Exploring the Sensitivity of Convection Initiation to Grid Spacing in Convection-Allowing NAM Simulations

Open Access
Author:
Dennis, Eli James
Graduate Program:
Meteorology
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 03, 2017
Committee Members:
  • Yvette P. Richardson, Thesis Advisor
  • Paul M. Markowski, Committee Member
  • David J. Stensrud, Committee Member
Keywords:
  • Convection initiation
  • NWP
Abstract:
Forecasting the timing and location of convection initiation (CI) often is a difficult problem that, if done inaccurately, can affect predictions of storm motion, storm mode, and ultimately storm impact. As numerical weather prediction (NWP) models use increasingly finer grid spacing, processes involved in CI might be expected to be better represented, leading to increased forecast ability. In this study, we compare observations to rare 5-minute model output from the operational North American Mesoscale Forecast System (NAM) at both 4- and 1.33-km grid spacing. Two severe weather cases (28 April 2014 and 6 May 2015) are simulated, and compared for evidence of increased forecast performance with decreased horizontal grid spacing. The results show similar convective environments between the two nests, especially for strongly forced events. The dryline dynamics are explored, and limitations related to the model setup are exposed. Model artifacts related to physics parameterizations and the numerical framework are unveiled, and they contributed directly to changes in the operational NAM that were implemented officially in March 2017.