Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
905 PM PDT sun Sep 14 2014
hot weather will continue through Tuesday under high pressure aloft.
Some moisture and instability will result in isolated showers and
thunderstorms each afternoon. Moisture and instability will increase
on Wednesday for more widespread showers and thunderstorms. The
added cloud cover and higher humidity will keep it from getting as
hot..but it will still be uncomfortable with the added humidity and
continued above average temperatures. Low pressure off the coast
will bring some drying Thursday and Friday with showers and
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Convective clouds were widespread this afternoon over northern
portions of the County Warning Area. The heat...combined with a slight increase in
middle-level moisture fueled the convection that erupted into a few
thunderstorms over the inland Empire. It was quite hot inland with
many sites recording temperatures well above the century mark.
Surface pressure gradients changed little from yesterday. Slightly
stronger offshore to Nevada and weakly onshore to the lower deserts.
The 00z Miramar sounding had a weak inversion near 1200 feet. Winds
were northwest at around 10 knots below 5k feet and easterly around 10 knots above
through 12k feet. Precipitable water had increased to 1.42 inch. The sounding had a
dry microburst signature and we did see one strong storm and a
nearby measured gust of 43 miles per hour in the inland Empire late in the
Some changes have been made to the forecast to keep the extreme heat
west of the mountains both Monday and Tuesday. Slight chances for thunderstorms
have been added as well west of the mountains with little change in
atmospheric conditions and full heating expected. Only limited
marine influence during the afternoons along the immediate coast...
and no significant marine clouds through Tuesday. Elevated sea
surface temperatures into the lower 70s continue to be reported at
The flat high pressure ridge will remain over the area through
Monday...then build northward on Tuesday. This may accelerate the offshore
slightly and actually result in higher daytime temperatures closer
to the coast. The days will remain quite hot inland...with a heat
advisory in effect through Tuesday. By Wednesday...moisture levels in
the atmosphere will be considerably higher as model precipitable waters climb above
1.5 to nearly two inches. The added clouds and humidity will put a
cap on the extreme heat...but it will remain uncomfortable due to
the higher humidity and light winds.
Isolated thunderstorms are expected again on Monday...increasing in
number on Tuesday over the valleys/mtns/deserts as precipitable water rises and
stability decreases ahead of approaching tropical cyclone Odile.
Showers and thunderstorms may affect the coastal areas as well due
to easterly steering winds aloft. The main threat from these storms
will be lightning and strong...gusty downdrafts on Monday...
transitioning into better rain producers later Tuesday and especially on
Wednesday. The threat for local flash flooding will be significant on Wednesday
if precipitable waters approach 1.75 inch or higher as forecast.
Odile remains a major hurricane this evening with winds of 125
miles per hour...but the forecast track along the Baja California coast will weaken it
considerably as it churns north-northwest at 17 miles per hour. The models have come
together on the demise of Odile...keeping the center again well to
the south of San Diego as a middle-latitude trough slides east toward
northern and central California. The latest NHC track has the storm falling
to tropical storm status by Tuesday evening...and stalling by the time
it reaches Punta eugenia on the west-central Baja California coast at 18z on
Wednesday. It weakens further and the remnants shear NE into Arizona by Friday.
The timing and intensity of the trough to the northwest will influence the
future movement of the soggy remnants of Odile...but confidence is
increasing that it will slide off to the south and east of socal...
similar to Norbert.
The middle-latitude trough to the north is handled differently by the
global models. A blend is favored which keeps the trough over California
into the weekend. Depending on the track of this trough...there will
be some chance of showers/thunderstorms continuing into Sat...but confidence
is quite low that amounts would be significant with much drier air
aloft. Lower heights/thickness...onshore flow and the return of the
marine layer will keep the weather cooler through the weekend.
due to the heat and deep dry layer below 10000 feet...developing
thunderstorms on Monday may produce isolated dry lightning
strikes...mainly along and west of the mountain crests. The chance
of dry lightning strikes will lessen Tuesday and are not expected to be
significant on Wednesday as humidity increases and the dry sub-cloud
layer thins under possible heavy-rain producing thunderstorms.
150330z...coast...very patchy stratus...with bases around 700 feet mean sea level
and tops near 1000 feet mean sea level...may develop along portions of the coast
tonight. Visibility could lower to 4-6sm br where low clouds near
higher terrain. Confidence in coastal aerodromes remaining VFR
overnight is high. Few middle-level clouds will be possible Monday
Valleys/mtns/deserts...mostly clear through Monday morning. Isolated
thunderstorms will be possible over far inland valleys and mountain
peaks Monday afternoon. Cloud-to-ground and cloud-to-cloud
lightning...reduced visibility due to heavy rain...gusty
winds...strong up/downdrafts and small hail will be possible near
830 PM...no significant marine weather expected through Tuesday.
Isolated showers and thunderstorms may develop over the coastal
waters at times Wednesday and Thursday. Gusty winds...cloud-to-water
lightning...heavy rain and rough seas will be possible near storms.
Skywarn activation is not requested. However...isolated
thunderstorms are expected Monday. Weather spotters are encouraged
to report significant weather conditions.
California...heat advisory until 7 PM PDT Tuesday for the Orange County
coastal areas...San Bernardino and Riverside County
valleys-the inland Empire...San Diego County valleys...
Santa Ana Mountains and foothills.