It’s that time of year when the flowers start blooming, the trees start budding and the grass starts growing.  This means the pollen index will be starting during the weather segments.  Pollen season normally begins at the beginning of April and ends during early May.  The height of the season is mid to late April.  This is the time you will notice a yellow powdery substance on your cars and porches.  Many local residents are highly allergic to specific pollens that bloom during this time of year.

Meteorologist Jon Cash

How can it get so warm during the day and so chilly at night this time of year?  The warmer days are simply caused by the longer days and higher sun angle but why are the nights sometimes cold after the warmer days?  The answer lies with the “dew point temperature.”  This is the actual amount of moisture in the air.  Higher levels of moisture mean a higher dew point (the temperature at which dew forms) and warmer nights.  The actual air temperature cannot drop below the dew point temperature.  During the early Spring the dew points are usually low and so the nighttime temps attempt to drop to those levels keeping the nights quite chilly.

Meteorologist Jon Cash

You bet it can!  It’s not rare at all to see snowflakes this time of year but it is very rare to see snow accumulate this time of year.  The ground is warming up as you get closer to Spring and temps are also moving higher.  Storms that move through the area can bring snow but it often winds up being a very wet snow that has alot of trouble covering the ground.  Everything has to be perfect to get accumulating snows including a perfectly placed low (usually just southeast of Cape Hatteras) and plenty of cold air filtering in from the northwest.  Will it happen this year?  Who knows…but not in the next week…

Meteorologist Jon Cash

Why does it warm up during Spring?  Simple!  The sun stays out longer and the angle that the sun moves across the sky is at a higher angle.  This higher angle allows more light and the heat associated with it to make it to the ground and warm things up.  The longer the sun stays out means warmer weather, too! 

Also the jetstream tends to move toward the northern U.S. and Canada during this time, cutting off strong cold fronts from Canada from penetrating the Mid-Atlantic area.  Without fresh supplies of northern air our temps naturally warm up and Spring-like conditons start.  I, for one, cannot wait!

Meteorologist Jon Cash

A nice pattern shift is setting up with no more Canadian air expected for a week.  The coldest air will stay well north of the area as the jet stream moves north to a more Spring-like position.  While we will see a couple of chilly damp days at the beginning of the week, the rest of the week should warm up nicely and some great weather is expected…especially Thursday, Friday and Saturday.

We are in mid-March and warmer weather is expected this time of year.  Hopefully the massive cold fronts and storms from Winter 2010 are over but it’s too early to say whether one or two more could invade the area later this month or into early April.

Meteorologist Jon Cash

A high pressure system from the Midwest will slowly push our way just in time for the weekend.  This means lots of sunshine both Saturday and Sunday.  With the high to our west and slowly pushing eastward the wind will continue to come in from the north keeping temps colder near coastal locations and warmer inland.

For Saturday highs will remain near 45 right along the coast with the wind 10-15 mph.  Inland areas will be in the low to mid 50s on Saturday.

For Sunday highs will range from the upper 40s along the coast to the upper 50s inland.

Water temps remain in the low 40s.  Any wind coming onshore this Spring season will have a drastic impact on temps.

Meteorologist Jon Cash

The answer is closer than you can imagine.  Mixed precipitation started late Tuesday afternoon and continued Tuesday night and into early Wednesday morning.  The area received between one and one and one half inches of water from the sky.  Most of that fell as rain and mixed snow but ending as snow with some accumulations.

The temps at the surface had little effect on what came out of the sky so if you were watching your thermometer, you should have been looking at the temperature a couple of thousand feet in the clouds.  Here’s how it worked.  The temperature between 1000  and 2000 feet was about 35 degrees and the precipitation from those clouds was in the form of light rain.  The temperature between 3000 and 5000 feet was moving back and forth between 31.5 degrees and 32.5 degrees.  This led to heavy rain when it was just above freezing and heavy, wet snow when it was 31.5.  If the temperature had stayed just above freezing at that cloud level, the precipitation would have stayed all heavy, wet snow.  This would have caused the temperature at 2000 feet to drop as well which would have cut off the light rain and turned it to light snow.

The bottom line…a foot or more of wet snow would have fallen and every forecaster in the region would have egg on their faces.  Forecasters in Dallas, Texas had this happen a couple of weeks ago…it’s no fun to the weather ego.

Meteorologist Jon Cash

It all started with a mix last night but this morning we had a change over to snow for most areas.  The rain snow-line pushed eastward this morning and heavy precipitation developed in the form of big wet snow flakes.  It was all due to strong and large area of low pressure just off the coast that bought some cold air and plenty of moisture.   As a result places on the peninsula picked up 2-4″ of snow with a dusting to around an inch on the southside.  In addition the wind field around the low was close enough to cause winds to gust as high as 40 mph.  The low pressure will continue to strengthen as it moves along the coast.   The bulk of the moisture will track north and east out to sea by late morning but moisture will continue to wrap around on the back side of the low pressure.  Some of the lingering wrap around moisture could produce a few lingering snow showers or sprinkles this afternoon and evening.  No additional accumulation is expected with temps well above freezing.

Meteorologist Jon Cash

Low pressure will move from Jacksonville, Florida late this afternoon along the southeast coast overnight tonight.  The low will rapidly strengthen during the overnight hours as it passes about 180 miles east of Hatteras, North Carolina.

Heavy rainfall will occur on a line from Elizabeth City to Sandbridge eastward.  Rainfall over an inch expected east of that line with rapidly lower precipitation amounts as you move west and north from that line.  Any deviation of the heavy precipitation can have a major impact on the forecast rain/snow line.

At this point the rain/snow line should meander overnight on a line from Franklin, Ahoskie, Western Newport News to Gloucester and the Northern Neck.  Temps will be just above freezing.  Most of this area will be in the lighter precipitation field so snowfall amounts will be limited…UNLESS…the heavy precipitation field near the coast gets pushed back into the colder air.  This could happen if the low pressure is located a little closer to the coast then predicted.

The low will also have some very strong winds associated with it.  The wind field will be a compact one so areas closer to the low will get a lot more wind than areas farther away.  At this point winds could gust to 50-60 mph on the Outer Banks tonight and 40-50 mph near the coast across Tidewater, with lower gusts just away from the coast.  The wind field will determine the amount of coastal flooding that will occur.  At this point I believe the tidal flooding tomorrow morning (9-11am) will be minor to moderate in nature.  If the low gets a little closer…it could be worse, so stay tuned!

Meteorologist Jon Cash

An area of low pressure will move across the Gulf of Mexico and across northern Florida tomorrow before turning the corner and heading up the southeast coast tomorrow night and Wednesday.  The low is expected to strengthen rapidly as it moves along the coast Tuesday night and Wednesday.

At this point the precipitation is expected to start tomorrow afternoon as mainly light rain.  Temps at the surface will be hovering around 40.  Northwest of the metro area could see a light mix of rain, sleet and snow tomorrow afternoon but it will be light.

The forecast concern is tomorrow night.  As the low gathers strength the rain/snow line will be hovering somewhere around southeast Virginia and northeast Carolina.  The exact location of this line will be determined by two variables.  One…the position of the low will determines the wind direction and the amount of cold air that will filter in the system.  Two…the intensity of the precipitation could very well be the determining factor for who gets snow and who gets rain.  Heavier precipitation would certainly be a wet snow that could easily accumulate rapidly.  Lighter precipitation would be a light rain/snow mix.

This storm will also bring minor to moderate coastal flooding Wednesday and possibly Thursday too.

Once again a super close forecast for snow…stay tuned!

Meteorologist Jon Cash