This is the first in a series of posts on the 2023 version of PHSnMWnABI modeling. CIMSS this year will again be supplying output to the Hazardous Weather Testbed (HWT, from late May through mid-June 2023) from a modeling system that includes Polar Hyperspectral Soundings (Infrared and Microwave) that are fused with ABI data (refer to this paper or this one on Data Fusion). Blog Posts on the efficacy of this modeling system from last year’s HWT can be viewed here. Model run output is available at this website where you will see a calendar. Choose the day to view. Consider the 500-mb analysis shown below, at 1700 UTC from the 1200 UTC run on 17 March, when a slight risk of severe weather over the central Gulf Coast was forecast by the Storm Prediction Center. The strongest convection stretched southwest to northeast across extreme southeastern Louisiana into southwestern Alabama — the forecast convection has not yet reached Mobile. A second line of showers lingers over southeast Texas.

Radar observations from 1658 UTC (from this site) are shown below. There are similarities between the forecast above and reality below. Convection hasn’t reached Mobile; an area of lingering showers persists over southeast Texas. The leading edge of the storms is over greater New Orleans in southeastern Louisiana.

How did other convective-allowing models do with this event? The 4-panel below shows four different forecasts intialized, as above, at 1200 UTC and valid at 1700 UTC, 5 hours later (Imagery taken from the excellent TropicalTidbits website)

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When clear skies are present (at night!), the Nighttime Microphysics RGB provides little information about the overlying atmosphere. You might see nice Sea Surface Temperature gradients, as in the image below from the CSPP Geosphere site; the North Wall of the Gulf Stream is readily apparent to the east of North Carolina and Virginia.

Can you identify gradients in moisture, or in stability, in the still image above? How about in the animation below from the CONUS (PACUS) sector of GOES-18? This is a big challenge, as knowledge of moisture and stability is important for situational awareness. GOES-R Level 2 products can be added to the animation to better define the thermodynamics of the atmosphere.

Add (clear sky only) Total Precipitable Water (or K Index), two level 2 derived products, underneath the RGB above, as in the animations below. Despite cloudiness, the longitudinally-constrained ribbon of relatively moist air (about 1.5″ in its center versus 1.2-1.3 to the north and south) approaching the central Mexican coast is apparent. Instability, however, shows a wider distribution. In both cases, the satellite is giving more information than can be inferred from just the RGB. It does take practice, however, to separate the colors of the RGB from the colors of the color enhancements used in the TPW or K Index fields.

The Level 2 Moisture distribution, above, is consistent with microwave estimates of moisture from the MIMIC Total Precipitable Water site, below.

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) included an overlay of GLM Flash Extent Density and surface fronts — which showed severe thunderstorms that developed across southern Oklahoma (along and ahead of a cold front) and North Texas (ahead of a dryline) during the afternoon and evening hours on 16 March 2023.

1-minute GOES-16 Visible images (above) included time-matched (+/- 3 minutes) plots of SPC Storm Reports — which included a few tornadoes in Texas, hail as large as 2.40 inches in diameter in Oklahoma and 3.00 inches in Texas, and wind gusts as high as 65 knots in Oklahoma.

The corresponding 1-minute GOES-16 “Clean” Infrared Window (10.3 µm) images with plots of time-matched SPC Storm Reports (below) indicated that some of the thunderstorm overshooting tops exhibited infrared brightness temperatures in the -70 to -73ºC range (lighter gray pixels embedded within darker black regions).

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Sentinel-1A overflew the Hawai’ian islands shortly before sunrise on 15 March and the derived winds from this descending pass are shown above (they are also available here, through this website). Southwesterly flow and the topography of Oahu has excited gravity waves that are observable downstream from the island in the SAR analysis. GOES-18 Band 13 (“Clean window”, 10.3 µm) imagery, below (that includes the Sentinel-1A SAR winds), also shows suggestions of mostly stationary clouds oriented parallel to the wind features. (This toggle showing 1624 UTC SAR winds and brightened visible imagery and 1646 UTC shows clouds aligned with the wind features as well).

Advanced Scatterometer (ASCAT) winds from the manati site, below, show the southwesterly winds to the northeast of Oahu from both ascending passes between 0700 and 0800 UTC, and from descending passes between 1900 an 2100 UTC.

Trapping the energy in the lower part of the troposphere requires the presence of an inversion. SkewT/LogP charts from Lihue to the west of Oahu, and from Hilo to the east (from the University of Wyoming Sounding Site) both show low-level stable air.

SAR data shows winds of 30 knots just north of Maui above (red in the enhancement). Should you believe those wind speeds? Sometimes (not today, but sometimes) reflection off ice within the clouds results in computed wind speeds that are too high. This typically occurs when feathery structures appear in the Normalized Radar Cross Section fields, shown below. The absence of such structures north of Maui lends credence to the computed wind speed.

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The waves also appeared in Water Vapor imagery, most prominently in the low-level (Band 10, 7.34 µm) imagery shown below.

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The conclusion from these images: the perturbation induced by the topography on Oahu affects the atmosphere from the sea surface all the way up into the upper troposphere!

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