textproduct: Eureka

SYNOPSIS

A frontal system is expected to bring moderate to heavy rain late today through Tuesday. Strong and gusty winds will also accompany the front tonight into early Tuesday.

KEY MESSAGES

* Increased risk for urban and small stream flooding tonight through the day on Tuesday as a moderate atmospheric river brings widespread moderate to heavy rain. Snow levels rising above 9000 feet tonight and Tuesday.

* Strong and gusty winds will accompany the storm tonight. Tree limbs could be blown down and a few power outages may result.

DISCUSSION

Light showers with a nearly stationary front continued across the area through the night. Greatest amounts of rain so far have been across Del Norte where over 2 inches has fallen in the last 24 hours. SW Humboldt mountains (King Range) also had just under 2 inches. Light showers will likely diminish this morning before increasing in coverage and intensity late today.

A long fetch of moisture emanating from a cluster of deep convection northeast of Hawaii will get ingested into a nearly stationary front just outside NW CA coastal waters. Satellite blended PWATS are 300% above normal. ECMWF and GFS has this subtropical moisture stream (PWATS over 300% of normal) and considerable integrated vapor flux (IVT) spiking up over 750 kg/m/s tonight and Tue morning. Widespread moderate to heavy rain rates from 0.25 to 0.75 inches per hour will spread into Del Norte, higher terrain of Trinity and portions of Humboldt this evening as the above mentioned moisture plume slams into the coastal terrain. Heavy rain is then forecast to spread south and east and expand in coverage overnight into Tuesday for Mendo and much of Trinity. Southeastern Lake County may not get any heavy rain with 24 hour storm totals no more than 1". We will need to keep an eye on the potential for flooding due to the rapid run-off and high snow levels above 10,000 feet. The heavy rain will likely tapper off by late afternoon on Tue. A flood watch remains in effect from 10 PM Mon to 10 PM Tue. Our prolonged dry spells this wet season and low flows on the rivers may mitigate the risk for major flooding.

Strong gusty winds are also expected with the incoming storm. A 1007mb surface low will spin up along the frontal boundary by late this afternoon into this evening offshore the North Coast. A 925mb speed max around 60-65 kt is forecast to develop just offshore. Mixing near the frontal boundary will likely bring this higher momentum air down to the surface and perhaps mean sea level. Winds gusts to 50-55 mph are likely for the coastal headlands and higher terrain of Humboldt and Del Norte. Multiple members from the HREF indicate wind gusts around 50 mph this evening for the Del Norte coast. Confidence in gusts over 45 mph is lower (30-50% chance) for the Humboldt Bay area and Eel delta. ECMWF ensemble indicated mean gusts near 40 mph for Crescent City, and gusts near 30-35 mph for the Humboldt Bay area and Eel delta. A wind advisory remains in effect for the coastal headlands and the higher terrain of Del Norte and Humboldt for gusts over 45 mph.

Conditions will begin to settle down around mid week with low chances for non-impactful light precip through the end of the week and next weekend. Temperatures should also remain mild and above normal as we head into the last week of February,

AVIATION....06Z TAFs

Wind shear will continue to be a concern for terminals along the North Coast as the low level coastal jet diminishes from the passing front. Southerly winds will diminish through the day Monday, but still remain elevated near 10 knots sustained. Occasional gusts to 25 knots could still occur along the Del Norte Coast early this morning. Rain showers will also linger this morning, while diminishing through Monday afternoon. Interior valleys have a higher chance for conditions as low as IFR, while coastal terminals will remain VFR/MVFR. More consistent rain and lower visibilities are possible into Monday evening as a deep plume of moisture brings periods of moderate to heavy rain late Monday and into Tuesday. /JLW

MARINE

Southerly winds continue to ease through Monday afternoon, yet will still remain above small craft advisory level in the outer zones. Occasional gale strength gusts will linger around Cape Mendocino and over the northern outer zone (470) through very early Monday morning. Steep and hazardous seas will also be slower to diminish through these areas. A Hazardous Seas Warning remains for Zone 470 through early Monday morning, with small craft conditions expected for other zones through Monday afternoon.

There will be a brief reprieve in advisory wind conditions in the inner marine zones (out 10 nm) early Monday morning through Monday afternoon, when thereafter southerly winds will quickly increase from a new frontal system. Seas will remain steep through Monday.

Gale strength gusts of 35 to 40 kts will arrive Monday evening over the waters, including portions of the inner zones, with isolated 45 kt gusts around the Cape and through zone 470. Gale warnings are out for the northern zones and the southern outer zone late Monday through early Tuesday. The responsible front will be relatively quick to pass, and winds will begin easing into Tuesday afternoon. /JJW & /JLW

HYDROLOGY

A moderate atmospheric river (AR3/AR4) is forecast to intersect the coastal terrain tonight through Tuesday bringing widespread moderate to heavy rain. Duration of the heaviest rain rates are forecast to last about 24 hours. Rates could locally exceed 0.75 in/hr for an hour or two per the most extreme HREF members. This bout of tropical-like rain will result in rapid rises on rivers, streams and creeks. Flooding of low-lying rural areas with poor drainage appears likely. Snow levels will pump up above 9,000-10,000 feet, so all the precip will go directly into run-off. Now the CNRFC continues to indicate all main stem rivers remaining below minor flood stage through this event. Our prolonged dry spells this wet season and low flows will probably mitigate the threat for major or severe main stem river flooding. Stay tuned for updates and possible issuance of warnings and advisories.

EKA WATCHES/WARNINGS/ADVISORIES

CA... Flood Watch from Monday evening through Tuesday evening for CAZ101>111.

Wind Advisory from 10 PM Monday to 4 AM PST Tuesday for CAZ101-102-105.

Wind Advisory from 7 PM Monday to 1 AM PST Tuesday for CAZ104-106.

Flood Watch from late Monday night through Tuesday evening for CAZ112>115.

NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 6 PM PST Monday for PZZ450-475.

Gale Warning from 6 PM Monday to 6 AM PST Tuesday for PZZ450-470-475.

Small Craft Advisory until 3 AM PST Tuesday for PZZ455.

Hazardous Seas Warning until 4 AM PST Monday for PZZ470.