Turbulence Probability and moisture with a strong jet

November 30th, 2021 |
GOES-17 Air Mass RGB, 2001 UTC on 30 November, along with Derived Motion Wind plots from 250-350 mb (red) , 350-450 mb (yellow), and 450-600 mb (green) (Click to enlarge)

The GOES-17 Air Mass RGB, above, shows a distinct jet in the northwestern quadrant of the image. Derived Motion winds are as strong as 170 knots between 250-350 mb (they’re almost as strong from 350-450 mb!) In contrast, winds from 450-600 mb are closer to 70 knots just to the northwest of that upper-level jet. As you might expect, Turbulence Probability fields have a maximum along that very strong jet, as shown below. High Probabilities of turbulence also exist northeast of Hawaii (in the lower left corner of the image), and near the upper-level low at 33 N, 134 W. Turbulence Probablities are derived from GOES-17 infrared data and from GFS estimates of upper level stability. (Training on this product is available here under ‘Machine-Learning for Turbulence Detection by Satellite’).

GOES-17 Air Mass RGB and Turbulence Probability fields, 2001 UTC on 30 November 2021 (Click to enlarge)

In addition to their availability in AWIPS, as shown above (via an LDM feed from CIMSS), Turbulence Probabilities are also available on line at https://cimss.ssec.wisc.edu/turbulence. Values from 2000 UTC are shown below in the GOES-17 ‘Gulf of Alaska’ and ‘Vancouver’ domains.

Probabilty of Moderate or Greater (MOG) turbulence over the Gulf of Alaska, and over regions just to the south of the Gulf of Alaska, 2000 UTC on 29 November 2021 (Click to enlarge)

Turbulence probability fields from 2120 UTC, below, show that most of the Pilot Reports of turbulence align with the axis of higher probabilities. But not all of them: Severe turbulence (denoted in red) is noted near Oahu in a region of small (but not zero!) probability.

The strong jet obvious in the Air Mass RGB is associated with strong transport of moisture towards the Pacific Northwest. MIMIC Total Precipitable Water (TPW) fields, below, show abundant moisture traveling across most of the Pacific. OSPO’s TPW Percent of Normal fields show values exceeding 200% in this moist airstream (image from 1500 UTC on 30 November).

MIMIC Total Precipitable Water (TPW) fields at 0600 UTC on 30 November 2021 (Click to enlarge)

Tropical Storm Nyatoh in the Philippine Sea

November 30th, 2021 |

A tropical depression in the Philippine Sea has developed into Tropical Storm ‘Nyatoh’. The system is currently moving northwestward. Once it enters the Philippine Area of Responsibility (PAR), it will likely exit the area within 24 hours. Forecasters have predicted the storm will strengthen quickly, but its track will not pass over the Philippine islands.  A Tropical Cyclone Advisory has already been issued by the NWS office in Guam.

The Himawari-8 satellite houses the Advanced Himawari Imager (AHI) that provides full disk geostationary data at a high temporal resolution, similar to the GOES-16/17 ABI. AHI’s domain is perfect for monitoring storms such as Nyatoh.

A composite of AHI true color and infrared imagery is shown, with the SSEC IR rain rate superimposed on top. Imagery is shown from 11-29-2021 at 22UTC to 11-30-2021 at 18UTC using RealEarth, a free data visualization web tool.
Tropical storm Nyatoh is currently moving northwestward but may change to move northeastward by December 2.

Standing waves to the lee of the Hawaiian Islands

November 29th, 2021 |

GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images, with pilot reports of turbulence plotted in cyan [click to play animation | MP4]

As a compact but anomalously-deep middle/upper-tropospheric low approached Hawai’i on 29 November 2021, GOES-17 (GOES-West) Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) showed complex lee wave structures southwest of the island chain. There were a few pilot reports of moderate turbulence in the general vicinity of these waves. 

Even though 250 hPa wind speeds along the western side of the upper-level low were relatively light (30-60 knots), those north-northeasterly upper-tropospheric wind speeds were higher than normal for Hawai’i during the end of November. A Turbulence Probability product (below) indicated that the risk for Moderate or Greater (MOG) turbulence was generally low (less than 50%), and focused along the dry slot near the axis of the 250 hPa jet streak. Note that the Turbulence Probability began to decrease later in the period, as those 250 hPa jet streak winds began to relax over the area. 

GOES-17 Mid-level (6.9 µm) Water Vapor images, with an overlay of Turbulence Probability after 1300 UTC [click to play animated GIF | MP4]

Training for this Turbulence Probability product is available here and here.

Strong gap flow into the Gulf of Tehuantepec

November 26th, 2021 |
GOES-16 True Color imagery, 1330 – 1520 UTC on 26 November 2021

GOES-16 True-Color imagery from the CSPP Geosphere site (link showing the data above) on 26 November, above, show features associated with strong flow through Chivela Pass in southern Mexico, gap winds often called Tehuano winds or Tehuantepecers. Strong descent associated with these events can often limit the presence of clouds that can be used as tracers. However, scatterometry (from this website) will show surface winds, and an MetopB overpass shortly after the end of the animation above, below, shows a core of strong winds over the ocean.

ASCAT Winds from Metop-B, 1532 UTC on 26 November 2021 (Click to enlarge)

The GOES-16 CONUS domain extends southward to the northern part of the Gulf of Tehuantepec (about 14.6 N Latitude). Visible imagery from 1516 UTC, below, is overlain with the Derived Motion Wind vectors (in the surface – 900 mb layer) at the same time. Strong northerly winds north of Chivela Pass are apparent, but the lack of clouds to track in the Gulf prevented the inference of winds there from the GOES-16 data.

GOES-16 Visible Imagery (Band 2, 0.64 µm) and Derived Motion Winds, surface-900 mb, 1516 UTC 26 November 2021 (Click to enlarge)

The strong winds are also associated with a local increase in Aerosol Optical Depth (AOD), as shown below.

GOES-16 Aerosol Optical Depth (AOD) at 1520 UTC on 26 November 2021 (click to enlarge)

Strong winds will cause significant mixing in the upper part of the ocean, which will result in cooling. Imagery from this website (shown below) shows cooling in the Gulf from previous events. Here is an animation from that website, courtesy Tim Schmit, NOAA/NESDIS/STAR

SST analysis valid at 24 November 2021 (Click to enlarge)


GOES-17 True Color RGB images [click to play animated GIF | MP4]

In GOES-17 True Color images created using Geo2Grid (above), enhanced forward scattering during the morning hours helped to highlight the offshore transport of airborne dust.

Other blog posts discussing Tehuano wind events can be found here.