Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Eureka California
557 am PDT Wednesday Jul 27 2016
Synopsis...strong high pressure will continue to bring hot
interior temperatures through mid-week with triple digit
temperatures across portions of the interior. Coastal areas will
continue to see a mix of clouds and sun as the marine layer
fluctuates in depth. Inland temperatures will start to cool this
Update...stratus has expanded north along the del norte coast in
conjunction with a light flow reversal. Sky cover has been adjusted
accordingly and patchy fog has been expanded to include coastal del
norte for this morning. Otherwise the forecast remains on track and
the previous discussion issued at 3 am is included below. /Rpa
Discussion...very hot conditions will continue across interior
areas of northwest California today through Friday as upper level
ridging remains in place. Afternoon high temperatures will exceed
100 degrees in most Interior Valley locations with some areas of
eastern Trinity County and interior Mendocino County approaching
110f. The current forecast calls for a high of 108f in Ukiah today,
just three degrees shy of the daily record of 111f, and similar
conditions are expected on Thursday. All guidance indicates that
Friday may be a few degrees cooler as mid- and high-level moisture
increases and a few clouds could restrict full heating potential.
Still, temperatures will exceed 100 degrees for most interior
areas Friday. Despite the hot afternoon temperatures, overnight
lows will remain relatively cool with temperatures falling into
the upper 50s and 60s across the interior. This will mitigate the
heat somewhat and preclude the issuance of heat advisories.
Moisture will also be on the increase in the low-levels as well on
Friday as a weak upper-level low develops off the central California
coast. The NAM, GFS, and European model (ecmwf) are all depicting very light quantitative precipitation forecast over
the higher terrain of Siskiyou and northern Trinity counties Friday
afternoon/evening. Model soundings are not too impressive with
minimal cape. However, there appears to be a small window of a few
hours with little cin which could support towering cumulus
development and a slight chance for a thunderstorm over the Trinity
horn. Thus slight chances for storms have been introduced to the
forecast in a small portion of northeastern Trinity County Friday
afternoon and evening. The upper low will gradually drift
northeast over northwest California on Saturday. Thus, though mid-
level flow will begin to shift even more out of the southwest
during the day Saturday, similar atmospheric conditions will be in
store and a slight chance of thunderstorms over far northeastern
Trinity County could develop again. For now chances for
precipitation have been kept below mentionable levels (below 15%)
As the very weak low moves overhead, 1000-500 mb thickness values
will decrease slightly resulting in lower afternoon temperatures.
Highs will fall back to near normal early next week for a few days,
followed by a likely return to above normal temperatures late next
week as strong ridging returns.
Coastal conditions will remain fairly consistent throughout the
next seven days with highs in the 60s and overnight and morning
cloudiness gradually dissipating through the day. Some areas with
downsloping/offshore flow, such as near Shelter Cove and Crescent
City, will see more sunshine and slightly warmer temperatures than
other areas. In other words, very typical conditions for late July
and early August. /Rpa
Aviation...MVFR to IFR conditions and light winds to calm
conditions will continue at kcec this morning. The lower
conditions will be due to stratus and patchy fog reducing ceilings
and/or visibilities. LIFR conditions may occur at times early this
morning at kcec due to fog reducing visibilities. MVFR to IFR
conditions and light winds to calm conditions will prevail at kacv
through the early morning primarily due to reduced ceilings.
Visibilities and ceilings will improve late this morning and this
afternoon and VFR conditions will prevail at kcec and kacv with
light to moderate winds occurring. VFR conditions and light winds
to calm conditions will continue at kuki through Thursday.
Marine...elevated winds and seas continue across the waters as
the offshore high pressure system and inland thermal low pressure
trough persist across the region maintaining a tight pressure
gradient across the waters. The winds and seas continue higher
across the outer waters. Elevated winds and seas will continue
across the waters through this week especially across the outer
waters. Gale warnings will continue across the northern outer
waters through early Friday morning and will likely be extended
due to increasing winds. Small craft advisories will continue
across the southern outer waters through early Friday monring.
Small craft advisories will continue across the southern near
shore waters through this afternoon due to short period seas.
Small craft advisories will continue across the northern near
shore waters through early Thursday morning primarily due to short
Fire weather...very hot afternoon high temperatures will persist
through Friday as strong upper-level ridging remains in place over
northwest California. Afternoon minimum relative humidity values will bottom out
in the single digits to lower teens while overnight recoveries
remain rather poor on mountain ridges overnight. However winds
will be light throughout the period resulting in no significant
fire weather threat. The one concern is a slight chance of
thunderstorms over northern Trinity County Friday and Saturday
afternoons. At this time, chances are very low, but not zero, so
model trends will be watched closely. If storms are able to form,
the best chances will be just north of the area into central and
eastern Siskiyou County with storms firing off the higher terrain
of northern Trinity County and moving northeast.
Coastal areas will be much cooler than the interior with a
continued marine influence throughout the next week. /Rpa
Northwest California coastal waters...
Small Craft Advisory until 2 am PDT Thursday for pzz450.
Gale Warning until 3 am PDT Friday for pzz470.
Small Craft Advisory until 3 PM PDT this afternoon for pzz455.
Small Craft Advisory until 3 am PDT Friday for pzz475.
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