Marine Weather and Tide Forecast for Manchester, CA

DISCUSSION

SHORT TERM
Through Wednesday...The storm system that brought showers to the region over the last few days has now moved east of the region leaving dry northerly flow over Northwest California. Lingering low level moisture has kept cloud cover fairly persistent overnight in many valley locations and across much of Humboldt County. As drier air continues to filter in, skies should clear through the day leaving a rather present day in store for this afternoon. Coastal clouds will expand again tonight into Tuesday morning.

A shortwave trough will dive through the Pacific Northwest on Tuesday. Model guidance is trending toward the potential of rain showers over the mountainous terrain Tuesday afternoon/evening.
However, the NBM has not yet caught onto this possibility. Have kept the chances for rain out of the forecast for now, but the day shift will need to increase the rainfall chances with the next update if model trends continue.

Ridging will once again build back over the west coast on Wednesday bringing warm temperatures to the interior with high temps in valley locations exceeding 80 degrees in some locations. /RPA


LONG TERM
Thursday through Sunday...(Issued 327 PM Apr 27) 500mb pattern on day 4 (Thursday) will resemble a rex block. A positive height anomaly will remain centered over the Pac NW (Washington and Oregon) and extend southward into northern California. A cut- back trough or closed 500mb cyclonic circulation offshore or over central/southern California will complete the rex-block pattern.
It is possible for wrap around moisture from the closed low to spread over Lake and eastern Mendocino for diurnal convection. All 6-hourly ensemble members from the ENS, GEFS and CMCE indicate no precip. Also, NBM probabilities for tstms > 15% are well to the east and southeast; over the Sierra Nevada MTN range. Interior high temperature will remain above average on Thu under large scale adiabatic warming from the ridge centered over the Pac NW.
High temps in the mid 70's to mid 80's are generally expected, however a few hot spots such Big Bar RAWS will probably exceed 90F.

Get ready for more cool and wet weather. A 500mb trough will dig southward from the Gulf of Alaska and approach NW Cal on day 5 (Friday). All deterministic models, GFS, ECMWF, GDPS, ICON as well as ensemble means were is good agreement with driving a frontal boundary across the northern portion of the area on Friday. 24-hour ensemble cluster means continue to depict subtle differences with placement, timing and overall evolution of the cold core aloft.
About 30-45% of cluster members were wetter than the grand ensemble mean. NBM continues to indicate 60-70% chances for 0.25in of rain in 24 hours Friday-Saturday in Del Norte, 30-50% chances for Humboldt, 20-45% chances of Trinity and 10-25% chances for Mendocino and Lake.
By 5AM Sat, over half an inch will be possible (50% chance) for interior Del Norte. Not a major rain event by any stretch but wet weather will impact outdoor activities and projects. Spring snowfall will also be possible above 4000-4500 feet with 1 to 2 inches of storm total accumulation by 5 AM Sunday.

Interior temperatures will be considerably cooler and well below normal again next weekend (Sat May 3 and Sun May 4). There might even be pockets of morning frost in the interior valleys with min temps below 36F. Precip chances generally diminish as we head into day 7 (Sunday) as the trough heads southward and eastward. To what extent and how fast this occurs are still not 100% certain. Precip could wrap back around a potential cut-off low or an upstream kicker may knock down the offshore ridge resulting in more light precip from the west. A faster SEWRD progression with stronger ridging offshore would result in a much drier and gusty north/northwest wind scenario for our forecast area. Most ensemble members support this scenario. Stay tuned. /DB

AVIATION
Coastal stratus is creating LIFR conditions along the redwood coast this morning. HRRR data shows these low clouds mixing out and away from the terminals by approximately 16-18Z this morning. Gusty north winds are to be expected through the daylight hours before weaning in strength into the evening. As winds die down, it is likely that fog will return to the terminal spaces. KUKI can expect VFR conditions.



MARINE
Northerly winds and steep waves are forecast to remain elevated through mid week. Expansion fan regions downwind of Cape Mendo and Pt St George will continue to result in localized ribbons of gale force winds through Monday. Area coverage of the southern expansion fan south of Cape Mendocino expands in the afternoon.
Thus gale warning has been issued. North winds and steep seas in the lee of Cape Mendo and over the outer waters will remain sufficient for a small craft advisory until Wednesday at the earliest, maybe into Thursday south of Cape Mendo. Inner waters north of Cape Mendo should calm down much more nearshore. Confidence remains low and details lacking at this point.

The large scale synoptic pattern indicates brisk noringtherlies diminishing more substantially toward the end of the week as a cold front busts down the upper level ridge and pressure gradient relaxes over the area. Inland low pressure may still serve to locally accelerate winds over the southern end of Mendocino waters. However, northwest and north winds will increase after the frontal passage this coming weekend with gusts over 34kt and steep waves over 10 ft are possible outcomes and forecast confidence will increase as we get closer to this event.



EKA WATCHES/WARNINGS/ADVISORIES
CA...
None.
NORTHWEST CALIFORNIA COASTAL WATERS...
Small Craft Advisory until 9 PM PDT Tuesday for PZZ450-455- 470.

Hazardous Seas Warning until 2 PM PDT this afternoon for PZZ475.

Gale Warning from 2 PM this afternoon to 11 PM PDT this evening for PZZ475.