POES AVHRR 12.0 µm IR image + SPC storm reports + METAR surface reports

Severe thunderstorms developed during the afternoon hours over eastern Colorado on 06 June 2012, which were responsible for a number of tornadoes in addition to widespread large hail and damaging winds (SPC storm reports). An AWIPS image of 1-km resolution POES AVHRR 12.0 µm IR channel data (above) showed a very pronounced “enhanced-V” storm top signature, with many of the severe weather reports located near the vertex of the enhanced-V.

A comparison of 1-km resolution POES AVHRR Cloud Top Temperature (CTT), Cloud Top Height (CTH), and Cloud Type products is shown below. The CTT cold/warm thermal couplet associated with the enhanced-V signature was -74 C/-55 C; the CTH values for the majority of the cirrus canopy were 13 km (12 km within the “warm spot” region of the enhanced-V); and the Cloud Type for the majority of the cirrus canopy was Overshooting (violet color enhancement), with the “Thick Ice” classification (yellow enhancement) within the warm region of the enhanced-V.

POES AVHRR Cloud Top Temperature, Cloud Top Height, and Cloud Type products

A comparison of the 1-km resolution POES 12.0 µm IR image with the corresponding 4-km resolution GOES-15 10.7 µm IR image (below) demonstrated the advantage of improved spatial resolution for detecting the more subtle aspects of the enhanced-V feature. Also note that the enhanced-V feature is displaced to the north and east on the GOES-15 image, due to the problem of parallax associated with the large viewing angle from the GOES-West satellite.

GOES-15 10.7 µm IR + POES AVHRR 12.0 µm IR images

The GOES-15 satellite was placed into Super Rapid Scan Operations (SRSO) mode, providing images as frequently as every 1 minute (see the VISIT Meteorological Interpretation Blog).

View only this post Read Less

GOES-13 11-3.9 µm legacy "fog/stratus product" (click image to play animation)

AWIPS images of the 4-km resolution GOES-13 11-3.9 µm brightness temperature difference (BTD) or “legacy fog/stratus product” (above; click image to play animation) began to display a signal of increasing coverage of fog and/or stratus across parts of the Allegheny Plateau region of New York and Pennsylvania during the pre-dawn hours of 06 June 2012. Strong nocturnal radiational cooling — Bradford, Pennsylvania (station identifier KBFD)  dropped to an overnight low temperature of 37 F — was helping to promote the formation of valley fog.

A more quantitative alternative to the legacy  BTD “fog/stratus product” is a new GOES Instrument Flight Rules (IFR) Probability product, developed as part of ASPB/CIMSS participation in the GOES-R Proving Ground. Note that the legacy fog/stratus product cannot make the distinction between fog and elevated stratus features (such as those found northwest of Lake Ontario, and also in west central Pennsylvania) — but the IFR Probability product does accurately make this discrimination. A trend of increasing areal coverage and magnitude of IFR Probability was noted (below; click image to play animation), especially along the New York/Pennsylvania border region where locations across southern New York such as Wellville (station identifier KELZ), Elmira (station identifier KELM), and Binghamton (station identifier KBGM) had surface visibilities drop to 1/4 mile and cloud ceilings drop to 100-200 feet above ground level.

GOES-13 IFR Probability product (click image to play animation)

A comparison of 4-km resolution GOES-13 and the corresponding 1-km resolution POES AVHRR “fog/stratus product” images at 07:40 UTC or 3:40 AM local time (below) demonstrated the importance of improved spatial resolution for the detection of small-scale features such as valley fog.

POES AVHRR vs GOES-13 legacy BTD "fog/stratus product" images

Similarly, a comparison of 4-km resolution GOES-13 and the corresponding 375-meter resolution (projected onto a 1-km resolution AWIPS grid) “fog/stratus product” images just after 08:00 UTC or 4:00 AM local time (below) showed much greater detail associated with the narrow fingers of valley fog.

Suomi NPP VIIRS vs GOES-13 legacy BTD "fog/stratus product" images

In addition, comparing the Suomi NPP VIIRS “fog/stratus product” with the VIIRS 0.7 µm Day/Night Band (DNB) image at that same time (below) showed that the DNB channel could detect a few of the narrow fingers of valley fog in far southwestern Pennsylvania and far northern Maryland that were obscured by high cirrus clouds (black features) on the “fog/stratus product” image. During periods of strong illumination from moonlight (as was the case on 06 June), the DNB can serve as a form of night-time visible channel imagery.

Suomi NPP VIIRS legacy BTD "fog/stratus product" vs VIIRS Day/Night Band image

After sunrise, McIDAS images of GOES-13 0.63 µm visible channel data (below; click image to play animation) showed the widespread valley fog features across parts of New York and Pennsylvania, which subsequently dissipated with daytime heating and boundary layer mixing.

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

View only this post Read Less

Suomi NPP VIIRS 11.45 µm IR image + 0.64 µm visible channel image

A cluster of thunderstorms developed over the interior of Alaska during the afternoon hours on 04 June 2012, and moved westward across the region — one of the stronger storms produced half-inch size hail in the Fairbanks area. AWIPS images of 375-meter resolution (projected onto a 1-km resolution AWIPS grid) Suomi NPP VIIRS 11.45 µm IR and 0.64 µm visible channel images (above) showed these storms before they moved over Fairbanks (station identifier PAFA); the coldest cloud-top IR brightness temperatures were -64º C, and the larger storm actually exhibited an “enhanced-V” signature (with a cold/warm thermal couplet differrence of 11º C).

A Fairbanks National Weather Service Special Weather Statement mentioned that the tops of the thunderstorms were around 40,000 feet. That height, along with the minimum VIIRS IR brightness temperature of -64º C suggests that the highest thunderstorm tops were overshooting the tropopause that was seen on a plot of the 00 UTC Fairbanks rawinsonde data (below).

Fairbanks, Alaska rawinsonde data (00 UTC 05 June)

View only this post Read Less

GOES-13 10.7 µm IR images + 0.63 µm visible images (click image to play animation)

A large Mesoscale Convective System (MCS) developed over far northeastern Oklahoma during the pre-dawn hours on 04 June 2012, which eventually produced a Mesoscale Convective Vortex (MCV) that moved into northwestern Arkansas the following morning. AWIPS images of 4-km resolution GOES-13 10.7 µm IR images (at night) followed by 1-km resolution  GOES-13 0.63 µm visible channel images during the day (above) showed the large nocturnal canopy of cold clouds (with cloud-top IR brightness temperatures as cold as -76º C at 05:01 UTC) — then the dissipating convection revealed the cyclonic circulation of the MCV during the late morning hours. As the atmosphere destabilized with daytime heating, new thunderstorms were seen to develop in the vicinity of the MCV as it moved toward Little Rock, Arkansas (station identifier KLIT).

A comparison of a 1-km resolution MODIS 11.0 µm IR image with the corresponding 4-km resolution GOES-13 10.7 µm IR image at 08:15 UTC or 3:15 AM local time (below) demonstrated that finer-scale cloud top details (such as subtle anvil-top gravity waves) were apparent on the higher resolution MODIS image.  Note that the satellite features are displaced slightly to the northwest on the GOES-13 IR images — this is due to parallax error resulting from the large viewing angle from the GOES-East satellite.

MODIS 11.0 µm IR image + GOES-13 10.7 µm IR image

These anvil-top gravity waves were even more evident on a comparison of 1-km resolution Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm Day/Night Band (DNB) images at 08:42 UTC or 3:42 AM local time (below). A full moon provided excellent illumination of the thunderstorm cloud top, allowing an very good night-time view of the subtle overshooting top and gravity wave structures (just as they might be seen on a daytime visible image). In addition, note that the city lights of the Wichita, Kansas area could be seen through the thin veil of cloud top cirrus along the northwestern edge of the storm.

Suomi NPP VIIRS 11.45 µm IR channel + 0.7 µm Day/Night Band images

As the MCV was approaching the Little Rock area, the CIMSS Cloud Top Cooling Rate product detected CTC rates in excess of 20º C per 15 minutes, just as the thunderstorms began to produce their first cloud-to-ground lightning strike at 17:45 UTC (below). This cluster of thunderstorms was responsible for a few reports of hail and damaging winds as it continued to move southeastward across Arkansas during the afternoon hours (SPC storm reports).

GOES-13 0.63 µm visible images + Cloud Top Cooling Rate + Cloud-to-ground lightning strikes

===============================

GOES-13/GOES-15 Sounder DPI Total Precipitable Water (click image to play animation)

MCVs typically are sustained in regions of low shear and abundant moisture. A plot of 850-500 mb shear from the NAM for 1800 UTC on 4 June show very low values of vertical wind shear in place over Arkansas. GOES Sounder DPI Total Precipitable water (the loop above) shows that the MCV developed in an axis of enhanced moisture. The blended TPW product (a product that blends together GOES Sounder and GPS measurements of precipitable water) shows an axis of values at or above 100% of normal through the mid-south where the MCV formed.

A visible image loop (every half-hour) from June 4 2012 that shows the evolution of the system is below.

GOES-13 0.63 µm Visible Imagery (click image to play animation)

View only this post Read Less