An inexact science

So, after barely running the irrigation since November, yesterday it seemed time to put some of that expensive municipal water on the groves. No rain was in the forecast, a once promising trough of low pressure for 14 February having changed trajectory and expected to go east of us. Drying winds and continued warmth were in the forecast, after a week of temperatures in the 70s and even over 80. Yes, clearly time to irrigate...

Today it is raining. The temperature has not broken above 47 since about 8:00 this morning. Up to a half inch is expected.

Sometimes the forecasters just get it wrong. Not very often, actually. And a forecast for no rain followed immediately by a day of rain is really rare here.

To their credit, the forecasters keep up links to several forecasts--and the accompanying discussions, where they indicate the models they are using and any doubts--in addition to the current one. And not until about 5:00 this morning was there even any mention of a slight chance of rain. Even at 5:00, the rain chance for the day was given as 30%. It started raining around 7:00, and a forecast issued about the time it started to rain actually downgraded the chance from 60% to 50%. Oops!

By 8:55 a.m. the discussion noted:

NWS DOPPLER RADAR SHOWS NUMEROUS SHOWERS OVER THE CWA [forecast areas] THIS MORNING
WITH SNOW SHOWERS REPORTED IN THE MOUNTAINS...EXTENDING TO SOME
AREAS OF THE INLAND EMPIRE DUE TO LOW WET BULB TEMPERATURES.
DARKENING IN THE WATER VAPOR IMAGERY INDICATES A VIGOROUS SHORT-WAVE
TROUGH DROPPING S THROUGH CA THIS MORNING...

EXPECT VIGOROUS SHORT-WAVE TROUGH WILL DRAW COLD UPPER LOW TO THE
SW...OVER SOCAL BY LATE TODAY. THIS WILL KEEP UNSTABLE CONDITIONS
AND CLOUDS OVER MOST AREAS WEST OF THE MOUNTAINS...

(No, I have idea what "low wet bulb temperatures" are, but I like the way it sounds.)_

Forecasting is an inexact science. And so is knowing when to irrigate. No doubt, had I not turned on the irrigation, it would not have rained.