Moist air over the tropical western Pacific Ocean

July 22nd, 2021 |
MIMIC Total Precipitable Water, 0000 UTC 21 July – 1200 UTC 22 July

Microwave estimates of total precipitable water over the western Pacific Ocean (available here) show a moist airmass — out of which Typhoon In-Fa (seen near Taiwan in the animation) emerged — over the western Pacific Ocean. (The circulation of Tropical cyclone Cempaka is also apparent near the Gulf of Tonkin) This rich moisture has led to very heavy rains and Flash Flood alerts on the island of Guam (at 13.4 N, 144.5 E). Are there any indications that a new tropical cyclone will emerge out of the moisture?

The toggle below shows Himawari-8 10.41 µm “Clean Window” infrared imagery (notice In-Fa in the northwest part of the image). A distinct trough is apparent in the scatterometery north of the Marianas islands (and north of 20 N latitude), with west-southwesterly surface winds bordered by east-southeasterlies to the north. Weaker winds are indicated south of Guam. (For a recent primer on Scatterometer winds, click here; ASCAT winds can be found online here)

ASCAT Scatterometry winds and Himawari-8 Band 13 infrared (10.41 µm)imagery, 1200 UTC on 22 July 2021

NOAA-20 overflew this region at 1600 UTC on 22 July. The imagery below shows Tropopause Heights as well as Total Precipitable water — along with Band 13 imagery (over a different location) at that time. NUCAPS estimates of TPW are in the 60-70 mm range (in agreement with the MIMIC animation above); Very high tropopauses are Equatorward of 20 N Latitude.

A ribbon of small wind shear exists, as shown in the 200-850 wind shear analysis below, taken from the CIMSS Tropical Website. Meteorologists continue to monitor this region of tropical activity.

200-850 mb wind shear, 1800 UTC on 22 July 2021, over the western Pacific Ocean.

Thunderstorms over the Chukchi Sea and Beaufort Sea north of Alaska

July 12th, 2021 |

Suomi NPP VIIRS Infrared Window (11.45 µm) and Visible (0.64 µm) images [click to play animation | MP4]

Suomi NPP VIIRS Infrared Window (11.45 µm) and Visible (0.64 µm) images [click to play animation | MP4]

A sequence of Suomi NPP VIIRS Infrared Window (11.45 µm) and Visible (0.64 µm) images (above) showed snapshots of thunderstorms over parts of the Chukchi Sea and the Beaufort Sea off the northern coast of Alaska on 12 July 2021. The coldest convective cloud-top infrared brightness temperatures were in the -30 to -40ºC range. Unusual aspects of these thunderstorms included their high latitude location over ice-covered waters — as far north as 75ºN latitude — and the large amount of cloud-to-surface lightning strikes that they produced.



These thunderstorms were not surface-based — instead, they were forced by an approaching cold front (surface analyses) which helped to release elevated instability within the 500-300 hPa layer (below).

Suomi NPP VIIRS Infrared Window (11.45 µm) images, with contours of NAM40 lapse rate within the 500-300 hPa layer [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) images, with contours of NAM40 lapse rate within the 500-300 hPa layer [click to enlarge]

Rawnsonde data from Utqiagvik (PABR) were not available (due to ongoing equipment malfunction at that site) — but a NUCAPS profile near the southernmost cluster of convection around 15 UTC (below) showed the layer of instability aloft.

NUCAPS profile near thunderstorms off the northern coast of Alaska [click to enlarge]

NUCAPS profile near thunderstorms off the northern coast of Alaska [click to enlarge]

Convective nowcasting over Wisconsin with NUCAPS

July 5th, 2021 |

Day Cloud Phase Distinction RGB, 1751 UTC on 5 July 2021 (Click to enlarge)

GOES-16 Day Cloud Phase Distinction at 1751 UTC, above, shows two cumulus fields over Wisconsin:    a linear cloud field oriented west-southwest-to-east-northeast over the southern part of the state, and a larger field of agitated cumulus over the northern half of the state, with isolated glaciated storms near the border of Wisconsin and the Upper Peninsula of Michigan.  Would you expect those cumulus fields to develop during the course of afternoon heating?  SPC had much of Wisconsin in a Marginal Risk of severe weather at 2000 UTC on 5 July (link; 1630 and 1300 UTC outlooks were the same), as shown below.

SPC Convective outlook, 2000 UTC on 5 July 2021 (Click to enlarge)


GOES-16 Day Cloud Phase Distinction RGB along with Sounding Availability points from NOAA-20 NUCAPS, 1849 UTC on 5 July 2021 (Click to enlarge)

A benefit of NUCAPS (NOAA-Unique Combined Atmospheric Processing System) profiles (click here for previous blog posts discussing NUCAPS) from NOAA-20 over the contiguous United States (CONUS) is timing: profiles occur between 1600 UTC on the east coast and 2100 UTC on the west coast and thereby sample the atmosphere before the development of diurnal convection. Such was the case over Wisconsin on 5 July 2021. The image above shows the GOES-16 Day Cloud Phase Distinction and the Sounding Availability points from NUCAPS (NOAA-20) at 1849 UTC. The NUCAPS profiles allow a forecaster an independent (independent of models such as NAM or HRRR; see for example, this screen-capture of a 6-h forecast of radar reflectivity from the 1800 UTC/5 July HRRR of convection showing some development over southern WI) estimate of atmospheric stability. How does this diagnosed stability agree with (or not) model forecasts?

700-900 mb NUCAPS relative humidity fields, below, show a drier atmosphere of over southern Wisconsin than over the northern half of the state. (NWS ITOs note: there are instructions in VLab to modify NUCAPS gridding so that the pieces shown in AWIPS are more contiguous than in this blogpost example!).  Lapse rates (also 700-900 mb), below, show weaker stability over northern Wisconsin.  The combination of weaker stability and more moisture might push a forecaster to diminish convective concerns over parts of southern Wisconsin, and maintain those concerns over the northern half of the state. (GOES-16 Total Precipitable Water fields at 1851 UTC — link — show two axes of moisture over Wisconsin: one with the southern area of cumulus development, and one over central Wisconsin)

NUCAPS-derived estimates of 900-700 mb relative humidity, 1901-1912 UTC on 5 July 2021 (Click to enlarge)

NUCAPS-derived estimates of 900-700 mb Lapse Rates 1901-1912 UTC on 5 July 2021 (Click to enlarge)


Convection did not occur with the southern line of cumulus. See the animation below.

GOES-16 Day Cloud Phase Distinction RGB, 1751 UTC 5 July – 0031 UTC 6 July 2021 (click to enlarge)

Displaying all NUCAPS profiles from a single granule

July 2nd, 2021 |

NOAA-20 NUCAPS Profiles over the USA Great Plains, 0845 UTC on 2 July 2021 (Click to enlarge)

As noted here, CIMSS scientist Tim Wagner has created a short python script to read NUCAPS files generated by Community Satellite Processing Package CSPP software and Direct Broadcast (DB) data at UW-Madison CIMSS. The script relies upon several python packages: netCDF4 (version 1.5.7), matplotlib (version 3.4.2), numpy (version 1.21.0) and sharppy. DB NUCAPS files are available from https://ftp.ssec.wisc.edu/pub/eosdb/j01/crisfsr/yyyy_mm_dd_jday_hhmm/edr/ ; Files have names like this:  NUCAPS-EDR_v2r0_j01_s202107020845119_e202107020845417_c202107020928000.nc (similar to the naming convention in NOAA CLASS); the filename above contains one data granule from 08:45:11.9 to 08:45:41.7 on 2 July 2021;  this orbital plot (from here) suggests that data is over the Great Plains of the United States.

The output from the python script is all the NUCAPS profiles from the granule.  There are 30 NUCAPS profiles for each scan line, and 4 scan lines per granule. The animation at top shows the soundings along with a mapping showing their location.

This retrieval of NUCAPS profiles occurred on a quiet weather day: the NUCAPS plot of sounding availability (here) showed mostly ‘green’ points (vs. yellow or red), signifying convergence in the infrared retrieval.  The image below compares the NUCAPS sounding in AWIPS (left) with the one processed via CSPP.  There is good agreement.

NOAA-20 NUCAPS Plot from AWIPS (left) and from CSPP (right) at 0845 UTC on 2 July 2021 for a point near the Nebraska/South Dakota/Wyoming border (Click to enlarge)[/caption