861 FXUS65 KTFX 030450 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 945 PM MDT SAT MAY 2 2009 AVIATION SECTION UPDATED .UPDATE... SATELLITE IMAGERY THIS EVENING SHOWS AN ELONGATED AXIS OF MOISTURE ORIENTED FROM NW TO SE AND LIFTING NORTHWARD INTO SW MT. RADAR IMAGERY AND OBSERVATIONS INDICATE GENERALLY LIGHT SHOWER ACTIVITY IN THIS BAND...WHICH IS ASSOCIATED WITH A WEAKENING SHORTWAVE TROUGH AXIS THAT IS LIFTING INTO THE AREA. EXPECT THIS AREAS OF PRECIPITATION TO GRADUALLY WEAKEN AS IT LIFTS NORTHWARD INTO CENTRAL MT THROUGH TONIGHT WITH BEST CHANCE FOR PRECIPITATION OVER THE HIGHER MTNS OF SOUTHERN GALLATIN/MADISON COUNTY AND ALONG THE CONTINENTAL DIVIDE. OBSERVATIONS INDICATE THAT SNOW LEVELS ARE A BIT HIGHER THAN PREVIOUSLY FORECAST AND CURRENTLY AT OR ABOVE 7000 FT IN THESE AREAS. WITH SOME COOLING LATER TONIGHT EXPECT SNOW LEVELS TO LOWER TO AROUND 6000 FT BY SUNDAY MORNING AND HAVE UPDATED SNOW LEVELS AS WELL AS MADE SOME MINOR ADJUSTMENTS TO POPS OVER SW MT BASED ON LATEST TRENDS. OTHERWISE...INCREASING CLOUDS FROM THE SW SHOULD LEAD TO MILDER OVERNIGHT LOW TEMPS TONIGHT...WITH LOWS DROPPING TO NEAR OR JUST BELOW 30 DEGREES OVER WESTERN PORTIONS OF NORTH CENTRAL MT IN AREAS WHERE A SIGNIFICANT SNOW PACK STILL EXISTS. HOENISCH && .AVIATION... UPDATED 0445Z. LARGE UPPER LEVEL LOW PRESSURE AREA OFF WA/BC COAST WILL SEND TWO WAVES OF MOISTURE OVER WESTERN HALF OF MONTANA OVERNIGHT AND TOMORROW. FIRST WAVE IS CURRENTLY IN SOUTHWEST MT AND PRODUCING LIGHT RAIN AND MIX OF VFR AND MVFR CEILINGS WITH MTN OBSCURATIONS NEAR KDLN. MOISTURE WILL CONTINUE TO LIFT NORTHEASTWARD TONIGHT BUT WILL DECREASE IN INTENSITY SO EXPECT PRECIP TO STAY FROM KHLN SOUTHWARD. SECOND WAVE PROJECTED TO ARRIVE IN SW MT ABOUT 18Z TOMORROW AND TRACK NORTHEASTWARD AS WELL. BETTER CHANCE FOR MORE WIDESPREAD LIGHT RAINSHOWERS WITH THIS WAVE...SPREADING FURTHER NORTH TO KCTB-KGTF-KLWT. EXPECT MOSTLY VFR CONDITIONS WITH AREAS OF MVFR AS THE DISTURBANCE MOVES ACROSS THE REGION. WINDS AT ALL TERMINALS SHOULD REMAIN BELOW 12-15 KTS TONIGHT AND TOMORROW. WARANAUSKAS ALONG ID/MT BORDER AND MOVING SLOWLY NORTHEASTWARD...PRODUCING JUST BKN-OVC SKIES AT FL150 OR HIGHER SOUTH OF KBZN. THIS LINE MAY GENERATE SOME AREAS OF LIGHT VALLEY RAIN/MTN SNOW MOSTLY SOUTH OF KHLN LATER TONIGHT AND WITH PRECIP ENDING BY MID SUN MORNING. CEILINGS WILL GENERALLY BE VFR BUT COULD LOWER TO MVFR IN PRECIP AREAS. && .HYDROLOGY... A SMALL STREAM FLOOD ADVISORY IS IN EFFECT FOR A PORTION OF NORTH CENTRAL MONTANA UNTIL TUESDAY. WARMING TEMPERATURES THROUGH THE WEEKEND WILL RESULT IN SNOWMELT...THAT WILL CAUSE SMALL STREAMS TO REACH OR EXCEED BANKFULL LEVELS. && .PREV DISCUSSION... /ISSUED 530 PM MDT SAT MAY 2 2009/ SATURDAY NIGHT THROUGH MONDAY...A SHORTWAVE TROUGH WILL CROSS THE CONTINENTAL DIVIDE AND MOVE INTO THE AREA TONIGHT BRINGING WITH IT WIDESPREAD PRECIPITATION THROUGH SUNDAY MORNING. CONFIDENCE IS RATHER LOW ON WHAT WILL HAPPEN AFTER THAT. MODELS ARE SUGGESTING THAT SOME PRECIPITATION MIGHT CONTINUE TO MOVE ACROSS WITH AN ISOLATED THUNDERSTORM OR TWO SUNDAY EVENING. OTHER MODELS REALLY SEEM TO TAKE THE SYNOPTIC SUPPORT AWAY AS THE SHORTWAVE RUNS INTO THE SUBSIDENCE FROM THE RIDGE THAT IS CURRENTLY IN PLACE. DUE TO THE TIMING AN LACK OF MODEL CONSISTENCY WITH THIS HAVE KEPT POPS IN CHANCE CATEGORY LATE SUNDAY NIGHT AND INTO MONDAY. TEMPERATURES HAVE BEEN SLOWER TO RISE THAN MODELS CONTINUE TO SHOW FOR MUCH OF THE REGION. THIS IS LIKELY DUE TO THE 10 INCHES OF SNOW CONTAINING AT LEAST 2 INCHES OF WATER STILL CURRENTLY IN PLACE OF MUCH OF CENTRAL AND NORTH CENTRAL MONTANA. THE SNOW WILL CONTINUE TO WORK LIKE MUCH OF A HEAT SINK THROUGH TOMORROW AND HAVE THEREFORE LOWER TEMPERATURES WHERE MODIS IMAGES SUGGESTS SIGNIFICANT ACCUMULATIONS STILL EXIST. SUK MONDAY NIGHT THROUGH THURSDAY...MEDIUM RANGE MODELS REMAIN IN DECENT AGREEMENT THROUGH THE MEDIUM RANGE PERIOD...EXCEPT FOR THE TIMING OF SHORTWAVE RIPPLES IN THE FLOW ALOFT. OVERALL PATTERN CALLS FOR A FAIRLY FAST WEST TO NORTHWEST FLOW ALOFT ACROSS THE REGION WITH THE AFOREMENTIONED SHORTWAVES BRINGING A SLIGHT CHANCE TO CHANCE OF SHOWERS AND ISOLATED THUNDERSTORMS TO THE PLAINS AND VALLEYS...WHILE THE WESTERN MOUNTAINS RECEIVE A GREATER LIKELIHOOD OF SNOW AT TIMES. FOR MUCH OF THIS TIME FRAME I HAVE GONE WITH POPS THAT ARE NEAR OR ABOVE CLIMATOLOGY. TEMPERATURES ARE ALSO EXPECTED TO BE NEAR OR SLIGHTLY ABOVE SEASONAL NORMALS DURING THIS TIME FRAME. HOWEVER... THIS ASSUMES THAT THE SNOWPACK CURRENTLY OVER THE WESTERN PORTION OF NORTH CENTRAL MONTANA MELTS COMPLETELY OFF OVER THE NEXT FEW DAYS. BREEZY CONDITIONS ARE ALSO LIKELY ACROSS NORTH CENTRAL MONTANA AND ESPECIALLY ALONG THE ROCKY MOUNTAIN FRONT. AT THIS TIME...IT APPEARS THAT THE STRONGEST WINDS WILL MOVE THROUGH THE REGION TUESDAY AND WEDNESDAY. MODELS ARE CURRENTLY SUGGESTING THAT WINDS SHOULD REMAIN BELOW WARNING CRITERIA...BUT THIS WILL NEED TO BE MONITORED. MPJ FRIDAY AND SATURDAY...THE REGION WILL REMAIN UNDER A RATHER A COOL...MOIST AND UNSTABLE NORTHWEST FLOW ALOFT THROUGH THE PERIOD AS A LONG WAVE RIDGE REMAIN OVER THE EASTERN PACIFIC WITH SEVERAL WEATHER DISTURBANCES MOVING THROUGH THE FLOW ALOFT. THUS..WILL LEAN TOWARD COOLER THAN SEASONAL AVERAGE TEMPERATURES ALONG WITH A CHANCE OF RAIN OR SNOW SHOWERS. WILLIAMSON DC && .PRELIMINARY POINT TEMPS/POPS... GTF 30 51 38 58 / 0 30 30 10 CTB 28 50 37 56 / 0 20 20 10 HLN 37 61 38 61 / 40 50 30 20 BZN 33 62 34 58 / 50 50 40 30 WEY 29 49 29 48 / 70 70 60 50 DLN 35 54 34 55 / 60 50 40 20 HVR 33 66 40 62 / 0 20 20 20 LWT 29 55 37 57 / 0 30 30 20 && .TFX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...SUK LONG TERM...BLANK AVIATION...WARANAUSKAS WEATHER.GOV/GREATFALLS