Monday, March 23, 2009

Mount Redoubt Still Active, 1/4 Inch Ashfall In Susitna Valley, Threat Of Ashfall Expected To Shift Further West And South Of Anchorage

Click HERE to view all previous posts on the 2009 Mt. Redoubt episode in inverse chronological order, with the most recent post appearing first.

Since my most recent post, Mount Redoubt continues to be active, although the Webicorder output shows little activity since the most recent eruption. The two webcams themselves have been disabled by the spate of eruptions. Primary media stories from CNN, and in the Anchorage Daily News, the Peninsula Clarion, and on KTUU Channel 2.

Other pertinent links:
-- National Weather Service Redoubt Page
-- Alaska Volcano Observatory Redoubt Page
-- Latest NOAA Ash Trajectory Forecasts
-- Mt Redoubt Webcam #1 (Hut)
-- Mt Redoubt Webcam #2 (CI)
-- Webicorder Graph Output

Five separate explosive eruptions of Mount Redoubt, occurring on Sunday March 22nd at 10:38 P.M. and 11:02 P.M., and today (Monday) at 12:14 A.M., 1:39 A.M., and 4:37 A.M. Alaska time (four hours earlier than EDT), spewed ash and steam as high as 60,000 feet into the atmosphere. The ash then began to travel north-northeast, depositing a layer from 1/8 to 1/4 inch on the Susitna Valley communities of Skwentna, Willow, Trapper Creek, and now Talkeetna; read this separate ADN story for a report on local effects in those communities.

Accurate forecasting of projected ashfall is hampered somewhat by the fact that the vertical wind profile is variable. If you look at the current Ash Trajectory Forecasts, you'll see that the wind changes direction with height. So the ash trajectory will also depend upon how high the eruption is spewed into the atmosphere. But Bob Hopkins, the meteorologist-in-charge at the National Weather Service office in Anchorage, clarifies the issue. He says that ash that is spewed up to the 40,000-50,000 ft. level is likely to stay at that level and not fall on South Central Alaska. He says it's the lower-level winds, between 10,000-20,000 ft., that are likely to carry the ash to the ground. So far, this prognostication has verified relatively well.

As a result, even though winds at 40,000 ft. and higher are expected to veer slowly towards Anchorage to Kenai over the next 24 hours, the chances of these winds producing an ashfall in either Anchorage or the northern Kenai Peninisula are negligible. In contrast, lower-level winds are expected to back further away from Anchorage and Kenai during that time, becoming more south-to-southeasterly, producing a greater threat of ashfall to the northwest and the west, should Mt. Redoubt continue to erupt. Regardless of where the ash falls, aviation will still be affected; numerous flights have already been cancelled, and if the trend continues, the effects will begin to show up on store shelves, although both Anchorage Home Depot outlets will remain open 24/7 and report an ample supply of materiel.

The NWS Fairbanks office has posted no ashfall advisories for any areas north of the Alaska Range. Consequently, no threat to Fairbanks exists at this time. If Fairbanks remains in the clear, cargo aircraft could use Fairbanks International Airport as an alternate destination, and goods trucked or trained down to Anchorage.

One of KTUU's news videos is quite enlightening. Meteorologist Scott Elnes provides an explanation of the Ash Trajectory Forecasts, and shows Doppler radar depictions in the volcano's vicinity on the video embedded below:

You'll find the most current volcanic activity information on the AVO Redoubt Page. The latest advisory information from the NWS Redoubt Page shows no ashfall advisories in effect, since there have been no significant eruptions since 4:37 A.M. this morning.

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