textproduct: Eureka

SYNOPSIS

Above normal warmth is forecast to continue through today in the interior and then trend cooler later in the week. Chance for showers and interior thunderstorms will arrive on Wednesday and continue on Thursday and Friday.

KEY MESSAGES

* Interior highs in the mid 70s into low 80s today with minor HeatRisk. * Light showers on Wednesday, followed by showers and interior thunderstorm chance Thursday and Friday.

* Shower activity will persist across the region through at least Saturday due to lingering moisture rotating around the cut-off low tracking southeastward into Southern California.

DISCUSSION

A weak shortwave trough embedded in southwesterly flow aloft is passing overhead the NW California overnight, with high level clouds streaming the area. In addition, a shallow marine layer have developed with stratus and patchy fog blanketed much of the coastal waters and adjacent land areas. Patchy dense fog is already observed around Humboldt Bay with visibility of 1/4 or less. HREF probability for dense fog continue suggesting there is a 30-50% chance of dense fog along the Hwy 101 between Eureka and Crescent City from 5 AM to 9 AM this morning. Fog and patchy dense fog is expected along the river valleys and adjacent coastal areas early this morning. The shallow marine layer and stratus should erode back and clear out in the afternoon, but areas of fog and low cloud may linger near or meander about near the shoreline through the day as winds remain light and variable.

Otherwise, quiet and dry weather and above normal high temperatures are forecast to prevail across the interior through at least Tuesday as a ridge aloft springs back up in the wake of the aforementioned shortwave trough. Above normal 500mb heights and 850mb temps may even last through Wednesday. High temperatures will begin to trend cooler; however, interior temperatures will be similar to Tuesday. Marine air and low clouds pushing into the coastal river valleys could also bring significant cooling around mid week if northwest winds increase offshore over the waters.

Precipitation chances return on Wednesday as a cut- off low burrows eastward into the dominant ridge. Latest WPC guidances suggest there is a 40% chance of light precipitation across the area on Wednesday and Thursday, with 50% on Friday. Overall not much rain is expected over 3 days (Wed-Fri), generally less than 0.25 inches with locally higher amounts due convection in the interior. Potential for interior convection/thunderstorms increases on Thursday with long CAPE profiles around 150-300 J/kg, lifted indices near -1C and PWATS over 200% of normal in the afternoon/early evening over eastern Trinity, NE Mendo and northern Lake where low level convergence of upslope winds occur. Wrap around moisture with above normal precipitable water (PWATS > 200% of normal) and greater CAPE on Friday should yield stronger storms that may result in heavy downpours and perhaps some small hail. Profiles are not too favorable to strong and gusty outflow winds (inverted-V profiles), however a few deterministic models, namely the ECMWF, indicate higher surface- to-500mb S-SE bulk shear around 25-35kt and strong multi-cell storm clusters seem possible in the interior.

Beyond Fri into next weekend, wrap around moisture with interior showers and thunder remains possible on Fri and Sat if the eastward progression of cut-off low slows down or stalls over the area. Another trough may come barreling down from the NW bringing considerable cooling and perhaps more light precip. Or the ridge will come back and leave the area in dry stable weather with a warm up for the interior.

AVIATION

Thick fog and very low stratus is evident on satellite data just offshore, but so far this evening VFR conditions have persisted. Most models show a high chance (75%) of fog pushing in before sunrise, bringing a period of IFR to LIFR along the post. There is an 80% chance of at least brief clearing back to VFR during the day, with a deeper (more likely IFR than LIFR) marine layer likely to build in Monday night. Stratus impacts will remain relegated to the immediate coast and near coastal valleys. /JHW

MARINE

Very gentle to calm northwest winds will persist into Tuesday. Similarly calm seas will persist as well. Low pressure slowly passing to the south will strengthen northerly winds mid week. There is relatively high wind strength uncertainty depending on the track of the low. The ensemble mean shows gusts only to around 21 kts by Thursday in the outer waters,but there is a 20% chance of near gale force gusts. Regardless there is little to no swell and sea will be dominated by whatever short period seas are generated. /JHW

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... None.