Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
925 PM PDT sun Sep 21 2014
a building ridge of high pressure will induce a warming trend
through midweek...with inland temperatures rising to 3-9 degrees
above average by Wednesday. The inland extent of night and morning
low clouds will also shrink to start the week...becoming confined to
coastal zones by Wednesday morning. A deepening trough of low
pressure along the West Coast by Friday will bring cool dry weather
with gusty mountain and desert winds Friday into the weekend.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
A high amplitude ridge is in place over the western US this
evening...with a moderate strength closed low riding the western
periphery of the ridge over northern Nevada. Dry southwest flow in the
middle and upper levels is keeping skies clear inland...while a
2500-2800 feet deep marine layer is bringing a few low clouds and
higher humidity values to areas west of the mountains.
Tonight and Monday...the 00z nkx sounding shows a marine inversion
of 6-7 degrees around 2500 feet mean sea level...this is slightly stronger and at
a similar height compared to yesterday evening. Given this...marine
stratus should develop well inland again tonight...covering the
majority of the inland valleys and inland Empire by 6 am. Continued
weakening in the onshore flow would also suggest similar to slightly
earlier burnoff time for the stratus Monday morning. Inland high
temperatures Monday afternoon will be 2-6 degrees warmer than
Sunday...with 500 mb heights building to around 590 dm by Monday
Tuesday through Wednesday...the marine layer will become
increasingly shallow...as a ridge amplifies over the west. Low
stratus should be limited to coastal zones by Wednesday morning.
Warming for southwest California will be moderated slightly by the position
of the ridge axis over western Arizona...with high temperatures climbing
to only 3-9 degrees above seasonal averages by Wednesday. Compared
to last weeks heat that featured highs of 10 to 20 degrees above
seasonal averages... this warm up should feel relatively mild.
Thursday into the weekend...temperatures level off Thursday as the
ridge axis shifts toward eastern Arizona...with a cooling trend
developing in earnest on Friday. Reasonable model consensus exists
for a deep trough along the West Coast by Thursday...but timing
differences between the European model (ecmwf)/Gem and GFS continue. The slower
European model (ecmwf)/Gem solutions...to which the current forecast is
weighted...would suggest cool weather Friday-Sunday. Regardless of
which model is the most correct...gusty westerly winds look likely
for the mountains and deserts Thursday into Saturday. This trough is
not expected to be a precipitation maker for socal...but a deepening
marine layer may produce some late night and early morning drizzle
along the coast Friday and Saturday.
220400z...coasts/valleys...areas of stratus will continue to develop
along the coast through 08z...then become more widespread and extend
20-30 Michigan inland by 13z. Bases will be 1200-1600 feet mean sea level with tops to
2000 feet mean sea level. Kont will likely be near the edge of the stratus. Most
visible will remain above 5 Michigan...except local visible under 1 Michigan could occur
in some inland valleys 10-15z...including vicinity krnm and kf70. Most
areas will clear by 17z Monday. Stratus Monday night will likely
continue the trend of lower ceilings.
Mountains/deserts...mostly clear with unrestricted visibility
through Monday night.
900 PM...no hazardous marine weather is expected through Thursday.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.