STMAS Aviation Weather Testbed (AWT-2011) case: 25 July 2011 Highlight: A line of storms over nw NY at 12z is moving to the southeast with potential to reach NYC airports, plus a second strong line develops behind this. Real-time runs examined 12z HRRR, STMAS_CI, STMAS_CI_CYC out to 6-h 18z HRRR and LAPS ensemble runs (members 2 through 8) out to 6-h 12z runs: HRRR overall somewhat weaker than STMAS runs Though overall the verification is mixed 18z runs: The most notable characteristic of the ensemble runs is that every member loses most of the convection by 21z Not sure why this is so, or whether it occurs suddenly or over the course of an hour

SPC Outlooks and reports for 25 July 2011 SPC severe reports through 1840z on 25 JulySPC Convective Outlook issued at 06z/25 July SPC Convective Outlook issued at 1230z/25 July Interesting how the outlook issued at 1230 UTC actually downplayed the risk of severe. The next outlook (shown later) brought back the Slight Risk area in NY state.

1200 UTC 25 July run – analyses of composite reflectivity STMAS_CI run The initial analysis is very good for both STMAS models, and weaker for the HRRR. NOTE that the observed reflectivity scale has a different color table then the models (where red = 50, not 60 dBZ) STMAS_CI_CYC run HRRR Observed: NOWRAD with obs dBZ

1200 UTC 25 July run – 1-h valid 13z/composite reflectivity STMAS_CI run Like the other case, there are differences between the 2 STMAS runs, with stronger and somewhat larger echoes in the CI run. The HRRR has stronger cells now, with some differences with the STMAS runs. Note for example the cell highlighted by the arrow, with verification between the STMAS runs (bit fast) and the HRRR (a bit slow). STMAS_CI_CYC run HRRR Observed: NOWRAD with obs

1200 UTC 25 July run – 2-h valid 14z/composite reflectivity STMAS_CI run Differences between the 2 STMAS runs continue, with somewhat stronger and larger echoes in the CI run. Note the organization into a line in nw NY (yellow arrow) only in the CI run, with an indication of such organization in the observed reflectivity. The cells approaching NYC are weakening a bit, but probably better in the STMAS runs at this point. STMAS_CI_CYC run HRRR Observed: NOWRAD with obs

1200 UTC 25 July run – 3-h valid 15z/composite reflectivity STMAS_CI run Kind of a mixed bag of verification at 3-h into the forecast. Looking at 2 areas, what is left of the cells approaching NYC airports (white arrow) is ~45 dBZ max. The HRRR is too weak, STMAS- CI too strong and fast, and the CYC run closest. The area in nw NY (yellow arrow) is probably closest to the STMAS_CI run and the HRRR. STMAS_CI_CYC run HRRR Observed: NOWRAD with obs

1200 UTC 25 July run – 4-h valid 16z/composite reflectivity STMAS_CI run Remains a mixed bag of verification at 4-h into the forecast. The cells approaching NYC (white arrow) pass to the north, but are maintained better in the STMAS runs than in the HRRR. A new line is forming in western NY, and all of the models are too slow to develop new storms in this area. STMAS_CI_CYC run HRRR Observed: NOWRAD with obs

1200 UTC 25 July run – 5-h valid 17z/composite reflectivity STMAS_CI run It looks like each model tries to produce a line in western NY, but all are too weak in this area. The other main area of cells that had been in sw-central PA is shifting eastward, with a roughly similar forecast in the STMAS models, and maybe a bit too slow in the HRRR. STMAS_CI_CYC run HRRR Observed: NOWRAD with obs

1200 UTC 25 July run – 6-h valid 18z/composite reflectivity STMAS_CI run Sort of mixed verification again. The position of the eastern echo area (white arrows) is roughly similar in all the models, with the strength perhaps between the HRRR and STMAS forecasts. Meanwhile some strong cells are found in the second line which is moving east, and all 3 models have some strong cells, but a slight lean towards the CYC run with more overall echo. STMAS_CI_CYC run HRRR Observed: Low-level radar reflectivity

More SPC Outlooks/Watches and reports for 25 July 2011 SPC severe reports through 12z on 26 JulySPC Convective Outlook issued at 16z/25 July SPC Severe Thunderstorm Watch valid from UTC/25 July

EWP3EWP4 EWP5 EWP6 EWP7EWP8 EWP9 Observed low-level reflectivity Ensemble analyses at 1800 UTC HRRR analysis The analyses from the ensembles are all very similar and capture the strength of the initial storms.

Ensemble 15-min forecasts valid 1815 UTC There is a significant increase in the area of stronger reflectivity in all the runs, with the exception of EWP5. Otherwise the rest of the runs are similar looking 15 min into the forecast. EWP3EWP4 EWP5 EWP6 EWP7EWP8 EWP9 Observed reflectivity at 1800 UTC

Ensemble 30-min forecasts valid 1830 UTC Some more differences between the runs are starting to be seen. EWP3/5/9 are similar, as are EWP4/7/8. EWP5, which was weaker at 15-min in (and maybe closer to the truth), but now it continues to weaken, and stands out from the other runs. EWP3EWP4 EWP5 EWP6 EWP7EWP8 EWP9 Observed reflectivity at 1800 UTC

Ensemble 45-min forecasts valid 1845 UTC Now it looks like similar run groupings might be EWP3/4/6/8/9, with EWP7 a little weaker and EWP5 too weak. Note there are also differences, some subtle, in the handling of the second line trying to form in western NY/PA. EWP3EWP4 EWP5 EWP6 EWP7EWP8 EWP9 Observed reflectivity and obs at 1900 UTC

EWP3EWP4 EWP5 EWP6 EWP7EWP8 EWP9 Observed low-level reflectivity and METAR plot Ensemble 1-h forecasts valid 1900 UTC HRRR 1-h forecast valid 1900 UTC Aside from the overly weak EWP5 run, differences between the other members are more subtle. The HRRR has a pretty good forecast at 1-h, doing a decent job with the second line (white arrow in the observed reflectivity).

EWP3EWP4 EWP5 EWP6 EWP7EWP8 EWP9 Observed low-level reflectivity and METAR plot Ensemble 2-h forecasts valid 2000 UTC HRRR 2-h forecast valid 2000 UTC Again, you can see some slight differences, but the biggest outlier is the overly weak EWP5 run. Overall there is a slight weakening trend in all the ensemble forecasts, especially notable with the second line (white arrows), which is handled better by the HRRR.

EWP3EWP4 EWP5 EWP6 EWP7EWP8 EWP9 Observed low-level reflectivity and METAR plot Ensemble 3-h forecasts valid 2100 UTC HRRR 3-h forecast valid 2100 UTC The most obvious characteristic of the ensemble forecasts is the sudden almost total weakening of the forecast reflectivity in all the runs. Not sure if this happened in one 15-min period or slowly over the course of the last hour, and did not look further into why this may have happened yet.

EWP3EWP4 EWP5 EWP6 EWP7EWP8 EWP9 Observed low-level reflectivity and METAR plot Ensemble 4-h forecasts valid 2200 UTC HRRR 4-h forecast valid 2200 UTC What little echo is left in the ensemble forecasts continues to disappear. The HRRR forecast is pretty good, even maintaining the second line that is now in PA.

EWP3EWP4 EWP5 EWP6 EWP7EWP8 EWP9 Observed low-level reflectivity and METAR plot Ensemble 6-h forecasts valid 0000 UTC HRRR 6-h forecast valid 0000 UTC The second line (white arrows) is pretty much gone and/or merged into the area of echo closer to the coast. There is a slight increase in some echoes in Upstate NY in some of the ensemble runs, but otherwise nothing in these (and some variation among the ensemble runs).