Area forecast discussion
National Weather Service Eureka California
1203 PM PDT Wednesday may 22 2013
Update...
quick update to account for latest sky cover and shower coverage
trends. Shortwave pushing southeast from Oregon offshore waters
along with increasingly cold and unstable air aloft is trying to
force showers further southeastward. However surface ridge and
associated low-level diffluence along with relatively stable air
along the coastal plain is keeping mostly sunny conditions in
place south of the Klamath. As some middle-level moisture and
instability pushes in cumulus build-ups and isolated showers will
continue to be possible over the higher terrain through early
evening. Looking like another cold night tonight for the interior.
Aad
&&
Previous discussion... /issued 446 am PDT Wednesday may 22 2013/
Synopsis...an upper level low over the Pacific northwest
will bring a chance of showers mainly to Humboldt and del
norte counties today through Thursday. Temperatures in the
interior have cooled significantly and will remain well
below seasonal normals for the next several days.
Discussion...some showers were moving into Humboldt and del
norte counties early this morning. Most of the showers were
fairly light according to radar and producing a hundredth of an
inch or two of rain. Snow levels appeared to be around 3kt
according to the RAWS. Isolated snow showers may produce a
dusting over the coastal ridges this morning before levels
rise above 3500-4000 feet later today with daytime heating.
Satellite imagery showed more open cell cumulus offshore heading for
the forecast area. The north-northwest flow will continue to bring these
cloud elements onshore today and tonight. The precipitation coverage
looks to remain scattered and confined mainly to the coast
and coastal ranges. With an onshore north-northwest flow...a few more
hundredths of an inch of rain with a little wet snow over
the ridges will be possible...mainly in Humboldt and del norte
counties today through tonight.
The upper level low parked over the Pacific northwest and responsible
for the cold weather will remain nearly stationary on Thursday.
Another impulse may drop down from the northwest into the forecast area
by Thursday night. The models were inconsistent on precipitation generation
and will not make any significant changes to the forecast at this
time. The cold upper low should kick out on Friday but another
trough will quickly follow. This trough will maintain below normal
temperatures and probably generate more showers on Sat and sun. A
ridge may build by Sun night or Monday. Another possibly
stronger/wetter storm may affect the area early next week.
This storm has the potential to produce a long period of rain.
Timing is still iffy and the models are still flip-flopping but
look to be converging.
Freeze warnings and frost advisories are currently in effect for
the interior this morning. Temperatures were mixed...with some
places at or below freezing while other locales were above 37f.
There has not been much cloud cover inland through the
night...but the blustery northwest winds has been keeping temperatures
from rapidly falling in the valleys. Winds may be a factor again
tonight...however will go ahead and issue another frost advisory
and freeze warning for early Thursday morning. The air mass is
unseasonably cold but the wind may be too strong again for rapid
overnight cooling and drying. Air mass should start to moderate over
the weekend...but suspect there will still be Micro-climates of
frost and freezing temperatures in the interior valleys if skies
go clear for a long period.
Aviation...Sat imagery shows upper low over the Pacific northwest with another
weak front moving S along the ctl or coast. This feature will reach
cec by 15z resulting in greater shower coverage moving onshore this
morning with majority of showers remaining north of acv. Tempo MVFR-IFR
conditions will accompany showers this morning...but visual meteorological conditions will
prevail today. Intermittent MVFR conditions will be more frequent
across del norte...interior Humboldt and western Trinity counties
but...visual meteorological conditions will prevail across the interior as well.
Marine...04z ascat pass showed winds around 20 knots across the outer
waters and buoy observation report seas 10-14 feet at 11 second with advisory
level winds at buoy14. Another weak front will move across the northern
waters this morning. Winds and seas will increase slightly as a
result...but seas are expected to remain advisory levels. Sea remain
elevated across the southern waters...so maintained hazard seas warnings
through late this morning. Fairly relaxed pressure gradient will persist
over the region as the upper low lingers over the Pacific northwest maintaining
light-fresh north winds through the week.
&&
Eka watches/warnings/advisories...
California...frost advisory from 2 am to 8 am PDT Thursday caz003.
Freeze warning from 2 am to 8 am PDT Thursday caz004-076.
Northwest California coastal waters...
Small Craft Advisory until 2 PM PDT this afternoon pzz450-470.
Small Craft Advisory until 9 PM PDT this evening pzz455-475.
&&
$$
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