554 FXUS66 KEKA 211250 AFDEKA AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE EUREKA CA 550 AM PDT TUE APR 21 2015 .SYNOPSIS...AN UPPER TROUGH WILL BRING A SLIGHT THREAT FOR THUNDERSTORMS TO THE INTERIOR TODAY. THE MARINE LAYER WILL CONTINUE TO DEEPEN TODAY AND PUSH CLOUD LOW COVER INLAND BY TONIGHT AS BREEZY NORTH WINDS DEVELOP AT THE COAST. && .DISCUSSION...THE MARINE LAYER WILL CONTINUE TO DEEPEN TODAY AS AN UPPER TROUGH APPROACHES THE COAST AND NORTHERLY FLOW INCREASES AT THE COAST. NAM12 PROFILES AND X-SECTIONS INDICATE HIGH HUMIDITY PERSISTING EVEN AS NORTHERLY WINDS AND MIXING INCREASES THIS AFTERNOON. SATELLITE IMAGERY DID SHOW A CLEAR SLOT OFFSHORE THE OREGON COAST. THIS SHOULD ADVECT SOUTHWARD BY THIS EVENING. HOWEVER NAM12 PROFILES SUGGESTS CLOUDS HANGING AROUND INTO THE EVENING HOURS. CONFIDENCE IS NOT HIGH WE WILL SEE COMPLETE CLEARING OF THE STRATUS CLOUDS THIS AFTERNOON INTO THIS EVENING. BETTER DRYING IS EXPECTED ON WED AS NORTH WINDS CRANK UP. WE SHOULD SEE MORE SUNSHINE ON WED...HOWEVER BLUSTERY NORTH WINDS WILL MAKE IT FEEL CHILLY ALONG THE COAST. CONVECTION WILL LIKELY DEVELOP ACROSS THE INTERIOR AGAIN TODAY. NAM12 CONTINUES TO INDICATE UNBELIEVABLE INSTABILITY WITH MUCAPES IN EXCESS OF 3000J/KG AND LIFTED INDICES AROUND -7C. GFS SURFACE BASED CAPE LOOKED MORE REASONABLE WITH VALUES AROUND 500J/KG AND LIFTED INDICES NEAR -3C. ISOLATED STORMS THAT SPROUTED UP WITH DAYTIME HEATING YESTERDAY COLLAPSED VERY QUICKLY. THERE WILL BE STRONGER 0-6KM BULK SHEAR TODAY...AROUND 20-25KT OVER THE HORN AND YOLLA BOLLA MOUNTAINS. THE STORMS MAY BE SLIGHTLY STRONG WITH LONGER LASTING UPDRAFTS TODAY...HOWEVER THE SW FLOW ALOFT WILL ALSO SERVE TO PUSH THE STORMS OFF TO THE NE. IT IS STILL QUITE DRY WITH PWATS AROUND 0.50IN AND 700-500MB HUMIDITY AROUND 40%. THUS EXPECT VERY LITTLE OR NO PRECIP WITH THE STORMS. THE APPROACHING UPPER TROUGH WILL MOVE OVER THE REGION TONIGHT. SHOWER ACTIVITY MAY DEVELOP PRIMARILY OVER THE HIGHER ELEVATIONS TONIGHT AS THE TROUGH SHEARS APART. THE LOWER ATMOSPHERE WILL COOL DOWN THROUGH THE NIGHT AS ROBUST ONSHORE FLOW DEVELOPS. THIS LOW LEVEL COOLING WILL WEAKEN THE MARINE INVERSION AND ALLOW THE COAST TO CLEAR OUT BY WED MORNING. THE MODELS CONTINUE TO SHOW WEAK INSTABILITY AND CONVECTIVE PRECIP ACROSS INTERIOR MENDOCINO COUNTY ON WED AS THE TROUGH ALOFT HEADS TO THE SOUTHEAST. I AM NOT TOO CONFIDENT THERE WILL BE ANY STORM ACTIVITY AS NORTH-NORTHEAST WINDS DEVELOP FROM THE SURFACE TO 500MB. THIS IS AN UNFAVORABLE WIND DIRECTION FOR STORMS. THE NAM12 AND GFS DO SHOW CONVECTIVE PRECIP DEVELOPING WITH DAYTIME HEATING...SO HAVE MAINTAINED A SLIGHT CHANCE OF THUNDERSTORMS...MAINLY OVER THE HIGHER ELEVATIONS IN EASTERN MENDOCINO COUNTY. FLAT RIDGING WILL DEVELOP WED NIGHT INTO THU MORNING BEFORE ANOTHER WEAK SHORT-WAVE TROUGH MOVES TOWARD THE AREA. THIS SHORT WAVE MAY GENERATE SOME SHOWER ACTIVITY OVER THE MOUNTAINS...HOWEVER CONVECTIVE PARAMETERS ARE UNFAVORABLE FOR MORE STORMS ON THU. IT WILL BE COOLER ACROSS THE ENTIRE AREA WITH THE POSSIBILITY OF LATE NIGHT/EARLY MORNING PATCHY FROST IN SOME OF THE INTERIOR VALLEYS. DRY WEATHER IS EXPECTED ON FRI AS A BROAD RIDGE DEVELOPS BEHIND THIS SHORT-WAVE. CONFIDENCE IN THE FORECAST FOR THE WEEKEND AND EARLY NEXT WEEK IS LOW. THE MODELS DIVERGE SIGNIFICANTLY SAT THROUGH TUE. THE ECMWF INDICATES OVER-RUNNING PRECIP ON SAT AND SUN WITH DRY WEATHER ON MON AND TUE. THE GFS ON THE OTHER HAND IS MOSTLY DRY WITH JUST LIGHT PRECIP OVER DEL NORTE COUNTY SAT AND SUN...THEN WET ON MON AND TUE. YESTERDAY THE GFS WAS MUCH WETTER AND FASTER THAN THE ECMWF AND HAD RAIN OVER THE AREA SAT NIGHT AND SUN. ON MON AND TUE...THE GFS IS WET WHILE THE ECMWF DRY. WITH THE MODELS FLIP FLOPPING AROUND FROM ONE RUN TO THE NEXT...CONFIDENCE IN THE FORECAST IS LOW. THUS WILL MAKE NO CHANGES AND LEAVE THE PRECIP CHANCES NEAR CLIMO. && .AVIATION...CEILINGS HAVE RISEN SEVERAL HUNDRED FT OVERNIGHT ALONG THE REDWOOD COAST...BUT LOW CLOUDS REMAIN ENTRENCHED. THE AREAL EXTENT OF THE LOW CLOUDS IS DIFFICULT TO DISCERN ON SATELLITE PIX DUE TO HIGH CLOUDS. NAM KEEPS LOW CEILINGS AT KACV THRU THE DAY WITH SOME INDICATION OF PARTIAL CLEARING AT KCEC. LOW CLOUDS HAVE ADVECTED UP THE RUSSIAN VALLEY TO KUKI AS PREVIOUSLY FORECAST. THESE CLOUDS SHOULD BREAK UP LATER THIS MORNING. ISOLATED THUNDERSTORMS ARE POSSIBLE OVER THE YOLLA BOLLYS THIS AFTERNOON. HOWEVER...THESE ARE EXPECTED TO REMAIN NE OF KUKI. WINDS ARE EXPECTED TO BECOME GUSTY BY THIS AFTERNOON ACROSS THE AREA...WITH THE HIGHEST SURFACE GUSTS ALONG THE COAST. GUSTS OVER 30 KTS ARE POSSIBLE AT BOTH KACV AND KCEC. /SEC && .MARINE...WINDS HAVE BEGUN TO INCREASE OVER THE COASTAL WATERS THIS MORNING...AND THIS WILL CONTINUE THRU TODAY AND TONIGHT AS THE PRESSURE GRADIENT TIGHTENS BETWEEN AN INLAND TROF AND PACIFIC HIGH PRESSURE. HAVE CONTINUED THE GALE WARNING FOR THE OFFSHORE WATERS FROM THIS AFTERNOON THRU THU EVENING. ALSO EXPANDED THE WARNING INTO THE N NEAR SHORE WATERS FROM THIS EVENING THRU WED NIGHT. WIND GUSTS IN THE OFFSHORE WATERS MAY APPROACH STORM FORCE TONIGHT...BUT THE AREAL COVERAGE...FREQUENCY...AND DURATION PRECLUDE ANY HEADLINE AT THIS TIME. WILL CONTINUE TO MONITOR CONDITIONS IN THE S NEAR SHORE WATERS FOR POSSIBLE HAZARDOUS SEAS WARNING...BUT AS OF NOW LOOKS TO BE JUST BELOW CRITERIA. WINDS ARE FORECAST TO MAX OUT EARLY WED MORNING...THEN GRADUALLY DIMINISH INTO THE WEEKEND. /SEC && .EKA WATCHES/WARNINGS/ADVISORIES... CA...NONE. NORTHWEST CALIFORNIA COASTAL WATERS... SMALL CRAFT ADVISORY UNTIL 9 PM PDT THIS EVENING FOR PZZ450. GALE WARNING FROM 9 PM THIS EVENING TO MIDNIGHT PDT WEDNESDAY NIGHT FOR PZZ450. SMALL CRAFT ADVISORY UNTIL 3 PM PDT THIS AFTERNOON FOR PZZ470-475. GALE WARNING FROM 3 PM THIS AFTERNOON TO 9 PM PDT THURSDAY FOR PZZ470-475. SMALL CRAFT ADVISORY FROM 9 AM THIS MORNING TO 9 AM PDT FRIDAY FOR PZZ455. && $$ VISIT US AT HTTP://WWW.WEATHER.GOV/EUREKA FOLLOW US ON FACEBOOK AND TWITTER AT: HTTP://WWW.FACEBOOK.COM/NWSEUREKA HTTP://WWW.TWITTER.COM/NWSEUREKA