Nighttime Microphysics RGB

Monitoring the Remnants of Ian from GOES-16

Posted by Kevin Thiel (CIWRO) on 10/03/2022
Posted in: G16-CH07_3.9_SWIR, G16-CH13_10.3_IR-Clean, Nighttime Microphysics RGB, SPC. Leave a comment

On Saturday October 1st the remnants of Hurricane Ian were moving northward through the Mid-Atlantic region, after making a second U.S. landfall the previous day in South Carolina. Overnight, the SPC was monitoring the final stages of Ian’s extra-tropical transition with a marginal threat for severe weather in the coastal North Carolina/Virginia region.

One forecaster on shift that night was monitoring the remnants from the perspective of GOES-16, and noted how various ABI products could be used to examine cloud layers and types in this dynamic environment.

CH7 shortwave and CH13/15 longwave IR shows mainly the cooler cloud tops associated with high-level clouds. Low-level clouds can be inferred by the warmer temps (CH7) or weaker grey features in CH13/15. However, the NtM [Nighttime Microphysics] RGB composite satellite data neatly contrasts colder, high-level clouds (western PA westward and in a warm conveyer belt over the Atlantic) from the lower but cool clouds (North Carolina into Virginia) and the very low, warm clouds (southeast Pennsylvania into New Jersey and Delaware). Though buoyancy is scant and severe is not expected in this area, the NtM RGB composite’s ability to contrast cloud types in this event demonstrates potential to identify important cloud features related to severe weather.

SPC Forecaster Comment

When overlaid with the RAP mesoanalysis field at 500 mb, the Channel-13 (Clean Longwave IR) and Channel-7 (Shortwave IR) bands from the ABI reveal the higher, cooler cloud tops north of the low into Pennsylvania. The warm conveyor belt over the Atlantic coast can be seen in the 500 mb RAP mesoanalysis with enhanced southerly winds east of low, and from the ABI infrared imagery with a lack of high clouds due to upper level subsidence.

Channel 13 (clean longwave IR) imagery of Ian’s remnants from the perspective of GOES-16. Overlaid with 500 mb RAP mesoanalysis data.
Channel 7(shortwave IR) imagery of Ian’s remnants from the perspective of GOES-16. Overlaid with 500 mb RAP mesoanalysis data.

While these bands individually can be used to point out these features, the forecaster notes that the Nighttime Microphysics RGB allows them to more readily identify and monitor these cloud features from the tropical cyclone remnants at night. This is driven by the RGB’s ability to combine information from multiple ABI bands (7, 13, and 15) to provide qualitative information for forecasters regarding cloud types and heights.

Nighttime Microphysics RGB imagery of Ian’s remnants from the perspective of GOES-16. Overlaid with 500 mb RAP mesoanalysis data.

Kevin Thiel, OU CIWRO

Forecasting on the Margins…Using ABI Imagery during Nighttime Mesoanalysis at the SPC

Posted by Kevin Thiel (CIWRO) on 09/08/2022
Posted in: Nighttime Microphysics RGB, SPC, Water Vapor Imagery. Leave a comment

During the early morning hours of September 7th, 2022, the SPC convective outlook issued at 1200 Z featured two upgraded areas from the previous outlook at 0500 Z (see image gallery below). Today we will focus on the upgrade from ‘Thunderstorm’ to ‘Marginal’ in southeast Texas and southwest Louisiana.

The question is..what caused the upgrade? The SPC Convective Outlook discussion from 0500 Z mentions thunderstorm activity in the area from a weak shortwave trough, but with little shear and poor lapse rates limiting thunderstorm severity potential. The Outlook from 1200 Z reveals that a mesoscale disturbance was moving into this area from the northeast, and modifying the mesoscale environment that would coincide with thunderstorms later in the day.

   …Southeast TX and southwest LA…

A minor mid-level impulse evident in water vapor imagery over the Ark-La-Tex should gradually move south-southwest into south TX by this evening. A pocket of relatively cooler mid-level temperatures and steeper lapse rates attendant to this impulse should support a plume of moderate to large MLCAPE of 1500-3000 J/kg. While deep-layer shear will be modest and generally offset west of the greater instability/buoyancy, isolated marginally severe hail and strong to localized severe wind gusts will be possible as scattered thunderstorms occur this afternoon.

SPC Day 1 Convective Outlook, 7 September 2022 (12Z)

Water vapory imagery shows the location of the mesoscale disturbance as it moves from southern Missouri into eastern Texas and western Louisiana, and begins to even initiate morning convection.

GOES-16 Upper Level Water Vapor Imagery (Channel 8) from 0300 Z to 1300 Z on 7 September 2022. Note the increased water vapor and cyclonic motion associated with the mid-level impulse identified in the 12Z SPC convective outlook discussion.

The SPC Mesoanalysis at 1400 Z reveals increased mid-level lapse rates and ML-CAPE moving southwest into the Marginal hazard area during the morning hours, driven by the mid-level impulse.

One potential failure mode in this scenario would be early morning cloud cover, which would keep the ML-CIN in place and limit thunderstorm development. High clouds from Hurricane Kay in the eastern Pacific are one potential source. In this scenario however, the SPC forecaster used the Nighttime Microphysics RGB to examine the locations of cloud layers before visible satellite imagery became available during the day. The following quote from the SPC forecaster on shift highlights this application.

Deep convection over the Ark-La-Tex. Patchy low clouds to the southwest of this into south-central TX beneath high-level cirrus loosely associated with TC Kay off southern Baja CA. Mainly cloud-free in between across southeast TX to southwest LA indicative of nearly full insolation this morning for the newly added MRGL in the 13Z outlook. Helpful to “see” before visible satellite imagery becomes available.

SPC Forecaster Comment
GOES-16 Nighttime Microphysics RGB product over central Texas from 0300 Z to 1300 Z on 7 September 2022. Note the initiating convection coinciding with the mesoscale disturbance, the cumulus clouds over central Texas, and the high clouds from Hurricane Kay in the eastern Pacific over southern Texas.

Kevin Thiel, OU CIWRO

Dense Fog in Ohio Viewed from the Nighttime Microphysics RGB

Posted by Kevin Thiel (CIWRO) on 04/22/2022
Posted in: Nighttime Microphysics RGB, RGB. Leave a comment

During the early morning hours of April 22nd, fog began to form across southern Ohio, West Virginia, and Pennsylvania. In anticipation of the fog, the NWS Weather Forecast Office in Wilmington OH issued a Dense Fog Advisory for a portion of their forecast area.

Latest guidance increases confidence in development of areas of dense fog late tonight. Based on this, have hoisted Dense Fog Advisory south of Interstate 71.

NWS ILN, AFD Issued at 0133 UTC (9:33 EDT)

Confirmation of the dense fog can be observed via satellite from the Nighttime Microphysics RGB starting around 0500 Z (1:00 AM EDT), with greater contributions from the Green Band (10.3 um – 3.9 um band difference) and minor contributions from the Blue Band (10.3 um band). The stationary, more faint, and highly localized appearance of the fog stands in contrast to the low level clouds in southwest Pennsylvania and central West Virginia, which often have a similar color due to similarities in their composition. Additionally the movement of cirrus and stratocumulus clouds into the area, from precipitation over Indiana, did obscure the extent of the fog in western Ohio by 1000 Z (6:00 AM EDT). This is one limitation of the product, as skies have to be fairly clear in order to properly identify fog.

Based on surface observations and imagery from the Nighttime Microphysics RGB, it was apparent by 0830 Z (4:30 AM EDT) that the dense fog was expanding north of Interstate 71. This confirms NWS Wilmington expanding the Dense Fog Advisory north into the Cincinnati and Dayton metro areas, prior to the increase of traffic during the morning rush. In this case the combination of surface observations and the Nighttime Microphysics RGB can provide confirmation of developing fog and its spread overnight for the Dense Fog Advisory. Using satellite RGBs in tandem with other observations can help maximize situational awareness, especially when satellite data cannot be relied on exclusively as shown in this example.

The fog is becoming dense in many locations across northern KY, southern Ohio, and southeast Indiana. Have expanded the dense fog advisory north to about I-70.

NWS ILN, AFD Issued at 0831 Z (4:31 AM EDT).

Kevin Thiel (OU CIWRO)

Thunderstorms Initiating Overnight in Kansas and Oklahoma

Posted by Kevin Thiel (CIWRO) on 04/13/2022
Posted in: G16-CH13_10.3_IR-Clean, Nighttime Microphysics RGB, RGB. Leave a comment

During the late evening hours on April 12th, 2022, convection initiated along a retreating dryline and advancing cold front in southern Nebraska and central Kansas. Initiation across the line can be observed from the Clean-IR band (Ch 13) from GOES-16 and the NEXRAD mosaic below. The near-uniform initiation of these thunderstorms along the dryline provided a unique example of how GOES imagery can be combined with radar data to monitor rapid thunderstorm development and dissipation.

Additionally, the initiation and subsequent outflow boundary along the leading edge of the front produced an undular bore, which traveled across central Oklahoma from 0600 Z to 1000 Z and initiated convection just after 1030 Z. Tracking the bore/front in this scenario could have been done by the Clean-IR band or radar (as seen below). However, the Nighttime Microphysics RGB can provide additional information not observed from a single ABI band or from radar.

Strong contributions from the Green band (Ch 13 – Ch 7) and moderate contributions from the Red band (Ch 15 – Ch 13) in the RGB recipe make the green-yellow clouds formed along the bore stand out from the magenta surface. Early signs of initiation along from the front can also be observed from strong contributions by both the Red and Green band, with low contributions from the Blue band (Ch 13), and the development of stratus clouds in central and eastern Oklahoma indicate an environment with greater low level moisture. In this scenario, the Nighttime Microphysics can provide an early ‘heads up’ that CI may be coming soon as the front moves into a more favorable environment for severe weather in southeast Oklahoma, southwest Arkansas, and northeast Texas. This coincides with the SPC Mesoscale Discussion issued just after 1200 Z.

Kevin Thiel (OU CIWRO)