Friday, February 18, 2005
Mid-day update: Interesting Forecast Problem
Steve Scolnik @ 1:00 PM
Under a strong mid-February sun (about the same as the last week of October), temperatures across the area are . . .
about 13 degrees colder than they were yesterday at the same time! At National airport the noon temperature of 29 compared to a reading of 42 Thursday at the same time. Strong cold-air advection (horizontal transport) in the form of a secondary cold front passage overnight has brought the lower temperatures. At 3am, a temperature of 28 and dewpoint of 19 were accompanied by light snow. (Looking between the blades of grass, I could see a very light dusting on the ground this morning.) By 5am, the dewpoint was down to 12, as the colder, drier air moved in. The dewpoint dropped another 7 degrees in the following hour, and it is now hovering well down in the single digits throughout the area, giving us relative humidities around 35%. At this rate, the thermometer will be struggling to make it past 35 this afternoon.
So, we have plenty of cold air in place, although the models predict that there is not much support at upper levels by Sunday for keeping it in place. There is also plenty of moisture being pumped into the southern U.S. by a nearly stationary low-pressure area off the southern California coast. This morning's models are bringing a storm through the central U.S. over the weekend, and they agree that any frozen precipitation here will change to rain, but it's a bit early to be confident of the exact timing, duration, and amounts of snow and/or rain. The models usually try to get rid of the cold air too soon in this type of situation. Most likely, we will see snow or sleet Sunday night, changing to rain sometime on Monday. Stay tuned, and we will keep you updated with the latest developments.
about 13 degrees colder than they were yesterday at the same time! At National airport the noon temperature of 29 compared to a reading of 42 Thursday at the same time. Strong cold-air advection (horizontal transport) in the form of a secondary cold front passage overnight has brought the lower temperatures. At 3am, a temperature of 28 and dewpoint of 19 were accompanied by light snow. (Looking between the blades of grass, I could see a very light dusting on the ground this morning.) By 5am, the dewpoint was down to 12, as the colder, drier air moved in. The dewpoint dropped another 7 degrees in the following hour, and it is now hovering well down in the single digits throughout the area, giving us relative humidities around 35%. At this rate, the thermometer will be struggling to make it past 35 this afternoon.
So, we have plenty of cold air in place, although the models predict that there is not much support at upper levels by Sunday for keeping it in place. There is also plenty of moisture being pumped into the southern U.S. by a nearly stationary low-pressure area off the southern California coast. This morning's models are bringing a storm through the central U.S. over the weekend, and they agree that any frozen precipitation here will change to rain, but it's a bit early to be confident of the exact timing, duration, and amounts of snow and/or rain. The models usually try to get rid of the cold air too soon in this type of situation. Most likely, we will see snow or sleet Sunday night, changing to rain sometime on Monday. Stay tuned, and we will keep you updated with the latest developments.
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