For the second time during its life cycle, Typhoon Rai reached Category 5 intensity (ADT | SATCON) east of Vietnam during the 18-19 December 2021 period. JMA Himawari-8 Infrared Window (10.3 µm) images (above) showed cloud-top infrared brightness temperatures of -90C and colder at times around the eye.

 VIIRS Infrared Window (11.45 µm) images from NOAA-20 and Suomi-NPP as viewed using RealEarth (below) provided a more detailed view of Rai around the time that it reached Category 5 intensity.

3 days earlier, Rai first reached reached Category 5 intensity at 0000 UTC on 16 December, shortly before making landfall in the Philippines; 2.5-minute Himawari-8 Infrared images (below) revealed a small-diameter “pinhole” eye. As Rai moved across the Philippines, it was responsible for hundreds of fatalities in addition to widespread flooding and power outages.

View only this post Read Less

Synthetic Aperture Radar (SAR) winds in select small domains are routinely available (with good latency, i.e., within 2 or 2-1/2 hours) at this website. Coverage over the Great Lakes typically occurs within an hour of 0000 UTC and 1200 UTC on each day. The image above (direct link) shows derived SAR winds (from the RCM2 satellite) over Lake Superior at 2348 UTC on 16 December 2021. Winds over Lake Superior are around 40 knots; weaker wind speeds are indicated in the lee of Isle Royale, the various Apostle Islands, Upper Michigan’s Keewenaw Peninsula, near Marquette Bay, and right offshore Minnesota. Fingers of stronger winds extend east-southeastward from just off the Minnesota shoreline. This small horizontal variability in the wind speeds is too small to be detected by other microwave detectors (such as ASCAT on Metop-B and Metop-C).

The toggle above shows the winds with a time-matched image of GOES-16 Band 7 (3.9 µm) data (created using Geo2Grid), stretched to enhance low-level clouds. The second toggle includes best-guess location-matched arrows of features in the SAR winds and the GOES-16 ABI brightness temperature. That figure is reproduced below with an AWIPS display of GOES-16 3.9 µm imagery at 2346 UTC (again with a stretched colortable to emphasize low-level temperature contrast).

GOES-16 satellite imagery over Lake Superior will have a parallax shift because the location is far from satellite nadir. Parallax shift is related to cloud-top heights, and derived Cloud-Top Heights (a Level 2 product) over the region show cloud tops between 3000 and 5000 feet near Minnesota, rising to about 7000 feet over Lake Superior in between Minnesota and the Keewenaw Peninsula. This parallax shift means that features will be displayed to the north and a bit to the west of their true location, displaced away from the GOES-16 sub-satellite point at 0^oN, 75.2^o W.

These images suggest that lake-effect clouds are regions of enhanced wind speeds. The inferred convective roll vortices present in the satellite imagery are also regions of enhanced convergence and upward moisture transport.

View only this post Read Less

A sequence of 1-minute Mesoscale Domain Sector GOES-16 (GOES-East) Dust RGB and Mid-level Water Vapor (6.9 µm) images (above) showed the development of dense plumes of blowing dust (whose source regions were primarily in southeast Colorado and the Oklahoma/Texas Panhandles) on 15 December 2021. These dust plumes were being lofted by strong winds along and behind a cold front — which was associated with a rapidly-intensifying midlatitude cyclone. This storm then caused a broad swath of severe weather (SPC Storm Reports) as it moved rapidly northeastward toward the Great Lakes. 

GOES-16 Mid-level Water Vapor images with and without contours of hourly RAP model PV1.5 pressure (below) identified a Potential Vorticity (PV) anomaly which tracked northeastward across the region, indicating that the “dynamic tropopause” descended to the 700-750 hPa pressure level — which helped to transfer the momentum of strong winds aloft toward the surface. The general appearance of the water vapor imagery was similar to that seen in other cases when a “sting jet” helped to transport momentum aloft to the surface where high winds were observed (a sting jet is often found near the hook-shaped “scorpion tail” portion of the water vapor signature). The downward transport of dry mid/upper tropospheric air was supported by a rapid decrease in surface dewpoint temperature, seen at at a number of sites where the dewpoint dropped to below 0ºF (for example, from west to east across Kansas at Johnson KS | Ulysses KS | Pratt KS). Note that the brightest shades of pink/magenta on the GOES-16 Dust RGB images were located behind the primary eastward-moving cold front, where stronger winds associated with the sting jet had descended to the surface.

A toggle between NOAA-20 NUCAPS-derived Tropopause Height, Total Column Ozone and Total Column Ozone Anomaly from the NASA SPoRT site (below) supported the presence of a PV anomaly over northwestern Kansas around that time, characterized by a low tropopause with anomalously-high total column ozone (2000 UTC GOES-16 Water Vapor image + PV1.5 pressure).

GOES-16 True Color RGB images created using Geo2Grid (above) highlighted the tan-colored blowing dust plumes (along with a couple of brighter-white wildfire smoke plumes) as they progessed northeastward across Kansas and Nebraska. A larger-scale view of GOES-16 Dust RGB images (below) showed that during the subsequent nighttime hours into the next morning, the brighter pink/magenta signature of blowing dust that became entrained into the circulation of the midlatitude cyclone could be followed as it eventually moved over parts of Minnesota, Wisconsin, Upper Michigan and Lake Superior — and eventually over far southern Ontario, Canada.  

It looks like some of the dust from Colorado and Kansas made it all the way to the Northland! The liquid from our rain guage was very cloudy this morning! #mnwx #wiwx #cowx #kswx https://t.co/2NxRvEkaV8 pic.twitter.com/1BuYc0Wn4O

— NWS Duluth (@NWSduluth) December 16, 2021

View only this post Read Less

NOAA-20 overflew the central United States twice in the afternoon of 15 December 2021 (NOAA-20 orbits that day shown here, from this website) as a potent weather system moved through. SPC‘s Convective Outlook showed a Moderate Risk of severe weather (link); There was widespread wind damage on this day (link). How could NUCAPS soundings (available in AWIPS as demonstrated here) on that day assist in understanding the state of the atmosphere? The toggle above shows where NUCAPS profiles were available. Blue boxes highlight profiles that are shown below. Note right away that the NOAA-20 orbits on the 15th allowed for multiple samplings of the atmosphere at the northern edge of the Moderate Risk. The soundings along the western edge of the ca. 1800 UTC NOAA-20 NUCAPS pass, below, show steep mid-level lapse rates, and MUCAPE values (as diagnosed by NSharp in AWIPS) increasing to the south.

GOES-16 data can also be used to diagnose instability, and the Level 2 Product (Derived Stability Index) Lifted Index at 1751 UTC is shown below. The Level 2 product also shows stability decreasing to the south in Iowa. Keep in mind that southerly surface winds at this time (as shown in this visible image with surface observations in a toggle with the Dust RGB and NUCAPS Sounding Availability) were very strong with this dynamic system: advection could be very large.

---

Select vertical profiles from the subsequent NUCAPS swath shortly before 2000 UTC are shown below.

Several profiles in the animation above deserve special mention. The first two comparisons, below, compare profiles from the two overpasses.

The sounding in southern Minnesota samples a region very close to a sounding location from 90 minutes earlier. The toggle below of sequential profiles shows a change in stability as diagnosed by NUCAPS. The mid-level lapse rate has steepened, and mid-level moisture has increased. Observations from sequential passes do not happen every day, but forecasters (north of about 41 N) can (and should!) take advantage of them, time permitting, when they do happen.

A similar comparison over southern Iowa is shown below, showing the ca. 1815 UTC profile first (the one with the highest diagnosed MUCAPE) toggled with two later adjacent profiles. Note how the mid-level lapse rates have destabilized in the later profiles

NUCAPS soundings that are in the moist air ahead of developing convection and within dry, dusty air behind the convective line at around 1953 UTC in Kansas are shown below. As with other soundings in the moist air, mid-level lapse rates show weak stability. The sounding closest to the developing convection shows abundant moisture in the lower troposphere. Soundings in the dusty air are very very dry : diagnosed total precipitable water is less than 0.3″. Visible imagery in the background image below shows the dusty air over western Kansas, it’s far more apparent in this toggle of visible imagery and the dust RGB at 1931 UTC!

NUCAPS profiles over Kansas in front of the developing convection, below, show very steep lapse rates in the mid-troposphere! (Among the largest values this blogger has seen!) This suggests explosive development is possible if convection develops.

---

Gridded values of NUCAPS temperature and moisture (and of values derived from those fields) are available at this website. In addition, those values will shortly be available in RealEarth. Gridded 850-500 mb Lapse Rates derived from the two sequential NOAA-20 NUCAPS profiles are shown below. Much of the central/southern Plains has very low mid-tropospheric stability.

NUCAPS profiles give timely and independent estimates of atmospheric temperature and moisture in the mid-afternoon over the central United States; thus they are frequently useful for estimating convective potential.

View only this post Read Less