE PERMIAN BASIN BY EARLY WED MORNING. THE BULK OF GUIDANCE KEEPS THE HIGHEST RAIN CHANCES PINNED ACROSS THE NORTH. OVERALL COVERAGE AND STRENGTH OF ACTIVITY IS EXPECTED TO WANE AFTER MIDNIGHT...ALTHOUGH WE WILL HAVE TO WATCH BACK TO THE WEST WHERE A OVERNIGHT COMPLEX MAY BEGIN TO FORM NEAR THE STATE LINE WHERE LIFT FROM NEXT SHORTWAVE STARTS TO IMPINGE ON POST-FRONTAL UPSLOPE. LONG TERM... AN UNSETTLED STRETCH OF WEATHER WILL KICK OFF THE EXTENDED FORECAST THANKS TO A PERIOD OF NORTHWESTERLY FLOW ALOFT AND A FRONTAL BOUNDARY IN/NEAR THE AREA. HOWEVER...THE DEVIL IS IN THE DETAILS WITH MUCH UNCERTAINTY IN THE SPATIAL AND TEMPORAL DISTRIBUTION OF THE BEST SHOWER/STORM CHANCES RESULTING FROM UNKNOWNS REGARDING THE EXACT FRONTAL POSITION AND TIMING OF SUBTLE SHORTWAVES MOVING THROUGH THE FLOW ALOFT. NORTHWESTERLY MID-LEVEL FLOW WILL BEGIN TO TAKE SHAPE ON WEDNESDAY AS AN UPPER RIDGE AMPLIFIES OVER THE ROCKIES DOWNSTREAM OF A LARGE VORTEX CENTERED OFF THE COAST OF BRITISH COLUMBIA. WEST TEXAS WILL BE POSITIONED BETWEEN THE RIDGE AND LARGE-SCALE TROUGHING ACROSS THE EASTERN PORTION OF THE CONTINENT. AT THE SFC...A FRONTAL BOUNDARY IS PROGGED TO SETTLE SOUTHWARD THROUGH MOST IF NOT THE ENTIRE CWA EARLY WEDNESDAY...WITH RICH POST-FRONTAL MOISTURE ADVECTING IN ON UPSLOPE WINDS. THIS MOIST ENVIRONMENT WILL READILY SUPPORT PRECIPITATION AND EFFICIENT RAINFALL RATES GIVEN ANY SUBTLE FORCING FOR ASCENT. INITIALLY THE FRONTAL FORCING AND PERHAPS WEAK UPPER SUPPORT WILL KEEP DECENT RAIN CHANCES GOING ON WEDNESDAY...WITH ADDITIONAL CONVECTION FOCUSED ALONG AND BEHIND THE FRONT AS DAYTIME HEATING PEAKS AND A POSSIBLE WEAK SHORTWAVE TROUGH APPROACHES. ONE QUESTION MARK IS HOW MUCH HEATING CAN DEVELOP WEDNESDAY AFTERNOON WITH THE NAM SUGGESTING LOW CLOUDS MAY HOLD TOUGH MUCH OF THE DAY AND LIMIT POTENTIAL INSTABILITY. THE ECMWF AND GFS ARE MORE OPTIMISTIC AND PROJECT SBCAPES CLIMBING TO NEAR OR IN EXCESS OF 1500 J/KG. IF THE STRONGER INSTABILITY IS REALIZED IT COULD BRING THE POTENTIAL FOR A FEW STRONG TO SEVERE STORMS AS 0-6 KM SHEAR CLIMBS TO AROUND 35 KNOTS. WE WILL ALSO LOOK FOR THE POSSIBILITY OF A MCS ROLLING IN LATE FROM THE NORTH...THOUGH THE COOLER AND MORE STABLE NAM SOLUTION DOES NOT SUPPORT THIS. FOR NOW...HAVE MADE ONLY MINOR ADJUSTMENTS TO THE POP/WX GRIDS...MAINTAINING A 30-40 PERCENT CHANCE OF STORMS WEDNESDAY AND WEDNESDAY NIGHT. THE OVERALL SETUP WILL NOT CHANGE MUCH THURSDAY...THOUGH THE FRONTAL ZONE MAY RETREAT A BIT...SO THUNDER CHANCES WILL CONTINUE WITH NWP CURRENTLY SUGGESTING ANOTHER SHORTWAVE WILL APPROACH FROM THE NORTHWEST LATE KEEPING STORM CHANCES GOING LATE INTO THE NIGHT. THE UPPER FLOW WILL TURN MORE NORTHERLY ON FRIDAY AS THE WESTERN RIDGE FURTHER AMPLIFIES AND BEGINS TO EDGE EASTWARD. THIS WILL REDUCE THE CHANCE THAT CONVECTION ORIGINATING OVER THE HIGHER ELEVATION OF NM AND CO CAN MAKE ITS WAY TO THE SOUTH PLAINS...BUT WITH THE RESIDUAL FRONTAL BOUNDARY STILL IN THE AREA AND A SHORTWAVE GRAZING WEST TEXAS FROM THE EAST...HAVE MAINTAINED LOW STORM CHANCES. DRIER AIR WILL GRADUALLY ADVECT IN ALOFT OVER THE WEEKEND AS THE UPPER RIDGE BENDS FURTHER EASTWARD AND A DRYING TREND WILL LIKELY ENSUE. THIS RIDGE WILL GRADUALLY BREAKDOWN LATE WEEKEND INTO EARLY NEXT WEEK AS A TROUGH EMERGES FROM THE CENTRAL/NORTHERN ROCKIES. THIS COULD BEND THE MONSOON MOISTURE EASTWARD...PERHAPS REJUVENATING STORM CHANCES. REGARDING TEMPERATURES...TENDED TO FAVOR THE COOL SIDE OF GUIDANCE GIVEN THE EXPECTED CLOUD COVER AND RAIN IN THE AREA MID TO LATE WEEK. TEMPERATURES WILL GRADUALLY TREND UPWARD BY THIS WEEKEND AS THE UPPER RIDGE BENDS OVER AND SOUTHERLY LOW-LEVEL FLOW RETURNS TO WEST TEXAS. && .PRELIMINARY POINT TEMPS/POPS... FRIONA 85 62 84 61 86 / 40 50 40 40 30 TULIA 86 64 82 63 84 / 40 50 40 40 30 PLAINVIEW 89 65 81 64 84 / 30 40 40 40 30 LEVELLAND 91 66 84 65 88 / 30 30 40 40 30 LUBBOCK 91 68 83 65 86 / 30 30 40 40 30 DENVER CITY 94 66 88 65 91 / 20 20 40 30 30 BROWNFIELD 93 68 86 65 90 / 20 20 40 40 30 CHILDRESS 89 68 85 68 87 / 40 60 40 40 30 SPUR 93 70 86 68 89 / 30 30 40 40 30 ASPERMONT 95 72 89 69 90 / 20 30 40 40 30 && .LUB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ 07