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.
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.
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.
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.
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.
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.
During the early morning hours of 14 March 2022, a plume of moisture from the Gulf of Mexico was advected northward prior to a severe weather setup later that day. Along with surface observations and RAP surface analysis data, imagery from the GOES-16 Nighttime Microphysics RGB provided conformation of this moisture advection with stratus clouds developing across eastern Texas and southern Oklahoma (green-yellow) from Figure 1. Strong contributions in the red and green bands signify thick clouds that mostly contain water, helping to determine that these are low level stratus clouds driven by the synoptic scale advection of low level moisture across the region.
The NWS Storm Prediction Center issued a Slight Risk for northeast Texas and the Ark-La-Tex region, with all hazards (tornadoes, large hail, and damaging winds) possible (see slideshow below). Use of the Nighttime Microphysics RGB in this scenario may provide conformation of the moisture advection, along with its current spatial extent in regions where few surface observations exist. Monitoring the extent of these stratus clouds also provides a ‘first look’ at which areas will receive more or less solar heating during the morning, which may impact the initiation time, coverage, and maximum strength of convection later in the day.