946  
FXUS63 KTOP 171725  
AFDTOP  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE TOPEKA KS  
1125 AM CST SUN DEC 17 2017  
   
..UPDATE TO AVIATION FORECAST DISCUSSION
 
 
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 258 AM CST SUN DEC 17 2017  
 
EARLY THIS MORNING AN UPPER LEVEL TROUGH WAS LIFTING NORTHEAST  
ACROSS NORTH CENTRAL OK AND SOUTH CENTRAL KS. THE PV ANOMALY MAX  
EXTENDED FROM NORTHWEST OF ICT, SOUTHEAST TO TUL. AHEAD OF THE PV  
ANOMALY THERE WAS STRONGER ASCENT MOVING NORTHEAST ACROSS THE  
SOUTHERN COUNTIES INTO EAST CENTRAL KS. A BAND OF LIGHT RAIN HAS  
DEVELOPED AND AT 2 AM EXTENDED FROM NORTH OF TOP, SOUTHWEST TO EAST  
OF SLN. THIS BAND OF RAIN WILL MOVE NORTHEAST ACROSS THE EASTERN HALF  
OF THE CWA THROUGH THE MORNING HOURS. AS THE UPPER TROUGH LIFTS  
NORTHEAST ACROSS EASTERN KS, THE STRONGER ASCENT WILL SHIFT  
NORTHEAST OF THE CWA BY 18Z AND WE SHOULD SEE OUR RAIN CHANCES COME  
TO AN END. EAST CENTRAL KS MAY SEE 0.10 TO 0.20" OF RAINFALL THIS  
MORNING WITH MUCH LESSER AMOUNTS ACROSS THE WESTERN COUNTIES. IF  
LIGHT RAIN OR SPRINKLES MAKE NORTHWARD INTO NORTH CENTRAL KS THEN  
THERE IS A CHANCE THAT SOME OF THE RAIN MAY MIX WITH A BIT OF SNOW  
ALONG THE NE BORDER FROM 12Z THROUGH 15Z.  
 
A WEAK COLD FRONT WILL MOVE SOUTHWARD ACROSS THE CENTRAL COUNTIES OF  
THE CWA BUT FRONTOLYSIS WILL OCCUR AND THE FRONT SHOULD BECOME LESS  
DEFINED DURING THE LATE AFTERNOON HOURS INTO TONIGHT. EXPECT THE  
EASTERN HALF OF THE CWA TO REMAIN MOSTLY CLOUDY TODAY WITH SLOWLY  
DECREASING CLOUD COVER ACROSS THE WESTERN COUNTIES DURING THE LATE  
AFTERNOON HOURS. HIGHS WILL ONLY REACH THE LOWER 50S ACROSS EAST  
CENTRAL KS WITH MID 40S ACROSS NORTH CENTRAL KS.  
 
TONIGHT, A FEW OF THE NUMERICAL MODELS SHOW SOME WEAK ISENTROPIC  
LIFT DEVELOPING ACROSS EASTERN KS THIS EVENING. THIS MAY RESULT IN  
PATCHY DRIZZLE OR SOME VERY LIGHT RAINFALL. TEMPERATURES WILL BE  
ABOVE FREEZING IF ANY DRIZZLE WERE TO OCCUR. SINCE THE QPF WILL BE  
ONLY A TRACE I KEPT ANY POPS OUT OF THE FORECAST. LATE TONIGHT  
TEMPERATURES WILL DROP OFF INTO THE LOWER TO MID 30S ACROSS EAST  
CENTRAL KS WITH MID 20S ACROSS NORTH CENTRAL KS AS SKIES CLEAR FROM  
WEST TO EAST.  
   
LONG TERM
 
(MONDAY THROUGH SATURDAY)  
ISSUED AT 258 AM CST SUN DEC 17 2017  
 
ANY CHANCE FOR SIGNIFICANT SENSIBLE WEATHER CHANGES IN THE LONG  
TERM FORECAST WILL HAVE TO WAIT UNTIL THE THURSDAY DAY AND EVENING  
TIME FRAME. IN THE MEANTIME, UPPER CONFLUENT TYPE FLOW REGIME SETS  
UP OVER THE CENTRAL PLAINS REGION. THIS ALONG WITH BROAD LOW  
AMPLITUDE MID LEVEL RIDGING WILL ALLOW FOR WARMER THAN NORMAL TEMPS  
TO BE THE STORY. HIGHS MONDAY THROUGH WEDNESDAY SHOULD BE QUITE  
PLEASANT GENERALLY IN THE 50S AND POSSIBLY LOW 60S OVER NORTHEAST  
KANSAS. MEANWHILE LOWS ONLY DIP INTO THE 30S AT MOST LOCATIONS WITH  
THE LOWEST LYING AREAS SEEING UPPER 20S.  
 
THURSDAY INTO FRIDAY WILL SEE THE PATTERN CHANGE AND HINGES ON THE  
EVOLUTION OF AN ALEUTIAN LOW PRESSURE SYSTEM AS IT SLAMS INTO THE  
PACIFIC NORTHWEST REGION OF THE CONUS. AT THIS TIME, 17.00Z  
EC/GFS/CANADIAN SOLUTIONS SEEM TO BE COMING INTO BETTER AGREEMENT  
THAT THE UPPER PATTERN WILL ESSENTIALLY SPLIT ONCE AGAIN AS THE  
PREVIOUSLY MENTIONED LOW ADVANCES INTO THE NORTHERN ROCKIES. SOME  
ENERGY REMAINS WITH A PORTION OF THE NORTHERN PFJ AND A PORTION  
DIVES SOUTH INTO THE DESERT SOUTHWEST. EVENTUAL SOLUTIONS SHOW A  
DEEP POSITIVELY TILTED TROUGH EXTENDING FROM CENTRAL CANADA INTO THE  
SOUTHERN PLAINS WITH THE TROUGH BROADENING INTO THE CHRISTMAS EVE  
TIME FRAME WITH REINFORCING SHOTS OF COLD DRY ARCTIC AIR MOVING INTO  
THE NORTHERN AND CENTRAL PLAINS. PRECIP CHANCES FOR THURSDAY ARE  
STILL MUCH IN QUESTION WITH A LOW LEVEL FRONTOGENETICAL RESPONSE  
MOVING THROUGH THE AREA (BEST UPPER FORCING REMAINS NORTHEAST AND  
SOUTH OF THE FORECAST AREA). BUT, THE CONSISTENT THEME IS TO KEEP  
BEST RAIN/SNOW CHANCES GENERALLY NORTH OF I-70. AMOUNTS STILL VERY  
HARD TO KNOW, BUT THE HINT IS ONLY LIGHT AMOUNTS MAY BE THE EVENTUAL  
RESULT. AGAIN, COLD ENOUGH AIR BEING ENTRENCHED IN THE REGION FOR  
ALL SNOW IS UNLIKELY AT THIS POINT. TEMPS MIGHT BE THE BIGGEST  
STORY IN THE END WITH THIS FRONTAL SYSTEM. THERE REMAINS A LARGE  
SPREAD IN OUTCOMES AT THIS POINT AMONGST THE MODELS IN EXACTLY HOW  
MUCH COLD AIR GETS PULLED IN THURSDAY NIGHT WITH STRONG CAA AND THEN  
SUBSEQUENT PERIODS. THE HIGHER CONFIDENCE OUTCOME WILL RESULT IN  
BELOW NORMAL TEMPS THOUGH WITH HIGHS STRUGGLING TO REACH INTO THE  
MID 30S AND LOW TEMPS PLUMMETING INTO THE LOW TEENS AND POSSIBLE  
SINGLE DIGITS BY CHRISTMAS EVE. SO, WHILE IT MAY NOT BE A WHITE  
CHRISTMAS, IT WILL LIKELY BE A COLD ONE.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)  
ISSUED AT 1122 AM CST SUN DEC 17 2017  
 
CLOUD HEIGHTS REMAIN THE PRIMARY FORECAST CHALLENGE IN THE SHORT  
TERM. WHILE CIGS ARE GENERALLY AT THE HIGH END OF MVFR, THERE ARE  
SOME PATCHES OF CLOUDS IN THE 1000FT AGL RANGE. DON'T THINK THESE  
WILL HOLD TOGETHER AND WOULD LIFT WITH HEATING, SO HAVE KEPT THEM  
OUT OF A PREVAILING FORECAST ATTM AND WILL MONITOR.  
 

 
   
TOP WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  

 
 

 
 
SHORT TERM...GARGAN  
LONG TERM...DRAKE  
AVIATION...67  
 
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