000 FXUS65 KBOU 121004 AFDBOU AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DENVER CO 400 AM MDT SUN OCT 12 2008 .SHORT TERM...LOTS OF INTERESTING WEATHER SWIRLING AROUND US THIS MORNING. UPPER LOW STARTING TO ELONGATE WITH THE MAIN AREA OF LIFTING SHIFTING NORTHEAST ACROSS WYOMING AND MONTANA. ORIGINAL FRONTAL CONVECTION WAS SUCCESSFUL IN MOVING EAST OF THE BOUNDARY AS STRONG UPPER LEVEL FEATURES HELD IN PLACE...REFORMING THE LOW LEVEL CONVERGENCE ACROSS NORTHEASTERN COLORADO. A NEW LINE OF SHOWERS IS DEVELOPING NOW AND I EXPECT TO SEE SOME LIGHTNING SOON. THIS BAND SHOULD ALSO PROGRESS SLOWLY EASTWARD. SEVERE WIND GUSTS ARE NOT OUT OF THE QUESTION WITH THIS LINE...BUT THE RISK IS SMALL SO WILL MENTION NONSEVERE GUSTS. AT MIDLEVELS WE CONTINUE TO HAVE A SERIES OF DRY/MOIST BANDS...MIDLEVEL TEMPERATURE GRADIENT IS ACROSS THE UPSTREAM BAND WHICH IS PROGRESSING EAST ACROSS THE MOUNTAINS MORE SLOWLY THAN EXPECTED. BEHIND THIS IS A PATCH OF VERY DRY AIR AND PRESUMABLY SIGNIFICANT SUBSIDENCE...FOLLOWED BY AN AREA WITH MORE MOISTURE AND INSTABILITY NOW COVERING UTAH. PLAN FOR THE DAY WAS THE DRY SLOT SPREADING NORTHEAST ACROSS THE AREA EARLY. THIS SEEMS TO BE A BIT SLOWER THAN EXPECTED BUT STILL LOOKS LIKE THE RIGHT IDEA. I WILL HOLD ONTO FAIRLY HIGH POPS IN THE MOUNTAINS THIS MORNING...THEN IT MAY CLEAR OUT PRETTY WELL. MEANWHILE THE LOW LEVELS EAST OF THE MOUNTAINS ARE ABOUT AS COMPLICATED AS YOU CAN GET. LIFT WITHIN THE MOIST LAYER SEEMS TO HAVE ENDED EARLY THIS MORNING...THOUGH THE LOW CLOUDS REMAIN AND THERE IS SPOTTY DRIZZLE IT IS NOT THE STEADY PRECIPITATION WE HAD YESTERDAY. STRONG SOUTH WINDS PUSHED THE TEMPERATURE INTO THE LOW 60S EAST OF AKRON AND LIMON...WHILE NORTH WINDS ARE STARTING TO PICK UP BEHIND THE DEVELOPING LINE OF CONVECTION. EARLY ON WE WILL HAVE THE EXITING CONVECTION IN THE EAST...THE WEAKER SHOWERS MOVING OFF THE MOUNTAINS AND LIKELY WEAKENING...WITH A BIT OF A BREAK IN BETWEEN. THEN THE LOW LEVEL AIR COMES SOUTH OUT OF NEBRASKA AND WYOMING WHICH WILL BRING SOME COOLING. HARD TO SAY HOW MUCH OF THE LOW CEILINGS/VISIBILITIES/PRECIPITATION THERE IS DUE TO THE LIFT OVER IT...BUT I HAVE SOME CONCERN ABOUT EVERYTHING GOING DOWNHILL AGAIN THIS AFTERNOON AS THIS AIR SLIDES SOUTH. NO REASON FOR THE STRATUS TO BREAK UP AT ANY RATE. I WILL MENTION SOME LIGHT RAIN OR DRIZZLE FOR THIS REASON. TONIGHT IS NOT ANY BETTER. TAIL END OF SYSTEM TRYING TO DEVELOP TO THE SOUTH WITH SOME DEFORMATION...EASTERLY LOW/MID LEVEL FLOW... ISENTROPIC LIFT TRYING TO REDEVELOP ESPECIALLY SOUTH OF OUR AREA. ALSO SOME QUESTION ABOUT THE AMOUNT OF COOLING AS NAM WOULD SUGGEST LIGHT SNOW IN DENVER TONIGHT. THE BETTER DEVELOPMENT AND COOLING SEEM AT ODDS...ESPECIALLY AT LOW LEVELS...SO I WILL KEEP THE TEMPERATURE PROFILE ABOUT WHERE IT IS NOW...A MIX OF RAIN/SNOW IN THE FOOTHILLS. I WILL RAISE POPS ALONG THE EASTERN BORDER AND IN THE FOOTHILLS BUT SINCE I HAVE SOME SKEPTICISM ABOUT MUCH PRECIP BEING PRODUCED IN THIS PERIOD NOT TOO MUCH YET. WHATEVER THERE IS SHOULD BE PRETTY LIGHT. EVEN IF IT IS A LITTLE COLDER THAN I EXPECT WARM GROUND WOULD LIMIT THE IMPACT OF ANY SNOW OR FREEZING DRIZZLE IN THE LOWER ELEVATIONS TONIGHT. .LONG TERM...MODELS CONTINUE TO SHOW MORE AND MORE ENERGY PINCHING OFF AT THE BOTTOM OF THE UPPER TROUGH NEAR THE FOUR CORNERS ON MONDAY. THEY ALSO CONTINUE TO SLOW THE ENTIRE UPPER TROUGH AXIS GETTING THROUGH HERE. SO NOW THE STRONG SOUTHWESTERLY FLOW ALOFT IS OVER THE FORECAST AREA THROUGH AT LEAST MID DAY TUESDAY...WITH THE TROUGH AXIS MOVING THROUGH TUESDAY AFTERNOON. THREE DAYS AGO THIS WAS SUPPOSED TO HAPPEN THIS AFTERNOON. OH WELL. NOW THE QG VERTICAL VELOCITY FIELDS ON BOTH MODELS HAVE UPWARD MOTION PROGGED FOR ALL THE FORECAST AREA MONDAY...MONDAY NIGHT...AND HALF OF TUESDAY. THE BEST LIFT STAYS SOUTH OF OUR FORECAST AREA THROUGH THE PERIOD. THE BOUNDARY LAYER FLOW WILL CONTINUE TO BE LIGHT EASTERLY MONDAY INTO TUESDAY AFTERNOON...THEN WEAK DOWNSLOPING AFTER THE UPPER TROUGH PASSAGE. MOISTURE-WISE...THE NAM HAS PLENTY FOR MUCH OF THE FORECAST AREA MONDAY AND MONDAY EVENING...THEN A GRADUAL DECREASE. THE GFS HAS SOMEWHAT LESS ON MONDAY...ESPECIALLY IN THE LOWER LEVELS...HOWEVER...IT HAS A BIT MORE IN THE MID AND UPPER LEVELS MONDAY NIGHT AND TUESDAY. NOW THE QPF FIELDS HAVE MINIMAL AMOUNTS OF MEASURABLE PRECIPITATION MONDAY THROUGH TUESDAY...FAVORING THE SOUTHERN FORECAST AREA. WILL STALL THE DRYING OUT UNTIL LATER TUESDAY...SO MORE CLOUDS IN MOST AREAS AND A BIT OF AN INCREASE IN POPS TOO. CONCERNING TEMPERATURES...THE GUIDANCE VALUES HAVE BEEN IN POOR AGREEMENT LATELY. FOR MONDAY...HIGHS ARE A TAD WARMER THAN TODAY`S EXPECTED HIGHS. TUESDAY`S ARE 1-3 C WARMER THAN MONDAY`S. FOR THE LATER DAYS...WEDNESDAY THROUGH SATURDAY...MODELS HAVE MAINLY ZONAL FLOW WEDNESDAY AND THURSDAY...WITH UPPER RIDGING FRIDAY...AND SOUTHWESTERLY FLOW ALOFT SATURDAY. IT STILL LOOKS DRY WITH TEMPERATURES GETTING BACK TO SEASONAL NORMALS. && .AVIATION...SCATTERED SHOWERS WILL CONTINUE THIS MORNING ALONG WITH LOW CLOUDS AND AREAS OF DRIZZLE. CEILINGS ARE EXPECTED TO LIFT INTO THE MVFR CATEGORY THIS AFTERNOON WITHOUT VISIBILITY RESTRICTIONS... BUT THERE IS A 30 PERCENT CHANCE OF LOW CLOUDS...DRIZZLE AND FOG WITH IFR CONDITIONS REDEVELOPING AS COOLER AIR MOVES IN FROM THE NORTH DURING THE LATE AFTERNOON AND EVENING. TEMPERATURES ARE EXPECTED TO REMAIN ABOVE FREEZING WITH LIQUID PRECIPITATION THROUGH MIDNIGHT...THERE IS A 20 PERCENT CHANCE OF SOME SNOW MIXED IN AFTER MIDNIGHT BUT NO ACCUMULATION IS EXPECTED DUE TO THE SURFACE TEMPERATURES. && .BOU WATCHES/WARNINGS/ADVISORIES...NONE. $$ GIMMESTAD/RJK