Case Description: 4 December 2018

Summary

Moderately sized system develops north of the AMF

Description

A system initiates and grows north of the AMF around 16 UTC. The system remains isolated from others until merging begins around 19 UTC. CAPE values are in the lower third of their ranges (at 15 UTC MUCAPE=1766; MLCAPE=395 J kg^-1).

Available assets

CSAPR2, G1 flight, GOES rapid scan, RELAMPAGO mission (33 soundings), CSU C-Band data

Critical period: 16:00–19:00

16:00 System initiates north of the AMF and grows

19:00 Merging begins with convection from behind the ridgeline

Brightness temperature, 2018-12-04 18 UTC — Figure 4 GOES16 band 13 brightness temperature at 2018-12-04 at 18:00 UTC. The system of interest initiates north of the AMF site starting around 16 UTC and remains isolated from others until about 19 UTC. The whole system should be captured by the CSAPR2.

Available LES ensemble members

Table 4 Summary of LES cloud behavior for 2018-12-04
Impression	Ensemble Member	Cloud Behavior
Acceptable	GEFS04-Morr	Pretty good. The initiation of the northern cell is very well captured in location and timing and its growth is reasonably well captured. Differences are that this cell is a bit smaller and perhaps less organized than observed and the model also generates an unobserved weak cell over the AMF and other convection south of the domain. However, the weak cell dissipates with the growth of the northern cell and overall agreement is good by the end of the critical period at 19 UTC. So, ignoring the weaker cells over the AMF and to the south and things look very good.(The meso GEFS04-Thomp northern cell is good, but also develops errant cell over AMF.)
Poor	GEFS16-Morr	Gets northern feature well but it does not develop into the large area observed; errant development over the AMF and to the south of the domain. CSI Skill about 50% of that in respective meso run for the critical period.
Could be better	GEFS18	Under develops northern cell and produces unobserved cell over the AMF (as does the meso run). CSI Skill 25% of the respective meso run.
Marginal	GEFS18-Morr	Very good development of the northern cell, but also produces large, errant, unobserved cell over the AMF (as does the meso run). Slightly better CSI Skill than the respective meso run.
Bust	GEFS19	No initiation.