NCHurricane2009's Blog

A Big Snow for Raleigh!

Posted by: NCHurricane2009, 2:47 AM GMT on January 30, 2010

This winter season promised to be above average for the eastern United States. For Raleigh (where I live), we haven't had any snow this winter except for a very weak event on December 19, 2009. This evening (January 29 evening), we've already well exceeded the December 19 event in just a couple of hours. Even more crazy, this could become the biggest winter storm for Raleigh since the January 25, 2000 blizzard 10 years ago!

January 29, 2010 Evening, The Onset
Forecasts were calling for a snow/sleet mix to develop around midnight, but the storm arrived in Raleigh instead at 7:30 PM EDT with temps in the mid-30s and a heavy snow/sleet mix kicking in. The atmosphere had been so dry hours prior that as the snow/ sleet evaporated before reaching the ground, it created evaporative cooling, which quickly dropped temps into the upper 20s by the time it reached the ground. The snow/sleet mix quickly became all snow in all its glory.

Radar image of the storm at the onset (from the National Weather Service). Where I am at (Raleigh) is in a steady west-east band of snow. A dry slot further west makes me wonder whether the snow will be interrupted hours later.

The surface setup is classic for a big snow in NC. First, you have a surface low pumping in Gulf moisture from the south, and you have a strong surface high pressure to the north forcing cold air into NC at the same time.

The upper air support for those surface features: (1) a very significant upper low over eastern Canada supporting the strong surface high with upper confluence (convergence) on its west side, and (2) an upper low/trough over the south-central United States producing upper air divergence on its east side supports the Gulf coast low. In addition, a strong jet streak on the south side of the east Canada upper low enhances the upper air divergence for the Gulf coast low further.

Photo of snowfall taken through my kitchen window. This was taken on January 29, 2010 10:00 PM EDT. By eyeballing the the rail of the deck and top of the grill, 1-1/2" of snow accumulation so far. Since the snow began around 7:30 PM EDT, that is a rate of 0.6" per hour.

Midnight Lull

After receiving slightly over 2" of snow, the snow stopped around midnight as we got caught in a dry slot. At about 1:50 AM EDT (January 30), light snow showers move back in. But the second larger dry pocket to the southwest seemed to increase the chance that the snow would have yet another pause. The pocket later passed just south of Raleigh, and we stayed in the light snow showers.

The Sleet
Around 3:30 AM, the precipitation intensity increased, but in the form of sleet. I heard sleet pellets knocking on the roof and windows, and peered outside to see a good sleet storm (visual estimate by this time around 2-1/2" of total snow/sleet accumulation). By 4 AM, the precipitation begins to return to snow, but the flakes were falling fast as if they were weighted down with sleet pellets, but they were not as noisy as the pure sleet.

Report of Thundersnow
Steady snow/sleet was falling, and the NWS Raleigh issued a special weather statement concerning an east-west band of intense snow that had rapidly formed just to our north (reports of lightning), plus road conditions around the US-64 corridor (where I live) were reported bad (by taking a peak outside, yes the roads were all covered with a snow/sleet layer):

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RALEIGH NC
412 AM EST SAT JAN 30 2010

...WINTERY PRECIPITATION WAS OCCURRING THROUGHOUT CENTRAL NORTH
CAROLINA...

AREAS OF HEAVY SNOW...MIXED AT TIMES WITH SLEET...WERE OCCURRING OVER THE NORTHERN PIEDMONT AND THE NORTHERN COASTAL PLAIN AT 4 AM. MANY REPORTS OF THREE TO FOUR INCHES OF SNOW WERE NOTED FROM ROXBORO EAST INTO HALIFAX COUNTY...WITH ONE REPORT OF LIGHTNING BEING OBSERVED WITH THE SNOW BY A SHERIFFS DEPUTY IN SOUTHERN HALIFAX COUNTY. FARTHER SOUTH...MIXED SNOW...SLEET...AND FREEZING RAIN WERE OCCURRING IN THE SOUTHWEST PIEDMONT...ACROSS THE
SANDHILLS AND INTO THE SOUTHERN COASTAL PLAIN. WHILE ANY MODERATE SNOW WILL BECOME MORE PATCHY IN THE TRIAD THROUGH 530 AM...AN INCREASE IN MIXED...WINTERY PRECIPITATION WILL OCCUR IN THE PREDAWN HOURS ACROSS THE SOUTHWEST PIEDMONT THROUGH THE SOUTHERN COASTAL PLAIN.

LAW ENFORCEMENT IN MANY LOCATIONS ALONG AND NORTH OF HIGHWAY 64 REPORTED THAT ROADS WERE COVERED WITH SNOW AND TERRIBLE TO DRIVE ON.

That intense snow band with the lightning was moving NE away from Raleigh, and I would not get a chance to witness it.

A "Sleetfest"
While waking up around 10:30 AM EDT (January 30), there was a light steady precipitation still going on, it had returned to pure sleet with a vengeance. Looking at NWS reports from RDU airport (3-day history), could not find the hour at which the precipitation changed from snow/sleet to pure sleet. Wind gusts had picked up, and sleet pellets were easily rolling off the roof & elevated surfaces (now the only way to judge how much accumulation is to put a ruler in the ground because all precipitation was blowing off of the elevated surfaces).

Icicles on blueberry plants branches near living room window (photo taken 11:00 AM EDT, January 30). The icicles were not due to freezing rain. Instead, they formed as snow on branches melted due to our house heat, afterwards re-freezing to icicles. In the background, it may be hard to see, but wind-driven sleet was rolling off of the roof above to the floor below.

NWS Radar image early afternoon on January 30. Light Sleet is tapering off from west to east, freezing rain to the south, and significant snow has moved NE into Virginia.

Winds are brushing off sleet from roofs. Winds picked up due to tighter pressure gradient between surface low and high.

The surface low continues to be supported by the upper trough to the west (500 mb map). Extratropical low pressure cyclones such as these are tilted westward with height. Looking at the 850 mb map, the 850 mb low pressure spin center is just west of us (unlike the surface center which is just east of us), producing warm air advection from the south over us (note the red above freezing isotherms over eastern NC). The snow flakes melt at 850 mb, and re-freeze as sleet pellets toward the surface (surface temp at the time is 22 F, brrr...).

Forecasts tonight indicate 40% chance of redeveloping snow showers as the upper trough (associated with cold upper air) moves over us. This is because as temps drop off aloft, this will allow clouds to thicken in the now moist atmosphere (like water condensing on a cold cup of water in a humid room). In order for snow to return, that 850 mb cyclone center has to be east of us so we get temps at 850 mb to be below freezing again with cold air advection on its back side.

We aren't going anywhere today! The car is buried with snow/sleet, driveway covered with snow/sleet/ice, and the neighborhood road doesn't look any better! (picture taken around 2:15 PM EDT)

Because all snow/sleet was brushed off the roof & the rail of the deck by wind gusts, now have to look at ground level or deck floor to estimate snow-sleet accumulation. Looking at that mound on the deck, it looked like 6" to me, but it was really hard to tell because the mound was very rounded at its edges. Time to get a ruler out! (picture taken around 2:15 PM EDT)

I was in for a surprise! The ruler says 9-1/2" to 10"! IF THIS VERIFIES, THAT IS THE BIGGEST WINTER STORM IN RALEIGH SINCE THE JANUARY 2000 BLIZZARD! But, I believe there is a higher bias on the measurement because the deck is next to a roof slope, and the snow/sleet that was on the roof was being brushed off all last night into today by wind gusts, which would add extra to the deck surface. I think somewhere in the middle of the front yard (away from roofs and trees) would be a better measurement (photo taken around 2:15 PM EDT)

How About Some Evening Snow Showers to Top it Off
The above mentioned forecast for some snow showers this evening (January 30) came true.

A band of snow showers developed across Central NC and Upstate SC, and was headed this way! I got my camera ready to take a photo of the snow showers when they arrived.

Shot from my kitchen window of the brief snow shower at its peak when it arrived at my house around 8:50 PM EDT (the snow flakes are hard to see in the background due to it being nighttime). Notice this is the same shot of our grill and deck in the back yard taken nearly 24 hours ago (shown above). For one thing, there is more snow/sleet in this photo than in the other. The big difference though is that the sloped surfaces on the grill lost all of their cover. This is because during the long sleet period today combined with wind gusts, any accumulations on sloped & elevated surfaces were brushed off. Plus, the snow was more wet and fluffy 24 hours ago than the dry powdery snow now, which stuck easier to sloped surfaces.

Interestingly, persistent snow echoes developed on radar across the Raleigh area over the next few hours, continuing additional light snow showers lasting into the early morning of January 31.

Storm Aftermath and Conclusion
It was a beautiful sight, I will let the pictures speak...

View of the total snow/sleet accumulation from bedroom window (morning of January 31, 2010).

Another view of the total snow/sleet accumulation from bedroom window (morning of January 31, 2010).

Photo of wondrous snow-sleet beauty under the sun taken from the front right yard (January 31, 2010).

Measurement of total snowfall on the front yard on the morning of January 31, 2010. I messed up the picture slightly by not capturing the full ruler in the photo. But still, the total accumulation at my house measured at 4.5", which is half of what I measured on the deck yesterday (photo above). I knew the deck measurement had a higher bias because sleet pellets had been rolling off of the roof onto the deck, which locally increased accumulations there. I consider the official measurement at my house 4.5"

Official NWS analysis of total snow-sleet accumulation. The red X is generally where I live (on the west side of Raleigh), the 4.5" measurement generally matches the trend on the map.

For the Raleigh area, I would consider this one of the bigger snows since the January 2000 blizzard, but not the biggest snow storm since then (that was last year's 5-incher in January 2009). Regardless, I certainly enjoyed the sights with this storm!

Updated: 10:40 AM GMT on February 04, 2010

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