Sunday, February 27, 2011

Severe Thunderstorms Possible Monday

A line of thunderstorms will race across the area from 3 PM to 10 PM on Monday. The strongest storms will be capable of damaging straight line winds and small hail.

Temperatures will soar into the upper 70s to near 80 on Monday. This heat will provide *just* enough fuel for thunderstorms later in the afternoon and evening.

Storms will initially start west of the Blue Ridge around midday. They should form into a squall line and then race our way. The leading edge of the storms will be moving into western parts of our area around 3 PM.

The atmosphere will only be marginally unstable once the storms arrive, so we could see some weakening of the squall. Nonetheless, any storms that survive the trek across the Blue Ridge will be capable of damaging wind gusts over 70 mph. There could also be some small hail with the strongest storms. Most of the rain will quickly taper after midnight.

Limiting Factors (technical):
Just like last time, we will have a highly sheared environment with only marginal instability. However, upper-level "lift" could overcome this obstacle.

CAPE, or energy in the atmosphere, will be somewhat limited. Here is a plot for tomorrow evening, which shows almost 1000 CAPE west of I-95 (not too impressive). In addition, CAPE is much less in central VA. This could lead to some weakening of storms, especially after sunset. The key will be sunshine...if we see more, then the air could become more unstable.

Shear is going to be very high. The upper level winds will be howling! This will add to the potential of some powerful downbursts. It could also help to maintain the strength of the squall line. On the flip side, it could also rip apart storms as they try to develop. This is something to watch closely tomorrow - shear vs instability.

Sunday, February 20, 2011

Long Range Outlook Into Early March

Brief Summary:

La Nina will continue to weaken heading into spring. NAO (North Atlantic Oscillation) will generally remain neutral or positive. Although we will see a brief cool down for the start of March, temperatures will remain roughly near or above average. Precipitation will stay near or below average. The chances for a significant snow (over 6") look slim to none.

Digging into the data (technical):

Meteorological winter is about to end (December through February), so it is now time to look at the overall pattern heading into spring. Earlier this winter, we had a strong La Nina, which typically brings mild and dry weather to our region. However, we experienced a strong -NAO (North Atlantic Oscillation), which is when a strong ridge in the jet stream persists over western Greenland and eastern Canada. This brought us cold and snowy weather for December and early January. This ridge eroded in late January, and we have been mild and dry ever since.

La Nina is starting to quickly weaken. In fact, we could be in neutral conditions by May or June. This is a plot of sea surface temperatures, which shows that Nina still exists, but it isn't as strong as earlier this winter. In addition, what you can't see is the water below, which is starting to warm.

Past La Ninas have brought us slightly cooler and wetter weather for March through May. However, this might not be the case this year because La Nina is weakening.

Here is a plot of NAO, which shows negative conditions early in the winter, and then neutral/positive conditions ever since mid January.

There are indications that NAO could turn slightly negative in early March, which would typically get any snow-lover excited. However, the ridge is too far east. I've posted the long range outlook for the upper-level atmosphere (first map), and temperatures for the lower atmosphere (second map). Notice on the first map how the ridge, indicated by the yellow blob, is located east of Greenland. Although this could bring us slightly below average temperatures, it is not in an ideal location for significant snow. Average highs for early March are in the mid 50s and average lows are in the mid 30s. We should generally stay near these numbers for early March. Of course, there will be some fluctuations.

Obviously, there could be some changes to the forecast, however, this isn't looking good for snow-lovers.

Saturday, February 19, 2011

Wind Gusts From Today

Wintergreen saw a gust of 71 mph...that's almost hurricane force winds! Here is a list of highest gusts from other areas across the state. You'll notice that winds were not as strong in southern Virginia. Luckily, winds will subside later tonight and the rest of the weekend looks nice!

Friday, February 18, 2011

High Fire Danger On Saturday

A front will sweep through the area early tonight and drag in extremely dry air for Saturday. In addition, we will see strong winds from the west/northwest sustained at 25 to 35 mph with gusts up to 45 mph. For these reasons, a Red Flag Warning has been issued from 9 AM to 9 PM on Saturday for high fire danger. Winds will eventually diminish by Saturday night.