Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 302311 AFDOAX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE OMAHA/VALLEY NE 611 PM CDT SUN AUG 30 2015 .SHORT TERM...(TONIGHT THROUGH WEDNESDAY) ISSUED AT 318 PM CDT SUN AUG 30 2015 POTENTIAL FOR ONE MORE MORNING OF FOG...THEN WARMER TEMPERATURES AND A COUPLE SMALL RAIN CHANCES THROUGH WEDNESDAY ARE THE PRIMARY FORECAST CONCERNS. ONCE AGAIN THIS MORNING WE SAW AREAS OF FOG AND STRATUS ACROSS A GOOD PORTION OF EASTERN NEBRASKA AND SOUTHWEST IOWA WITH LIGHT FLOW AND TRAPPED MOISTURE UNDER STRONG INVERSION. FOG HAD LIFTED BUT CLOUDS WERE SLOWER TO CLEAR AT EARLY AFTERNOON...BUT STRONGER SOUTHERLY FLOW SHOULD SCOUR THOSE OUT A LITTLE MORE EFFICIENTLY THAN SATURDAY. STRONGER LOW LEVEL FLOW IN RESPONSE TO SHORTWAVE MOVING ACROSS THE NORTHERN PLAINS WILL MAKE FOG LESS OF AN ISSUE ESPECIALLY WEST OF OUR AREA...BUT WEAK SURFACE WINDS TONIGHT/MONDAY MORNING SUGGEST MUCH OF SOUTHEAST NEBRASKA AND WESTERN IOWA WILL AGAIN SEE AT LEAST PATCHY AREAS OF FOG. OVERALL MID LEVEL PATTERN WILL BEGIN AMPLIFICATION PROCESS THROUGH THE MIDDLE OF THE WEEK. LOW/TROUGH IN ALASKA/BRITISH COLUMBIA IS EXPECTED TO SETTLE SOUTH ALONG THE PACIFIC NORTHWEST COAST AS DOWNSTREAM RIDGE BEGINS TO PUMP UP ACROSS THE EASTERN TWO-THIRDS OF THE COUNTRY. DURING THIS TRANSITION...MODEST SOUTHWEST FLOW OVER THE PLAINS WILL PROVIDE A COUPLE OF RAIN POSSIBILITIES AS SHORTWAVES EJECT THROUGH OUR AREA. THE FIRST WILL COME MONDAY NIGHT INTO TUESDAY MORNING. THIS APPEARS WEAKER THAN PREVIOUS MODEL RUNS...BUT WILL STILL INDUCE AREA OF ISENTROPIC UPGLIDE ACROSS NORTHEAST NEBRASKA. NO STRONG CONSENSUS AMONG MODELS OR THEIR ENSEMBLE MEMBERS...SO WILL MAINTAIN A SLIGHT CHANCE FOR CONVECTION THERE MONDAY NIGHT. THE NEXT SHORTWAVE IS SCHEDULED INTO OUR AREA TUESDAY NIGHT INTO WEDNESDAY. AGAIN THIS IS NOT A STRONG IMPULSE BY ANY MEANS...BUT LOW LEVEL JET AND THUS THETA-E ADVECTION IS STRONGER. AND AGAIN THERE IS NO REAL CONSENSUS BETWEEN MODELS AS FAR AS QPF IS CONCERNED. HOWEVER WE WILL SEE DECENT ISENTROPIC UPGLIDE SPREADING FROM CENTRAL INTO EASTERN NEBRASKA OVERNIGHT...LEADING TO MODEST ELEVATED INSTABILITY. AND A SMATTERING OF MODEL OUTPUT CONVERTS THIS INTO THUNDERSTORMS OVER A GOOD PART OF EASTERN NEBRASKA AND SOUTHWEST IOWA LATE TUESDAY NIGHT AND WEDNESDAY. THUS AM INCLINED TO RETAIN A SMALL CHANCE FOR THUNDERSTORMS DURING BOTH OF THOSE PERIODS...THOUGH COVERAGE IS NOT EXPECTED TO BE WIDESPREAD. OTHERWISE A GENERAL INCREASE IN TEMPERATURES IS FORECAST MONDAY THROUGH WEDNESDAY AS LOWER ATMOSPHERE WARMS DUE TO PERSISTENT SOUTHERLY FLOW AND BETTER AFTERNOON MIXING REGIME. HAVE HIGHS INTO THE UPPER 80S FOR THE MOST PART EACH DAY...WITH SOME AREAS SEEING LOWER 90S. HIGHER DEW POINT TEMPERATURES SHOULD ALSO HOLD...SUGGESTING OVERNIGHT LOWS WILL REMAIN WELL INTO THE 60S IF NOT LOWER 70S. .LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY) ISSUED AT 318 PM CDT SUN AUG 30 2015 A SLOW PROGRESSION OF LONGWAVE PATTERN IS EXPECTED DURING THE LONGER TERM PERIOD. GFS/ECMWF AND THEIR ENSEMBLE MEANS ARE FAIRLY SIMILAR IN SHOWING THIS...WITH A FEW SMALLER SCALE DETAILS STILL NEEDING TO BE WORKED OUT WITH TIME. WE WILL START OUT THE LONGER TERM WITH WESTERN TROUGH AXIS EXTENDING FROM BRITISH COLUMBIA INTO NORTHERN CALIFORNIA...WITH AN EASTWARD SHIFT TO A SASKATCHEWAN TO NEVADA LINE BY SUNDAY AFTERNOON. MEANWHILE...BROAD RIDGE FROM THE PLAINS TO THE EAST COAST WILL INITIALLY AMPLIFY FROM OUR AREA INTO THE GREAT LAKES BEFORE STRONGER MID LEVEL FLOW ON FRONT SIDE OF TROUGH WORKS INTO THE PLAINS FOR THE WEEKEND. THUS A MAINLY DRY AND WARM PATTERN IS FORECAST THROUGH THE END OF THE WEEK...WITH INCREASING RAIN CHANCES FOR THE WEEKEND. GFS DIFFERS FROM ECMWF THIS WEEKEND IN THAT IT SHOWS A MUCH MORE PRONOUNCED SUB-TROPICAL MOISTURE PLUME EXTENDING FROM OFF THE NORTHERN BAJA COAST INTO THE PLAINS. THUS IT IS MUCH MORE BULLISH ON PRECIPITATION BOTH SATURDAY AND SUNDAY. THERE IS STILL A LOT OF UNCERTAINTY ON HOW MOISTURE PROFILES WILL PAN OUT...BUT WITH A MAJORITY OF MODEL OUTPUT SUGGESTING DECIDEDLY HIGHER RAIN CHANCES...FEEL FAIRLY CONFIDENT WE WILL SEE SCATTERED STORMS SATURDAY AND SUNDAY. OTHERWISE LOOK FOR HIGHS CLOSE TO 90 BEFORE CLOUDS/PRECIP KEEP TEMPS IN THE 80S FOR THE WEEKEND. && .AVIATION...
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(00Z TAFS FOR KOFK...KLNK AND KOMA.) ISSUED AT 610 PM CDT SUN AUG 30 2015 VFR CONDITIONS EARLY IN THE PERIOD. MVFR FOG COULD REDEVELOP AT ALL SITES 10-14Z. COULD BE TEMPORARILY IFR AT KOMA DURING THIS TIME. SOUTH SOUTHEASTERLY WINDS INCREASE TO 12 TO 20 KNOTS AT KOFK BY 16Z.
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&& .OAX WATCHES/WARNINGS/ADVISORIES... NE...NONE. IA...NONE. && $$ SHORT TERM...DERGAN LONG TERM...DERGAN AVIATION...DEWALD

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