Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Eureka California
308 PM PDT Tuesday Mar 31 2015
Synopsis...a cooler air mass will settle over the area tonight
and remain in place through Thursday. Frost will be possible each
night this week in the interior valleys. Another weather system
will affect northwest California this weekend.
Discussion...a cooler air mass will settle over northwest California tonight
and remain in place through Thursday. Hoisted the frost advisory for
the Mendocino zones tonight. The advisory for zone 2 will be
marginal and confined to a few cold spots in the Anderson Valley.
It will be borderline for a freeze warning in zone 76 as a few
cold spot reach 32f or less for an hour or so early Wednesday morning.
For the north coast interior zone (interior Humboldt and del
norte counties)...frost will be possible as well by early Wednesday
morning as the atmosphere dries out through the night under
light to moderate NE and east flow. For now will hold off on
hoisting an advisory for zone 3. Frost advisories are not
required for zone 4 until April 15th.
A reinforcing shot of cold air will arrive Wednesday night after
another short wave trough moves into the Great Basin. Stronger northerly
winds Wednesday night will initially keep temperatures from rapidly
falling...however it will also serve to substantially lower dew
points. The northerly winds should eventually decouple in the
valleys and allow temperatures to fall into the lower to middle 30s.
So another frost advisory and perhaps a freeze warning will be
necessary Wednesday night. Temperatures aloft warm up slightly on Thursday
and Friday...however the air will be really dry and if skies remain
clear all night expect another chilly morning on Friday.
The models were in good agreement showing a short-wave brushing
the area on Wednesday. All continue to show very limited moisture and
weak dynamics for thunderstorms. 500mb temperatures do fall to
-30c with mu-convective available potential energy hitting 500j/kg and lifted indices around -2c
during peak heating. There will be a stable middle layer which will
probably limit cumulonimbus growth. Will add thunder in the grids over the
elevated terrain of del norte and Trinity counties in the off
chance one punches through the cap.
The 500mb height fields from the GFS...Gem and European model (ecmwf)...have come
into better agreement this weekend. The surface and precipitation fields
were very similar as well with subtle timing differences Sat into
Sat night. With all three models converging on the Sunday through
Sunday night time frame...precipitation chances have been beefed up. The
GFS does show instability as the 500 mb trough acquires a slight
negative tilt...so a slight chance of thunderstorms has been added
north of cape mendo out toward the coast. The models fall out of
sync days 6 and 7...Monday and Tuesday...so did not make any adjustments to
our broad and vague chance or slight chance of showers those days.
The broad trough aloft will persist with near or below normal
temperatures early next week...however nailing down precipitation chances
remains elusive at this time.
Aviation...skies are clearing as subsidence behind the departing
cold front takes hold. A few lingering showers are expected to
bring brief periods of lower ceilings through this evening...but
otherwise VFR will persist through midnight. The recent rains will
likely allow some valley fog to form in interior valleys primarily
north of Mendocino County tonight bringing some IFR/LIFR conditions.
The majority of Mendocino County and all coastal areas will remain
VFR with the exception of some ground fog early Wednesday morning
along the coast. North winds will increase through the day on
Wednesday becoming gusty by the afternoon hours. /Rpa
Marine...north winds have developed over the coastal waters with a
cold front now well inland. Winds are gusting to 25 knots at buoy 14
where the pressure gradient is now tightest...so the small craft
advisories for the southern waters look good at this time. Winds
will decrease tonight in advance of another weak frontal boundary.
Winds will never turn fully around to out of the south...but will
become fairly light Wednesday morning before ramping up
significantly behind the front. All guidance indicates gale force
gusts will develop in the southern waters Wednesday
afternoon/evening while conditions reach near gale in the northern
waters. Thus gale warnings have been raised for the southern water
zones while the northern waters have been kept as small crafts at
this time. All products begin at 20z (1 pm) Wednesday afternoon
though a few gusts in excess of small craft criteria may develop
The winds...and therefore seas...will remain elevated for much of
the next 5 days as high pressure settles over the eastern Pacific
though winds will likely fall below gale force in the southern
waters late Wednesday night. Seas will be dominated by short period
northerly seas during the highest winds but will also be mixed with
two separate westerly swell trains that will traverse through the
waters this week. /Rpa
frost advisory from 3 am to 8 am PDT Wednesday for caz002-076.
Northwest California coastal waters...
Small Craft Advisory until 3 am PDT Wednesday for pzz455-475.
Gale Warning from 1 PM Wednesday to 1 am PDT Thursday for pzz455.
Small Craft Advisory from 1 PM Wednesday to 9 PM PDT Thursday
Small Craft Advisory from 1 PM Wednesday to 3 PM PDT Friday for
Gale Warning from 1 PM Wednesday to 3 am PDT Thursday for
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