Weather Service Report


211 
FXUS66 KSGX 212046
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA 
1245 PM PST TUE NOV 21 2017

.SYNOPSIS... 
High pressure aloft will bring hot, dry weather this week. Record 
highs are likely. A slow cooling trend will begin Friday, but above 
average temperatures will continue through Sunday. The ridge breaks 
down next week, but the storm track will remain too far north for 
any real chance for rain through the end of November.  

&&

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

The heat wave has begun. Temperatures this morning skyrocketed under 
mostly clear skies and weak offshore flow. At noon today they were 5-
15 degrees higher than at noon yesterday. Highest temperatures were 
89 at Corona, Montgomery Field and Miramar. Lindbergh Field was 78 
and Palm Springs was 80. 

SAN-TPH pressure gradients were more strongly offshore today (-7.8) 
compared to yesterday (-2.5), and produced east to northeast wind 
gusts from 25-40 mph in and below the favored mountains passes this 
morning. Peak winds today were 40 mph at Pleasants Peak and Sill 
Hill. A 1030 mb surface high over western Colorado will remain in 
place through Thursday morning so these local offshore winds will 
continue until then. 

The strong upper level ridge will be the dominate feature over the 
Southwest this week. 5H peak at 594 dm on Wednesday, then trend ever 
so slowly downward to 588 dm Sunday. Record highs are likely just 
about anywhere from the coast to the deserts on Wednesday and 
Thursday. Weak offshore flow and the associated downslope warming 
will send valley temperatures soaring into the mid 90s. It's quite 
likely that temperatures here in Southern California will be the 
highest in the land.  

The forecast challenge today is determining just how hot it will be 
Wednesday and Thursday. Numerical guidance usually under-forecasts 
the max temperatures in these highly anomalous patterns, especially 
in the coastal zones and western valleys. In this case the guidance 
has been fairly consistent the past couple of days with a high of 86 
or 87 at KSAN Wednesday. The current forecast has incorporated these 
values and no major changes were made to Max T. 

The ridge weakens this weekend and it won't be quite as hot, but 
temperatures will still be 5-15 degrees above average Saturday and 
Sunday. We will see greater cooler early next week when a weak 
trough passes by to our north. The feature will be too far north for 
rain down here, and dry weather is looking likely through the end of 
the month. The last time San Diego failed to record measurable rain 
in November was 1980.
&&

.AVIATION... 
212017Z...SCT-BKN clouds AOA 20000 ft msl becoming FEW after 22/0300 
UTC. P6SM vis will continue through Wednesday morning. After 22/1200 
UTC, NE to E winds increasing to 15-25 kt with gusts 30-35 kt 
resulting in moderate-strong uddfs/llws over and W or SW of the 
mountains. 
  
&&

.MARINE...
No hazardous marine weather is expected through Sunday.


&&

.FIRE WEATHER...
A Santa Ana weather pattern will be in place through Thursday with 
warm, dry weather and locally gusty winds of 25-40 mph in and below 
the mountain passes and canyons. The strongest gusts this morning 
were 40 mph at Pleasants Peak in Orange County, and Sill Hill in San 
Diego County. Below the Cajon Pass, winds gusted to 35 mph at 
Devore. These localized winds will continue through Thursday, 
strongest each morning. Afternoon humidities will fall into the 
teens the next few days. Although Red Flag conditions are not 
expected, fire weather conditions will be elevated and any fires 
that start may spread quickly. Areas of greatest concern include 
locations below the Cajon and Banning Passes, and the passes and 
canyons of the Santa Ana and San Diego County Mountains. 

&&

.SKYWARN... 
Skywarn activation will not be needed this week.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.
&&

$$

PUBLIC/FIRE WEATHER...Moede
AVIATION/MARINE...Harrison

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Western Regional Climate Center, wrcc@dri.edu