099 FXUS65 KGGW 221519 AAA AFDGGW AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE GLASGOW MT 919 AM MDT WED MAY 22 2013 .SHORT TERM...FOR NORTHEAST MONTANA...TODAY THROUGH FRIDAY... A TIGHT SURFACE PRESSURE GRADIENT IS APPARENT OVER CENTRAL MONTANA WHERE WIND IS PICKING UP STRONGLY. MODELS SUGGEST THIS GRADIENT WILL TRANSITION EAST OVER NORTHEAST MONTANA WITHIN A FEW HOURS PICKING UP SOUTHEAST WIND HERE. THERE IS A WIND ADVISORY FOR FORT PECK LAKE THAT WILL GO IN EFFECT A 10 AM THIS MORNING. THIS ADVISORY WILL GO THROUGH THURSDAY. THE SURFACE HIGH OVER SOUTHERN SASKATCHEWAN WHICH IS HELPING TO PRODUCE THE PRESSURE GRADIENT IS ALSO DRYING THINGS FROM THE EAST. THE MID-LEVEL OVERCAST WILL DISSIPATE TODAY BRINGING IN CLEARER SKIES BY AFTERNOON AND EVENING. FEW CHANGES TO THE FORECAST...OTHER THAN WIND AND SKY GRID ADJUSTMENTS. SCT PREVIOUS DISCUSSION... HIGH PRESSURE DROPPING INTO NORTH DAKOTA ALONG WITH NARROW UPPER RIDGE OVER EASTERN MONTANA FOR DRY CONDITIONS TODAY. STRONG CLOSED UPPER LOW PUSHING INTO THE PACIFIC NORTHWEST BEGINNING TO DEVELOP TROF ALONG THE ROCKIES FOR TIGHTENING GRADIENT ACROSS MONTANA TODAY. STRONG SOUTHEAST WINDS EXPECTED BY LATE THIS MORNING SO TIMING OF THE START OF THE LAKE WIND ADVISORY LOOKS ON TRACK. UPPER SYSTEM TO THE WEST MOVES VERY LITTLE OVER THE NEXT FEW DAYS ALTHOUGH UPPER RIDGE AXIS EXPECTED TO SHIFT INTO THE DAKOTAS. VORTICITY AROUND THE UPPER LOW GRADUALLY PUSHES THE LOW LEVEL TROF INTO THE PLAINS...PROVIDING SOME FOCUS FOR CONVECTIVE ACTIVITY ACROSS MAINLY CENTRAL MONTANA TONIGHT INTO THURSDAY...THEN MOVING INTO EASTERN MONTANA THURSDAY NIGHT INTO FRIDAY. STRONG SOUTHEAST LOW LEVEL FLOW WILL CONTINUE AHEAD OF THE FRONT FOR LAKE WIND CONDITIONS THROUGH THURSDAY EVENING...PERHAPS INTO FRIDAY MORNING. AS FRONT LIFTS ACROSS NORTHEAST MONTANA ON FRIDAY...COULD GET DRIER DOWNSLOPE FLOW INTO THE SOUTHWEST ZONES IN THE AFTERNOON. EBERT .LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY... FRIDAY NIGHT THROUGH SATURDAY NIGHT...A CLOSED UPPER LEVEL LOW SITUATED OFF OF THE PACIFIC NORTHWEST WILL SEND LOBES OF SHORTWAVE ENERGY THROUGH SOUTHWEST FLOW ALOFT INTO NORTHEAST MONTANA THROUGH THE EXTENDED. THE PRECISE TIMING OF THESE SHORTWAVE FEATURES WILL BE CRITICAL IN DETERMINING THE POTENTIAL FOR CONVECTION INITIATION ON ANY GIVEN DAY. IF A TIME OCCURS WHERE THE SHORTWAVE ENERGY TRACKS THROUGH NE MT DURING PEAK HEATING AND COINCIDENT WITH THE BEST INSTABILITY...THERE COULD BE RESULTANT STRONG THUNDERSTORM DEVELOPMENT. BOTH THE 00Z ECMWF AND GFS HAVE BOTH SHIFTED THE VIGOROUS UPPER LEVEL SHORTWAVE TRACK FURTHER TO THE NORTHWEST INTO ALBERTA AND SASKATCHEWAN. THE TRACK IS AS SUCH THAT IT WOULD FAVOR THE BEST CHANCES OF CONVECTION INTO THOSE LOCATIONS AND PERHAPS EXTENDING INTO THE NORTHERN ZONES OF THE CWA. ANOTHER RIPPLE OF SHORTWAVE ENERGY PASSES THROUGH THE CWA ON SATURDAY AFTERNOON. THE GFS IS A BIT STRONGER THAN THE ECMWF AND GIVEN THE DIFFERENCES IN MODEL SOLUTION HAVE ONLY MADE MINOR TWEAKS TO POPS IN THAT PERIOD. SUNDAY INTO SUNDAY NIGHT...THE 00Z MODEL SUITE HAS SHOWN BOTH CONSISTENT AGREEMENT AND EXCELLENT CONTINUITY THAT THIS PERIOD COULD OFFER THE BEST POTENTIAL FOR THUNDERSTORM DEVELOPMENT ACROSS THE FORECAST REGION...WITH THE POTENTIAL FOR SOME STRONG THUNDERSTORMS CAPABLE OF HAIL AND GUSTY WINDS. ACROSS THE CWA IS THE PRESENCE OF A NICE THETA-E RIDGE INDICATING ABUNDANCE OF WARM LOW LEVEL MOISTURE. FORECAST SOUNDINGS IN THE MODELS DO SHOW DRYING AT THE MID LEVELS. CONVECTIVE INDICIES ACROSS THE CWA ARE ALSO FAVORABLE WITH LIFTED INDICIES SUNDAY AFTERNOON AND EVENING RANGING BETWEEN -3 AND -7. ALSO NOTED THAT CAPE REACHES AROUND 1000 TO 1500 J/KG. SOUNDINGS FURTHERMORE ARE INDICATING A NICE VEERING WIND PROFILE WITH A LOW LEVEL EASTERLY 850MB JET OF AROUND 40 KTS. WHILE NOT IMPRESSIVE...THIS DOES PROVIDE DECENT DIRECTIONAL AND SPEED SHEAR ACROSS THE CWA. PWATS ALSO LOOK TO BE OVER 1 INCH INDICATING ABUNDANT MOISTURE IN THE VERTICAL COLUMN. UPPER LEVEL DYNAMICS COULD LINE UP VERY WELL WITH THESE THERMODYNAMIC PARAMETERS AS MODELS ARE IN EXCELLENT AGREEMENT ON GOOD DIFFLUENT FLOW ALOFT SUPPORTIVE OF FORCED VERTICAL ASCENT AND LOWERING PRESSURES. WITH SHORTWAVE ENERGY APPROACHING THE AREA DURING THE AFTERNOON AND EVENING HOURS...TIMING SHOULD BE IDEAL...BEING COINCIDENT WITH MAXIMUM HEATING AND BEST INSTABILITY. WILL NEED TO WATCH THIS CLOSELY OVER THE NEXT SEVERAL DAYS...HOWEVER...CURRENT THINKING IS THAT GIVEN EXCELLENT MODEL AGREEMENT...RUN TO RUN CONTINUITY...AND FAVORABLE UPPER LEVEL DYNAMICS LINING UP IN BOTH IDEAL TIMING AND PLACEMENT WITH THERMODYNAMIC VARIABLES...SUNDAY AFTERNOON AND EVENING COULD PROVE TO BE A BUSY WEATHER DAY ACROSS NORTHEAST MONTANA. THIS IS STILL OUT IN DAY 5 AND SO THERE IS UNCERTAINTY THIS FAR OUT...BUT AS IT GETS CLOSER...MESOSCALE DETAILS WILL BECOME CLEARER AND SO WILL BE ABLE TO HAVE A BETTER HANDLE ON THE MODE OF CONVECTION THAT WOULD OCCUR AS WELL AS BETTER CONFIDENCE ON PRECISE TIMING AND LOCATION. MONDAY AND BEYOND...LONG RANGE GUIDANCE CONTINUES TO KEEP NE MT IN A SOUTHWEST FLOW ALOFT REGIME...WITH ADDITIONAL CHANCES FOR SHOWERS/THUNDERSTORMS DEPENDENT ON EMBEDDED SHORTWAVE FEATURES THAT ARE DIFFICULT TO PINPOINT THAT FAR IN ADVANCE...AND SO PAINTED THE CWA WITH LOW END CHANCE POPS THROUGH MUCH OF THE EARLY TO MIDDLE PORTION OF NEXT WEEK. WITH NOT MUCH CHANGE IN THE OVERALL FLOW PATTERN...WOULD NOT EXPECT MANY FLUCTUATIONS IN TEMPERATURES...AND SO DID NOT INTRODUCE MUCH IN THE WAY OF WARM UPS OR COOL DOWNS IN THE EXTENDED PERIOD. MALIAWCO && .AVIATION... VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. PERSISTENT SOUTH EAST WINDS LIKELY TO OCCUR TODAY AND TONIGHT FROM 15 TO 25 KTS WITH SOME GUSTS POTENTIALLY OVER 30 KTS AT THE TERMINAL SITES. MALIAWCO && .GLASGOW WATCHES/WARNINGS/ADVISORIES... LAKE WIND ADVISORY UNTIL MIDNIGHT MDT THURSDAY NIGHT FOR FORT PECK LAKE FOR CENTRAL AND SOUTHEAST PHILLIPS...CENTRAL AND SOUTHERN VALLEY...GARFIELD...MCCONE...PETROLEUM. && $$ WEATHER.GOV/GLASGOW |