Low cloud / fog over snow covered ground on 25 February 2019
February 25th, 2019 by Dan BikosDuring the overnight hours of 25 February 2019, low clouds and fog developed over portions of northwest Kansas, eastern Colorado and southwest Nebraska. The low cloud and fog developed over a field of snow on the ground from a recent blizzard. Low cloud and fog on top of snow on the ground can be difficult to detect in some satellite imagery, while in other satellite imagery it is easy to detect, for example see this 4 panel GOES-16 imagery:
The loop spans the nighttime to daytime hours.
Upper left is the GeoColor product.
Upper right is the Day Cloud Phase Distinction product.
Lower left is the nighttime microphysics product.
Lower right is the 10.3 micron (IR) band.
During daytime hours, note how difficult it is to discriminate between low cloud / fog versus snow on the ground in the GeoColor product, both features appear white. However, during the daytime we can make the discrimination between low cloud / fog versus snow on the ground in the day cloud phase distinction RGB. Snow on the ground appears green, why? There is little contribution from Red (10.3), large contribution from Green (highly reflective at 0.64 microns) and small contribution from Blue (absorptive at 1.6 microns). The low cloud and fog appears cyan since the contribution from Blue is larger (liquid water clouds reflect much more than snow on the ground at 1.6 microns).
The low cloud and fog during the nighttime hours is observed as bright green in the nighttime microphysics product and light blue in the GeoColor product. It may be seen in the 10.3 micron band as well, but is much more difficult to detect due to the lack of contrast relative to the other 2 RGB products. High clouds are also observed moving over the low cloud / fog region in northwest Kansas, these are observed as black or dark red colors in the nighttime microphysics product. The high clouds acted to seed ice crystals into the low level clouds underneath, leading to snow flurries across the area.
Another product that shows all of this quite well is the CIRA Snow/Cloud-Layers product:
This loop spans daytime hours only since the discrimination between clouds versus snow on the ground can only be made during the daytime in this product. Snow appears white in color, which may be more intuitive compared to other RGB products. Bare ground is dark green, low clouds or fog are yellowish-green and high level clouds are pink.
Posted in: Ceilings, Fog, Visibility, | Comments closed
Popocatépetl Volcanic Eruption
February 15th, 2019 by Jorel TorresPopocatépetl Volcano erupted overnight, spewing volcanic ash emissions, from 0200-1600UTC, 15 February 2019. Geostationary and polar-orbiting satellites observed this atmospheric phenomenon from 00-16 UTC, 15 February 2019.
GOES-16 3.9um
A hot spot (i.e. white, warm brightness temperature) is produced from the volcanic eruption, along with its ash plume (i.e. elongated, cooler, black, brightness temperatures). Notice how the ash plume advects to the southwest, due to moderate, surface-to-mid-level northeasterly winds.
GOES16 – Split Window Difference (SWD)
In the animation, SWD observes low-level atmospheric water vapor (i.e. moisture) and is derived from the 10.3um-12.3um channel difference. Once the volcano erupts, notice the elongated volcanic ash plume (i.e. seen in purple), that comprises of ash and cloud liquid droplets. In the animation, note how the plume is conspicuous compared to the 3.9um observations.
GOES-16 – Volcanic Ash Microphysics (EUMETSAT)
The EUMETSAT RGB shows the volcanic ash plume in red, where different shades of red, indicate varying levels of volcanic ash concentrations. Also, volcanic eruptions can produce varying levels of sulfur dioxide (SO2), which is bad for human health. In this animation, there was no SO2 detected; no yellow (i.e. indicates mixed ash and SO2), or shades of green colors (i.e. purely SO2) were observed near the volcanic eruption.
SNPP – Near-Constant Contrast (NCC) (Nighttime visible imagery)
SNPP, a polar-orbiter, also captured the volcanic ash plume, utilizing NCC nighttime visible imagery. NCC, a derived product of the Day/Night Band (DNB), utilizes a sun/moon reflectance model that illuminates atmospheric features, and senses emitted and reflected light sources during the nighttime. In the static SNPP NCC image below, notice the emitted light sources produced from cities and towns (i.e. Mexico City and Acapulco) and the reflected light sources (i.e. clouds and in this case, the volcanic ash plume).
Posted in: Aviation Weather, GOES R, POES, Satellites, Volcano Weather, | Comments closed
14 February 2019 California Atmospheric River event
February 15th, 2019 by Dan Bikos
Advected Layer Precipitable Water loop:
Blended Total Precipitable Water loop:
Percent of Normal TPW loop:
Posted in: Heavy Rain and Flooding Issues, Hydrology, Satellites, | Comments closed
VIIRS Captures Ice/Ocean Movements
February 13th, 2019 by Jorel TorresBy Lewis Grasso and Jorel Torres
VIIRS captures interesting imagery in the Arctic. From 0314 UTC to 1233 UTC, 13 February 2019, VIIRS, on-board NOAA-20 and S-NPP, imaged fascinating features in the Arctic. In particular, imagery from Band I4 (3.74um) with a sub-satellite footprint size of 375-meters captured several features: 1) oscillation of an ice field due to lunar tides, 2) the boundary where the ice sheet is melting due to the interaction of relatively warm waters associated with the Gulf Stream, and 3) the melt water and associated currents in the ice-free ocean. Animation below, shows a loop beginning at 0314 UTC and extending to 1233 UTC. Within the loop the dark-greenish color represents the very cold ice sheet, northeast of Greenland, which is located in the lower right corner of the loop. Incidentally, portions of Svalbard, Norway are located in the upper-left corner. The lightest grey color represents the relatively warm ice-free ocean. The rapidly moving cloud-field is evident over the ice free ocean by a black color. Interpretation is the following: periodic oscillations are associated with the lunar tide, note the back and forth motion of the ice sheet. As the boundary of the ice sheet melts, the cold melt water flows into the relatively warm ocean and appears relatively dark. The left most dark plume of melt water is reminiscent of a drop of black ink falling downward in a tank of clear water. We invite the reader to think, when was the last time you have seen this type of view in the Arctic? Kudos to the JPSS Program.
Posted in: Miscellaneous, POES, Satellites, | Comments closed
4 February 2019 significant ice storm in the Upper Great Lakes
February 7th, 2019 by Dan BikosOn 4 February a shortwave tracked across the Upper Great Lakes towards the east, ahead of the shortwave, anomalously high moisture at low to mid-levels existed which contributed to a historic ice storm for the region.
The NWS forecast office in Marquette, MI has a great web-page summarizing this event including pictures and the meteorological environment:
https://www.weather.gov/mqt/February4th2019IceStorm
This blog entry will focus on various satellite imagery and products, particularly those that highlight the anomalously high moisture for this event.
We lead off with a synoptic scale perspective of this event with the 3 Water Vapor bands from GOES-16 along with the Air Mass RGB:
The imagery clearly shows a shortwave in the North Dakota / Minnesota vicinity moving eastward. Ahead of this shortwave, precipitable water values were anomalously high, in fact record breaking TPW values were observed for this time of year in the Upper Great Lakes. The anomalously high precipitable water values can be seen in the Advected Layer Precipitable Water product for the various layers. Moisture plumes are observed with origins from the Gulf of Mexico in the SFC-850, 850-700 and 700-500 mb layers. This shows that the moisture was relatively deep, particularly for this time of year in the Upper Great Lakes region.
An experimental product at CIRA that is still under development is the model minus ALPW PW for each layer. For example, the HRRR minus ALPW PW for a given layer shows the difference between observations from ALPW versus different HRRR 3 hour forecasts (4 panel shows the same layer arrangement as the ALPW loop above). We primarily see positive values in the Upper Great Lakes region ahead of the shortwave, meaning that there’s more moisture in the HRRR 3 hour forecast compared to ALPW observations. A similar theme exists for the GFS (these are also 3 hour forecast fields).
Interestingly, the HRRR forecast a substantial ice storm, as seen in this set of forecasts:
The anomalously high precipitable water played a key role in contributing to a historic ice event for this region, which typically observes snow during precipitation events this time of year.
The ALPW product is available in AWIPS from CIRA via LDM, however the model minus ALPW difference fields are not available since these are still in an experimental stage.
Posted in: Icing, | Comments closed