textproduct: Eureka

SYNOPSIS

A weakening front will bring a chance for rain to mostly Del Norte and northern Humboldt Counties late this evening and into very early Wednesday morning. Blustery to strong northerly winds are forecast to develop behind the front on Wednesday and continue into Thursday.

DISCUSSION

The broad ridge influencing conditions over Northwest California will flatten more today as a weak front, associated with a trough to the north, clips the northern reaches of the region. As a result, rain chances will increase today, mainly for Del Norte County and the northern Humboldt Coast. Southerly winds at 925 mb (near 2000 ft) will increase with the front today. This may bring a period of breezy conditions to some of the North Coast and interior ridges. An associated warm front and downsloping winds will drive coastal temperatures warmer today ahead of the precipitation.

A long southwesterly fetch of subtropical moisture (PWATS >1" or >200% of normal) associated with a cold front will intersect the coastal topography late this evening and into very early Wednesday morning. High resolution mesoscale models show the highest chances for hourly rates over 0.10 inches arriving late in the day, generally after 5 PM, along the Del Norte Coast. 90th percentile 24-hour rainfall is around 1 inch near the OR/CA border while the 10th percentile ending at 5 AM Wednesday is on the order of 0.10 inches. The front will likely struggle to maintain strength as it descends south against the ridge. With high PWATS values and weakening moisture flux, a brief period of moderate rainfall (~0.30 inches) will be possible for Del Norte County this evening. Chances are much less for northern Humboldt with generally less than a tenth or two for the North Coast over 24-30 hours. Rain chances are forecast to wind down on Wednesday as northerlies steadily increase offshore. Residual drizzle and low clouds may persist into the evening hours on Wednesday as chilly N-NW breezes develop. Very little rain (trace to 0.03 inches) is expected south of Cape Mendocino.

In general, the above average warmth (mid 70's to lower 80s') and minor heat risk in the interior will persist for the remainder of the week and into this weekend for Lake and Mendocino counties. Minor cooling is expected on Wednesday as northerlies increase in the wake of the front. Robust offshore flow and dry air will also lead to exceptional longwave cooling later this week. The chance for early morning frost and subfreezing temperatures will increase for mostly the interior valleys Thursday and Friday. Persistent east to northeast breezes through the night will limit the frost/freeze threat for wind sheltered valleys.

AVIATION...(06z)

Southerly winds picking up at KCEC ahead of the incoming front, likely to arrive by 12z Wednesday with a decent amount of rain for Del Norte county and subsequently KCEC. KACV had more of a westerly bearing which has changed as of 03z and likely to veer from the south by 07z with the approach of the eastern pacific low, pulling moisture and stronger winds into the area terminals. Ceilings are likely to lift as the marine layer deepens with the active boundary area. Showers are likely to start in KCEC by 00z, cascading down to KACV by Tuesday night and lasting through Wednesday. KUKI is less likely to see any precip with VFR categories expected. /EYS

MARINE

Seas will lower into Tuesday morning before southerly winds increase ahead of an approaching frontal systems. Wind gusts will create hazardous conditions to small crafts, and an advisory has been hoisted for the northern zones for Tuesday. The quick duration of these southerly winds will not allow for much short period seas development.

Northerly winds will quickly build in behind the front Wednesday morning as a strong area of high pressure strengthens in from the west over the Pacific Northwest. The strengthened pressure gradient will generate sustained gale strength winds, with gusts currently forecast to reach 45 kts starting Wednesday afternoon in the southern waters. The strong northerlies will quickly expand northward through Wednesday evening. Steep seas will reach 11 to 14 ft in the northern zones, and are forecast at 13 to 16 ft in the southern waters where the strongest winds are forecast. Winds will not begin to ease until Friday. Gale Watches are out for all zones, but there is still some uncertainty with how much coverage of the gales makes it into the inner zones. Currently, there does seem to be enough gale coverage to warrant a Warning upgrade, but higher resolution guidance will give better details soon.

EKA WATCHES/WARNINGS/ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 11 AM to 8 PM PDT Tuesday for PZZ450.

Gale Watch from Wednesday evening through Thursday afternoon for PZZ450.

Gale Watch from Wednesday afternoon through Thursday afternoon for PZZ455.

Small Craft Advisory from 8 AM to 8 PM PDT Tuesday for PZZ470.

Gale Watch from Wednesday evening through late Thursday night for PZZ470.

Gale Watch from Wednesday afternoon through late Thursday night for PZZ475.