Scientific Forecaster Discussion
fxus66 ksgx 231548
Area forecast discussion
National Weather Service San Diego California
847 am PDT sun Jul 23 2017
mid-level moisture will increase today, with a chance of isolated
thunderstorms near the mountains in the afternoon. A greater influx
of moisture tonight and Monday will bring slight inland cooling,
more clouds, higher humidity, and a better chance for showers and
thunderstorms, with the chances greater near the mountains, and in
the afternoon. Moisture will decrease Tuesday into Wednesday, but a
few thunderstorms are still possible over the mountains on Tuesday.
Dry for the rest of the week with seasonal temperatures.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
The marine clouds exited terrestrial areas rather quickly early this
morning, but remained nearshore and at 8 am PDT were attempting to
return. The culprit may have been perturbations from the advancing
clouds/weather well to the east that have long since wound down. The
left over mid/high clouds continue to drift into southeast portions of the
County Warning Area this morning and thin. Surface pressure gradients remain weakly
onshore and winds are light. The 12z Miramar sounding had a 10
degree c inversion based near 1480 feet mean sea level. Inversion top temp was
27 degrees c near 4100 feet mean sea level. The inversion base was about 500 feet
lower than yesterday morning, with the greatest warming of
4.5 degrees c near 1900 feet mean sea level. This should make it hotter today
over the inland valleys.
The current forecast looks OK. It may get a bit hotter than
advertised at places like Ramona, and across the inland Empire, but
tough to find guidance to accurately reflect this. Some isolated
thunderstorms do look possible given The Jump in mountain-top
dewpoints this morning and expected heating. But limiting factors
will be the moderate easterly flow in the mid-levels at 15-20 kts
and the weakly unstable profiles from the nkx 12z sounding, and the
12z wrfems projections. This will most likely make it difficult
to sustain updrafts over our limited higher terrain.
From previous discussion...
Short term (today through tuesday)...
mid level moisture was just sufficient Saturday afternoon for a
few cumulus clouds on the east slopes of the mountains. Mid level
moisture will continue to increase today in easterly flow aloft.
Combined with weak instability...greater convective cloud
development is expected over the mountains today...possibly
sufficient for a few thunderstorms in the afternoon.
With the gradual influx of monsoonal moisture and easterly flow
aloft...there has been some clearing of the stratus off the Orange
and San Diego County coasts overnight...but with stratus beginning
to redevelop near the beaches...extending locally inland.
For tonight and Monday...a greater influx of monsoonal moisture is
expected in easterly flow aloft. It is possible some convection
could spread into southwest California late tonight into Monday
morning from the east...but there is little model agreement in
such details. The models are similar on Monday in showing more mid
level moisture and precipitable water values increasing to around
2 inches. There could be greater thunderstorm development near
the mountains Monday afternoon and given the available
moisture...flash flooding would be a possibility from the
thunderstorms that do develop. There are some potential limiting
factors...however. The instability is weak and if there is
convection in the morning...that could stabilize the atmosphere
somewhat for the afternoon.
Moisture is expected to gradually decrease Monday night into
Tuesday...but still be sufficient for thunderstorm to develop
Tuesday afternoon in the mountains and deserts.
Long term (wednesday through saturday)...
additional drying is expected for Tuesday night and Wednesday with
some afternoon clouds at times near the mountains...but little
chance for thunderstorms. Areas of night and morning low clouds
and patchy fog will return to coastal areas and extend locally
inland. With the drying...high temperatures will warm from near
average on Wednesday...to near to slightly above average on
Thursday and Friday.
As the axis of high pressure over the southwest states begins to
shift slowly northward next weekend...mid level moisture in
southeast to east flow aloft could gradually return with minor
cooling and more afternoon clouds near the mountains.
231500z...coast/valleys...areas of low clouds with bases near 1200
ft msl may expand some along the San Diego County coast through 17z,
with patchy low clouds hanging in along the beaches through 20z.
Ksan could see ceiling impacts through 19z. Minimal to no ceiling impacts
expected at kcrq or ksna during this period. Otherwise,
predominantly sky clear will prevail between 18z Sunday and 00z Monday.
Low clouds with bases near 1200 ft msl will filter back in along the
coast after 00z, likely spreading inland 15-25 miles by 14z Monday,
then clearing by 17z Monday. An isolated rain showers or -tsra is possible
between 09z and 18z Monday, with the best potential over San Diego
County. Any precipitation should have little to no impact on the taf
Mountains/deserts...few-sct at or above 10000 ft msl and unrestricted
visibility through 19z. Cumulonimbus and isolated thunderstorms and rain should slowly develop
over the mountain peaks after 19z then spread to the deserts after
21z. Any storms that form will produce locally strong up/downdrafts
and gusty surface winds. Cloud tops and base this afternoon should
range from 9000 ft msl to 35000 ft msl. An isolated rain showers or thunderstorms and rain
will remain possible overnight.
an isolated shower or thunderstorm is possible late tonight through
Monday. Cloud-to-water lightning will be the primary threat. No
hazardous marine weather is expected Monday night through Friday.
a high tide near 7 ft this evening could result in minor tidal
overflow in low-lying beach areas, therefore a beach hazard
statement remains in effect through this evening. Surf heights will
mostly be 1-3 ft, and this should limit the potential for tidal
overflow to some degree.
There is a slight chance of thunderstorms at the beaches late
tonight through Monday, with the best thunderstorm chances Monday
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...beach hazards statement through this evening for Orange County
coastal areas-San Diego County coastal areas.