Quiet until later…maybe

Upper level analysis has large ridge over the central CONUS with trof digging into the Southwest. Skies are partly cloudy with mid level cumulus streaming across the area. At the surface…above average temps are in place with dryline nearly bisecting the CWA. Dewpoints are in the 60s across eastern portions of the forecast area…with dewpoints in the teens and 20s in far northwest OK. Moisture across the eastern zones is very shallow, as indicated by OUN sounding.

Southerly boundary layer flow will continue to transport moisture into the area. Nearcast Low level Theta E increases across the area around 00z with cap weakening a bit across far southwest portions of the CWA.

In addition…Nearcast mid level Water Vapor increases across southern portions of the area after 00Z will help to weaken the cap.

Water vapor imagery depicting weak shortwave moving into western Texas…moving northeast at 45 knots. This shortwave will enter the far southwest corner of the CWA between 2Z and 3Z. With a weak cap still in place…surface based convection is not expected…but elevated convection will be possible.

Both RAP and NAM also showing this weak shortwave at 500mb and 700mb over southwestern areas by mid evening.

So 55 dBz will be possible across the far southwest OUN CWA before 3Z.

Scott Rudge.

Update 23Z…Convection firing in Abiline’s area.

Convection has initiated just ahead of the dryline just east of Abiline, TX. Convective Initiation probs show high probability of severe wx, but upper level jet has proceeded to shear the tops off of these storms within a matter of 30 minutes.

Scott Rudge.

Update 2330Z…60+ dBz just south of the OUN CWA.

A storm that formed along a boundary just ahead of the dryline is showing some promise. Prob severe increased to 77% before levelling off – with estimated hail size around an inch.

Scott Rudge.

Storms in Wyoming

Isolated severe storms near NE of Riverton, at least identified by Prob severe model, continue to weaken this afternoon.  Strongest cell is between Lost Cabin and Hiland.  Latest GOES vertical theta-e diff indicates better instability over northeast Wyoming.  A few light returns are increasing across southeast WY and several ensembles members develop convection across this region around 23z.  CI product not very useful at this time in SE WY.

BT

WY convection this PM

Monitoring eastern WY, western NE in an area outlooked for the possibility for some severe storms.

Was going to provide an outlook concerning the pros/cons concerning getting convection to launch…but storms developed in central WY that are headed east.

A severe storm developed…Probsevere was all over it.  CI was not a very useful tool as this developed due to quite a bit of cirrus

Also for the first time today saw an overshooting top.  It did display on the already severe storm.  Interesting is the fact that we need to mentally adjust to the parallax between this product and actual radar truth.  Products will not match up lat/lon to lat/lon!—db

Update 2115Z:  storm still strong with possible severe hail…but has shown some weakening.  Overshooting top detection is no longer pinpointing anything,  Storm does continue to travel along a maximum in instability as seen in the vertical theta-e differences.  Interesting is that, while the forecast keeps that general instability around and along a path to the northeast of this storm, the Nearcast model also brings the highest instability back through to the west of where these storms are occurring.  Meaning current convection would be moving from higher to lower instability, relatively speaking—db

Riverton, Wyoming Severe Thunderstorm Warning

Widely scattered convection was developing over central Wyoming Tuesday afternoon, aided by up slope flow and strong southwesterly winds aloft.  The NOAA/CIMSS ProbSevere model indicated a 71% probability of the storm over northern Fremont county Wyoming to produce severe weather in following 60 minutes (Figure 1) at 1956 UTC 6 May 2014.  The probability continued to increase as the radar estimated intensity correspondingly increased.  The NWS in Riverton, WY issued a severe thunderstorm warning on this storm at 2013 UTC 6 May 2014.  The ProbSevere model could have been used to potentially increase lead-time on the issuance of a severe thunderstorm warning.  The storms that warranted a severe thunderstorm warning have since weakened, the largest reported hail size was 0.75".

Figure 1. NOAA/CIMSS ProbSevere and KRIW 0.5 degree reflectivity valid 1956 UTC 6 May 2014.

-Sieglaff

EWP Big Spring Day 2: 6 May 2014

We chose to sectorize the forecasters to two different regions…  Cheyenne, WY for Thoren/Bickford and Norman, OK for Rudge / Maples.

The forecasters have been asked to provide a mesosale forecast/graphicast discussion for each region (on the blog) by 2100 UTC.

The Wyoming group overlaps a bit with the forecast area of the EFP for day 1:

Though current convection is located farther westward in mountainous terrain.

Meanwhile the OK group is watching mixing in central and western Oklahoma:

Nothing severe at the moment, but some interesting features including virga / mammatus visible at the same time:

Expectation for severe weather increase Wed / Thurs for the experiment.

-K. Calhoun, Week 1 Coordinator

Virginia Nocturnal Hailer

Late Monday evening more thunderstorms developed over portions of southeastern Virginia.  The environment was marginal; ~600 J/kg of MUCAPE and ~35 kts of effective bulk shear.  By 0216 UTC 6 May 2014, the developing storm near Sussex county, VA had moderate MRMS MESH values (~0.85 inches).  The moderate MESH and environmental fields yielded a 31% ProbSevere probability (Figure 1).  Four minutes later, at 0220 UTC, the GOES scan from 0215 UTC captured both strong normalized vertical growth rate and strong glaciation rates associated with this storm, which caused the ProbSevere output to jump to 79%--demonstrating the value of satellite growth rates!  The probabilities continued to increase as the radar storm intensity increased.  The NWS issued a severe thunderstorm warning for this storm at 0241 UTC (21 minutes after the first ProbSevere value in excess of 50%) and first severe hail report was received at 0238 UTC (18 minutes after the first ProbSevere > 50%).  (For a more detailed analysis of GOES-EAST imagery for this event check out the CIMSS Satellite Blog!)

Figure 1.  Animation of NOAA/CIMSS ProbSevere and MRMS composite reflectivity valid 0216 - 0242 6 May 2014. 

Additionally there were storms further east from the storm described above.  These storms also exhibited ProbSevere values in excess of 50%.  These storms had similar GOES inferred vertical growth rates and glaciation rates and similar MRMS MESH values, however these storms were not warned nor were associated with severe reports.  This example demonstrates key points made in the NOAA/CIMSS ProbSevere training--the model skill is comparable, yet lower than an experienced forecaster, but often provides additional lead-time.   One also wonders given the late evening timing of these additional storms if severe hail occurred but was never reported.

-Sieglaff/Cintineo

ProbSevere in Montana

The generally quiet weather continued over much of the US on Monday.  Isolated convection developed over Montana in an environment marginally supportive for severe thunderstorms.  The SPC outlook probabilities for severe wind and hail were both less than 5% over much of Montana.  The NOAA/CIMSS ProbSevere model had probabilities in the 20-40% range from ~2220 UTC onward for a developing storm and then jumped over 50% at 2250 UTC (Figure 1).  The NWS office in Billings issued a severe thunderstorm warning for this cell at 2253 UTC.  The ProbSevere model probabilities continued to increase (to near 80% at 2310 UTC, Figure 2) as the radar estimated storm intensity increased.  The first severe hail report associated with this storm was received at 2335 UTC (1.00"; 1 mile SW Hardin, MT)--good lead-time for both the ProbSevere model and NWS warning.

Figure 1.  NOAA/CIMSS ProbSevere contours valid at 2250 UTC 5 May 2014 (no radar was displayed as the HWT radar domain was being shifted to encompass these storms.)

Figure 2.  NOAA/CIMSS ProbSevere and MRMS composite reflectivity at 2310 UTC 5 May 2014.  The ProbSevere output continued to increase to near 80% as the radar intensity increased.

-------UPDATE-----

Further west at 2328 UTC 5 May 2014, the ProbSevere model produced probability of 50% on a storm near Laurel, MT (Figure 3).  The storm continued to evolve with probabilities between 50 and 60%.  The storm was not warned, but a severe hail report (1.00" 2 miles S Laurel, MT) was received at 2341 UTC--13 minutes after the initial probability in excess of 50%.

Figure 3.  NOAA/CIMSS ProbSevere output and MRMS composite reflectivity highlighting the western storm near Laurel, MT valid at 2328 UTC 5 May 2014.

-Sieglaff

Nearcast Convection

I had been scouring through some of the satellite and radar images in East Central Wyoming. WV/IR was showing some of the higher cloud tops through Southeast Wyoming. At one point a small area was depicted on the OTD. At this time, there was no activity on radar through southeast Wyoming.

On visible satellite, clouds began to develop in East Central Wyoming. This is where some of the first radar returns were coming in at 40+ dbz. When referring to the Nearcast the vertical Theta-e Diff was showing as much as -10.6K. It was on the edge of this difference (gradient) where convection was taking place, as seen below.

-Forecaster

CI Hit in TN…no storms

21:45 Z…had an area of 60% CI in NE TN (Claiborne Co.) on Cu developing in conjunction with a little disturbance and perhaps some outflow from convection farther west.  No storms an hour later.  A reminder to use these tools in conjunction with all your other tools and be aware of the overall set-up.   Minima in theta-e and precip. water were trending that direction as well.

-Forecaster

Surface Convective Initiation Application

The CI product is deemed most useful leading up to a severe weather event. As intended, it seems that it can provide at least an idea where convection will occur. There are two things that came to mind when looking at this tool.

On quieter days this tool can become noisy. By editing the colors in the RGB color model, I was able to black out all probabilities below 50% and to clean up the product. This will bring attention to the higher probabilities, as opposed to cluttering the field with lower end probabilities. The threshold (<20%, <30%, <40% etc) a person chooses to ignore is up to the user. To do this, though, you must continually edit the color model. This isn’t difficult, but  takes time. It would be nice if a default button existed that allows you to black out a specified range. Below is a result between the two (normal view 1-100% and 50-100% probabilities, respectively):

The second thought pertains to what application this could have during lake effect snow events. In the proper environment, convective snow banding could lead to heavy, consistent snowfall of greater than 35 Dbz. This may be a useful tool for updates to geographical locations of higher intensity snowfalls in these events.

- Forecaster