Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 190946 AFDOAX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE OMAHA/VALLEY NE 346 AM CST FRI DEC 19 2014 .SHORT TERM...(TODAY THROUGH SUNDAY) ISSUED AT 303 AM CST FRI DEC 19 2014 DRY BUT CLOUDY APPEARS TO BE THE THEME FOR THIS PERIOD. THE SOUNDING FROM 00Z LAST EVENING AT OAX HAD A SATURATED CLOUD LAYER APPROXIMATELY 5000 FEET THICK...FROM 1500 FEET UP TO 6500 FEET. SURFACE HIGH WAS ANALYZED IN EASTERN IOWA WITH LIGHT SOUTH FLOW OVER THE REGION. HEIGHT GRADIENT AT 850MB WAS LOOSE WITH WEAK FLOW FROM THE SURFACE UP TO 700 MB...THEREFORE ADVECTING THE THICK STRATUS LAYER DOESNT SEEM LIKELY ANYTIME SOON. MODEL CLOUD COVER FROM SHORT TERM MODELS ALSO FAVOR KEEPING THE OVERCAST INTO SATURDAY. LOCATIONS NEAR THE WESTERN EDGE OF THE CLOUDS WILL BE A CHALLENGE IF THERE IS EROSION OR CLOUD ADVECTION IN THOSE AREAS...YIELDING THE POTENTIAL FOR MORE WARMING DURING THE DAY AND COOLING AT NIGHT. FORECAST TEMPERATURES HAVE SOME HINT OF THIS POSSIBILITY BUT GENERALLY THINK CLOUDS WILL KEEP DIURNAL FLUCTUATIONS LIMITED. REGARDING THE CHANCES FOR FOG...DRIZZLE...OR FREEZING DRIZZLE... ONE LACKING INGREDIENT FOR DRIZZLE/FREEZING DRIZZLE IS VERTICAL MOTION TO GENERATE THE PRECIPITATION. THERE IS NO OBVIOUS LIFTING MECHANISM...SO UNTIL THERE ARE SIGNALS FOR MORE VERTICAL WE THINK CHANCES ARE QUITE LOW FOR THAT. LIGHT FOG MAY OCCUR AS CLOUDS LOWER...BUT DENSE FOG DOES NOT LOOK LIKELY. .LONG TERM...(SUNDAY NIGHT THROUGH THURSDAY) ISSUED AT 303 AM CST FRI DEC 19 2014 A POTENT SHORTWAVE WILL HAVE A SIGNIFICANT IMPACT ON OUR WEATHER SUNDAY NIGHT INTO MONDAY NIGHT. MODEL SOLUTIONS ALWAYS HAVE SOME SPREAD AT THIS TIME FRAME OF 72+ HOURS...BUT GIVEN HOW DYNAMIC THIS SYSTEM APPEARS AND THE PROGRESSIVE FLOW...MODELS ARE RATHER SIMILAR WITH THE MAIN UPPER FEATURES AND TRACK OF THE SURFACE LOW. THIS IS A NORTHERN STREAM WAVE THAT DEEPENS AS IT DROPS SOUTHEAST THROUGH THE DAKOTAS AND INTO IOWA...CUTTING OFF AND DIGGING WHILE THE UPSTREAM UPPER RIDGE OVER THE WEST COAST BUILDS. SURFACE LOW MOVES FROM NORTHEAST MONTANA SUNDAY EVENING INTO IOWA BY 18Z MONDAY. COLD FRONT WILL MOVE THROUGH THE FORECAST AREA ON MONDAY. ALTHOUGH NOT NECESSARILY A HEAVY PRECIPITATION SYSTEM...IT DOES WARRANT LIKELY POPS FOR MONDAY ESPECIALLY IN EASTERN COUNTIES. THE WARM SECTOR AREA AHEAD OF THE FRONT WILL HAVE RESPECTABLE MOISTURE AND WARMTH WITH SURFACE DEWPOINTS AROUND 40 AND TEMPERATURES IN THE 40S. COLUMN UP TO 850 MB WILL ALSO BE ABOVE FREEZING SO MUCH OF THE PRECIPITATION WILL FALL AS RAIN. EVENTUALLY THE COLUMN COOLS BEHIND THE FRONT FOR A MIX OR CHANGE TO SNOW...BUT ANY SNOW WOULD BE BRIEF AND LIGHT. ANALOGS INDICATE THAT THESE SYSTEMS TYPICALLY BRING STRONG WINDS BEHIND THE FRONT...AND THIS SYSTEM LOOKS TO BE NO EXCEPTION. 850 WINDS ON ECMWF AND GFS ARE 50 KNOTS LATE MONDAY...WITH GFS ENSEMBLE PROBABILITY OF 850 WINDS GREATER THAN 40 KNOTS AT 100 PERCENT. IN THE WAKE OF THIS LOW...A QUIETER RIDGE PATTERN SETTLES IN FOR TUESDAY AND WEDNESDAY. THURSDAY IS MORE QUESTIONABLE WITH SOME MODELS BRINGING ENERGY FROM A WESTERN US LONGWAVE INTO THE PLAINS...BUT SOME DO NOT. SMALL POPS ARE IN THE FORECAST FOR THURSDAY BUT CONFIDENCE IS VERY LOW. IF THERE IS PRECIPITATION... SOUTHERN AREAS MIGHT BE WARM ENOUGH FOR RAIN. && .AVIATION...(06Z TAFS FOR KOFK...KLNK AND KOMA.) ISSUED AT 1120 PM CST THU DEC 18 2014 STILL EXPECT CEILINGS AND VSBYS TO DECREASE OVERNIGHT. WILL LIKELY SEE AT LEAST TEMPO IFR CEILINGS AND MVFR TO IFR VSBYS INTO MID MORNING. CEILINGS SHOULD INCREASE INTO THE MVFR CATEGORY LATER IN THE DAY WITH POSSIBLY SOME BREAKS IN THE CLOUDINESS. LOW CEILINGS MAY RETURN AGAIN THEN FOR FRIDAY NIGHT. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...NONE. IA...NONE. && $$ SHORT TERM...NIETFELD LONG TERM...NIETFELD AVIATION...MILLER

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