EWP Blog

So far this week, I’ve been impressed with the performance of NUCAPS and for the most part Modified NUCAPS with providing thermodynamic profile information in areas that there are overpasses.  However, what would be the best setup to figure out how well NUCAPS is doing.  Let’s dive in:

Today we’re located in Binghamton, NY (BGM) office with a Enhanced risk over the region.  We’ve also got a NUCAPS sounding directly over the region which can help us with evaluating how well things like the SPC Mesoanalysis graphics or other models are doing:

But, visible satellite shows that there are some clouds that could be interfering with the retrievals:

After playing around a bit, it may be a good idea to load the Day Cloud Phase RGB, NUCAPS points, and surface observations into one pane:

This is useful for three reasons:

1. We can see that the red in the Day Cloud Phase are mainly high clouds that are pretty thin and has enough gaps to allow for good retrievals underneath the cirrus.
2. The low clouds are pretty thin except over the southern part of the CWA where some of the retrievals are yellow indicating that caution should be taken when looking at the profiles
3. The surface observations can be used to give an idea of how well the surface T/Td are in the soundings which will impact all of the convective parameter calculations (especially CAPE/CIN)

So what about the soundings?  Looking at the NUCAPS and Modified NUCAPS here:

We can see how things are handled by the soundings.

Here is the original NUCAPS sounding at this point:

Of note, the surface conditions in the NUCAPS sounding is too warm (85 vs 80 at the nearest ob) while the Td were fairly close 69 vs 70.  How did the modified NUCAPS do?

80/70 in the sounding which is a much more likely scenario based on surface observations closest to the time of the overpass/sounding.

Why is this important?  Well, all your convective parameters are based on these two conditions.  MLCAPE drops by around 400 J/kg (~3900 J/kg vs ~3500 J/kg) AND CIN increases from -19 J/kg in the unmodified to -49 J/kg in the modified NUCAPS.  This too lines up with what the visible satellite shows; a lack of boundary layer CU potentially meaning the CAP is holding strong.

-Pym

With the threat for severe weather today, WFO Pittsburg launched a 19z special sounding to access the atmosphere. The atmosphere featured a moist boundary layer with dewpoints the lower 70s and decent lapse rates throughout much of the atmosphere of around 7 C/km. The low-level wind profile in the observed sounding indicates veering winds with height and low level winds generally from the west southwest to west. The wind profile was helpful in determining the severe weather threat. Based on this low-level wind profile, one can conclude that the tornado threat appears to be fairly low.

There was also a NUCAPS pass across the region around 1741 UTC. I selected a point just to the west of the Pittsburgh office based on the general atmosphere advection to the west based on the observed sounding. Due to this, it would seem that the point just to the west of Pittsburgh at 1741 UTC would be a good approximation of the atmosphere near the Pittsburgh area at the time of the 19 UTC sounding.

The Observed sounding indicates major fluctuations in the dewpoint temperature throughout the atmosphere but the NUCAPs sounding indicates a much smoother moisture profile. Overall, these different methods indicate rather similar PW values to the observed around 1.31 inches and NUCAPS PW of 1.27 inches. Overall, a fairly consistent moisture profile. There are some noticeable differences in the boundary layer moisture profile. The modified NUCAPS is included as the last image. It seems that the modified NUCAPS introduces a bit too much moisture with PW values of 1.43 inches. These higher PW values also lead to higher values of instability as well.

Overall, the NUCAPS sounding was helpful in diagnosing the thermodynamic profile of the atmosphere. It also arrived over an hour earlier than the observed sounding. The sounding indicates a moderately unstable atmosphere across the region capable of leading to severe weather. The moisture profile is smoother in the NUCAPs but it doesn’t seem to affect the overall moisture with PW values being the same. It would be nice to add a model wind profile to the NUCAPs sounding. This way it would be possible to access the tornado threat as well because there is not much available in the thermodynamic profile alone to make this assessment. However, I’m very impressed by the similarity between the NUCAPs and observed sounding.

Observed 19 UTC PIT sounding and NUCAPS from 1741 UTC.

19 UTC PIT Observed Sounding

Location of Observed 19z PIT sounding.

1741 UTC NUCAPS Sounding.

1741 UTC NUCAPS soundings point, brighter green dot.

1741 UTC Modified NUCAPS.

– Marty McFly

It took until the end of the week to think of trying this, but it turns out that the AWIPS cross section tool works with gridded NUCAPS (and it turns out some folks have already been using it). Mainly this suggests the usefulness of gridded NUCAPS at spatially comparing many sounding points (rather than the somewhat klunkly process of loading many soundings into NSHARP).

Here’s the cross section used to sample the ~1730Z NOAA20 NUCAPS soundings (lineB). Initially I thought the cross section would actually interpolate the 7 sounding points, but later I realized that the griddedNUCAPS would be sampled across the lineB.

The AWIPS volume browser (in cross section mode) allowed me to select griddednucaps as the source, and then both native and several derived parameters for display, and then of course the baseline (i.e. lineB) along which to calculate the cross section.

The main challenge with this workflow is knowing to find the exact time where your griddedNUCAPS is valid.  I loaded up griddedNUCAPS in a regular D2D panel to see that it was valid at 1730Z, then I increased the framecount of my cross section enough to allow me to step back in time to that point. Then, voila… I was able to plot images and/or contours across the line I’d drawn on the map.

Above: Cross-section of griddednucaps over ~7 sounding points, showing dewpoint as both image and contour

Above: Cross-section of griddednucaps over ~7 sounding points, showing dewpoint as image and lapse-rate as contour

Above: Cross-section of griddednucaps over ~7 sounding points, showing Temperature as image and relative humidity as contour

– Buzz Lightyear