Wednesday, November 7, 2007

Blast From the Past


Variable clouds, windy, chilly. A brisk blast of northwesterly breezes gusting over 20 mph at times has brought a reinforcement of cold air to the metro area, along with some leftover clouds from lake and mountain induced snow showers to the west. Today's highs (National 53°, Dulles 51°, BWI 52°) were 3-5° below yesterday's, although they were still in the 50s . That is less likely to be the case tomorrow, when highs could remain in the 40s for the first time since back on April 16.

Tonight and Tomorrow

Partly cloudy, cold. Winds will die down somewhat tonight, and lows under mostly clear skies will be near freezing in the city to the upper 20s in the 'burbs. Tomorrow will be variably cloudy with highs 46-50°.

For the outlook through the rest of the week and into the weekend, scroll on down to Jason's post below.

November Nostalgia

The weather map to the right is for 1:30pm, November 6 . . . 1953. As Matt posted yesterday, Nov. 6-7, 1953 was the earliest significant snow in modern times, with 6.5" being measured at National Airport on the 6th and an additional 0.1" on the 7th. (Earlier measurable November snowfalls were 4" on the 4th in 1910 and 2.5" on the 5th in 1891.)

The map shows that a wave which developed near the northeastern Gulf coast on the 5th moved across northern Florida into the Atlantic, where it developed into a strong low pressure area as it came up the East Coast. In the early morning hours of the 6th, snow with 1.5 mile visibility was observed as far south as Raleigh. The strengthening of the storm was assisted and the supply of cold air for the snow was provided by a humongous high pressure area anchored over the Great Lakes and southern Canada. Note that the high at 1038 millibars and the low, which reached a depth of at least 990 mb off the New Jersey coast, produced a very strong pressure gradient (rate of change with distance). The gradient wasn't quite as fierce as it might appear, however, since the convention in those days was to draw isobars every 3 mb, as opposed to the 4 mb interval seen on today's weather maps. The NOAA Library archive has the full original Nov. 7 Daily Weather Map (1.9 MB download, requires DjVu viewer plugin).

Tuesday, November 6, 2007

November Chill Arrives, Unpacks for a Visit


Sunny, windy, chilly. You won't be needing those L.L Bean flannel-lined jeans quite yet, but you might want to start thinking about where you filed them away in the spring. Aided by a deep low pressure area just north of the Great Lakes, a strong cold front has brought windy and cooler conditions to the Mid Atlantic area. By mid afternoon, temperatures had already dropped a couple of degrees from their earlier highs (National 58°, Dulles 54°, BWI 55°). The very dry dewpoints in the 20s and even upper teens are producing relative humidities mostly in the 25-30% range.

In keeping with our longer-term drought condition, rainfall amounts through this morning were quite puny, barely equal to the daily average in the immediate area: National 0.12", Dulles 0.11", BWI 0.22".

Following the first sustained cold spell in about 6 weeks, a warmup is starting to look possible for the holiday weekend, at least according to one major model.

Tonight and Tomorrow

Mainly clear, cold. Under mostly clear skies tonight, lows will be in the upper 30s downtown and near to a little below freezing in the 'burbosphere. Tomorrow will be sunny and chilly, with highs only in the low 50s.

For the outlook through the rest of the week and into the weekend, scroll on down to Dan's post below.

Tropical Topics

Following up on Andrew's discussion of Noel 2.0 on Sunday, Senior Meteorologist Stu Ostro has a nice analysis (with graphics) of the transition of The Storm Formerly Known as Noel in The Weather Channel blog.

Climate Corner: Washington De Sea?

The current (November) Washingtonian, now on display at a checkout line near you, has an article which asks, "Will Rising Sea Level Swamp DC?" A quick glance indicates the article may have fallen prey to the traditional tendency of journalism to sensationalize the graphics and to conflate the effects of sea level rise with storm surge and flooding precipitation. On the other hand, last year's heavy rains provided ample evidence that the National Mall and Federal Triangle areas are highly vulnerable to flooding, even without storm surge effects, and that mitigation efforts for this potential threat are slim to none.

Monday, November 5, 2007

Nearing Normal November


Sunny, mild. After temperatures running at or above average for 4 out of the first 5 days this month, a cooler spell is poised to arrive in the Washington metro area. Under nearly clear skies this afternoon, temperatures are almost uniformly in the low 60s throughout the region. The daily highs were: National and Dulles 62°, BWI 61°. Humidity is also quite low with dewpoints generally in the low 30s and even a few upper 20s, but an approaching cold front is bringing with it the possibility of some showers tonight.

Temperature chart at 3pm today from Unisys shows cold air massing from the Northern Plains to southern Canada, ready to sweep eastward with the coolest temperatures of the season for the Mid Atlantic region.

Tonight and Tomorrow

Cloudy, chance of showers, then clearing and cooler. This evening's forecast is brought to you by guest second shift meteorologist Claudio Vernight. Along with the clouds, there is a 50% chance of showers tonight after 8 p.m. Lows will be in the low to mid 40s. Following a lingering chance of showers in the morning, clouds will give way to sunshine and breezy conditions tomorrow with afternoon highs 53-57°.

For the outlook through the rest of the week and into the weekend, scroll on down to Dan's post below.

Tropical Topics: Naming Names

Except for the myriad of storms called "Not Named" before 1950, this year's Noel was only the 9th "N" storm (2 of which were also named Noel, in 1995 and 2001) to occur in the Atlantic . The others, in alphabetical order, were Nadine (2000), Nana (1990), Nate (2005), Nicholas (2003), and Nicole (1998, 2004). Nicole 1998 and Noel 2001 were the only other November storms; the others all occurred earlier in the season.

Weather on the Go

The latest (December) issue of PC World has a pointer to the National Weather Service cell phone data page. Features available include: Detailed 7-day Forecast, Your Local Radar, Current Conditions, Satellite Image, Hazardous Weather, and Area Forecast Discussion for individual locations, plus regional radars, surface observations, satellite images, convective outlooks, and tropical weather.

Seasonal Outlook

Latest seasonal forecast: Click here.

Latest 3-month temperature outlook from Climate Prediction Center/NWS/NOAA.