Thursday, June 19, 2014

Identifying Low-Level Boundaries

During the convective season, strong thunderstorms will form, if all the ingredients are in place (moisture, instability, and lift), along some types of a boundary.  The low-level boundary can range from a synoptic scale front to a previous day storm’s outflow.  Often low-level boundaries act as a focus for the concentrated upward vertical motion necessary to initiate deep convection.  Moisture maximum along a boundary can enhance the strength of the updraft as well.  Finally, interaction between multiple boundaries can set off new convection.  Boundaries occur year round but the small-scale types are mainly a warm season phenomena.
Processes necessary for deep moist convection to occur. Adopted from Doswell (WAF, 1996).
Surface data is one of the best source to analyze low-level boundaries. Temperature and dew point temperature gradients are areas where boundaries tend to form. Pressure trough and wind shift can be used to locate low-level boundaries as well.  Discontinuity in low cloudiness or fog and in precipitation or precip-type (mainly cold season) can signal a possible existence of a low-level boundary.
The image shows the Denver Convergence Vorticity Zone (DCVZ) on June 8 2012 at 0200 UTC.
An example of a dryline that occurred on 1800 UTC May 4 2003.
Upper-air data can be used to locate low-level boundaries, as well but mainly on the larger scale (synoptic range).  Frontal inversion from a sounding can hint at a boundary that has already passed. In addition, plotting a 1000-500 mb thickness map can provide incite where a front is located. This method is very useful in analyzing an occluded front.

An example of a frontal inversion from Denver sounding on 10/26/20006 at 1200 UTC.
Finally, remote sensing data have proven to be robust ways on locating low-level boundaries. Initial precipitation echo pattern from a radar can verify an existence of a boundary.  While in clear air mode, a fine line on a radar display can provide the location of the low-level boundary.  Visible satellite imagery can reveal cloud lines (Cu, Cb or St) which shows correlation with low-level boundaries.  
FTG radar in clear air mode indicating a boundary east of Denver on Nov 2 2005.
Visible satellite image from June 19 2014 at 2045 UTC.  The circle indicates where a boundary has initiated thunderstorms.
Surface observations plotted with radar data on Aug 7 2010 at 2100 UTC.
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About Me

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Denver, CO
I am an Associate Professor of Meteorology at Metropolitan State University of Denver (MSUDenver). I have been at Metro State since 2005, teaching various courses from Synoptic to Mesoscale Meteorology and everything in between. I also manage the weather lab at MSUDenver. While my duties are focused primarily on teaching, I remain active in serving the student body. I am the faculty advisor of the student chapter of the American Meteorological Society. In 2005, I received a Ph.D. in Meteorology from Saint Louis University for my research on processes associated with heavy banded snowfall in the Midwest under the tutorage of the late James T. Moore. My other degrees are from Millersville University of Pennsylvania (1998) for a B.S. in Meteorology and Texas Tech University (2001) for a M.S. in Atmospheric Science. My weather interests include but no exclusive to quasi-linear convective system (QLCS), mesoscale snowband, rapid cyclogenesis, severe local storm prediction, and numerical weather prediction refinement in operational forecasting. I am also a contributor to Weather5280 Team (http://www.weather5280.com).