textproduct: Eureka

SYNOPSIS

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

DISCUSSION

Broad flat 500mb ridging continued to dominate across NW California today, bringing another day of dry stable weather. Daytime highs have been above average, especially for Lake, Trinity and interior Mendocino Counties. 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. Minor cooling is expected on Wed as northerlies increase in the wake of a front. Robust offshore flow and dry air will also lead to exceptional longwave cooling. The chance for early morning frost and subfreezing temperatures will increase for mostly the interior valleys Thu and Fri. Persistent east to northeast breezes through the night will limit the frost/freeze threat to wind sheltered valleys.

Rain chances will increase for mostly the North Coast Tuesday afternoon and evening. A long southwesterly fetch of subtropical moisture (PWATS >1" or >200% of normal) associated with a cold front will intersect the coastal topography late Tue into Tue night. High resolution mesoscale models shows 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 exceeds 1 inch near the ORCA border while the 10th percentile ending 5 AM Wed is on the order of 0.50 inches. The front will likely struggle to maintain strength as it descends south against the ridge. With high PATS values and weakening moisture flux, a brief period of moderate rainfall (~0.50 inches) will be possible for Del Norte County (Tuesday 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 Wed as northerlies steadily increase offshore. Residual drizzle and low clouds may persist into the evening hours on Wed as chilly N-NW breezes develop. Very little rain (trace to 0.03 inches) is expected south of Cape Mendocino.

AVIATION...18Z TAFs

VFR to isolated MVFR conditions took over Monday afternoon. A coastal eddy may continue to occasionally drive in some MVFR CIGS along the North Coast until the eddy dissolves into the evening. An approaching frontal system will increase southerly winds for CEC after 6Z Tuesday, and winds will become gusty farther south through ACV into Tuesday afternoon. 925 mb southerly winds will strengthen to 30 to 40 kts over Del Norte County, bringing a threat for low level wind shear after 6Z Tuesday. Otherwise, VFR conditions will prevail ahead of the rainfall to move into to mainly Del Norte starting Tuesday afternoon.

MARINE

Northerly winds and steep seas continue their trend lower Friday afternoon while a mid period northwest swell fades. 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... Gale Watch from Wednesday evening through Thursday afternoon for PZZ450.

Gale Watch from Wednesday afternoon through Thursday afternoon for PZZ455.

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

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