FXUS63 KGID 181115 AFDGID AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HASTINGS NE 615 AM CDT THU MAR 18 2010 .AVIATION...12Z KGRI TAF. EXPECT MOSTLY SUNNY START TO THE DAY WITH HIGH CLOUDS INCREASING DURING THE AFTERNOON IN ADVANCE OF THE NEXT STORM SYSTEM. CLOUDS THEN BEGIN TO LOWER BY LATE EVENING AND COULD SEE MVFR CEILINGS TAKE HOLD AFTER MIDNIGHT. WINDS WILL START OFF SOUTHWESTERLY THIS MORNING AND GRADUALLY BECOME MORE SOUTHERLY BY AFTERNOON. A COLD FRONT WILL TURN THE WINDS TO NORTHERLY BY AROUND 10 PM AND QUICKLY BECOME BLUSTERY DURING THE LATE NIGHT HOURS. RAIN WILL EVENTUALLY SLIDE SOUTH INTO THE KGRI AREA JUST PRIOR TO DAWN. RAIN WILL THEN TURN OVER TO SNOW ON FRIDAY MORNING. && .PREV DISCUSSION... /ISSUED 435 AM CDT THU MAR 18 2010/ DISCUSSION...MAIN CONCERN FOR THIS FORECAST IS THE RETURN OF RAIN...SNOW...AND WIND LATE TONIGHT THROUGH FRIDAY NIGHT. EARLY MORNING WATER VAPOR IMAGERY SHOWED A POSITIVELY TILTED UPPER RIDGE EXTENDING FROM THE SOUTHERN AND CENTRAL ROCKIES THROUGH THE CENTRAL PLAINS AND MID MS VALLEY. AN UPPER LOW TRANSLATING EAST ACROSS SASKATCHEWAN/MANITOBA WAS ACTING TO FLATTEN THE RIDGE...WHILE FARTHER WEST THE NEXT SHORTWAVE TROUGH WAS DIVING THROUGH THE PAC NW AND WILL TURN INTO OUR WEATHER MAKER OVER THE NEXT COUPLE OF DAYS. OBJECTIVE SURFACE ANALYSIS SHOWED LOW PRESSURE STARTING TO DEEPEN IN THE LEE OF THE ROCKIES. SOME CIRRUS CONTINUED TO FILTER OVER THE AREA AS MID/HIGH LEVEL PAC MOISTURE CONTINUED TO STREAM EAST OVER THE ROCKIES. ONE MORE NICE DAY...IN FACT THE NICEST DAY OF THE WEEK...IS IN STORE TODAY BEFORE THINGS TAKE A SHARP TURN TOWARD THE COLDER AND WETTER SIDE LATE TONIGHT. FLATTENING UPPER RIDGE WILL CONTINUE TO IMPACT THE AREA TODAY AHEAD OF UPPER TROUGH DIGGING SOUTHEAST THROUGH THE INTERMOUNTAIN WEST. SURFACE LOW WILL CONTINUE TO DEEPEN OVER EASTERN COLORADO THROUGH THE DAY IN RESPONSE TO INCREASING CROSS MOUNTAIN FLOW ALOFT OVER THE ROCKIES. CIRCULATION AROUND THE SURFACE LOW WILL BRING SOUTH/SOUTHWEST WINDS TO THE AREA...WHICH COMBINED WITH WARM TEMPS ALOFT AND ONLY SOME CIRRUS CLOUDS THROUGH THE DAY WILL PUSH TEMPS INTO THE 60S. THINGS WILL CHANGE QUICKLY HOWEVER TONIGHT AS THE UPPER TROUGH CONTINUES TO DIG SOUTHEAST THROUGH THE INTERMOUNTAIN WEST AND ROCKIES. THE DIRECT CIRCULATION ASSOCIATED WITH THE ENTRANCE REGION OF A 110 KT UPPER JET STREAK EXTENDING THROUGH THE NORTHERN HIGH PLAINS WILL HELP PUSH A STRONG COLD FRONT SOUTH THROUGH THE CWA TONIGHT. THE OVERALL TIMING OF THIS SYSTEM AS A WHOLE...INCLUDING THE COLD FRONTAL PASSAGE...HAS SPED UP SOME FROM FORECASTS 24 HOURS AGO AND AM NOW EXPECTING THE FRONT TO CLEAR THE WHOLE CWA BY SUNRISE FRIDAY. STRONG LOW TO MIDLEVEL FRONTOGENETIC FORCING BENEATH INCREASING UPPER-LEVEL DIVERGENCE UNDER RRQ OF UPPER JET STREAK WILL BRING PRECIPITATION INTO THE NORTHWEST CWA STARTING VERY LATE THIS EVENING...WHICH WILL THEN WORK SOUTHEAST ACROSS THE AREA OVERNIGHT INTO FRIDAY. A 45 KT SOUTHWESTERLY LLJ IMPINGES ON THE FRONTAL BOUNDARY AS IT SLICES THROUGH TONIGHT...PROVIDING ADDED CONVERGENCE/LIFT. THE PRECIP WILL START OUT AS RAIN INITIALLY AND THEN TRANSITION TO SNOW FROM NORTHWEST TO SOUTHEAST AS COLD AIR PLUNGES SOUTH BEHIND THE FRONT. DEBATED ADDING AN ISOLATED THUNDER MENTION TO SOUTHWEST PORTIONS OF THE CWA TONIGHT (GENERALLY WEST OF HWY 281/SOUTH OF THE INTERSTATE) WHERE THE NAM SHOWS MUCAPES OF 200-300 J/KG DEVELOPING AS COOLER AIR MOVES IN ALOFT PRODUCING STEEPENING MID-LEVEL LAPSE RATES. HOWEVER THE GFS AND ECMWF SHOW MUCAPES OF LESS THAN 100 J/KG AND SREF PROBS AREN/T SHOWING MUCH OF ANYTHING...SO DECIDED TO KEEP OUT ALTHOUGH AN ISOLATED RUMBLE OF THUNDER OR TWO ISN/T OUT OF THE QUESTION. EXPECT ANY SNOW ACCUMULATIONS TONIGHT TO BE LESS THAN A HALF INCH AND CONFINED TO THE FAR NORTHWEST AS NOT EXPECTING TO SEE THE FIRST FLAKES FALL UNTIL 09Z OR SO AND SURFACE/SOIL TEMPS WILL BE WARM INITIALLY AND THE GROUND WET. THE PRECIP WILL CONTINUE TO WORK SOUTHEAST ACROSS THE AREA ON FRIDAY...WITH SNOW EXPECTED IN ALL AREAS BY LATE AFTERNOON AS STRONG CAA CONTINUES...PRODUCING FALLING TEMPS THROUGH THE DAY. NORTH WINDS CRANK UP BEHIND THE FRONT...BUT THEY ARE LOOKING A TAD WEAKER BEHIND THE INITIAL SURGE COMPARED TO EARLIER PROGS. STILL EXPECTING SUSTAINED WINDS OF 15-25 MPH WITH GUSTS TO AROUND 35 MPH. SNOW ACCUMULATIONS ARE STILL A CHALLENGE DUE TO THE BATTLE BETWEEN A WET GROUND AND WARM SURFACE/SOIL TEMPS INITIALLY...AND STRONG FRONTOGENETIC FORCING PRODUCING AT LEAST A PERIOD OF MODERATE SNOWFALL. CROSS SECTIONS ALSO INDICATE SOME NEGATIVE EPV ABOVE THE FRONTAL CIRCULATION THAT MAY LEAD TO SOME ENHANCED MESOSCALE BANDING. ALL IN ALL...NO BIG CHANGES WERE DEEMED NECESSARY OR MADE TO TOTAL SNOW ACCUMULATIONS...WITH AMOUNTS STILL IN THE 1-3 INCH RANGE. STILL THINK MOST PLACES WILL BE AROUND 2 INCHES OR LESS WITH ANY 3 INCH AMOUNTS MORE LOCALIZED. THE MAIN IMPACT WITH THIS SYSTEM WILL LIKELY BE THE BLOWING OF FALLING SNOW...AND HOW LOW VSBYS GET. NOT EXPECTING ANY SIGNIFICANT BLOWING OF SNOW ON THE GROUND DUE TO ITS WET NATURE AND AS ALREADY MENTIONED...ACCUMS NOT EXPECTED TO EXCEED A FEW INCHES. MAINTAINED THE BLOWING SNOW MENTION IN THE GRIDS DURING THE DAY ON FRIDAY WHEN WINDS WILL BE STRONGEST AND WILL CONTINUE TO HIGHLIGHT IN THE HWO. A WINTER WEATHER ADVISORY FOR THE SNOW/BLOWING SNOW COMBINATION STILL MAY BE NEEDED...BUT WITH THE FIRST FLAKES NOT EXPECTED UNTIL WELL AFTER MIDNIGHT TONIGHT...DECIDED TO HOLD OFF ON ANY HEADLINES FOR NOW. AS MENTIONED...THE WHOLE SYSTEM HAS SPED UP AND EXPECT ALL SNOW TO BE PRETTY MUCH OUT OF THE AREA BY SUNRISE SATURDAY. A FEW FLURRIES ARE NOT OUT OF THE QUESTION ON SATURDAY AS UPPER TROUGH AXIS WORKS ACROSS AND SOUNDINGS SHOW A LITTLE MOISTURE EXTENDING INTO THE DENDRITIC LAYER...BUT NOT GOING TO WORRY ABOUT IT AT THIS POINT. TEMPERATURES REMAIN COLD ON SATURDAY WITH HIGHS ONLY REACHING THE LOWER/MID 30S...BEFORE STARTING TO REBOUND SUNDAY INTO EARLY NEXT WEEK. && .GID WATCHES/WARNINGS/ADVISORIES... NE...NONE. KS...NONE. && $$ DISCUSSION...KB