401 FXUS63 KLBF 112330 AFDLBF AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NORTH PLATTE NE 630 PM CDT THU SEP 11 2014 .SHORT TERM...(THIS EVENING THROUGH FRIDAY) ISSUED AT 328 PM CDT THU SEP 11 2014 SEVERAL FORECAST CONCERNS TONIGHT AS SURFACE HIGH MOVES SOUTHEAST. THE PRIMARY FORECAST CHALLENGE IS TEMPERATURES WITH HEADLINES ISSUED FOR THE EASTERN PANHANDLE AND NORTHWEST SANDHILLS FOR TONIGHT. MUCH COLDER AIR WILL SETTLE SOUTH AS THE 1037 MB SURFACE HIGH OVER MONTANA MOVES SOUTHEAST. TEMPERATURES HAVE STRUGGLED TO RISE TODAY AS THE SURFACE RIDGE EXTENDS SOUTH ON THE HIGH PLAINS...KEEPING MOISTURE FLOWING WESTWARD. THE UPSLOPE FLOW HAS KEPT THE AIR SATURATED WITH TEMPERATURES AT 18Z IN THE UPPER 30S NORTHWEST TO MIDDLE 40S SOUTHWEST. THIS EVENING A H5 SHORTWAVE TROUGH WILL MOVE SOUTHEAST WITH INCREASING LIFT FOR RAIN CHANCES TO INCREASE THIS EVENING...ESPECIALLY IN THE SOUTHWEST. BEFORE MIDNIGHT CRITICAL TEMPERATURES WILL BE REACHED AND THE RAIN BECOMING MIXED WITH SNOW IN THE WEST...WEST OF HIGHWAY 83. THEN THE FAR NORTHWEST TRANSITIONING TO ALL SNOW OVERNIGHT BEFORE ENDING EARLY MORNING FRIDAY. SNOW ACCUMULATIONS ARE POSSIBLE OVER SHERIDAN COUNTY WHERE UP TO 2 INCHES OF SNOW ACCUMULATION MAY BE SEEN ON GRASSY SURFACES. THEN AN INCH OR LESS FOR NEARBY COUNTIES AS THE MAIN FORCING LIFTS OUT. THE WEATHER CONDITIONS WILL IMPROVE BY MID MORNING FRIDAY WITH CLEARING FROM THE NORTHWEST TO SOUTHEAST AS THE SURFACE HIGH BUILDS SOUTHEAST. THE CLOUDS WILL STEADILY CLEAR FOR MORE SUNSHINE INTO THE AFTERNOON AND DAYTIME HIGHS ONLY IN THE 50S. .LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY) ISSUED AT 328 PM CDT THU SEP 11 2014 THE MAIN CHALLENGE FOR THE FORECAST FRIDAY NIGHT IS TEMPERATURES. WITH CLEAR SKY AND LIGHT WIND...TEMPERATURES IN THE 30S ARE POSSIBLE. THE COLDEST AREAS...ACCORDING TO THE NAM AND GFS STATISTICAL OUTPUT...WOULD BE IN THE PANHANDLE...THE WESTERN SANDHILLS AND IN THE PLATTE RIVER VALLEY. THIS IS SUPPORTED BY THE SURFACE ANALYSIS THIS MORNING WHICH INDICATED THE COLDEST AIR IN THE NORTHWEST QUADRANT OF THE HIGH ON THE PLAINS OF ALBERTA AND WESTERN SASKATCHEWAN. ALSO...THE 500 METER TEMPERATURES FROM THE DETERMINISTIC OUTPUT SUPPORTS THAT RELATIVE LOCATION AS WELL...AND IT INDICATES COLDEST TEMPERATURES IN THE UPPER 30S. ASSUMING THE WIND DECOUPLES...WIDESPREAD SURFACE TEMPERATURES OF 30 TO 35 ARE LIKELY WITH LOCALIZED COLDER TEMPERATURES POSSIBLE IN AREAS PRONE TO COLD AIR BEING TRAPPED SUCH AS RIVER VALLEYS. CLIMATOLOGICALLY...IT IS NOT RARE THAT THE COLDEST TEMPERATURES OCCUR THE SECOND NIGHT OF AN ARCTIC OUTBREAK. THERE ARE A FEW THINGS THAT REDUCE THE LIKELIHOOD OF FROST. WITH THE SURFACE HIGH HAVING MOVED TO SOUTH CENTRAL KANSAS...RETURN FLOW MAY HELP COUNTER THE DIURNAL TEMPERATURE DECREASE AND...IF THE WIND DOES NOT COMPLETELY DECOUPLE...LOWS WILL BE CLOSER TO 40. FINALLY...MOST OF THE AREA IS AT THE 10 PERCENT PROBABILITY OF FIRST FROST OCCURRENCE...SO FROST IS NOT FAVORED CLIMATOLOGICALLY. WEIGHING IT ALL...MY CONFIDENCE IS ABOUT 60 PERCENT THAT FROST WILL OCCUR AND THAT IS HIGH ENOUGH TO INCLUDE AREAS OF FROST IN THE FORECAST FOR THE PANHANDLE...THE WESTERN HALF OF THE SANDHILLS AND THE PLATTE RIVER VALLEY AND PATCHY FROST ELSEWHERE. THE HIGHER PROBABILITY OF FROST IS ROUGHLY ALONG AND NORTH OF INTERSTATE 80 AND ALONG AND WEST OF U.S. HIGHWAY 83. SINCE THERE ARE ALREADY ADVISORIES FOR FROST AND FREEZE TONIGHT... WE WILL DEFER THE DECISION ON ISSUING ANY ADVISORY FRIDAY NIGHT TO THE FRIDAY MORNING ISSUANCE. FOR THE TIME BEING...WE WILL COVER FRIDAY NIGHT AND EARLY SATURDAY WITH A SPECIAL WEATHER STATEMENT. A LOW COMING OUT OF WYOMING AND CROSSING THE PLAINS ALONG THE SOUTH DAKOTA/NEBRASKA STATE LINE WILL GENERATE SOME ISENTROPIC LIFT OF NEARLY SATURATED AIR OVER NORTHERN AND EASTERN NEBRASKA. THIS IS APPARENT WITH THE GFS40 FORECAST FOR THE 300-315K THETA LAYER. THERE IS SOME ELEVATED INSTABILITY INDICATED...SO THUNDERSTORMS ARE POSSIBLE AT LEAST FOR THE AFTERNOON AND EVENING. THEN HIGH PRESSURE WILL FORCE THE PRECIPITATION OUT OF THE AREA MONDAY MORNING. THE NEXT CHANCE FOR PRECIPITATION WILL BE TUESDAY NIGHT AND WEDNESDAY WITH THE BEST CHANCES IN CENTRAL...SOUTH CENTRAL AND SOUTHWEST NEBRASKA AS A WARM FRONT COMES OUT OF THE COLORADO AND WYOMING PLAINS INTO SOUTHWEST AND THEN WESTERN NEBRASKA. THAT SYSTEM IS LIKELY TO BRING PRECIPITATION TO CENTRAL AND NORTH CENTRAL NEBRASKA WEDNESDAY AFTERNOON AND NIGHT AS IT MOVES FARTHER INTO CENTRAL AND WESTERN NEBRASKA. VERY UNSTABLE CONDITIONS ARE EXPECTED IN CENTRAL NEBRASKA WEDNESDAY AFTERNOON AND EVENING. WITH CONVECTIVE POTENTIAL ENERGY AT OR ABOVE 2000J/KG AND 0-6KM SHEAR 35-40KT... STRONG THUNDERSTORMS ARE POSSIBLE. && .AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING) ISSUED AT 629 PM CDT THU SEP 11 2014 CEILING THRESHOLDS WILL VARY BETWEEN IFR AND MVFR AT LEAST UNTIL 03Z...THEN SHOULD PREVAIL AS IFR OVERNIGHT. 3SM -RA TO AT TIMES AS LOW A 1SM AT KLBF UNTIL 12Z...IMPROVING VSBY AND CEILING TO BKN025 AFTER 15Z. AT KVTN...MVFR CEILINGS SHOULD ALSO FALL TO IFR BY 06Z...THEN IMPROVE TO MVFR BY 12Z. && .LBF WATCHES/WARNINGS/ADVISORIES... FROST ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM MDT FRIDAY FOR NEZ022>024-035-056-094. FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM MDT FRIDAY FOR NEZ004. && $$ SHORT TERM...KECK LONG TERM...SPRINGER AVIATION...ROBERG