220 FXUS65 KTFX 161731 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 1131 AM MDT WED MAY 16 2012 .UPDATE... MINOR UPDATES TO FORECAST THROUGH THIS EVENING. 12Z MODEL FORECAST RUNS ARE SPREADING ISOLATED THUNDERSTORM ACTIVITY A BIT FARTHER NORTH THAN THE PREVIOUS RUNS. HAVE THEREFORE SPREAD THE THREAT NORTH A BIT...BUT AM KEEPING THE MENTION SOUTH AND EAST OF A GREAT FALLS-TO-HAVRE LINE. WITH VERY DRY AIR AT THE LOW/MID LEVELS...SOME OF THESE STORMS MAY PRODUCE GUSTY WINDS THIS AFTERNOON AND EVENING...SO HAVE ADDED MENTION OF THIS TO THE FORECAST. OVERALL...TEMPERATURES ARE RISING A BIT FASTER THAN PREVIOUSLY FORECAST...SO HAVE INCREASED TODAYS HIGHS AROUND 3 DEGREES...WHICH WILL ENABLE SOME AREAS TO REACH NEAR RECORD HIGHS. COULSTON && .AVIATION... UPDATED 1731Z. AN UPPER LEVEL HIGH PRESSURE RIDGE IS OVER THE REGION WHILE...TO THE WEST...A LOW PRESSURE TROF IS MOVING OVER THE WEST COAST. THE AIRMASS WILL BECOME SLIGHTLY UNSTABLE THIS AFTERNOON...MAINLY OVER SOUTHWEST MONTANA. ISOLATED THUNDERSTORMS WILL DEVELOP AND STRONG...GUSTY WINDS CAN BE EXPECTED FROM THESE STORMS. CONVECTION WILL DIMINISH QUICKLY IN THE EVENING AND VFR CONDS WILL PREVAIL THROUGH THE NEXT 24 HOURS. && .PREV DISCUSSION... /ISSUED 535 AM MDT WED MAY 16 2012/ TODAY THROUGH FRIDAY...THE UPPER RIDGE CONTINUES TO FLATTEN TODAY AS AN UPPER TROF MOVES TO THE PACIFIC NORTHWEST. SHORTWAVE ENERGY MOVING OUT FROM THE BASE OF THE TROF COMBINED WITH STEEP AFTERNOON LAPSE RATES AND MODEST CAPE AND LI VALUES...WILL AID IN THE DEVELOPMENT OF ISOLATED THUNDERSTORMS MAINLY OVER SOUTHWEST MONTANA. GUSTY AND ERRATIC WINDS WILL BE THE PRIMARY THREAT FROM THESE STORMS. SOUTHWEST FLOW ALOFT WILL INCREASE THURSDAY AS THE UPPER TROF APPROACHES FROM THE WEST. MOISTURE WILL CONTINUE TO INCREASE...500 MB HEIGHTS WILL FALL AND AN ASSOCIATED SURFACE COLD FRONT WILL PUSH ACROSS THE AREA. SHOWERS AND THUNDERSTORMS WILL INCREASE IN AREAL COVERAGE. SHOWERS AND ISOLATED THUNDERSTORMS WILL BECOME EVEN MORE WIDESPREAD ON FRIDAY AS THE UPPER TROF MOVES ACROSS THE CONTINENTAL DIVIDE AND A SECONDARY COLD FRONT WILL BRING EVEN COOLER AIR TO THE AREA. SOME OF THE HIGHER PEAKS ALONG THE ROCKY MOUNTAIN FRONT MAY SEE A LITTLE OF THE WHITE STUFF AS SNOW LEVELS DROP TO BELOW 7000 FEET. TEMPERATURES WILL REMAIN SOME 20 DEGREES ABOVE SEASONAL AVERAGES TODAY BUT DROP TO NEAR SEASONAL AVERAGES BY FRIDAY. EMANUEL FRIDAY NIGHT THROUGH WEDNESDAY...THE BROAD UPPER LEVEL TROUGH OF LOW PRESSURE MOVES OVER THE AREA AS THE HIGH PRESSURE RIDGE CONTINUES TO EXIT TO THE EAST. THIS COOLER MOIST FLOW...ALONG WITH THE INSTABILITY ASSOCIATED WITH THE THROUGH..WILL MOVE INTO THE AREA CREATE SHOWERS THROUGH FRIDAY EVENING. LOW TEMPERATURES WILL DROP INTO THE UPPER AND MID 30S OVERNIGHT AS THE COOL AIR REMAINS IN PLACE THROUGH SATURDAY. BY SUNDAY ANOTHER RIDGE MOVES INTO THE AREA AND USHERS THE LOW PRESSURE THROUGH TO THE NORTH EAST. THE TROUGH REMAINS RELATIVELY WEAK AND FLATTENED...ALLOWING MOISTURE TO MOVE OVER THE AREA. MAINLY AS HIGH LEVEL CLOUDS...HOWEVER SOME ISOLATED AFTERNOON CONVECTION WILL BE POSSIBLE THROUGH THE FIRST PART OF THE WEEK...HOWEVER THIS WILL BE GENERALLY LIMITED TO THE MOUNTAINOUS TERRAIN. BY MIDDAY TUESDAY THE UPPER LEVEL RIDGE WEAKENS AS ANOTHER THROUGH MOVES INTO THE PACIFIC NORTHWEST...HOWEVER MODELS ARE IN DISAGREEMENT OVER THE PLACEMENT AND TIMING OF THE NEXT FRONTAL PASSAGE. HAVE LEANED TOWARD THE ECMWF SOLUTION OF A BROAD UPPER LEVEL TROUGH MOVING THROUGH THE AREA TUESDAY...WITH ZONAL FLOW AFTER THE TROUGH MOVES INLAND. SUK && .PRELIMINARY POINT TEMPS/POPS... GTF 87 47 70 45 / 10 10 30 50 CTB 84 42 66 40 / 10 10 20 50 HLN 86 47 72 43 / 20 20 40 50 BZN 84 42 73 41 / 30 30 30 40 WEY 73 34 65 34 / 40 40 40 50 DLN 82 43 70 40 / 30 30 40 50 HVR 90 46 72 45 / 10 10 20 60 LWT 83 45 69 42 / 20 30 30 60 && .TFX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...EMANUEL/COULSTON LONG TERM...SUK AVIATION...EMANUEL WEATHER.GOV/GREATFALLS