City lights shining through clouds

July 19th, 2012 |
VIIRS Day/Night Band from Suomi/NPP satellite

VIIRS Day/Night Band from Suomi/NPP satellite

The New Moon on 18 July means that no visible light reflected from the Moon can illuminate clouds, and the day/night band on the Suomi-NPP satellite can therefore view any clouds only with difficulty. However, it still views city lights, and illuminated roads, or gas field flares, among other things. The region above shows data contaminated by stray light. The Suomi/NPP satellite as it took this image was, although on the night side of the planet, nevertheless outside the shadow of the Earth, and radiation from the Sun was able to contaminate the image. Despite this, the lights of Minnesota and Iowa, both the main cities and the smaller towns, are plainly visible. City lights in eastern Wisconsin and Illinois have a more diffuse character because they are being viewed through cirrus clouds from a departing convective complex, as evident in this enhanced 10.7 micrometer imager from 0800 UTC.

VIIRS Day/Night Band from Suomi/NPP satellite

VIIRS Day/Night Band from Suomi/NPP satellite

The GOES-R IFR Proabability image from 0801 UTC, above, shows high probabilities of low clouds over north-central Iowa and south-central Minnesota. Surface observations plotted on the image confirm IFR conditions, with low visibilities and low ceilings. In addition, GOES-R Cloud Thickness values in the region are from 800 and 1000 feet thick. It is interesting that the Day/Night band can view the city lights through a low stratus deck that is hundreds of feet thick.

It is very difficult to distinguish between low stratus and clear regions in the stray light zone. That task is somewhat easier when there is no stray light, as shown in this image over the southern United States: In low light conditions, such as during a New Moon, low clouds have a smudgey appearance, but that signature is overwhelmed in the stray light zone. How thick does a cloud have to be before it is opaque to visible light?

GOES-13 Sounder Filter Wheel Anomalies Return

July 17th, 2012 |
GOES Sounder Imagery during Filter Wheel Anomaly

GOES Sounder Imagery during Filter Wheel Anomaly

The GOES-13 Sounder imagery has shown signatures intermittently over the past 4 days that suggest a Filter Wheel Anomaly is ongoing. The image above is from 0246 UTC on 17 July 2012. Similar events occurred on 16 July (at 0046 and 1446 UTC), on 15 July (at 2346 UTC), on 14 July (at 1946 UTC) and on 13 July (1346, 1846, 2046 and 2146 UTC). The GOES-13 Sounder suffered from Filter Wheel Anomalies in June, as well, as noted here.

As before, when the GOES Sounder Data are degraded by filter wheel anomalies, derived products (such as Total Precipitable Water, or Lifted Index), are also degraded. An example of Total Precipitable Water computed when there are Filter Wheel Anomalies in the data is shown below. The Blended Total Precipitable Water products in AWIPS are unaffected, however (Link), because they rely on GPS data over land.

GOES Sounder DPI Imagery of Total Precipitable Water showing effect of Filter Wheel Anomaly

GOES Sounder DPI Imagery of Total Precipitable Water showing effect of Filter Wheel Anomaly

[Update, 23 July 2012 and 25 July] Sounder anomalies persist, and occurred at 2246 UTC and 2346 UTC on 19 July, at 0346 UTC on 20 July, and 2046 UTC on 22 July; at 0046 UTC, 1446 UTC and 1546 UTC on 24 July; at 0046 UTC, 0146 UTC and 0246 UTC on 25 July; at 0546 UTC and 2346 UTC on 26 July; at 2046 UTC and 2146 UTC on 30 July and at 1847 UTC and 2047 UTC on August 4th.

Saharan dust moving westward across the Atlantic Ocean

July 16th, 2012 |
Meteosat-9 Saharan Air Layer (SAL) product (click image to play animation)

Meteosat-9 Saharan Air Layer (SAL) product (click image to play animation)

One of the more pronounced in a series of pulses of Saharan dust moving westward across the Atlantic Ocean was seen during the 14 July – 16 July 2012 time period. The Meteorsat-9 “split window” Saharan Air Layer (SAL) tracking product (above; click image to play animation) displayed a very strong signal of a large area of SAL dust (yellow to orange to dark red color enhancement) approaching the Lesser Antilles and the Greater Antilles islands of the West Indies.

The hazy signature of the dust cloud was also seen during the daytime hours on Meteosat-9 pseudo-natural color images  Red/Green/Blue (RGB) images (below; click image to play animation). A large area of sun glint was prominent over the middle Atlantic Ocean on the 18:00 UTC images, but the dust cloud could always been seen to the west of the sun glint.

Meteosat-9 pseudo natural color imagery product (click image to play animation)

Meteosat-9 pseudo natural color imagery product (click image to play animation)

First thunderstorm at Barrow, Alaska since 2004

July 15th, 2012 |

NOAA-15 AVHRR 0.6 µm visible channel and 10.8 µm IR channel images [click to enlarge]

NOAA-15 AVHRR Visible (0.6 µm) and Infrared (10.8 µm) images [click to enlarge]

McIDAS images of 1-km resolution NOAA-15 0.6 µm visible channel and 10.8 µm IR channel images from 01:30 UTC on 16 July 2012 or 5:30 PM local time on 15 July (above) showed the development of the first thunderstorm recorded at Barrow, Alaska since July 2004:

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE FAIRBANKS AK
556 PM AKDT SUN JUL 15 2012

…FIRST THUNDERSTORM IN BARROW SINCE 2004…

A LINE OF THUNDERSTORMS DEVELOPED JUST EAST OF BARROW LATE THIS AFTERNOON. A FEW RUMBLES OF THUNDER WERE HEARD AT THE NATIONAL WEATHER SERVICE OFFICE IN BARROW BETWEEN 515PM AND 535PM. THE ALASKA FIRE SERVICES LIGHTNING DETECTION NETWORK RECORDED FEW STRIKES JUST SOUTHEAST OF DEASE INLET.

THIS IS THE FIRST THUNDERSTORM AT BARROW SINCE JULY 3RD 2004.

$$
RT JUL 12

The coldest thunderstorm cloud-top IR brightness temperature on the 01:22 UTC NOAA-15 image was -37º C (green color enhancement). The surface winds at Barrow had switched to light northerly at the time of the thunderstorm, but a few hours prior to that had been from the southeast at 15-20 mph (helping to increase dew point temperatures into the low 50s F).

Due to the extreme viewing angle from the GOES-15 (GOES-West) satellite, the narrow line of weak thunderstorms was poorly resolved on Infrared (10.7 µm) images (below), and the apparent location was shifted to the north over the Arctic Ocean due to the parallax effect.

GOES-15 Infrared (10.7 µm) images [click to enlarge]

GOES-15 Infrared (10.7 µm) IR images [click to enlarge]