5-minute GOES-16 (GOES-East) Day Cloud Phase Distinction RGB images with overlays of GLM Flash Extent Density, LightningCast Probability and Buoy/METAR reports (above) showed glaciating (brighter shades of green) and glaciated (pale shades of yellow) cloud bands streaming eastward and southeastward off Lake Ontario and Lake Erie on 08 October 2023. Some of these cloud bands were producing lake effect rainfall across parts of western New York and northwestern Pennsylvania.

The 2-km resolution GOES-16 CLAVR-x Cloud Top Height derived product (below) indicated that the maximum cloud top height of these lake effect rain bands was generally in the 25000-30000 ft range (lighter shade of green).

In addition to the rainfall, there were a few areas of GLM-detected lightning associated with these lake effect cloud bands: at 1826 UTC, 1831 UTC and 1951 UTC. LightningCast Probability values had been fairly high at times for several of these lake effect cloud bands throughout the day (particularly the dominant cloud band moving inland from far eastern Lake Ontario) — and had reached 55-75% about 30-50 minutes prior to the majority of the GLM observations of lightning.

Similar to another case, this particular event demonstrated that the LightningCast model does possess some skill in predicting lightning during the cool season.

View only this post Read Less

Tropical Storm Bolaven formed southeast of the Mariana Islands at 1200 UTC on 07 October 2023 (about 540 miles southeast of Guam, according to the initial advisory issued by JTWC). With sufficient illumination from the Moon (which was in the Waning Crescent phase, at 41% of Full), a nighttime Suomi-NPP VIIRS Day/Night Band (0.7 µm) image valid at 1625 UTC (above) showed Bolaven as it was centered about 200 miles northeast of Chukk International Airport (METAR identifier PTKK) on Weno Island.

JMA Himawari-9 AHI Infrared Window (11.2 µm) images from the CIMSS Tropical Cyclones site (below) showed that Bolaven was moving through an environment of low to moderate deep-layer wind shear — and deep convection was beginning to increase south of the storm center.

A Himawari-9 Infrared / Water Vapor Difference product (reference) (below) highlighted areas of deep convection where overshooting tops were likely penetrating the local tropopause (yellow to red to violet enhancement).

Bolaven was also traversing very warm warm water, where Sea Surface Temperature and Ocean Heat Content values were rather high (below).

View only this post Read Less

Tropical Storm Bolaven has formed in the western Pacific and is moving towards the Marianas Islands. Were there satellite products useful in monitoring the atmosphere prior to the storm’s development? One such useful product is the Advanced Scatterometer (ASCAT) that is on both MetopB and MetopC polar orbiters at this website (or this one). The stepped animation above, from late on 05 October through late on 07 October, shows 6 different MetopB/MetopC observations of the developing system. At around 2300 UTC on 5 October, a belt of strong westerlies between 2^oN and 6^oN Latitude is Equatorward of easterly winds closer to 10^oN. Twelve hours later, near 1100 UTC on 6 October, a cyclonic circulation is apparent near 9^oN, 156^oE, with winds approaching 25 knots away from the cyclonic center. By 2200 UTC on 7 October, a well-defined storm is shown near 153^oE with tropical-storm forced winds diagnosed by the ASCAT.

MIMIC Total Precipitable Water fields from this same time show a band of rich moisture in the same location of the storm’s formation. The observations of moisture in these fields are from microwave instruments on polar orbiters that sample the Equator occasionally. The movement of the fields is determined by GFS wind output (as described in mp4 / PowerPoint training) A slow increase in cyclonic motion in the moisture fields is apparent south of 10^oN latitude around 155^oE longitude.

Moisture and a cyclonic circulation can mean that a storm is present. For a tropical cyclone to develop and strengthen, low values of vertical wind shear are also required. A wind shear analysis from 0000 UTC on 3 October to 2100 UTC on 5 October, showing wind shear fields from the SSEC/CIMSS Tropical Weather website, below, shows a band of low shear values between the Equator and 10^oN Latitude between 150^oE Longitude and the Dateline. Low shear values, abundant moisture, and a cyclonic circulation all co-located over the warm waters of the tropical Pacific all suggest a storm might develop.

View only this post Read Less

Seasonably cool Fall-like temperatures overspread the western Great Lakes and northern Plains on 5 October. The animation above shows the Day Cloud Phase Distinction overlain with LightningCast probability from 1321-1721 UTC on 5 October (that is, 8:21-12:21 CDT). SPC on this day was anticipating general thunder over northern Minnesota. Given that, and the autumnal temperatures, as shown below (dewpoints in the 40s, temperature in the 50s) — do you think lightning occurred?

Of course, you should expect lightning to occur. The training data set that was used to create the LightningCast probabilities via Machine Learning includes data from all months. Day Cloud Phase Distinction RGB is showing glaciation, and LightningCast is highlighting regions where lightning subsequently occurs. Recall that the probabilities are for lightning (in the form of a GLM observation) to occur in the next 60 minutes.

---

LightningCast probabilities are available online here.

---

Looking ahead for the next 2 hours, GOES-16 Day Cloud Phase Distinction RGB images with overlays of GLM Flash Extent Density, LightningCast Probability and Local Storm Reports (above) revealed that some of the convection reached severe levels, producing wind gusts as high as 78 mph at Stannard Rock Lighthouse (identifier STDM4) in western Lake Superior at 1943 UTC (SPC Storm Reports) along with several reports of small (sub-severe) hail.

Given the relatively low GLM Flash Extent Density values associated with this cool-season convection, the default Color Table Min/Max values were changed to 0.5/5.0 (to help identify subtle lightning jumps that preceded some of the high wind reports).

View only this post Read Less