RAMMB: GOES-R Proving Ground Blog

Upon inspection of the synthetic infrared (10.35 micron) imagery from the NSSL WRF-ARW model:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/13oct11_syn_ir

your attention may be drawn to the region of southwest Colorado since we see a region of cold brightness temperatures  that does not move and persists for the duration of the loop (1600-0000 UTC).  Could these be low clouds / fog? Let’s look at the GOES visible imagery for 1630 UTC:

Skies are clear across southwest Colorado, so we are not looking at low clouds / fog.  However, note that there is snow cover over the mountains.

What we’re looking at in the synthetic imagery is a representation of  snow cover.  The snow cover data that goes into the NSSL WRF-ARW model is relatively coarse, therefore the cold ground signature is spread out over relatively large areas when there is snow cover in the model.  This signature shows up quite easily early in the cold season with the large temperature difference between snow cover and no snow cover, and will increase in coverage moving into winter as snowfall coverage increases.

Let’s analyze the following loop of the synthetic fog product, generated from the 4-km NSSL WRF-ARW model:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/10oct11_syn_fog/

In this color table, grey into light blue represents increasing confidence in liquid water clouds.  Our example from the 0000 UTC 10 October 2011 NSSL WRF-ARW model run shows a large area of liquid water clouds (most likely stratus) across Texas extending northward through the central US.  The darker shades of grey and black correspond to ice clouds (most likely cirrus) forecast by the model.

The region of blue in Arizona and Utah extending southward into northwest Mexico that does not move catches your attention.  A quick look at the visible satellite imagery:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/10oct11_goes_vis

shows that the region is mostly cloud free.  However, the lighter shade of grey extending northwest to southeast through the four corners of AZ/CO/UT/NM corresponds to the blue in the synthetic fog product; this false cloud signature is a consequence of surface emissivities at the two channels.  This is not a model error, rather, an observed feature in GOES-11.  Similarly, the other blue region in the northeast quadrant of AZ and southwest AZ into northwest Mexico are also consequences of the surface emissivity.

The easiest way to identify a false signature is to look at the loop, and the areas that don’t move at all throughout the duration of the loop are likely false emissivity signatures.

Synthetic satellite imagery can be useful in forecasting temperature.  This example from September 20-21, 2011 demonstrates the utility of synthetic imagery from the 4-km NSSL WRF-ARW model in forecasting the overnight low temperature.

Focusing on southeast Wyoming, examine the synthetic infrared imagery from late afternoon (2000 UTC) through the late night hours (0800 UTC):

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/20sept11_syn&image_width=800&image_height=600

Early in the loop, there is afternoon convective clouds in southeast Wyoming, which diminishes by 0300 UTC.  However, notice the region of clouds (indicated by the colder brightness temperatures) developing across southeast Wyoming in the 0300-0800 UTC time range.  If the forecast is correct, the cloud cover would keep temperatures from cooling down as quickly.

Now let’s analyze what actually happened by looking at the GOES IR imagery:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/20sept11_goes&image_width=800&image_height=600

Note the clouds developing into southeast Wyoming in the 0500-0745 UTC time range, similar to what was forecast by the WRF-ARW model.  This caused locations under the cloud cover to not cool off as quickly, for example, look at the temperature trace (red line) for Cheyenne, WY:

Temperatures at Cheyenne cooled off gradually to about 1000 UTC, then the cloud cover dissipated allowing temperatures to cool more rapidly to an overnight low of 36 F.

Similarly, at locations further east in the southern Nebraska panhandle, cloud cover kept Kimball, NE from cooling off too rapidly for an overnight low of  42:

And an overnight low of 40 at Sidney, NE:

Meanwhile, at Douglas (about 150 miles north of Cheyenne) in east central Wyoming:

Temperatures cooled off more rapidly as skies remained clear, and the overnight low was 25 F.

Real-time synthetic imagery from the 4-km NSSL WRF-ARW model may be viewed here:

http://rammb.cira.colostate.edu/ramsdis/online/goes-r_proving_ground.asp#Synthetic_GOES-R_Imagery_from_Real-Time_NSSL_4_km_WRF-ARW

Contributor:  Becca Mazur, NWS forecast office, Cheyenne, WY

Synthetic Fog Product based on the 15- to 18-hour forecasts from the NSSL WRF-ARW (left), and GOES-11 Visible Imagery (right)

A new synthetic difference product is now being produced from the NSSL WRF-ARW output: the fog product, or 10.35 – 3.9 μm.  In order to generate synthetic 3.9 μm imagery in a timely manner, it’s necessary to assume that it’s always night because the solar reflected calculations are too expensive.  This allows the traditional fog product to be displayed for all forecast hours of the WRF.  In the example above, the color scheme for the synthetic fog product (left) is designed such that grey into light blue represents increasing confidence in liquid water clouds.  Note the forecast stratus clouds in the San Francisco Bay area, and compare that to the observed GOES-11 visible imagery on the right.  The WRF-generated fog product forecast does a good job with the location and dissipation time of the low clouds.  Such a forecast might be quite useful for the aviation industry given how often low clouds and fog cause delays at the West Coast airports.

Synthetic imagery from the 4-km NSSL-WRF ARW model is produced at CIRA and is available in real-time here:

http://rammb.cira.colostate.edu/ramsdis/online/goes-r_proving_ground.asp#Synthetic%20GOES-R%20Imagery%20from%20Real-Time%20NSSL%204%20km%20WRF-ARW

The following loop shows Hurricane Irene at the time it was east of Florida:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=dev/lindsey/loops/nssl_wrf_g13_irene&image_width=1024&image_height=384

The right side shows the synthetic infrared imagery from the 0000 UTC 25 August model run, and the corresponding GOES infrared imagery is on the left.  Keep in mind some of the known biases with the model such as brightness temperatures typically warmer than GOES, and anvil cirrus from convection that is typically underdone.  Synthetic imagery can be compared with GOES imagery to look for forecast trends in the Hurricane.