textproduct: Eureka

SYNOPSIS

Drier and colder weather is expected to last through Tuesday. Light rain return from south to north Wednesday into Thursday, followed by a frontal system with moderate to locally heavy rain, high mountain snow and gusty winds on Friday. Bouts of rain and gusty winds are forecast to continue into the weekend.

DISCUSSION

High pressure remains over the area today bringing clear skies in many areas and some valley fog this morning across many areas of the interior. Tonight similar conditions are expected across the area. Frost is expected in many locations and have issued a frost advisory again for the northern Humboldt coast where the growing season is ongoing. The Mendocino and Del norte coasts may be a few degrees warmer with lows only in the upper 30s so will hold off on a frost advisory in those locations. Tuesday clear skies are expected once the fog clears out the valleys. Temperatures in the interior valleys will likely stay in the 50s in all but the warmest valleys. Tuesday night into Wednesday clouds are expected to start moving over the area in advance of an upper level low approaching the area from the south. This is expected to keep overnight temperatures slightly warmer.

Rain is expected to start in the afternoon on Wednesday in the southern portion of the area and spread north Wednesday evening and overnight. This has been trending slightly faster and some models still show it coming in earlier. So this will need to be watched as it gets closer. It looks like this will taper off in the afternoon on Thursday, but the timing is still in question. Some of the faster solutions show it ending by late morning. Generally amounts are expected to around a half inch to 1 inch with locally higher amounts in the mountains. There may be a short break in the rain before the next system. There is still enough uncertainty on the timing of this that the pops remain fairly high. Snow levels are expected to be fairly high with this first system, likely over 6,000 feet.

The next system is expected to bring heavier rain starting Friday midday or afternoon. This is a more typical trough approaching from the west. It is more dynamic and negatively tilted. The GFS is hinting at a secondary area of low pressure developing along the front and closer to the coast. This may bring some higher winds to the coastal ridges, the gfs shows 60 kt winds at 925mb just off Cape Mendocino. There is still quite a bit of uncertainty on how much these will mix down to the low elevations around Humboldt Bay and other areas along the coast. Rainfall amounts are expected to be higher with this system as well. The current forecast has around 1 inch in the valley and rain shadow locations with 1.5 to 2.5 inches in the higher terrain and windward slopes. The ensembles are still showing some differences in the IVT with low probabilities of over 500 kg/m/s. Overall this doesn't look like a flooding situation aside from near Humboldt Bay and along the coast where the high tides may prevent areas from draining. Snow levels are expected to stay fairly over 5,000 feet through Friday evening and then start to fall late Friday or Saturday depending on the timing of the system. It looks like the colder air will move in after the heavier precip, but there may be some light snow down to 3,000 or 4,000 feet. Additional rain is expected over the weekend.

AVIATION...18Z TAFs

VFR conditions firmly took hold after the localized interior valley fog cleared out. Calm to light and variable winds with high pressure building in. A very similar forecast is expected over the next 24 hours. Light winds and VFR are forecast, and some interior valleys which include UKI have another chance fog. Chances for fog at UKI increase to 30% by 16Z Tuesday. JJW

COASTAL FLOODING

Another round of very high tides is coming up the 31st through 4th. At the North Spit Tide gauge on Humboldt Bay these are expected to be peak around 8.7 above MLLW on January 2nd and 3rd. There is still a lot of uncertainty on the winds, bu there is the potential for gale force southerly winds during this time period. The storm surge models are already showing nearly a foot of surge, but higher amounts are possible if the winds line up with the highest tides. This could yield quite a bit of flooding in the low lying areas around Humboldt Bay. Rain may also be occurring which exacerbate flooding surrounding Humboldt as creeks and low areas may not be able to drain during high tide. There are still a lot of variables, but this could bring 1 to 1.5 feet of saltwater onto normally dry ground around Humboldt Bay. The impacts are less clear outside of Humboldt Bay and will be more driven by the wave size and running up much farther than normal. MKK

EKA WATCHES/WARNINGS/ADVISORIES

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