Issued by NWS Kansas City/Pleasant Hill, MO
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000 FXUS63 KEAX 222127 AFDEAX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO 327 PM CST SUN NOV 22 2009 .DISCUSSION... PRECIP CHCS DURING THE EARLY PORTION OF THE WEEK ALONG WITH THE EVOLUTION OF SFC TEMPS ASSOCIATED WITH THIS SYSTEM WILL REMAIN THE ITEMS OF MOST CONCERN FOR THIS FCST. THIS AFTN...PROFILER AND WV IMAGERY CONFIRM THE PRESENCE OF A RATHER FAST MOVING UPR S/W TROUGH RACING THROUGH CENTRAL KANSAS ATTM. THIS S/W TROUGH IS HANDLED WELL BY THE DETERMINISTIC MODEL GUIDANCE...WITH THE UPR TROUGH AXIS CROSSING THE MO/KS STATE LINE AROUND MIDNIGHT. WITHOUT A LARGE QUANTITY OF LOW-LVL MOISTURE FOR THIS SYSTEM EXPECT THE IMPACT TO BE MINIMAL. ISENTROPIC LIFT REMAINS RATHER UNFOCUSED IN NATURE...BUT MAY BE STRONG ENOUGH TO TAP INTO THICKER MID-LVL MOISTURE PLUME AHEAD OF THE S/W IN THE NORTHERN AND EASTERN CWA. WILL MAINTAIN SLIGHT CHC POP. OF OTHER CONCERN IN THE IMMEDIATE SHORT TERM WILL BE THE POTENTIAL FOR PATCHY DENSE FOG ACROSS THE NORTHERN PORTIONS OF THE CWA. MODELS SUGGEST THE DEVELOPMENT OF A WEAK SURFACE WARM FRONT ACROSS THE CENTRAL CWA BY MID-MORNING. BOUNDARY LAYER MOISTURE IS EXPECTED TO REMAIN RATHER HIGH OVERNIGHT. HOWEVER THE AMOUNT OF CLEARING AND MID-LVL SUBSIDENCE BEHIND THE UPR S/W REMAIN IN DOUBT. SOUNDINGS...NUMERICAL GUIDANCE...AND SREF PROBABILITIES SUGGEST AT LEAST MVFR FOG WITH PATCHY DENSE FOG POSSIBLE SHOULD SKIES CLEAR MORE THAN CURRENTLY ANTICIPATED. FOR MONDAY...NEXT UPR WAVE CURRENTLY IN THE PAC NW EXPECTED TO DIG ACROSS THE WESTERN PLAINS BY MON AFTN AND QUICKLY PIVOT NE INTO THE GREAT LAKES BY TUE NIGHT. 12Z DETERMINISTIC MODELS REMAIN IN GENERAL AGREEMENT...WITH THE GFS SLIGHTLY FASTER AND DEEPER THAN THE 12Z NAM AND ECMWF. THE 18Z NAM IS A DISTANT OUTLIER...WITH A SOLN THAT IS DIGGING THE UPR TROUGH TO FAR TO THE SOUTH GIVEN THE AMPLITUDE OF THE KICKER WAVE UPSTREAM. NEVERTHELESS...IT SHOULD BE NOTED THAT THERE HAS BEEN A SLIGHTLY SLOWER AND FURTHER SOUTH TREND IN DETERMINISTIC GUIDANCE DURING THE PAST 2 MODEL RUNS AND THESE TRENDS HAVE BEEN CONSIDERED IN THE CURRENT FCST GIVEN THE STRONG PAC JET ACCOMPANYING THIS SYSTEM. ENSEMBLES REMAIN SUPPORTIVE OF THE 12Z GFS/ECMWF SOLNS KEEPING THE OVERALL UPR TRACK ACROSS CENTRAL KS ACROSS NORTHERN MO. OVERALL EXPECTING A FAIRLY DRY AND WARM DAY ON MON AS WE REMAIN STUCK IN MID-LVL S/W RIDGING BETWEEN UPR TROUGHS. WILL CONTINUE TO ADVERTISE LOW 60S FOR TEMPS ALONG WITH A SLIGHT CHC POP IN THE NW CORNER. FOR MON NIGHT AND TUE...BIGGEST QUESTIONS ARISE TO JUST HOW FAST THIS UPR TROUGH WILL EJECT EASTWARD. BY MON EVE STRONG UPR SUPPORT BEGINS TO MOVE NE INTO THE AREA AS THE SYSTEM REACHES PEAK INTENSITY. HOWEVER THE TILT AND INTENSITY OF THIS SYSTEM REMAIN KEY TO THE FCST...WITH CURRENT INDICATIONS OF THIS SYSTEM APPROACHING THE CWA IN A POSITIVE TILT AND PIVOTING OVER THE WESTERN CWA MON NIGHT. IN RETURN THIS MAY FORCE TWO DIFFERENT AREAS OF PRECIP...AN AREA OF RAIN IN NORTHEAST QUADRANT OF THE UPR LOW SUPPORTED BY PV ADVECTION AND THE UPR JET IN NORTHERN KS AND NW MO...AND A SECONDARY AREA OF PRECIP FURTHER SSW OVER SE KS AND SOUTHERN MO. ADDITIONALLY...POINT SOUNDINGS AND PLAN VIEW FCST MAPS SUGGEST A RAPID PERIOD OF LOW-LVL WAA AND THETA-E ADVECTION ENHANCING THE 850-600 MB LAPSE RATES ENOUGH TO INDUCE ISOLATED TO SCT CONVECTION AS THE PRIMARY BAND MOVES THOUGH. DEPENDING ON THE TRACK OF THE UPR LOW...SIGNIFICANT DRY SLOT IS EXPECTED TO ROTATE INTO THE AREA LATE MON NIGHT OR EARLY TUE FORCING LINEAR AREA OF PRECIP QUICKLY OUT OF THE ARE BY 12Z TUE. MOISTURE IS EXPECTED TO WRAP AROUND THE UPR LOW AS A EXTENSIVE TROWAL DEVELOPS...THIS MOISTURE MAY DEVELOP INTO ADDITIONAL PRECIP TUE AFTN AND NIGHT. FROZEN PRECIP CHCS STILL REMAIN VERY LOW WITH THIS SYSTEM DESPITE THE SLIGHTLY DEEPER TRACKS AS SUGGESTED BY GUIDANCE. NO COLD AIR WILL BE PRESENT PRIOR TO THIS SYSTEMS ARRIVAL...AND EVEN DYNAMICAL COOLING PROCESSES WON`T BE ABLE TO OVERTAKE THE LOW-LVL WARM AIR PRESENT PRIOR TO THE ARRIVAL. I WON`T RULE A RA/SN MIXTURE OUT IN THE WRAP AROUND TROWAL TUE AFTN...ESPECIALLY IF SOME OF THE COLDER LOW- LVL AIR CAN BE TAPPED OFF THE WESTERN PLAINS. HOWEVER FEEL GIVEN THE TIMING OF ARRIVAL AND THE FACT THAT THE SYSTEM WILL BE NEARLY VERTICALLY STACKED DOESN`T BODE WELL. FCST LOW AND HIGH TEMPS WILL BE A BIG CONCERN MON NIGHT AND TUE. A SLIGHTLY SLOW SYSTEM WILL KEEP SFC TEMPS WELL INTO THE UPR 40S TO PERHAPS LOW 50S MON NIGHT. HIGHS ON TUE WILL BE DICTATED BY THE SPEED OF THE SFC FRONT AND COLDER AIR WRAPPING IN FROM THE SW. HAVE ISSUED A NON-STANDARD DIURNAL CURVE...AND BUMPED UP MON NIGHT READINGS AND LOWERED TUESDAYS TEMPS. MD MEDIUM RANGE (WEDNESDAY THROUGH SUNDAY)... BY THE MIDDLE OF THE UPCOMING WORK WEEK THE CENTRAL PLAINS WILL BE UNDER THE INFLUENCE OF A NORTHWEST FLOW ON THE BACKSIDE OF A SYSTEM THAT WILL HAVE PASSED THROUGH THE PLAINS EARLIER IN THE WEEK. MID RANGE MODELS FROM THE ECMWF TO GFS AND GEM...PLUS MANY OF THE ENSEMBLE MEMBERS...HAVE ALL COME IN LINE WITH EACH OTHER OVER THE PAST SEVERAL RUNS...SO SYNOPTIC SCALE FEATURES ARE IN DECENT AGREEMENT. SHORTWAVE WILL DESCEND THROUGH THE NORTHWEST FLOW WEDNESDAY AND THURSDAY HELPING RELOAD/SLOW THE TROUGH THAT WILL BE MOVING EAST ACROSS THE CONUS MID-WEEK. RESULT WILL BE THAT TEMPERATURES SHOULD BE A BIT COOLER THAN OUR GOING FORECAST NUMBERS...WITH NORMAL TO BELOW NORMAL READINGS EXPECTED THROUGH FRIDAY. FOR THE WEEKEND THE SLOWER TROUGH PROGRESSION IMPLIES THAT THE WEEKEND WARM UP...WITH THE RIDGE FOLLOWING THE TROUGH...COULD BE MUTED A BIT WITH TEMPERATURES BARELY ABLE TO CLIMB ABOVE SEASONALLY NORMAL VALUES. HAVE ADJUSTED TEMPERATURES TO REFLECT THIS TREND...WITH NEW NUMBERS NEAREST THE MEX GUIDANCE VALUES. OTHERWISE...AS FOR PRECIPITATION...EVEN WITH THE TROUGH SLOWING EXPECTATIONS ARE THAT THE SHORTWAVE IN THE NORTHWEST FLOW WILL BE TRAVERSING THE REGION FROM THE NORTHERN PLAINS INTO THE OHIO RIVER VALLEY RATHER QUICKLY WEDNESDAY AND THURSDAY. THIS SHOULD LIMIT THE POTENTIAL FOR ANY PRECIPITATION IN THE FORECAST AREA MID WEEK TO REGIONS OF NORTH CENTRAL AND NORTHEAST MISSOURI. EVEN THEN... THOUGHTS ARE THAT SLIGHT CHANCE POPS ARE ALL THAT ARE WARRANTED AT THIS TIME GIVEN MOISTURE CONCERNS AND TIMING. FOR THE WEEKEND...THE RIDGE THAT WILL BE MOVING IN SHOULD KEEP CONDITIONS DRY. CUTTER && .AVIATION... FOR THE 18Z TAFS...VFR CONDITIONS ARE EXPECTED TO REMAIN IN PLACE THROUGH THE DAYTIME HOURS AS WELL AS INTO THE EVENING. S/W TROUGH CONTINUES TO RACE EASTWARD ACROSS WESTERN AND CENTRAL KS THIS AFTN...WITH BROAD ISENTROPIC LIFT GENERATING LIGHT SHRA/SPRINKLES NORTH OF THE TERMINALS. IN ADDITION...MODEST LOW-LVL THETA-E ADVECTION HAS RESULTED IN A BAND OF MVFR/IFR STRATUS ACROSS CENTRAL KS ALONG A STATIONARY FRONT AND SFC LOW. THIS S/W WILL LIFT NE THROUGH THE TERMINALS OVERNIGHT TONIGHT...HOWEVER ISENTROPIC LIFT DOES NOT LOOK STRONG ENOUGH TO PRODUCE ANYTHING MORE THAN SPRINKLES...WITH HIGHER POPS NORTH OF KSTJ. HOWEVER...LATER SHIFTS WILL NEED TO KEEP AN EYE ON MVFR/IFR CIGS TO OUR WEST WITH ARE PROGGED TO LIFT NORTHWARD ALONG A DEVELOPING SFC WARM FRONT BY 3 AM. THIS FRONT SHOULD SLOWLY LIFT NORTHWARD AFTER DAYBREAK AND MAY PRODUCE A 4 TO 6 HOUR SPAN OF MVFR TO PERHAPS EVEN IFR CIGS...WITH INCREASING BOUNDARY LAYER MOISTURE TRAPPED ALONG THIS FRONT ALSO REDUCING VIS INTO MVFR TO PERHAPS IFR CATEGORIES. WILL INCLUDE A TEMPO GROUP FOR THIS OCCURRENCE...WITH REDUCED VISIBILITIES MORE PREVALENT AT KSTJ WHERE LOW-LVL ISENTROPIC LIFT WILL BE THE GREATEST. AS UPR S/W LIFTS NE BY MID-MORNING A RETURN TO VFR CONDITIONS WOULD BE LIKELY. DUX && .EAX WATCHES/WARNINGS/ADVISORIES... MO...NONE. KS...NONE. && $$
