The addition of a 2nd satellite (MetopC) producing NUCAPS profiles means that places such as Guam have twice as much Satellite information over the otherwise data-sparse western Pacific Ocean. The three-panel above shows the 1200 UTC sounding at Guam (on the left) with a nearly coincident 1208 UTC NUCAPS profile from NOAA-20 data in the middle, and a 1516 UTC MetopC NUCAPS profile on the right. It’s a lot easier to use these satellite soundings to infer how things are changing because of the increased number of soundings available. The toggle below compares the two NUCAPS profiles.

The Sounding Availability Plot from AWIPS, below, shows the distribution of points from the NOAA-20 and MetopC overpasses centered on the island of Guam. The points chosen above were the closest ones to the island of Guam.

Gridded NUCAPS fields are also created in AWIPS from these vertical profiles. Those fields allow a user to easily pick out gradients and thresholds.

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GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed 2 swaths of fresh snow cover across central/eastern Iowa, far northern Illinois and far southern Wisconsin on 23 March 2024 — which were produced  by consecutive systems on 21 March and 22 March (below). Total snowfall accumulations contributing to the 22 March southern snow swath included 8.0″ in eastern Iowa and 9.3″ in northern Illinois (NWS Quad Cities | NWS Chicago).

As daytime air temperatures warmed as a result of abundant incoming solar radiation, the zone of lesser snow depth (along the Wisconsin/Illinois border) between the 2 primary swaths of deeper snow cover revealed their northern and southern boundaries. The sharp southern boundary of the Illinois snow cover was particularly notable.

The GOES-16 Land Surface Temperature (LST) derived product at 1201 UTC (above) revealed several pockets of LST values as cold as +5ºF (darker shades of purple) within the swath of snow cover across Iowa and northern Illinois. The coldest minimum shelter air temperature reported that morning was +9ºF at Webster City, Iowa (KEBS), which was located within one of the darker purple pockets of coldest LST.

A toggle between the GOES-16 Land Surface Temperature derived product at 1201 UTC and a Visible image at 1331 UTC (below) demonstrated how the LST product could be useful for identifying areas where snow depth was likely the greatest (especially in areas having sparse observations) — with deeper snow cover exhibiting a colder LST value.

A comparison of GOES-16 Visible and Land Surface Temperature at 1301 UTC (above) showed that shortly after sunrise the METAR air temperatures were generally several degrees F colder over the deeper snow cover (and colder LSTs), as would be expected — but air temperatures were several degrees warmer than LST values. 5 hours later at 1801 UTC (below) the air temperatures lagged the rate of warming seen in LST (often by about 20-25ºF), especially to the south of snow cover over bare ground in Illinois.

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It bears mentioning that some lightning activity was seen during the 22 March snowfall event, with two sites — Cedar Rapids, Iowa (KCID) and Savanna, Illinois (KSFY) — briefly reporting thundersnow. Toggles between GOES-16 Water Vapor (6.9 µm) images + GLM Flash Extent Density on 22 March and Visible images on 23 March (below) indicated that the lightning occurred near the southern edge of the resulting swath of heavy snow across Iowa and Illinois.

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The animation above shows true-color imagery from the CSPP Geosphere site (direct link to animation). Of particular interest is the cloud band that forms along the western shore of Lake Michigan, especially near Chicago, and north of Milwaukee. The toggle below of the True Color imagery and Cloud Top Height suggests the cloud tops are at or above 700 mb (see this 1951 UTC image of Cloud Top Height), perhaps too high to be affected by the Lake Michigan. A curious feature (at least to me) of this animation is that the cloud band does not appear underneath the high clouds over southeast Wisconsin. Does that mean that solar forcing plays some role in this band’s development?

This event was brought to our attention by Gino Izzi at WFO LOT (i.e., Chicago) via this email that concludes:

visible imagery starting just before 18z this standing wave looking mid level cloudiness formed on the southwestern shores of Lake Michigan. Eventually some subtle waves form just a hair downstream over the lake and the standing wave seems to propagate upwind just a bit. These wave clouds appear to be around 10kft (~700mb) and looking at ACARS soundings this is at the top of a deep isothermal layer based at around 850mb. The strength of the inversion around 850mb should preclude any lake or marine influence from affecting cloudiness at 10kft. Any idea why these standing waves are there and apparently connected to the western shores of Lake Michigan (even up into central WI) when thermodynamically the lake shouldn\'t be influencing cloudiness that high up.

He followed up the email with NAM-12 output, below, showing a pretty good simulation of the rising/sinking motion couplet that might accompany such a band of clouds. In addition, this ACARS sounding from a plane landing at O’Hare, approaching from the southwest, shows stable air below 700 mb

Mid-level water vapor infrared (Band 9, 6.95 µm) imagery below, from Scott Bachmeier, CIMSS, suggests cooler cloud tops along the Lake Michigan shoreline, but also warming upstream of that, suggesting, perhaps that downward motion is occurring immediately upwind of the cloud band. (Note also how a break in the cooler brightness temperatures develops over southeast Wisconsin).

West-to-east oriented cross sections of RAP40 model Omega and Winds along Baseline A-A’ (below) showed a fairly deep column of elevated subsidence (darker shades of blue to violet) just inland over southern Wisconsin, which roughly corresponded to the band of subsidence (warmer/dryer air, darker shades of blue) seen in GOES-16 Water Vapor imagery.

 

Relocating Baseline A-A’ farther south across the Chicago area, note the colder signature of the cloud band (brighter shades of white) seen just inland on the 2101 UTC Water Vapor image (above), along with a signature of subsidence (darker shades of blue) immediately to the west — the 2100 UTC RAP40 Omega field (below) depicted an elevated couplet of downward (blue) / upward (green) motion located over those two Water Vapor features.

A GOES-16 Day Cloud Type RGB image at 1901 UTC (below) included cursor sampling of the Cloud Top Phase, Cloud Top Pressure and Cloud Top Height derived products along the cloud band (near Baseline A-A’). An animation of Day Cloud Type RGB imagery is available here.

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This write-up concludes with more questions than answers. The exact answer why the standing wave develops is not yet clear.

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The incorporation of MetopC NUCAPS files into AWIPS also means that MetopC Gridded NUCAPS fields are available for forecasters to help diagnose the state of the atmosphere. The toggle above shows two swaths of data, one from MetopC over China, and one from NOAA-20 over the western Pacific. The imagery also includes estimates of the 850-500 mb lapse rates in two regions (that I accessed through AWIPS’ Product Browser). Those are viewed a bit more closely below.

The time of the MetopC and NOAA-20 overpasses was near 0140 UTC on 19 March. Himawari-9 Band 13 (Clean Window infrared, 10.4 µm) and Air Mass RGB imagery (taken from Real Earth) show evidence of a polar front over China. Much of the West Pacific is in a tropical airmass.

MetopC Gridded NUCAPS fields, below, show the very cold (ca. -40^oC) 500-mb temperatures and steep lapse rates associated with the upper level front over China.

At about the same time, NOAA-20 saw very steep lapse rates each of Japan, but relatively warmer 500-mb temperatures (i.e., the lower levels were likely warmer).

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Use gridded NUCAPS fields to determine what’s going on in the troposphere in regions where other sources of data are scarce, and also over data-rich regions where more thermodynamic information will be useful.

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