Merged TPW Composite Values running low

A quick comparison at 21Z reveals that Merged TPW Composite is running about .3 inches lower than Blended Total PW.

NUCAPS Comparison with Special 17Z Sounding

Today we were tasked with the LIX CWA (New Orleans/Slidell, LA), and the NUCAPS sounding went overhead at 1824Z. Luckily there was a special sounding out of the LCH (Lake Charles, LA) office at 1700Z so there was at least a loose chance to compare the data. So, let's do just that! First the LCH sounding...



Shows a relatively unstable atmosphere with decent lapse rates in the mid-levels.  And now the nearest good-value NUCAPS sounding (taken just north of Vermilion Bay)...



The two soundings aren't an exact comparison, they aren't in the same location or taken at the same time, but synoptically it should be a pretty similar environment ahead of the broken line of storms moving into the area. The biggest problem comes in the boundary layer with values that are way off. The profiles were showing a 2m value of 76/70 when in the observed sounding it was 82/75. Given that the sounding was taken earlier in the day, it's troublesome that the temps were much higher than the NUCAPS sounding. Unfortunately, modified soundings were not available on this day and given the unmodified soundings inability to correctly analyze the boundary layer, it makes trusting any surface derived data near-impossible. The only application I can see for these soundings are to analyze the upper-level synoptic environment (i.e., upper-level lapse rates, relative humidities, etc.) For this, you can compare some values... 850-500 Lapse Rate was 6.1 C/km in the NUCAPS sounding it was 6.7 C/km, some variability is expected and it's not too bad but the difference is worthy of caution. In the gridded product somehow the Lapse Rate was 6.48 C/km, much better given the expected variability but I'm not sure these values are different. Are the gridded data not derived from the soundings or vice versa? Mid-level RH in our LCH sounding is 90%, yet in our NUCAPS sounding it's 79%. I'd expect these values to be a bit closer given the strengths of NUCAPS, but it's close enough to perhaps chalk up to differences in space and time.

Afterwards, I saw that LIX also had a Special Sounding that could be comparable, I'll leave the comparisons below...



#ProtectAndDissipate

This was interesting

Since things were kinda boring over HGX today I had to look for things to blog about. Here is something interesting that I noticed with the Vis/IR Sandwich RGB. At the beginning of the loop the RGB didn't show any IR brightness temperatures. As the TCU continued to develop we saw pixels of IR brightness temperatures starting to show up indicating cold cloud tops and the potential for glaciation to start. Low and behold, if we continue to watch the loop, more pixels start showing up...and a few minutes later both GLM and ground based networks picked up on a couple of CGs. As the thunderstorm developed, cloud tops cooled and more pixels started getting displayed we began to see more lightning.  This was something that I didn't expect the RGB to pick up on and potentially helpful for situational awareness and IDSS in the west where most lightning tends to come from single cell thunderstorms. If you are able to pick up on these ahead of time you may be able to some lead time before lightning occurs.



Update...it happened again, pixels starting being displayed and then lightning occurred within a couple of minutes. If this generally hold true for single cell thunderstorms this would be awesome for outdoor IDSS.

Life and Death in One Loop

Well, the convection is trying. And dying.  Case in point, the full life cycle of a pair of storms across the  northern suburubs of Houston.  Thoughts below:


You are looking at the 1-minute Mesoscale Sector scan with GLM Flash Extent Density, the Vaisala GLD dataset, and ProbSevere overlays. Some things to look at:

ProbSevere struggled when the storms were most intense by merging two individual storm objects, splitting them apart, then re-merging back into one object.  Trends were a mess because of this.

GLM lightning activity ceased a full 10 minutes before ProbSevere dissipated the tracking associated with the cells.  However, it continued to show flashes taking place for 7-minutes after the last CG was detected in the GLD data.  Good use for IDSS to let people know that cloud-to-ground strikes are still possible.

The storms initially were moving northwest along a boundary then deviated to the northeast as they strengthened.  As soon as the moved off the boundary...bye bye!

-Dusty

NUCAPS FCAST

Knowing that the NUCAPS FCAST information was in today for the first time this week, I decided to do some analysis of the fields. Initial thoughts are that the missing blocks of data (not sure if that is typical - more visible in the CAPE field in top image - similar data holes observed in LCL, LFC and EL) make it hard to have confidence in it at first glance.

CAPE (Top Image)
NUCAPS FCAST CAPE data isn't good in the pre-storm environment along the LA coast. RAP13 initialization is overlayed for comparison. RAP13 values are 2500-3500+ and much more representating thatn the NUCAPS values that in some cases are less than  500 ahead of the line.

CINH (Lower Image)
While these values appear to be more closely representative compared to the RAP13, the inability of the product to adequately represent the boundary layer at times during the week don't provide me much confidence for these surface based stability parameters.

-icafunnel

ProbSevere Helped to Hold Off On TOR Warning

Here is an example of a long lived supercell where the trends are very important to monitor. Notice the uptick in Prob TOR but then backed off.  AZShear has been impressive for several volume scans.  Prob TOR trends kept me from issuing a TOR warning, and provides some security in not issuing a warning along with other products.  As a side note,  it would be nice to sample some sort of maximum wind gust product, much like we get from MESH with the estimated max hail size.




ZDR_Arcophile

Warning Decision Influenced by ProbSevere

Since our shields have been engaged all afternoon I decided to look at a storm to our east. Below are a series of reflectivity images from the three lowest scans (0.5, 0.9, and 1.3)...







I won't lie to you, if I were back in my home CWA I would have probably issued a SVR based on these scans, but I decided to hold off on issuing one today to see how ProbSevere did.  So what did ProbSevere show? Here is a sample of various MRMS products overlaid with ProbSevere contours...


And here is a time series for this storm looked like...

These trends looked pretty impressive, with ProbHail peaking around 86%. The increase in probabilities make sense, with MESH peaking around 1.4 in (below in purple).


We will have to wait and see if my decision to not issue a SVR based on a ProbHail is justified, but based on the lack of any reports, I think it may have been a good call.

NUCAPS_Ahead of Line

NUCAPS data in advance of convective line today. Iberia County METAR station coincides with NUCAPS operational sounding (modified soundings not available today).



As you can see from the plotted NUCAPS sounding below, the surface values are too low. From the METAR in western Iberia County, you can see in the first image the the T/Td values are 81/76. Sounding surface values are 76/70. Other sounding points in the pre-storm environment are also about 5 degrees too low on temp and dew. While I can modify these, it doesn't give me confidence in an accurate representation of the boundary layer and on any day expected to be busy I'd likely use other products.

-icafunnel

Four Views of TPW

After making some adjustments to the color scaling, we're able to mix model and analysis products of TPW.   The GOM was mostly clear, while clouds covered most of the land.  A very moist airmass was onshore, the Hammond LA GPS site measured 2.25" of TPW.
The GFS and HRRR forecasts both indicated this maximum.  The All-Sky LAP also did well, although it's field is a reflection of the good GFS forecast.  The Merged TPW did not generate these very large purple values (> 2" of TPW) except in a very small area.  The polar orbiter TPW retrievals used in Merged TPW must not have sampled these large values to advect in.  The operational blended TPW (which relies heavily on GPS sites for the analysis over land) also showed a maximum.  This points to the possibility that including the surface GPS network into Merged TPW and All-Sky LAP might be a way to increase the precision of these analyses.

Cloud Mask from CIRA Merged TPW (blue = clear; yellow = cloudy)

[caption id="attachment_16647" align="alignnone" width="1422"]
Four Views of TPW along the Gulf Coast at 19 UTC 09 May 2019: Upper Left: CIRA Merged TPW: Upper Right: All-Sky LAP. Lower Left: GFS 6 hour forecast @ 18 Z, Lower Right: HRRR 1 hour forecast @ 19 Z.

Analyses and forecasts all agreed well on the drier air over the central GOM.

JohnF

Prob Severe New Cell Detection

Here's an example where Prob Severe was slow to detect a new cell on the southwest flank, which is a fairly typical severe scenario.  And when it finally does detect the cell, it is combined with the already large conglomeration of convection.



ZDR_Arcophile