000 FXUS63 KLBF 300807 AFDLBF AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NORTH PLATTE NE 307 AM CDT SAT AUG 30 2008 .SYNOPSIS... FAST WESTERLY UPPER LVL FLOW IS PRESENT ALONG AND NORTH OF THE U.S. AND CANADIAN BORDER. AN UPPER LVL RIDGE IS BEGINNING TO AMPLIFY OVER THE NORTHERN HIGH PLAINS...IN RESPONSE TO STRENGTHENING LOW LVL WAA AHEAD OF A STRONG S/W TROUGH OVER BRITISH COLUMBIA. THIS TROUGH WILL DIG TOWARD THE INTERMOUNTAIN WEST OVER THE WEEKEND. MEANWHILE...AS THE UPR RIDGE BEGINS TO PROGRESS EAST OF THE REGION...LEE SIDE TROUGHING WILL BEGIN TO TAKE PLACE OVER THE CENTRAL/NORTHERN HIGH PLAINS...WHICH WILL FAVOR AN INCREASE IN TEMPERATURES TOWARD THE LOW TO MID 90S. && .DISCUSSION... HIGHER QUALITY/DEEPER BOUNDARY LAYER MOISTURE IS LOCATED OVER SOUTHWEST KANSAS THIS EVENING...AND HAS SHOWN SIGNS OF MOVING NORTH DURING THE LAST FEW HOURS. THIS TREND IS EXPECTED TO CONTINUE THROUGH SATURDAY MORNING...WITH FCST SOUNDINGS OVER SOUTHWEST NEB DEPICTING MARGINALLY FAVORABLE THERMODYNAMIC PROFILES FOR LOW CLOUDS/BR/FG. THUS...MADE A SLIGHT UPWARD ADJUSTMENT IN CLOUD COVER OVER THAT REGION AT AROUND 12Z TODAY. WELL MIXED PBL IS EXPECTED TO DEVELOP OVER THE NORTHERN AND WESTERN PORTIONS OF THE CWFA DURING THE AFTERNOON. WITH FLOW STRENGTHENING OVER THE LOWEST 6000 FT...BREEZY CONDITIONS ARE LIKELY /GUSTS APPROACHING 30 KT OVER THE NORTHERN HALF OF THE CWA/. MAV INDICATES THAT SUSTAINED WINDS WILL MEET WIND ADVISORY CRITERIA THIS AFTERNOON...WHILE THE MET IS NOT AS STRONG. WILL ADVISE DAY SHIFT THIS MORNING TO REEVALUATE ISSUING AN ADVISORY FOR THE AFTERNOON. A STRONG /50 KT/ LLJ IS FCST TO DEVELOP OVER THE NORTHERN PLAINS SATURDAY NIGHT. THIS WILL FAVOR RELATIVELY WARM LOW TEMPERATURES /MID 60S/ DUE TO STRONGER MIXING...WITH BREEZY CONDITIONS PERSISTING THROUGH THE NIGHT IN NORTH CENTRAL NEB. A WEAK PV DISTURBANCE IS ALSO FCST TO LIFT NORTHEAST ACROSS THE SOUTHERN AND EASTERN HALF OF THE CWA SATURDAY NIGHT. HOWEVER...THE ATMOSPHERE APPEARS TO BE TOO DRY TO SUPPORT PRECIPITATION DEVELOPMENT. A WINDY DAY IS AGAIN EXPECTED ON SUNDAY...AS A TIGHT SFC PRESSURE GRADIENT REMAINS IN PLACE...AND FAVORABLE BOUNDARY LAYER MIXING BRINGS 25-35 KT FLOW /WITH LOCALLY HIGHER GUSTS OVER NORTH CENTRAL NEB/ DOWN TO THE SFC. A WIND ADVISORY WILL LIKELY BE NEEDED...AS MAV FCSTS SUSTAINED WIND SPEEDS AT OR ABOVE THE 26 KT CRITERIA DURING THE MID TO LATE AFTERNOON. SIMILAR TO SATURDAY NIGHT...AN INTENSE 50-60 KT LLJ REDEVELOPS DURING SUNDAY NIGHT...LIKELY ENHANCED BY EJECTING LEAD S/W TROUGH LIFTING NORTHEAST ACROSS THE NORTHERN HIGH PLAINS. AN UPR LVL TROUGH THEN BECOMES POSITIONED OVER THE INTERMOUNTAIN WEST ON MONDAY...AND THEN BEGINS TO MOVE EAST/NORTHEAST TOWARDS THE HIGH PLAINS MONDAY NIGHT. THE LATEST GFS OUTPUT BRINGS A LEAD S/W TROUGH EAST INTO THE NORTHERN PLAINS MONDAY AFTERNOON...WHICH DRAGS A SFC FRONT EAST ACROSS THE DAKOTAS INTO MN. THE 00Z ECMWF HAS TRENDED SLIGHTLY CLOSER TO THE GFS SOLUTION...THOUGH THE GFS STILL REMAINS MORE PROGRESSIVE. AT THIS POINT...WILL FOCUS HIGHEST POPS ON MONDAY AFTERNOON OVER OUR WESTERN COUNTIES...WITH LOW POPS EXTENDING EAST ALONG THE NORTHERN TIER OF COUNTIES IN ANTICIPATION OF THE NORTHERN PLAINS FRONT PROGRESSING EAST. REGARDING THE EVOLUTION OF THE WESTERN CONUS TROUGH...THE ECMWF DEPICTS A MORE MERIDIONAL EJECTION OF THE UPR LVL S/W TROUGH BY 12Z TUESDAY...WHILE THE GFS IS MORE AGGRESSIVE IN DIGGING THE TROUGH EAST INTO THE CENTRAL HIGH PLAINS...RESULTING IN A FASTER FROPA. THE SLOWER FRONTAL PASSAGE SUGGESTED BY THE ECMWF WILL FAVOR AT LEAST A CHANCE OF SHOWERS AND STORMS INTO TUESDAY AFTERNOON...AS PLENTIFUL MOISTURE RESIDES ALONG THE SLOW MOVING BOUNDARY. THE ECMWF THEN BRINGS THE CIRCULATION OF GUSTAV NORTH INTO THE ARKLATEX REGION BY WED/12Z...AND THEN MERGES IT WITH THE SOUTHEASTWARD PROGRESSING FRONT BY WEDNESDAY AFTERNOON/NIGHT. THE DETERMINISTIC GFS SOLUTION STALLS GUSTAV OVER THE TX/LA COAST. HOWEVER...THE TWO SOLUTIONS ARE STARTING TO COME INTO BETTER AGREEMENT WITH THE EVOLUTION OF THE PASSING FRONT...AND SUGGEST THAT PRECIP SHOULD COME TO AN END OVER THE WESTERN HALF OF THE CWA BY 12Z WED...AND LIKELY ACROSS THE REMAINDER OF THE CWA SOON AFTER. AT THIS TIME...WILL LEAVE LOW POPS OVER THE EASTERN HALF OF THE CWA THROUGH THE END OF THIS FCST PACKAGE...MAINLY FOR BLENDING PURPOSES. ON THE OTHER HAND...TEMPERATURES DO APPEAR TO BE SUBSTANTIALLY COOLER WITH EITHER MODEL SOLUTION THAT IS FOLLOWED. && .AVIATION... SHORT TERM MODELS INDICATE THAT SOME MARGINAL CEILINGS MAY MAKE IT INTO SOUTHWEST NEBRASKA TO NEAR OGALLALA AND MCCOOK. HOWEVER...WE DO NOT EXPECT THEM TO REACH THE NORTH PLATTE OR VALENTINE AREAS. OF SOME CONCERN TODAY IS WIND WHICH WILL PROBABLY BE SUSTAINED AT 15 TO 25KT WITH GUSTS TO ABOUT 30KT POSSIBLE IN NORTH CENTRAL NEBRASKA. BY EARLY SUNDAY...A LOW LEVEL JET OF 40-50KT MAY DEVELOP IN NORTH CENTRAL NEBRASKA EAST OF VALENTINE. THIS COULD MEAN FAIRLY STRONG NON-CONVECTIVE LOW LEVEL WIND SHEAR...AND WILL NEED TO BE WATCHED WITH SUBSEQUENT FORECAST CYCLES. THERE ARE ALSO HINTS OF INCREASED LOW LEVEL MOISTURE FROM VALENTINE AND NORTH PLATTE AND EAST BY EARLY SUNDAY...ANOTHER ELEMENT THAT MAY WARRANT SOME CHANGES TO THE TERMINAL FORECASTS. && .LBF WATCHES/WARNINGS/ADVISORIES...NONE. && $$ GARNER/SPRINGER