Large CAPE Spread Between AllSkyLAP & NUCAPS

Satellite loops showed a diminishing CU field across SJT CWA and surface dew points have been decreasing. AllSkyLAP CAPE has been diminishing over the past couple of hours, but was still near 1500 J/kg. A NUCAPS sounding (Improved Latency) around the same time had CAPE values well under 1000 J/kg and a distinct cap. The CAPE values over the past couple of days have been closer on AllSkyLAP & NUCAPS, and the NUCAPS values have typically been higher. NUCAPS  appears to be picking up stability changes more quickly than AllSkyLAP in this case.

1929Z AllSkyLAP CAPE with NUCAPS sounding point overlay

1941Z NUCAPS Improved Latency Sounding (North-central portion of SJT CWA)

Alex Brown

ProbSevere Color Table

The ProbSevere model color table doesn't make it easy to discriminate between very low probabilities and medium-high probabilities. With both ends having something of a purple/pink color, I had to look at the included table to determine where it fell on the scale. The high end of the table looks fine, but I think the lower end could use some modifications.

Fig 1. ProbSevere model overlayed on MRMS RALA product.

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Afternoon Forecast Thoughts for SJT

Quiet conditions are ongoing across SJT forecast area as of 20Z. Surface temperatures have climbed to near 90F, with accompanying dew points in the mid-upper 50s. Current CAPE values per AllSky LAP imagery are approaching 1500 J/kg which is in line with short-range guidance (these values were a few hundred J/kb higher than derived GOES CAPE).  Temperatures are forecast to climb into the mid 90s over the next couple of hours, which will help push CAPE values over 2000 J/kg. This should be sufficient to initiate convection, along with the arrival of a weak upper-level impulse and an increase in bulk shear values up to 35 kts.

Mostly clear skies at 20Z with weak West/East boundary across southern CWA

AllSky LAP CAPE near 19Z (1000-1500 J/kb over CWA)

AllSky LAP PW 4 Panel showing ample low-mid level moisture

Alex Brown

GOES/All-Sky Instability Images

The 4-panel loop below shows some of GOES/All-Sky LAP stability product, from about 1630z to 1900z. Much of this data comes from the GFS, which generally blends pretty well with the GOES data, but sometimes you can see the "seams". There is an area of relative stability around the MCV over eastern OK, and a nose of relative instability pushing into southern AR.  A.Cope

Forecast 5/16/18

An MCV from overnight convection is located over northeast OK and will drift eastward over the Ozarks later this afternoon. Moderate instability is observed over much of AR with AllSkyLAP CAPE values on the order of 1000-1500 J/kg.  The 12z raob from LZK indicated a fair amount of instability aloft, aided by relatively steep lapse rates from near 700mb through approx 550 mb. The AllSkyLAP PWAT was ~1.3" at 12z which compared very nicely to the 1.33" observed by the raob. Relatively dry air was observed aloft per the AllSkyLAP 0.7-0.3 sigma PWAT.  MLCAPE is progged to increase to around 2000 J/kg this afternoon with a DCAPE just over 1000 J/kg.

Fig 1. Split Water Vapor depicting MCV over northeast OK.

Fig 2. MCV evident in the high-level water vapor imagery.

Storms are ongoing over the Ozarks, but are expected to increase in coverage across the state throughout the afternoon in the weakley capped, low-shear environment. Shear will be limited today given the overall weak synoptic flow and vicinity of the aforementioned MCV. In general, anticipate strong to marginally severe, pulse ordinary cells but a few multicellular clusters are possible should storms develop strong enough cold pools. The primary hazards will be hail up to 1 inch in diamter and localized damaging winds.

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All Sky Layered PW

The first 4-panel below shows the GOES layered PWAT products for AR and vicinity. Upper left is total PW, upper right is Sfc-900 mb, lower left is 900-700mb, and lower right is 700-300 mb. (These are actually sigma levels, e.g., .7 to .3)  The latter shows deeper moisture around the MCV over eastern OK and extending into west AR, with drier air aloft farther east. Perhaps a more favorable environment for deep convection and/or heavier rain.

The next image below is the same except for the upper left panel, which shows the GOES derived-product total PWAT. Note there is a lot of blank area or missing data due to cloud cover. In the first image above, these gaps are filled in with data from the latest GFS, to make a smoother and more complete product. Where both sources have data, the values are similar but not exactly the same.

Starting Day3 at LZK

Today, Wednesday May 16, we are "located" at WFO Little Rock (LZK). As of 18Z temps have risen to the mid 80s with dewpts in the mid 60s. MLCAPE is about 1500 to 2000 J/kg. Wind fields are not particularly strong but dynamics are a little stronger due to an MCV moving slowly southeast toward our area from eastern OK. About the western half of the CWA is in a marginal risk area according to SPC.  Showers and a few t-storms have begun to develop over this area but nothing severe yet. A.Cope

Week 3 Day 3 Operations

We will be operating today in the Little Rock, AR and San Angelo, TX CWAs. An MCV is currently moving across Eastern Oklahoma and should spawn some thunderstorms across Arkansas throughout the afternoon with a marginal chance for severe weather. A few storms are also anticipated to develop in west Texas later this afternoon/evening with an opportunity for some severe hail or damaging wind gusts. The overall environment is pretty marginal today.

-Michael

Day 2 Wrap Up and Feedback

Below is the feedback from yesterday provide in this morning's debrief:

NUCAPS

Modified NUCAPS did a pretty good job capturing the surface correction and gave a pretty good

representation of the environment

Liked looking at the gridded lapse rates

There were some gaps in the data the last two days

Gridded CAPE is confusing and doesn’t calculate well

Would rather have some sort of SBCAPE or MLCAPE calculation instead of from pressure levels

It would also probably be better to use the modified soundings especially for CAPE calculations in the
gridded data

Soundings captured the gradient in CAPE values in the Lubbock CWA and predicting how the
convection can evolve

Like having any sounding outside of the normal hours is a good thing

All-Sky LAP

Showed a very distinct moisture boundary in west Texas and delineated between the storms that were
struggling and the ones that took off

The all-sky was extremely important with all of the cloud cover in the northeast, the baseline GOES
were not useful with all of the cloud cover

Having the layered feature is very helpful to see the levels of moisture

Able to distinguish the EML with the upper level layered product in west Texas

Again would be helpful to have maybe a CONUS grid using RAP instead of GFS for better updates.

CI

The highest probabilities weren’t really near where the storms were developing

It would flash spurious higher values for one scan and then go away

The severe CI would spike the most it seemed like

It’s hard to have much confidence in the values when they are jumping around so much

Would want to see a consistent trend in the values to have confidence in the product

Didn’t seem to pick up on any of the storms developing over Virginia

Did seem to do well at the southern end of the squall line in Pennsylvania

GLM

The 2 minute data was helpful in showing a more recent trend and not having the older data hold on
longer can age the data a little more than the 2 minute

Have found the most use out of the flash extent density and flash area. The total energy is also good at
bringing the two together and looking at where the flashes are coming from in the storm

Still a question on whether some type of smoothing should be done to make it a little more pleasing to
the eye but could lose some of the maximum values

The lightning data pulsing within the squall line helped draw attention to the cells that were intensifying

The tracking meteogram actually worked pretty well at showing trends in the flash extent density

The data has more value when you can see the trends

ProbSevere

Came up with some really high values on wind and tor yesterday which was good to see with it being
more calibrated for the different hazards

The first day I thought that the combined was the best, but found the separated hazard models to be
more valuable when looking for the different hazards

It’s especially useful when looking at the Tor

Think it is worth having them separate even in a WFO environment when working warnings

Still trying to figure out the best way to display it

Tried running it on MRMS products instead of base data as it covers up some of the data

Use more on a broad view of data and not on the pane used for interrogation

New Cell and Lightning Trend

I watched a new cell develop over southern NJ.  The main reason this cell stood out was because of a significant increase in Flast Extent Density.  This increase really drew my eye to that part of the line where a cell was rapidly intensifying. 

Fig 1. Flash Extent Density increased rapidly.

Fig 2. Corresponding new cell growth. Note cell in center of image.

This was just another example of the GLM data providing a good overview for situational awareness.

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