Aspects of 6 June 2007: A Null “Moderate Risk” of Severe Weather Jonathan Kurtz Department of Geosciences University of Nebraska at Lincoln NOAA/NWS Omaha/Valley, NE

Project Outline Definition of a Moderate Risk as defined by the Storm Prediction Center (SPC). Overview of Synoptic Scale conditions of 6 June Study of the different forecast models available and their predictions of the events of 6 June 2007; including Quantitative Precipitation Forecasts (QPF), their forecasts of the closed surface low, forcing mechanisms, shear and instability.

6 June 2007 Moderate Risk SPC Forecasted Moderate at 0600 UTC 6 June 2007 for the majority of the north central Plains, including North Dakota, South Dakota, western Minnesota, central and eastern Nebraska, western Iowa and north central Kansas.

SPC Definition of a Moderate Risk “moderate risks imply a greater concentration of severe thunderstorms, and in most situations, greater magnitude of severe weather. Within a moderate risk area, at least 30 reports of hail 1 inch or larger, or 6-19 tornadoes, or numerous wind events (at least 30 reports that likely would be associated with a squall line, bow echo or derecho).”

Overlay Map of the 0600 UTC Moderate and Preliminary Storm Reports Red Triangles: Tornadoes == Blue Triangles: Hail == Green Squares: Wind 19 Reports of Hail 1 inch or greater 6 Tornado Reports 13 Wind reports of speeds over 65 mph

Synoptic Situation

HPC (Hydrometeorological Prediction Center) Surface Fronts Analysis 21 UTC 6 June UTC 7 June UTC 7 June 2007

Closed 979 hPa Low High Wind Warning Criteria Met… 63 mph observed at Fairbury, NE out of the South!

GFS BUFKIT Data 21 UTC Lincoln, NE: 00 UTC Model Run Indices CAPE: 1381 J/kg CIN: 370 J/kg Lifted Index: -2.8 K index: 17 SWEAT: 426 Showalter: -2 Bulk Richardson:21.19 Shear 0-3 Km: 35 m/s 0-6 Km: 46 m/s Helicity 0-3 Km: Km: 362

NAM BUFKIT Data 21 UTC Lincoln, NE: 00 UTC Model Run Indices CAPE: 1697 J/kg CIN: 333 J/kg Lifted Index: -4.6 K Index: 23 SWEAT: 502 Showalter: -4 Bulk Richardson:35.39 Shear 0-3 Km: 32 m/s 0-6 Km: 38 m/s Helicity 0-3 Km: Km: 313

NAM Mixed Layer Computed CAPE and CIN 2100 UTC 6 June 2007

RUC Km Bulk Shear and Bulk Shear Vectors 2100 UTC 6 June 2007

RUC BUFKIT Data 21 UTC Lincoln, NE: 21 UTC Model Run Indices CAPE: 216 J/kg CIN: 439 J/kg Lifted Index: -0.7 K index: 20 SWEAT: 397 Showalter: -1 Bulk Richardson:3.13 Helicity 0-3 Km: Km: 425 Shear 0-3 Km: 42 m/s 0-6 Km: 56 m/s

NAM12 Surface Dew Point and Temperatures (2100 UTC 6 June 2007)

GFS40 Surface Dew Point and Temperatures (1800 UTC 6 June 2007)

Surface Observations and RUC 80 Surface Dew Point Analysis 21 UTC 6 June 2007

Model Predicted Moisture vs. Observations On average there was a significant difference in the surface dew point temperatures predicted by the models and the dew points observed throughout the day. The NAM was predicting close to 10 degree higher dew points and the GFS was predicting 3 to 5 degree higher dew points than were actually observed during the course of the day. The forecasting of greater moisture led to the models predicting higher CAPE and lower CIN values than what would occur. Given the low available moisture, actual CAPE values were much lower than predicted, and more importantly, the values of CIN were extremely high.

Visible Satellite Image 2115 UTC and METAR OBS 2100 UTC 6 June 2007

RUC hPa Winds: 18 UTC 6 June UTC 6 June UTC 6 June UTC 7 June 2007

RUC hPa Divergent Q Vectors: 6 June UTC 6 June UTC 6 June UTC 7 June 2007

NAM Time-Height Cross Section of RH and Omega 12 UTC 6 June – 00 UTC 7 June

NAM 40 and GFS hPa Omega 24 hour forecast valid at 00 UTC 7 June 2007 NAM 40GFS 40 Strong Vertical Motion

MSAS Moisture Flux Divergence and METAR OBS 0100 UTC 0.5 Reflectivity 0136 UTC and METAR OBS 0200 UTC 0800 PM CDT 6 June 2007

0.5 Reflectivity 0200 UTC and METAR OBS 0200 UTCMSAS Moisture Flux Divergence and METAR OBS 0200 UTC 0900 PM CDT 6 June 2007

GFS 40: 6 June UTC Initiation 18 UTC 6 June UTC 7 June UTC 7 June 2007

NAM 80 7 June UTC Initiation 18 UTC 6 June UTC 7 June UTC 7 June 2007

NAM 12 6 June UTC Initiation 21 UTC 6 June UTC 7 June UTC 7 June 2007

NGM 80 6 June UTC Initiation 18 UTC 6 June UTC 7 June UTC 7 June 2007

NOAA SPC Spring Program Experimental Forecast Program involving the National Severe Storms Laboratory (NSSL) and the SPC The 2007 Spring Experiment included high resolution NWP forecast data and observed data from the 6 June 2007 event. Studied the WRF data comparing WRF model runs from the Advanced Research WRF (ARW) at 2 and 3 km resolution, the Nonhydrostatic Mesoscale Model (NMM at 4 km resolution, the NSSL at 4 km resolution and the Storm Scale Ensemble Forecast (SSEF) model with the Base reflectivity for the north central Plains. Tried to conclude which of the WRF models best represented the observed storm complex across the north central Plains.

ARW3-NMM4-NSSL4-ARW2-SSEFCN (1km AGL REFL) vs. Base Reflectivity 00Z 7 June 2007

ARW3-NMM4-NSSL4-ARW2-SSEFCN (1km AGL REFL) vs. Base Reflectivity 03Z 7 June 2007

ARW3-NMM4-NSSL4-ARW2-SSEFCN (1km AGL REFL) vs. Base Reflectivity 06Z 7 June 2007

Conclusions The models erroneous prediction of high surface dew points was a major contributor to the erroneous forecast of high CAPE and low CIN. Vertical forcing over the region was hampered by the convergence at the nose of the jet, causing subsidence over the majority of central Nebraska. Shear was sufficient for the development of well structured storms but the vertical motion was far too weak to over come the strong cap. Later outlooks issued by the SPC took into account these forecast concerns and properly decreased the moderate risk area.

Thank You Any Questions? Special Thanks to: Dan Nietfeld, NOAA/NWS Omaha/Valley, NE Josh Boustead, NOAA/NWS Omaha/Valley, NE Becky Griffis, NOAA/NWS Omaha/Valley, NE