Winter Storm Harper

A large low pressure system, slammed into the western United States (US), bringing heavy rain and snow, high winds, along with producing blizzards (for the Sierra Nevadas) and localized flooding for low-lying areas.

The areal extent of the system is seen via ‘Preliminary, Non-Operational‘ GOES-17 Day Cloud Phase Distinction RGB (below) at 1925 UTC, 16 January 2019, as the storm approached the Western US.  The RGB differentiates between liquid water clouds (blue), glaciated clouds (green) and mid-to-high level ice clouds (yellow-to-red clouds). Note the elongated rope cloud, associated with the cold front, in the southwest portion of the image, depicted in quasi-linear blue and green colors.

The winter storm can also be seen via Advected Layered Precipitable Water (ALPW) product, that is derived from polar-orbiting satellites and identifies areas of high moisture content and moisture transport that can lead to heavy precipitation and flooding. Animation below, shows the ALPW product from 06 UTC, 16 January 2019 –> 15 UTC 17 January 2019, highlighting Winter Storm Harper as it moves into California, Oregon and Washington. The colorbar is at the top of the animation depicting 0-32 mm (black to pink colors) precipitable water values. ALPW is different from Total Precipitable Water (TPW) products, in that ALPW identifies precipitable water from four atmospheric layers (surface-850mb, 850-700mb, 700-500mb, and 500-300mb), rather than specifying the total precipitable water values for the entire atmospheric column.

In this case, as Winter Storm Harper approaches land, notice high concentrations of precipitable water between the surface-to-500mb (blue/aqua colors), and significantly lower precipitable water concentrations in the upper atmosphere (i.e. 500-300mb, grey to black colors). Also note an elongated atmospheric river on the southeast side of the low pressure system. The atmospheric river moved into and impacted south-central and southern California, where the Sierra Nevadas experienced heavy snowfall rates (up to ~3 inches per hour) and high snow accumulations.

Speaking of the Sierras, earlier this morning there were reports of thundersnow in the Sierras. Reports were near Mammoth Mountain, CA, in which the ‘Preliminary, Non-Operational‘  GOES-17, Geostationary Lightning Mapper (GLM) detected lightning signatures near Mammoth Mountain. Animation below shows GOES-17 GeoColor imagery overlaid by GLM – Group Flash Count Density signatures. Time period observed is between 12-1445 UTC, 17 January 2019. Notice the lightning signatures observed in the Sierras that experienced thundersnow.

 

Winter Storm Harper plans to create more havoc throughout today and into the weekend, moving into and impacting the Rocky Mountains, Central Plains and Eastern United States.

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Fog and Low Clouds over Snow Cover in the Midwest: A case from 10 December 2018

Areas of snow cover can often lead to areas of persistent fog and low cloudiness under the right conditions.  And determining the areas of fog and low clouds from snow cover can be tricky during the daytime hours.  Here we look at a case from 10 December 2018 over the Midwest the snow cover likely contributed to low cloudiness and fog that either was slow to clear or lasted through the day in some areas.  We’ll use a couple of CIRA products for this case.

We begin with a look at the extent of low clouds and fog around pre-dawn (1202 UTC on 10 Dec) using the CIRA GeoColor product from GOES-16 displayed using the CIRA SLIDER tool (available at http://rammb-slider.cira.colostate.edu).

GeoColor is not an operational product, but it is available for display on AWIPS and is widely used across the NWS (if you don’t have this product at your WFO and would like to get this product on AWIPS send us an email).  In the nighttime city lights are displayed in the background and low clouds (water clouds) or fog are colored blue, while higher (ice) clouds are white.   Observations at this time (shown below) suggest that much of the blue area in MN into WI is fog, with more low cloudiness in the area farther to the east.

During the daytime hours GeoColor uses the visible band 2 with a true color background.  A look at the GeoColor image at 1802 UTC on 10 Dec shows that it can be hard to distinguish snow from clouds or fog with the visible band during the daytime.

Here is the NOHRSC snow cover analysis for this day.

There are RGB products that can be used to help discriminate clouds from snow (such as the Day Snow/Fog product developed by EUMETSAT.  CIRA has developed a product that also discriminates clouds and fog from snow but retains white as the color for the snow cover.  The CIRA Snow/Cloud Layer Discriminator product for the same time as the image above is shown below.

The color scale is shown at the bottom of the image.  This product is also experimental but should soon be available for AWIPS as well.  In this version of the product there is a discrimination made between lower (water) clouds and higher (ice) clouds, adding additional information.  This product is for use during the daytime hours, with the image for a couple of hours later showing some breaking up of the low clouds and fog in areas without snow cover but otherwise the low clouds and fog persisting, in fact through the day as shown in the GeoColor image for 2202 UTC.

 

 

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Advected Layer Precipitable Water (ALPW) comparison for events in December 2018 – January 2019

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New Mexico Snowstorm

Due to an upper-level disturbance passing through the southwestern United States, abundant snowfall has fallen in New Mexico, southwestern Colorado and parts of Texas (see social media snowfall image here). Snow totals range from a few inches to 16 inches at higher elevations. Snowfall has been observed via surface observations and by satellite this morning, 28 December 2018 at ~16Z.  Surface observations and satellite images are offset by ~13 minutes.

RAP Real-Time Weather Data – Surface Observations @ 1558Z, 28 December 2018.

Snowfall is observed (i.e. weather station plots displaying purple, asterisk symbols) in parts of New Mexico, Texas, and southwestern Colorado. Multiple asterisks imply heavier snow rates observed by site. Notice, large areas of New Mexico, that do not have surface observations; this is where satellite and radar data are helpful in observing snowfall rates in ‘surface data’- sparse regions.

NESDIS Snowfall Rate Product (NASA-SPoRT) – Snowfall Rate Product @ 1611Z, 28 December 2018.

The NESDIS Snowfall Rate Product utilizes microwave snowfall rate data derived from polar-orbiting satellites (e.g. S-NPP, MetOp, DMSP; note more polar-orbiters are implemented into the algorithm). Snowfall rate is shown in ‘liquid equivalent’, displayed in inches per hour, and millimeters per hour. Product utility is in observing snowfall rates in data-sparse regions, and identifying areas of heaviest snow. The image below, highlights the snowfall rate product at approximately 13 minutes after surface observations were observed. Snowfall rate product imagery indicates a widespread distribution of snowfall rates in New Mexico, and the surrounding states, where areas of heaviest snow are indicated in southwestern Colorado, central New Mexico and northern Texas. Maximum values range from 1-1.5 mm/hr or 0.04-0.06 inches/hour.

COD Weather – Radar Imagery @ 1610Z, 28 December 2018.

Collocated in time with satellite observations, the Albuquerque, NM radar imagery, shows regions of precipitation (green-to-yellow colors), in this case, areas of snowfall. However, take note that Albuquerque, NM is at high elevation (i.e. ~5300 feet) and is surrounded by high terrain. The Albuquerque, NM radar will interact with mountain ranges that may produce anomalous features (e.g. high dBZ values in an areas where it is not snowing). Radar coverage can also be poor in some areas, due to high terrain blocking radar signals, obscuring ambient atmospheric features.

More snowfall is expected for Albuquerque, NM for the next 24 hours.

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