Nothing to See Here, Move Along

Well, that was certainly exciting. We actually saw some of that white stuff in the Washington area this morning, you know, what do you call it? Oh, yeah, I think it's coming back to me now: snow. In the snow-starved Washington region, what was nearly a meteorological non-event created a bit of a buzz among the snow fans. If you were stuck in one of the backups reported on radio and TV along I-270, the Beltway, I-66, or the Dulles Toll Road, you have my profound sympathy. Please don't blame the weather for the effects of your fellow rudely aggressive drivers, however. They can turn even the sunniest Monday holiday into a commuting disaster.

American Legion Bridge on President's Day, photo from TrafficLand via WTOP

Arriving a few hours ahead of schedule from yesterday's PM Update forecast, a weak disturbance racing eastward to the south of the area left mostly under an inch of slushy snow on some grassy and elevated surfaces in the metro area. Light rain which began at Washington National at 6:17 became mixed with snow by 9:15 and changed to light snow for about an hour before ending at 10:45. Total precipitation: a tad under ¼". A similar amount was reported at Dulles, where the precipitation was all snow, occasionally moderate, after a few minutes of rain at the beginning. By early afternoon, some drizzle and fog was being reported around the area.


Now you see it, now you don't: Regional radar to the right from The Weather Channel shows snow falling in most of the metro DC area at 9:38 this morning. An hour and a half later, it's all rain, some moderate, on the Eastern Shore back across the Bay to the Northern Neck.


As for the forecasts, you can scroll on down and make your own judgment. Personally, I think we did pretty well, along with the TV forecasters I saw last night (Sue Palka on 5 and Topper Shutt on 9) and the National Weather Service. (FWIW, the Weather Channel Local on the 8s was still predicting a 40% chance of snow at noon today in Montgomery County.) Take my word for it, boys and girls, I've seen enough decades (yes, that goes back close to half a century) of busted DC snow days to have not gone out on any more of a limb than I did 24 hours ago. The vast majority of these weak systems fall apart crossing the mountains or move just a little too far north or south to be of any consequence to our area.

In fact, I'm very impressed that the current generation of high-resolution numerical models was able to pick up anything at all with this system. If you looked at the surface weather map about 18 hours before the event, I don't think you would have seen any signs of precipitation to occur here. To see the entire sequence of maps at 6-hour intervals through this afternoon, click here, here, here, and here.

Another wave moving along that pesky front hanging around the Carolinas could bring us a similar event tomorrow, but as of now the indications are that any precipitation will stay mainly to the south of us. Once again, temperatures will be marginal, but cloud cover overnight will keep readings above freezing in most places.

Tonight and Tomorrow

Areas of fog and drizzle will persist through this evening. Tonight will remain cloudy with lows in the low and mid 30s. Tomorrow there is a slight chance of light rain or mixed rain and snow in the morning. Clouds will decrease in the afternoon with highs around 49.

High-Def Open Mike

Overheard this morning when the studio audio was inadvertently left on during Local on the 8s on The Weather Channel was Kristina telling Kevin, "'CNN buys new line of high-def makeup.' . . . I'm really not looking forward to that day."

Zoning Out

It was exciting while it lasted, but the dip in the jet stream which brought Arctic air into the Washington DC area over the weekend has been replaced by more "zonal" (east-west) flow. The chart to the right shows the 500 mb height (approximately the middle of the atmosphere) over North America this morning. The colors represent areas of roughly equal height, and the solid lines are the barometric pressure at the surface.

The milder temperatures have reached above the long-term average, nearing or hitting 50° by mid afternoon throughout the area with westerly and southwesterly breezes. Despite the 17° departure below "normal" on Sunday, we are still nearly 2° above average for the month so far. A weak disturbance moving eastward south of the area will bring the threat of light precipitation tomorrow afternoon, mainly rain through central Virginia and some mixed rain and snow to the north.

Graphic from Unisys

Tonight and Tomorrow

Clouds will increase tonight with lows near 32 in the city and upper 20s in the colder 'burbs. Tomorrow will be cloudy with a 40% chance of light precipitation by late morning or early afternoon, mainly rain with some snow possibly mixed in to the north and highs in the mid 40s.

"In Life, Accuracy Counts"

It's not really about weather, but the "Weather Man" movie (2 Thumbs Up®) is out on DVD today. The movie, which is rated "R", stars Nicolas Cage as Chicago weatherman David Spritz, whose "professional successes are overshadowed by his personal failures." The DVD bonus features include:

• Extended Outlook: The Script
  
• Forecast: Becoming a Weatherman
  
• Atmospheric Pressure: The Style and Palette
  
• Relative Humidity: The Characters
  
• Trade Winds: The Collaboration

Waning Winter Wednesday

The spring catalogues coming through the mail slot have been accompanied by spring-like temperatures in the Washington DC area this afternoon. At 10¾ hours of daylight, our sunshine 5 weeks before the equinox is as strong as it was the week before Halloween. South-facing roofs and some sections of grass are now bare in this outside-the-Beltway neighborhood. Temperatures around the metro area are in the upper 50s with some 60s in the southern fringes of the region.

A low pressure area moving northeastward from Oklahoma toward the Great Lakes on this afternoon's weather map will keep us in the warm temperatures for a couple more days until the colder air behind it brings some of the chilliest (no, not "silliest", Spell-Check!) readings of the season for the weekend. After that, some type of storm activity is likely to develop along the front to the south, but nothing major is showing up yet. We'll be keeping an eye on it as usual in the days ahead. (Even though the PM Update will be taking a "non-snow" day tomorrow, we'll still be watching while we catch up on some other projects.)

Surface weather map at 1pm today from HPC/NWS/NOAA

Tonight and Tomorrow

For tonight, lows will be near 40 in the city to the mid 30s in the 'burbs under scattered to broken clouds. Tomorrow's highs will be near 60 with some scattered clouds.

Budget Blues

Yesterday's WaPo Federal Diary reports that budget cuts are prompting the National Weather Service to offer early retirement to about 1000 employees. Based on past experience, only 50 are likely to volunteer, but naturally such a program impacts the areas with the most experience. The St. Petersburg Times points out that 13 out of 42, or 30%, of the staff members at the National Hurricane Center are eligible. This has prompted Florida Senator Bill Nelson to say,

"That's the most ridiculous budgetary policy decision I've ever heard, when you're dealing with a matter of life and death, of inbound hurricanes."

Calling Inspector Morse

There hasn't been much of a thaw today except in the sunnier spots. Temperatures are maxing out mainly in the high 30s, but melting will be accelerating into this week. The model statistical outputs are all suggesting at least an approach to the 60 degree level by midweek.

Tonight and Tomorrow

For tonight, lows under partly cloudy skies will range from the upper 20s in the city to low 20s in the 'burbs. The warmup begins tomorrow with highs around 47 and partly cloudy skies.

Snow Intensity and Depth

The development of the storm which brought our snow over the weekend and record-breaking amounts to New York City and central New England will certainly provide a lot of material for future investigations. Detailed data on snowfall rates are hard to obtain, because snowfall measurement is very subjective and therefore not easily automated. I took a stab at analyzing the intensity of the storm over time with the chart on the right. It's based on the "hourlies" (METAR data, or aviation reports), from Washington National for the 36-hr period from early Saturday morning through early Sunday afternoon.

Time is shown on the horizontal scale. Bear in mind that distance along the axis is not directly proportional to time, because the observations are not evenly distributed in time. They are made every hour on the hour, and then whenever a change in conditions requires an update. Although Microsoft® Excel is the Swiss Army Knife® of data analysis, it is notoriously inept at handling unevenly distributed data points.

The vertical scale represents the type and intensity of precipitation. Positive values are snow reports, and negative values are rain reports. A magnitude of 1 is "light", 2 is "moderate", and 3 is "heavy". You can see that most of the morning had intermittent light rain, then light snow mixing in the afternoon. This became all snow by late afternoon, occasionally moderate through the evening. The real fun began after midnight, when there were 8 reports of heavy snow. By 9am, the steady snow was over, and there was a snow flurry in early afternoon (and possibly 1 or 2 more after the cutoff time in the chart).

I think an important factor in the higher snow depths which were recorded was not just the usual temperature-dependent frozen-to-liquid ratio, but also the very high rate of fall, which prevented the kind of settling which would happen over a longer period. Depths have visibly decreased a lot today, but I would suggest that this is more an effect of settling, rather than melting, given the temperatures we've had.

Chart © CapitalWeather.com, photo © Kevin Ambrose

Taking Snow for an Answer

After 6 weeks of non-winter, conditions are shaping up for a classic Gulf of Mexico to Cape Hatteras to Cape Cod snowstorm track, and the Washington DC area is included in the festivities (or not, depending on your view of snow). If you're just joining us and want the background, check out Camden's excellent review below. Otherwise, here's the bottom line based on the latest model runs from this afternoon's data:

Timing: Light snow will overspread the area from the southwest during the morning tomorrow, increasing in intensity toward evening. The heaviest snow will fall overnight Saturday, tapering off Sunday morning.

Amount: The most likely accumulations in the immediate DC area are in the range of 5-8", although some areas of more than 8" are possible.

CapitalWeather.com chart above, photo © Kevin Ambrose

Winter Storm Forecast: Saturday midday, Feb. 11 -- Sunday A.M., Feb. 12
	TIMELINE 10am SAT to 2pm: Light snow overspreads the area from SW to NE. Best guess for first flake inside the beltway is around 11am. 2pm to 5pm: Snow increases in coverage and intensity. 1-2" possible. 5pm to 3am SUN: Snow, heavy at times. 3-4" possible in metro area. 3am to 11am: Snow gradually diminishes SW to NE - up to 2" additional accumulation, more N & E. Becoming windy, cold.
Storm Impact: Travelcast:Schoolcast (Mon.):

Commentary

Don't be fooled by the widespread sunshine and seasonable temperatures (low 40s) this afternoon. There is plenty of cold air available for this system, so the main risk to the forecast is that the storm will track further east and give less precipitation, rather than mixing with rain in the DC area. There is plenty of moisture available along the Gulf Coast; latest radar shows moderate to heavy rain as far east as western Alabama. Barometric pressure falls along the Louisiana and Alabama coast over the last several hours have been at rates as high as nearly 2 mb/hr, which indicates strong storm development.

The CapitalWeather.com team will be monitoring the storm's progress through the evening, including the model runs from data just now being collected, and posting an update around midnight.

Round Rodent vs. Regression

Happy Groundhog Day! Even the most diehard snow fan must admit that temperatures pushing toward 60°, and even above on the southern fringes of the region, can't be all bad on the 2nd day of February. Meanwhile, unless you've been totally isolated from all media, you know by now that our Phurry Phriend Phil has done his duty for another year by seeing his shadow and predicting 6 more weeks of winter.

Regional radar is mainly clear as clouds gradually increase from a developing low pressure area moving northeastward from the Gulf states. Some widely scattered showers have reached into West Virginia and southwestern Pennsylvania. This low will bring some rain to the area overnight. Current indications are that the next system may end as some wet snow or flurries on Sunday, with little or no accumulation in the immediate area. The models are becoming more consistent on this, but there is still some difference in timing.

Tonight and Tomorrow

Clouds will increase this evening, with showers beginning around 1am and lows in the mid 40s. Showers will end in the morning tomorrow, with some sun in the afternoon and highs in the upper 50s.

Snow Statistics

A couple of weeks ago, we noted that, statistically at least, January snowfall gives virtually no clue to February's amount. Today's chart shows that there is one element which does provide some insight, and that is February temperature. Colder temperatures do correlate to some extent with more snow. As some site visitors have pointed out in earlier comments, however, this is far from a lock. There is a lot of scatter in the data, and some quite cold Februaries have had little or no snow, even a few which averaged below 30° (13° colder than this January).

The dashed regression line shows that for each degree the monthly average temperature is below about 44.1°, the expected monthly snow total increases by about ¾". The value of R² indicates that about 25% of the variance in snow amounts is accounted for by the average temperature.

CapitalWeather.com chart from NWS data

DC Comics

Tom Toles' cartoon in today's WaPo commenting on political science:

"But With a Different Feeling"

Here's the statistic Bob Ryan was probably referring to last night: In 54 years of history, Washington National has averaged 0.2 thunderstorms in January out of the 30.6 total per year. This is now the third time thunder has been reported this month. Thunder was last observed in January before this year on New Year's Day, 2003.

CapitalWeather.com chart from NWS data

Following the fast-moving cold front which passed through last night, it's a blustery January day in the Washington DC metro area, but temperatures are close to seasonal levels, in the low 40s. Winds gusting as high as 45 mph in some places are making it feel a lot colder. With a low of 35 last night, whether today becomes only the second day this month of below-average temperatures depends on how cold it gets before midnight.

A few snow flurries are widely scattered around the area, but most of the activity is west of the Shenandoah Valley. Hagerstown was reporting 1¾ mile visibility in light snow around 3:30.

Tonight and Tomorrow

Lows tonight should be in the upper 20s with partly cloudy skies and diminishing winds. Tomorrow will be sunny with highs in the low 40s.

Broadcast News

Set the TiVo! From the WaPo TV listings comes the news that Doug Hill has escaped the 2½ minute straightjacket to host a 30 minute special about the WeatherBug network tonight. The show is on at 8:00, Channel 7. Way to go, Doug!

DC Comics

Tom Toles has a cartoon in today's WaPo on the subject of the Katrina reports we mentioned yesterday.