Scientific Forecaster Discussion
fxus66 ksgx 220423
Area forecast discussion
National Weather Service San Diego California
823 PM PST Tuesday Nov 21 2017
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
Satellite imagery at 8 PM PST, showed scattered high clouds drifting
southeast over the forecast area, otherwise it was clear. The 00z Miramar
sounding indicated some drying aloft and a few degrees c of warming
below 500 mb. There was also a wind shift below 10k feet from northwest to NE
up to 15 kts. The offshore sfc pressure gradient was accelerating to
around 10 mbs (sw Nevada to ksan) it was about neutral to the lower
deserts. Easterly winds continued this evening over wind prone
coastal slope and foothill areas at 15 to 25 miles per hour with peak gusts 30
to 40 miles per hour. It was warmer in many areas as well, temperatures were
generally from 5 to 10 degrees f higher without wind. With the wind
on those exposed slopes and foothill areas, temperatures were in the
80s at 8 PM PST. That is about 20 degrees higher than yesterday
evening. Get ready for a couple of very warm days.
No forecast changes this evening.
From previous discussion...
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. 500 mb 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.
220300z...NE to east surface wind gusts of 25-35 mph will develop
tonight through Wednesday, creating areas of moderate-strong
uddfs/llws over and west or SW of the mountains through the period.
Otherwise, few clouds at or above 20000 ft mean sea level with p6sm visible through
no hazardous marine weather is expected through Sunday.
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 activation will not be needed this week.