How many times does this happen? The National Weather Service forecasts rain coming in at a certain time and the forecast is off by a few hours, either early or late. The truth is that this happens all the time and such timing error increase with the length of a forecast. And variations in timing of consecutive forecasts provide valuable information on forecast uncertainty. Consider the rain over Saturday night.
Here is a radar image from the new Langley radar at 7 PM on Saturday night.
A frontal band is moving in, crossing the north-central WA Coast. Now here is the 74 forecast valid this time (1-h precipitation at ending 7 PM). Got the right idea of frontal system...but too far south.
The 26hr forecast? Similar, but slightly weakened.
Forecasters have a special name for the variation in forecast for the same time (e.g., 10 PM August 5) but for different forecast intervals (12, 24, 36 hr forecast, etc): dmodel/dt. If any of you have calculus you know why. For those who haven't, this translates as the change in model solution over a specific time interval... a.k.a. the time derivative. Large dmodel/dt--low confidence in the forecast, small dmodel/dt--more confidence.
Ten years I did a paper with Brian Colle and David Ovens that showed that models were typically fast by an hour or so. I haven't repeated this study, but I suspect that although the errors are probably less now, errors in timing are not usual. That is why the coastal radar is so important. When our models are off by a few hours--too fast or slow, the radar will give us a heads up when weather systems are 6-9 hrs out.
There have been repeated sightings of our dog in and near Terrace Creek Park in Mountlake Terrace. If you are in that area, please let us know if you see her.