The PNA is forecast to go negative

The Pacific/North American pattern is forecast to go quite negative over the next month. Take a look at the CFS forecast below.

PNA forecast from the CFS

A negative PNA implies ridging over the east and troughing over the west, which would extend the warmth we’ve seen along the East Coast this winter. Predictably, this corresponds with a CFS temperature forecast that shows precisely that, as well as some incredible warmth over eastern Europe and western Asia.

CFS temperature forecast

If this warmth keeps up during the next few weeks, it’s possible that grapes will begin growing for the season in the East. About half of the nights at the end of February have temperatures at or below freezing in DC, and the possibility of a March frost is quite high. This could have a negative impact on wine yields if the vineyards can’t keep their temperatures high enough.

How warm is it really?

It’s 67°F at National Airport as I write this. We had temperatures in the 70s this past weekend; Saturday topped out at 68° and Sunday hit 71°. So yes, it’s warm. But in the broader context, this warmth is actually more common than you might expect. The data presented below are from the National Centers for Environmental Information, which are part of NOAA. These are maximum daily temperatures from February 15-25 at National Airport (located in Arlington, VA) from 1981 through 2015.

Histogram of Maximum Temperatures at DCA

The average high temperature for that timeframe is 49.2° with a standard deviation of 10.7°. Thirty-three days between Feb. 15-25, 1981-2015 have had high temps above 65° (roughly 8.6%). About half of those days were during active La Niña events.

So how common are these warm temperatures? Well, they’ve happened about 8.6% of the time, which seems rare. However, they occurred in 19 of the 35 years I looked at, which is just over half the time. That’s quite common.

When drought hits Wine Country

Most of California has been in a drought for about five years now. Over the past couple of months we’ve seen this drought erode as precipitation and snow pack has taken over the area. Below is a map showing the changes in the drought conditions over the past three months (from US Drought Monitor).

Drought Conditions (redder colors indicate stronger drought conditions) from the United States Drought Monitor

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