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Forecast Discussion for San Diego, CA

933
FXUS66 KSGX 170422
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
922 PM PDT Mon Oct 16 2017

.SYNOPSIS...
Weakening high pressure aloft will bring another hot day to the
region on Tuesday. A weak trough may trigger an isolated
thunderstorm on Wednesday, but the chances are small. The trough
will bring cooling Thursday and Friday along with a deeper marine
layer and gusty west winds in the mountains and deserts. There is
the potential of a Santa Ana wind event and heat wave across
southwest California beginning next Sunday and lasting into the
middle part of next week as high pressure builds.

&&

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

It was another hot day away from the beaches with temps well into
the 90s and even some triple digit readings. Two record highs were
reached today - Ramona hitting 99F degrees (previous record 96 in
1997) and El Cajon hitting 101F degrees (previous record 100 in
1997.) A tranquil evening prevails and will continue overnight.

The flow aloft will become more zonal on Tuesday, but surface
cooling will be minor, and tomorrow will be another very warm day
with temperatures 10-15 degrees above average west of the
mountains, and 5-10 degrees above average in the mountains and
deserts.

On Tuesday night and Wednesday a couple of weak Pacific shortwaves
traverse central and southern CA. The first wave passes over Santa
Barbara and San Bernardino County Tuesday night. Moisture advection
is not in phase with this first shortwave and that will limit the
potential for elevated convection. Deeper moisture is available with
the second wave on Wednesday. The WRF point sounding forecast shows
near saturation in the 400-600 mb layer resulting in a PW of 1.57"
Wednesday afternoon. Most unstable CAPE values range from 200-400
J/kg Wednesday, and the NAM High Level Total Totals reach 31-33,
which has historically been the trigger values for isolated to
scattered thunderstorms. Have introduced a slight chance of
thunderstorms on Wednesday to the mountains and parts of the deserts
and valleys. This will be likely be adjusted over the next few
shifts as more hi-rez model data becomes available. Precip amounts,
if any, will be light with most of the precip evaporating in the dry
subcloud layer. Best chances for measurable rain will be in the
mountains.

On Thursday and Friday a broad longwave trough moves into the
Pacific Northwest where rain is likely. Farther south in our area
the precip chances are minimal, but the trough will bring cooling, a
deeper marine layer, and stronger onshore flow with gusty afternoon
and evening west winds in the mountains and deserts.

On Saturday the trough moves east and a strong ridge of high
pressure will build over the West. This Santa Ana weather pattern
will bring another round of hot, dry weather and elevated fire
weather concerns early next week.

&&

.AVIATION...
170400Z...FEW-SCT clouds AOA FL200 and unrestricted vis through
Tuesday evening.

&&

.MARINE...
No hazardous marine weather is expected through Thursday. Winds will
increase to around 20 kt or more on Friday as a front traverses the
region.

&&

.BEACHES...
A south southwest swell from 200 degrees will peak Tuesday-Wednesday
at 3-4 ft/16-18 seconds. This will produce 3-6 ft surf with sets to
7 ft north of Del Mar. Highest surf will occur along southwest
facing beaches. Strong rip and longshore currents will accompany the
elevated surf. Swell and surf will begin to lower on Thursday. A
Beach Hazard Statement is in effect for elevated surf and strong rip
currents Tuesday and Wednesday.

&&

.FIRE WEATHER...

Light winds, hot weather and low humidities will continue through
Tuesday. The RH will start to increase and temperatures start to
cool Wednesday and Thursday as the ridge aloft weakens and onshore
flow and the marine layer slowly return. A weak disturbance aloft
interacting with increasing midlevel moisture may trigger an
isolated thunderstorm Wednesday. Measurable rain is unlikely except
in the mountains, where 0.01-0.10" are possible with any storms that
do form.

Thursday and Friday...Onshore winds will be increasing over
mtn/desert areas and become strong and gusty from the west with
increasing RH driving well inland.

Outlook...Saturday looks to be a transition day from onshore flow
to offshore. A Santa Ana wind event and heat wave looks possible
beginning on Sunday and lasting through at least next Wednesday.
We will continue to closely monitor this potential in the coming
days.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement from 6 AM PDT Tuesday through Wednesday
     evening for Orange County Coastal Areas-San Diego County
     Coastal Areas.

PZ...NONE.
&&

$$

PUBLIC...Gregoria/Moede
AVIATION/MARINE...SS

NWS San Diego, CA (SGX) Office Area Forecast Discussion

Discussion Script by Ken True at Saratoga Weather - WFO Script by SE Lincoln Weather