Cyclone Chapala approaches Yemen

November 2nd, 2015
METOP-B Imagery (0.63 µm Visible and 10.8 µm Infrared) over Chapala, ~0615 UTC on 2 November 2015

METOP-B Imagery (0.63 µm Visible and 10.8 µm Infrared) over Chapala, ~0615 UTC on 2 November 2015 (Click to enlarge)

Cyclone Chapala continued its unusual approach towards Yemen on the southwestern edge of the Arabian Peninsula. Early on 2 November, the storm has passed just north of the Island of Socotra and entered the Gulf of Aden. METOP-B overflew the storm at ~0615 UTC on 2 November; Visible and Infrared data, above, show a still-compact storm with an obvious eye ringed by cold cloud tops (the coldest brightness temperatures are near -75º C) tucked into the mouth of the Gulf of Aden. Wind shear in the region is very low and sea-surface temperatures are warm. The morphed microwave imagery, below (taken from this site), indicates that the eyewall brushed the island of Socotra as it passed (a comparison of Meteosat-7 Infrared and DMSP SSMIS microwave images around 15 UTC on 01 November can be seen here).

Morphed Microwave Imagery ending 1645 UTC 01 November 2015

Morphed Microwave Imagery ending 1645 UTC 01 November 2015 (Click to enlarge)

Subsequent microwave imagery, below, for the 24 hours ending 1200 UTC on 2 November (the image below overlaps the one above) show a decrease in the eyewall structure and intensity.

Morphed Microwave Imagery ending 1200 UTC 02 November 2015

Morphed Microwave Imagery ending 1200 UTC 02 November 2015 (Click to enlarge)

Satellite-based intensity estimates at around 0000 UTC on 2 November (link) suggest a central mean sea-level pressure around 940 mb with sustained winds near 120 knots. The 0000 UTC Meteosat-7 image is shown below.

Meteosat-7 Window Channel Infrared (11.5 µm) 0000 UTC, 2 November 2015

Meteosat-7 Window Channel Infrared (11.5 µm) 0000 UTC, 2 November 2015 (Click to enlarge)

Suomi NPP overflew the region shortly after 2100 UTC on 1 November, and the Day/Night Band imagery from VIIRS is shown below, toggled with the 11.45 µm Infrared imagery. The storm is centered just northwest of Socotra; mesovortices are evident within the eye, as are overshooting tops in the eyewall convection; the bright streak seen on the Day/Night Band image is a region of the western eyewall illuminated by intense lightning activity. Zoomed-out versions of the imagery are available here for Day/Night Band and here for 11.45 µm Infrared. (VIIRS Imagery courtesy William Straka, SSEC/CIMSS).

Suomi NPP VIIRS Day/Night Band Visible Image and 11.45 µm Infrared Image 2149 UTC, 2 November 2015

Suomi NPP VIIRS Day/Night Band Visible Image and 11.45 µm Infrared Image 2149 UTC, 2 November 2015 (Click to enlarge)

A comparison of Meteosat-7 Infrared and DMSP SSMIS Microwave images around 1530 UTC on 2 November, below, showed the northern edge of the eyewall very near to the coast of Yemen.

Meteosat-7 Infrared and DMSP SSMIS Microwave images {click to enlarge)

Meteosat-7 Infrared and DMSP SSMIS Microwave images (click to enlarge)

At landfall, below, as viewed by Suomi NPP’s VIIRS instrument and a timely overpass, the eye of the storm had filled. The change in storm structure prior to landfall was very apparent in this toggle of two METOP Infrared images, at 0558 and 1644 UTC on 2 November. However, Meteosat-7 Infrared images showed that there was a large convective burst that developed as Chapala made landfall. Chapala was the first tropical cyclone on record to make landfall in Yemen while still at hurricane intensity.

Suomi NPP VIIRS I05 (11.45 µm) Infrared Image, 2127 UTC on 2 November [click to enlarge]

Suomi NPP VIIRS I05 (11.45) Infrared Image, 2127 UTC on 2 November (click to enlarge)

A 6-day animation of the storm using VIIRS true-color imagery from RealEarth can be seen here. Cyclone Chapala is also discussed in this blog post.

===== 05 November Update =====

A 14-day animation of UK Met Office OSTIA Sea Surface Temperature, below, reveals the cold wake of upwelling water (yellow color enhancement) following the passage of Hurricane Chapala.

UK Met Office OSTIA Sea Surface Temperature analyses [click to enlarge]

UK Met Office OSTIA Sea Surface Temperature analyses [click to enlarge]

Strong Convection over the Upper Midwest

July 13th, 2015
MODIS 11 µm infrared imagery and GOES Sounder DPI Lifted Index, 0400 UTC (Click to enlarge)

MODIS 11 µm infrared imagery and GOES Sounder DPI Lifted Index, 0400 UTC 13 July 2015 (click to enlarge)

A strong mesoscale convective system (MCS) moving southeastward through the Upper Midwest from late 12 July 2015 into early morning 13 July caused numerous severe wind reports across Minnesota and Wisconsin. This MCS was forecast to drop southeastward and continue to produce severe weather during the day on 13 July 2015 (Storm Prediction Center outlook). The toggle above shows the 0420 UTC Terra MODIS 11.0 µm image and the 0400 UTC GOES-13 Sounder DPI Lifted Index product (which is available in realtime here). As the MCS moved over southern Wisconsin, the coldest cloud-top IR brightness temperature on the 0826 UTC MODIS 11.0 µm IR image was -85º C. The strong system continued to move southeastward as very unstable air as diagnosed by the Sounder fed into it (click here for 850-mb RAOB plots). The 0746 UTC Suomi NPP VIIRS 11.45 µm IR image, below, also toggled with a GOES-13 Sounder Lifted Index product, showed a similar story: very strong convection downwind of a source of strong instability. The GOES Sounder can also diagnose Convective Available Potential Energy (CAPE), with values from 5000-6000 J/kg seen over southern Minnesota and eastern Iowa.

Suomi NPP VIIRS 11.45 µm infrared imagery and GOES Sounder DPI Lifted Index, 0746/0800 UTC (Click to enlarge)

Suomi NPP VIIRS 11.45 µm infrared imagery and GOES Sounder DPI Lifted Index, 0746/0800 UTC 13 July 2015 (click to enlarge)

The Suomi NPP VIIRS Day/Night Band, below, which is a source of visible imagery at night, depicted signatures of the active lightning that accompanied this system: numerous along-scan bright streaks over southern Wisconsin were caused by lightning illuminating the cloud as the VIIRS instruments scanned the cloud top. This toggle showed a comparison of Day/Night Band and 11.45 µm Infrared imagery.

Suomi NPP VIIRS Day/Night Band 0.70 µm visible imagery 0746 UTC (Click to enlarge)

Suomi NPP VIIRS Day/Night Band 0.70 µm visible imagery 0746 UTC 13 July 2015 (click to enlarge)

A closer view comparing the 0746 UTC VIIRS IR and Day/Night Band images, below, includes overlays of METAR reports and both 15-minute and 1-hour cloud-to-ground lightning strikes. The coldest VIIRS cloud-top IR brightness temperature was -78º C.

Suomi NPP VIIRS 11.45 µm IR and 0.7 µm Day/Night Band images, with overlays of METAR surface reports and cloud-to-ground lightning strikes (click to enlarge)

Suomi NPP VIIRS 11.45 µm IR and 0.7 µm Day/Night Band images, with overlays of METAR surface reports and cloud-to-ground lightning strikes (click to enlarge)

At 0805 UTC, the coldest CLAVR-x POES AVHRR Cloud Top Temperature value was -81º C, with maximum Cloud Top Height values of 15 km along the southwestern portion of the MCS.

POES AVHRR Cloud Top Temperature and Cloud Top Height products at 0805 UTC (click to enlarge)

POES AVHRR Cloud Top Temperature and Cloud Top Height products at 0805 UTC (click to enlarge)

This image of Radar Composites of the main line of storms was produced by Greg Carbin of SPC and was posted on Facebook on 13 July 2015.

Typhoons Chan-Hom and Nangka in the same Suomi NPP VIIRS Overpass

July 8th, 2015
Suomi NPP Day/Night Band (0.70 µm) and Infrared Window Channel (11.45 µm) images at 1616 UTC 8 July 2015 (Click to animate)

Suomi NPP Day/Night Band (0.70 µm) and Infrared Window Channel (11.45 µm) images at 1616 UTC on 8 July 2015 (click to enlarge)

The toggle above shows Suomi NPP VIIRS 0.7 µm Day/Night Band and the 11.45 µm Infrared images (courtesy of William Straka, SSEC). It is unusual because two strong tropical cyclones (Category 2 Typhoon Chan-Hom on the left, and Category 4 Typhoon Nangka on the right) are captured in one satellite overpass.

The Day/Night Band (DNB) image shows little evidence of lightning (bright white streaks) with either storm; due to ample illumination from a Third Quarter Moon (at 54% of Full),  the DNB was able to provide a “visible image at night”. Both images show Nangka to be the stronger storm: the eye is more pronounced, and is more symmetric. More information on these storms is available here.

Severe thunderstorms in the Midwest

April 9th, 2015
GOES-13 0.63 µm visible images, with Cloud-Top Cooling Rate, Overshooting Tops Detection, and SPC storm reports (click to play animation)

GOES-13 0.63 µm visible images, with Cloud-Top Cooling Rate, Overshooting Tops Detection, and SPC storm reports (click to play animation)

A deepening area of low pressure (21 UTC surface analysis) was moving northeastward across the Midwest region of the US on 09 April 2015; GOES-13 0.63 µm visible images combined with the Cloud-Top Cooling Rate and Overshooting Tops Detection products (above; click image to play animation) showed a line of severe thunderstorms which quickly developed along the associated cold frontal boundary as it moved eastward across Iowa and Missouri during the afternoon hours. Cloud-Top Cooling Rates with some of the storms in Missouri were in excess of 50º C per 15 minutes (violet color enhancement) during their early stage of development (18:25 UTC image).

A comparison of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 18:51 UTC or 1:51 PM local time (below) showed that the line of thunderstorms was beginning to produce a number of cloud-to-ground lightning strikes.

Suomi NPP VIIRS 11.45 µm IR channel image and 0.64 µm visible channel image with cloud-to-ground lightning strikes

Suomi NPP VIIRS 11.45 µm IR channel image and 0.64 µm visible channel image with cloud-to-ground lightning strikes

Focusing our attention on eastern Iowa and northern Illinois — where there were widespread reports of large hail, damaging winds, and tornadoes (SPC storm reports) — the organization of large, discrete supercell thunderstorms can be seen on GOES-13 0.63 µm visible channel images (below; click image to play animation), which exhibited numerous overshooting tops.

GOES-13 0.63 µm visible channel images, with SPC storm reports (click to play animation)

GOES-13 0.63 µm visible channel images, with SPC storm reports (click to play animation)

The corresponding GOES-13 10.7 µm IR channel images (below; click image to play animation) showed that the coldest cloud-top IR brightness temperatures were -67º C (darker black enhancement).

GOES-13 10.7 µm IR images, with Overshooting Top Detection and SPC storm reports (click to play animation)

GOES-13 10.7 µm IR images, with Overshooting Top Detection and SPC storm reports (click to play animation)

The NOAA/CIMSS ProbSevere product (below; click image to play animation) gauges the likelihood of a storm first producing severe weather (of any kind) within the next 60 minutes. It combines information about the environment (Most Unstable CAPE, Environmental Shear) from the Rapid Refresh Model, information about the growing cloud (Vertical Growth Rate as a percentage of the troposphere per minute and Glaciation Rate, also as a percentage per minute), and Maximum Expected Hail Size (MESH) from the MRMS. In this event, the ProbSevere product performed well for the storm that spawned the EF-4 tornado, although due to the cloudiness of the satellite scene the ProbSevere model was unable to diagnose vertical growth rate and glaciation rate (which diminished the potential lead-time). Below is a chronological timeline of events for that storm:

2308 UTC: first ProbSevere > 50%
2310 UTC: first ProbSevere > 70%
2311 UTC: NWS Severe T-Storm Warning
2312 UTC: ProbSevere = 88%
2323 UTC: 1.00″ hail 2 SE Dixson (15 min lead-time for ProbSevere@50, 13 min for ProbSevere@70, 12 min for NWS Svr Warning)
2335 UTC: NWS Tornado Warning (ProbSevere = 94%)
2340 UTC: Tornado report 2 NE Franklin Grove

Radar reflectivity with NOAA/CIMSS ProbSevere model contours and NWS warning polygons (click to play animation)

Radar reflectivity with NOAA/CIMSS ProbSevere model contours and NWS warning polygons (click to play animation)

In spite of widespread cloudiness, the GOES-13 Sounder single-field-of-view Lifted Index (LI), Convective Available Potential Energy (CAPE), and Total Precipitable Water (TPW) derived product images (below) were able to portray that the air mass in the warm sector of the low ahead of the strong cold front was was both unstable — LI values of -4 to -8º C (yellow to red color enhancement) and CAPE values of 3000-4000 J/kg (yellow to red color enhancement) — and rich in moisture, with TPW values of 30-40 mm or 1.2 to 1.6 inches (yellow to red color enhancement).

GOES-13 Sounder Lifted Index derived product images (click to play animation)

GOES-13 Sounder Lifted Index derived product images (click to play animation)

GOES-13 Sounder Lifted CAPE derived product images (click to play animation)

GOES-13 Sounder CAPE derived product images (click to play animation)

GOES-13 Sounder Total Precipatable Water (TPW) derived product images (click to play animation)

GOES-13 Sounder Total Precipatable Water (TPW) derived product images (click to play animation)

On the following day (10 April), it was cloud-free as the Landsat-8 satellite passed over northern Illinois at 16:41 UTC or 11:41 AM local time — and the 30.2 mile long southwest-to-northeast oriented tornado damage path that produced EF-4 damage and was responsible for 2 fatalities and 22 injuries (NWS Chicago event summary) was evident on 15-meter resolution Band 8 0.59 µm panchromatic visible images viewed using the SSEC RealEarth web map server (below). An aerial survey of part of the tornado damage path can be seen here.

Landsat-8 0.59 µm panchromatic visible image of southwestern portion of tornado damage track (click to enlarge)

Landsat-8 0.59 µm panchromatic visible image of southwestern portion of tornado damage track (click to enlarge)

Landsat-8 0.59 µm panchromatic visible image of northeastern portion of tornado damage path (click to enlarge)

Landsat-8 0.59 µm panchromatic visible image of northeastern portion of tornado damage path (click to enlarge)

A Landsat-8 false-color image (using Bands 6/5/4 as Red/Green/Blue) is shown below. The 2 tornado-related fatalities occurred in Fairdale.

Landsat-8 false-color image (using Bands 6/5/4 as R/G/B)

Landsat-8 false-color image (using Bands 6/5/4 as R/G/B)

On a side note, in the cold (northwestern) sector of the low it was cold enough for the precipitation type to be snow — and up to 4 inches of snow fell in western Iowa. GOES-13 0.63 µm visible channel images (below; click image to play animation) showed the swath of snow cover as it rapidly melted during the daytime hours on 10 April.

GOES-13 0.63 µm visible channel images (click to play animation)

GOES-13 0.63 µm visible channel images (click to play animation)

In fact, the swath of snow cover across eastern Nebraska and western/northern Iowa was also evident on a Suomi NPP VIIRS Day/Night Band (DNB) image at 08:49 UTC or 3:39 AM local time (below), highlighting the “visible image at night” capability of the DNB (given ample illumination from the Moon).

Suomi NPP VIIRS 0.7 µm Day/Night Band image

Suomi NPP VIIRS 0.7 µm Day/Night Band image