Scientific Forecaster Discussion
fxus66 keka 221136
Area forecast discussion
National Weather Service Eureka California
436 am PDT Sat Jul 22 2017
very warm and dry conditions will persist for much of the interior
this weekend, with somewhat more seasonably warm conditions
expected closer to the coast. Coastal low clouds and areas of patchy
fog will develop each night, burning off by late morning. A few
thunderstorms may develop Sunday through late Tuesday for portions
of Humboldt and Trinity counties, and all of del Norte County.
(today through Sunday morning)
A developing offshore flow will help erode the coastal stratus this
morning, with a repeat performance likely Sunday. In fact, stratus
penetration inland should be less tomorrow morning, as increased
mixing further east helps act as a Road block for its progression.
Otherwise, as heights and temperatures aloft continue to rise, very
warm conditions will develop for our interior valleys. Here, the
latest numerical guidance continues to support highs at least in the
90s, with some of the more typical hot spots climbing into the 100
to 105 degrees fahrenheit range.
Closer to the coast, a surface trough will set up near the coast.
With northeast to easterly surface winds found just to its east,
downsloping affects will help increase afternoon temperatures,
especially just a few miles inland from the shore.
(sunday afternoon through friday)
The sixty-four thousand dollar question continues to be which
numerical model is correct, and what are our thunderstorm chances
during the first half of the week. In short, all of the guidance is
in good agreement with the development of a mid-level low off the
northwestern California coast. Disturbances are also seen crossing
northern portions of the state as the rotate around the low, but
that's where the model agreement ends. So lets look at some of the
more often-used convective models.
The GFS has been very consistent for several days now, with the
convective signal expanding in coverage and precipitation amounts.
Meanwhile, although the NAM still has no hint of precipitation, it
does tip its hand when taking a closer look at the 700-500mb
relative humidity (rh) values. Here, it develops "increasing relative humidity
bombs" as disturbances rotate around the low, and they indicate
precipitation falling aloft, evaporating in the dry sub-cloud
airmass. This model indicates cloud bases running in the 13,000 to
15,000 feet range, compared to 8000 feet seen int he GFS soundings.
This makes sense why it's showing no precipitation, as it's
literally mixing it our before reaching the surface. Our European
counterpart (the ecmwf) has a smaller grid scale resolution than the
American models, yet it also develops precipitation (albeit not
until Tuesday afternoon/evening), just not to the extend of the
GFS. However, both the GFS and NAM do show decent some instability
in the soundings, with the GFS being much higher.
So what's going to happen remains still remains a question. From a
pattern recognition standpoint all models have what would be a
favorable setup for at least isolated thunderstorms to develop
during the first half of the week. Given the consistency seen in the
GFS with some indication from the other models as well, thunder
potential was maintained and expanded in the zones. Although severe
weather is not expected as a whole, any thunderstorm that develops
may produce some gusty winds given the dry sub-cloud airmass seen in
the data, with perhaps some small hail in the strongest storms given
very good lapse rates in the mid-levels seen in the numerical
Heading into the second half of the week, a zonal southwest to
westerly flow will advect drier air across the region, with seasonal
temperatures expected. /Pd
coastal stratus is observed this morning along the coast
from Cape Mendocino northward to Crescent City, while areas inland
are mostly clear. Stratus is forecast to dissipate along the coast
during the afternoon, and then redevelop tonight, with the highest
probability for IFR ceilings occurring in the vicinity of acv.
Farther north at cec, low clouds may be more scattered tonight due
to northeasterly offshore winds developing immediately above a
stable surface inversion.
temperatures over inland portions of northern California
are forecast to warm to around 100 f Saturday and Sunday afternoon,
which will aid in lowering surface pressure and subsequently
tightening the gradient along the coast. Northerly winds will
strengthen as a result, with gale force gusts forecast to occur over
the northern outer waters Saturday afternoon through Monday
afternoon. In addition, large waves will build in response to the
increasing winds...especially for the outer waters. By midweek,
model guidance indicates the tight pressure gradient may shift
slightly westward, which would favor weakening winds across the
high pressure aloft will build across the region today, resulting in
strong warming and drying. Easterly ridge top winds will also
increase as a surface trough develops near the coast. The upper
elevations will likely have poorer recoveries as a result. Interior
temperatures of 95 to 105 degrees are expected this weekend, with
very low humidities in the afternoon. Gusty easterly winds will
likely develop across the upper elevations of del norte and far
northern Humboldt counties tonight into Sunday morning.
As we head into the Sunday through Tuesday evening time frame, an
upper-level low will develop off the coast and interact with
increasing instability. As a result, a few thunderstorms may develop
across all of del Norte County, and across portions of Humboldt,
Trinity, and northeastern Mendocino counties. Soundings continue to
indicate cloud bases running near 8000 feet, making gusty winds a
concern in addition to the lightning with any storm that develops.
Drier westerly flow aloft will put an end to our convective threat
for the middle to end of the week. /Pd
Northwest California coastal waters...Small Craft Advisory from 3 PM this afternoon to 5 PM PDT Monday
Small Craft Advisory until 3 PM PDT this afternoon for pzz470.
Gale Warning from 3 PM this afternoon to 5 PM PDT Monday for
Small Craft Advisory until 11 am PDT Sunday for pzz455.
Small Craft Advisory until 5 PM PDT Monday for pzz475.
Visit US at http://www.Weather.Gov/Eureka
Follow US on facebook and twitter at: