GOES-16 (GOES-East) Red Visible (0.64 µm) images (above) revealed the presence of horizontal convective roll clouds — a signature often associated with blowing snow — across parts of North Dakota, Minnesota and Wisconsin on 04 December 2024. Strong northwesterly winds in the wake of an arctic cold front were gusting in excess of 40 knots at several locations (including a peak gust of 57 knots or 66 mph in northeastern North Dakota), with blowing snow restricting the surface visibility to near zero at times. These near-blizzard conditions prompted the issuance of several Snow Squall Warnings, with some of those warnings covering portions of Interstates 29 and 94 in North Dakota and Minnesota.

Day Snow/Fog RGB images from GOES-19 (Preliminary/Non-operational) — created using Geo2Grid — provided a more detailed view of the widespread horizontal convective rolls (below). Existing snow cover appeared as darker shades of red in the RGB imagery.

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Cold air over the Great Lakes (see the plot of 850-mb temperature from RAOB stations at 1200 UTC below; note the similarity in temperatures and wind speeds over the Great Lakes states) means Lake Effect Snow. The animation above (source) shows snow bands over western lower Michigan and also downwind of Lake St. Clair, and in a single band over Lake Erie. An interesting aspect to this animation (to your blogger, at least), is the distance before the radar detection of snow occurs is pretty large over Lake Michigan, but the band development is almost immediate over Lake St. Clair and just a bit slower over Lake Erie. In addition, lake-effect band development over Lake Ontario is a bit slower than over Erie. Why?

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Day Cloud Phase Distinction RGB Imagery from near Noon, below, shows that the bands over Lakes Erie and St. Clair are likely glaciating almost immediately (this is based on the color — yellowish/green — of the RGB in those bands) compared to non-glaciated clouds (cyan or reddish in the RGB) over western Michigan with the lake-effect there. The atmospheric motions one might infer from the cloud and radar motions is from Lake Michigan (where moisture is added to the lower troposphere) across southern Michigan. Once the air re-emerges over Lake Erie, the moisture added over Lake Michigan means an atmosphere more pre-conditioned to the development of clouds.

GOES-East Low-level water vapor infrared imagery, below, at 1200 UTC, shows little variability in that field. This suggests that moisture being added to the atmosphere is confined to the lowest part of the atmosphere, below what is detected by the 7.3 µm band. The weighting function for KDTX (that is, White Lake Michigan near Detroit), below, shows information at 7.3 µm is predominantly from the 600-700 mb (assuming clear skies, an admittedly dubious assumption). The GeoXO (the follow-on to the GOES-R series of satellites, scheduled to launch in the mid-2030s) satellite will detect radiation at 5.15 µm, a wavelength that allows moisture detection at even lower levels than bands on GOES-16/GOES-18; perhaps that channel will detect the moistening caused by Lake Michigan that allows Lake Effect Bands to develop more rapidly over downwind lakes, given a suitable trajectory.

For those (correctly!) wondering if lake surface temperatures might drive the difference in band development, consider the temperature analysis below for 28 November 2024 (source). Michigan and Erie temperatures are very similar.

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GOES-19 (Preliminary/Non-operational) Day Cloud Phase Distinction RGB images (above) — created using Geo2Grid — displayed supercooled “lake effect” clouds (shades of white) streaming southeast off Lake Sakakawea in northwestern North Dakota on 25 November 2024. A smaller cloud plume was also seen streaming southeast off Devils Lake in northeastern North Dakota. Existing snow cover appeared as shades of green in the RGB images, with bare ground appearing as shades of blue.

GOES-16 (GOES-East) Near-Infrared “Snow/Ice” (1.61 µm) images (below) included 15-minute plots of METAR surface reports — which showed brief periods of light snow at Hazen (KHZE) and Bismarck (KBIS). Snow cover appeared as darker shades of gray to black in the Snow/Ice imagery. Note the cold air — having temperatures in the single digits to teens F — that was flowing across the still-unfrozen reservoirs of the Missouri River (in addition to Devils Lake). Water surface temperatures on Lake Sakakawea were in the middle to upper 40s F.

Lake effect clouds near Devils Lake today, with even a few flurries underneath!#ndwx @NWSGrandForks pic.twitter.com/yymtTRqsIt

— Dillon Vogt (@DillonvWx) November 25, 2024

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GOES-West imagery centered over the Samoan Islands, shown above in an animation, shows a region of rich moisture surrounding those islands (purple in the enhancement, which suggests values or 2-2.2″), but the islands themselves are within a dry pocket (TPW values closer to 1.7″, orange/rust in the enhancement used). Total Precipitable Water derived from Microwave data, below (from the MIMIC website), shows similar values, including the local minimum over Samoa. A benefit with microwave observations of atmospheric moisture (compared to ABI) is the ability to detect values in the presence of clouds.

Pago Pago airport does have an upper-air station. However, hydrogen generation difficulties at that site in the past months have meant that balloon launches are limited, and one did not occur at 1200 UTC on 25 November. However, NOAA-20 overflew the region shortly thereafter and NUCAPS soundings can estimate the thermodynamic profile. The plot below shows where profiles are available; green points signify profiles for which the infrared retrieval converged to a solution, typically in regions of mostly clear skies (as might be inferred from the GOES-18 imagery above!)

The toggle below shows two NUCAPS profiles, one just west of Tutuila (at 14.2^oS, 171.5^oW) and one 6 points to the south (at 16.55^oS, 171.5^oW). Note the larger values of TPW in the more southerly sounding, consistent with what is discussed above. Otherwise, the profiles are quite similar.

Level 2 products also include clear-sky measures of instability, such as Lifted Index and Convective Available Potential Energy (CAPE). The Lifted Index field below shows pockets of stability (blue in the enhancement used) surrounded by minor instability (yellow in the enhancement) surrounding the Samoan Islands.

CAPE values (scaled from 0-400 J/kg) similarly show relatively weak regions of stability and instability surrounding the Samoan islands.

The TPW fields, and the Derived Stability Indices, do have similarities as might be expected. The toggles below compare TPW, LI an CAPE at 0300 and at 1300. Interestingly, the strong values of CAPE at the eastern edge of the domain at 0300 UTC seemingly have no echo in the other fields. In other regions (north of the Samoan Islands, for example), minima in CAPE and relative stability in Lifted Index occur where local minima in TPW exist. This case demonstrates how one stability index might not give the same information as another; make sure you have access to both!

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The (anti-clockwise) motion of the cloud features above suggests that an anticylone is present over the islands The animation below includes GOES-West derived motion wind vectors computed from Band 9 (mid-level water vapor, 6.95 µm) infrared images. The wind vectors are from near 350 mb, which height is determined by matching the Band 9 brightness temperature to GFS model temperatures.

Level 2 Products, especially in regions — like the South Pacific Ocean — where conventional data are lacking, can give a forecaster needed insight into how the atmosphere might evolve with time.

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