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Area forecast discussion 
National Weather Service Eureka California
929 PM PDT Tuesday Jul 29 2014

Synopsis...coastal regions will again be subject to fog and areas
of drizzle tonight and in the morning while interior locations of
northwest California will simply deal with passing high clouds overnight.
Hot conditions and instability will bring another threat of
thunderstorms to Trinity County Wednesday afternoon.



&&

Update...updated the forecast this evening to show the lack of
convective activity occurring across the interior and to decrease
cloud cover overnight. Also added drizzle along the coast.
Otherwise left the rest of the forecast in tact. As conditions
remain on track. Bfg

&&

Previous discussion......issued at 326 PM PDT...

Synopsis...coastal regions will again be subject to fog and areas
of drizzle tonight and in the morning. Interior locations will see
afternoon and evening clouds dissipate over night by morning. A
disturbance passing over the region this afternoon and evening
will bring a threat of thunderstorms across much of the northwest
California interior this afternoon and early evening.

Short term (today through wednesday)...coastal areas this evening
will see a redevelopment of the low clouds and fog along with areas
of drizzle overnight. An approaching weak upper level disturbance will
bring middle and upper level clouds to northwest cal causing at least partly
cloudy conditions over to all areas tonight. Have extended the
coverage of isolated thunderstorms over eastern parts of Trinity
County until near midnight. Hot temperatures will continue inland through
the end of the week while the coast remain moderate.

Synoptically speaking; monsoonal moisture continues to be pulled
into California around the western periphery of The Four Corners high
over the Desert Southwest. This is being joined today by a
vigorous shortwave rounding the bottom a broad upper low over the
Gulf of Alaska. Water vapor satellite images continue to show two
shortwaves moving from the south-southwest to the NNE, the first is now NE of
35n135w and should arrive over northwest California overnight.

The second of these shortwaves should move across northern cal
and into Oregon at about the time when monsoonal moisture
streaming northward of Southern California reaches the area...during
peak heating of the day Wednesday. The shortwave and daytime heating should
provide enough instability to trigger isolated thunderstorms
across Trinity, NE Mendocino, and eastern del norte counties.
Daytime heating should be plenty to blast through this cap. Mkn

Thursday continues to look like the weakest day for convection
over the area, but Friday will bring yet another threat of
convection across the northeastern areas of northwest cal. I will say the
06z GFS is trying to pop convection again on Thu, but not hoping
on board quite yet. Will wait for more model consistency. Bfg on
Thursday and Friday...the models continue to indicate nebulous
southwesterly flow aloft with poorly defined and hard to time
short-wave features. Convective parameters look favorable for
afternoon or early evening storms in the northern zones both days.
Lapse rate look decent...but there will still be a middle level
stable layer to overcome. Without the moisture and extra lift from
a short-wave...it will be hard for the convection to development
into deep storms. Thus for now will maintain a slight chance of
thunderstorms...mainly over the higher elevations in the northern
zones...forced by daytime heating and terrain.

Long-range (sat through tue)...GFS continues to indicate favorable
convective parameters for storms over the northern zones through the
weekend. Both the European model (ecmwf) and GFS have an upper trough/low approaching
the coast this weekend. The approach of this trough should produce
better shear profiles for possibly more organized and sustained
convection. However there is virtually no cooling aloft indicated in
the model data. For now I will continue with just a slight chance of
thunderstorms on Sat and sun in the northern interior zones. On Monday
and Tuesday...the GFS and ecwmf try to push the upper trough through the
forecast area...with westerly flow aloft bringing drier air into the
region. The European model (ecmwf) was slower with this transition. The GFS does show
instability...mainly in eastern Trinity County on Monday and Tuesday...so
will maintain the slight chance of thunderstorms. The forecast along the
coast has been based largely on climatology and persistence.

Marine....high pressure offshore coupled with a thermal trough
over the norcal interior will maintain moderate northerly winds
across the outer waters through the week. The northerly winds will
continue to produce short period northerly waves through the week
which will propagate into the inner waters as a short period swell.
Advisories in the outer waters have been maintained for steep seas
of 7-9 feet at 8 seconds and winds of 20-25 knots. Northerlies may reach
gale force with seas up to 13 feet late in the week into the weekend.
The possibility for low end gales has been highlighted in the mww.

Aviation...LIFR ceilings hugging the coast at 3pm while towering cumulus
developing over South Fork Ridge line and further east. Expect
stratus to push back inland up Eel River valley pushing past kfot
after 2200 PDT with with visibilities also becoming to IFR. A short wave off
the coast will be grazing the area and this should be enough to
continue isolated cumulonimbi and thunderstorms till about midnight in eastern Trinity
County. Dean

&&

Eka watches/warnings/advisories...
California...none.
Northwest California coastal waters...Small Craft Advisory until 5 PM PDT Sunday pzz470-475.

&&

$$

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