Scientific Forecaster Discussion
fxus66 ksgx 241019
Area forecast discussion
National Weather Service San Diego California
319 am PDT Mon Jul 24 2017
monsoonal moisture will bring a chance of showers and
thunderstorms wthis afternoon and evening for the
mountains...deserts...and inland Empire with smaller chances
elsewhere and at other times. The chance for mountain and desert
thunderstorms will continue on Tuesday...decreasing on Wednesday.
Warming with decreasing humidities for Wednesday through Friday.
Slow cooling and a slow return of monsoonal moisture for next
weekend through early next week may return the chance for
afternoon thunderstorms for the mountains and deserts.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Short term (today through wednesday)...
early this morning...water vapor imagery shows the northern edge
of greater higher level moisture extending from around Oceanside
to the southern tip of Nevada with drier air to the north of that.
The edge of that boundary is shifting only very slowly towards the
north and may move only move northward to around Los Angeles if
that. Precipitable water values over the lower deserts have
increased to a little more than 2 inches...around 200 percent of
normal...and is expected to peak today. The models mostly keep
those higher values from the mountains eastward across the lower
Radar imagery shows a band of scattered showers and isolated
thunderstorms moving slowly westward across northern baja to just
north of the border with most of thunder near the border. That
band is expected to continue moving slowly westward the next few
hours with showers and isolated thunderstorms possible across far
southern San Diego County near the border.
The higher resolution models are in better agreement today in
showing the focus for afternoon convection near the mountains into
the upper deserts...possibly extending into the inland Empire with
lesser chances elsewhere. Steering level flow is weakening with
slow cell movement expected with thunderstorms. The slow movement
and available moisture is favorable for heavy rainfall sufficient
for flash flooding...however instability remains quite weak.
For Tuesday...the steering level flow becomes weakly south
southwesterly. The most likely locations for afternoon
thunderstorms on Tuesday would be near the mountains into the
upper deserts...possibly drifting into the San Diego County
deserts with the weak southwesterly steering level flow and with
the inland progression of low level convergence as the sea breeze
Moisture will continue to decrease on Wednesday with smaller
chances for afternoon thunderstorms...mainly near the mountains
into the upper deserts. The moisture will keep inland high
temperatures a little cooler today with slow warming for Tuesday
Long term (thursday through sunday)...
for Thursday and Friday...slowly decreasing humidities will allow
for slow warming with high temperatures for inland areas warming
to a few degrees above average for Friday.
For next weekend into early next week...the axis of high pressure
aloft over the southwest states will begin to shift northward
slightly allowing for the return of southeast flow aloft over
southwest California. This will allow for a gradual return of
monsoonal moisture and slow cooling with more afternoon clouds
near the mountains and a return of afternoon thunderstorms for the
mountains and deserts possible some time during this period.
240940z...coasts/valleys...patchy stratus with bases near 1500 ft
mean sea level may bring occasional ceilings to the coastal airports through 16z.
Coverage will be somewhat patchy again tonight, with periods of ceilings
1400-1700 ft mean sea level mostly after 25/05z.
Isolated -shra and possible -tsra over San Diego County this
morning, then a slight chance of -shra/-tsra over the far inland
valleys this afternoon with bases 9000 ft mean sea level and tops to
30000 ft mean sea level. Otherwise scattered-broken cloud layers at or above 10000 ft mean sea level.
Mountains/deserts...scattered rain showers/isolated thunderstorms and rain over southern San
Diego County this morning, then a chance of thunderstorms over the
mountains and deserts this afternoon. Bases will likely be 9000 ft
mean sea level with tops to 35000 ft mean sea level. Strong up/downdrafts and local gusty
surface winds will be possible. Otherwise scattered-broken cloud layers at or above
10000 ft mean sea level.
isolated showers are possible today, with a small potential for
thunderstorms later this morning. No hazardous marine weather is
expected this afternoon through Friday.
a few showers are possible this morning near the beaches. There is a
very small chance of thunderstorms near the coast, but coverage
would be isolated and mainly in San Diego County.
A large south swell generated by Hurricane Hilary may produce high
surf along south facing beaches Friday through early next week.
Confidence in forecast surf heights is low to moderate as this will
largely depend on the intensity and track of the storm over the next
Skywarn activation might be need for this afternoon for the
mountains...the upper deserts...and possibly the inland Empire.