Hayfork, CA Weather

Key Messages

* Probable rainfall totals trend higher Wednesday through Thursday afternoon, mainly for the interior.

* Seasonable temperatures, with a higher chance for frost and subfreezing temperatures for the interior late in the week and beyond.

* A drier scenario is becoming more likely for the expected weekend disturbance.

Synopsis

Chance for rainfall increases throughout Wednesday, with higher chances overnight and into Wednesday. A cold front will then quickly dry out the environment and bring broad areas of frost and some interior freezes late in the week.

Discussion

An area of low pressure is observed on mid level water vapor imagery off the coast of central and southern California. The low is sending wraparound moisture into N California from the SE. Ongoing shower activity will increase through the day for areas initially generally south of Cape Mendocino. This moisture will then push farther north through Humboldt and likely to Del Norte County later Wednesday through Thursday.

The low is forecast to tap into some deeper subtropical moisture south of southern California and send it our way. Now to complications in the forecast. There remains question in how much moisture wraps into our area from over the higher terrain to the east. The current forecast of total rainfall is on the lower end, with areas east through Lake, Southern Mendocino, and Trinty County in the 0.25 to 0.5 in inch total through Thursday. These forecast amounts have increased, and align closer to the mean estimate. There is very large differences from the high resolution REFS ensemble max, which has a broad area over 1 inch, and locally 1.75 inches that expands farther west into Humboldt for the extreme scenario.

We've discussed the argument for the lower end amounts, but a scenario for the higher end is plausible. The low will usher in modest elevated instability, with a potential for some thunderstorms. The mentioned subtropical moisture will yield some precipitable water values over 1 inch. Given the nature of cutoff, stalled lows, small deviations in the track are possible, and this can yield much large changes in the rainfall amount. Anytime there is instability with anomalously high precipitable waters amounts, models can underestimate what is actually produced.

Northerly winds will turn gusty Friday, followed by a strong NE wind surge Friday night. Any valleys that do clear out Thursday night will likely see frost or freezing temperatures, and if we get the forecast coverage of rainfall, interior fog would suppress the chances for frost and freezes. The dry offshore winds Friday night should allow for things to clear and and get cold, particularly Saturday morning when frost conditions may expand to the coast. JJW

Aviation

6Z TAFs...Low level moisture is increasing under a shallow inversion. There is a potential for shallow marine stratus advancing down the coast, with at least tempo fog visibility. Probability of LIFR CIGS are around 40 to 50% at CEC and up to 64% for ACV. Chances for visibly under 1sm is near 30%. An area of low pressure offshore will deliver instability, which has been know to weaken the inversion and allow for scattering. This continues to give uncertainty in the forecast, though the instability is elevated which may keep to TAF forecast on track.