An isolated severe storm brought large hail to northern portions of Oklahoma City on 23 March 2019. GOES-16 1-min imagery was available over the region to support severe weather forecast and warning operations.

Water vapor imagery shows convective development across Oklahoma south of a broad upper low (Fig 1).

Prior to convective initiation, stable wave clouds (aka billow clouds) were apparent over the OKC area and east, signaling the presence of low level stability. As the day progressed, destabilization was apparent west of OKC as a cumulus cloud field developed. A southwest to northeast oriented axis of enhanced cumulus cloud growth (towering cu and clumping cu) eventually become apparent, signalling the most likely zone of imminent convective initiation (Fig 2).

The Day Cloud Phase Distinction RGB further highlights imminent initiation through the transition of cu from “light blue” to “green” within the cu field (Fig 3). This color change comes from the blue contribution (snow/ice band) decreasing (ice increasing in clouds), while the green contribution (red VIS) is relatively high (highly reflective clouds). The red contribution (IR window) is low, but may also be increasing as the cloud tops cool. In other words, glaciation is starting to occur within the cloud.

Moving forward another hour, convection initiates within the zone of increasingly agitated cumulus clouds (Fig 4).

Plotting GLM Flash Extent Density during the first hour of initiation, a rapid increase in lightning activity is apparent leading up to the first NWS warning and hail report (Fig 5). The increased lightning activity signals a strengthening updraft.

Finally, looking at storm evolution with respect to GOES-16 derived CAPE, convection developed within a local max of CAPE of around 800 j/kg (Fig 6).

Bill Line, NWS

Strong to severe thunderstorms brought swaths of accumulating hail, including some large severe hail, to parts of the Texas Panhandle on 22 March 2019. Reports of hail up to 2.75″ in diameter were received by the National Weather Service. Photos and videos on social media showed hail covered roads and highways. IR satellite imagery showed the storms advancing across the Panhandle during the early evening (Fig 1).

Temperatures during the evening behind the storms dipped into the upper 30s, preventing much of the hail from melting. GOES visible and RGB imagery the next morning showed hail swaths still in place, extending from well southwest of Amarillo to northeast of Amarillo. The hail-covered surface appears as green in the Day Cloud Phase Distinction RGB imagery, similar to snow (Fig 2). This RGB combines the 0.64 um VIS, 1.6 um snow/ice NIR, and 10.3 um IR to differentiate low clouds (light blue) from high clouds (red) from snow/ice-covered ground (green) from bare ground (darker blue). This differentiation is much more difficult when using any single band alone.

Bill Line

It has been great year so far for snow across the mountains of southern Colorado. Current snowpack (as of Mar 21) across the Gunnison, Upper Rio Grande, and Arkansas River Basins are 152%, 140%, and 147% of normal, respectively. The above normal snowpack is appreciated, as it is coming on the heals of a year in which snowpack was well below normal. These trends are captured in Fig 1.

The snowpack is easily diagnosed in satellite imagery (MODIS imagery here). A ridge of high pressure over the western US allowed for clear views of the snow cover over Colorado on 16 March 2019, several days removed from a significant snowstorm (Fig 2).

Compared to the same day last year (Mar 16, 2018), the improved snow cover is easily apparent (Fig 3).

Next, we look at the trend of snow cover across Colorado on clear days during the 2018/2019 winter (Fig 4).

The National Operational Hydrologic Remote Sensing Center (NOHRSC) runs a model that assimilates satellite data, ground observations, and airborne observations to create daily snow maps. Figure 5 includes a comparison of NOHRSC snow depth for March 16 in 2018 and 2019. The improved snow cover and snow depth is obvious from these images.

Bill Line, NWS

A well forecast snowstorm struck Colorado on March 13, 2019. NWS forecasts mentioned the blizzard and high wind potential over parts of the eastern Colorado plains days in advance. GOES-West water vapor imagery was utilized by forecasters to track the relevant features leading up to the event, and assess model analyses and forecasts. Forecast models had a great handle on the evolution of the system from its early stages. Water vapor imagery was also used on social media to aid in messaging about the incoming storm (Figs 1 and 2). This type of messaging not only engages “weather nerds”, but also helps to capture the public’s attention in a unique way, and educates them on a tool used by forecasters that many are not familiar with.

On March 10, the main trough was already off the California west coast, pumping moisture into the southwest US (Fig 1).

GOES-West Water Vapor Satellite Imagery from today shows the early evolution of a large storm system that will bring varying weather impacts to much of the United States this week. Visit https://t.co/359SEz69Xz for your forecast. pic.twitter.com/p85FY2S7ws

— NWS Pueblo (@NWSPueblo) March 11, 2019

By March 12, apparent in water vapor imagery were the key features that would come together to develop an intense cyclone (Fig 2).

Analysis of GOES-17 satellite water vapor imagery reveals the key ingredients coming together to bring a significant winter storm to Colorado. #cowx pic.twitter.com/S0lOYSn6Zd

— NWS Pueblo (@NWSPueblo) March 12, 2019

As forecast, the storm caused widespread blizzard conditions from Colorado Springs north, strong winds elsewhere across the eastern Colorado plains, and snow in the mountains. In fact, the Colorado Springs airport recorded a 96 mph wind gust, a record for the airport (data preliminary). Additionally, Lamar ASOS recorded a (preliminary) record low pressure for the state of Colorado of 970.4 mb! GOES-West water vapor imagery showed the rapid cyclogensesis that took place as the storm advanced across southern Colorado from the evening of the 12th through the 13th (Fig 3).

1-min imagery from GOES-17 (per BOU request) was available over the region to aid forecasters in detecting and tracking storm details, particularly convective elements and areas of potentially enhanced snowfall rates. The 90-minute animations below takes place during the period of lowest pressure, and when snow became heavy (with 60+ mph gusts) in Colorado Springs (Figs 4 and 5). A tight circulation is found over far eastern Colorado, and the coldest cloud tops extend from Denver to Colorado Springs, and west.

The NESDIS Snowfall Rate product, which derives snowfall rates from microwave satellite imagery from an array of satellites, confirmed the areas of heaviest snowfall during the peak of the storm. This product is particularly useful in data sparse areas, such as over the mountains.

Further south, GOES-East split window difference (10.3-12.3 um) imagery captures widespread dust lofted by the strong winds across the southern plains on the backside of the system (Fig 7). Recall, negative values of this difference (brown here) highlight lofted dust particles. This imagery helps forecasters to identify the onset of dust being lofted and to track its evolution, and then communicate that information to the public and partners, and include it in forecast grids and text products.

Bill Line, NWS