Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
155 PM PDT Thursday Jul 31 2014
warm conditions will continue to prevail through this evening...as
high clouds increase across the region. Isolated thunderstorms will
be possible through this afternoon over the higher elevations of the
San Bernardino County mountains. Subtropical moisture will then
spread into the region on Friday and Saturday...with a slight chance
of afternoon mountain thunderstorms on Friday and a better chance of
showers and thunderstorms over the mountains...deserts...and inland
valleys on Saturday. The threat of showers and thunderstorms will
continue through Sunday...with drier conditions developing next week.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Water vapor imagery continues to show high pressure over the Desert
Southwest this afternoon...with an outflow boundary lifting
northwestward across Southern California at this time. This
boundary is primarily bringing a high cloud shield to the region.
That being said...some cumulus are trying to form over the San
Bernardino County mountains ahead of this cloud shield...and it
appears that this boundary may be providing enough lift in this area
that we could see a stray shower or thunderstorm develop late this
afternoon or evening...mainly between san gorgonio...Onyx
Peak...and the big bear area. Otherwise...conditions are relatively
warm and and somewhat muggy at this time. Temperatures are only
within a couple of degrees of this time yesterday...but the dew
points are up a bit. Especially in the Coachella Valley...where the
associated surface boundary is finally increasing the dew points in
Subtropical moisture will continue to spread into the region through
the first part of the weekend...as this ridge lifts to our north.
Models are suggesting that the precipitable water values will increase to between
1.5 and 1.8 inches over by Saturday. Therefore...think that some
afternoon showers and thunderstorms will be possible on
Friday...mainly over the mountains. However...a better chance of
showers and thunderstorms will be possible for Saturday...as the
models show a disturbance lifting over the area. The track of this
disturbance though is still waffling though depending on the model
and the model run. Given the current trends...think the areas with
the best chance of showers and thunderstorms on Saturday will be
over the mountains and deserts as well as across the inland
Things get more complicated and less clear though as we head into
Saturday night and Sunday. The 12z GFS finally trended towards the
more consistent 00z European model (ecmwf)...and brought this disturbance up through
San Diego County and tracked into northwestward along the coast by
Sunday. If this scenario pans out...then there would be a good
chance of nocturnal thunderstorms on Saturday night as well as a
slight chance of thunderstorms even along the coast. As for
Sunday...there should be enough moisture and instability to continue
the threat of showers and thunderstorms as well.
Unfortunately...the 12z European model (ecmwf) looks very similar to the 12z
NAM...which moves the disturbance over our mountains and deserts on
Saturday night...before pushing it off the our east on Sunday. The
best area of moisture and instability would be over the Colorado
River Basin then...with only residual moisture over our mountains
and deserts for Sunday. To make matters worse...the 18z NAM is now
trying to split the difference between the 12z GFS and 12z European model (ecmwf).
Needless to say...confidence is low for what will actually happen on
Saturday night and Sunday. For this reason...have not changed the
forecast for Sunday...and even kept the chance of thunderstorms in
for the valley at this time...which is somewhat questionable.
Either way...will wait a few more model runs before making any major
Drier conditions will then develop for the work week...as this
disturbance shifts east. A minor warm up will also occur early in
the work week...but the models are showing that another trough will
move inland across the West Coast by midweek...which should help
moderate temperatures once again...with a deeper marine layer and
onshore flow prevailing.
312000z...coasts/valleys...through 01/0500 UTC...unrestricted
visibility and scattered-broken clouds at or above 15000 feet above
mean sea level. 01/0500-1500 UTC...patchy stratus gradually forming
within 20 miles of the coast...with bases 900-1200 feet above mean sea
level...tops around 1500 feet above mean sea level and local
visibility 3-5 miles. Confidence in timing of stratus for taf sites
is low...with moderate-to-high confidence in stratus occurrence.
Stratus will clear 01/1500-1700 UTC.
Mountains/deserts...some cumulus clouds with bases around 9000 feet
above mean sea level developing over the mountains through 01/0200
UTC. Otherwise...increasing clouds at or above 15000 feet above mean
sea level through Friday morning.
100 PM PDT...no hazardous marine weather expected through Monday.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.