Pocatello Storms

We’re currently monitoring conditions in eastern Idaho. Right now I’m using various applications to analyze and initialize current conditions. Currently AllSky is showing cape around 1000kj, and PWATS around .80 inches.

That PWAT value on the morning sounding just west of the area was close to .64″. Seeing how moisture levels are lower to west I can interpolate that the moisture values are similar to what’s show on allsky. The allsky 900-700mb also seems to pick up on the relatively moist area in the lower half of the atmosphere.

Looking downstream we’re noticing a line of developing convection using the Day land cloud RGB. It’s helpful to analyze just how high the tops of the storms are getting combined with cloud tops.

Zooming in closer I can examine the few storms that have popped up more closely. The RBG help the differentiate between the ambient cirrus clouds from the growing storms. That might not have been as easy to see using a typical visible view.

The AFA and Minimum flash area maximums are hinting at growing convection just downwind.  That growth leads to me to anticipate further intensification as these storms move into a more favorable environment in eastern Idaho.

As storms begin to intensify probsever eis picking up on the strongest activity. Probsevere began to ramp up for the cell just south pf Pocatella. That combined with traditional radar methods lead me to issues a warning for that cell.

A similar situation unfolded with a south just south of CWA that I debated on warning. The probsevere values did show and uptick. Eventually the storm fell apart as it pushed into southern Idaho.

We’re watching a few cells in the southern half of the viewing area.  As NUCAPS comes in I’m comparing it the allsky cape. The allsky cape is around 1100kj.

The modified sounding is putting out about 700kj of ml cape. While the nonmodified is much lower down to 500kj.

We don’t have a midday sounding to see which one is initializing the best. For what it’s worth. The rap cape output is around 500kj.

The TPW was close to the observed pwats as well. It was outputting about .65″.

The FED has been fairly low this afternoon which isn’t typical for what I have been usually see. However, the AFA and the MFA are higher indicative of growing updrafts. I’m thinking the FED might be lower because of potential hail in the updraft.

The cell pushing out of Freemont county Idaho continues to intensify as it pushed into Montana. Both the MD, and NMDA were picking up on a high meso that was clearly seen on SRM.

 

The CPTI was showing high probabilities as well.  I still wasn’t as concerned about a tornado threat due to how high the base of the storm was. It was interesting to see though.

The forecast cape and cin values came in from the NUCAPS,  but it wasn’t usable for my area because their was a lot of missing data.

The actual Pocatella office issued a warning for Freemont county. Using typical radar methods the storm didn’t look like it warranted a severe thunderstorm warning, but satellite and MFA showed new convection was still firing up. Right after looking at satellite there was a report of a 54mph wind gusts.

 

EWX Mesoscale Discussion

AllSky_LAP ML CAPE Forecast as of 1930z

19z Surface analysis shows the nearly stationary effective dryline boundary draped SW to NE across the CWA from roughly Del Rio through Briggs, TX. This boundary continues to play epicenter for semi-discrete super-cellular development this afternoon, with additional cold pool driven activity likely to form over the next few hours, especially as a back door cold front begins to slide southward through south-central TX. Latest AllSkyLAP CAPE analysis shows destabilization continues southeast of the dryline, with ML CAPE values nearing 3000 J/KG in and around San Antonio as of 19z. TPW values also remain relatively high southeast of the boundary, with 1.5 to 1.75 inch readings common place. Mid to upper-level kinematics remain favorable for some supercellular structures, so we’ll continue to  keep large hail, damaging winds, and an isolated tornado threat in the forecast. Best chance for seeing a tornado (even with relatively week 0-1km shear values) will likely be through 7pm tonight in a cells that can remain discrete for awhile. Flash flooding concerns will continue thanks to the abnormally high PWAT values, especially in areas that see several rounds of convection this afternoon and evening.

—————————————————————————————————-Mountain Bone

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Lightning over the Mountains

Having the different lightning products from GLM as well as data from ENTLN allows you to pick out which cells have started producing lightning.  One flash up in northern WY on this image, the dot in the upper left, did show up in the FED data a couple minutes later.

Charley

Modified Sounding for RIW

Modified the RIW 12Z sounding for low 70s over around 40 in the southwest WY area, and got an MUCAPE of 655 over  A little higher than what AllSky is showing there…

…around 200 in the image above.

Charley

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ProbSevere Values Affected by Shape/Size of Polygon

The following series of images shows the change in ProbHail/ProbWind values based on the size/shape of the polygon area. Initially, at 1806Z, ProbSevere was targeting the stronger cell to the south, indicating Hail/Wind 78%/85%. (At this point V was indicating around 20kt). At 1818Z, the northern cell intensified and ProbSevere grouped the two cells together, as a result, Hail/Wind both fell to 42%/61%. At 1827Z, after the southern cell split, the ProbSevere polygone became more filled with deep convection, thus Hail/Wind values increased to 59%/71%. Soon after, around 1834Z, ProbSevere polygons split and then indicated increased probs on the southern cell back to 69%/75% (Hail/Wind).

Incidentally, the larger the polygon, it becomes increasingly likely that ProbSevere values will decrease.

 

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Western Wyoming Cell Developing

IR imagery showing a taller/colder cell in western Wyoming.  KRIW radar just switched from VCP 35 to 12.  Peak Z aloft now only around 30.  Lightning data, below, shows relatively low FED, but higher TOE, with peak values in the 300’s, similar to some of the storms we saw yesterday.

One other thing to note in these, is the relatively low FED and number of ENTLN/NLDN flashes.  That doesn’t mesh with the brightness of the TOE.

Charley

Suggested Hail 4-Panel Procedure

This is a 4-panel display that I find very useful with respect to hail potential monitoring in a convective environment. By incorporating Prob-Hail and/or GLM, along with MRMS Isothermal reflectivity, a forecaster can really get a good feel for hail potential within cells. Due to up to 2 minute latency within MRMS products, would not recommend as a substitute for All-Tilts methodology, but certainly could be used for situational awareness.

Top Left: MRMS_1000 0.5 km MSL Isotherm Reflectivity at 0*C

Top Right: MRMS_1000 0.5 km MSL Isotherm Reflectivity at -10*C with blinking ENTLN C-G and C-C Flashes (Could substitute GLM data here also).

Bottom Left: MRMS_1000 0.5 km MSL Isotherm Reflectivity at -10*C with ProbHail Model output

Bottom Right: MRMS VII or legacy VIL.

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

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Derived Products Comparison

Merged TPW, image above showing an area of higher TPW, 0.5-0.6 in PIH’s area, with values of 0.25-0.4 more over RIW.  AllSky product shows a little more variation, with a drier airmass, 0.15-0.25 inches moistening up over the course of a few hours, over the western border to 0.5″.  Also seeing those values in the far eastern part of RIW’s area.

Total Totals are ramping up over time in the AllSky product, from around 40 to a more severe 55. LI’s also are going negative.  K index also going for some storm activity, getting to the mid 30s.  CAPE’s are higher over PIH, but likewise rising across the region…with a similar max in the eastern RIW area.

Charley

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Storms tracking toward St. Louis

A line of storms is north of St. Louis as of 630 pm CDT and is tracking southward toward an area of increased CAPE per All Sky LAP product.  This convection continues to trigger along the leading outflow.  The overall environment has limited shear so it is primarily cold pool driven.  ProbWind has consistently displayed around 65-78% since around 600 pm CDT.

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