000 FXUS65 KGGW 122130 AFDGGW AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GLASGOW MT 230 PM MST TUE FEB 12 2008 .SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH THURSDAY... ISSUED SNOW AND BLOWING SNOW ADVISORY FOR NORTHEASTERN THIRD OF CWA WITH INCOMING SYSTEM. SATELLITE SHOWING SHORTWAVE MOVING INTO WESTERN CANADA THIS AFTERNOON FROM THE GULF OF ALASKA. MODELS...WHICH INCLUDE MAINLY THE SREF AND THE 12Z GFS...SHOW THE SURFACE LOW CENTER TO DROP SOUTHEAST ACROSS THE SOUTHWESTERN ZONES ABOUT NOON WEDNESDAY. MODELS HAVE BEEN SHOWING A SLIGHT TREND TO THE SOUTHWEST WITH THE TRACK SO THE HEAVIEST BAND LOOKS TO NOW SKIRT THE NORTHEAST ZONES. TONIGHT...SHORTWAVE BEGINS TO MOVE INTO THE NORTHWEST QUADRANT OF THE COUNTRY WITH THE SURFACE LOW NEAR HAVRE ABOUT 12Z. GOOD ISENTROPIC LIFT WILL INTRODUCE SNOW TO THE NORTHERN ZONES AFTER MIDNIGHT WITH AN INCH ACCUM POSSIBLE BY WEDNESDAY MORNING. MODELS GIVING THE BEST QPF ACROSS SOUTHERN SASK AND VERY CLOSE TO THE NORTHEASTERN ZONES. WEDNESDAY...THE SURFACE LOW WILL MOVE INTO SOUTH DAKOTA DURING THE LATE AFTERNOON. A DRY SLOT WILL MOVE ACROSS THE AREA...THROUGH THE CENTRAL ZONES ABOUT NOON...ALLOWING MOST PLACES TO SEE THE SNOW END UNTIL AFTER AN ARCTIC FRONTAL PASSAGE. THIS TRAILING FRONT WILL BE IN THE FOOTSTEPS OF THE LOW...MOVING THROUGH THE WESTERN ZONES ABOUT NOON THEN EXITING THE CWA BY EVENING. MID LEVEL (ABOUT 850 MB) WINDS OF UP TO 45 KTS WILL COMBINE WITH STRONG COLD AIR ADVECTION TO GIVE A WINDY AFTERNOON. A DEFORMATION ZONE FOLLOWING THE FRONT SHOULD BRING LIGHT SNOW BACK TO MOST AREAS (AND ALSO THE PERCEPTION OF BLOWING SNOW SOUTH AND WEST OF A MALTA-WIBAUX LINE). TEMPS LOOK TO FALL DURING THE AFTERNOON IN MOST PLACES BUT DOES NOT SEEM TO BE SIGNIFICANT ENOUGH AT THIS TIME TO MENTION. WEDNESDAY NIGHT AND THURSDAY...THE ARCTIC FRONT BACKDOORS UP AGAINST THE CONTINENTAL DIVIDE IN CENTRAL MONTANA BY THURSDAY MORNING. THE LIGHT SNOW WILL SLOWLY TAPER OFF FROM THE NORTHWEST AS ARCTIC HIGH PRESSURE MOVES INTO SOUTHERN SASK. WIND CHILLS AND BLOWING SNOW PROBLEMS MAY CONTINUE INTO THE EVENING HOURS IN THE SOUTHEAST ZONES BUT ADVISORY CONDITIONS ARE NOT EXPECTED AT THIS TIME. ON THURSDAY...WEAK UPPER LEVEL DISTURBANCES WILL RIPPLE ALONG THE STATIONARY ARCTIC FRONT...HELPING TO CREATE SCATTERED FLURRIES ACROSS MOST AREAS. TEMPS WILL BE ABOUT 15 DEGREES BELOW NORMAL. JAMBA .LONG TERM...THURSDAY NIGHT THROUGH TUESDAY... LONG TERM PATTERN FEATURES A DEVELOPING HIGH AMPLITUDE RIDGE OVER WESTERN NORTH AMERICA AND A DEEPENING LONGWAVE TROUGH OVER EASTERN NORTH AMERICA. A POLAR VORTEX REMAINS SITUATED OVER HUDSON BAY...WHICH WILL MAINTAIN A SOURCE OF COLD AIR OVER CANADA. A PATTERN SUCH AS THIS FAVORS ARCTIC AIR TO BE DRAWN SOUTHWARD INTO THE CONTERMINOUS UNITED STATES. HOWEVER...AT THIS TIME THE BRUNT OF THE COLD AIR SHOULD BE WELL TO THE EAST OF THE REGION AS IT TARGETS THE UPPER MIDWEST AND GREAT LAKES. THIS WILL ALLOW MILDER PACIFIC AIR TO MOVE INTO THE AREA AT MID LEVELS. IT IS MORE LIKELY THAT TEMPERATURES WILL WARM IN THE WESTERN ZONES EARLY NEXT WEEK. THE EASTERN ZONES COULD BE MUCH SLOWER TO SEE ANY WARMING AS SHALLOW COLD AIR COULD LINGER. A QUICK MOVING SYSTEM LOOKS TO AFFECT THE AREA SOMETIME FRIDAY NIGHT THROUGH SATURDAY. THERE IS POOR MODEL AGREEMENT TO THE TIMING AND AS TO HOW IT WILL TRACK. THE 12Z ECMWF BRINGS IN THROUGH SATURDAY...THE 12Z GLOBAL CANADIAN BRINGS IN THROUGH FRIDAY NIGHT...AND THE 12Z OPERATIONAL GFS HAS A FRIDAY NIGHT TIMING...AND IN MUCH FARTHER NORTH AND EAST WITH THE TRACK...WITH THE SYSTEM ONLY CLIPPING THE NORTHEAST ZONES. GFS ENSEMBLES ARE SLOWER AND FURTHER SOUTH THAN THE OPERATIONAL MODEL. BEYOND THAT THE REST OF THE EXTENDED PERIOD WILL BE PRIMARILY DRY. AJZ PREVIOUS LONG TERM DISCUSSION... LARGE SCALE PATTER OF RIDGE IN THE EASTERN PACIFIC AND POLAR VORTEX OVER HUDSON BAY CONTINUES. EASTERN MONTANA REMAINS ON THE BOUNDARY BETWEEN THE TWO AIRMASSES SO SEE-SAW TEMPERATURES EXPECTED TO CONTINUE. MODELS IN GOOD AGREEMENT INTO THE WEEKEND BEFORE DIVERGING. REGION TAKES A GLANCING BLOW FROM ARCTIC AIRMASS MIDWEEK FOR A COLD START TO THE LONG TERM PERIOD WITH COLD HIGH PRESSURE OVER THE NORTHERN PLAINS. WESTERN RIDGE PUSHES WARMER AIR INTO MONTANA WITH FAIRLY STRONG CHINOOK POSSIBLE ON FRIDAY. NEXT SHORTWAVE SLIDES THROUGH WESTERN CANADA...CLIPPING NORTHEAST MONTANA ON SATURDAY. BEST DYNAMICS AND MOISTURE REMAIN IN CANADA BUT WITH COLD FRONT SLIDING SOUTHWARD COULD SEE SOME SNOW DURING THE DAY SATURDAY. LONG WAVE PATTERN AMPLIFIES FOR EARLY NEXT WEEK WITH TROF DIGGING INTO THE MISSISSIPPI VALLEY AND RIDGE BUILDING ALONG THE WEST COAST. ECMWF SLIGHTLY FURTHER WEST WITH BOTH RIDGE AND TROF ...AND THUS KEEPS FRONTAL BOUNDARY OVER CENTRAL MONTANA. GFS AND MOST OF ITS ENSEMBLE MEMBERS DROP ANOTHER SHORTWAVE THROUGH WESTERN CANADA WHICH WOULD PUSH ARCTIC BOUNDARY EAST FOLLOWED BY ANOTHER COLD FRONT THE MIDDLE OF NEXT WEEK. WITH MODEL UNCERTAINTIES TRENDED TOWARD CLIMATOLOGY FOR THE END OF THE PERIOD. EBERT && .AVIATION... VFR CONDITIONS SHOULD DETERIORATE TONIGHT AS LOWER CEILINGS AND AREAS OF LIGHT SNOW MOVE INTO THE REGION. MVFR AND LOCALIZED IFR CONDITIONS ARE LIKELY THROUGHOUT THE DAY TOMORROW. A NORTHWEST WIND OF 10 TO 15 KT OR LESS WILL BECOME SOUTHEAST THIS EVENING. THE WIND WILL TURN BACK TO THE NORTH BY TOMORROW AFTERNOON WITH THE SPEED INCREASING TO 20 TO 30 KT. AJZ && .GLASGOW WATCHES/WARNINGS/ADVISORIES... SNOW AND BLOWING SNOW ADVISORY FROM MIDNIGHT TONIGHT TO 6 PM MST WEDNESDAY FOR DANIELS-SHERIDAN-WESTERN ROOSEVELT-RICHLAND- NORTHERN VALLEY-EASTERN ROOSEVELT. && $$ WEATHER.GOV/GLASGOW