Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 221141 AFDOAX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE OMAHA/VALLEY NE 641 AM CDT FRI MAY 22 2015 .SHORT TERM...(TODAY THROUGH SUNDAY) ISSUED AT 311 AM CDT FRI MAY 22 2015 ...TIMING WET AND DRY PERIODS IS THE MAIN CHALLENGE... LARGE SCALE PATTERN OVER NORTH AMERICA CONTINUES TO INCLUDE THE BLOCKY RIDGE EXTENDING INTO NORTHWEST CANADA/ALASKA WITH SLOW MOVING CLOSED LOWS AND SHORTWAVES DRIFTING SOUTH OF THE POSITIVE HEIGHT ANOMALY AND INTO THE WESTERN US. THIS FLOW PATTERN IS CONDUCIVE TO TRANSPORTING HIGH AMOUNTS OF WATER VAPOR FROM THE SUB TROPICS INTO THE SOUTHERN US AND POTENTIALLY INTO THE PLAINS AND ROCKIES. HOWEVER...RESIDUAL SURFACE HIGH PRESSURE IS CURRENTLY ENTRENCHED OVER THE CENTRAL PLAINS REGION WITH A DRY AIRMASS IN PLACE. SENSIBLE WEATHER FROM THIS PATTERN WILL BE PERIODS OF FAIRLY LIGHT RAIN THAT IS GENERATED BY THE SHORTWAVES TO OUR WEST AND MOISTURE ADVECTION FROM THE SOUTH...BUT A THERMODYNAMICALLY STABLE AIRMASS WILL LIMIT THUNDER POTENTIAL AND KEEP RAINFALL SOMEWHAT LIGHT. THE CHALLENGE IS DETERMINING THE MOST LIKELY PERIODS OF RAIN AND THE DRY GAPS BETWEEN THEM. FIRST ROUND SHOULD BE TIED TO A WELL DEFINED SHORTWAVE CURRENTLY MOVING THROUGH COLORADO PER WATER VAPOR LOOP. THERE IS ALREADY A LARGE AREA OF RAIN ASSOCIATED WITH THIS FEATURE FROM COLORADO EAST AND SOUTH WITH LEADING EDGE NEAR DODGE CITY...MOVING THIS DIRECTION. INITIALLY THE DRY AIR IN PLACE OVER THE FORECAST AREA WILL LIMIT RAIN UNTIL AIR BECOMES MORE SATURATED. MIGHT BE CLOSER TO THIS EVENING BEFORE MOST OF THE AREA SEES RAIN REACHING THE GROUND. FRIDAY NIGHT INTO SATURDAY SHOULD BE PERIODS WITH THIS RAIN MOVING THROUGH. BY EARLY SUNDAY MOST MODELS ARE IN AGREEMENT THAT THE MAIN UPPER LOW WILL DRIFT NORTH THROUGH COLORADO AND WYOMING...WHICH WILL PULL A DRY SLOT INTO THE PLAINS. IF THIS HAPPENS...THE BULK OF THE RAIN SHOULD END FOR SUNDAY...ESPECIALLY FOR NEBRASKA COUNTIES. IOWA COUNTIES MAY STILL SEE LINGERING LIGHT SHOWERS MOVE THROUGH ON SUNDAY. AGAIN...MAINLY LIGHT RAIN IS EXPECTED WITH RAINFALL TOTALS UNDER AN INCH FOR THE WEEKEND...AND ALTHOUGH SOME ISOLATED THUNDERSTORMS MAY BE POSSIBLE...MUCH OF THIS RAIN SHOULD BE SANS THUNDER. SATURDAY TEMPERATURES SHOULD BE COOL WITH RAIN IN THE AREA...BUT SUNDAY HIGHS WILL BE WARMER IF THE DRY SLOT BRINGS MORE SUNSHINE. .LONG TERM...(SUNDAY NIGHT THROUGH THURSDAY) ISSUED AT 311 AM CDT FRI MAY 22 2015 MONDAY THERE IS REASONABLY GOOD MODEL AGREEMENT ON THE POSITION OF THE UPPER LOW NEAR THE SOUTH DAKOTA-MONTANA BORDER AREA...BUT DISAGREEMENT ON QPF. ALL MODELS HINT AT SOME QPF DURING THE WEEK AS MORE SHORTWAVES MOVE THROUGH THE PLAINS...SO WILL MAINTAIN THE CHANCE FOR RAIN MONDAY AND INTO THE WEEK. LOWER CHANCES APPEAR TO BE TUE AND WED SO REDUCED POPS A BIT THOSE DAYS. && .AVIATION...(12Z TAFS FOR KOFK...KLNK AND KOMA.) ISSUED AT 630 AM CDT FRI MAY 22 2015 VFR CONDITIONS ARE LIKELY THROUGH THE TAF PERIOD. CLOUDS WILL INCREASE IN COVERAGE...WITH LOWERING CEILINGS THROUGHOUT THE PERIOD. CEILINGS CLOSER TO 12Z MAY COME CLOSE TO HIGH-END MVFR THRESHOLDS...BUT KEPT THEM AT VFR FOR NOW. ALSO COULD BE A PERIOD OF RAIN AT ALL SITES MAINLY AFTER 00Z...BUT GIVEN LOWER CONFIDENCE IN COVERAGE...HAVE OPTED TO KEEP MENTION OUT FOR NOW. WINDS WILL INCREASE FROM LIGHT AND VARIABLE TO SOUTHWEST AT AROUND 10KT...THEN BACK TO SOUTHEASTERLY TONIGHT. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...NONE. IA...NONE. && $$ SHORT TERM...NIETFELD LONG TERM...NIETFELD AVIATION...MAYES

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