Analyzing Mid Level Lapse Rates Between NUCAPS and Model Guidance

Posted in NUCAPS, SPG2023 on by Kevin Thiel.

Mid-level lapse rates are important in judging instability when combined with boundary layer moisture content in the lower levels. With boundary layer moisture being poor for much of the MAF CWA today, the low to mid level temperature profile may be even more important, as it will define both convective inhibition and CAPE potential with a greater potential for inhibition with such a dry moisture profile. The convective forecast in MAF for the day featured generally weak forcing mechanisms, focused on orographic lift and a moisture gradient on the eastern side of the CWA. With any sort of convective inhibition, it would be difficult to forecast convective initiation away from the strongest forcing points until later in the day when convection is forecast to move in from outside the CWA.

Shown below is the SPC mesoanalysis page depicting this afternoon’s 700-500mb lapse rates. The RAP guidance driving this page is showing very steep mid-level lapse rates of 8 to near 9.5 degrees/km over the MAF CWA. While steep mid-level lapse rates (indicative of cooler temperatures atop a warmer lower level air mass) are important for instability, very steep mid-level lapse rates could be due to a very warm low level air mass potentially creating a convective “cap” which may inhibit convection. With the very low surface dew points (into the 30s in some spots), a mid-level lapse rate exceeding 8.5 should mean convection struggles to initiate outside of areas of strong forcing.

Looking at the afternoon NUCAPS satellite pass, it shows a fairly different picture for mid-level lapse rates over the MAF CWA. The observed lapse rates of 7 to near 8 degrees here are more normal for a convectively active environment compared to the 8.5 to near 9.5 degrees given by the RAP guidance.  It’s worth looking into how NUCAPS and guidance is handling temperatures at different levels to understand the differences between the lapse rates.

Shown below are both the NUCAPS sounding (first) and then the RAP sounding for a similar spot near the center of the MAF CWA. It’s interesting to note that it isn’t actually the 700mb temperature that is the main difference between the two soundings, but the 500mb temperature, with a 2-3 degree difference at 500mb. This could explain why there is still convection away from the previously discussed initiation points (such as out in the Fort Stockton area), however the warmer than forecast 500mb temperatures could be indicative of an environment that isn’t quite as unstable as forecast, and why the central MAF convection is notably weaker than convection well to the north in the Lubbock CWA. There are other contributing factors of course (weak surface convergence, very dry low to mid levels), but this is a major factor in judging updraft strength potential, and today lines up with where updrafts have develop but struggled to truly develop into strong or severe thunderstorms. The late afternoon Day Cloud Phase Satellite product shown below includes the non-severe convection in the south-central portions of the MAF CWA with the severe convection to the north (and their noticeably better defined anvil clouds).

One quick screenshot to show is the NUCAPS LCL product, highlighting the better moisture on the eastern and northeastern edge of the CWA, lining up with the higher SPC risk.

-Joaq

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Satellite HWT Day 1 Analysis Carl

Posted in NUCAPS, OCTANE Speed Sandwich, PHSnMWnABI, ProbSevere, SPG2023 on by Kevin Thiel.

PHS Model Analysis

PHS model struggled to properly capture convective initiation within the Texas Panhandle on the day. While it did see a few cells possibly starting, overall coverage was significantly underdone with many of these storms reaching severe thresholds including numerous reports of hail over 1″. The overall output shared many of the same struggles as the HRRR model on the day. Unclear what the exact problem was, but dry line convergence may have been better than in models on this day.

Above: 15Z PHS model output forecast for 17Z to 22Z from 5/22 with MRMS Reflectivity overlaid.

Below: 15Z PHS model output for 17Z to 22Z from 5/22.

NUCAPS Forecast

As I was beginning to test out these products, this caught my eye as a forecaster on the east coast that regularly deals with Cold Air Damming along the Appalachians. Models regularly struggle with multiple aspects of the dam, including extent, depth, and actual temperature and strength. Additionally, one of the most common pathways for large winter storms in the southeast is when low pressure passes across the Gulf Coast and into the Atlantic while an Arctic high in the northeast helps drive cold air damming into the area. Models again struggle with the dam, but also with strength of the warm nose aloft. I would love to see how this system performs in these scenarios – I know it isn’t “convective”, but it still is an incredibly impactful event, where the strength of the warm nose can be the difference between a few inches of snow or half an inch or more of ice. We regularly attempt to send up special soundings to get the best sample we can, but since GSP does not do a sounding, we rarely get a meaningful sample of the cold air damming in the SE states.

Above: NUCAPS Forecast from morning pass over east coast showing CAD feature over the east coast.

Octane Speed and Direction

Above: Octane image around 22Z for storm just south of AMA.

The Octane product was extremely useful in seeing when updrafts were really “taking off” and hitting the tropopause, immediately highlighting storms which require quick attention. Another extremely useful feature is sampling the actual speed, which gave a potential proxy for storm top divergence. Noticed that the Octane product gave a value around half of what the radar was measuring on this storm – ~50 kts on the Octane product vs ~100-110 kts on the radar. I’m assuming the resolution combined with some of the smoothing within the algorithm may be playing a role here, but it would be interesting to see if there is a consistent way to match the two up, even if there is just a “rule of thumb” or something. This would be huge in areas of sparse radar coverage (portions of the west or the ocean, for example).

Below: Radar image of storm top divergence near 22Z from KAMA.

ProbSevere v3

Noticed an interesting time period where two close updrafts – one fading, one picking up, resulted in some jumping of the ProbSevere product as it would sometimes combine the objects and then sometimes track them separately. I think this shows the importance of pairing the algorithm with analysis – just looking at the time series of the product could lead to misinterpretation of what was happening.

-Carl Coriolis

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ProbSevere_V3 Captures Hail

Posted in HWT, ProbSevere, SPG2023 on by Kevin Thiel.

Severe storms developed over Hale County, TX on the afternoon of 5/22.  KLBB 0.5 Z reflectivity at 2109Z (top left image) indicated intense convection, especially just southeast of Hale Center.  ProbSevere V3 (the 4-Panel) did well at 2108Z.  The upper left has the ProbSevere Model at 84% with the MRMS 0.5 Comp Reflectivity peak value of 66 dBZ.  The upper right has ProbHail at 85% and MRMS Maximum Estimated Hail Size (MESH) peaking at 1.85″.  The lower right has ProbTor at 12% and MRMS Low-Level Rotation Tracks.  The lower left has ProbWind at 35% and MRMS Vertically Integrated Liquid (VIL) at 55.  Notice how the ProbSevere Time Series ProbHail was at 60% at 2020Z, nearly an hour before this.  What happened?  Here is the LSR…

SSW PLAINVIEW Hail Report
County, State: HALE, TX
(marker location is approximate)
Lat.: 34.12, Lon.: -101.76
Time: 2023-05-22 21:09 UTC
Hail Size: 1.75 IN. DIA.

HAIL FELL ALONG I-27 BETWEEN HALE CENTER AND PLANVIEW (LUB)

Since forecasters should consider warning with lower ProbSevere values for V3 compared to V2, these high values supported a warning.

-Champion

 

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Monitoring Storm Evolution Via ProbSevere & Octane Speed/Direction

Posted in OCTANE Speed Sandwich, ProbSevere, SPG2023 on by Kevin Thiel.

This video shows a storm’s evolution as it moves into far SW Lamb County just before 21Z. The upper left hand shows the Octane Speed product…the upper right shows the Octane Direction product…the lower left is the GOES-16 Ch. 13 Clean Window IR Band…the lower right is the Day Cloud Phase Distinction RGB product.

Looking at the Octane Speed product, as this storm is initially growing,  the cloud top features moderate cloud top divergence with the variation in Octane Speed (as the greens and yellows nearby). The storm evolution then plateaus and eventually diminishes in intensity, shown as the cloud top speed becomes more consistent (with the loss of the yellow colors). The Octane Direction product shows a southerly component to the direction across the north of the storm with a westerly component along the southern side of the cloud top. At the end of the loop you can see the yellow (the southerly component) begin to disappear as the loss of cloud top divergence causes the direction to change from the motion of the divergence to the environmental westerly component. Below is an image showing the storm’s trends via the ProbSevere Time Series (storm location now just NNW of Anton). Though the ProbSevere values will lag behind the satellite imagery, one can note the storm’s gradual increase in ProbSevere values with the “warming” colors of the Octane Speed product. The values then also level off, before dropping off as the cloud tops become more consistent.

Joaq & Bubbles

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Octane Speed/Direction Severe vs Normal Thunderstorm

Posted in OCTANE Speed Sandwich, SPG2023 on by Kevin Thiel.
If we look at the top two panels you will see a line of storms. The northern storms have small differences in wind and speed difference (green/light blue for speed and yellow and green for direction). However one of the thunderstorms to the south stick out. It has must stronger difference in wind speed (3m/s vs 16m/s) and direction (180 degrees vs 280 degrees). At the time of this image only the southern storm was severe while the northern storms were below severe.  I feel this is a great example to see how you can use OCTANE flow to spot the strongest storm in a line of developing storms. 

 

-Thunderstruck

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GLM and Lightning Cast

Posted in GLM, LightningCast, ProbSevere, SPG2022 on by Kevin Thiel.

The GLM parallax showed up again Thursday, June 16th, over the PBZ area. This was even more evident than yesterday’s event in WI that was written about in a blog post.  Figure 1 has ProbSevere, LightningCast, GLM Flash Extent Density, and ENTLN data overlaid in a 4-panel.  This case was fairly simple to “self correct” the parallax as the GLM was clearly displaced to the north of ProbSevere (as well as the base reflectivity).  Really once you get a few cases under your belt recognizing the parallax, it’s not too challenging to keep that “self correct” in the back of your mind.  One interesting thing to note about Figure 1 is the storm just outside the PBZ CWA just south of Mount Veron, Ohio (See bottom left in Figure 1).  The ProbSevere and GLM FED are lined up perfectly and this is a great example of utilizing the lower threshold in the colormap. The bullseye shows up much nicer than the larger thresholds in the top two images.

Figure 1: GLM with ProbSevere and LightningCast

– Podium

What’s the best way to look at NUCAPS?

Posted in NUCAPS, SPG2022 on by Kevin Thiel.

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

ProbSevere V3 Adjusting During New Cell Formation

Posted in ProbSevere, SPG2022 on by Kevin Thiel.

ProbSevere V3 has been showing much improvement over version two, with this particular day featuring somewhat pusley mixed-mode storms across upstate New York. This particular group of cells had habitual new updraft development, with storms nearing or briefly becoming severe as high dBZ cores develop aloof then make their way downward. These particular cells were able to form 1.00” hail. The ProbSevere V3 time series reflected the marginally severe nature of these storms very well, with values peaking at 60 to 65%. The very encouraging sign was the peaks and valleys in the ProbSevere V3 time series that showed this group of cells peaking at over 50% severe probabilities, dipping below 50% as the new updraft takes over, and then once again peaking above 50% once the new updraft strengthened. I’d definitely recommend forecasters to take a look at the timeseries to build confidence in cell trends during warning applications.

Shown above is the group of cells, with the initial one showing a core of 60+ dBZ that begins to drift off to the northwest while a newer updraft takes over and moves more east-northeast.

– aerobeaver

ProbSevere Time Series

Posted in ProbSevere, SPG2022 on by Kevin Thiel.

I utilized the ProbSevere Time Series in warning operations today (June 16, 2022) within the Pittsburgh, PA CWA.  With only using basic radar products and no other products  (that I’d normally use during warning operations), it was extremely helpful in warning decision making.  After issuing several warnings already and monitoring a storm quickly developing in the western portions of the CWA that was getting close to severe, I issued a warning based on an uptick in the ProbSevere Time Series (See Figure 1 vs Figure 2).  The uptick in ProbHail occurred within about 5-6 minutes or roughly 2 radar scans of the PBZ WSR-88D prompted a warning.  The storm continued for several minutes and regenerated about 30 minutes later that prompted another warning downstream (See Figure 3).

Figure 1: ProbSevere Time Series at 2056z

Figure 2: ProbSevere Time Series at 2100z

Figure 3: ProbSevere Time Series Plots.

– Podium