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Posted at 5:00 AM ET, 12/15/2010

Forecast: Chill persists, chance of snow Thurs.

By Matt Rogers

Slight snow chance for weekend

Today's Daily Digit
A somewhat subjective rating of the
day's weather, on a scale of 0 to 10.


Slightly less blustery with more sun, but this is still not fun.
Get the 'Digit' on Twitter


Today: Breezy, very cold. Mostly sunny. 28-32. | Tonight: Increasing clouds late. 16-22. | Tomorrow: Cloudy, good chance of light snow. 28-32. | A Look Ahead | Get Express Forecast by E-mail


Yesterday's high at Reagan National only topped out at 28 degrees. That's four degrees colder than our normal LOW for the date. And with yesterday's average wind speed of 18.2 mph, it was a painful cold. I don't believe any day over the next week will top yesterday's temperature misery index, but the cold along with snow chances Thursday and this weekend dominate this unusually wintry weather story.

Snow Potential Index: 5 (↑) Light snow during the day tomorrow with a slight chance of a bigger storm Saturday into Sunday.

The SPI is a daily assessment of the potential for accumulating snow for the next week on a 0-10 scale. Get the 'SPI' on Twitter

Temperatures: Latest D.C. area temperature map powered by iMapWeather (base map by Google). Click and hold on map to pan. Double-click to zoom. Refresh page to update. See larger map on our Weather Wall.

Today (Wednesday): Frigid Canadian high pressure continues its advance toward us today as a large, stalled storm sits over Eastern Canada and helps spin the pinwheel of cold air transport. The low and high pressure combination keeps our winds up today too, although they should be slightly less wretched than yesterday (15-25 mph range). Highs hold in the upper 20s to maybe, possibly the low 30s as sunshine is the dominant sky condition. Confidence: High

Tonight: Mostly clear skies this evening are accompanied by breezy conditions (10-15 mph) and cold temperatures again (teens to low 20s). Clouds creep into the region late. Confidence: High

Keep reading for the forecast through the weekend...

Tomorrow (Thursday): The easy part of the forecast includes cloudy skies, cold conditions (upper 20s to low 30s again), and lighter breezes (only 5-10 mph). The hard part of the forecast is the weak weather system that should (60% chance) offer light snow to the area later in the morning (after rush hour) and into the afternoon hours. Right now, my feeling is that the dry air mass will make it difficult to snow a lot but some models have been shifting the moisture a little closer to us so it's a close call. Accumulation potential, at this point, is probably around an inch with higher amounts possible south. Confidence: Low

Tomorrow Night: Partly to mostly cloudy skies with lows in the 20s and light breezes. Confidence: Medium-High


Friday should be the warmest day of this week since Monday- but that isn't saying all that much. Look for highs in the mid-to-upper 30s with partly to mostly sunny skies and light breezes again. Lows are again in the 20s with partly cloudy skies Friday night. Confidence: Medium

Saturday is looking trickier as a stalled front to the south could send ripples of moisture toward us. That means more cloud cover is likely along with a slight chance flurries, especially by afternoon. The flurry or light snow chance continues into Saturday night (around a 30% chance overall). Highs should be in the 30s with lows Saturday night in the 20s to maybe low 30s in the District. Confidence: Low

Sunday could find stronger low pressure riding up along that boundary off the Mid-Atlantic coast. If that storm hugs the coast, we could see heavier snowfall totals. However, my current belief and the latest model guidance argues that this low pressure will ultimately go far enough offshore to only supply us with light snow chances during the day on Sunday with maybe some flurries on Sunday night. Highs should again be in the 30s with lows Sunday night back into the 20s again as winds pick back up again. Chance of snow: 30%. Confidence: Low

Look for more in-depth coverage of our upcoming winter weather makers from our expert, Wes Junker, around midday

By Matt Rogers  | December 15, 2010; 5:00 AM ET
Categories:  Forecasts  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: Deep freeze in deep South
Next: Federal leave for severe weather revamped


Man! These models oscillate more than even our adept Washington politicians! Let's just hope for those jet streams to meet closer to our shore :)

Posted by: kolya02 | December 15, 2010 6:31 AM | Report abuse

LOL, Kolya02. Let's hope! :)

Posted by: Rcmorgan | December 15, 2010 6:38 AM | Report abuse

"Some day the wind will end..." Sung to the tune of Someday My Prince Will Come.

But not today apparently. Well, I'm going for a hike anyway.

We've got a record cold interior house temp this a.m.: 41 degrees. Our pets want to be served breakfast in bed.

Posted by: tinkerbelle | December 15, 2010 7:22 AM | Report abuse

I went out last night to look for meteors and there were none (too much moon I think). But I noticed right away the sound of the river was gone and then saw in the moonlight that it had frozen over. My section did not freeze at all last winter.

Posted by: eric654 | December 15, 2010 7:39 AM | Report abuse

How do you get an average wind speed? Isn't it much more variable minute to minute than temperature? Also, wind is a vector, not a scalar, isn't it?

Posted by: wiredog | December 15, 2010 7:50 AM | Report abuse

I believe the National Weather Service averages out all the hourly observations to achieve the mean wind speed each day. After midnight last night, they revised the daily mean to 17.5 mph.

Posted by: MattRogers1 | December 15, 2010 7:58 AM | Report abuse

There are sheets of ice in sections of the Potomac River near me, though it doesn't extend unbroken from bank to bank in any location. It's rare to see any ice at all this early. Mid-December! Amazing. In November some rafting co's were still taking customers out.

Posted by: tinkerbelle | December 15, 2010 8:01 AM | Report abuse

yesterday's SLCB brought out snowlovers in droves, and of course the requisite "tsk tsk tsk" from nervous uh...folks admonishing us childish snowlovers that we should be more concerned about the dangers of snow etc... sigh...

here's something along the lines of snow days being safer than "regular" days:

In a study of more than one million crashes in 48 U.S. states, Researcher Daniel Eisenberg was surprised to find that the more it rained or snowed in a month, the fewer deadly traffic accidents there were. And he found that in any given month, an additional 10 centimeters of rain is linked with a 3.7 percent decrease in the fatal crash rate!


Crash rate: Based on literature, we can assume that the crash rate approximately doubles during rain. The size of the crash rate depends on, among others, the speed limit, the day of the week, and the time of day. Less research has been done on crash rates during other weather conditions. Snow seems to lower the crash rate because it makes people drive more carefully and there probably are fewer vulnerable road users on the road (Fridstrøm et al., 1995).

hhhmmm... it's seems counter-intuitive, but there it is. at least in these studies, snow days were safe days. so, to the extent these studies reflect reality, it's irresponsible to root against snow...

on yesterday's SLCB thread you talked about low homicide rates during big storms. i hadn't read that, but i'm sure it applies to virtually all crimes. and, i heard someone the other day talking about all the "blizzard babies" born in september and november this year... snow storms seem good for life.

sadly, i imagine it's bad for many businesses. especially retailers, especially just before christmas. (go christmas shopping early this year!) otoh, shoveling driveways could be easy money for enterprising teens.

oh well... ultimately, it doesn't matter what we want to have happen, because, snow dancing aside, what's gonna happen with the weather is gonna happen regardless.

Posted by: walter-in-fallschurch | December 15, 2010 8:15 AM | Report abuse

tinkerbelle, I can only guess that it might be a combination of wind and low dewpoints that cooled the water. Maybe also the preceding dryness and the cold rain.

Posted by: eric654 | December 15, 2010 8:16 AM | Report abuse

Yup, snowy roads, not dangerous at all, MUCH better than dry roads.

Much safer.

Posted by: nocando | December 15, 2010 8:50 AM | Report abuse

It is so cold. Anything that comes down tomorrow will stick like bubblegum.

Posted by: FIREDRAGON47 | December 15, 2010 8:53 AM | Report abuse

@nocando --

Awesome rant on the other thread, and I'm with ya!

Posted by: natsncats | December 15, 2010 8:58 AM | Report abuse

Tsk tsk yerself, Walter! ;) Looks like I'm not the only person with too much time on my hands this morning....

My excuse: I'm waiting for the 2-hour-delay school buses to git outta the road so I can go climb a hill.

Posted by: tinkerbelle | December 15, 2010 9:08 AM | Report abuse

Walter, great post, thanks for finding the numbers to refute this snow-increases-motorist-deaths argument.
I'll add that the stress-reducing value of using an unexpected day off to relax and enjoy nature possibly also reduces deaths by fending off heart disease (no numbers there; just an off-the-cuff theory).

Unfortunately, as tsk-tsker nocando so wonderfully demonstrates in his post above, there are many, many people out there who for some reason trust/believe/quote anecdotal evidence more than statistics and research. It simply shocks me! I have a good friend who consistently claims that welfare abuse must be common because of his anecdotal evidence of seeing people in front of the store selling food stamps for half their value in order to buy liquor. The numbers don't back that, but he's convinced. To me that's as simple as thinking that planet Earth is flat because you've never seen its curves!

Posted by: kolya02 | December 15, 2010 9:34 AM | Report abuse

What happened to La Nina? Did she decide to spend the winter in the Caribbean? Or is this a delayed arrival?

So far, the big storms have been moving as forecast (i.e., well west and north) but the meat locker chill doesn't seem typical for a La Nina pattern.

Posted by: JerryFloyd1 | December 15, 2010 11:35 AM | Report abuse

90% of you cannot drive in snow.

Incidentally, kolya02 - when was the last time hundreds were trapped in their cars and needing rescue on a sunny, bright and clear day?

And of course there are fewer fatal accidents - those of us with intelligence don't get out there on the roads with those who cannot handle their cars in snow! Fewer people on the roads = fewer total fatal accidents, on a per-incident basis.

And, here's Virginia's report on traffic fatalities:

"Environmental conditions also contribute to traffic fatalities. Weather like heavy rain, sleet and snow increase the hazards of driving, as do roads in disrepair."

Statistics are meaningless when taken out of context. And, BTW - UK and Netherlands drivers are MUCH better trained than US drivers (re: the study linked above from the Netherlands). Ever driven in Europe? it's night and day compared to here.

But, I can certainly "research" with the best of you:

"Objectives. We estimated the effects of snowfalls on US traffic crash rates between 1975 and 2000.

Methods. We linked all recorded fatal crashes (1.4 million) for the 48 contiguous states from 1975 through 2000 to daily state weather data. For a subsample including 17 states during the 1990s, we also linked all recorded property-damage-only crashes (22.9 million) and nonfatal-injury crashes (13.5 million) to daily weather data. Employing negative binomial regressions, we investigated the effects of snowfall on crash counts. Fixed effects and other controls were included to address potential confounders.

Results. Snow days had fewer fatal crashes than dry days (incidence rate ratio [IRR] = 0.93; 95% confidence interval [CI] = 0.90, 0.97), but more nonfatal-injury crashes (IRR = 1.23; 95% CI = 1.18, 1.29) and property-damage-only crashes (IRR=1.45; 95% CI=1.38, 1.52). The first snowy day of the year was substantially more dangerous than other snow days in terms of fatalities (IRR = 1.14; 95% CI=1.08, 1.21), particularly for elderly drivers (IRR=1.34; 95% CI=1.23, 1.50)."

Two can play this statistics game - and it's not the same as being a "flat Earther" - nice straw man argument though.

Posted by: nocando | December 15, 2010 11:38 AM | Report abuse

I can recall several winters during the mid to late 70's, early 80's when you could count on the Potomac being frozen over by XMAS or shortly thereafter.

Posted by: SteveT-CapitalWeatherGang | December 15, 2010 11:38 AM | Report abuse


Huh. The situation up there seems to be pretty well under control. That's very inconvenient for those folks, but being inconvenienced is not, in and of itself, dangerous. Since they are Canadians, they probably have blankets in their cars, relatively full fuel tanks to keep the motor running for heating. Snow is inconvenient, at worst, and cannot be considered a disaster when compared to.

I have no sympathy for people who complain about snowstorms and winter weather. When I was growing up in SoCAL, each member of the family kept a three day supply of food, water, meds, and light in a duffel under his or her bed for earthquake preparedness. You never knew when the next Northridge, Loma Prieta, or worse was going to occur. Snow, on the other hand, occurs every year during the winter. That people are caught out unprepared for it boggles my mind.

From people who know snow

Posted by: mason08 | December 15, 2010 11:45 AM | Report abuse

like that one study said, the only reason for any statistical drop has to be due to less people driving - which is very inconvenient for lots of people. i'm sure it's much more dangerous for each individual driver out there.

nocando, tinkerbell,
i'm just excited about the chance of snow. we don't get much around here. i remember winters w/none. whatever happens, it's not gonna be like in that blizzard in nocando's video from canada, or even like the storms here last year. last year was crazy. that was like 4 or 5 average winters' snow in one winter. unless you're 12 years old, you're probably not gonna see another winter like that around here - so don't worry about that. as far as our typical 2"-6" storms, they'll seem like a breeze after last year.

i think what people are really annoyed by with snow is the inconvenience. there may be fewer deaths, but everything is affected by a snowstorm - much much more so than by a rain storm. childcare, shopping, school, school activities, work, construction, parties, travel plans, all go out the window... maybe... so you've got to call someone and check the schedule or the website and everything's wet and messy and etc... it can be inconvenient. and when the power goes out - that changes everything. I can see how things would go from festive to "uh oh" in a hurry. just be prepared and adjust your expectations.

Posted by: walter-in-fallschurch | December 15, 2010 11:55 AM | Report abuse

nocando -
There are no statistics in your first link. That's just the state telling you to slow down in non-ideal driving weather. You should know that already.

The second link is about what I'd expect, since, KE = .5*M*V*V, and KE is proportional to likihood of death in a crash.

Oh... And from your link (emphasis added):
"It is important to keep in mind that first snowfalls represent just a small fraction of exposure to inclement weather that drivers face each year. Thus, while these relative risks are high, the absolute risks in terms of total mortality and morbidity are modest. The estimates in Table 2Go suggest that, for example, if drivers were as safe on first snow days as they are on other snow days during the year, approximately 12 fatal crashes and 210 nonfatal-injury crashes would be avoided in the United States each year. These results, combined with the comparable risks of second and third snow days reported earlier, imply that about 30 fatal crashes and 600 nonfatal-injury crashes in total might be avoided on the first 3 snow days of the year if drivers were more prepared."

If you're a crappy driver before the snow, you're going to be a crappy driver when it snows, and you'll be a crappy driver after the snow is gone.

Posted by: mason08 | December 15, 2010 12:03 PM | Report abuse

I agree with you that that is the root of the problem. It is inconvenient. Like I said, though, I have no sympathy, because people and governments refuse to prepare. I was walking out of the Home Depot in Hybla Valley yesterday with at heavy duty snow shovel and to bags of snow-melt, I had no two people ask me if we were expecting a storm. When I told them we might be, they scurried off to buy shovels. Really? After last year, you don't have a shovel?

Posted by: mason08 | December 15, 2010 12:15 PM | Report abuse

"like that one study said, the only reason for any statistical drop has to be due to less people driving - which is very inconvenient for lots of people. i'm sure it's much more dangerous for each individual driver out there."

Precisely. For those lamenting the snow because they believe it "will cause MORE people to die", thats just wrong. Snow will cause LESS people to die (in total) simply because there will be fewer people on the road, and slower speeds.

Now, a plausible argument can be made that among those that do drive during the snow, more will die, but thats an entirely different argument. In any event, the takeaway should be the argument "more snow = more deaths on the road" is incorrect. Refine your arguments to bend more sympathetic ears.

Posted by: SJ43560 | December 15, 2010 12:21 PM | Report abuse

Mason08, the shovel done be broken after last winter :)

Posted by: wilson7 | December 15, 2010 12:27 PM | Report abuse

@Steve, there was also one winter in the early 2000s when the Potomac was frozen by Christmas.

Posted by: JerryFloyd1 | December 15, 2010 12:28 PM | Report abuse

There is a new post to bicker at, ya'll.


Posted by: megamuphen | December 15, 2010 12:38 PM | Report abuse

Hoping we can get into that two-inch "sweet spot" tomorrow.

Unfortunately the forecasts seem to be trending south and east for the big weekend storm, though that should give us swing dancers a worry-free Saturday night at Glen Echo. the Tom Cunningham Band is in for its monthly live performance, and Christmas weekend is "dead" insofar as dance schedules are concerned.

Posted by: Bombo47jea | December 15, 2010 12:53 PM | Report abuse

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