Prediction:  this is the best animation you’ll see this week!  SSEC is creating daily global composites of True-Color visible imagery.  (Previous Blog Post)  The animation below shows 1 image from each day between 6 March and 4 April 2019.  The animation is also available as an animated gif, or as a YouTube video.  Also, Tim Schmit has placed the animation within a container.

View only this post Read Less

Snow fell over the southeastern United States, principally North and South Carolina, late on 20 February/early on 21 February 2020. This blog post, one in a series, investigates how gridded NUCAPS thermal fields perform in analyzing the rain/snow line. The snow totals are shown above, an image that was taken from this website at the National Operational Hydrologic Remote Sensing Center (NOHRSC).

NOAA-20 overflew the Carolinas shortly after 0700 UTC on 21 February, and gridded values of 950-mb, 900-mb and 850-mb Temperatures are shown below. (Note how the 950-mb field intersects the ground at the western edge of the Piedmont).  The 0º C isotherm at 850 and 900 mb is close to the coast;  it is sub-freezing over most of the land at those levels.  The analysis from 950-mb shows cold air stretching southwestward from southeastern Virginia, and that region is also where the accumulating snow was focused.  This is an argument in favor of the temperature fields in NUCAPS giving useful information about the rain/snow line.

One of the gridded NUCAPS fields available in AWIPS via the Product Browser (there are many!) is the binary probability of a temperature occurring.  The 850-mb binary probability of 0º C is close to the coast, at 900-mb, just slightly inland.  The 950-mb values also suggest cold air is more likely over the region where snow fell.  There are also some embedded cold pockets at 950 mb over interior North/South Carolina.

Note that gridded NUCAPS fields include data from infrared retrievals, microwave-only retrievals, and from retrievals that do not converge. The gridding can mask behavior in the vertical profiles that might not necessarily engender confidence in a meteorological analyst. The plot below shows NUCAPS points (Green points are infrared retrievals that successfully converged, yellow points are microwave-only retrievals, and red points occur where the microwave-only and infrared retrievals failed to converge; this is typically where precipitation is falling) plotted on top of the 850-mb temperature analysis.  Note, however, that values do show up everywhere!  Users of the gridded data should keep in mind the quality of the data that goes into the analysis when they use it.  Two vertical soundings from which gridded data are derived are shown at bottom.  Users can decide if they would use those vertical soundings in isolation.

View only this post Read Less

GOES-17 (GOES-West) “Clean” Infrared Window (10.35 µm) images (above) showed the movement of numerous thunderstorms across American Samoa during the 16-18 February 2020 period. This deep convection was being forced by an active South Pacific Convergence Zone or “Monsoon Trough” (surface analysis) and the presence of Tropical Invest 96P (named TD07F by the Fiji Met Service / Nadi Tropical Cyclone Centre) northwest of Samoa. Due to outflow from a nearby thunderstorm, winds gusted to 60 knots at Pago Pago, American Samoa (NSTU) at 11 UTC on 17 February.

With an increasing probability of Invest 96P becoming better organized (aided by low values of deep-layer wind shear along with modest upper-level divergence), a GOES-17 Mesoscale Domain Sector was positioned over the Samoan Islands on 18 February — providing “Red” Visible (0.64 µm) and “Clean” Infrared Window images at 1-minute intervals (below). During this period, the coldest convective overshooting tops exhibited infrared brightness temperatures in the -80 to -85ºC range (which corresponded to the tropopause temperatures seen in Pago Pago rawinsonde data).

===== 20 February Update =====

Another tropical depression (Invest 97P/TD09F) developed along the active Monsoon Trough on 20 February (surface analyses), intensifying just south of American Samoa to become Tropical Cyclone Vicky (TC 17P) as of 18 UTC (JTWC advisory). Once again a GOES-17 Mesoscale Sector was positioned over the region — “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed the gradual organization of Vicky; the coldest cloud-top infrared brightness temperature of convective overshooting tops was -90ºC. Surface observations revealed a wind gust to 65 knots at Pago Pago, American Samoa just before 20 UTC.

GOES-17 Infrared Window (11.2 µm) images from the CIMSS Tropical Cyclones site (below) showed that Vicky was moving through an environment characterized by of low values of Deep Layer Wind Shear, a favorable factor for further intensification.

Hourly MIMIC Total Precipitable Water images during the 16-20 February period (below) displayed the northwest-to-southeast oriented band of elevated moisture along the South Pacific Convergence Zone (or Monsoon Trough). The Samoan Islands are centered near 14.3° S latitude, 170.1° W longitude.

View only this post Read Less

GOES-16 (GOES-East) Mid-level Water Vapor (6.9 µm) images (above) showed the circulations associated with a pair of Hurricane Force low (surface analyses) during the 13-15 February 2020 period. At the limb of the GOES-16 Full Disk view, plots of hourly surface wind revealed gusts in the 70-80 knots range at stations in Iceland — including Keflavik International Airport near Reykjavik and Akurnes along the southeast coast. One site north of Reykjavik recorded a wind gust of 138 knots.

Sequences of VIIRS Infrared Window (11.45 µm) and True Color RGB images from NOAA-20 and Suomi NPP during those same days as viewed using RealEarth are shown below.

EUMETSAT Meteosat-11 Water Vapor (6.25 µm) images during the 14-16 February period are shown below. Named “Storm Dennis” by the UK Met Office, the system brought high winds to much of Europe.

Additional information about this event is available on the Satellite Liaison Blog.

View only this post Read Less