APRIL 2012 WEATHER SUMMARY
RIVERSIDE FIRE WEATHER CENTER
PREDICTIVE SERVICES UNIT
A series of Pacific troughs and ridges of high pressure brought big temperature swings to the
region in April. A couple of strong troughs brought showers to the entire region April 11th –
April 13th and April 25th – April 26th. Scattered showers with light rainfall totals occurred
mainly over Central California with the weaker troughs. General winds were mainly south to
west ahead of and with the Pacific troughs and north to east behind the Pacific troughs and with
the ridges of high pressure. There was one weak Santa Ana wind event during the month. It
occurred April 6th – April 7th.
A series of Pacific troughs moving across California brought near to below normal temperatures
to most of the region April 1st, April 5th, April 10th – April 15th, April 23rd, and April 26th – April
27th. A ridge of high pressure centered off the California Coast brought above normal
temperatures April 2nd – April 4th, April 6th – April 9th, April 16th – April 22nd, April 24th – April
25th, and April 28th through the end of the month. Across Southern California, many inland
valley locations had maximum temperatures in the upper 70s to upper 90s with the ridges of high
pressure and 60s to mid 70s with the Pacific troughs. Normally the valley locations of Southern
California are in the low 70s to start the month and upper 70s to end the month. For the month,
maximum temperatures over the region averaged out to 0 to 2 degrees above normal. However,
maximum temperatures ranged from 2 to 4 below normal over some coastal locations in southern
Santa Barbara County to 6 to 8 degrees above normal over some desert locations in southern
Inyo County. For the most part, almost the entire region was within a couple degrees of normal.
Riverside set a daily high minimum temperature on April 25th with 57 degrees. Riverside tied a
daily high minimum temperature of 55 degrees on April 22nd, 56 degrees on April 23rd, and 59
degrees on April 30th.
A couple of strong Pacific troughs moving through California brought showers to the entire
region April 11th – April 13th and April 25th – April 26th. Otherwise, scattered showers with light
rainfall totals occurred mainly over Central California when other troughs moved inland to the
north. For the month, most locations over the region received between 1 and 3 inches of rainfall.
However, most Sierra locations received between 4 and 6 inches of rainfall and most desert
locations received less than a half inch of rainfall. The snow level was between 7,000 and 8,000
feet. The higher mountains in the Sierra and Southern California received several feet of new
snow. For the most part, the region received well above normal rainfall. However, some desert
locations received below normal rainfall. Riverside received 0.86 inches of rainfall for the
month, when normally they receive 0.66 inches.
General winds were mainly south to west ahead of and with the Pacific troughs and north to east
behind these troughs and with the ridges of high pressure most of April. South to west winds
with the Pacific troughs were mainly 10 to 20 mph and north to east winds with the ridges of
high pressure were mainly 5 to 15 mph. However, the stronger troughs brought south to west
winds over some mountain and desert locations to 20 to 40 mph with gusts to 60 mph. There
was one weak Santa Ana wind event during the month. It occurred April 6th – April 7th. Winds
over the mountains and below the canyons and passes of Southern California were mainly north
to east 15 to 25 mph with gusts to 40 mph.
According to the ICS-209, there were no significant fires in April.
Overall, for much of the region April had a little above normal temperatures and well above
normal rainfall. Winds were mainly south to west ahead of and with the Pacific troughs and
north to east behind these troughs and with the ridges of high pressure. There was one weak
Santa Ana wind event during the month.