Daily VIIRS True-Color images from NOAA-20 for the Great Lakes in November 2020

December 1st, 2020 |

Daily true-color images from NOAA-20 VIIRS over Lake Erie, 1-30 November 2020 (Click to animate)

CIMSS provides sectorized VIIRS true-color imagery for each of the five Great Lakes, and for the entire Great Lakes basin at the Direct Broadcast ftp site (ftp://ftp.ssec.wisc.edu/pub/eosdb/j01/viirs/ and ftp://ftp.ssec.wisc.edu/pub/eosdb/npp/viirs for NOAA-20 and Suomi-NPP, respectively). The imagery above shows NOAA-20 images saved from that site and merged together to make an animation (except for 12, 13, 14 November. Mea Culpa) over Lake Erie. Click here to view the animation as an mp4. (Additional animations for the other Great Lakes have also been created:  Lake Ontario in animated gif / mp4) Lake Huron in animated gif / mp4 ; Lake Michigan in animated gif / mp4; Lake Superior in animated gif ; mp4)

The daily views allow a user to view slow changes in the Lake’s circulation — when skies are clear. Such was the case on 8, 9 and 10 November, shown below. A slow anticyclonic motion in the widest part of central Lake Erie is apparent.

NOAA-20 VIIRS true-color imagery over Lake Erie on 8, 9, and 10 November 2020 (Click to enlarge)

Comparing NUCAPS temperature values to forecast fields

November 29th, 2020 |

Gridded NUCAPS estimates of 850-mb Temperature, 1851 UTC on 30 November 2020 (Click to enlarge)

Late November is a time when cold outbreaks can pass over relatively warm Great Lakes waters (click here for recent observations) and produce lake-effect snow. Gridded NUCAPS observations derived from NOAA-20 CrIS and ATMS data, above, shows a large area with temperatures colder than -12ºC over northwest Ontario and northern Minnesota, just upwind of the Great Lakes;  Lake Superior’s surface temperature at the time was around 5ºC —  a temperature difference that support lake-effect precipitation.  How well do the NUCAPS observations compare to model predictions of the environment?

Forecasts from the 1200 UTC run of the NAM, below, valid at 1800 UTC, and from the 1500 UTC run of the Rapid Refresh, valid at 1900 UTC, show -12ºC in bright magenta.  (Model analyses taken from this website)  NUCAPS analyses suggest the cold air is moving south faster than anticipated by the model.


6-h forecast of 850-mb Temperature, valid 1800 UTC on 29 November 2020 (Click to enlarge)

4-hour forecast of 850-mb temperature from the Rapid Refresh, valid 1900 UTC on 29 November 2020 (Click to enlarge)

This site can be used to view gridded NUCAPS fields outside of AWIPS.  The 850-mb analysis from the pass is shown below.  It’s important to recall that Gridded NUCAPS fields include data from all retrieved profiles — including profiles for which the infrared retrieval failed (usually in locations with thick clouds, and those from which the infrared and microwave retrievals both failed (usually in locations with rain). This mapping for the temperature gridding below shows where infrared retrievals failed (yellow) and where infrared and microwave retrievals both failed (red).

850-mb Temperature fields, 1849 UTC on 29 November 2020 (Click to enlarge)

The ‘yellow’ points north and west of the Great Lakes were associated with clouds that are apparent in this VIIRS True Color image, taken from the UW-Madison Direct Broadcast ftp site (Link). The clouds were associated with a departing low pressure system (link).

NOAA-20 VIIRS True-Color imagery, 1850 UTC on 29 November 2020 (Click to enlarge)

Great Lakes water temperatures in late November

November 29th, 2020 |

ACSPO SSTs from VIIRS on NOAA-20, 28 November (1728 and 1911 UTC) and 29 November (0727 UTC). Click to enlarge

Clear skies over most of the five Great Lakes on 28-29 November allowed the VIIRS instrument on NOAA-20 to gather information for Advanced Clear-Sky Processing for Ocean (ACSPO) Sea Surface Temperatures.  The animation above shows two afternoon images (from 28 November 2020, at 1728 UTC and 1911 UTC) and one morning image (from 29 November 2020 at 0727 UTC).  The color enhancement shows values from 35ºF to 55ºF.

Lake Erie shows the warmest temperatures, just over 50ºF in the eastern part of the Lake. High Pressure over the Ohio River valley on 28 November (2100 UTC analysis) meant light winds over Lake Erie. The lack of wind-induced mixing allowed for warming (a few degrees F between 1728 and 1911 UTC) of the surface skin of the lake. Lake Superior shows temperatures around 40º F (albeit a bit warmer along just off the Upper Peninsula of Michigan); Lakes Michigan and Huron, western Lake Michigan and northwest Lake Ontario show temperatures in the mid-40s. Eastern Lake Ontario shows temperatures in the upper-40s.

Note: You can compare these observations to previous years here, for Lake Michigan. (Links to comparisons at other lakes are at that link as well). Thanks to the Blog Reader for this link!

Mesoscale snowband effects on temperature in Kansas

November 25th, 2020 |

Day Snow Fog RGB, 1421 – 1926 UTC on 25 November 2020 (Click to animate)

An extratropical cyclone deposited a mesoscale snowband — a few counties wide — in south-central Kansas late in the day on 24 November 2020 (Click here to see the storm at 0300 UTC on 25 November). As is often the case, such bands have profound impacts on surface temperatures. It is therefore important to monitor their precise location. The animation above shows the Day Snow Cloud RGB; its use of the 1.61 µm band allows the RGB to distinguish easily between snow and clouds, both of which are bright in the visible, as shown in the image below, courtesy Mike Umscheid, NWS ICT, that shows the snow band and the similarly reflective clouds to the east. (Imagery created at this nifty website!)

GOES-16 Visible imagery, 25 November 2020, and morning snow depths over central Kansas (Click to enlarge; imagery courtesy Mike Umscheid, NWS ICT)

GOES-16 Land Surface Temperatures (a baseline level 2 product) shows the effect of the snow on skin temperature, below. Shortly after sunrise, temperatures over the snowband are several degrees (Fahrenheit) cooler, as expected with clear skies and a fresh snowpack. (Warm lakes also shine through!)  Bare land in Kansas warms quickly, with Skin Temperatures reaching into the upper 60s and 70s by 1900 UTC, whereas the snow band remains in the 30s!

GOES-16 Land Surface (skin) Temperature, 1421 – 1916 UTC, 25 November 2020 (Click to animate)

A comparison of GOES-R Land Surface Temperatures with METAR observations, below, underscores the notion that the skin temperature can be much warmer than the temperature 1.5 m above the ground, where METAR thermometers (or thermistors) measure the air temperature. The warmest METAR temperature at 2000 UTC is 57º F at Scott City, KS. Land Surface Temperatures there are in the mid-60s, with 70 just to the northeast.

GOES-16 Land Surface Skin Temperatures with surface METAR plots, 2000 UTC (Click to enlarge)

Note that the default bounds of the colorbar range in Land Surface Temperature have been changed. Default values range from -10º to 110º F; values shown above range from 10º to 80º F. The toggle below compares the two, at 1501 UTC.

GOES-16 Land Surface Temperature with default color bounds (-10 to 100 F) and more useful bounds for this day (10 to 80 F) (Click to enlarge)

Towards sunset, the Day Snow Fog RGB (or any RGB that relies on reflectances from visible, near-Infrared or infrared channels) can become dim. In that event, an AWIPS user can edit the Composite Options, reducing the upper bounds of all three RGB channels o that the image retains brightness and utility (in this case upper bounds were reduced for Red from 100 to 60; for Green from 70 to 40; for Blue from 30 to 19).

GOES-16 Day Snow Fog RGB at 2241 UTC, 25 November 2020, with default bounds (dimmer image: Red 0-100; Green 0-70; Blue 0-30) and adjusted bounds (brighter image: Red 0-70; Green 0-40; Blue 0-19) (Click to enlarge)