700  
FXUS63 KOAX 251108  
AFDOAX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE  
608 AM CDT TUE JUL 25 2017  
   
SHORT TERM
 
(TODAY THROUGH THURSDAY)  
ISSUED AT 345 AM CDT TUE JUL 25 2017  
 
FORECAST CONCERNS WILL PRIMARILY BE TEMPERATURES AND HEAT  
HEADLINES THEN THUNDERSTORM CHANCES TONIGHT NIGHT THROUGH  
WEDNESDAY NIGHT.  
 
THUNDERSTORMS DEVELOPED MONDAY AFTERNOON NEAR AN AREA OF SURFACE LOW  
PRESSURE IN SOUTHWEST SOUTH DAKOTA. GOOD SOUTHEAST INFLOW WAS STILL  
NOTED OVER SOUTHERN SOUTH DAKOTA AS THE CENTER OF LOW PRESSURE WAS  
STILL NEAR PIERRE, SD, HOWEVER THIS BETTER FLOW HAD SHIFTED INTO  
MN BY 08Z. THE STORMS WERE WEAKENING AS THEY SPILLED SOUTHEAST  
INTO THE OAX CWA AT 05Z, HOWEVER STORMS CONTINUED FARTHER NORTH IN  
NORTHEAST SD AND PARTS OF MN AT 05Z AND SOUTHERN MN AT 08Z AS THE  
LOW LEVEL JET SHOULD CONTINUE TO STRENGTHEN TO 50KTS THROUGH 12Z.  
 
EARLY TODAY...THE SHORTWAVE OVER MN WILL CONTINUE TO PUSH INTO THE  
GREAT LAKES...MEANWHILE...A STRONG H3 100KT JET AND THE CLOSED H5  
LOW PRESSURE SYSTEM TRACKS OVER MANITOBA. AS THE UPPER LEVEL JET  
INCREASES NEAR THE U.S./CANADA BORDER UPPER LEVEL DIVERGENCE  
INCREASES AND OMEGA INCREASES WITHIN THE AREA OF STEEP LAPSE RATES  
OVER SD/WESTERN NEBRASKA. THE OPERATIONAL AND CAM MODELS TEND TO  
RAPIDLY INCREASE CONVECTION ALONG THE FRONT THIS AFTERNOON BETWEEN  
21-00Z NORTHWEST OF THE OAX FORECAST AREA. ALTHOUGH THE LOW LEVEL  
JET IS AROUND 25 TO 45KTS THIS MORNING, THE FLOW DECREASES TO  
25KTS BY MID AFTERNOON...AND BEGINS TO STRENGTHEN AGAIN TO 30KTS  
BY 00Z AND 40KTS+ BY 06Z. A POCKET OF DRIER AIR OVER PARTS OF THE  
FORECAST AREA SHOULD HELP BOOST TEMPERATURES TO 95 TO 100 DEGREES  
OVER THE NORTHWEST HALF OF THE FORECAST AREA...MEANWHILE...HIGHER  
LOWER LEVEL MOISTURE RETURNS FROM THE SOUTHEAST.  
 
THE COMBINATION OF HOT TEMPERATURES AND RETURNING DEEPER  
MOISTURE/EVAPOTRANSPIRATION FROM CROPS SHOULD BOOST HEAT INDEX  
VALUES FOR AREAS ALONG THE MISSOURI RIVER INTO SOUTHWEST IOWA TO  
AROUND 105 DEGREES OR HIGHER. A HEAT ADVISORY WILL BE ISSUED FOR  
THIS AFTERNOON.  
 
AS THE MID TROPOSPHERIC TROUGH PROGRESSES ACROSS THE NORTHERN  
PLAINS...THUNDERSTORMS WILL GRADUALLY SINK SOUTHWARD. IN ADVANCE  
OF THE MAIN AREA OF STORMS, THERE IS WEAK LIFT, THUS SCATTERED  
SHOWERS AND THUNDERSTORMS COULD DEVELOP FARTHER SOUTH WHERE IT IS  
UNCAPPED AND VERY MOIST.  
 
PWAT VALUES WERE 1.32 INCHES ON THE 00Z SOUNDING AND ARE FORECAST  
TO INCREASE TO 2 TO 2.75 INCHES DURING THE EVENING. K-INDEX  
VALUES OF 42 TO 44 ARE FORECAST OVER THE FORECAST AREA BY 12Z WED.  
CHANCES FOR THUNDERSTORMS BECOME LIKELY NEAR THE SD BY 06Z  
TONIGHT...AND PERIODS OF STORMS ARE FORECAST FOR THE FORECAST AREA  
THROUGH WED/WED NIGHT...WITH A SLIGHT CHANCE IN THE SOUTHEAST  
THURSDAY MORNING. RAINFALL IS NEEDED DUE TO THE RECENT HOT WEATHER  
AND FOR NOW HAVE AMOUNTS BETWEEN .3 AND 1.3 INCHES. SHOULD  
TRAINING OF STORMS OCCUR, MUCH HIGHER AMOUNTS COULD BE REALIZED  
DUE TO THE VERY MOIST ENVIRONMENT.  
 
THE ENHANCED RISK OF SEVERE STORMS IS FROM SD INTO MN FOR DAY 1  
AND A SLIGHT RISK LOCALLY FOR DAY 2. THERE IS SOME RISK FOR WINDS  
WITH STORM OUTFLOWS AND LOCALLY HEAVY RAINS. 0-3KM 40 TO 50KT  
SHEAR VECTORS TRACK ACROSS THE AREA WED. THE RISK FOR EXCESSIVE  
RAINFALL IS MORESO IN IOWA WHERE THICKNESS DIFFLUENCE/FORCING  
LINING UP BETTER WITH MOISTURE PARAMETERS, HOWEVER SHORT-TERM  
METWATCH IS NEEDED FOR TRAINING OF STORMS.  
   
LONG TERM
 
(THURSDAY NIGHT THROUGH MONDAY)  
ISSUED AT 345 AM CDT TUE JUL 25 2017  
 
COOLER WEATHER FOR THE EXTENDED WITH HIGHS IN THE 80S. THERE ARE  
SOME SPOTTY STORMS FORECAST, HOWEVER NOTHING ORGANIZED.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)  
ISSUED AT 605 AM CDT TUE JUL 25 2017  
 
VFR CONDITIONS ARE EXPECTED THE BULK OF THE TAF PERIOD. AXIS OF  
LOW LEVEL JET ORIENTED FROM CENTRAL KANSAS INTO NORTHEAST NEBRASKA  
THIS MORNING, THUS LLWS REMAINS A CONCERN FOR KOFK UNTIL SURFACE  
MIXING BEGINS IN EARNEST AROUND 14UTC. INCREASING SURFACE PRESSURE  
GRADIENT AND DEEP MIXING WILL ALLOW SURFACE WINDS TO INCREASE BY  
LATE MORNING INTO THE 10 TO 20 KT RANGE WITH GUSTS UP TO 25KT BY  
THIS AFTERNOON. AS FRONTAL BOUNDARY APPROACHES THE AREA TONIGHT,  
THUNDERSTORM ACTIVITY ACROSS SOUTH DAKOTA INTO CENTRAL NEBRASKA  
WILL SPREAD 10-25K CEILINGS INTO KOFK BY EVENING. CURRENT  
INDICATIONS ARE THAT STORMS WILL NOT AFFECT KOFK UNTIL 06Z OR  
LATER, WITH CEILINGS LOWERING INTO 4-6K RANGE. THUNDERSTORMS LIKELY  
WILL NOT AFFECT KLNK OR KOMA UNTIL THE END OR AFTER THE TAF  
PERIOD.  
 

 
   
OAX WATCHES/WARNINGS/ADVISORIES
 
 
NE...HEAT ADVISORY FROM 1 PM THIS AFTERNOON TO 7 PM CDT THIS EVENING  
FOR NEZ034-045-052-053-067-068-091-093.  
 
IA...HEAT ADVISORY FROM 1 PM THIS AFTERNOON TO 7 PM CDT THIS EVENING  
FOR IAZ055-069-079-090.  
 

 
 

 
 
SHORT TERM...ZAPOTOCNY  
LONG TERM...ZAPOTOCNY  
AVIATION...FORTIN  
 
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