Tuesday, March 29, 2011

A Rainy Forecast Is A Good Thing

Although rain can be disruptive to our day-to-day lives, we desperately need some in our area. You can see on the graph below that we are 1.7" below normal for the year.

We aren't the only ones dealing with dry conditions. You can see on the map below that most of the Southeast is 2 to 8" below normal for rainfall this year.

Not surprisingly, numerous rivers and streams are now running below normal (indicated by the red and orange dots). The rivers to the west are near normal from the heavy rains we saw earlier this month (indicated by green dots).

Right now, moderate drought extends across central and southern Virginia.

Luckily, we will see an active weather pattern over the next several days. In fact, two back-to-back storm systems could bring 1 to 2" of rain from Wednesday into Thursday. This is great news!

Saturday, March 12, 2011

Winter 2010-2011 Recap: Cool & Dry

Wintry weather can sometimes randomly pop up in late March and early April. In fact, the latest snowfall in Richmond recorded history was on April 28, 1898, where there was 2" of snow. Regardless, for the most part, winter is over. So let's look at some of the stats.

December was the 7th coldest in history (link The cold weather persisted into the first half of January, then the overall pattern changed. Temperatures generally remained above normal for the rest of winter. The map below shows that the entire Southeast U.S. experienced temperatures that were 2 to 6 degrees above normal for the month of February.

If you combine all months together, the overall average temperature for this winter was slightly below normal.

There is no doubt about it: this winter was dry. We were roughly 2 to 4" below average across the entire state. Interestingly, we received 10.8" of snow, which is only slightly below the average of 11.9". Most of the snow fell in December and early January before the pattern change. You can see on the map below that we weren't the only ones dealing with dry conditions. It was even worse in Louisiana, Mississippi and Alabama.

Saturday, March 5, 2011

Here is a rough timeline for today's rain. The shades of green indicate light to moderate showers, while yellows and reds indicate downpours or possibly thunderstorms. There is a very slim chance for severe storms in central and southeast Virginia today.

Rain totals should range from around 0.75" to 1.25" (give or take 0.25"). This is great news considering that we are about 2.5" below normal for the year.

Severe Weather Checklist
  1. Instability (heat and humidity)
    Moisture should be high enough to support thunderstorms. Temperatures will be hindered by clouds and rain, especially along and west of I-95. Highs should climb into the mid 60s for central and southeast VA. This should be *just* warm enough for isolated thunderstorms.

  2. Trigger (something to spark thunderstorm development)
    A strong front will pass the area in the afternoon, which is typically ideal for severe storms.
  3. Wind Shear
    We will have strong speed shear (winds increase with height), and minor directional shear (winds change direction with height).
  4. Sunshine
    Clouds will prevent any sun for today, which in turn keeps us cooler.

This looks like yet another event where wind shear will be very high but instability will be low. If temperatures climbed into the mid 70s, we would have a bona fide severe weather threat. Regardless, we still have to watch this very closely today. If a thunderstorm develops, it could quickly become severe.