SHORT TERM
Issued at 235 PM PST Wed Jan 22 2025 (This evening through Thursday)

While record breaking cold and a little snow continues across the eastern US, largely quiescent conditions are forecast tonight and into Thursday across the Bay Area and Central Coast. We will likely have to contend with at least another night of chilly to cold conditions across the North Bay, East Bay, and Central Coast interior. We'll roll with another Frost Advisory where temperatures fall into the mid 30s tonight into Thursday morning.
A few locales in far southern Monterey County have around a 70-80% or greater chance of dipping below 32 degrees, but the small spatial extent doesn't warrant a separate freeze product. Regardless, take preparations to mitigate impacts due to cold for people, pets, plants, and sensitive infrastructure.

Thursday is shaping up to be another pleasant and dry day with diurnal wind patterns. This means largely offshore during the overnight and early morning hours, with onshore flow returning late in the afternoon. High temperatures are anticipated to average between the 50s and 60s across most regions, except across the Salinas and Santa Clara Valleys where temperatures will climb into the 70s.

LONG TERM
Issued at 235 PM PST Wed Jan 22 2025 (Thursday night through next Tuesday)

Key Messages *Stronger offshore flow regime Saturday *20-30% chance for showers across the Central Coast on Saturday *20-30% chance for a rain/snow mix at or above 4,000' in the Santa Lucias on Saturday *10% chance for very isolated thunderstorms

Thursday Night into Friday morning will feature weaker offshore flow during the nighttime hours. This should translate to a slightly stronger onshore or even calm wind pattern in some locations and help keep temperatures in check. Cloud cover will also invade portions of the North Bay. With less optimal conditions for radiational cooling due to clouds and less in the way of offshore flow, most areas are forecast to remain above 32-34 degrees. The exception will be some of the sheltered/low- lying regions away from the coasts. At this time, cold weather headlines may not be needed, but future shifts will examine trends and latest NWP.

The increasing cloud cover noted above will precede our next upper storm system. The general synopsis is that an upper low will dive southward through the Central Valley late Friday and into Saturday. Some deterministic guidance advertises in excess of 150 meter 12 hour height falls with this feature. These 12 hour height tendencies are a sign of robust ascent. The GFS and its associated ensemble members advertise a much lower 500mb height anomaly (so a stronger storm system) compared to the EPS and GEPS ensemble members. The deterministic NBM forecast does output mentionable PoPs (perhaps influenced by the GEFS suite of guidance) largely across the Central Coast late Friday and into Saturday. This seems to be a pretty decent starting point for PoPs given these types of tricky patterns where the low levels remain dry, but ascent is strong. Forecast soundings do show increased moistening (RH > 70%) within the 800-900mb layer with lapse rates approaching 7 C/km atop that. With the aforementioned ascent, it won't take much to generate widespread shower-type activity. The radar scope will likely appear very illuminated Saturday, however, as forecast soundings indicate dry low levels. This will translate to virga for *most* locations. Outside of some minor tweaks for consistency, we'll advertise 20-30 PoPs as a result.
The greatest opportunity for measurable precipitation is forecast across southern Monterey and San Benito County as well as across the higher terrain. If lapse rates steepen further, a lightning strike or two cannot be ruled out. NBM probability of thunder amounts around 10% seem reasonable, and we'll use more of the high-res output as we venture closer to fine tune the thunder forecast. It should be noted that these types of patterns can overproduce in terms of the coverage of precipitation (including small hail or graupel) and/or lightning.

Precipitation amounts, will remain largely below 0.10" as the boundary layer will remain parched after an extended period of offshore flow. Snow levels do fall down to around 4,000', but at this juncture, the dry low levels precludes anything above trace accumulations of snow. Again, if this system overproduces (e.g, stronger ascent or more moist low levels than expected) then we may need to entertain adding measurable snow amounts across the Santa Lucias.

Finally, with respect to the wind headlines. Overall, it appears that wind gusts of 30 to 40 mph or greater will be confined to the higher terrain of the North Bay and East Bay on Saturday. These wind prone areas have a tendency to exceed the model consensus, potentially due to the combination of momentum transfer, terrain influences, and isallobaric forcing as high pressure builds across the Great Basin. An addition of the higher NBM percentile NWP into the grids appears appropriate to account for these factors and it's not out of the question that wind headlines for a small portion of the Bay Area may be needed by this weekend.

Sunday afternoon and onward should see a return to tranquil conditions across the area. However, after a slightly stronger push of offshore flow, cold hazards may resurface, especially on Monday morning when ideal radiational cooling conditions set up.
For now we'll monitor trends and consider appropriately messaging this next round of cold hazards as we progress through the weekend.

AVIATION
(06Z TAFS)
Issued at 935 PM PST Wed Jan 22 2025

VFR through the TAF period. Mostly light to moderate winds will affect the the region through the TAF period with mostly northerly to easterly winds. Some southeast drainage winds look to the Monterey Bay terminals overnight.

Vicinity of SFO...VFR through the TAF period. Light and variable winds linger into the mid afternoon before turning more northwesterly and becoming more moderate. Expect winds to become light again in the late night.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR through the TAF period. Southeast drainage winds are developing and look to last into the afternoon before northwest winds arrive. Winds look to become light and variable into Wednesday night.



MARINE
(Tonight through next Tuesday)
Issued at 935 PM PST Wed Jan 22 2025

Northerly winds are increasing with and moderate seas are expected through Thursday. Seas become rough to very rough by Friday as a new storm system approaches with gale force gusts expected Friday and Saturday over the northern outer waters.

MTR WATCHES/WARNINGS/ADVISORIES
CA...Frost Advisory until 9 AM PST Thursday for CAZ506-510-516-518.

PZ...Gale Watch from Friday evening through Saturday afternoon for Pt Arena to Pt Reyes 10-60 NM.

Small Craft Advisory from 9 PM Friday to 3 PM PST Saturday for Pigeon Pt to Pt Pinos 10-60 NM.