TPW in a convective environment

Below is a comparison of two different TPW products (AllSkyLAP layer Precipitable water and Merged TPW Composite Sat Sfc Merged Total Precipitation Water) compared to RAP Analysis from the SPC Mesoanalyst page.

Control group: SPC Mesoanalysis Precipitable Water

The AllSkyLAP product (below) seems to do a better job at “painting the picture,” however, it’s reliance on the GFS model often leads to a delay in PWAT drops in areas of convection. This is highlighted the best across central IL, where RAP Analysis shows PWATs in the 1 – 1.25 inch range while the AllSkyLAP product shows values closer to the 1.5 inch range straight from GFS output.


TPW (below) does a better job at accounting for this, at least across the central IL study area, resulting in more realistic 1.1 to 1.3 inch values.

Tags: None

ILX Mesoscale Discussion

GOES_East Mesosector 2 Imagery (Band 2)

The effective surface cold front remains well north of Illinois, draped west to east across central Wisconsin as of the 22z surface analysis. Further south across the state, two main forcing mechanisms continue to play host to strong to severe convection. The first (southernmost boundary) is nearly stationary acting as the area of primary convergence, while also service as the dividing line between 70 degree dewpoints (south) and mid to upper 60s (north). The second is an outflow boundary loosely associated with earlier day convection, which continues to race southward driven largely by cold pool propagation. This boundary is anticipated to overtake the primary boundary over the next few hours, ushering the majority of shower and storm activity south of the Lincoln IL CWA later this evening (Showcased well by NUCAPS forecasts). With ample CAPE (1500 – 2500 J/KG per the 22z AllSkyLAP product) remaining along and south of said boundaries, storms are expected to retain their intensities through the early evening hours. Primary threats will remain damaging wind gusts, large hail, and flash flooding primarily in areas that see repeat thunderstorm convection this afternoon and evening.

—————————————————————————————————–Mountain Bone

Tags: None

ILX Upper-Air Sounding comparison to NUCAPS and Modified NUCAPS

Above is a special sounding released by the ILX office around 17z on June 5th, 2019. Below is the output for the NUCAPS and sequential Modified NUCAPS sounding from around the same time and as close to the same area as possible.

The NUCAPS pass pictured above was primarily in a cloud-free environment behind an old outflow boundary to its south and ahead of a developing line of convection to its north. Visually, it tended to underdue the CAPE values in the environment, especially in the low to mid levels.

The modified NUCAPS sounding (above) did show some skill in incorporating more accurate boundary layer conditions, which in turn, upped the CAPE values considerably (almost 2x in some cases). This brought the values into better agreement to the in-situ observation from NWS ILX with the exception of the SFC based CAPE which remained considerably underdone.

—————————————————————————————————Mountain Bone



Tags: None



(Top Left): GLM Event Density w/ ENTLN Lightning Data; (Top Right): MRMS -10C with ENTLN overlayed; (Bottom Left): GLM Minimum Flash Area; (Bottom Right): GLM Total Optical Energy

Had a unique opportunity to watch a line of strong to eventually severe storms ignite and strengthen rapidly along an old outflow boundary this afternoon using GLM data. It was interesting using the above 4 panel display to not only witness the ignition, but also the strengthening of each sequential cell along the line. By utilizing the GLM Minimum Flash Area (Bottom left) 1 minute imagery in a loop, we were able to sample the early-onset updraft core strengthening of each sequential cell along said line, and watch the event density jump up in accordance. It was also interesting to utilize the Prob-severe lightning jump data in time-series format to watch in a real-time basis. Suggested best practice would be to make these 4-panel layouts available for events like this.

All Three Meso Detection Algorithms Struggle to ID Lone Supercell

CPTI upper left, New MDA upper right, legacy MDA lower right, digital MD lower left.

A discrete supercell tracked out of the Oklahoma Panhandle into southwest Kansas from 2120Z to 2220Z on 5/23/19.  During the first portion of this loop, the mesocyclone detection algorithms had a very difficult time latching on to one dominant meso, plotting up to four separate IDs for the same storm.  Eventually, both the legacy and new meso algorithms resolved one primary circulation, while the digital version continued to jump around a bit with the ID number and location.  For the last 15 min. of this animation, the MDA data completely dropped out.  The main point here is it was nearly impossible to utilize this product operationally because of the meso identification and data dropout issues.  It’s worth a mention that the legacy and new MDAs had about a 15-20 min. window of good meso tracking after the consolidation to one ID and before the data was lost. -Roy

AllSkyLAP Resolves Dry Mid-Level Layer

An eastward moving plume of moisture and instability was clearly depicted in the GOES16-Merged GFS AllSkyLAP products.  Estimated MLCAPE in the lower left panel is similar to the SPC mesoanlaysis data.  Into central Pennsylvania, values were in the 500-700 J/kg range.  So certainly on the low end for severe weather potential in the State College CWA based on instability alone.  However, one interesting feature caught my eye in the 700-300mb AllSky PWAT analysis — a west-to-east band of low values advecting through Indiana and Ohio into western PA. This mid-level drying is attendant to the eastern periphery of an EML that originated over the southwest U.S.  A plume of warmer 700mb temperatures in the RAP analysis matches up well with this dry band of mid-level air.  With the chance for scattered convection later today in central PA, the influx of a dry mid-level layer may aid in the production of strong convective winds/downbursts. -Roy

GLM RGB first view…

So, here’s an interesting concept…GLM data merged with GOES-16 IR (10.3 um) to create an RGB.  I think I like it!  Data fusion concepts like this are increasingly important in data-heavy AWIPS, especially during severe weather events and for situational awareness activities.  So, this RGB uses Flash Extent Density as the Red component, Minimum Flash Area as the Green component, and 10.3 um imagery from GOES as the Blue component.  The RGB has been tailored such that high FED results in increased red values, while Minimum Flash Area is reversed with respect to green colors (lower values equal increased green) and the IR temperatures from the 10.3 um band are also reversed so that lower temperatures result in higher blue colors.  So, for example, the end result is that high FED, low minimum flash area and cold IR temperatures result in brighter colors (near white) that physically indicate intense lightning, collocated with intense updrafts and cold cloud tops.  Meanwhile, anvil-type lightning (cold cloud tops, generally low FED and high minimum flash area result in colors more towards purple.  Colors leaning towards reds, yellows are relatively young, but intense convection in new, warmer convective cloud tops.  This shows up well, watching young convection feeding into an area of ongoing convection at the tail end of the convective complex today.  Ok…I’m writing this at the tail end of activities today, so I had to rush through this.  =)


NUCAPS Soundings Observations…Finally a Swath Over our Area of Severe Weather…

Hi all,

Ok, just a couple of quick observations and comparison of a NUCAPS (direct broadcast) sounding with a modified sounding over an area of interest this afternoon.  The NUCAPS sounding locations and the particular sounding of interest can be seen in Image 1 below.

Image 1: NUCAPS Sounding locations near 20 UTC 20 May 2019.  The Direct Broadcast and Modified Soundings that appear in this analysis were taken from the location of the pointer (notice this is in the far SW portion of the High Risk in north Texas).

The next image below (image 2) shows the Direct Broadcast NUCAPS sounding valid ~2000 UTC 20 May 2019.   The sounding indicates high CAPE values at this sounding location (~2800 J/Kg MUCAPE, and 2400 J/Kg MLCAPE), and steep lapse rates aloft, in excess of 8 C/km.  This type of atmospheric profile would support severe weather in the area today.

Image 2:  DB Sounding taken in SW corner of High Risk (location shown at pointer above).

The next image is the modified sounding taken at the same location.  Notice the increased CAPE values…

Image 3: Modified NUCAPS sounding from the same location as above.  However, with the modified boundary layer, notice the higher overall CAPE values.

By the way, soundings in this general area, including the yellow soundings indicated high CAPEs with “reasonable” looking values.  However, there was a fairly significant gradient noticed in overall low-level instability noticed in soundings to the east of this location.  This could be a good case for the NUCAPS team to go back and take a further look.

-Kris W

NUCAPS swath…just a bit too far east…

So, hello from my initial post from HWT, here during the week of May 20th.  Yes, this is shaping up to be an active day and perhaps week.  Taking a first look at the NUCAPS soundings for this afternoon…and…the latest ~18 UTC swath is just a bit too far east to be of a lot of use here in the primary action area for severe convection.  Notice in the first image the SPC Outlooks (High Risk area nearly entirely to the west of the soundings).   Nevertheless, I’ll take a look at the next swath to see the coverage over the main area of expected severe weather.

Image: Day One Convective Outlook (from SPC), NUCAPS Improved Latency soundings (~1817 UTC), and GOES-16 Vis (0.64 um).

-Kris W