Mesoscale Convective System in Argentina

February 14th, 2020 |

GOES-16

GOES-16 “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

GOES-16 (GOES-East) “Clean” Infrared Window (10.35 µm) images (above) showed a large Mesoscale Convective System (MCS) west of Resistencia (station identifier SARE) in far northern Argentina on 14 February 2020 — this MCS developed southeast of an area of low pressure that was situated well north of a slow-moving cold front (surface analyses). The coldest GOES-16 cloud-top infrared brightness temperature was -94.1ºC on the 0750 UTC image.

VIIRS Infrared Window (11.45 µm) images from NOAA-20 (at 0452 UTC) and Suomi NPP (at 0541 UTC) as viewed using RealEarth (below) revealed intricate patterns of cloud-top waves and radial banding.

VIIRS Infrared Window (11.45 µm) images from NOAA-20 (at 0452 UTC) and Suomi NPP (at 0541 UTC) [click to enlarge]

VIIRS Infrared Window (11.45 µm) images from NOAA-20 (at 0452 UTC) and Suomi NPP (at 0541 UTC) [click to enlarge]

Plots of available NOAA-20 NUCAPS sounding points are shown below. NUCAPS profiles immediately north and south of the MCS revealed a very moist and unstable atmosphere, with Total Precipitable Water values around 2.4 inches and Most Unstable air parcel Convective Available Potential Energy (CAPE) values of 4500-5200 J/kg. The red NUCAPS profile dots indicate points where both the infrared and microwave retrievals failed — these are located within the core of the MCS.

Plots of available NUCAPS sounding points at 0341 UTC [click to enlarge]

Plots of available NOAA-20 NUCAPS sounding points [click to enlarge]

NUCAPS profile north of the MCS [click to enlarge]

NOAA-20 NUCAPS profile just north of the MCS [click to enlarge]

NUCAPS profile south of the MCS [click to enlarge]

NOAA-20 NUCAPS profile just south of the MCS [click to enlarge]


Plots of rawinsonde data from Córdoba, Argentina (below) — located not far southwest of the MCS — indicated a tropopause temperature of -74.7ºC at an altitude of 16.4 km on 14 February at 12 UTC.

Plots of rawinsonde data from Córdoba, Argentina [click to enlarge]

Plots of rawinsonde data from Córdoba, Argentina [click to enlarge]

 

Bore-like feature over Lower Michigan

February 13th, 2020 |

GOES-16 Advanced Baseline Imager (ABI) “red” visible imagery (0.64 µm), 1435 – 1840 UTC on 13 February 2020 (Click to enlarge)

TJ Turnage, the Science and Operations Officer (SOO) at the National Weather Service forecast office in Grand Rapids, noted today the presence of smooth, curving bands over Lake Michigan. The animation above shows their development — and the smooth appearance of the bands (just offshore of Ottawa Co, and curving into Allegan Co) is in marked contrast to the north-south oriented lake-effect bands over central Lake Michigan. This falls into the “What the Heck is this?” Blog Category.

An hourly animation that includes surface conditions sheds little light. The bore-like feature seems to arise out of an interaction of the atmospheric flow with Big and Little Sable Points, and surface winds at Muskegon (just north of Ottawa Co) and Holland (in Allegan Co) change as the feature moves over — but no snow is observed at those stations during the bore passage.

GOES-16 Advanced Baseline Imager (ABI) “red” visible imagery (0.64 µm) and surface METARS hourly from 1300 – 2100 UTC on 13 February 2020 (Click to enlarge)

Radar imagery (from the College of Dupage) also shows little return associated with the bore-like features.  (Click to see images from 1720 and 1800 UTC, when the bands were on shore).

NEXRAD Composite Radar Imagery (Composite Reflectivity) centered on MI, 1655-1820 UTC on 13 february 2020 (Click to enlarge)

 

Water vapor imagery, below, suggests that the stable layer that is trapping the energy and causing the bore-like feature originated near Big and Little Sable Points, around 1600 UTC.  The enhancement also suggests the bore-like feature is higher than the tops of lake-effect bands in the middle of Lake Michigan.  (Click here for a rocking animation of the water vapor imagery;  the rocking allows for better tracking of the impulse back to the source near the Sables, its earliest hint is at 1610 UTC — vs. about 1635 UTC in visible imagery).

GOES-16 ABI Band 10 (7.34 µm, low-level water vapor) infrared imagery, 1520 to 2015 UTC, 13 February 2020 (Click to play animated gif)

GOES-16 ABI Band 2 (0.64 µm) visible imagery, 1520 to 2015 UTC, 13 February 2020 (Click to play animated gif)

Bore-like features require stable layers.  The Gaylord Michigan sounding at 1200 UTC — upstream from the region out of which the bore emerged — shows several inversion layers.  The weighting function for the sounding (from this site) shows peak contributions for 7.34 µm (indeed, from all water vapor channels) from above 500 mb.  The coldest brightness temperature in the bands is -28 º C;  based on the Gaylord sounding, that’s a pressure level near 560 mb.  These Bore-like features are not Lake-Effect snow bands, despite having the correct aspect ratio — their width and length both suggest Lake-effect bands, but their height suggests otherwise.

NOAA-20 overflew this region shortly after 1700 UTC, and a NUCAPS sounding is close to the Michigan shoreline, just east of Holland, where the cloud band is coming onshore. The sounding from NUCAPS at that point/time is below.  The very smooth sounding does bear a passing resemblance to the Gaylord Sounding, but the smoothness of the NUCAPS profile — sampling a volume of air that in this case is about as wide as a county, makes identification of sharp inversions difficult.

NOAA-20 NUCAPS Profile points over Lake Michigan and lower Michigan, ca. 1730 UTC on 13 February 2020 (Click to enlarge)

NUCAPS Profile of temperature and moisture, 17 UTC on 13 February 2020 (Click to enlarge)

Can you use gridded NUCAPS fields to diagnose the rain/snow line?

February 13th, 2020 |

900-mb Temperature fields (color-shaded; the 0ºC line is in black) derived from NOAA-20 NUCAPS profiles, 0624 UTC on 13 February, along with 0600 UTC METAR observations (Click to enlarge)

Gridded NUCAPS fields include a wide range of thermodynamic variables. The plot above shows the 900-mb temperature field. Is it possible to use this data to diagnose a rain/snow transition line?

Over southern New England, the relationship between 900-mb temperatures and surface precipitation observations seems robust: snow is restricted to most (but not all!) places where 900-mb temperatures are cooler than 0ºC. and rain falls where temperatures exceed 0ºC. Where terrain might be an influence in trapping cold air near the surface — the Catskills, for example, or the Alleghenies over New York and Pennsylvania, the relationship is not so straightforward. This data source warrants future investigations on its utility in these situations.

Ground blizzard in North Dakota and Minnesota

February 12th, 2020 |

GOES-16 Air Mass RGB images, with surface fronts plotted in cyan and NAM80 model 500 hPa geopotential height plotted in yellow [click to play animation | MP4]

GOES-16 Air Mass RGB images, with surface fronts plotted in cyan and NAM80 model 500 hPa geopotential height plotted in yellow [click to play animation | MP4]

GOES-16 (GOES-East) Air Mass RGB images (above) displayed the characteristic pale yellow hues associated with cold arctic air that was moving southward behind a deep area of low pressure centered over Hudson Bay and northern Quebec, Canada on 12 February 2020.

A sequence of GOES-16 “Red” Visible (0.64 µm), Near-Infrared “Snow/Ice” (1.61 µm) and Air Mass RGB images (below) revealed north-to-south oriented horizontal convective rolls that highlighted areas where blowing snow was creating ground blizzard conditions across the Red River Valley of North Dakota/Minnesota (the strongest winds were being channeled southward through the lower terrain of the RRV).  The surface visibility was reduced to near zero in rural areas — and in eastern North Dakota, Interstate 29 was closed from the Canadian border to the South Dakota border. Toward the end of the day, conditions slowly began to improve in the northern portion of the Red River Valley — from Grand Forks (KGFK) northward — as surface winds decreased, horizontal convective rolls dissipated, and visibility started to increase. More information on this event is available from NWS Grand Forks and the Satellite Liaison Blog.

GOES-16

GOES-16 “Red” Visible (0.64 µm), Near-Infrared “Snow/Ice” (1.61 µm) and Air Mass RGB images, with plots of surface reports [click to play animation | MP4]



Another feature of interest was the rapidly intensifying Hurricane Force low pressure system just south of the Canadian Maritime Provinces (surface analyses) — with a lowering tropopause along the western edge of the storm, a swath of the NOAA-20 NUCAPS Total Column Ozone product (below) showed a lobe of higher ozone extending southward behind the surface low (and along the axis of its 500 hPa trough). That region of higher ozone was also apparent the day before, on 11 February, as shown in this blog post.

NOAA-20 NUCAPS Total Column Ozone product [click to enlarge]

NOAA-20 NUCAPS Total Column Ozone product [click to enlarge]