Wednesday, February 15, 2006

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."

Monday, February 13, 2006

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 ©, photo © Kevin Ambrose

Seasonal Outlook

Latest seasonal forecast: Click here.

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