Pattern Change Transition Day

9/26 Sunday 8:30 am

For today, isolated showers will develop over the higher terrain this afternoon. Moisture will slowly stream into the area from a closed circulation low-pressure system which is currently centered in the vicinity of Las Vegas. Scattered showers will redevelop on Monday as the low-pressure system approaches from the West. By Tuesday showers will become more widespread as the system combines with a large trough approaching from the Pacific Northwest

Although subtle differences exist among the models, there is good general agreement that the next 5 to 10+ days will bring well above-average precipitation to our forecast area. If I were a betting man, I would say that the temperatures we reached yesterday will be the warmest we experience until next May or June.

High temperatures today will likely be the highest of the week. Starting on Monday high temperatures will run just slightly below average for this time of year. Overnight lows will run above average as the sub-tropical moisture keeps the cooler temps at bay.

At the moment it looks like snow levels will be high (above 12,500′) for the next couple of days. As the closed low gets entrained into the trough of low pressure coming in from the Pacific Northwest on Tuesday, cooler temperatures will prevail. Late Tuesday and Wednesday, snow levels are likely to fall. I will be tracking that, stay tuned for daily updates this week.

As I said earlier, the models are in good agreement through Wednesday but start to diverge on Thursday. For that reason, the best way to look at the forecasted precipitation amounts is over the long term.

The Weather Prediction Center’s blended model only extends 7 days into the future. Here are those 7-day totals.

WPC

Euro 10 day total

Canadian 10 day total

I am leaving off the GFS this morning because it has veered off the rails from its ensemble family’s mean (average) run.

Here are the 15-day ensemble mean runs for the European model family (50 members) and GFS model family (30 members).

Euro ensemble

GFS ensemble

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