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.

Party Like It's 1950

Even the snow-lovers would have to admit that a nice day is better than an ice day. Except for the notoriously unrepresentative locations near cold bodies of water, temperatures were in the 60s by early afternoon today in the Washington DC metro area. To the south, Stafford claimed a reading of 68 by 3pm. That certainly qualifies as a nice day in January, on average the coldest month. The best part is that the warmth is not accompanied by rain (yet), and you don't have to wait until The Midnight Hour. It's not warm enough to set a record in the century-plus history of the city locations, but for Dulles today easily surpasses the old record of 57 in 1991. (That leaves only 2 January dates, tomorrow and the 10th, which have never exceeded 60 there.)

A low pressure area working its way northeastward toward the Great Lakes will bring the threat of showers to our region tomorrow, but for now, the radar is clear for hundreds of miles.

Tonight and Tomorrow

For tonight, lows in the low to mid 40s will be accompanied by increasing cloudiness. Tomorrow's highs will be in the low 60s under mostly cloudy skies and a 50% chance of showers in the afternoon or evening.

How Warm Is It?

This year's warm start has many people asking how unusual it is for January. The monthly average temperature of 42.7 through yesterday has moved up the charts to 9th place on the 135-year official Washington hit parade.

One record which is not in jeopardy of being broken any time soon, however, is the amazing 48 degree average in January 1950. That month's 13-degree excess over the January average for the entire period of record makes it the warmest month of all time in Washington history, relative to average. It's enough to be warm for March (3.2 degrees above the period-of-record average) and equal to or warmer than the 2 coldest Aprils. The chart of the daily temperatures from the NOAA National Climatic Data Center shows that the month started off warm, with highs in the 70s on 3 consecutive days in the first week and reaching 70 again on the 10th. The coldest day was the 20th, with a high of 35 and a low of 22, but after that the temperature rose steadily for 6 straight days, reaching over 70 on 3 of them, including the all-time January record of 79 on the 26th. Five of those daily records still stand over half a century later.

CapitalWeather.com chart from NWS monthly records

It Could Happen the Day After Tomorrow (Or Not)

• Last week's IMHO distinctly underwhelming Category 3 Hurricane Destroys New York will be followed by F5 Tornado Does Dallas on TWC's "It Could Happen Tomorrow", Sunday at 9:30pm.
  
• WeatherTalk radio has inexplicably invited conspiracy nut Scott Stevens, tinfoil hat and all, back for a second week, Sunday at 3pm, WCBM 680. As the CarTalk guys say, "You've wasted another perfectly good hour . . ."
  
• A site visitor has pointed us to the dcrtv news that the, shall we say, "flamboyant" Joe Bastardi has been pulled from national broadcast duty by AccuWeather. I have personally noted his absence from CNBC since late summer or early fall. (Currently at the top of dcrtv is an interesting item about Rush and Daryn, but that's a subject for another blog.)

Winter Marches On

Some clouds associated with a weak warm front have moved out, and temperatures throughout the Washington DC metro area have reached or exceeded 50 degrees by mid afternoon today. Some mixed precipitation earlier on radar from the West Virginia panhandle northeastward to Pennsylvania was apparently not reaching the ground, and it has now disappeared. Tomorrow looks like a fine day to sneak out early for your favorite outdoor activity (as long as it doesn't involve snow), so get your excuses ready.

Tonight and Tomorrow

Lows tonight under a few clouds should be around 37 in the city, lower 30s in the colder 'burbs. Mostly sunny and low 60s are on tap for tomorrow.

Betting on Snow

Whether you believe in the gambler's fallacy (a coin is more likely to come up heads after 9 consecutive tails) or persistence (a coin is more likely to come up tails after 9 consecutive tails), you don't have much support in Washington snow statistics. Last month, we looked at whether December snowfall amounts can give any clue for January and found that they were almost completely uncorrelated. If it's possible, February snowfall in DC is even less correlated with January. The chart shows an almost completely flat regression line, with a correlation coefficient nearly equal to 0. Stay tuned as we try to figure out what Momma Nature's cooking up for the February menu.

Six out of Seven EPA Administrators Recommend

It's stuck under an equal-sized White House Iraq photo-op on page A4 (dead last in the online A section), but today's WaPo has an article about a meeting in which 6 former EPA administrators, 5 of whom are Republicans, recommended mandatory limits on CO2 and other greenhouse gas emissions. The immediately previous administrator, Mike Leavitt, who is now secretary of HHS, could not attend because of "schedule conflicts". Russell Train, who held the position from 1973 to 1977 under Nixon and Ford, said,

"This is not a sort of short-term cycle problem. This is a major disaster for the world. To say we'll deal with it later and try to push it away is dishonest to the people, and self-destructive."

Come on, Mr. Train, stop being so partisan!

Fifty/Fifty

Southerly winds ahead of a developing low pressure area in the lower Ohio Valley are bringing mild conditions to most of the East Coast this afternoon. Temperatures are above freezing everywhere except northernmost New England, and the 60s are being observed as far north as northern and western West Virginia. Aided by strong upper level support (For the geeks, that means "positive vorticity advection" and a "negative tilt" to the trough axis), squall lines broke out in early afternoon from southern Ohio through Kentucky and in the western Carolinas.

By 3pm, temperatures at all reporting locations in the Washington DC metro area were in the 50s, except for the river-contaminated readings at National and Quantico. At 4pm, however, the official temperature did make it to 51. Radar is showing some showers scattered from north of Pittsburgh through West Virginia into southwest Virginia.

Tonight and Tomorrow

Latest indications are that any serious showers won't arrive in our area until around midnight tonight, ending by mid afternoon. The heaviest rain should be well to the south, through the eastern Carolinas and far southeast Virginia. There is a 70% chance of rain by morning with low temperatures from 41 to 45. Rain probabilities will decrease to 40% by early afternoon tomorrow with highs around 50.

Fifty BELOW

I've been a scifi fan ever since I discovered the Tom Swift, Jr. series not long after they were originally published. One current author who's been below my radar screen, however, is Kim Stanley Robinson, since I'm still working through the backlog of books acquired in a decade of the annual New Year's sales at the Golden Notebook. Robinson has won multiple Hugo and Nebula awards, which scifi fans will recognize as two of the most prestigious awards in the field. His book, Forty Signs of Rain, published last year, was recommended by Books from the Crypt of North Potomac in the book issue of the Bulletin of the American Meteorological Society in May. It was the first in a trilogy about the effects of climate change right here in River City.

The second book, Fifty Degrees Below, was recently published, and it was reviewed in the WaPo Style section last week. The author was interviewed by the UK Guardian back in September in connection with the publication of the latest book:

"In the wake of a tropical storm, a low-lying American city is drowning. Buildings are demolished and bridges knocked out; tens of thousands of people are without electricity or fresh water; hospitals are bursting at the seams with the sick and the dead."

The city, in this case, is not New Orleans, but Washington DC, which has been flooded at the end of the first book. The premise of the second book is a severe cooling triggered by the shutdown of the Gulf Stream. This is similar to that of "The Day After Tomorrow", but apparently much more scientifically plausible.

As December Goes . . .

After yesterday's official high of 48, temperatures are closer to seasonable levels for late December in the Washington DC metro area, mainly in the mid 40s under partly cloudy skies. Winds have been brisk at times, but well below yesterday's levels. Across the country, there is virtually no precipitation east of the Rockies, except for the Dakotas.

Tonight and Tomorrow

Tonight's lows will range from the mid to upper 30s. Tomorrow will see increasing cloudiness and highs around 54.

. . . So Goes January?

Someone suggested in the previous comments that this weather is so boring it should have a web site called "LowercaseWeather.com". The one thing that is constant about weather is that it will always change. Since things are a little slow now, I had the chance to do some homework.

Following on to Matt's earlier discussion, I looked at the historical relationship between December and January weather in Washington. The chart on the left is a plot of each year's December average temperature (x-axis) vs. the following January's average (y-axis). As you can see, there is a lot of scatter to the data. The solid sloping line is a regression line, which minimizes the collective distance to all of the plotted points. The algebraic equation for that line is shown in the upper part of the graph, along with R². R is known as the correlation coefficient. It is a measure of how well two sets of data are correlated (in this case, December and January temperatures). The value of R can vary all the way from -1 (perfect, but opposite, correlation) to +1 (directly correlated). A value of 0 indicates the relationship is completely random. In this case, the value of R is 0.4, since R² is 0.16. This shows that the quantities are related, but not very strongly. Without getting too technical about it, R² represents the amount of variability of one set of data (January temperature) which is "explained" by the variability in the other set of data (December temperature). In this case, a little over 16% of the variance is explained---not random, but not terribly strong, either.

In the case of snowfall, all bets are off. The chart on the right shows a plot of total snowfall for December vs. January (trace amounts were considered 0). Notice how the points are much more random than in the temperature chart. In fact, the R² value is much less than 0.01; about ¼ of 1% of the variability of January snowfall is explained by the December amount. This is shown by the regression line being almost completely flat. What relationship does exist is actually negative, indicated by the negative coefficient of x in the regression equation. So, there is a non-zero probability that January snowfall will be low when December's is high, but the statistical reliability of that connection is extremely low.

Last night's quick storm was anything but dull. It had a little something for everyone. The snow lovers got their fix, although not as much as if there had been no mixing of sleet and freezing rain. The snow haters got a storm which had the decency to arrive at night and depart almost in time for the morning rush.



Thanks to Camden for pulling an all-nighter. Here at Afternoon Blog Central, we're not as young as we used to be, so we turned in shortly after the first flakes around 1:00 and missed the whole thing. I'm especially sorry to have missed the thundersnow. Despite 9 winters in the Hudson Valley and a couple in Boston, my only recollection of thundersnow was in the Presidents' Day storm of 1979 right here in the DC area. It was spectacular: the whole works, including lightning and snow so thick it seemed to fill the air.



A check of the initial reports shows an official snow total of 1.6", ranging up to 3.5" in the immediate northern and western suburbs and lower to the south and east. Here at the Afternoon Update in west-central Montgomery County, we had 2¼" of crunchy snow and ice. Overall, this was an excellent result for the forecast from the collective wisdom of the CapitalWeather team in a very tricky situation. Please let us know how much you received.



Tonight and Tomorrow



Fortunately for everyone's nerves, the next few days look a lot quieter. After lows tonight in the mid 20s in the city and upper teens in the colder 'burbs, tomorrow will be partly cloudy with highs around 41.



Epsilon, RIP



A quick review of the tropics for old times' sake reveals that "General Franco is still dead!"



Climate Conference



Today is the last day of the U.N. Climate Change Conference in Montreal. If this 2-week event has been covered at all by the local MSM Paper of Record with anything other than reprints of wire-service stories, someone please let me know. The RealClimate blog reports that the N.Y. Times has been podcasting from the conference, and it's also being blogged by attendees. Former President Bill Clinton was scheduled to speak today.



The Afternoon Update will be taking a few days off next week. Please behave yourselves in the meantime, and remember Momma Nature's Rule #1 of Snow Day Wishcasting: "Do your homework!"