Scientific Forecaster Discussion
fxus66 ksgx 222023
Area forecast discussion
National Weather Service San Diego California
130 PM PDT Mon Jul 22 2019
high pressure aloft will expand over the southwest early this week,
bringing warm days and less extensive night and morning coastal
low clouds. Increasing moisture from the southeast will mean more
high cloudiness and an increasing chance of showers and
thunderstorms, mainly in the afternoons and early evenings and
mainly over the mountains and deserts. The best chances of strong
thunderstorms with locally heavy rain is Tuesday through Thursday.
Dry weather will likely return by next weekend.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Some thunderstorms had formed over the region as of early afternoon
as the decrease in mid-high clouds have allowed for better surface
heating. A few lightning strikes in quick-moving weak convective
cells occurred earlier, including a couple near Palm Springs a
little before 10 am. Scattered thunderstorms will occur mainly over
the mountains this afternoon, but given the southeast flow, a few
cells could drift into the valleys. Durations will generally be
short as, evidenced by the northern baja convection, the
thunderstorms modify the environment by the cooling. Hrrr and href
show relatively limited amounts of precip, so total amounts should
generally be under 1/2 inch this afternoon.
The upper high is now over the 4 corners and will stay in that area
through about Thursday and bring US moist southeast flow aloft.
Winds in the mid levels will decrease by about half, which will help
the taller pulse-type thunderstorms to better form, though near
saturation at times in the 500-300 mb layers may produce enough
clouds at times to inhibit the convection. Some of the higher level
moisture will be dependent on convection upstream, such as over
Sonora, the day before. Where thunderstorms form, there could be
brief heavy rain, with a possibility of isolated flash flooding,
though href solutions show a very low chance of greater than one
inch of precipitation anywhere Tuesday, at least for now.
Thunderstorms will mostly be over the mountains and deserts, but
some convergence along the Elsinore convergence zone in the inland
Empire could produce a few thunderstorms there Tuesday or Wednesday
afternoon, especially with surface temperatures around 100 degrees
providing some instability. The moisture decreases some Thursday,
though the height level of the moisture, more around 700 mb, less
above, may be more favorable for thunderstorms partly due to fewer
Gefs is consistent with its ensemble solutions with the placement of
the upper high over the 4 corners through Friday, then the solutions
gradually divergence over the weekend with more than half the
solutions having the upper high shift south which would place US
under drier southwest flow, mostly due to troughing in the northern
part of the west, but other solutions only have a slight shift
southwest, which could maintain isolated thunderstorms. For now,
will lean towards the drier solution but keep our eyes open.
Temperatures will be a little above normal this week, except near
or just slightly below normal in the deserts due to the moisture,
though the humidity will make it feel warmer there. With the drying
late in the week, temperatures in the deserts could rebound above
110 degrees again.
221945z...coast/valleys...few-sct low clouds with bases around 1000
ft mean sea level and tops to 1600 ft mean sea level this afternoon. Low clouds will be
less in coverage tonight, but could impact ksan, kcrq and ksna with
cigs 800-1000 ft mean sea level at times between 08z and 16z Tuesday.
Mountains/deserts...sct-bkn clouds at or above 10000 ft mean sea level early this
afternoon. Few-scattered thunderstorms and rain over the mountains this afternoon/evening.
Lightning vicinity kpsp, ktrm, ksbd and kont is possible but low
no hazardous marine weather expected through Friday.
there is a small chance that Skywarn activation will be needed later
today. Skywarn could be activated any afternoon and early evening
through Friday due to thunderstorm activity.