Global Visible True-Color Imagery

February 14th, 2020 |

True-Color visible imagery from 9 February 2020 (Click to enlarge)

Prediction: This is the most beautiful satellite image you will see today. The above imagery, from the talented Rick Kohrs at the Space Science and Engineering Center, knits (seemingly seamlessly) together vertical local-noon swaths of multispectral visible/near-infrared Geostationary imagery, all using McIDAS-X. At some point in the near future, daily imagery will be created, and then an annual movie. (Click here for an image from 21 March 2019, or from 21 September 2019).

In each image, the sub-point of a satellite used to create the image is evident in the Sun Glint (at 140.2ºE for Himawari-8, or 137.2ºW and 75.2ºW for GOES-17 and GOES-16, respectively). Values at the eastern and western edges do not match up because they are offset by 1 day. A break-point has to be inserted, so why not at the edge?

Bore-like feature over Lower Michigan

February 13th, 2020 |

GOES-16 Advanced Baseline Imager (ABI) “red” visible imagery (0.64 µm), 1435 – 1840 UTC on 13 February 2020 (Click to enlarge)

TJ Turnage, the Science and Operations Officer (SOO) at the National Weather Service forecast office in Grand Rapids, noted today the presence of smooth, curving bands over Lake Michigan. The animation above shows their development — and the smooth appearance of the bands (just offshore of Ottawa Co, and curving into Allegan Co) is in marked contrast to the north-south oriented lake-effect bands over central Lake Michigan. This falls into the “What the Heck is this?” Blog Category.

An hourly animation that includes surface conditions sheds little light. The bore-like feature seems to arise out of an interaction of the atmospheric flow with Big and Little Sable Points, and surface winds at Muskegon (just north of Ottawa Co) and Holland (in Allegan Co) change as the feature moves over — but no snow is observed at those stations during the bore passage.

GOES-16 Advanced Baseline Imager (ABI) “red” visible imagery (0.64 µm) and surface METARS hourly from 1300 – 2100 UTC on 13 February 2020 (Click to enlarge)

Radar imagery (from the College of Dupage) also shows little return associated with the bore-like features.  (Click to see images from 1720 and 1800 UTC, when the bands were on shore).

NEXRAD Composite Radar Imagery (Composite Reflectivity) centered on MI, 1655-1820 UTC on 13 february 2020 (Click to enlarge)


Water vapor imagery, below, suggests that the stable layer that is trapping the energy and causing the bore-like feature originated near Big and Little Sable Points, around 1600 UTC.  The enhancement also suggests the bore-like feature is higher than the tops of lake-effect bands in the middle of Lake Michigan.  (Click here for a rocking animation of the water vapor imagery;  the rocking allows for better tracking of the impulse back to the source near the Sables, its earliest hint is at 1610 UTC — vs. about 1635 UTC in visible imagery).

GOES-16 ABI Band 10 (7.34 µm, low-level water vapor) infrared imagery, 1520 to 2015 UTC, 13 February 2020 (Click to play animated gif)

GOES-16 ABI Band 2 (0.64 µm) visible imagery, 1520 to 2015 UTC, 13 February 2020 (Click to play animated gif)

Bore-like features require stable layers.  The Gaylord Michigan sounding at 1200 UTC — upstream from the region out of which the bore emerged — shows several inversion layers.  The weighting function for the sounding (from this site) shows peak contributions for 7.34 µm (indeed, from all water vapor channels) from above 500 mb.  The coldest brightness temperature in the bands is -28 º C;  based on the Gaylord sounding, that’s a pressure level near 560 mb.  These Bore-like features are not Lake-Effect snow bands, despite having the correct aspect ratio — their width and length both suggest Lake-effect bands, but their height suggests otherwise.

NOAA-20 overflew this region shortly after 1700 UTC, and a NUCAPS sounding is close to the Michigan shoreline, just east of Holland, where the cloud band is coming onshore. The sounding from NUCAPS at that point/time is below.  The very smooth sounding does bear a passing resemblance to the Gaylord Sounding, but the smoothness of the NUCAPS profile — sampling a volume of air that in this case is about as wide as a county, makes identification of sharp inversions difficult.

NOAA-20 NUCAPS Profile points over Lake Michigan and lower Michigan, ca. 1730 UTC on 13 February 2020 (Click to enlarge)

NUCAPS Profile of temperature and moisture, 17 UTC on 13 February 2020 (Click to enlarge)

GOES-17 IFR Probability Fields in Testing at CIMSS

February 13th, 2020 |

GOES-16 and GOES-17 IFR Probability fields over California, 1641 UTC on 13 February 2020, along with surface observations of ceilings and visibility (Click to enlarge)

GOES-17 IFR Probability fields are being evaluated at CIMSS (the Cooperative Institute for Meteorological Satellite Studies), with a plan to release them to the field via an LDM request in the near future.  The toggle above compares GOES-16 IFR Probability and GOES-17 IFR Probability for the same time over central California. Differences in resolution and parallax shifts are apparent (You can investigate the effect of parallax in a WebApp here).  A similar comparison is shown for Oregon, below, and for Washington, at bottom. GOES-17 IFR Probability fields for CONUS are also available at this website.

GOES-16 and GOES-17 IFR Probability fields over Oregon, 1641 UTC on 13 February 2020, along with surface observations of ceilings and visibility (Click to enlarge)

GOES-16 and GOES-17 IFR Probability fields over Washington, 1641 UTC on 13 February 2020, along with surface observations of ceilings and visibility (Click to enlarge)

Can you use gridded NUCAPS fields to diagnose the rain/snow line?

February 13th, 2020 |

900-mb Temperature fields (color-shaded; the 0ºC line is in black) derived from NOAA-20 NUCAPS profiles, 0624 UTC on 13 February, along with 0600 UTC METAR observations (Click to enlarge)

Gridded NUCAPS fields include a wide range of thermodynamic variables. The plot above shows the 900-mb temperature field. Is it possible to use this data to diagnose a rain/snow transition line?

Over southern New England, the relationship between 900-mb temperatures and surface precipitation observations seems robust: snow is restricted to most (but not all!) places where 900-mb temperatures are cooler than 0ºC. and rain falls where temperatures exceed 0ºC. Where terrain might be an influence in trapping cold air near the surface — the Catskills, for example, or the Alleghenies over New York and Pennsylvania, the relationship is not so straightforward. This data source warrants future investigations on its utility in these situations.