Issued by NWS Glasgow, MT
000 FXUS65 KGGW 210947 AFDGGW AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GLASGOW MT 247 AM MST SAT NOV 21 2009 .SHORT TERM...FOR NORTHEAST MONTANA...TODAY THROUGH MONDAY... AN ENERGETIC SHORT WAVE TROUGH AND COLD FRONT SWEEP OVER THE ZONES TODAY. THE MAIN EFFECT WILL BE STRONG WINDS WESTERLY WINDS BEHIND THE FRONT. A STRONG SURFACE TROUGH ANCHORED BY A LOW CENTERED IN SOUTHERN SASKATCHEWAN WILL MAINTAIN A STRONG PRESSURE GRADIENT ACROSS THE SURFACE. THESE WINDS WILL BE REINFORCED BY 850MB WINDS OF 35-40KTS RESULTING IN SURFACE WIND GUSTS OF EQUAL STRENGTH. THE LWA SEEMS LIKE A SLAM-DUNK SO WILL RENEW THE NPW DURING THIS PACKAGE. MOISTURE IS RATHER ANEMIC WITH THIS SYSTEM SO EXPECT MOSTLY CLOUD COVER WITH LITTLE PRECIPITATION. A VORT MAX AROUND THE BASE OF THE UPPER LEVEL TROUGH COULD PRODUCE SOME MOISTURE IN SOUTHERN ALBERTA/SASKATCHEWAN THAT MIGHT SPREAD A BIT ACROSS THE INTERNATIONAL BORDER. SO WILL MAINTAIN POPS JUST BELOW TEXT MENTION FOR NOW. THE OTHER PREVIOUSLY MENTIONED CONCERN WAS THE EXPECTED LOW RH VALUES FOR TODAY WHICH COULD PRODUCE NEAR CRITICAL FIRE WEATHER CONDITIONS. SEE FIRE WX SEPARATE DISCUSSION BELOW. TONIGHT/SUNDAY...UPPER FLOW VEERS TO THE NORTHWEST LATE TONIGHT AS THE UPPER TROUGH BASE MOVES EAST. A SHORT WAVE UPPER RIDGE FOLLOWS BUT IS QUICKLY FOLLOWED BY THE NEXT SHORT WAVE TROUGH. THIS NEXT WAVE SENDS A WEAK COLD FRONT INTO THE CWA BY AFTERNOON WHICH COULD PRODUCE LIGHT PRECIPITATION OVER THE WESTERN ZONES. 850MB TEMPERATURES REMAIN NEAR 0*C OR JUST BELOW SO MIXED PRECIPITATION IS A POSSIBILITY. WITH THE ATMOSPHERE DECOUPLING AT SUNSET...THE RELAXING GRADIENT WILL ALLOW WINDS TO DROP BELOW LWA CRITERIA. SUNDAY NIGHT/MONDAY...THE BASE OF THE TROUGH DROPS SOUTH INTO NORTHERN COLORADO...TAKING MOST OF THE ENERGY TO OUR SOUTH. HOWEVER THE INVERTED SURFACE EXTENDS NORTH INTO NORTHEASTERN MONTANA WHICH WILL KEEP CONDITIONS A BIT UNSETTLED. WHILE NAM...UKMET AND EC STAY DRY...BASED ON GFS...GEM AND SREF...SLIGHT CHANCE POPS SEEM APPROPRIATE FOR SNOW OVERNIGHT. CONDITIONS DO NOT CHANGE MUCH FOR MONDAY SO WILL KEEP SLIGHT CHANCE POPS GOING. SURFACE HIGHS WILL DROP DOWN MUCH CLOSER TO NORMAL WHILE 850MB TEMPERATURES HOVER AROUND -4*C. SO EXPECT ANY PRECIPITATION TO FALL AS SNOW AND POSSIBLY RAIN SHOWERS. QPF AMOUNTS WILL NOT PRODUCE ACCUMULATIONS. SCT .LONG TERM...MONDAY NIGHT THROUGH SATURDAY... SHORTWAVE TROUGH DROPS SOUTHEAST OUT OF SASKATCHEWAN DURING THE DAY TUESDAY AND MAY BRING A SLIGHT CHANCE OF RAIN OR SNOW. THIS FAST MOVING SYSTEM WILL HAVE LIMITED MOISTURE WITH IT. AN UPPER RIDGE BUILDS INTO THE AREA ON WEDNESDAY AND WILL BRING WARM AND DRY WEATHER THROUGH THANKSGIVING DAY FOR SURE. MODELS HAVE SOME DIFFERENCES ON TRACK OF A SHORTWAVE THAT MOVES INLAND FROM THE PACIFIC ON FRIDAY. ECMWF TAKES THE SYSTEM SOUTH OF THE AREA WHILE THE GFS BRINGS IT ACROSS MONTANA. EITHER WAY...A COLD FRONT WILL AFFECT THE FORECAST AREA ON FRIDAY WITH COOLER TEMPERATURES EXPECTED NEXT WEEKEND. WILL KEEP THE FORECAST DRY FOR THE MOST PART FOR NOW. FORRESTER && .AVIATION... VFR CONDITIONS. A MIX OF MID AND HIGH LEVEL CLOUDS WILL MOVE THROUGH THE AREA TODAY WITH SKIES CLEARING TONIGHT. SOUTHEAST WINDS EARLY THIS MORNING WILL BECOME WEST AROUND 15Z AND INCREASE TO 20 TO 25 KNOTS BY 18Z. THE WINDS WILL DIMINISH TO 10 TO 15 KNOTS THIS EVENING. && .FIRE WEATHER... A STRONG WEST WIND WILL DEVELOP TODAY BEHIND A COLD FRONT. WIND SPEEDS ARE EXPECTED TO REACH 20 TO 30 MPH...WITH GUSTS TO 40 MPH DURING THE LATE MORNING AND AFTERNOON HOURS. AFTERNOON MINIMUM RELATIVE HUMIDITY VALUES ARE EXPECTED TO BRIEFLY DROP INTO THE 20 TO 30 PERCENT RANGE BEFORE BEGINNING A STEADY RECOVERY NEAR SUNSET. THEREFORE...A BRIEF PERIOD OF CRITICAL FIRE WEATHER CONDITIONS ARE POSSIBLE THIS AFTERNOON...BUT HIGHLIGHTS ARE NOT EXPECTED AT THIS TIME DUE TO THE SHORT DURATION OF LOW RELATIVE HUMIDITY DUE TO SHORTENING SUNLIGHT HOURS. THE MOST SUSCEPTIBLE AREAS WILL BE THE LITTLE ROCKY MOUNTAINS AND THE MISSOURI BREAKS REGION OF ZONES 119 AND 121...WHICH WILL EXPERIENCE A RATHER POOR RELATIVE HUMIDITY RECOVERY LAST NIGHT. AJZ/SCT && .GLASGOW WATCHES/WARNINGS/ADVISORIES... LAKE WIND ADVISORY FROM 10 AM THIS MORNING TO 5 PM MST THIS AFTERNOON FOR FORT PECK LAKE. && $$ WEATHER.GOV/GLASGOW
