03.14.11
Posted in Weather Education at 8:00 am by Rebekah
Last week I described how upper-air observations are made with radiosondes. This week we’re going to start looking at remote sensing observing systems, beginning with radar.
Radar
(Photo from the National Weather Service in Seattle)
Radar stands for radio detection and ranging. A radar system emits high power radio waves, some of which bounce off objects (e.g., raindrops and snowflakes) and return to the radar. The round-trip time of the energy pulse is used to calculate the distance of an object from the radar.
The current generation of weather radars in use by the National Weather Service is the WSR-88D, standing for Weather Surveillance Radar, 1988 Doppler. These radars, as you can probably guess, were established in the ’80s and are Doppler radars.
The following map shows the locations of the National Weather Service radars.
Doppler Radar
Consider a passing train, blowing its whistle. As the train moves away from you, the pitch of the whistle drops. The same goes for emergency vehicles; sirens will sound higher pitched as the vehicle is coming towards you, and lower pitched as the vehicle is going away from you.
This shift in frequency is known as the Doppler shift, and we can apply this principle to radars, in order to determine the wind speed and direction across the radar domain (e.g., useful in determining when a tornado may be present, where we have rotating winds).
Other Radars
There are numerous other types of radars used to observe precipitation and wind as well, such as dual-pol and phased-array radars and wind profilers.
A wind profiler is a type of radar or sodar (uses radio or sound waves) that points up and gives frequent updates on wind speed and direction over a certain location. This is helpful as we only have soundings go up twice a day, and sometimes we may want to know what the winds are doing in-between soundings. Most wind profilers are located in the central U.S.
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Next Monday we will talk about weather satellites.
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03.13.11
Posted in Weather News at 8:00 am by Rebekah
The Passaic River, in northern New Jersey, reached peak flood stage last night. The river gauge at Little Falls, New Jersey, recorded the 5th highest flood peak since records began.
Here are a couple of hydrographs from the Passaic River when it was near peak.
Little Falls (click to enlarge; click here to view the latest hydrograph and info for this station):
Pine Brook (click to enlarge; click here to view the latest hydrograph and info for this station):
Many other rivers in the Northeast rose quite a bit as well, forcing hundreds of people from their homes. The flood waters in some parts of northern New Jersey are not expected to recede for a few days.
The rivers have been rising as a result of heavy rains recently, on top of snow that is melting with more springlike temperatures. Much of the area affected should be rain-free for a little while now, though, and the river levels have already begun to drop.
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03.12.11
Posted in General News, Weather News at 8:00 am by Rebekah
Yesterday was a pretty wild day, from the Japanese earthquake and the Pacific tsunami to wildfires in Oklahoma and Texas and flooding in the Northeast.
Here are some U.S. tsunami amplitudes I found via the National Weather Service (note the amplitude is the height above normal sea level):
LOCATION – TIME – AMPLITUDE
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PORT ORFORD OR – 1724UTC – 6.1FT/1.85M
ADAK AK – 1755UTC – 3.6FT/1.09M
KODIAK AK – 2211UTC – 0.9FT/0.28M
LOS ANGELES CA – 2115UTC – 1.7FT/0.51M
SAN DIEGO CA – 2131UTC – 1.7FT/0.51M
LA JOLLA CA – 2007UTC – 1.4FT/0.43M
WESTPORT WA – 1920UTC – 2.0FT/0.62M
ST PAUL IS. AK – 1228UTC – 2.1FT/0.65M
OLD HARBOR AK – 2154UTC – 1.1FT/0.33M
DUTCH HARBOR AK – 1204UTC – 1.3FT/0.41M
SHEMYA AK – 1136UTC – 5.2FT/1.58M
ARENA COVE CA – 1834UTC – 8.7FT/2.65M
CRESCENT CITY CA – 1656UTC – 8.2FT/2.49M
SAN FRANCISCO CA – 1749UTC – 2.1FT/0.64M
MONTEREY HARBOR CA – 2013UTC – 2.4FT/0.72M
NORTH SPIT CA – 1639UTC – 3.3FT/1.01M
PORT SAN LUIS CA – 1745UTC – 8.6FT/2.64M
SANTA BARBARA CA – 2229UTC – 3.2FT/0.97M
SANTA MONICA CA – 2223UTC – 2.8FT/0.84M
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In other news, the Passaic River is still nearing its crest, now expect to peak around 12 feet tonight.
Also, Oklahoma yesterday was going up in flames (as well as parts of Texas and Colorado); the governor declared a state of emergency for the entire state, as we had at least three dozen or so wildfires burning as a result of strong winds (gusting to 47 mph), temperatures near 80, and very dry conditions. Several grass fires wound up burning a few homes, as firefighters were having a very difficult time trying to get these fires under control.
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03.11.11
Posted in Weather News at 8:00 am by Rebekah
7-day total precipitation across the U.S., from the National Weather Service (click to enlarge)
Probably the biggest weather story in the U.S. right now is the flood event in the Northeast. Between melting snow and copious rainfall, many rivers are at or near flood stage.
For example, the Passaic River at Little Falls, in northern New Jersey, is expected to peak at 12 feet tomorrow night. Flood stage is 7 feet and major flood stage is 9 feet.
Hydrograph from the National Weather Service
The Passaic River is not the only river to watch, though; the following National Weather Service map shows the number of river gauge stations that are at or near flood stage. Yellow is near flood stage, orange is minor flooding, red is moderate flooding, and pink is major flooding (green is no flooding).
Welcome to spring!
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03.10.11
Posted in General News at 8:00 am by Rebekah
Yesterday I went to a very interesting seminar on the extreme weather events lately in Australia, and how they may be tied to La Niña, natural climate variability, and climate change. I took some notes from the talk and plan on writing up a summary of the seminar for the blog next week.
Today I just want to give you a taste of one of the many projects I’m working on in the lightning research group at OU.
Lately I’ve been analyzing a lightning flash that got my attention last July. While coming back from a chase in northern Oklahoma on July 11th, I saw a lightning stroke that went from the ground to the cloud. I know this type of lightning occurs in areas with tall towers, but I had never seen this with my own eyes before. Now I’m looking at lightning data for the storm and also looking into studying upward-going lightning in other storms, as well as studying up on the literature on the subject as I don’t know much about it.
Captured with my HD camcorder.
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