Summer solstice TROWAL over the Upper Midwest

June 21st, 2018 |

Aqua MODIS Water Vapor (6.7 µm) image, with overlays of surface pressure/fronts (cyan), RUC model 310K equivalent potential temperature (red) and 24-hour precipitation (green) [click to enlarge]

Aqua MODIS Water Vapor (6.7 µm) image, with overlays of surface pressure/fronts (cyan), RUC model 310K equivalent potential temperature (red) and 24-hour precipitation (green) [click to enlarge]

A nighttime Aqua MODIS Water Vapor (6.7 µm) image (above) showed the well-defined circulation of a mid-latitude cyclone that was centered over northwest Iowa at 0814 UTC (3:14 am local time) on 21 June 2018. Contours of RUC model equivalent potential temperature along the 310 K isentropic surface indicated that a Trough of Warm Air Aloft (TROWAL) existed just to the north of the occluded surface frontal boundary, curving cyclonically from northeastern Iowa across southern Minnesota into southeastern South Dakota and then southward across eastern Nebraska. 24-hour precipitation totals in excess of 2-3 inches had already been observed at that time.

Suomi NPP VIIRS Infrared Window (11.45 µm) images (below) displayed minimum cloud-top brightness temperature values of -50 to -55ºC (yellow to orange enhancement) near the TROWAL axis.

Suomi NPP VIIRS Infrared Window (11.45 µm) images, with plots of surface reports [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) images, with plots of surface reports [click to enlarge]

An animation of GOES-16 (GOES-East) Mid-level Water Vapor (6.9 µm) images (below) revealed that the storm system moved very slowly during the 00-20 UTC time period, while moderate to occasionally heavy rainfall was observed beneath the TROWAL air stream. 24-hour precipitation amounts reached 4-6 inches by 12 UTC in parts of southwest Minnesota, northwest Iowa and southeast South Dakota (FSD PNS) — and a number of river gauges were reporting minor to major flooding by the afternoon hours.

GOES-16 Mid-level Water Vapor (6.9 µm) images, with hourly plots of surface weather type [click to play MP4 animation]

GOES-16 Mid-level Water Vapor (6.9 µm) images, with hourly plots of surface weather type [click to play MP4 animation]

It should be noted that TROWAL formation is rather unusual over this region during the summer months — but during the cold season a TROWAL can help to produce heavy snowfall (some examples are documented here, here and here).

Trail Mountain Fire in Utah

June 20th, 2018 |

GOES-16

GOES-16 “Red” Visible (0.64 µm, left) and Shortwave Infrared (3.9 µm, right) images, with hourly plots of surface reports [click to play MP4 animation]

GOES-16 (GOES-East) “Red” Visible (0.64 µm) and Shortwave Infrared (3.9 µm) images (above) showed the smoke plume and thermal anomaly or “hot spot” (dark black to red pixels) associated with the Trail Mountain Fire in Utah on 20 June 2018. Once the smoke was lofted to higher altitudes (in 2 distinct pulses) it quickly fanned out southeastward toward the Utah/Colorado border, transported by northwesterly winds around the periphery of a ridge of high pressure that was building into the Southwest US.

Fixed-Grid Format Data flowing in AWIPS

June 19th, 2018 |

AWIPS imagery of GOES-16 Low-Level Water Vapor (7.34 µm) at 1527 and 1532 UTC on 19 June (Click to enlarge)

Until today, GOES-16 Data that flowed into AWIPS was remapped twice: First, from the observational perspective (that is, how the satellite views it) to a spherical fixed-grid projection that approximates the Earth, and then to a Lambert Conformal projection with (for infrared data) 2-km resolution over the Globe. That Lambert Conformal data was then shipped to AWIPS, where the data were again re-projected into the observational perspective desired by the meteorologist.

The 2-km resolution of the data shipped to AWIPS before today is applicable only at the sub-satellite point (nadir) for GOES-16. Thus, the second remap was suggesting better resolution than was warranted by the data. Additionally, the number of data points needed to be sent was very big.

At 1532 UTC on 19 June, the first fixed-grid format data were directly shipped to AWIPS; remapping to a Lambert Conformal projection is no longer done upstream of AWIPS. The toggle above shows the difference in the 7.34 µm “Low-Level” Infrared Water Vapor imagery over the coast of Oregon, near 46º N, 124º W (very far from the GOES-16 sub-satellite point at 0º N, 75.2º W), in the AWIPS CONUS projection.  At 1532 UTC, after the double remap is removed, the pixels are more distinct, and as expected they splay away from the sub-satellite point.

Removing a remapping in the data processing means that pixel-sized extremes — such as overshooting tops, or fires — and gradients will be better represented in the data.  Consider the Clean Window (10.3 µm) Infrared imagery below of strong convection over the Gulf of Mexico east of Texas.  Overshooting tops Brightness Temperatures are colder and the tops themselves more distinct after 1532 UTC than at 1527 UTC.

AWIPS imagery of GOES-16 Clean Window Infrared Data (10.3 µm) from 1347 to 1612 UTC on 19 June. The animation pauses on the last double-remapped image at 1527 UTC, and the first fixed-grid format image at 1532 UTC (Click to enlarge)

 

See also this blog postThis training also discusses the remapping.  And here (or here) is the National Weather Service announcement on the change.

Large hail in north central Colorado

June 18th, 2018 |

GOES-16

GOES-16 “Red” Visible (0.64 µm, left) and “Clean” Infrared Window (10.3 µm, right) images, with plots of SPC storm reports [click to play MP4 animation]

Severe thunderstorms developed  over the Front Range of Colorado during the late afternoon and early evening of 18 June 2018. One of the GOES-16 (GOES-East) Mesoscale Domain Sectors positioned over that region provided 1-minute data — shown above is a comparison of “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images of these storms as they produced large hail (up to 3 inches in diameter) across parts of the Front Range Urban Corridor. SPC storm reports are plotted on the images.