A Case of Upper and Lower-Level Jet Coupling: July 11, 2006,

Springfield, Missouri NWS County Warning Area Joshua Kastman, Laurel McCoy, and Patrick Market

1 Department of Soil, Environmental, and Atmospheric Sciences, University of Missouri

Introduction Upper level and lower level jet streak coupling is known to produce intense regions of upward motion that can result excessive precipitations rates. This case is an example of the manifestation of upper and lower level jet streak coupling. This case is unique because it was short lived yet produced rainfall in excess of 3 inches of rain within 6 hours.

References Hakim, Gregory J., Louis W. Uccellini, 1992: Diagnosing Coupled Jet-Streak Circulations for a Northern Plains Snow Band from the Operational Nested-Grid Model. Wea. Forecasting, 7, 26–48. Uccellini, Louis W., Paul J. Kocin, 1987: The Interaction of Jet Streak Circulations during Heavy Snow Events along the East Coast of the United States. Wea. Forecasting, 2, 289–308.

Moore, James. "Jet Streak Circulations." University Corporation for Atmospheric Research. 2005. Lecture. Accessed 9/1/2013

Acknowledgements This work is supported in part by the National Science Foundation (NSF), Award No. AGS-1258358. Any opinions, findings, conclusions or recommendations expressed herein are those of the author(s) and do not necessarily reflect the views of NSF.

Summary and Conclusions The presence of an upper-level jet streak overlying a low-level jet produced an enhanced region of omega. The result of this process in a very saturated environment produced heavy rainfall (>3in.) in the Springfield, Missouri NWS County Warning Area. The convection that formed did so above a stable boundary layer (seen in the cross sections).The interaction of the two jets is very apparent in the ageostrophic circulation vector field when plotted in a cross-section normal to the upper-level jet. The cross-section reveals that the direct thermal circulation, as shown by Moore (2005) (figure 2), of the upper level jet streak combined with the upward sloping low level jet to produce the heavy rainfall.

Environmental Conditions A small appendage off of the main jet stream trunk is in place as the low level jet forms around the 00z time step. During

this time the omega field rapidly intensifies and dissipates as the appendage is absorbed into the main jet stream. The columns shown below show the conditions at 00z and 03z. Those were the time steps where the precipitation occurred.

While not depicted here, there was a warm front into place across the Missouri-Iowa border.

00z

03z

P0.17

Fig. 2. Taken from Moore (2005). This image show the direct and indirect thermal circulation that

forms in response to an upper level jet streak.

Fig. 1. Map of U.S. Unified Daily Precipitation Analysis showing 24-hour accumulated precipitation from 12Z July 10, 2006 through 12Z

July 11, 2006

03z 00z

Green is 25 ms-1 isosurface above 550 hPa, and blue is 12.5 ms-1 isosurface below 550 hPa.

Cross Sections The cross sections below illustrates how the upper and lower level jet streaks are

working together to produce a region of intense upward vertical motion. These figures are showing the process depicted from this image taken from Moore

(2005)