We worked with the LAPS 800 x 800 grid as it was centered over a portion of the Midwest, which was under a Severe Thunderstorm Watch until 8PM local time. The model’s maximum reflectivity product was pretty well matched up with radar at 19Z on May 12th for the area with a precip shield, and it even had a pretty good match with the areas of heavier intensity. The first image is of the LAPS max reflectivity product from its 18Z run, valid at 19Z:

And here is the Davenport, IA radar base reflectivity, also at 19Z:

Notice that the spatial coverage of the precipitation is a pretty close match over central and eastern Iowa at this time period. The model also correctly forecast a sort of “dividing line” between the eastern and western areas of precip. However, the intensity of the precip is a bit overdone on LAPS, especially in the cluster of storms on the left side. The heavier rain toward Iowa City did not materialize as of 19Z, though it was forecast by LAPS to have reflectivity above 50 dBZ.

However, as I continued to watch the radar in Iowa, I noticed some more convective cells developed in the region that the LAPS had predicted higher values of max reflectivity. So the timing was a bit off on the forecast of convective initiation and heavier precipitation. We’ll have to continue to watch this product throughout the week as other convective situations arise in order to see if it’s valuable for nowcasting.

The ProbSevere Model indicated an 83% probability of a severe storm within an environment of 2968 J/Kg of MUCAPE and 34.6 kts of EBShear at 2020Z. It also indicated MESH of 1.07inch at this time. The following 2-minute resolution updates continued to show 80+% prob and 1 inch+ MESH as the storm tracked northeast from the NE Missouri/SW Iowa border into SW Iowa except for one frame at 2028z where it showed a 64% prob. WFO DMX issued a SVR at 2037z. ProbSevere may have helped give up to 17 minutes additional lead time if the warning was issued once the ProbSevere crossed above 80%. At the time of this post there were not yet any confirmed hail reports.

Visible satellite data started to show a resemblance of an enhanced updraft on this storm at 2015z with a developing anvil and anvil shadowing at 2025z.  SRSOR VIS data was missing between 2011z and 2030z so had to use conventional visible images for the attached screen captures.
Shawn Smith

EDIT: Missing GOES-14 SRSOR images were due to “daily housekeeping” – BL

The following images depicted the expansion in overshooting tops depicted by the CIMMS Auto Overshooting Tops Detection Algorithm 2015 to 2045 UTC May 12 across southern Iowa.

The first image had a small red blob in southwest Davis county at 2015 UTC, which greatly enlarged in area by 2025 UTC in the second image.   By 2030 UTC in the third image, the area split up into three blobs.  By 2037 UTC, the fourth image indicated four blobs with the two blobs to the northeast representing the fastest growth and expansion of the storm.  By 2045 UTC, the last image, three blobs were with this storm, possibly indicated that storm was intensifying or at least maintaining intensity.

A SVR was issued for Van Buren county, on the southeast part of the enclosed circular area, with the overshooting tops blobs at 2037 UTC.  A 60 mph gust along with heavy rainfall and low visibility was observed in the warned area at 2127 UTC. The great expansion and splitting of blobs indicated by the Auto Overshooting Top Detection Algorithm could have increased SVR lead time another 10-30 minutes.

Michael Scotten

While awaiting convection in my CWA (St. Louis), I used the vLAPS model to diagnose the potential for pre-frontal convection across my CWA.  These images depict the model-derived reflectivity versus the observed radar at 21Z Monday May 12th.  The model is quite a bit overdone with the convection in the warm sector in Missouri (although perhaps being on the edge of the model domain may be affecting this to some extent…).

-Deitsch

An area of very high CI probailites (90%) caught my eye at thresholds around 90%.  Sure enough, convection did indeed form around the time of the highest probabilities, so the product worked well in highlighting the area of potential convection.  However, convection quickly died out after reaching the dBZ thresholds to blank out the CI algorithm out (30-40 dBz).  So while it proved well in identifying an area of potential storm development, in this case, the storms simply failed to materialize into anything more then a few light showers/sprinkles (although I realize the algorithm is not meant to diagnose storm sustainability).

– Deitsch

Monday 12 May 2014 begins the second week of our four-week spring experiment of the 2014 NSSL-NWS Experimental Warning Program (EWP2014) in the NOAA Hazardous Weather Testbed at the National Weather Center in Norman, OK.  This week we will evaluate multiple experimental products geared toward WFO applications.   This evaluation – known as “The Big Experiment” – will have three components including a) an evaluation of multiple CONUS GOES-R convective applications, including satellite and lightning;  b) an evaluation of the model performance and forecast utility of two convection-allowing models (the variational Local Analysis Prediction System and the Norman WRF); c) and an evaluation of a new feature trending tool.  We will also be coordinating with the Experimental Forecast Program and evaluating their probabilistic severe weather outlooks as guidance for our warning operations.  Operational activities will take place during the week Monday through Friday.

For the week of 12-16 May, our distinguished NWS guests will be Kevin Deitsch (WFO Louisville, KY), Shawn Smith (WFO Buffalo, NY), and Michael Scotten (WFO Norman, OK).  In addition to our NWS forecasters, we will be hosting a broadcast meteorologist to work at the forecast desk; this week, our distinguished guest will be Erica Grow of WUSA-TV (Washington, DC).  If you see any of these folks walking around the building with a “NOAA Spring Experiment” visitor lanyard, please welcome them!   The GOES-R program office, the NOAA Global Systems Divisions (GSD), and the National Severe Storms Laboratory have generously provided travel stipends for our participants from NWS forecast offices and television stations nationwide.

Visiting scientists and observers this week will include Hongli Jiang (GSD), John Cintineo (UW-Madison/CIMSS), John Mecicalksi (University of Alabama – Huntsville), Elise Schultz (University of Alabama – Huntsville), Sara Stough (University of Alabama – Huntsville), Ben Baranowski (Weather Decision Technologies), Jason Lynn (Weather Decision Technologies), Chris Schwarz (Weather Decision Technologies), and Mike Smith (AccuWeather / WeatheData),.

Bill Line will be the weekly coordinator.  Lance VandenBoogart (WDTB) will be our “Tales from the Testbed” Webinar facilitator. Our support team also includes Darrel Kingfield, Kristin Calhoun, Gabe Garfield, Chris Karstens, Greg Stumpf,  Karen Cooper, Vicki Farmer, Lans Rothfusz, Travis Smith, Aaron Anderson, and David Andra.

Here are several links of interest:

You can learn more about the EWP here:

https://hwt.nssl.noaa.gov/

NOAA employees can access the internal EWP2014 page with their LDAP credentials:

https://hwt.nssl.noaa.gov/ewp/internal/2014/

 
Gabe Garfield
CIMMS/NWS OUN
2014 EWP Operations Coordinator

All output of Prob severe model are white text.  Change font/color based on certain thresholds. For example, MESH output changes to yellow once 1 inch hail is predicted etc.

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