Area Forecast Discussion
Issued by NWS Eureka, CA
Issued by NWS Eureka, CA
458 FXUS66 KEKA 241147 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 447 AM PDT Tue Sep 24 2024 .SYNOPSIS...Another round of seasonably warm weather with fair conditions and hot interior temperatures, expected today. Cooling is expected on Wednesday, followed a warming trend Thursday and Friday. Coastal stratus with patchy fog will likely return around mid week. && .DISCUSSION...Synoptic views of satellite imagery in the IR as well as water vapor wavelengths, show a large synoptic scale anticyclonic rotation over the Pacific and Mountain-West states. This clockwise rotation is indicative of high pressure and subsidence which is also keeping skies clear to partially cloudy over land. Modeled pressure maps in the 500mb heights are also showing the signature 588mb isobar over the area which is bringing high temperatures to bear once more on the CWA. The max temperatures observed for some of the interior hot spots yesterday, were 5-7% above normal when compared to max temperature mean values. With similar conditions today, absent some of the gusty winds, we expect to see inland valley temperatures as high as 102F. Water vapor imagery also shows a distinct boundary of dry air along the 36N-37N latitude, which is getting entrained into the anticyclonic rotation and bringing dry air with easterly flow. The long wave ridging pattern aloft will begin to shift eastward towards the Midwest tonight. An upper level trough approaches the Pacific Northwest simultaneously. Meanwhile, a dry cutoff low located offshore of southern California will drift northward parallel to the coast before being absorbed by the upstream trough by early Wednesday. The marine layer will likely develop during this time frame. Daytime high temperatures will diminish to near or below seasonal averages in the interior. Seasonal averages range from 82- 88F in the interior. Chances for precipitation with this incoming trough is quite meager, generally 10% or less. If anything, some light drizzle may occur in coastal areas with no impacts. Ensemble means and deterministic guidance indicates above normal 500mb heights and above normal 850mb temperatures Thu-Sun. This will most likely result in above normal interior high temperatures. How much above normal is not 100% certain. Looking at the National Blend of models (NBM), sure enough chance for 90-95F increases as early as Friday. Dry weather and above normal interior high temps are most probable Fri-Mon. /DB /EYS && .AVIATION...Continued offshore flow has allowed VFR conditions to prevail across the area, even along the immediate coast. An extensive bank of marine stratus is visible about 50 miles offshore but so far has been kept at bay thanks to offshore winds. The only concerns early this morning would be patchy and inconsistent radiation fog bringing MVFR conditions along the coastal plain, which would be most likely to happen briefly this morning around Humboldt Bay (less than 25% chance of actually impacting the airport). Otherwise, VFR conditions should prevail during day alongside mostly calm wind. There is high model agreement that the stratus bank will gradually approach the coast but the timing of impacts is highly uncertain. Some high resolution models imply the bank should already be at the coast while others show it hang off until early Wednesday morning. All show any impacts occur right along the coast with very little progress inland. All told, and impacts are very unlikely until at least 2000 this evening. After that point, NBM is implying a 30 to 60% chance of IFR ceilings at some point Tuesday night into Wednesday, the the greatest chance after midnight though ceilings at any point are likely to be inconsistent. /JHW && .MARINE...High pressure moving onshore today combined with a disrupted pressure gradient due to a closed low moving up the coast will combine to generate mostly gentle to calm northerly wind across the waters today. Early this morning there are still some isolated, steep short period seas above 6 feet in the outer waters, but these will quickly fall later this morning. Seas won`t be totally calm, however. A mid period, northwest swell will build in this afternoon through Thursday. This swell will most likely peak around 8 feet at 14 seconds early Thursday morning. In absence of meaningful short period seas, this swell will dominate the sea state, especially in the northern waters. Also with calm seas, the first front runners of the swell hold the potential for some minor sneaker waves, though the generally mid period and middling heights of the swell will limit the overall sneaker wave risk. Northerly winds will begin to rebuild Thursday afternoon first in the southern waters with moderate breezes. Winds will continue to increase and spread north by Friday. There is uncertainty as to the exact strength of winds, but model ensembles generally show around a 30 to 50% chance of gusts reaching gale force Friday into the weekend. Regardless of exact strength, steep short period seas over 8 feet should be expected, especially in the outer waters and fanning south of both Cape Mendocino and Pt. St. George. /JHW && .FIRE WEATHER...Elevated conditions with low daytime RH`s and locally gusty winds are forecast to continue. Temperatures will remain hot today with daytime RH`s from 10-20%. Offshore flow will continue, however ridge level winds will become southeasterly by early morning, and then turn westerly to southwesterly in the afternoon. A trough will move across the area on Wed and daytime temperatures will cool down. RH`s should also increase on Wed-Thu, but minimum RH`s will still be low, around 20-30% in the interior. Warmer and drier conditions with stronger N-NE winds expected Fri-Sat. Elevated to locally critical conditions will be possible. DB && .EKA WATCHES/WARNINGS/ADVISORIES... CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 8 AM PDT this morning for PZZ470. && $$ Visit us at https://www.weather.gov/eureka Follow us on Facebook and Twitter at: https://www.facebook.com/NWSEureka https://www.twitter.com/NWSEureka For forecast zone information see the forecast zone map online: https://www.weather.gov/images/eka/zonemap.png