AFDSEW AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SEATTLE WA 412 AM PST WED JAN 17 2024 .SYNOPSIS...UNSETTLED CONDITIONS REMAIN THROUGH MUCH OF THE WEEK AHEAD AS A SERIES OF DISTURBANCES BRING ROUNDS OF PRECIPITATION. A COLD FRONT ON WEDNESDAY WILL MAINTAIN COOLER AND WET CONDITIONS AHEAD OF A SERIES OF WARM FRONTS THAT WILL MAINTAIN PRECIPITATION INTO EARLY NEXT WEEK. WINTRY PRECIPITATION WILL CONTINUE IN THE MOUNTAINS WITH THE POTENTIAL LINGERING IN PARTS OF THE LOWLANDS FOR THE NEXT FEW DAYS. TEMPERATURES WILL SLOWLY WARM UP THROUGH THE WEEK, BRINGING A RETURN TO NORMAL TEMPERATURES AND A MORE TYPICAL PATTERN OF RAIN IN THE LOWLANDS. && .SHORT TERM /TODAY THROUGH FRIDAY/...THE LOW PRESSURE SYSTEM OFFSHORE BROUGHT A MIX OF PRECIPITATION TYPES TO THE REGION OVERNIGHT AS THE MAIN BAND OF PRECIP LIFTED NORTH ACROSS THE REGION. AT THIS POINT, STILL SEEING PRETTY WIDESPREAD SHOWERS ACROSS THE REGION, WITH TEMPERATURES GENERALLY WITHIN A FEW DEGREES ON EITHER SIDE OF THE FREEZING MARK FROM THE LOWLANDS FROM SNOHOMISH COUNTY SOUTHWARD. SOME OF THE WARMEST TEMPERATURES REMAIN ALONG THE COAST AND THE SOUTHERN PORTIONS OF THE AREA WHERE SOUTHERLY WINDS HAVE BEGUN TO SPREAD WARMER AIR BOTH ALOFT AND AT THE SURFACE, WHILE POCKETS OF COOLER AIR REMAIN TRAPPED NEAR THE SURFACE. MEANWHILE, SNOW CONTINUES ACROSS PORTIONS OF WHATCOM AND SKAGIT COUNTIES, AS WELL AS THE SAN JUAN ISLANDS AND OF COURSE UP IN THE MOUNTAINS. THE REST OF THE MORNING REMAINS A BIT TRICKY AS GRADUAL WARMING IS STILL EXPECTED WITH MANY AREAS JUST SEEING RAIN, BUT FOR THE SPOTS WITH ENOUGH SHALLOW SUB-FREEZING AIR AT THE SURFACE IT MAY REMAIN A BIT SLICK WITH LINGERING ICE FROM FREEZING RAIN. THOSE WHO NEED TO BE OUT EARLY THIS MORNING SHOULD EXPECT CONDITIONS TO VARY WITH MANY SPOTS JUST WET AND OTHER REMAINING SLICK. UNTREATED AND RESIDENTIAL SIDE STREETS, SIDEWALKS, AND ELEVATED SURFACES ARE MOST LIKELY TO REMAIN ICY, BUT AGAIN THIS IS HIGHLY VARIABLE. A FEW AREAS WORTH CALLING ATTENTION TO FOR THE MORNING: THE FAR NORTHERN PARTS OF THE AREA (WHATCOM/SKAGIT/SAN JUAN COUNTIES), AS WELL AS SOME AREAS ALONG THE STRAIT OF JUAN DE FUCA AND NORTHERN ISLAND COUNTY, WILL LIKELY SEE SNOW CONTINUE THIS MORNING AS NORTHEAST WINDS CONTINUE TO MAINTAIN A DEEPER LAYER OF COLD AIR. SIMILARLY, EAST WINDS THROUGH THE CASCADE GAPS MAY SLOW THE SCOURING OF COLD AIR IN PLACES SUCH AS NORTH BEND AND THE CASCADE FOOTHILLS. A RELATIVE LULL IN PRECIPITATION IS EXPECTED EARLY THIS MORNING FOR MOST, BEFORE ANOTHER ROUND MOVES THROUGH LATE THIS MORNING TOWARD MIDDAY. EXPECT THAT SOME SHOWERS MAY LINGER LATER THIS AFTERNOON NEAR THE TYPICAL CONVERGENCE ZONE LOCATIONS, BUT THIS TOO LOOKS SHORT-LIVED GIVEN ANOTHER SWITCH IN THE WIND PATTERN AHEAD OF THE NEXT FRONTAL SYSTEM. THIS WARM FRONT LIFTING NORTHWARD WILL BRING ANOTHER ROUND OF PRECIPITATION AND PERHAPS MORE IN THE WAY OF SNOW OR FREEZING RAIN, BUT THIS GENERALLY LOOKS TO BE A LESS FAVORABLE SET-UP. NEVERTHELESS, THIS AGAIN LOOKS VERY TEMPERATURE AND TIMING DEPENDENT. HOOD CANAL AND THE LOWLANDS NORTH OF SEATTLE APPEAR THE MOST LIKELY TO SEE A MIXED PRECIPITATION TYPE. THE PATTERN REMAINS RATHER ACTIVE WITH YET ANOTHER ROUND OF MOISTURE MOVING INTO THE REGION LATE THURSDAY INTO FRIDAY, BUT FINALLY WE`VE SEEN ENOUGH OF A WARMING AIR MASS FOR SNOW LEVELS TO CONTINUE TRENDING HIGHER AND THE THREAT OF WINTER PRECIP INCREASINGLY CONFINED TO THE CASCADES. WITH EASTERLY FLOW CONTINUING NEAR THE CASCADES THOUGH, WILL NEED TO KEEP AN EYE ON POTENTIAL FREEZING RAIN NEAR THE PASSES AS SNOW LEVELS RISE BUT COLDER AIR REMAINS USHERED WESTWARD. OTHERWISE, HIGH TEMPERATURES BEGIN TO TREND INTO THE 40S AND A COLD RAIN BECOMES THE DOMINANT WEATHER. AS MENTIONED IN THE HYDRO SECTION BELOW, WIDESPREAD RIVER FLOODING ISN`T EXPECTED, BUT THE SKOKOMISH MAY BEGIN TO RISE. SEE MORE DETAILS IN THAT SECTION. CULLEN .LONG TERM /SATURDAY THROUGH TUESDAY/...TROUGHING RETURNS TO THE PACIFIC NORTHWEST FOR THE WEEKEND AND GENERALLY CONTINUING INTO THE START OF NEXT WEEK. THIS WILL BRING CONTINUED ROUNDS OF PRECIPITATION, BUT WITH SNOW LEVELS GRADUALLY TRENDING HIGHER AND TEMPERATURES ON AN UPWARD TREND. EXPECT TEMPERATURES CLOSE TO NORMAL FOR MUCH OF THE LONG TERM. SNOW LEVELS IN THE MOUNTAINS WILL BE RISING TO AROUND 4000-4500 FT BUT EASTERLY FLOW WILL KEEP TEMPERATURES AT THE PASSES NEAR OR BELOW FREEZING WITH A WINTRY MIX EXPECTED AT TIMES. ENSEMBLE GUIDANCE FOR NEXT WEEK CONTINUES TO FAVOR AT LEAST SOME UNSETTLED WEATHER THROUGH MIDWEEK. && .AVIATION...WEST TO NORTHWEST FLOW ALOFT WILL CONTINUE TODAY AS AN UPPER TROUGH SLIDING SOUTHWARD DOWN THE SOUTHERN BRITISH COLUMBIA COAST SHIFTS INLAND ACROSS THE REGION THIS AFTERNOON. THE LOW LEVEL FLOW REMAINS OFFSHORE, BUT IS EXPECTED TO TURN WEAKLY ONSHORE FOR A BRIEF PERIOD THIS AFTERNOON AS A WEAK FRONTAL BOUNDARY MOVES INLAND. CEILINGS WILL REMAIN LOW MVFR OR IFR THROUGHOUT THE DAY. COLD AIR TRAPPED ACROSS THE INTERIOR OF WESTERN WASHINGTON WILL CONTINUE TO PRODUCE A WINTRY MIX OF PRECIPITATION NORTH OF A KSEA-KPWT LINE THIS MORNING. HOWEVER, THE PRECIPITATION WILL REMAIN AS SNOW IN THE VICINITY OF KBLI. MOST AREAS WILL PRIMARILY SEE RAIN AFTER 16Z WITH THE EXCEPTION OF AROUND KBLI WHERE CONTINUED FRASER OUTFLOW WILL SUPPORT ADDITIONAL SNOWFALL. KSEA...SURFACE OBS SOUTH OF THE TERMINAL INDICATE THAT A SUBTLE INTRUSION OF WARMER NEAR SURFACE AIR IS UNDERWAY. THUS, FEEL THAT PRIMARY PRECIPITATION TYPE FOR THE TAF PERIOD WILL NOW BE PRIMARILY RAIN. CEILINGS WILL REMAIN IFR OR LOW MVFR THROUGH THE FORECAST PERIOD WITH SURFACE VSBYS OCCASIONALLY REDUCED TO 3-5SM. SURFACE WINDS E/SE 4 TO 7 KNOTS BECOMING SOUTHERLY 6 TO 11 KNOTS THIS AFTERNOON. 27 && .MARINE...A SURFACE LOW AND ASSOCIATED FRONT WILL SHIFT ONSHORE BY THIS AFTERNOON. SMALL CRAFT ADVISORIES FOR THE COASTAL WATERS AND WEST/CENTRAL STRAIT REMAIN IN EFFECT AHEAD OF THIS FEATURE. ANY TRANSITION TO ONSHORE FLOW BEHIND IT WILL BE RATHER WEAK AND BRIEF AS OFFSHORE GRADIENTS WILL QUICKLY INCREASE TONIGHT AHEAD OF BROAD SURFACE LOW AND ASSOCIATED WARM FRONT SWEEPING ACROSS THE OFFSHORE WATERS. GALE WATCHES WILL BE POSTED FOR THE COASTAL WATERS AND WEST/CENTRAL STRAIT AS EAST/SOUTHEASTERLIES LOOK TO BECOME RATHER STRONG OVER THE WATERS AS THE SYSTEM APPROACHES. WE WILL LIKELY NEED TO EXPAND HEADLINES TO MORE OF THE INTERIOR WATERS BY THURSDAY NIGHT AND FRIDAY AS THIS FRONTAL FEATURE LIFTS ONSHORE. THE PATTERN WILL REMAIN QUITE ACTIVE INTO THE COMING WEEKEND AS A MEAN UPPER TROUGH OVER THE NORTHEAST PACIFIC SENDS A SERIES OF FRONTS ACROSS AREA WATERS. COMBINED SEAS OVER THE COASTAL WATERS WILL BUILD TO AROUND 10 FEET BY TONIGHT AND LIKELY REMAIN NEAR OR ABOVE THAT THRESHOLD INTO THE WEEKEND. 27 && .HYDROLOGY....INCREASING RAIN OVER THE SOUTHERN SLOPES OF THE OLYMPICS COMBINED WITH LOW ELEVATION SNOW MELT COULD PUSH THE SKOKOMISH RIVER TO MINOR FLOOD STAGE LATE THURSDAY INTO FRIDAY. WITH AN ACTIVE PATTERN AHEAD, RIVER FLOODING ALONG THE SKOKOMISH IS POSSIBLE THROUGHOUT THE UPCOMING WEEKEND. WILL ALSO NEED TO MONITOR RIVER LEVELS ALONG THE NOOKSACK RIVER IN WHATCOM COUNTY AS THE WARM UP OCCURS WITH THE POTENTIAL FOR ICE JAM FLOODING. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...WINTER WEATHER ADVISORY UNTIL 10 AM PST THIS MORNING FOR SAN JUAN COUNTY. WINTER STORM WARNING UNTIL 10 PM PST THIS EVENING FOR WESTERN WHATCOM COUNTY. WINTER WEATHER ADVISORY UNTIL 7 AM PST THIS MORNING FOR ADMIRALTY INLET AREA-EAST PUGET SOUND LOWLANDS-EVERETT AND VICINITY-WESTERN SKAGIT COUNTY. WINTER WEATHER ADVISORY UNTIL 6 AM PST EARLY THIS MORNING FOR BELLEVUE AND VICINITY-BREMERTON AND VICINITY-HOOD CANAL AREA-SEATTLE AND VICINITY-TACOMA AREA. WINTER WEATHER ADVISORY UNTIL 7 PM PST THIS EVENING FOR EASTERN STRAIT OF JUAN DE FUCA-OLYMPICS. WINTER STORM WARNING UNTIL 7 PM PST THIS EVENING FOR WESTERN STRAIT OF JUAN DE FUCA. WINTER STORM WARNING UNTIL 1 PM PST THURSDAY FOR WEST SLOPES NORTH CASCADES AND PASSES-WEST SLOPES NORTH CENTRAL CASCADES AND PASSES-WEST SLOPES SOUTH CENTRAL CASCADES AND PASSES. PZ...SMALL CRAFT ADVISORY UNTIL 4 PM PST THIS AFTERNOON FOR COASTAL WATERS FROM CAPE FLATTERY TO JAMES ISLAND 10 TO 60 NM- COASTAL WATERS FROM CAPE FLATTERY TO JAMES ISLAND OUT 10 NM- COASTAL WATERS FROM JAMES ISLAND TO POINT GRENVILLE 10 TO 60 NM-COASTAL WATERS FROM JAMES ISLAND TO POINT GRENVILLE OUT 10 NM-COASTAL WATERS FROM POINT GRENVILLE TO CAPE SHOALWATER 10 TO 60 NM-COASTAL WATERS FROM POINT GRENVILLE TO CAPE SHOALWATER OUT 10 NM. &&