634 FXUS63 KFSD 181146 AFDFSD AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SIOUX FALLS SD 546 AM CST WED NOV 18 2015 .SHORT TERM...(TODAY AND TONIGHT) ISSUED AT 410 AM CST WED NOV 18 2015 BAND OF PRECIP...WITHIN TROWAL OF STRONG UPPER LEVEL SYSTEM LIFTING NORTH-NORTHEAST THROUGH FAR WESTERN IOWA THIS MORNING...HAS BEEN FAIRLY WELL-BEHAVED THUS FAR THIS MORNING. LOW-MID LEVEL FLOW OF DRIER AIR HOLDING WESTERN EXTENT OF PRECIP NEAR DE SMET TO LAKE ANDES LINE. EXPECT THIS WESTERN EDGE TO SLOWLY WORK EASTWARD THROUGH THE DAY AS THE UPPER WAVE LIFTS INTO MINNESOTA AND ASSOCIATED TROWAL SHIFTS EAST OF I-29. CANNOT COMPLETELY REMOVE POPS FROM OUR WESTERN AREAS THOUGH...AS APPROACHING NORTHERN STREAM WAVE AND ASSOCIATED COLD FRONT WILL KEEP POTENTIAL FOR SCATTERED SHOWERS ACROSS OUR WEST INTO THE AFTERNOON. THIS CHANCE WILL DIMINISH WITH PASSAGE OF THE FRONT...SLATED TO ENTER OUR FAR WEST IN THE EARLY AFTERNOON...AND PUSH THROUGH FAR EASTERN PORTIONS OF THE CWA BY EARLY EVENING. WITH WESTERN EDGE OF PRECIP SHIELD FARTHER EAST THAN EARLIER THOUGHT... POTENTIAL FOR SNOW IS EVEN MORE LIMITED AND SHOULD SEE LITTLE IF ANY SNOW IN OUR AREA WITH THIS SYSTEM TODAY. POST-FRONTAL CONCERNS TURN TO WINDS...WIND GUSTS IN PARTICULAR AS FORECAST SOUNDINGS SHOW 40-45KT MIXED LAYER WINDS DEVELOP ACROSS OUR WESTERN COUNTIES AS COLD AIR ALOFT PUSHES INTO THE AREA AFTER 21Z... EVEN STRONGER IN THE HIGHER ELEVATIONS OF GREGORY COUNTY. STRONGEST COLD ADVECTION SHIFTS EAST ACROSS THE CWA THROUGH 03Z THIS EVENING AND ANTICIPATE WINDS WILL DIMINISH SOME AFTER THAT TIME. HOWEVER WITH WINDS EXPECTED TO RAMP UP AGAIN THURSDAY MORNING...WILL CARRY WIND ADVISORY FOR LOCATIONS ALONG/WEST OF KBKX-KYKN LATE THIS AFTERNOON ALL THE WAY THROUGH TONIGHT. LOWER CONFIDENCE EAST OF THIS LINE THAT WINDS WILL REACH ADVISORY CRITERIA WITH THE PASSAGE OF THE FRONT THIS EVENING. THUS DECIDED TO HOLD OFF START OF ADVISORY FOR THESE AREAS UNTIL AFTER DAYBREAK THURSDAY. DAY SHIFT WILL HAVE TO REEVALUATE THIS THOUGH...ESPECIALLY SOUTHWEST MINNESOTA WHERE HIGHER ELEVATION MAY FAVOR ADVISORY LEVEL WINDS REACHING THE SURFACE DURING THE NIGHT. AS FOR TEMPERATURES...EXPECT LITTLE MOVEMENT TODAY WITH WIDESPREAD CLOUDS/PRECIP HOLDING READINGS PRETTY STEADY. EXCEPTION WILL BE IN THE WEST WHERE DRIER AIR HAS ALLOWED FOR MORE COOLING THIS MORNING AND POST-FRONTAL MIXING SHOULD BRIEFLY WARM READINGS INTO THE UPPER 40S THIS AFTERNOON. STEADY DOWNWARD FALL BEHIND THE FRONT TONIGHT WITH LOWS IN THE MID-UPPER 20S. .LONG TERM...(THURSDAY THROUGH TUESDAY) ISSUED AT 410 AM CST WED NOV 18 2015 STRONG WINDS WILL CONTINUE TO LEAD OFF THE LONGER RANGE PERIOD. GFS AS PER USUAL HAS SOMEWHAT BETTER MIXED BOUNDARY LAYER AND THUS SLIGHTLY STRONGER WINDS THROUGH THE LOWEST PROFILE COMPARED TO NAM/SREF/ECMWF. EVEN IF A BIT TOO STRONG...45 TO 50 KNOT WINDS ATOP THE MIXED LAYER...AND A DECENT 30 TO 40 KNOTS AT THE MID POINT MAKE FOR A SOLID WIND ADVISORY...AND AS LONG AS HIGHER LOCATIONS DO NOT START EARLIER...WILL GO WITH AN 8 AM START TIME AVERAGING BETWEEN MORE AND LESS EXPOSED AREAS. SHOULD GET A FAIRLY MARKED DECREASE IN WINDS AFTER 21-22Z AS MIXING ATTEMPTS TO HOLD ON TO A RAPIDLY WEAKENING SUPPORT NEAR SURFACE...WITH NO HELP FROM DIURNAL CYCLE AT THAT POINT. FAIRLY CONSISTENT 925 HPA TEMP FORECAST BETWEEN MODELS SUGGESTS UPPER 30S TO LOWER 40S FOR HIGHS. WINDS MOST AREAS SHOULD BE FAIRLY LIGHT BY EARLY EVENING...WITH EXCEPTION OF PARTS OF SW MN...WITH CLEAR SKIES AND VERY DRY AIRMASS HELPING TEMPS TO FALL QUICKLY. CLOUDS WILL BEGIN TO INCREASE AS NEXT UPSTREAM WAVE PUSHES THROUGH THE NORTHERN ROCKIES...WITH GENERALLY CLOUDY SKIES MOST AREA BY DAYBREAK. TEMPS MAY ACTUALLY LEVEL OFF OR RISE A BIT LATER NIGHT IN THE WEST...ESPECIALLY THE FAR SOUTHWEST WHERE COULD START TO SEE A LITTLE LIGHT SNOW TOWARD DAYBREAK. TO SAY THERE IS A BIT OF DIVERSITY WITH FRIDAY SYSTEM IS REALLY MAKING A MOLEHILL OUT OF A MOUNTAIN. JET STREAK CURRENTLY WELL OUT TO THE EDGE OF THE GULF OF ALASKA WILL BE RIDING THE NORTHWEST FLOW INTO THE CENTRAL PLAINS ON FRIDAY. GIVEN THE LARGER SCALE PATTERN... MUCH MORE LIKELY TO GET A MORE SOUTHWARD SOLUTION PER GFS/CANADIAN AND TO A LESSER DEGREE THE MODERATE ECMWF...COMPARED TO THE NAM/SREF AND OTHER DERIVATIVES. HAVE DESIGNED FORECAST OFF BLEND OF THE MORE SOUTHERN SOLUTIONS...BUT EVEN THEN...A VAST DIFFERENCE IN TIMING WITH GFS PRACTICALLY FINISHING UP THE PRECIPITATION IN THE EAST AS ECMWF IS REALLY JUST GOING WELL. KEPT THINGS MORE ON A MID TIMING PER ECMWF/CANADIAN. AS FAR AS FORECAST DETAILS...COOL AND QUITE DRY AIRMASS WILL BE IN PLACE AT LOWER LEVELS TO BEGIN ON FRIDAY...WITH WELL DEFINED MID LEVEL BOUNDARY ACROSS THE SOUTHERN CWA. FRONTOGENESIS REACTS TO APPROACHING UPPER JET STREAK...WITH LIFT PROFILES WELL PLACED IN THE DENDRITIC ZONE. NO REASON TO EXPECT ANYTHING OTHER THAN A SOLID PRECIPITATION FORM WITH WET BULB QUICKLY MAKING ANY NEAR SURFACE WARM LAYER A MEMORY. NOT VERY UNSTABLE ABOVE THE FRONTAL ZONE...SO NOT LOOKING FOR RATES TO GET OUT OF HAND. SNOWFALL ALONG THE BAND SHOULD REALLY START ENHANCING BY MID MORNING...WITH BROAD BANDING NEAR/NORTH OF THE MISSOURI RIVER INTO NORTHWEST IOWA. MAX PRECIP SHOULD BE IN THE EARLY TO MID AFTERNOON...BEFORE EASTWARD SHIFT OF BETTER FRONTAL DYNAMICS AS WELL AS THE EROSION FROM RENEWED NORTHERLY FLOW. ON THE REALM OF POSSIBILITY WOULD BE A BIT MORE AMPLIFICATION OF SYSTEM AND PERHAPS A BIT OF A PIVOT DEVELOPING NEAR THE SOUTHEAST CORNER OF THE CWA. THIS COULD ENHANCE AMOUNTS EVEN A BIT MORE TOWARD HIGHWAY 20...BUT FOR NOW AM GENERALLY LOOKING FOR 2 TO 5 INCH BAND OF SNOWFALL SOUTH OF A WAGNER TO SPENCER IOWA LINE. ONCE MORE CONSISTENCY IN RUNS APPEARS...WOULD EXPECT THAT MAY BE DEALING WITH THE FIRST WINTER WEATHER HIGHLIGHT FOR THE SEASON. DRY AIR TO NORTH COULD EASILY RESULT IN A SHARPER NORTHERN CUTOFF TO SNOW...BUT ENOUGH MID LEVEL MOISTURE/LIFT OVER THE DRIER LOW LEVELS TO WARRANT AT LEAST LIKELY POPS TO JUST NORTH OF I 90...WHERE AMOUNTS COULD REACH AROUND AN INCH. FOLLOWING EXIT OF SYSTEM ON FRIDAY EVENING WILL BE INFLUX OF THE COLDEST AIRMASS OF THE SEASON...850 HPA TEMPS -12 TO -14C BY SATURDAY. HAVE TRENDED TEMPS GENERALLY DOWNWARD FROM INITIAL BLEND THROUGH SAT NIGHT...ESPECIALLY FOR THOSE AREAS EXPECTING SNOWFALL. NOT OUT OF THE QUESTION THAT SOME LOCATIONS COULD GET FAIRLY CLOSE TO ZERO ON SATURDAY NIGHT WHEN GRADIENT EASES. SUNDAY WILL START MODERATING TREND...AND THIS WILL CONTINUE UNABATED THROUGH MIDWEEK AS UPPER LEVELS ONCE AGAIN REARRANGE TO THE FAMILIAR WESTERN TROUGH/PLAINS RIDGE. WEAK BOUNDARY WILL SLIDE THROUGH AROUND SUNDAY NIGHT/MONDAY MORNING...BUT LITTLE MORE THAN A BETTER MIXING SET UP TO AID IN WARMING. WILL HAVE TO SEE HOW QUICKLY ANY SNOWCOVER WILL GO AWAY...AND VERY WELL MAY REQUIRE SOME SLOWING OF WARMING TREND OVER THOSE MINOR CHANGES ALREADY MADE. BY WEDNESDAY...MAY SEE ENOUGH DURATION TO SOUTHERLY FLOW TO RETURN THREAT FOR STRATUS/FOG WITH A LIGHT RAIN/DRIZZLE THREAT. && .AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING) ISSUED AT 546 AM CST WED NOV 18 2015 FAIRLY WIDESPREAD IFR-LIFR CEILINGS ACROSS THE AREA TO START THE PERIOD...THOUGH SEEING POCKETS OF MVFR OR EVEN VFR CONDITIONS NEAR EDGES OF RAIN SHIELD. EXPECT SUB-VFR CEILINGS TO BE DOMINANT CONDITION FOR KFSD/KSUX THROUGH THIS MORNING...BUT GRADUAL UPWARD TREND IS LIKELY AS PRIMARY RAIN SHIELD SLOWLY SHIFTS EAST INTO MINNESOTA/IOWA. AFTER 18Z-20Z...MAIN AVIATION CONCERN WILL SHIFT FROM SUB-VFR FLIGHT CONDITIONS TO INCREASING WEST-NORTHWEST WINDS. EXTENDED PERIOD OF WIND GUSTS IN EXCESS OF 25KTS LIKELY SPREADING ACROSS ALL LOCATIONS AFTER 21Z...WITH GUSTS AT OR ABOVE 35KTS POSSIBLE FOR A FEW HOURS DURING THE LATE AFTERNOON/EVENING IN AREAS WEST OF INTERSTATE 29. THOUGH WINDS WILL SUBSIDE SLIGHTLY OVERNIGHT...INCREASING SPEEDS LIKELY THROUGHOUT THE AREA AGAIN BEYOND THIS TAF PERIOD...AFTER DAYBREAK THURSDAY. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...WIND ADVISORY FROM 3 PM THIS AFTERNOON TO 6 PM CST THURSDAY FOR SDZ038>040-050-052>055-057>061-063>065-068. WIND ADVISORY FROM 8 AM TO 6 PM CST THURSDAY FOR SDZ056-062-066- 067-069>071. MN...WIND ADVISORY FROM 8 AM TO 6 PM CST THURSDAY FOR MNZ071-072-080- 081-089-090-097-098. IA...WIND ADVISORY FROM 8 AM TO 6 PM CST THURSDAY FOR IAZ001>003- 012>014-020>022-031-032. NE...WIND ADVISORY FROM 8 AM TO 6 PM CST THURSDAY FOR NEZ013-014. && $$ SHORT TERM...JH LONG TERM...CHAPMAN AVIATION...JH