GOES-16 7.34 micron band applications for the 6 March 2017 event

The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing.  Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.

Authors: Dan Bikos, Chris Gitro, Ed Szoke and Chad Gravelle.

On 6 March 2017, a developing cyclone moved eastward across the central US, causing a number of hazards including severe thunderstorms, strong winds and wildfires.  This blog entry will focus on GOES-16 applications of the 3 water vapor bands, in particular, the 7.34 micron band.  The 3 water vapor bands may be viewed in this animation:

http://rammb.cira.colostate.edu/training/visit/loops/6mar17/loop.gif

Upper left image is the 7.34 micron (low-level water vapor) band, upper right image is the 6.95 micron (mid-level water vapor) band, lower left image is the 6.19 micron (upper-level water vapor) band, and lower right are surface observations with surface fronts annotated.  Analyzing the 3 water vapor bands in tandem provides a three-dimensional perspective since the bands “see” different levels in the vertical, where it “sees” can be identified from the weighting function profile of each band.  The GOES-16  weighting function profiles for clear sky conditions based on the 12Z sounding at Dodge City, KS for the three water vapor bands:

ddc_wf

Indicates the relative contribution in the vertical for each band.  All 3 bands show two peaks in weighting function profiles, near 400 mb and between 550 and 600 mb, however note the 7.34 micron band (blue line) has a more significant contribution as we look lower in altitude.  The 7.34 micron band has a peak weighting function around 600 mb, and generally is looking lower in the atmosphere than the other two water vapor bands.  This is the level we typically find important meteorological phenomena such as the elevated mixed layer (EML) or elevated cold front (ECF) therefore this band is better suited to identify these features compared to the other 2 water vapor bands.

The EML may be tracked in the GOES-16 7.34 micron band once it is positively identified as being associated with an EML with other datasets such as soundings.  The brightness temperatures with an EML tend to be relatively warm, however there are a number of reasons why relatively warm brightness temperatures may be observed (i.e., subsidence).  Morning soundings from Omaha and Dodge City within regions of warmer brightness temperatures confirm the presence of an EML:

OAX_12z

 

DDC_12z

 

The EML can be tracked eastward if there are no clouds to obscure the layer where the EML exists.  Note that this technique does not indicate if a low-level moist layer exists or not, since the weighting function response at low-levels is insufficient (it peaks above the moist layer usually).

In this case, the EML tracked well to the east, including regions where cloud cover exist to obscure the eastern edge of the EML:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/6mar17/B10&loop_speed_ms=80

Afternoon thunderstorms developed along the surface cold front, within the EML, which provided multiple factors favorable for thunderstorms to be severe.  In this case there were many severe reports.

Another feature that may be tracked in the GOES-16 7.34 micron band is the elevated cold front (ECF).  The ECF can be identified as a line of relatively warmer brightness temperatures, ahead of the surface cold front as seen in the earlier loop above:

http://rammb.cira.colostate.edu/training/visit/loops/6mar17/loop.gif

This annotated image from 16Z highlights the ECF:

Slide1

 

Note the ECF is ahead of the cold front (and dryline – hatched).

Additional confirmation of the ECF can be viewed via model output (RAP in this case), in this case a cross section oriented East-West from Denver to St. Louis:

Slide2

The contours of theta-e indicate the position of the surface cold front – tight gradient near the surface and sloping to near vertical with height – and the elevated cold front, at the nose of the sloping isentropes east of the surface cold front.  A loop of the cross section may be viewed here: 6Mar17_Ruc_Xsect

Additional supporting evidence of the ECF may be found in HRRR output of the 700 mb heights, temperature and wind:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/6mar17/hrrr

The loop shows a bulge of colder temperatures at 700 mb moving into eastern Nebraska / western Iowa that is ahead of the surface cold front.  Also, notice the gradient tightens in time.  This seems to agree with the line of warmer brightness temperatures we noted above in the 7.34 micron imagery.

A loop of HRRR 700 mb analyses between 15 and 23 Z demonstrates that the model forecast above appears to have captured the ECF:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/6mar17/hrrr/analysis

A RAP model cross section from eastern Colorado to just east of Kansas City of temperature advection, specific humidity and winds:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/6mar17/rap

Depicts cold advection aloft ahead of the surface cold front at 15Z, by 18Z downslope warming / diabatic heating decrease the cold advection signature west of the ECF, however by 21Z we see deep cold advection associated with the surface cold front beginning to catch up with the ECF.  Why does the ECF show up as a line of relatively warmer brightness temperatures (at least in the annotated image shown above at 1602 UTC and more subtly later in the afternoon)?  The cold advection is  accompanied by lower specific humidity (and lower RH as shown above) values, and in this drier air (assuming clear skies) the weighting function profile would “see” lower in the atmosphere, thus warmer brightness temperatures.

What effect does the ECF have on severe thunderstorm development?

Note the thunderstorms that develop ahead of the line of thunderstorms associated with the surface cold front in southwest Iowa:

Slide3

 

These storms appear to be in association with the ECF since no distinct surface convergence in that region is apparent in the METARs (lower right panel above) and this is where the ECF would be expected if we closely analyze the loop:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/6mar17/B10&loop_speed_ms=80

Let’s zoom in on the storms of interest in Iowa by analyzing the radar loop:

radar_warnings

Note the storms ahead of the main squall line associated with the surface cold front were difficult to discern in the GOES-16 loop (anvil cirrus from the squall line), however here these storms can be clearly seen and produced multiple severe hail reports.  By the end of the loop the surface cold front likely catches up with the ECF as noted by the squall line overtaking the isolated storms ahead of it.

Reference:

Parker, D.J., 1999: Passage of a tracer through frontal zones: A model for the formation of forward-sloping cold fronts. Q.J.R. Meteorol. Soc., 125, 1785-1800.

Posted in GOES R, Severe Weather | Leave a comment

Madagascar: Tropical Cyclone Enawo

Madagascar! A small country located in Africa, just east of Mozambique was hit by Tropical Cyclone Enawo making landfall today, 7 March 2017. Right before landfall the tropical cyclone was near ‘Category 4 status’ with winds approximately 145 mph. It was the strongest landfall in 13 years. The storm will bring heavy precipitation and flooding to the country.

To aid in monitoring this storm, one can use the Day/Night Band (DNB) that utilizes a sun/moon reflectance model to monitor tropical storms, observe atmospheric features, sense emitted lights and assist with cloud monitoring during the nighttime. A static Day/Night Band (DNB) image of the cyclone at 2146Z, 6 March 2017 can be seen below in Figure 1.

DNB_2146Z_6_March_2017_modifiedFigure 1: The DNB highlighting the location of the Tropical Cyclone Enawo at 2146Z, 6 March 2017, just northeast of the country of Madagascar. The DNB can observe atmospheric features such as lightning, clouds and the eyewall of Tropical Cyclone Enawo. DNB can also sense anthropogenic lights (i.e. emitted city lights) in Madagascar and from neighboring islands east of Madagascar. In the top-right corner of the image, the moon percent visibility and moon elevation angle are also provided.

For the latest updates on Tropical Cyclone Enawo click here.

Posted in Miscellaneous | Leave a comment

Comparison of GOES-16 with GOES-13

The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing.  Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.

One of the 1-minute mesoscale sectors for GOES-16  captured a series of polar low-like circulations over northeastern Lake Ontario moving into New York:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/3mar17/B02&loop_speed_ms=80

Notice how much more clearly these circulations appear in GOES-16 as compared to current GOES-13:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/3mar17/GOES13

 

Posted in GOES, GOES R, Satellites | Leave a comment

GOES-16 Mountain Wave clouds on 3 March 2017

The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing.  Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.

Mountain wave (orographic cirrus) clouds were observed in the Rocky Mountain region on the morning of 3 March 2017 as observed in this 10.35 micron image:

annotation_20170303

 

Let’s examine a series of loops of different channels available from GOES-16.  The loops will span through sunrise (i.e., start in darkness and transition to daytime).

The familiar IR channel at 10.35 microns has always been a good channel for identifying mountain wave clouds and will continue to be an ideal channel for identification:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/3mar17/B13&loop_speed_ms=80

The mountain wave clouds in western Montana develop during the loop while the mountain wave clouds downwind of the Bighorn range in north central Wyoming dissipate during the loop.  Mountain wave clouds are easily identified since brightness temperatures are particularly cold, making them stand out when compared, for example, to the clouds associated with the disturbance passing from eastern Montana into western North Dakota.  Mountain wave clouds in north central Colorado exist at the beginning of the loop and expand in time.

One of the new channels on GOES-R is the 1.38 micron channel (“Cirrus band”), which is useful for identifying mountain wave clouds since cirrus clouds stand out while low-level level clouds do not:

 http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/3mar17/B04&loop_speed_ms=80

Next we will look at the 3 water vapor channels available on GOES-R.

First, the upper-level water vapor band at 6.2 microns:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/3mar17/B08&loop_speed_ms=80

Next, the mid-level water vapor band at 6.9 microns:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/3mar17/B09&loop_speed_ms=80

Finally, the low-level water vapor band at 7.3 microns:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/3mar17/B10&loop_speed_ms=80

What additional information do the water vapor bands show?

The water vapor bands typically have a subsidence signature (relatively warmer brightness temperatures) slightly upwind (i.e., west in this case) of the mountain wave clouds.  This subsidence signature can be seen on all 3 water vapor channels, but it’s more subtle in the upper-level water vapor imagery.  The depth of the subsidence can be assessed by looking at all 3 channels in tandem.  It may be worthwhile noting trends in the subsidence signature for the mountains in your forecast area during these mountain wave cloud events.

Our last loop will be a channel difference product, the 3.9 minus 11.2 micron loop, commonly known as the fog / low-stratus product since it’s been around for a long time with current GOES channels.  Since this product involves the 3.9 micron channel, we have to be aware of the solar reflected component during the daytime hours.  This can easily be tracked before and after sunset in this loop:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/3mar17/fog&loop_speed_ms=80

Recall from this training session that mountain wave clouds tend to be composed of relatively small ice crystals which are highly reflective.  By subtracting out the emitted component we are left with the solar reflected component during the daytime, this helps make the mountain wave clouds stand out from other clouds.

Posted in Orographic Effects | Leave a comment