000 FXUS65 KTFX 011744 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 1130 AM MDT WED APR 1 2009 AVIATION SECTION UPDATED .UPDATE... MADE UPWARD ADJUSTMENTS TO POP AND QPF FOR PORTIONS OF CENTRAL MONTANA DUE TO LINGERING SNOW SHOWERS AND A BAND MOVING SOUTH FROM HAVRE TOWARDS LEWISTOWN. ALSO TWEAKED SNOW TOTALS A BIT IN ACCORDANCE WITH QPF. THE REST OF THE FORECAST LOOKS GOOD FOR NOW. && .AVIATION... UPDATED 1730Z. MOIST AND SLIGHTLY UNSTABLE NORTHWEST FLOW CONTINUES AS WEAK UPPER LEVEL DISTURBANCE MOVES ACROSS CENTRAL/SOUTHERN MT...WITH A MIX OF MOSTLY VFR TO MVFR CEILINGS AND MTN OBSCURATIONS CURRENTLY BEING REPORTED AT LOCAL TERMINALS. AREAS OF LIGHT RAIN/SNOW WILL PERSIST THRU MID AFTERNOON PERIOD FROM KCTB TO KGTF TO KLWT WITH ONLY SPOTTY PRECIPITATION COVERAGE FROM KHLN SOUTHWARD. SHOULD SEE SLOW IMPROVEMENT IN CEILINGS TOWARD EVENING AS UPPER WAVE MOVES DOWNSTREAM...WITH VFR EXPECTED OVER THE REGION TONIGHT AND EARLY THURS. NEXT WEATHER SYSTEM DUE TO ARRIVE THURS EVE WITH RETURN TO MVFR-IFR CONDITIONS AND SCATTERED LIGHT RAIN/SNOW. WARANAUSKAS && .PREV DISCUSSION... /ISSUED 333 AM MDT WED APR 1 2009/ TODAY THROUGH FRIDAY...UNSETTLED PATTERN CONTINUES TODAY. MOIST NORTHWEST FLOW ALOFT PERSISTS OVER THE AREA WITH SHORT WAVE ENERGY MOVING WITHIN THE FLOW AND PRODUCING PERIODS OF LIGHT SNOW. EXPECT NO SIGNIFICANT SNOW ACCUMULATIONS OVER THE PLAINS AND A FEW INCHES POSSIBLE IN THE MOUNTAINS. WEAK UPPER RIDGING BEGINS TO MOVE OVER THE AREA TONIGHT AND THURSDAY BUT ENOUGH INSTABILITY PERSISTING FOR ISOLATED MOUNTAIN SNOW SHOWERS. BY THURSDAY NIGHT...ANOTHER UPPER TROF APPROACHES WESTERN MONTANA. THE FLOW ALOFT SPLITS ONCE AGAIN AS THIS FEATURES MOVES ACROSS THE STATE WITH MOST OF THE ASSOCIATED ENERGY DIVING WELL SOUTH OF THE AREA INTO THE SOUTHWEST US. SNOW WILL AGAIN DEVELOP OVER THE AREA WITH THE GREATEST THREAT FOR ACCUMULATING SNOW OVER THE HIGH COUNTRY OF SOUTHWEST MONTANA. AGAIN...SIGNIFICANT SNOW TOTALS ARE NOT EXPECTED. TEMPERATURES WILL REMAIN BELOW SEASONAL AVERAGES. EMANUEL FRIDAY NIGHT THROUGH MONDAY NIGHT...THE PERIOD STARTS OFF WITH A AN UPPER LOW OVER THE GREAT BASIN WITH A MOIST AIRMASS OVER THE FORECAST AREA. THERE IS SOME QUESTION ABOUT HOW FAR NORTH THE LOW WILL BE BUT MODELS TEND TO AGREE IN HAVING PRECIPITATION EXTEND FROM SOUTHWEST MONTANA TO ALONG THE WESTERN MOUNTAINS. IN LINE WITH THIS HAVE INCREASED THE CHANCES OF SNOW IN THOSE AREAS BUT ALSO INCREASED THE CHANCES OF PRECIPITATION A LITTLE OVER THE PLAINS. CONTINUED THIS TREND INTO SATURDAY. YESTERDAY THERE WAS A HUGE DIFFERENCE AMONGST THE MODELS IN HOW FAST THE UPSTREAM UPPER RIDGE WOULD MOVE OVER THE AREA. LATEST ECMWF MODEL RUN HAS COME AROUND TO THE FASTER SOLUTION OF THE GFS BUT STILL IS NOT AS FAST AS THE GFS MODEL RUN IN MOVING THE UPPER RIDGE OVER THE AREA. BOTH THE LATEST GFS AND ECMWF HAVE LINGERING MOISTURE OVER THE AREA INTO SATURDAY NIGHT SO HAVE ADDED SLIGHT CHANCE POPS TO THE MOUNTAINS NEAR LEWISTOWN AND BOZEMAN FOR THAT PERIOD. ALSO FEEL THE GFS MODEL IS TOO FAST IN MOVING THE UPPER RIDGE EAST EARLY NEXT WEEK SO HAVE SLOWED DOWN THE EASTWARD SPREAD OF PRECIPITATION FOR MONDAY AND MONDAY NIGHT OVER THE WESTERN ZONES AND RAISED TEMPERATURES FOR THE WESTERN ZONES FOR MONDAY. BLANK TUESDAY THROUGH WEDNESDAY...MEDIUM RANGE MODELS DEPICT A TYPICAL SPRING PATTERN ACROSS THE WESTERN U.S. WITH HIGHLY AMPLIFIED FLOW AND A CLOSED UPPER LEVEL LOW PRESSURE SYSTEM DRIFTING EAST ACROSS THE SW U.S. THIS PERIOD. MODELS ARE HAVING DIFFICULTY WITH THE TIMING OF THESE FEATURES WHICH LEADS TO LOW CONFIDENCE IN THE OVERALL FORECAST AS A SLIGHT JOG TO THE NORTH IN THE STORM TRACK WILL MEAN WETTER/COOLER CONDITIONS FOR THE AREA WITH THE REVERSE TRUE IF THE SYSTEM TRACKS FARTHER SOUTH. LATEST MODEL RUNS KEEP THE SYSTEM TO THE SOUTH AND HAVE GENERALLY GONE WITH POPS NEAR CLIMATOLOGICAL AVERAGES...WITH A TENDENCY TOWARD ABOVE CLIMO POPS FOR SOUTHERN ZONES CLOSER TO THE CIRCULATION OF THE UPPER LEVEL LOW WITH TEMPERATURES REMAINING SOMEWHAT BELOW SEASONAL AVERAGES. HOENSICH && .PRELIMINARY POINT TEMPS/POPS... GTF 38 22 43 24 / 40 20 40 30 CTB 34 19 36 22 / 40 20 40 30 HLN 41 23 43 22 / 50 20 60 30 BZN 40 20 45 21 / 40 20 60 40 WEY 35 17 39 16 / 60 40 80 60 DLN 36 20 41 20 / 20 20 70 30 HVR 38 20 39 25 / 50 20 20 20 LWT 37 20 40 22 / 60 20 30 30 && .TFX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...GUSTAFSON LONG TERM...WARANAUSKAS AVIATION...WARANAUSKAS WEATHER.GOV/GREATFALLS