Area Forecast Discussion
Issued by NWS Charleston, WV

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000 FXUS61 KRLX 211845 AFDRLX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON WV 145 PM EST SUN DEC 21 2014 .SYNOPSIS... WEAK HIGH PRESSURE EXITS THIS EVENING. SYSTEM CLIPS THE MOUNTAINS MONDAY. STRONG LOW PRESSURE SYSTEM LIFTS NORTHEAST ACROSS THE OHIO VALLEY THROUGH CHRISTMAS EVE. && .NEAR TERM /THROUGH MONDAY/... HIGH PRESSURE AND LIGHT E FLOW HAD MANAGED TO ERADICATE THE STRATUS ALONG AND E OF THE OHIO RIVER TODAY. THIS HAS ALLOWED FOR DAYTIME HEATING BUT WILL ALSO ALLOW FOR RADIATIVE COOLING THIS EVENING. A WARM WAVE RIDES UP THE SE COAST LATE TONIGHT AND MON. THE QUESTION IS TO WHAT DEGREE THIS FLAT WAVE CAN THROUGH PRECIPITATION BACK INTO THE FCST AREA...AND WHEN WILL SUCH PRECIPITATION REACH THE GROUND GIVEN THE DRY MID LEVEL AIR TO START OUT WITH. MOST OF THE GUIDANCE SUGGESTS TEMPERATURES NEAR OR JUST BELOW FREEZING IN THE NRN WV MOUNTAINS...MAINLY ON THE HIGHER PEAKS AND DOWN THE ERN SLOPES INTO THE GREENBRIER VALLEY. MODELS DEPICT A WARM LAYER ALOFT WITH TEMPERATURES 1-2C IN THE H925-H85 LAYER. THIS SUGGESTS MELTING OF SNOW WHICH MEANS THERE COULD BE SLEET AND SNOW MIXED IN WITH ANY FREEZING RAIN. TEMPERATURES IN CLOUD SUPPORTIVE OF ICE CRYSTALS ARE LOST EARLY ON AS THE MOIST LAYER BECOMES MORE SHALLOW. THIS WOULD TEND THE PRECIPITATION BACK TOWARD FREEZING RAIN OR FREEZING DRIZZLE. THIS LEAVES THE TIMING OF THE ARRIVAL OF PRECIPITATION CRUCIAL AS TEMPERATURES SLOWLY CLIMB ABOVE FREEZING IN THE GREENBRIER VALLEY. CURRENT GRID DEPICTION IS FOR POPS CLIMBING ABOVE 50 YIELDING MEASURABLE QPF AS TEMPERATURES CLIMB. THIS LIMITS ICE ACCRETION TO AT MOST A HUNDREDTH AND NOT VERY WIDESPREAD. THE SREF DOES INTERSECT HIGH POPS WITH POCKETS OF HIGH PROBABILITIES FOR SFC TEMPERATURES AT OR BELOW FREEZING MON MIDDAY INTO THE AFTERNOON. COORD WITH WPC/WWD-PBZ-LWX-RNK ON ISSUANCE ADV FOR FREEZING RAIN POCAHONTAS COUNTY 11-17Z. THE REMAINDER OF THE FCST AREA SEES A RETURN OF CLOUD COVER TONIGHT...SETTING THE STAGE FOR ANOTHER GREY DECEMBER DAY...ALTHOUGH THE CLOUDS DO DECREASE BEHIND THE SYSTEM MON AFTERNOON. USED NEAR TERM...IN PARTICULARLY THE WRFNMM...RUC AND THE HRRR FOR TEMPERATURES TONIGHT AND NAM-BASED VALUES FOR THOSE ON MON...WHICH SHOULD FEATURE A MILDER AFTERNOON. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/... PESKY MOISTURE FROM WEAK SURFACE LOW ALONG THE E COAST AS WELL AS WAA WILL COMBINE FOR LIGHT PRECIP MOVING UP THE MOUNTAINS MONDAY MORNING. THERMAL PROFILES CONTINUE TO INDICATE A BRIEF ONSET OF FZRA WITH PSBL SLEET...BEFORE CHANGING OVER TO LIQUID BY MIDDAY AND PULLING OUT IN THE AFTERNOON. TEMPS SHOULD RECOVER BEHIND THIS SYSTEM FOR THE AFTERNOON WITH AID OF DEVELOPING SE DOWN SLOPE FLOW. SOME PEAKS OF SUN IS PSBL S OF I64 LATE IN THE DAY. AS THE SE FLOW INCREASES MONDAY NIGHT AND WAA ALOFT CONTINUES...THINK THE RIDGES WILL SEE RISING TEMPS OVERNIGHT AMID INCREASING CLOUDS OVER THE AREA. THERE HAS BEEN A NOTICEABLE TREND IN THE MODELS REGARDING THE MIDWEEK SYSTEM. MOST DELAY PHASING AND RAPID PRESSURE DROPS UNTIL INTO CANADA. WHAT THIS DOES IS TO SLOW THE FRONT/NOW ABOUT 6 HRS/ AND LESSEN THE MAGNITUDE OF SENSIBLE WX EFFECTS FROM THIS SYSTEM...INCLUDING POST FRONTAL CAA...SURFACE TEMPS...AND EXTENT AND DURATION OF SHSN BEHIND THE FRONT. HAVE MODIFIED THE GRIDS TO INCORPORATE THIS TREND IN THE MODEL SUITE AND DELAYED CHANGEOVER TO SHSN. WITH THE SLOWER TIMING OF THE FRONT...LOOKS LIKE CHRISTMAS EVE MAY BE JUST AS WARM AS TUESDAY WITH LOW TO MID 60S POSSIBLE BOTH DAYS. STILL THINKING TUESDAY THE DAYLIGHT HRS ON TUESDAY IS DRY E OF THE OH RIVER WITH SHRA MOVING INTO SE OH AND NE KY IN THE AFTERNOON WHICH THEN OVERSPREADS REMAINDER OF AREA TUESDAY NIGHT AND WEDNESDAY. IT WILL BE A MILD TUESDAY NIGHT DESPITE THE SHRA AS LOW LEVEL SE FLOW REACHES ITS MAXIMUM. WHAT STILL LOOKS LIKELY ARE THE STRONG GUSTY WINDS CHRISTMAS EVE NIGHT AND CHRISTMAS DAY ITSELF...WITH 30 KTS PSBL ESPECIALLY ACROSS N ZONES AND IN THE MOUNTAINS WHERE EVEN HIGHER GUSTS ARE EXPECTED. && .LONG TERM /THURSDAY THROUGH SATURDAY/... ACTIVE WEATHER PATTERN CONTINUES IN THE LONG TERM PERIOD...WITH A DEEPENING UPPER TROUGH ACROSS THE CENTRAL PLAINS AT THE BEGINNING OF PERIOD...WITH A SURFACE LOW MOVING NORTHEAST OUT OF THE GULF STATES TOWARDS THE REGION. STRONG SOUTHERLY WINDS WILL DEVELOP OUT AHEAD OF THE SYSTEM...WITH GOOD MOISTURE TRANSPORT INTO THE AREA AS A RESULT. THIS IS A STRONG SYSTEM...WITH STRONG PRESSURE FALLS/BOMBOGENESIS AS THE LOW MOVES TOWARDS THE REGION. COLD FRONT STILL PROGGED TO MOVE THROUGH THE AREA WEDNESDAY...WITH FALLING TEMPERATURES...STRONG GUSTY WINDS ALONG AND BEHIND THE FRONT DUE TO TIGHT PRESSURE GRADIENT...AND POTENTIAL FOR STRONG WINDS ALOFT TO MIX DOWN...AND EVEN A SLIGHT CHANCE FOR THUNDER...MAINLY ACROSS THE WEST...AS THE FRONT MOVES INTO THE REGION. STARTING TO LOOK MORE AND MORE LIKE WINTER PRECIPITATION WILL NOT BE A HUGE HAZARD WITH THIS SYSTEM...DUE TO THE OVERALL SPEED...AND THE FACT THAT BY THE TIME ENOUGH COLD AIR IS IN PLACE...BULK OF MOISTURE SHOULD HAVE EXITED. IN ADDITION...STILL QUITE A BIT OF UNCERTAINTY AS TO HOW MUCH WILL ACTUALLY BE ABLE TO STICK TO THE GROUND IF GROUND TEMPERATURES ARE TOO WARM AS TEMPERATURES WILL RISE INTO THE 50S OUT AHEAD OF THE SYSTEM. HOWEVER...WILL STILL SEE A CHANGE OVER TO SNOW WEDNESDAY NIGHT INTO THURSDAY...ALONG WITH FALLING TEMPERATURES. WILL CONTINUE TO MAINTAIN HWO. ON THURSDAY...UPPER LOW LIFTS NORTH ACROSS CANADA...BECOMING NEARLY STACKED WITH SURFACE LOW. STILL A CHANCE FOR SOME LIGHT SNOW SHOWER ACTIVITY ON THURSDAY...BUT WILL GRADUALLY SEE A DRYING TREND FROM SOUTH TO NORTH AS THE SYSTEM PULLS AWAY. ANOTHER FRONT APPROACHES LATE IN THE EXTENDED. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... LIGHT E FLOW ON S SIDE OF HIGH PRESSURE HAD FINALLY ERADICATED THE MVFR TO HIGH IFR STRATOCU...WITH ALL SITES VFR TO START THE FCST. THIS WILL HOLD THROUGH SUNSET. A WEAK WAVE OF LOW PRESSURE MOVES UP ALONG THE SE COAST OVERNIGHT TONIGHT AND MON. THIS WILL SPILL CLOUDS BACK INTO THE AREA OVERNIGHT...WITH RAIN LIKELY IN THE MOUNTAINS...MAINLY ON THE EASTERN SLOPES...WHERE SNOW...SLEET AND FREEZING RAIN ARE LIKELY TO BE MIXED IN THROUGH THE MORNING HOURS. MVFR TO HIGH IFR STRATOCU SHOULD RETURN TO BKW TONIGHT...WITH A MORE WIDESPREAD MVFR DECK DEVELOPING BY MON MORNING. CLOUD HEIGHTS SHOULD INCREASE MON AFTERNOON AS CLOUD AMOUNT LOWERS. LIGHT AND VARIABLE TO E SFC FLOW WILL BECOME LIGHT SE TONIGHT AND REMAIN SO ON MON. SE WINDS WILL BECOME A BIT GUSTY ON THE RIDGES INCLUDING BKW OVERNIGHT INTO MON. FLOW ALOFT WILL REMAIN LIGHT S TO SW. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 18Z MONDAY... FORECAST CONFIDENCE: MEDIUM. ALTERNATE SCENARIOS: TIMING AND LOCATION OF A MVFR STRATUS DECK COULD VARY CONSIDERABLY OVERNIGHT INTO MON. EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY OF WFO FORECAST TO AVAILABLE MODEL INFORMATION: H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS. L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. UTC 1HRLY 18 19 20 21 22 23 00 01 02 03 04 05 EST 1HRLY 13 14 15 16 17 18 19 20 21 22 23 00 CRW CONSISTENCY M M M M H H H H H H H H HTS CONSISTENCY H M M M H H H H H H H H BKW CONSISTENCY H H H H H M M M M M L L EKN CONSISTENCY M M H H H H H H H H H H PKB CONSISTENCY M M M M M M M H H H H H CKB CONSISTENCY M M M M M M H H H H H H AFTER 18Z MONDAY... IFR POSSIBLE IN MOUNTAINS INTO MON AFTERNOON IN A WINTRY MIX. IFR POSSIBLE IN RAIN TUE NT INTO WED...CHANGING TO SNOW SHOWERS WED NT...AS AN INTENSE LOW PRESSURE CENTER PASSES. && .RLX WATCHES/WARNINGS/ADVISORIES... WV...FREEZING RAIN ADVISORY FROM 6 AM TO NOON EST MONDAY FOR WVZ046. OH...NONE. KY...NONE. VA...NONE. && $$ SYNOPSIS...TRM/RPY/SL/30 NEAR TERM...TRM SHORT TERM...30 LONG TERM...SL AVIATION...TRM

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