Drought Update Thursday: Improvement Expected Through Fall

We've picked up as much as 2"-3" (or more in spots) of rain the past several days in central Virginia as a stalled front lingered in the state and upper disturbances continued to track over the region. Richmond currently stands at 1.83" for our storm total rainfall, with another batch of showers on the way from southwest Virginia today.

RIC August to date: 3.86"

RIC Year to date: 22.67" (-5.79" from average)

This has been beneficial rainfall for much of our region, but isn't enough to pull us out of the drought...yet. The seasonal outlook just released this morning shows that we should see significant improvement in the drought through November:

If we can avoid more persistent high pressure ridges parking over us the rest of the Summer, storm tracks and fronts can reach us, leading to rain events like we've had this week. In addition, we still have more than half of hurricane season to get through, which could significantly help our rainfall deficit if a system or its remnants track over the Commonwealth. In fact, tropical systems account for 10% to 40% of Virginia's September rain totals.

The climatological "peak" of hurricane season is September 10, but systems can continue to impact the East Coast generally through October.

This week's Drought Monitor map doesn't include the rainfall over the past two days (because it only considers data through Tuesday morning, before the rain started) so it might not reflect how we are really faring after the past couple of days. Nevertheless, the past two days of rain likely isn't enough to end severe drought conditions like this:

Rain Totals Through Noon Wednesday

A swath of much-needed rain tracked from the southwest to the northeast over central Virginia last night and into much of this morning. These are the radar-estimated accumulations over the last 24 hours (through Noon Wednesday), which match up pretty well with totals reported in by weather watchers.

An upper wave is tracking over the Commonwealth while a surface front remains stalled over central Virginia. With this boundary lingering in the area this afternoon, new scattered showers and embedded thunderstorms are developing, especially where there are some breaks in the clouds. Keep your umbrella handy because these showers can produce locally heavy rainfall. I am not anticipating a severe threat today, but some of these heavy showers may have occasional lightning with them.

La Nina Update Mid-August

While our Summer months have been the hottest on record so far in Richmond and central Virginia, the Equatorial Pacific has been cooling significantly into La Nina conditions (above: blue shades indicate ocean cooling along the equator. For your reference, here's a broader view below).

You can see the deviation below the long-term average ocean surface temperature in this chart below where there is blue coloring:

The different Nino levels (1+2, 3, etc.) are simply different indicators used to determine the strength of the La Nina/El Nino event. Our dip out of El Nino toward La Nina began in late February, reaching negative anomolies by late April. La Niña conditions are likely to continue through early 2011, according to the Climate Prediction Center forecast data:

(Outlook figure provided by the International Research Institute for Climate and Society, updated 16 July 2010.)

What does this mean for Virginia through October? We should keep running warmer than average into the Fall. As for rainfall, we can go either way in a La Nina setup in the Fall with being wetter or drier than normal. Let's hope we are wetter than average so we get out of this drought!