textproduct: Eureka

SYNOPSIS

Breezy to strong offshore winds are expected through dawn for ridgetops. Dry conditions with above normal high temperatures are expected for the interior through the weekend. Potential for significant precipitation still on track for next week.

DISCUSSION

Dry conditions expected through dawn under offshore flow. Adiabatic warming from the large scale subsidence is resulting in a wide range of overnight low temperatures, varying greatly depending on elevation. With a warmer airmass building and winds generally restricted to the ridgelines, wind sheltered valleys and coastal areas will stand the best chance for frost and freezing/subfreezing temperatures. Some wind sheltered valleys will dip down into the low 30's, while breezier wind prone areas exposed to adiabatic warming may not even dip below 60F (mostly in/above the thermal belts for ridges). Frost advisories have been issued for the interior valleys of Mendocino County as well as coastal areas of Del Norte and Humboldt again. Interior portions of Humboldt and Del Norte are 6 days from the start of the growing season (Apr 1) while Trinity County is 21 days away (Apr 15). That is why frost/freeze products have not been issued for these zones.

This dry and stable weather is expected into the weekend. Daytime temps will generally be above normal high temperatures with areas of minor heat risk mostly the interior as a broad, flat, upper- lvl ridge dominates. The warmest locations will continue to be in Lake, Trinity and interior Mendocino Counties where max temps are projected to peak into the upper 70s to mid 80s Fri-Sun. This is 10- 20F above late March averages. Overnight low temps will remain seasonably chilly with valley sites (especially for Trinity Co.) continuing to to cool into the lower to mid 30's as stable, colder, denser air pools into the valleys each night. As this cool air drains each night, a thermal belt will continue to develop around midslopes keeping higher elevations warmer and dryer through the night. No huge changes are anticipated this weekend except for an increase in coastal stratus and perhaps a ramp up in onshore or NW winds.

The National Blend of Models (NBM) and NOAA CPC is still supporting the trend of much cooler and wetter next week. Our long stretch of above normal interior warmth will finally end next week with highs trending near (or even just under!) early April normals by mid week. With this incoming cooler air, there is increasing confidence in at least a few days of precipitation next week. How much precipitation and the exact timing remains uncertain, yet the window looks to be wettest for Tuesday and Wednesday as the highest WPC/NBM 6-hourly rates appear to arrive on Wednesday (+/- 12-24hrs). The NBM 3-day/72hr totals from 5 AM Mon-5AM Thu range from over 2-5" inches on the higher end (top 75th percentile) to 0.5-1.00" on the lower end (bottom 25th percentile). Most of the precip is concentrated in the usual wet spots of Del Norte, SW Humboldt and NW Mendocino, while southern Lake and southern Mendocino may end up with much less.

As for snowfall, this incoming cold weather pattern will lower the snow levels a few times for this upcoming storm next week. Model data shows an initial lowering of snow levels down to 4500- 5000ft by Wednesday morning before a secondary lowering to 3000-3500ft by Thursday morning. Its important to remember that snowlevels are very dependent on where the low pressure actually arrives and that this amount of detail is subject to change by next week as a clearer forecast becomes available, yet for right now this is what we know. Finally, The NBM still has 6-hr and 12-hr thunderstorm chances less than 15%. However, if the cold core aloft dips far enough south, we could definitely see some low top thunderstorms and small hail. Stay tuned for updates and more details. DS

AVIATION

(27/06Z TAFs)..Prevailing VFR conditions at all terminals during the next 24-36 hr, with high-level clouds streaming across the area. Northerly winds continue to decouple from the surface, becoming light ENE overnight. After 27/17Z, winds will shift to the NW and increase for the coastal terminals. Meanwhile, very light and variable winds will persist at UKI. /ZVS

MARINE

Northerly winds are beginning to diminish across the coastal waters. Near-gale to gale northerly winds are expected to continue across the outer waters through early Friday, leaving very steep seas over the northern outer waters through late Friday morning. Small craft conditions will most definitely persist through Friday night.

Winds will decrease over the weekend as an area of low pressure begins to develop off the California coast. This will significantly reduce the pressure gradient across the waters. A weak front is forecast to move through the waters on Monday allowing the northerly winds to increase slightly in its wake. The next chance for strong winds will be mid next week as a more potent frontal system moves into the region. /ZVS&RPA

EKA WATCHES/WARNINGS/ADVISORIES

CA... Frost Advisory from 4 AM to 8 AM PDT this morning for CAZ101-103.

Frost Advisory until 9 AM PDT this morning for CAZ110>113.

NORTHWEST CALIFORNIA COASTAL WATERS... Hazardous Seas Warning until 6 AM PDT early this morning for PZZ450-455.

Gale Warning until 6 AM PDT early this morning for PZZ470- 475.

Hazardous Seas Warning from 6 AM to 11 AM PDT this morning for PZZ470.