AFDPDT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PENDLETON OR 938 PM PST MON JAN 17 2022 UPDATED AVIATION DISCUSSION. UPDATE...AFTER SEEING A BRIEF BREAK IN THE FOG AND LOW STRATUS THIS AFTERNOON, LIGHT NORTHWEST WINDS HAVE PUSHED THE FOG BACK UP AGAINST THE FOOTHILLS OF THE BLUES WHERE VISIBILITIES ARE CURRENTLY 1/4SM WITH FREEZING FOG OBSERVED. ELSEWHERE, THE LOW STRATUS HAS BEEN MORE PERSISTENT AND IS STILL APPARENT ON SATELLITE IMAGERY ACROSS THE YAKIMA AND KITTITAS VALLEYS, THE COLUMBIA BASIN, AND PORTIONS OF CENTRAL AND NORTHEAST OREGON. WITH LITTLE WIND TO MIX OUT THE INVERSION IN THE AFOREMENTIONED AREAS, DETERIORATING CEILINGS WITH MIST AND FOG WILL LIKELY CONTINUE OVERNIGHT. OTHERWISE, SOME LIGHT RADAR ECHO ASSOCIATED WITH A WEAK SHORTWAVE IS PRESENT ACROSS FAR SOUTHEAST WASHINGTON AND NORTHEAST OREGON. HAVE MADE SMALL CHANGES TO THE FORECAST THIS EVENING TO ACCOUNT FOR CURRENT TRENDS. PLUNKETT/86 SHORT TERM...TONIGHT THROUGH WEDNESDAY NIGHT...AN UPPER RIDGE THAT HAS BEEN OVER THE REGION DURING THE PAST FEW DAYS WILL WEAKEN TONIGHT AS A WEATHER DISTURBANCES MOVES INTO THE RIDGE. THIS WILL ALLOW FOR SOME PRECIPITATION TO MOVE INTO MAINLY THE CASCADES AND THE NORTHEAST MOUNTAINS. MOST OF THE PRECIPITATION WILL BE RAIN DUE TO HIGH SNOW LEVELS, BUT THE HIGHER PEAKS AND RIDGES WILL RECEIVE SOME LIGHT SNOW. THERE WILL ALSO BE THE POSSIBILITY OF SOME LIGHT FREEZING RAIN IN SOME SHELTERED VALLEYS, AND ALONG THE BASE OF THE BLUE MOUNTAINS IN THE FOOTHILLS WHERE COLD AIR WILL BE TRAPPED. HOWEVER, ICE ACCUMULATIONS WILL BE VERY LIGHT AND WILL LIKELY ONLY LEAVE A LIGHT COATING OF ICE, WHICH WOULD NOT BE ENOUGH FOR ANY KIND OF HIGHLIGHTS DUE TO FREEZING RAIN. THIS WEATHER SYSTEM WILL BE WEAK, BUT IT WILL PROVIDE SOME MIXING OF THE FOG/STRATUS, BUT NOT ENOUGH TO SCOUR OUT THE LOWER ELEVATION`S TRAPPED COLD AIR AND INVERSIONS WHERE THERE IS WIDESPREAD STRATUS AND SOME FOG. A FREEZING FOG ADVISORY WILL BE ISSUED AGAIN TONIGHT FOR THE YAKIMA/KITTITAS VALLEYS, NORTH CENTRAL OREGON, ALL OF THE BLUE MOUNTAIN FOOTHILLS AND WALLOWA COUNTY. HOWEVER, DENSE FREEZING FOG WILL MAINLY BE ABOVE ELEVATIONS OF 1200-1400 FEET, WHERE THE STRATUS CLOUD LAYER MEETS THE HIGHER TERRAIN. ON WEDNESDAY, AND WEDNESDAY NIGHT, AN AMPLIFIED UPPER RIDGE WILL BUILD OFF THE COAST AND MOVE INLAND. IT WILL INITIALLY BRING JUST A DRY NORTHERLY FLOW, BUT THEN ANOTHER WEATHER SYSTEM, WHICH WILL BE STRONGER THAN TUESDAY`S SYSTEM WILL MOVE OVER THE TOP OF THE RIDGE AND THEN DROP DOWN THE EAST SIDE OF THE RIDGE AND ACROSS THE FORECAST AREA BY WEDNESDAY NIGHT GOING INTO THE EXTENDED PERIOD. THERE ARE SOME MODEL DIFFERENCES WITH THE DETERMINISTIC MODELS, BUT THE ENSEMBLE SREF AND GEFS ARE ALSO SHOWING THIS TROUGH, BUT NOT AS AMPLIFIED OR AS STRONG AS THE DETERMINISTIC MODELS. THEREFORE, CONFIDENCE IN THE FORECAST IS LOWERED, AND WHILE THIS SYSTEM WILL BRING A BETTER CHANCE OF PRECIPITATION AND WIND, THE PRECIPITATION AMOUNTS HAVE A GREATER UNCERTAINTY, AND WIND SPEEDS ALSO WILL HAVE A GREATER UNCERTAINTY. AS A RESULT, THERE IS MORE UNCERTAINTY AS TO IF THERE WILL BE ENOUGH MIXING TO COMPLETELY SCOUR OUT THE LOWER ELEVATION`S TRAPPED COLD AIR, INVERSIONS AND THE STRATUS/FOG, AS WELL AS HOW MUCH PRECIPITATION FALLS. FOR NOW WILL JUST GO WITH LIGHT ACCUMULATIONS OF ANY SNOW, RAIN OR ICE, AND INCREASE WINDS, BUT NOT ENOUGH TO COMPLETELY SCOUR OUT THE TRAPPED COLD AIR IN THE LOWER ELEVATIONS. 88 LONG TERM...THURSDAY THROUGH SUNDAY...THE EXTENDED PERIOD BEGINS AS AN UPPER LEVEL RIDGE FLATTENS AND SHIFTS EAST IN RESPONSE TO AN INCOMING SHORTWAVE TROUGH. THIS WILL PROVIDE WIDESPREAD RAIN AND HIGH MOUNTAIN SNOW THROUGH MUCH OF THE DAY THURSDAY BEFORE CONFINING PRECIPITATION TO MOUNTAIN ZONES LATER IN THE EVENING HOURS. WARMER AIR WILL BE ADVECTED AHEAD OF THIS SYSTEM, ALLOWING FOR SNOW LEVELS TO HOVER BETWEEN 6000-7000 FEET ON THURSDAY. HIGH TEMPERATURES WILL ALSO EXHIBIT AN INCREASE THURSDAY, AS HIGHS WILL BREAK INTO THE LOW TO MID 50S ACROSS THE LOWER COLUMBIA BASIN. BREEZY WINDS WILL ACCOMPANY THIS SHORTWAVE AS SOUTHERLY WINDS AHEAD OF THE SURFACE FRONT WILL ALLOW FOR A SLIGHT DOWNSLOPING EVENT TO OCCUR. THIS WILL ALLOW WIND GUSTS OF 20-30 MPH ALONG THE EAST SLOPES OF THE WASHINGTON CASCADES, 20-25 MPH THROUGH THE GRANDE RONDE VALLEY, AND 10-20 MPH GUSTS ALONG THE BLUE MOUNTAINS. A STRONG UPPER LEVEL RIDGE THEN REBUILDS OFFSHORE BEFORE INFILTRATING INTO THE PACIFIC NORTHWEST ON FRIDAY, WHICH STRENGTHENS AND EXTENDS THROUGH THE WEEKEND. THE RETURN OF AN UPPER LEVEL RIDGE DOMINATED WEATHER PATTERN WILL AGAIN PROVIDE THE NECESSARY INGREDIENTS FOR VALLEY INVERSIONS AND OVERNIGHT AND MORNING FOG TO DEVELOP THROUGH THE BASIN AND PROTECTED VALLEYS OVER THE WEEKEND. TEMPERATURES ALSO STABILIZE INTO THE WEEKEND AS HIGHS HOVER IN THE LOW TO MID 40S AND LOWS IN THE MID TO UPPER 20S FOR LOWER ELEVATIONS. GUIDANCE IS IN GOOD AGREEMENT WITH THE OVERALL PATTERN THROUGH THE EXTENDED PERIOD, WITH SLIGHT DIFFERENCES IN RIDGE STRENGTH AND LOCATION. THE ECMWF STILL INCURS A STRONGER AND QUICKER INFILTRATING RIDGE OVER THE WEEKEND, WHICH ACTUALLY BECOMES POSITIVELY TILTED ON SUNDAY VERSUS THE GFS WHICH IS SLOWER, LATER, AND BECOMES NEGATIVELY TILTED. THIS DOES NOT REFLECT MUCH DIFFERENCE BETWEEN OVERALL OUTCOMES, WITH THE EXCEPTION OF COOLER TEMPERATURES AND BETTER VALLEY INVERSION EFFICIENCY ON SUNDAY VIA THE ECWMF. THE EFI HIGHLIGHTS SOME ENSEMBLE MEMBERS PICKING UP ON THE ELEVATED WINDS ON THURSDAY, BUT AT THIS TIME CONFIDENCE IS STILL MARGINAL. ENSEMBLE VARIANCE IS RATHER LOW THROUGH THE PERIOD WHEN OBSERVING THE 500MB EOF PATTERNS, AS CLUSTERS LEAN TO A STRONGER AND MORE INFILTRATING RIDGE AS SUGGESTED WITH THE ECMWF. THE CLUSTER PHASE SPACE ALSO PROVIDES MORE CONFIDENCE IN THE ECMWF SCENARIO, THUS FOG RETURNING LATER IN THE EXTENDED PERIOD IS REFLECTED IN THE CURRENT FORECAST, ALONG WITH COOLER TEMPERATURES ON SUNDAY. 75 AVIATION...06Z TAFS...VARIABLE CONDITIONS ARE CURRENTLY BEING OBSERVED AT TAF SITES; VFR AT KDLS/KRDM/KBDN WITH ONLY FEW-SCT CIRRUS, LIFR AT YKM/PSC WITH A LOWERING STRATUS DECK OF OVC004, AND VLIFR AT KPDT/KALW DUE TO A SHALLOW LAYER OF 1/4SM TO 1/2SM FOG WITH VV001 TO VV002. EXPECTING CONDITIONS TO REMAIN FAIRLY STABLE INTO MORNING AT KPDT/KALW WHILE FOG MAY DEVELOP AT KYKM/KPSC. OTHERWISE, CEILINGS WILL LOWER AT KDLS/KRDM/KBDN OVERNIGHT THROUGH MORNING TO AROUND 2-5KFT AS A WEAK SYSTEM APPROACHES. WINDS WILL GENERALLY BE LIGHT THROUGH THE PERIOD. PLUNKETT/86 && .PRELIMINARY POINT TEMPS/POPS... PDT 29 48 33 45 / 0 20 10 10 ALW 31 47 34 46 / 20 20 20 10 PSC 31 43 32 43 / 0 10 0 0 YKM 27 42 29 41 / 10 10 10 10 HRI 32 47 32 43 / 0 10 10 10 ELN 30 41 29 39 / 10 10 10 10 RDM 29 48 31 48 / 0 10 10 10 LGD 26 39 31 41 / 10 20 20 10 GCD 27 44 32 44 / 0 20 20 10 DLS 35 46 36 45 / 10 20 10 10 && .PDT WATCHES/WARNINGS/ADVISORIES... OR...FREEZING FOG ADVISORY UNTIL NOON PST TUESDAY FOR ORZ050-507-508- 510. WA...FREEZING FOG ADVISORY UNTIL NOON PST TUESDAY FOR WAZ026-027-029- 521. &&