Weather and Forecasting Abstract � ID: 67449��� PW:� 813602 Analysis of the Texas Norther: Case Study The Texas Norther, according to the Glossary of Meteorology (2001), is �... a cold air outbreak associated with the southward movement of a cold anticyclone ... [which comes as] ... a rushing blast and brings a sudden drop of temperature of as much as 25 ^oF in one hour...�� During the Spring of 2003, there were several Texas Northers in the U.S.� One of these cases is examined here using observations and mesoscale model output from both the Penn State/NCAR Mesoscale Model, version 5 (MM5) and the National Centers for Environmental Prediction (NCEP) Eta model.� On March 5, 2003, Whichita Falls, TX, recorded a� temperature change of 11 ^oC in one hour, and 24 ^oC over a time span of 6 hours, as the winds changed from southerly at 10 knots to northerly at 20 knots.� The NCEP Eta model 24 hour temperature forecasts for the area near Wichita Falls, TX were in error by more than 10 ^oC.� In Figs. 1-4 below, taken from a MM5 simulation initialized at 12 UTC, 04 March, winds and temperatures at about 25 meters, as well as sea-level pressure are shown both before and after the cold surge reached the area near Wichita Falls, TX.� The sharp edge of the temperature gradient is evident.� Also, notice how the winds blow straight down the pressure gradient, a feature typical of Texas Northers.� Observations and MM5 model output will be used to show the mesoscale details of the leading edge of the cold air, including the temperature structure, horizontal winds, and vertical motion.� In addition, the movement will be compared to that expected for a gust front, to determine if Texas Northers are driven mainly by density differences, or if they propagate as edge waves.� Schultz, et al., 1997, noted in an extraordinary case they examined from 1993, that the� �� cold surge had characteristics reminiscent of a Kelvin wave, a tipped-forward cold front, a pressure-jump line, a bore, and a gravity current, but none of these conceptual/dynamical models was fully applicable. �� By studying this case from 2003, we hope to gain a better understanding of the structure and dynamics of these cold-season events.  

References: Shultz, D.M., W. E. Bracken, L. F. Bosart, G. J. Hakim, M. A. Bedrick,

M. J. Dickinson, K. R. Tyle, 1997:� The 1993 superstorm cold surge: frontal structure, gap flow, and tropical impact.� Mon. Wea. Rev., 125, 5-38.
Figure 1.� Output from MM5 run valid at 21 UTC, 04 March 2003.� Sea-level pressure contoured at 2 hPa intervals.� Winds are at about 25 m above ground, with the scale shown at lower right (m/s). Location of Whichita Falls, TX is shown by circled cross. Figure 2.� As in Fig. 1, except 25 m temperatures contoured at 5 ^oC intervals are shown instead of sea-level pressure. Figure 3.� As in Fig. 1, except valid for 09 UTC, 05 March 2003. Figure 4.� As in Fig. 2, except valid at 09 UTC, 05 March 2003.