Mountain waves over Colorado

June 22nd, 2009 |
MODIS 6.7 µm and GOES-12 6.5 µm water vapor images

MODIS 6.7 µm and GOES-12 6.5 µm water vapor images

Moderate southwesterly flow aloft over the Rocky Mountains was aiding in the formation of mountain waves across much of Colorado and parts of the adjacent states on 22 June 2009. AWIPS comparisons of the 1-km resolution MODIS 6.7 µm water vapor image with the corresponding 4-km resolution GOES-12 6.5 µm water vapor image (above) and the 8-km resolution GOES-11 6.7 µm water vapor image (below) demonstrated the value of better spatial resolution for detecting such mesoscale features.

MODIS 6.7 µm and GOES-11 8-km 6.7 µm water vapor images

MODIS 6.7 µm and GOES-11 6.7 µm water vapor images

The appearance of these banded “mountain wave signatures” on water vapor imagery indicates the potential for clear air turbulence in those areas; however, there were no pilot reports of turbulence until 13:02 UTC near Fort Collins (at an altitude of 15,000 feet). An animation of the GOES-12 6.5 µm water vapor imagery (below) also showed the presence of a lee-side cold frontal gravity wave, which could be seen propagating southward across eastern Colorado and western Kansas. In fact, a small packet of waves could be seen along and behind the leading edge of this lee-side cold frontal gravity wave on the MODIS water vapor images above — surface winds behind this front had gusted to 36 knots at McCook, Nebraska (station identifier KMCK) and 20 knots at Goodland, Kansas (station identifier KGLD).

GOES-12 6.5 µm water vapor images

GOES-12 6.5 µm water vapor images

Mesoscale Convective System moves across southern Wisconsin

June 19th, 2009 |
GOES-12 10.7 µm IR images

GOES-12 10.7 µm IR images

A cluster of thunderstorms developed over extreme northeastern Iowa and extreme southeastern Minnesota, and merged into a large Mesoscale Convective System (MCS) across southern Wisconsin during the early hours of 19 June 2009. AWIPS images of the 4-km resolution GOES-12 10.7 µm IR channel (above) displayed the rapid growth of this MCS, which was responsible for a number of reports of hail and damaging winds (SPC storm reports) along with heavy rainfall (5.60 inches was reported in Dodgeville, Wisconsin). GOES-12 IR brightness temperatures associated with this MCS were as cold as -75º C.

Even though the region was well to the north of a stationary frontal boundary, GOES-12 Sounder images (below) of the Lifted Index (LI), Convective Available Potential Energy (CAPE), and Total Precipitable Water (TPW) indicated that the pre-convective environment across much of southern Wisconsin was characterized by instability (LI values to -10º C and CAPE values to 3958 J/kg) and moisture (TPW values to 51 mm, or 2.00 inches).

GOES-12 sounder LI, CAPE, and TPW

GOES-12 sounder LI, CAPE, and TPW

A 1-km resolution MODIS 11.0 µm IR image at 04:11 UTC (11:11 pm local time) with an overlay of cloud-to-ground lightning strikes (below) showed the tendency for lightning strikes to cluster around the many “enhanced-v” and “cold/warm couplet” signatures on the IR image. During the 15-minute interval ending at 04:15 UTC this storm produced 881 negative lightning strikes and 158 positive lightning strikes.

MODIS 11.0 µm IR image + cloud-to-ground lightning strikes

MODIS 11.0 µm IR image + cloud-to-ground lightning strikes

The was a report of baseball-size hail (2.75 inch diameter) just to the northwest of Madison, Wisconsin (station identifier KMSN), which was near the coldest -80º C MODIS IR cloud top pixel (below).

MODIS 11.0 µm IR image + SPC storm reports

MODIS 11.0 µm IR image + SPC storm reports

East Pacific Tropical Depression 1E

June 18th, 2009 |
GOES-11 10.7 µm IR images

GOES-11 10.7 µm IR images

The first tropical depression of the East Pacific season (Tropical Depression 1E) formed off the southwest coast of Mexico on 18 June 2009 — this was the latest date of the start of the tropical cyclone season in that particular ocean basin since reliable records began in 1970. The previous record for the latest start of the season in the East Pacific basin was the development of Tropical Storm Aletta on 19 June in 1994.

GOES-11 10.7 µm IR images (above) showed that the tropical depression exhibited some very cold cloud tops early in the day on 18 June (IR brightness temperature values as low as -87º C, darker purple color enhancement), but then the cold cloud canopy collapsed fairly quickly later in the day, with cloud top temperatures warming from -86º C at 19:00 UTC on 18 June to -64º C at 01:00 UTC on 19 June. A new series of convective bursts then developed in the northern quadrant of the tropical depression after about 03:00 UTC on 19 June.

Volcanic ash plume from Sarychev Peak eruption

June 16th, 2009 |
GOES-11 split window IR difference product (10.7 - 12.0 µm)

GOES-11 "split window" IR difference product (10.7 - 12.0 µm)

A series of volcanic eruptions from Sarychev Peak (located in the central Kiril Islands) began on 10-11 June 2009, and GOES-11 “split window” IR difference images (above) showed a good signature of one of the ash plumes (yellow to cyan color enhancement) as it began to move eastward across the North Pacific Ocean on 16 June 2009.

AWIPS images of the MTSAT + GOES-11 IR channel with overlays of the MTSAT high density winds (below) showed the high-altitude flow that was helping the volcanic ash plume features to move southeastward around 40-60 knots (according to the Volcanic Ash Advisories that were issued on 16 June).

GOES-11 is the last of the current GOES series to have the 12.0 µm IR channel on the imager instrument package, which allows the calculation of such a “split window” IR difference product for volcanic ash detection. Once GOES-11 is replaced by either GOES-13 or GOES-14 as the operational GOES-West satellite, the geostationary volcanic ash detection ability will be greatly diminished over the eastern North Pacific Ocean…until the launch of the Advanced Baseline Imagery (ABI) on the GOES-R satellite.

MTSAT + GOES-11 IR images, MTSAT high density winds

MTSAT + GOES-11 IR images, MTSAT high density winds