Parts of interior Alaska experienced heavy rainfall and significant river flooding during the last week of July 2008; AWIPS  composite images of the GOES-11 and GOES-12 water vapor channels (above) showed a rather unusual moisture plume — one having a long northwesterly fetch — stretching from the Russian arctic coast across the Chukchi Sea and into the interior of Alaska on 30-31 July. Rainfall amounts during the 28-31 July period were in the 2-6 inch range; in the Fairbanks area, 2.17 inches fell at North Pole (their second-highest daily rainfall amount on record), and this rainfall helped Eielson Air Force Base reach 7.30 inches for the month of July (their wettest July on record).

A comparison of the 06:00 UTC GOES water vapor image and the 05:20 UTC POES AMSU Total Precipitable Water (TPW) image (below) revealed  that TPW values were as high as 38 mm or 1.49 inches (green colors) within the moisture plume over the Chukchi Sea.

The heavy rainfall caused flooding along parts of the Chena River and the Tanana River in the Fairbanks area — the flood crest of the Tanana being the highest since August 1967 — and many residential areas had to be evacuated. The photo composite shown below (taken just after attending the Alaska Environmental Satellite Workshop) is of the Chena River at the “Ice Bridge” at  Pike’s Landing in Fairbanks on the afternoon of 31 July, when portions of the river were near flood stage (for additional photos and video, see the Fairbanks Daily News-Miner and the Alaska Superstation websites). In addition, the Alaska Railroad was forced to suspend passenger service north of Denali National Park because of rising waters in the Nenana area, with train passengers  being bused between the park and Fairbanks.

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There are a number of satellite signatures that denote areas of potential turbulence, and AWIPS images of the GOES-12 10.7 µm IR channel on 27 July 2008 (above) displayed two of the more common indicators: rapidly developing convection, and transverse banding. A decaying mesoscale convective system was moving southeastward across Minnesota and Iowa, with pulses of new convection developing rapidly over northern Iowa — one pilot reported a severe updraft that caused a rapid increase in altitude of 2000 feet as the aircraft was flying over the Minnesota/Iowa border region.

Along the periphery of the northeastern quadrant of the decaying MCS, a well-defined area of “transverse banding” formed (the narrow cloud band features were generally perpendicular to the mean wind direction aloft) –  there were a few reports of turbulence that appeared to be associated with this transverse banding feature: over Lake Michigan around 17:30 UTC,  over northeastern Wisconsin around 19:20 UTC, and over western Lower Michigan around 20:09 UTC.

The transverse banding features that were seen on the 4-km resolution GOES IR imagery were even more obvious on an AWIPS image of the 1-km resolution MODIS 11.0 µm IR channel (above), and also on a comparison of 250-m resolution MODIS true color images from the SSEC MODIS Today site (below).

Since we’re on the topic of potential aviation hazards, also note the hazy features that were evident on the MODIS true color images (just to the east of the transverse banding) — these hazy features were due to the presence of thick smoke from wildfires that had been burning over parts of northern Saskatchewan, Canada for several days (see the US Air Quality “Smog Blog” for details).  GOES-12 visible imagery indicated that this smoke began moving southeastward across Manitoba and into the north-central US on 25 July (QuickTime animation). The smoke was likely confined to layers aloft, but aircraft flying through those smoke layers would encounter significantly reduced visibilities at those altitudes. An AWIPS image of the 1-km resolution MODIS 3.7 µm IR channel (below) showed a large number of fire “hot spot” signatures across far northern Saskatchewan at 04:05 UTC (10:05 PM the previous evening, local time).

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The GOES-12 satellite was placed into Rapid Scan Operations (RSO) mode to monitor Tropical Storm Dolly on 21 July 2008 — the RSO visible images at 5-10 minute intervals (above) showed that deep convection was increasing around the core of the tropical cyclone. Dolly was moving northwestward across the Gulf of Mexico –  AWIPS images of the MODIS Sea Surface Temperature (SST) product (below) showed rather warm SST values (mid 80s to near 90 F, red colors) across much of the western Gulf of Mexico on the previous day, which argued in favor of a trend of intensification to hurricane strength. For additional satellite imagery and the latest information on  Dolly, see the CIMSS Tropical Cyclones site.

** 23 July UPDATE: Dolly reached hurricane intensity late in the day on 22 July (CIMSS Advanced Dvorak Technique intensity plot). GOES-12 RSO visible images (below) show the ragged eye of Hurricane Dolly approaching  South Padre Island along the southern coast of Texas. A peak wind gust of 76 mph was reported at Port Mansfield and Rincon in Texas, with a ship captain off South Padre Island estimating a wind gust of 100 mph — wave heights over 24 feet were recorded by an offshore buoy. In addition to the strong winds, there were also several tornadoes and waterspouts, along with rainfall in excess of 12 inches.

AWIPS  images of the 4-km resolution GOES-12 10.7 µm IR channel (below) revealed that cloud top brightness temperature values around the eye and in the outer band regions were in the -70º to -80º C range (black to white colors).

AWIPS images of the 1-km resolution MODIS 11.0 µm IR channel (below) indicated that cloud top brightness temperatures were as cold as -84º C (purple colors) on 22 July as the storm reached hurricane intensity.

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On the morning of 17 July 2008, we received the following email from Ron Miller at the National Weather Service forecast office in Spokane, Washington:

Can you tell me what you think the “clouds” are over the PacNW this morning. You can only see them on the first few visible images of the morning. Looking out out window we can’t detect them. Given the flow pattern over the past 24-48 hours, I have a hard time believing that it’s wildfire smoke from CA. One possibility is Volcanic Ash from Okmok, since after it’s eruption, the ash cloud drifted southeast and essentially hung out in the Gulf of AK trough. Any ideas?

Excellent question, Ron — thanks for bringing this case to our attention! As it turns out, the Okmok volcano erupted in the Aleutian Islands on 12  July, as can be seen in a comparison of visible images from the MTSAT-1R and GOES-11 satellites (above | QuickTime animation; see also:  Google Earth AVHRR false color image | VISIT Meteorological Interpretation Blog | GOES-11 visible Java animation) — and 5 days later, GOES-11 (GOES-West) visible imagery (below) did indeed reveal a portion of the volcanic plume  (actually, three separate thin plumes) drifting eastward over the Pacific Northwest region early in the day on 17 July. The thin volcanic plumes seen on the GOES visible imagery  — which were likely composed primarily of ice crystals and sulfur dioxide (SO2) — were  high-altitude features (verified to exist at an altitude around 11-12 km by CALIPSO), so they showed up on the visible imagery before  the lower-altitude smoke (from to wildfires that had been burning in northern California) which  became illuminated by the rising sun a bit later in time. Forward scattering was more favorable at the times of the earlier visible images, enhancing the appearance of the volcanic plume features  — then, as the sun angle increased into the mid-morning hours, the thin volcanic plumes became less apparent on the visible imagery (but the thick low-level smoke drifting northeastward across Oregon continued to remain  obvious).

The corresponding GOES-11 10.7-12.0 µm “split window IR difference” product did not show a clear signal of volcanic ash content in the plume (nor was there an obvious plume signal in either the GOES-11 10.7 µm IR window, 3.9 µm shortwave IR, or 6.5 µm water vapor imagery). However, an Aqua MODIS IR difference image (below) did show the signature of an SO2-rich plume (darker blue colors) stretching east-northeastward across the Pacific Ocean and  reaching western Washington and Oregon around 11:00 UTC (5am local time). The daily evolution of the SO2 plume can also be seen in an animation of Ozone Measuring Instrument (OMI) images. Compare the 3-plume structure seen on the MODIS IR difference image with the similar plume structure seen on an AIRS brightness temperature difference image.

NOAA Air Resources Laboratory HYSPLIT model backward trajectories (below) indicated  that high-altitude air parcels arriving over western Washington and far northwestern Oregon at 11:00 UTC on 17 July had likely been transported southward, then east-northeastward across the Pacific Ocean during the previous 72-hour period.

A comparison of AWIPS images of the MODIS visible, IR window, water vapor, and cirrus detection channels from 18:47 UTC (11:47 am local time) on 17 July (below) show that there was no obvious volcanic plume signature on either the visible or IR images at that time. However, a brighter “plume signal” did show up in the cirrus detection channel image (which seems to correspond roughly to the northernmost of two moist plumes on the water vapor image).

The MODIS cirrus detection channel is a daytime-only “near-IR” channel (centered at 1.6 µm) which is sensitive to particles that are efficient scatterers of light (such as ice crystals, volcanic ash particles, airborne dust or sand, etc). Two consecutive  MODIS cirrus detection images from the Terra (18:47 UTC) and Aqua (20:26 UTC) satellites (below) both show evidence of a subtle volcanic plume  signal (brighter white streaks), which appeared to be moving farther inland over the Pacific Northwest.

By the end of the day on 17 July, a favorable forward scattering angle (with the sun getting lower in the western sky) allowed the volcanic plume to again be seen on GOES visible channel imagery — but this time using the GOES-12 (GOES-East) satellite (QuickTime animation).  The plume had moved eastward along the US/Canada border during the day, drifting across parts of northern North Dakota and even far northwestern Minnesota by sunset!

===== 18 July Update =====

The volcanic plume was again evident on early morning  GOES-11  visible imagery (Animated GIF), stretching from the Pacific Northwest states all the way to southern  Manitoba and southern Ontario in Canada. During the afternoon and early evening hours, there were numerous pilot reports from aircraft encountering the plumes over northern Oregon, southwestern Washington, and other parts of the Pacific Northwest region, prompting the issuance of a Volcanic Ash SIGMET advisory.

MODIS 1.3 µm near-IR "cirrus detection" image

A 17:49 UTC AWIPS image of the MODIS 1.3 µm near-IR “cirrus detection” channel (above) suggested that the Volcanic Ash SIGMET advisory could perhaps have been extended a bit farther northeastward across Montana — note the slightly brighter “streaky” volcanic plume signature  heading northeastward across Idaho into Montana, beyond the eastern boundary of the SIGMET (outlined in yellow). In fact, the boundary of the Volcanic Ash SIGMET was indeed extended northeastward soon thereafter (Animated GIF).

Blog reader Tom Patton later sent us an email asking about some photos taken over western Montana around sunset on the evening of 18 July:

"...driving through the upper Deer Lodge Valley at about sunset. I recall coming over the divide into the southeast end of the valley, which offers a good westerly view of the mountains, and noticing what I considered to be a striking sunset. The "clouds" were almost iridescent in whites and blues. I think what I noticed most was the lack of red. The clouds were also unusually 'streaky'."

Volcanic clouds over western Montana on 18 July (photo by Margaret Patton, Research Office, Montana Tech of The University of Montana)

So are the “clouds” seen in the photo above simply cirrus clouds, or are they volcanic clouds from the Okmok eruption?  If we examine the GOES-12 10.7 µm IR images for the few hours leading up to the time that the photo was taken, we see that  there is no obvious signal of “meteorological clouds” (such as thick cirrus) evident on the IR imagery over western Montana or to the west over Idaho. However, the thin volcanic plumes really jump out on GOES-12 visible images, with a favorable “forward scattering angle” late in the day. At first glance, the GOES-12 water vapor images suggest that the volcanic plumes may have been embedded in a much broader “moisture plume” — however, the volcanic clouds were likely at an altitude above which was being sampled by the GOES-12 water vapor channel (which is generally the 300-700 hPa layer, or altitudes between 10,000 and 30,000 feet).

There were also photos of the volcanic clouds taken by aircraft pilots over Billings, Montana the following  evening (photo 1 | photo 2 | photo 3).

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