Special Weather Statement, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
203 PM PDT Tue Aug 1 2017

.SYNOPSIS...
A couple upper level disturbances will move through Southern
California today through Wednesday, bringing chances for showers
and thunderstorms for all areas. Monsoonal moisture will likely
result in afternoon and early evening thunderstorms over the
mountains, deserts and possibly valleys Thursday. Decreasing
moisture will lead to lessening chances for afternoon
thunderstorms over the mountains Friday, with a dry forecast
starting Saturday. Expect night and morning marine layer stratus
becoming more widespread in the coast and western valleys by this
weekend. High pressure aloft will continue to bring above warm to
hot conditions inland through Friday before gradual cooling takes
place this weekend through early next week.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

An upper level short-wave trough is currently moving through the
region, and we are getting surface based thunderstorms developing
over the valleys and San Bernardino county mountains, with the
storm over Alpine being the most impressive one of the day so far.
Latest SPC mesoanalysis shows about 1000-2000 J/KG of over eastern
San Diego county and Riverside county. Also, the morning sounding
from Miramar shows a precipitable water of 1.7 inches. Models are
indicating potentially another round of nocturnal showers and
thunderstorms tonight/Wednesday morning for all areas as another
wave rotates into the area from the southeast. There's been enough
sun today in many areas to result in temperatures being a few to
several degrees higher than 1 pm yesterday for inland areas. Finally,
marine layer stratus has cleared this afternoon but may move
inland again 10-15 miles tonight/Wednesday morning.

For Wednesday afternoon/evening, moisture increases further and
models also show another wave moving over the area, in addition to
surface based CAPE greater than 1000 J/KG. The 12Z GFS shows
precipitable water increasing to 2 inches, and the 12Z NAM12
shows it increasing to near 2.2 inches in some locations! Although
east to southeast flow aloft of around 10-20 kt could move some
storms, with such a high amount of moisture and instability,
there's enough of a flash flood threat to issue a Flash Flood
Watch for the mountains, deserts and Inland Empire for Wednesday
afternoon and evening. There's also the chance that some storms
could occur at the coast again.

Although there may be some drying on Thursday, there should still
be enough moisture and instability around for a fairly active
afternoon/early evening thunderstorm day over the mountains,
deserts and valleys, with wind flow turning to the south.

Models show significant drying (precipitable water possibly below
1 inch) taking place Friday as southwest flow moves in due to a
trough developing along the west coast, with continued drying
this weekend through Monday. Thus, starting Friday,
afternoon/early evening thunderstorm chances should be greatly
decreased, and altogether gone by Saturday.

Look for high temperatures 5-10 degrees above normal to continue
through Friday with a strong ridge to the north (centered near
northwest Nevada and northern California) extending down into
Southern California. Once the trough develops, we should start to
see gradual cooling this weekend into early next week, with highs
falling below normal by Sunday. The marine layer should be able to
re-establish itself late this week into early next week as the
monsoon moisture goes away, so expect night and morning marine
layer stratus along the coast and western valleys during that
time. Before Friday, the night and morning stratus along the coast
will likely be very patchy.

&&

.AVIATION...
012000Z...A thunderstorm risk will continue across the entire area
through Wednesday evening, but direct impacts at any terminal are a
low risk. The greatest threat for TSRA is at KPSP and KTRM on
Wednesday, so included VCTS there. At the other terminals, the risk
is too low to include in the TAFS at this time, but will monitor for
possible amendments.

Brief moderate to heavy rain and gusty, erratic outflow winds are
possible with these storms. Low clouds are forecast to only briefly
affect KSAN, KCRQ, and KSNA late tonight and early Wednesday morning
at around 1000 FT MSL. Elsewhere, a SCT-BKN cloud deck at or above
8000 ft layered to 25000 ft will prevail. Strong updrafts/downdrafts
in and near TSRA.

&&

.MARINE...
A chance of showers and thunderstorms will continue through
Wednesday evening. These storms may produce gusty outflow winds,
locally heavy rain, and cloud-to-water lightning. A Marine Weather
Statement remains in effect through 11 PM Wednesday.

&&

.BEACHES...
A Beach Hazards Statement remains in effect for elevated surf and
strong rip currents through this evening. South swells will produce
surf of 4-6 feet with max sets to 7 feet in Orange county and far
northern San Diego County. Surf will range from 2-4 feet elsewhere.

Isolated thunderstorms are possible at the beaches through
Wednesday evening.

&&

.SKYWARN...
Skywarn activation is requested for San Diego, Riverside and San
Bernardino counties.

Skywarn activation will likely be needed again for Wednesday
afternoon and evening.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Flash Flood Watch from Wednesday morning through Wednesday
     evening for Apple and Lucerne Valleys-Coachella Valley-
     Riverside County Mountains-San Bernardino County Mountains-
     San Bernardino and Riverside County Valleys-The Inland
     Empire-San Diego County Deserts-San Diego County Mountains-
     San Gorgonio Pass Near Banning.

     Beach Hazards Statement until 8 PM PDT this evening for Orange
     County Coastal Areas-San Diego County Coastal Areas.

PZ...NONE.
&&

PUBLIC...Harrison
AVIATION/MARINE/BEACHES...Gregoria

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
235 PM PDT TUE AUG 1 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0230 PM     TSTM WND DMG     ALPINE                  32.85N 116.76W
08/01/2017                   SAN DIEGO          CA   LAW ENFORCEMENT

            LARGE TREE BRANCHES DOWN BLOCKING TWO LANES
            ON N. VICTORIA DRIVE.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
247 PM PDT TUE AUG 1 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0246 PM     TSTM WND GST     1 E ALPINE              32.84N 116.74W
08/01/2017  E75 MPH          SAN DIEGO          CA   TRAINED SPOTTER

            TRAINED SPOTTER REPORTS ESTIMATED WINDS OF
            75 MPH. RADAR INDICATES WIND GUSTS OF 65
            MPH.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
331 PM PDT TUE AUG 1 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0329 PM     TSTM WND DMG     4 SSW MARCH AFB         33.84N 117.30W
08/01/2017                   RIVERSIDE          CA   LAW ENFORCEMENT

            TREE DOWN BLOCKING ENTIRE ROAD.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
336 PM PDT TUE AUG 1 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0320 PM     TSTM WND DMG     2 SSW TEMECULA          33.47N 117.14W
08/01/2017                   RIVERSIDE          CA   LAW ENFORCEMENT

            THREE TREES DOWN AND BLOCKING LANES.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
344 PM PDT TUE AUG 1 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0337 PM     TSTM WND DMG     4 NNW QUAIL VALLEY      33.76N 117.28W
08/01/2017                   RIVERSIDE          CA   LAW ENFORCEMENT

            TREE AND POWER LINES ACROSS STREET.

&&

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