NUCAPS profiles derived from CrIS and ATMS data on NOAA-20 provide model-independent estimates of atmospheric thermodynamics globally, including, for this case over the central Pacific Ocean, in regions otherwise bereft of data.  NUCAPS lapse rates show a minimum in stability in low-levels in between two cloud features; the region includes mostly ‘green’ NUCAPS retrieval points:  where infrared and microwave retrievals have both converged.  It is difficult in the case above to relate differences in cloud features to differences in the diagnosed stability.

Four minutes later (shown below), NOAA-20 was closer to the Pole on this ascending pass and the diagnosed stability does relate well to differences in cloud structures.  In particular, the change from lapse rates around 5 C/km northeast of Hawai’i to lapse rate closer to 2 or 3 C/km even farther northeast aligns with a boundary between cloud types.

The subsequent NOAA-20 pass was west of the main Hawai’ian Island chain.  Again, differences in lapse rates are related to cloud features in the visible imagery.  Stable air — with lapse rates between 3 and 4 C/km — overlies a region of very little cumuliform development.  A region of larger lapse rates over the eastern 1/3rd of the pass, just to the west of the Hawai’ian Islands is accompanied by cumulus development.  NUCAPS thermodynamic fields, even though they have limited resolution in the vertical (at most 10 layers in the enter tropopause), can give useful information on stability over the ocean that can help in the real-time diagnosis of the atmosphere.

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1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Clean” Infrared Window (10.35 µm) images (above) showed thunderstorms associated with the South Pacific Convergence Zone (SPCZ) on 21 February 2021. The 3 METAR stations plotted on the imagery are, from left to right, Hihifo Airport, Wallis and Fotuna (NLWW), Apia, Samoa (NSFA) and Pago Pago, American Samoa (NSTU).

In spite of their degraded quality due to GOES-17 ABI Loop Heat Pipe thermal issues (which reaches one of its peaks at the end February), the Infrared images were still helpful in confirming that the primary SPCZ axis was remaining just north of the Samoan islands — and since the NWS Pago Pago office lacks radar coverage, they highlighted the importance of satellite imagery in one of their forecast discussions:

The active South Pacific Convergence zone (SPCZ) is lingering over the Samoan 
island chain, as seen on latest GOES-17 mesoscale this afternoon.

We have a very difficult time with confirming the wind forecast by model data, 
as there are no observations available of the persistent convection brewing 
just off-shore the islands. However, the models coupled with satellite are 
our only tools.

===== 22 February Update =====

The Fiji Meteorological Service determined that Tropical Depression 10F formed along the SPCZ  around 00 UTC on 22 February (surface analysis). Shortly after that time, a convective burst developed just east of the disturbance center, which exhibited cloud-top infrared brightness temperatures as cold as -94.3ºC — which indicated a significant overshoot of the Equilibrium Level as analyzed on 00 UTC rawinsonde data from Pago Pago, American Samoa.

GOES-17 Infrared images with plots of upper-level satellite winds and contours of upper-level convergence (above) and plots of low-level satellite winds and contours of low-level convergence (below) from the CIMSS Tropical Cyclones site showed that the deep convection developing within the SPCZ was sustained by an environment of favorable kinematic fields. Tropical Depression 10F was also located within a narrow ribbon of relatively low deep-layer wind shear.

The MIMIC TPW product (below) highlighted the rich tropical moisture within the NW-SE oriented SPCZ.

A closer look at the MIMC TPW product over the Samoan islands at 16 UTC on 22 February is shown below. With such high tropical moisture in place across the region, thunderstorms were producing heavy rainfall and/or wind damage in some of the islands (local storm reports).

===== 23 February Update =====

GOES-17 “Red” Visible (0.64 µm) images (above) showed that as deep convection began to diminish, the low-level circulation center of TD 10F slowly became more exposed as the tropical disturbance weakened — prompting the Fiji Meteorological Service to discontinue classifying feature as a tropical depression as of 2100 UTC on 23 February (below).

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An uncommon somewhat clear day on 20 February 2021 allowed VIIRS on Suomi-NPP to provide a true-color image of all 5 Great Lakes. The true-color image above is shown in a toggle with GOES-16 “Snow-Ice” Band 5 near-infrared data (1.61 µm) that allows for discrimination between clouds made up of water droplets (bright white) and underlying snow/ice (darker grey).  Much of western Lake Superior shows ice:  highly reflective in the true color imagery and much darker in the snow/ice channel (but not quite as dark as open water).  Lake Superior has about 50% ice coverage (this figure, originally from this website).  Western Lake Michigan shows little ice coverage (except over Green Bay);  ice coverage on Michigan is less than 30%.   Lake Erie is the most ice-covered of the Lakes:  around 80% ice-covered.  Recent northwesterly winds have moved the pack ice away from the northern shore (except for the far western basin).

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) revealed the fracturing of land-fast ice in the far southern portion of Lake Michigan on 19 February 2021. Although the westerly wind speeds were not particularly strong — generally 15-20 knots over water, including Metop ASCAT winds early in the day — these winds in tandem with lake currents were enough to move some of this ice eastward.

Farther to the north over western Lake Superior, 5-minute CONUS sector GOES-16 Visible images (below) also showed a significant amount of ice motion during the day.

A 30-meter resolution Landsat-8 False Color RGB image viewed using RealEarth (below) provided a more detailed look at the ice structure over western Lake Superior at 1653 UTC. Ice and areas of vegetation-sparse snow cover (rivers, lakes and wildfire burn scars) appear as shades of cyan in the RGB image.

===== 20 February Update =====

On 20 February, another look at 1-minute GOES-16 Visible images over southern Lake Michigan (above) indicated that new ice leads were opening up within individual ice floes that had broken free a day earlier.

===== 21 February Update =====

On 21 February, GOES-16 Visible images (above) showed how southerly winds were shifting much the ice in Lake Erie to the north. However, the effects of lake currents on the ice motion were also evident. As mentioned in this blog post, ice coverage on Lake Erie was around 80%.

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