Atmospheric River: Northern and Central California

The state of California, is about to experience an atmospheric river this weekend. For readers that are not familiar with atmospheric rivers, they are long moisture plumes that originate from the tropical/subtropical regions that advect to higher latitudes. Atmospheric rivers are capable of producing large amounts of precipitation, in the forms of rain and snow and can lead to flooding in low-lying areas.

For central and northern California, precipitation will start today, 5 April 2018, and last through Saturday, 7 April 2018. Precipitation will vary depending on location, and forecasts can be seen here.

Satellite imagery products, highlighting the atmospheric river can be seen below. They consist of the Blended Total Precipitable Water (TPW), Advected Layered Precipitable Water (ALPW) and the Near-Constant Contrast (NCC) products.


At 1109Z, this morning’s SNPP overpass highlights the NCC product (at 750-m resolution) that utilizes a sun/moon reflectance model that illuminates atmospheric features, and senses emitted and reflected light sources during the nighttime. Notice the large low-pressure system, embedded with the atmospheric river, located west of the United States.

Blended TPW

The Blended TPW product is derived from several satellite sources, and is at a spatial resolution of 16 kilometers and temporal resolution from 1-3 hours. The product is useful in identifying rich moisture plumes such as the one recognized this morning, seen below, at 0341Z, 5 April 2018. A limitation of the Blended TPW is that it determines the ‘total’ TPW throughout the atmosphere, however, does not differentiate how much TPW exists in specified layers in the atmosphere (e.g. surface-850mb).

Advected Layered Precipitable Water (ALPW) 

The ALPW product, unlike its predecessor, Blended TPW, incorporates model data, in this case, the Global Forecast System (GFS) wind data. ALPW addresses where the TPW is predominately located within the atmosphere, separated by 4 layers, the surface-850mb, 850-700, 700-500mb and 500-300mb. The video below shows the atmospheric river advecting form the East Pacific to north and central California, between 4-5 April 2018.

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Colorado Fog

Fog engulfed northeastern Colorado this morning. Thick fog persisted over several hours, along the northern, I-25 corridor and eastern Colorado plains. Real-time surface observations below, can point out the foggy areas, indicated by the horizontal, parallel, pink lines. Surface observations (05-14Z, 26 March 2018) are over Colorado, and the neighboring states.

In complement to surface observations, fog can be seen via satellite imagery. The following two satellite images show the Near-Constant Contrast (NCC) product, that illuminates atmospheric features (e.g. liquid and ice clouds) and senses emitted lights (i.e. city lights) during the nighttime, in comparison to the GOES-16 satellite fog product. For both images, the domain of interest is highlighted by the large box over northeastern Colorado and the time is approximately 0915Z (0315 local time), 26 March 2018.

The NCC, below, shows cloud cover over the majority of the state along with emitted city lights. An interesting feature to point out in the imagery, is the difference in cloud texture. The clouds within the large box are grey and smooth, in comparison to the clouds southeast of the box, that are rather apparent and reflective . If one had not looked at surface observations, how could one tell where the fog is located? That is, how could one tell where the liquid water clouds (i.e. fog) are located, in comparison to the ice clouds? The GOES-16 Fog product assists in addressing the question.


The GOES-16 Fog Product (below) is a difference channel product between the 3.9um and 11.3um spectral channels, where negative values (white colors), indicate liquid water clouds and positive values (magenta) indicate ice clouds. The GOES-16 Fog Product can differentiate between the two types of clouds easily, where liquid water clouds are predominately located within the domain of interest. Additionally since fog was reported by surface observations in this domain, we can be confident that low-lying liquid water clouds were present this morning, in northeastern Colorado.

GOES-16 Fog Product (3.9um – 11.3um)

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Faka-Union Fire (Southwest Florida)

The Faka-Union Fire, located in southwest Florida has burned over 9,000 acres with only 50% containment. The fire is located near the Picayune Strand State Forest. The fire started out as a ‘prescribed burn’ last weekend, but due to erratic weather conditions, started to burn out of control. The smoke and fires have caused temporary road closures in southwestern Florida, however, as of 9 March 2018, no structures have been burned. For additional information on the Faka-Union Fire, click the following link.

The latest CIRA – GeoColor loop of the fire via the CIRA-RAMMB Slider between 15-18 UTC, 9 March 2018 (shown below). Notice the elongated trail of grey/white smoke, emanating from the fire.


Below, is the latest Near-Constant Contrast (NCC) satellite imagery of the Faka-Union fire from this past week, 2-8 March 2018. NCC imagery is also known as ‘nighttime visible’ imagery, that can identify atmospheric features, and sense emitted and reflected light sources during the nighttime. All times are between 6-8 UTC. Notice the change in emitted lights from the fire (embedded in the yellow circle). The fire is close in proximity to the emitted city lights of Naples, Florida.


To get an idea of where the smoke from the fire will disperse, one can utilize the ‘experimental’ High Resolution Rapid Refresh (HRRR) Smoke Model. The model had been developed to simulate emissions and the transport of smoke from wildfires. The model is at 3 kilometer spatial resolution and is initialized everyday, at 00, 06, 12, and 18 UTC, and the model produces 36-hour forecasts.

For the Faka-Union Fire, click on the following HRRR Smoke link, to see where the smoke from the fire is forecasted to disperse. The model animation was initialized at 12 UTC, 9 March 2018.

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Synthetic imagery from the NSSL WRF-ARW for 7 March 2018 event

A nor’easter occurred on 7 March 2018 which resulted in heavy snow, strong winds and rain across portions of the Northeast U.S.  In this blog entry we’ll examine the performance of the NSSL WRF-ARW via synthetic water vapor imagery in relation to the cyclogenesis aspects.

The following 4 panel display:

shows the following:

Upper left:  GOES-16 7.34 micron imagery (5 minutes)

Lower left: NSSL WRF-ARW synthetic 7.34 micron imagery from the 00Z 7 March run (hourly)

Upper right:  GOES-16 6.95 micron imagery (5 minutes)

Lower right: NSSL WRF-ARW synthetic 6.95 micron imagery from the 00Z 7 March run (hourly)

Early in the loop we observe colder cloud tops offshore, adjacent to a dry slot just west of that region, followed by colder cloud tops  associated with proximity to the upper low.  Soon thereafter, we see the rapid development of clouds in proximity to the upper low (the red oval on the image below):

The warm conveyor belt is denoted by the red “WCB” at this time.  Up to this point, this may be considered a cold air type of cyclogenesis event.  However what happens afterwards in the yellow oval above would transition this to an (more intense) instant occlusions type of cyclogenesis.  In the yellow oval, watch the development of convection.  This signifies the development of a secondary warm conveyor belt which peels cyclonically from the warm conveyor belt back towards the position of the upper low.  Once occlusion begins, this is generally referred to as the TROWAL airstream.  The significance of this is that the TROWAL advects air from the warm sector, back towards the low, allowing more baroclinic energy for the cyclone to act upon.  This generally results in rapid pressure falls, and associated hazardous weather (heavy precipitation, strong winds etc.).  A conceptual diagram with these features can be viewed on slide 3 of this training module:

The NSSL WRF-ARW output, as viewed via the synthetic imagery generally did a good job capturing the development of the various components of cyclogenesis discussed above, albeit the position was slightly off.  The synthetic imagery provides an efficient visual comparison between model output and observations (GOES), allowing for a rapid assessment of how the model is performing.  This assessment in model forecast confidence allows the forecaster to have more or less confidence in future forecast hours.  The region of rapidly cooling cloud tops denoted by the red oval shows a more uniform extent of colder cloud tops compared to the NSSL WRF-ARW synthetic imagery.  This is primarily due to a known weakness in the WSM6 microphysics scheme used in the NSSL WRF-ARW.  Due to this known weakness, it’s the location and timing of the colder cloud tops that matters, not so much the areal extent of colder cloud tops.

The GOES-16 1-minute visible imagery provided a spectacular view of the development of the convection associated with the TROWAL:

An alternate view of the same scene is the Day Cloud Phase Distinction RGB, which provides different colors to various growth stages of the convection:


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