FXUS63 KBIS 010802 AFDBIS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BISMARCK ND 302 AM CDT SUN AUG 1 2010 .SHORT TERM...TODAY THROUGH TUESDAY NIGHT... FORECAST HIGHLIGHTS CONTINUE TO FOCUS ON SEVERE WEATHER PROSPECTS TODAY INTO TONIGHT AS A SURFACE LOW PRESSURE OVER SOUTHEASTERN MONTANA AND ASSOCIATED FRONTAL REGIME MOVE SLOWLY EAST. LATEST WATER VAPOR IMAGERY SHOWS AN UPPER LOW PRESSURE AND ASSOCIATED SHORTWAVE TROUGH OVER THE PACIFIC NORTHWEST. THIS IS FORECAST TO REACH NORTHEASTERN MONTANA BY 12Z MONDAY AND THEN INTO EASTERN NORTH DAKOTA BY 00Z TUESDAY. JET STREAK EVIDENT OVER SOUTHWESTERN IDAHO AND THIS IS CAPTURED WELL BY THE NAM/GFS. MSAS ANALYSIS THIS MORNING SHOWS LOW PRESSURE OVER SOUTHEASTERN MONTANA WITH A WARM FRONT OVER NORTHERN SOUTH DAKOTA. AN INVERTED TROUGH WAS DEPICTED OVER EASTERN MONTANA. WITH THESE SURFACE FEATURES ALONG WITH UPPER DISTURBANCES MOVING THROUGH TODAY AND LARGE SCALE ASCENT INCREASING WITH THE AFOREMENTIONED JET STREAK...WILL CONTINUE TO SEE SHOWERS AND THUNDERSTORMS DEVELOP AT ANY TIME TODAY. SPC IS KEEPING WITH A BROAD AREA OF SEVERE POTENTIAL ACROSS EASTERN MONTANA THROUGH NORTH DAKOTA. HOWEVER THE HIGHEST PROBABILITY STRETCHES FROM CENTRAL AND SOUTHWESTERN SOUTH DAKOTA INTO WEST CENTRAL AND NORTH CENTRAL MINNESOTA. THIS LEAVES PORTIONS OF SOUTH CENTRAL NORTH DAKOTA IN PERHAPS A GREATER RISK THEN THE REST OF THE FORECAST AREA. HOWEVER WITH THE ENTIRE AREA IN A SLIGHT RISK...WILL NOT DEVIATE TOO MUCH FROM PREVIOUS FORECASTS AND WILL MAINTAIN SEVERE WORDING OVER ALL OF WESTERN AND CENTRAL NORTH DAKOTA THROUGH THE DAY. THE SURFACE LOW PRESSURE AND INVERTED TROUGH LOOKS TO REACH KBIS BY AROUND 00Z MONDAY AND THEN OVER THE JAMES RIVER VALLEY BY 12Z MONDAY. DURING THE DAY MONDAY A COLD FRONT WILL MOVE ACROSS SOUTHERN CANADA AND INTO NORTH DAKOTA RESULTING IN A WIND SHIFT TO THE NORTHWEST. THIS WILL PRODUCE LOWER DEWPOINTS/DRIER AIR MONDAY NIGHT INTO TUESDAY. A SLIGHT CHANCE OF A SHOWER/THUNDERSTORM HAS BEEN INTRODUCED ACROSS MOST OF WESTERN AND CENTRAL NORTH DAKOTA MONDAY WITH RECENT MOISTURE AND INSTABILITY ASSOCIATED WITH THE ABOVE FRONT AND UPPER WAVE. DRY MONDAY NIGHT AND TUESDAY BEHIND THE DEPARTING WAVE...BUT THIS SHOULD BE SHORT LIVED. THE NEXT UPPER TROUGH SWINGS THROUGH SOUTHERN CANADA DURING THE DAY TUESDAY AND INTERACTS WITH A LEE SIDE LOW OVER EASTERN MONTANA LATE IN THE DAY. AS THIS EJECTS EAST TUESDAY NIGHT WILL LOOK FOR ANOTHER THREAT OF SHOWERS AND THUNDERSTORMS MAINLY OVER WESTERN NORTH DAKOTA AND POSSIBLY INTO PORTIONS OF SOUTH CENTRAL NORTH DAKOTA BY WEDNESDAY MORNING. .LONG TERM...WEDNESDAY THROUGH SUNDAY... CURRENT LARGE SCALE PATTERN PERSISTS...WITH A LONGWAVE TROUGH ALONG THE WEST COAST AND BROAD UPPER RIDGING OVER THE SOUTHEASTERN CONUS WHICH WILL ACT TO MAINTAIN AN ACTIVE WEST TO SOUTHWESTERLY FLOW ACROSS NORTH DAKOTA. WILL HAVE TO CONTINUE WATCHING FOR SHORTWAVES EJECTING OUT FROM THE WEST/PACIFIC NORTHWEST AND INTERACTING WITH ENERGY ACROSS SOUTHERN CANADA. MODELS IN PRETTY GOOD AGREEMENT WITH ANOTHER SHORTWAVE TROUGH MOVING THROUGH WEDNESDAY. THUS A SLIGHT CHANCE TO CHANCE WORDING OF SHOWERS AND THUNDERSTORMS LOOKS SUFFICIENT FOR NOW. BRIEF TRANSITION TO A NORTHWESTERLY FLOW AGAIN THURSDAY SHOULD BRING A DRY DAY TO WESTERN AND CENTRAL NORTH DAKOTA. HOWEVER FRIDAY INTO THE UPCOMING WEEKEND ANOTHER SHORTWAVE IS SLATED TO MOVE THROUGH. HOWEVER TIMING DIFFERENCES ON THE MODELS MAKES IT DIFFICULT TO DISCERN WHICH DAY MIGHT BE THE BEST DAY FOR CONVECTION. BOTH THE GFS AND ECMWF SHOW NO CHANGE TO THE CURRENT PATTERN THROUGH 240HR OR THROUGH AUGUST 10TH. && .AVIATION...SCATTERED SHOWERS AND THUNDERSTORMS...SOME SEVERE...WILL CONTINUE TODAY INTO TONIGHT. SCT TO BKN VFR CONDITIONS ARE EXPECTED OUTSIDE OF ANY SHOWER OR THUNDERSTORM. HOWEVER IN/AROUND SEVERE THUNDERSTORMS THAT DEVELOP...EXPECT BRIEF MVFR TO IFR CEILINGS AND VISIBILITIES. WILL LIKELY SEE SOME PATCHY FOG OVER THE NEXT COUPLE OF MORNINGS GIVEN THE RECENT HEAVY RAINS. && .BIS WATCHES/WARNINGS/ADVISORIES... NONE. && $$ KS