Extreme Precipitation in Weakly Forced Environments
Along the Northwest Gulf (147)
Robert Megnia, National
Weather Service WFO Lake Charles, LA, Lake
Charles, LA
Jared Rackley, National
Weather Service WFO Lake Charles, LA
Timothy Humphrey, National
Weather Service WFO Lake Charles, LA
Seth Warthen, National
Weather Service WFO Lake Charles, LA
Andrew Patrick, National
Weather Service WFO Lake Charles, LA
Abstract:
Previous research has
suggested that extreme precipitation events (EPEs) are fairly well forecasted
in strongly forced synoptic environments with high values of integrated water
vapor transport (IVT). However, EPEs in weakly forced environments with lower
values of IVT have presented challenges. A weakly forced can be characterized
by a lack of any obvious forcing mechanisms (highly amplified flow, frontal
boundaries, vorticity advection, large IVT ect.) Extreme precipitation events
that occur in weakly forced environments are common occurrences in the National
Weather Service Lake Charles (LCH) county warning area. The precipitation that
occurs in these events is at times under-forecast. Thus, there is a need to
identify the forcing mechanisms behind EPEs in weakly forced environments. For
this study, the 99th percentile of precipitation days (excluding days with
tropical cyclone related precipitation) are gathered from the five LCH climate
sites. Days with tropical precipitation are excluded so composites of the
strongly forced events (made up mostly of mid-latitude events) can be compared
to weakly forced events. IVT data from the North American Regional Reanalysis
(NARR) data set from the 99th percentile days are examined to identify which
days had weakly forced environments. Various forcing parameters are then examined
on these days to identify any mechanism(s) that contribute to extreme
precipitation. Although this study is primarily focused on a local region, the
results may be applicable to other regions that experience EPEs in weakly
forced environments as well.