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Posted at 10:52 AM ET, 02/27/2013

Asheville, N.C.: Suffering worse snow drought than Washington, D.C.

Here’s some news that may shock snow-starved Washingtonians: we don’t have it all that bad. For all the attention that’s been given to D.C.’s longest drought without a 2 inch or greater snow event, and rightfully so, one city in the South, Asheville, N.C., is actually suffering through a longer period of even paltrier snow amounts. Asheville averages about the same amount of snow as D.C. in a typical winter.

Asheville Regional Airport has failed to record a 0.3 inch or greater snow event for 779 consecutive days, which is the longest such period in the airport’s observed weather history (since 1964). Just over 7.5 inches fell on January 10, 2011, but, in the two-plus years since that date, mostly trace amounts have grazed the airport’s weather station. It’s been almost a complete shutout the last two winters, as no measureable snow was recorded for the 2011-12 season and only a measly two-tenths of an inch has fallen to date this winter.

The record-setting warmth of last winter and elusive synergy between Arctic air and moisture this go around offer no such easy reminder of what snow looks like.

A long term decline

Should Ashevillians temper expectations for the winters ahead? Well, in examining the long term record of snowfall at Asheville, it appears that, like in Washington, D.C., its recent snow deficit is just continuing a downward trend. A look at the total snowfall by decade confirms the trend, as amounts have been declining gradually since the end of the 1960s.


Decadal snowfall amounts starting in the 1889-90 season and ending with the current winter. Several NWS Cooperative Observer Program (COOP) sites located within the Asheville city limits have provided this data on a continuous monthly basis since the winter of 1889-90 (all observations are posted on the site of the NWS forecast office serving Greenville/Spartanburg, S.C.).

It’s also a fact that the number of one inch or greater snow events per winter at the airport has dwindled markedly since the 1965-66 season (daily snowfall observations taken prior to 1965 were reported inconsistently at the COOP sites, which caused some gaps in the data. This made it more reliable to consider the shorter recording history of the airport). Consider, for instance, that the number of one inch or greater snow events per winter averaged around 3.7 from 1965-66 to 1988-89. From that season forward, the average has dropped by almost half to just under 2.5 such events per winter.


The number of 1 inch snow events runs along the x axis. Note the linear trend, which shows a pronounced decrease in these events with time, from more than four per season in the 1960s to fewer than two in the 2010s. The downward-pointing red arrows indicate the winters (2001-02, 2011-12 and, thus far, 2012-13) in which a single 1 inch or greater snow event had not occurred.

To further appreciate these findings, it’s worth discussing another average, that of seasonal snowfall totals since the winter of 1965-66. The long term trend has been moving downward (see graph below), and when the period of record is split almost evenly between the 1960s-80s and the 1990s-today, mean seasonal snowfall totals have precipitously declined. The earlier 24-year period saw an average of 16.8 inches fall per season, whereas the last 24 years have averaged only 9.7 inches per winter.


As before, I have plotted the linear trend to show the decrease in seasonal snowfall with time. An early-period average of nearly 20 inches per season has trended to under 10 inches late in the record. On this graph, the downward-pointing red arrow indicates the seasonal total of zero inches recorded in 2011-12.

Lowering expectations

According to Doug Miller, Professor and Chair of Atmospheric Sciences at UNC Asheville, many in the region have been forced to accept low expectations for future snow chances.

“There’s no doubt that, after last winter, the expectations [for much heavier snow] were probably unrealistic for this winter,” Miller said.

Before this winter started, UNC-Asheville’s Miller said students and locals felt that the North Carolina mountain town was due for a big storm. Ultimately, though, Miller and his fellow residents have found the last few months to be “extremely frustrating … the pickings this winter have been pretty slim.”

Because of that frustration, Miller says that he and his students have refused to look at forecasts from the GFS (and other weather models) more than 5 days out. As Miller explains, “It’s not that we’ve been without moisture. Clearly, there’s a disconnect between when you have the moisture and when you have the cold air. This year, we have been getting cold air, but after the moisture has moved out of the area.”

Misery loves company: D.C. and Asheville in similar boat

The D.C. area can certainly relate to the many hapless attempts at merging the cold with precipitation. Asheville and D.C. can also relate to one another when it comes to their seasonal snowfall averages, despite marked differences in elevation (2140 feet at Asheville vs. 16 feet at DC) and latitude (Asheville is about 470 miles south of the District). Sixteen inches accumulate in the mountain town on average, while 15.4 inches fall throughout a Washington winter. It’s true that the small scale (mesoscale) processes that enhance snowfall over the two regions are quite distinct; however, they do require many of the same large scale (synoptic) features to come together for a widespread snow storm.

A lack of Miller Type A systems

Most important among these features is a favorable storm center track from the Gulf of Mexico up along the Eastern Seaboard. These storms (known as Miller Type A systems) will often form along an old weather front, which had passed through the piedmont sections of the East and, in so doing, deposited an air mass sufficiently cold for snow in its wake.


A schematic of an idealized Miller Type A low pressure system and a select storm track. Image courtesy of the NWS forecast office serving State College, Pa.

Miller Type A cyclones feed off the large temperature contrast (which marks the baroclinic zone, a common meteorological term) between the pre- and post-frontal air. The emergent low pressure center typically deepens as it moves northeast, wrapping rich amounts of Atlantic and Gulf of Mexico moisture back across the Southeast and Mid-Atlantic. Subfreezing air meets up with this moisture and snow falls in earnest over areas from Asheville to D.C. (and points north).

Miller B systems have favored rain

Both cities could only dream of these Miller Type A systems the last two winters. Alas, as Miller explains, the pattern has not been accommodating, favoring “a double-barreled low track from the southern Plains to the Northeast in a warm ‘Miller B’ situation, which [this setup in advance of the low promotes] moderate temperatures for the Mid-Atlantic and Southeast.”


HPC’s daily weather maps from earlier this winter, showing a Miller Type B system lifting north through the Tennessee Valley (Dec. 26, 2012), weakening and, on the next day, reforming along the Mid-Atlantic coast. Asheville received all rain from this storm, while areas north and west of DC saw light snow accumulations (Reagan Nat’l officially reported 0.2”).

These systems characteristically cut up to the west of the Appalachians and weaken before reforming to the east, commonly near the Mid-Atlantic coast. The Miller B synoptic scenario (not named after the professor) provides a clear example of one of the ways in which western North Carolina and, more often than not, the Washington, D.C. region avoids a significant snowfall.

Northwest flow snow events have yielded little

A second scenario involves the earlier mentioned small scale processes, principally northwest flow snow (NWFS). Ingredients such as a consistently strong wind flow blowing in from an angle of 310 degrees (due northwest), shallow low level moisture and a touch of atmospheric instability (air parcels that undergo dramatic temperature changes with altitude, which meteorologists would identify as steep lapse rates) contribute to NWFS. Following a cold frontal passage, the air cools and condenses as it ascends the northwest facing slopes of the Appalachians, and snow can fall heavily along these mountaintops within the North Carolina-Tennessee border counties.


Satellite imagery produced after a NWFS event in February 2006, showing snow cover over the Tennessee and North Carolina mountains, and a relative lack of snow across the adjacent valley (Asheville’s location is marked by the red dot, which is situated within the French Broad River Valley). Note that this event was associated with the Nor’easter that left a thick blanket of snow over the DC area. Image courtesy of UW-Madison’s Space Science and Engineering Center, and adapted from NWS meteorologist Patrick Moore’s (Greenville/Spartanburg) report on the event.

In some cases, the snow can spill over into areas downwind of the higher peaks, including Asheville. It is rare, though, that the atmosphere wrings out enough moisture in the drying downslope flow for the immediate Asheville area or D.C., for that matter, to receive anything more than light snow showers.

The winter of 2009-2010: the good ole days...

The almost futile prospects of significant snowfall associated with either the Type B or NWFS setups cause Miller to speak very fondly of the winter of 2009-10, when an almost endless train of Type A storms dumped 39 inches of snow on Asheville and 56 inches on D.C. Those were indeed the halcyon days.

“I can’t tell you how many times we saw that Gulf [of Mexico] low tracking up the Eastern Seaboard,” said Miller.

Hope for the near future?

While the chances of seeing a big snow storm this winter are rapidly fading, the month of March does show some promise for ending the 0.3 inch or greater streak. Below-normal March temperatures could unite with well-timed precipitation over the area and snuff out the snow drought. Or not, as has been the case over the last several weeks.

No matter the result, Miller has seen enough to conclude, “It has been a strange winter.”

* Meteorologist Rick Grow blogs about the weather for The Frederick News-Post . He has a degree in atmospheric sciences from UNC-Asheville and previously worked at MDA EarthSat as a forecaster.

By Rick Grow*  |  10:52 AM ET, 02/27/2013

Categories:  Latest, Local Climate, U.S. Weather

 
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