Area Forecast Discussion

KEY MESSAGES

* Slightly warmer temperatures and northerly breezes are expected today.

* A weak frontal system arriving Wednesday will likely lead to cooler temperatures and generally unsettled weather with an increased chance for thunderstorm development

* Warmer temperatures and dry conditions return end of the week.

SYNOPSIS

Surface high pressure building offshore will strengthen the onshore pressure gradient against the interior thermal low into early this week. Expect a shallow marine layer pinned along the coast while the interior valleys have dry and seasonably warm conditions. For Wednesday, an evolving upper low will bring cooler temperatures and slight chance for interior thunderstorms.

DISCUSSION

Warm temperatures remain inland as high pressure and weak upper level ridging remains over the areas today. This will result in strong winds for the coast and valleys inland with gusts up to 20mph possible inland and up to 30mph for the direct coastline. Any coastal cloud coverage in the morning will likely dissipate early as daytime mixing and a deepening marine layer impact the North Coast. Inland valleys could also see morning temps in the low 40s.

COme Wednesday afternoon, global models have been steady on an upper level trough ripping down the PacNW coastline before stalling over Del Norte as well as N. Humboldt and N. Trinity counties. This trough will create abnormally cooler temperatures inland and stronger winds for the ridgetops due to the unstable atmosphere. CAPE values and vorticity signals continue with this system even as Hi-Res models start to reach out as far as Wed P.M. which increases the forecast confidence on thunderstorm potential. The Storm Prediction Center has also included the Northern portions of the CWA in a thunderstorm potential. Storms will be limited by forcing and moisture, yet ample life could create a thunderstorm if the ingredients line up well enough. Storm track currently shows storms forming inland before potentially flowing westward towards the coast from the Klamath, Salmon, and Trinity Alp mountains. A small chance of storms is possible Thursday as a weaker impact from this system will still be felt. After this system migrates eastward, ridging returns and will give warmer temperatures for Friday into the weekend. DS

AVIATION

VFR and northerly winds are expected to continue for coastal terminals. Terminals near Humboldt Bay could see MVFR ceilings develop late tonight with periods of IFR as cloud development has begun in the Eel River Valley. Any ceilings will likely give way to VFR by mid morning as northerly winds return. Inland areas will experience continued afternoon gusts and VFR conditions.

MARINE

A fairly strong land-sea surface pressure gradient is creating strong breezes with near gale force winds through the overnight hours before building again this afternoon, especially across the area outer waters. Steep waves are to be expected across all of the coastal waters through Wednesday morning with waves of 8 to 10 feet. Winds are still expected to diminish slightly through the afternoon on Wednesday and more significantly Wednesday night as an upper level trough moves down over the area. Some models do show these winds diminishing earlier, but confidence is low on the exact timing. Light southerly winds are expected Thursday as the low moves through and then out of the area. Northerly winds are expected to increase on Friday and more so over the weekend. MKK

FIRE WEATHER

High pressure building off the coast will continue the warming and drying trend across Northwest California today. Wednesday afternoon or overnight an upper low entering over Del Norte, Humboldt, and N. Trinity counties has the potential to cause a few thunderstorms. There is still a lot of uncertainty on the details of these storms, yet the most likely scenario seems to be storm forming over the Salmon, Klamath, and Trinity Alps before flowing towards the coast. Storm chances remain low overall, yet the potential area for these storms has increased due to the models remaining fairly steady with this systems storm track. There will likely be rain with each of these storms, yet some lightning that strokes away from the core of the storm could start a fire. It is possible that the there could be a few storms on Thursday, but these are expected to be limited to northern Trinity county and Siskiyou county. Warmer and drier weather along is expected to return Friday and Saturday. MKK/DS

EKA WATCHES / WARNINGS / ADVISORIES

CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 9 AM PDT Wednesday for PZZ450.

Small Craft Advisory until 8 PM PDT Wednesday for PZZ455- 470.

Small Craft Advisory until 3 AM PDT Thursday for PZZ475.