This study analyses the time-varying acoustics of laterals and their adjacent vowels in Manchester and Liverpool English. Generalized additive mixed-models (GAMMs) are used for quantifying time-varying formant data, which allows the modelling of non-linearities in acoustic time series while simultaneously modelling speaker and word level variability in the data. These models are compared to single time-point analyses of lateral and vowel targets in order to determine what ana- lysing formant dynamics can tell about dialect variation in speech acoustics. The results show that lateral targets exhibit robust differences between some positional contexts and also between dia- lects, with smaller differences present in vowel targets. The time-varying analysis shows that dia- lect differences frequently occur globally across the lateral and adjacent vowels. These results suggest a complex relationship between lateral and vowel targets and their coarticulatory dynamics, which problematizes straightforward claims about the realization of laterals and their adjacent vow- els. These findings are further discussed in terms of hypotheses about positional and sociophonetic variation. In doing so, the utility of GAMMs for analysing time-varying multi-segmental acoustic signals is demonstrated, and the significance of the results for accounts of English lateral typology is highlighted.