Risk for Severe Storms Saturday

An intensifying low pressure storm system in the Four Corners region of the western U.S. this Thursday morning is going to track through the southern Plains today, then move northeast toward the Great Lakes at the end of this week. Along the way, it should produce rounds of severe weather. This storm system will impact the Commonwealth by Saturday with overcast skies in the morning with showers.

But as we get into our afternoon hours of peak heating, instability will be at its greatest as the surface cold front linked to that low pressure system in the Great Lakes begins its sweep through the state. Ahead of that front, there will be sufficient wind shear, lift, and instability for strong to severe (potentially rotating) thunderstorms to develop in the afternoon and continue through the evening until the cold front passes into the Bay by Midnight.
Here's a time-line of the storm system on Saturday:

We'll be overcast in the Commonwealth by Saturday morning, and showers should expand east into central Virginia from the west before Noon.

Saturday afternoon, as mentioned above, is when we'll have our enhanced threat for severe thunderstorms.

Isolated thunderstorms that develop in central Virginia (east ahead of the main line of storms along the cold front) will be the most likely to rotate and potentially produce a few tornadoes.

Once the cold front starts sweeping through central Virginia, storms should be in a long "squall" line with damaging straight-line winds being our primary threat into the evening.

The cold front will reach the Chesapeake Bay around Midnight, pushing storms to the east.

Although we'll have the downside of a severe weather threat, the good news out of this storm system is that it should bring heavy rain into the entire Commonwealth, which is something we still need in most of the area! Widespread accumulations of a half-inch to around an inch look likely. Here's the potential rainfall accumulation by late Saturday night:

Stay with CBS 6, we'll keep you ahead of the storm!
--Meteorologist Carrie Rose--

Things To Watch Heading Into Hurricane Season

Colorado State came out with their forecast for the upcoming hurricane season. They are calling for an above average season with 16 named storms, 9 hurricanes and 5 major hurricanes. Here are a few things we will be watching over the next couple months leading to the start of hurricane season.

La Nina

Hurricanes like warm ocean water and low wind shear. Wind shear is typically low during La Nina, which would lead to an active season. However, La Nina is rapidly weakening (see the map below), so the forecast isn't as clear-cut.




Atlantic Water Temperatures

As I stated above, hurricanes strive in warm ocean water. Sea surface temperatures (SST) have been above normal over the past few months, which points towards an active season.



NAO

The North Atlantic Oscillation (NAO) has an impact on the Trade Winds. We saw a dramatic shift to a positive NAO during January. This increased the Trade Winds and has consequently cooled the Atlantic waters slightly. If we remain in a positive phase, then ocean temperatures could continue to cool.



Conclusion

Colorado State has already decreased it's initial forecast for this upcoming hurricane season. If La Nina continues to weaken and NAO remains mostly positive, then we might see the number of named storms and hurricanes decrease. We will continue to track this and bring you more updates.

Spring Allergens Hitting Hard

It's that time of year...when the world falls in love. Oh, no wait; wrong season. It's actually (cough, sniffle, sneeze) Spring Allergen Season and it's hitting hard a little earlier than usual for those of you allergic to seasonal pollen and mold producing flora and fauna.

We've had some much-warmer than normal days in March and April and some much-needed rounds of rain during our Spring temperature roller coaster, and that gave the grass pollen an early start (typically we don't see pollinating grasses like timothy, Bermuda and orchard with higher counts until late Spring). The latest Virginia Adult & Pediatric Allergy & Asthma (VAPA) report has the following allergen update:
Pollen and Mold Counts
Last Updated: 4/7/2011

Tree Pollen
509 High (oak, birch, pine, sweet gum)

Grass Pollen

16 Moderate- EARLY!

Mold

1,200 Moderate
Weed Pollen- none

So not only are those of you allergic to the tree pollens listed above dealing with that, you're also having to contend with the grass pollen a little earlier than normal in central Virginia. Recent rains are also enhancing the mold spore production.

Although we'll be a little cooler the next two days, much-warmer-than-normal temperatures and sunshine are expected Sunday and Monday: 80 and 90 degree highs, respectively. Monday's high temperature will be very close to the record high for that date, 92 degrees (1930).

Here's some great FYI from VAPA:

• Most pollens are emitted between 5-10 AM, so you may find it helpful to delay outdoor activities until late morning.
• Beware of high mold spore counts after a heavy rain or in the evening.
• Hot, dry, windy days are the worst for kicking up and spreading allergens! Stay indoors if you can.
  
• Don't hang your laundry out to dry, as allergens will attach to your "fresh" laundry.
• Wear a filter mask when you garden, mow the grass, or rake leaves.
• As tempting as it is to open the windows and let in the fresh air, you're also letting in all those allergens into your home. Keep the windows closed during high pollen count days and run the AC if you can. And replace those air filters on time! Apply this same principle to your vehicles, as well.
  

Typical early Spring allergens include: oak, cedar, elm, maple, and hickory trees. Typical late Spring allergens include: pollinating grasses like timothy, Bermuda and orchard.