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Low‐level stratiform clouds modulate California's coastal climate during the warm season. Previous work describing the seasonal and daily variability of coastal low cloudiness (CLC) suggests that in July, August, and September southern California's CLC is under the influence of an additional driver, which has less impact in northern California. In this work, we introduce the link in which free‐tropospheric moisture dictated by North American Monsoon (NAM) processes can impact southern California CLC. We use in situ and remote sensing observations, as well as reanalysis and single column model simulations to identify and investigate this previously missing component. We find that monsoonal moisture advected by southeasterly flow from the core NAM region into southern California reduces CLC by diminishing cloud‐top longwave cooling. To add to an already complex brew of known factors influencing coastal cloudiness, another one is hereby introduced and should be accounted for in future work. Plain Language Summary Low‐altitude marine layer clouds shade and cool coastal California in spring and summer. When these clouds are low enough that the base of the cloud intercepts terrain (which is known as fog), they additionally add moisture to the landscape during a typically dry time of year in California. Future trends in coastal low cloudiness (CLC) are uncertain. Although CLC impact the whole coast of California and beyond, previous studies have exposed differences in seasonal and daily CLC behavior in southern and northern California. The North American Monsoon (NAM), which becomes active in the US Southwest in summer, brings rain and thunderstorms to the desert southwest. Coastal southern California is on the northwest edge of the NAM influence and typically does not receive much rain from NAM. In this study, we show how low altitude coastal cloud cover in southern California and northern Baja California can be diminished by higher altitude moisture from the NAM. Dry and stable air above the top of low clouds helps to maintain the cloud layer, and higher altitude moisture interrupts this process. To better understand how CLC varies and may change, an accounting of all key drivers of CLC behavior, including the NAM, is needed. Key Points An increase in free‐tropospheric moisture over coastal southern California in summer is attributed to the North American Monsoon (NAM) NAM moisture intrusions can diminish southern California coastal low cloudiness by decreasing longwave cloud‐top cooling These results link two iconic regional climate phenomena of the U.S. Southwest

We examine the spatial and temporal evolution of heat waves through California and consider one of the key modulating factors of summertime coastal climate—coastal low cloudiness (CLC). Heat waves are defined relative to daytime maximum temperature (Tmax) anomalies after removing local seasonality and capture unseasonably warm events during May—September. California is home to several diverse climate regions and characteristics of extreme heat events are also variable throughout these regions. Heat wave events tend to be shorter, but more anomalously intense along the coast. Heat waves typically impact both coastal and inland regions, although there is more propensity towards coastally trapped events. Most heat waves with a strong impact across regions start at the coast, proceed inland, and weaken at the coast before letting up inland. Typically, the beginning of coastal heat waves are associated with a loss of CLC, followed by a strong rebound of CLC starting close to the peak in heat wave intensity. The degree to which an inland heat wave is expressed at the coast is associated with the presence of these low clouds. Inland heat waves that have very little expression at the coast tend to have CLC present and an elevated inversion base height compared with other heat waves.

During the North American Monsoon, low-to-midlevel moisture is transported in surges from the Gulf of California and Eastern Pacific Ocean into Mexico and the American Southwest. As rising levels of precipitable water interact with the mountainous terrain, severe thunderstorms can develop, resulting in flash floods that threaten life and property. The rapid evolution of these storms, coupled with the relative lack of upper-air and surface weather observations in the region, make them difficult to predict and monitor, and guidance from numerical weather prediction models can vary greatly under these conditions. Precipitable water vapor (PW) estimates derived from continuously operating ground-based GPS receivers have been available for some time from NOAA’s GPS-Met program, but these observations have been of limited utility to operational forecasters in part due to poor spatial resolution. Under a NASA Advanced Information Systems Technology project, 37 real-time stations were added to NOAA’s GPS-Met analysis providing 30-min PW estimates, reducing station spacing from approximately 150 km to 30 km in Southern California. An 18–22 July 2013 North American Monsoon event provided an opportunity to evaluate the utility of the additional upper-air moisture observations to enhance National Weather Service (NWS) forecaster situational awareness during the rapidly developing event. NWS forecasters used these additional data to detect rapid moisture increases at intervals between the available 1–6-h model updates and approximately twice-daily radiosonde observations, and these contributed tangibly to the issuance of timely flood watches and warnings in advance of flash floods, debris flows, and related road closures.

Floods caused by atmospheric rivers and wildfires fanned by Santa Ana winds are common occurrences in California with devastating societal impacts. In this work, we show that winter weather variability in California, including the occurrence of extreme and impactful events, is linked to four atmospheric circulation regimes over the North Pacific Ocean previously named and identified as the “NP4 modes”. These modes come in and out of phase with each other during the season, resulting in distinct weather patterns that recur throughout the historical record. Some phase combinations favor atmospheric river landfalls and extreme daily or multi-day precipitation, while other phase combinations favor anomalously hot weather and drying Santa Ana wind conditions over Southern California. This historical perspective of atmospheric circulation and impacts over 70 years reveals that weather patterns are changing in a way that enhances wildfire hazard in California, while the frequency of weather patterns linked to historical floods is not diminishing. These changes highlight the rising hazards of cascading weather extremes in California’s present and future.

The brown pansy, Junonia stygia (Aurivillius, 1894) (Lepidoptera: Nymphalidae), is a widespread West African forest butterfly. Genome skimming by Illumina sequencing allowed assembly of a complete 15,233 bp circular mitogenome from J. stygia consisting of 79.5% AT nucleotides. Mitochondrial gene order and composition is identical to other butterfly mitogenomes. Junonia stygia COX1 features an atypical CGA start codon, while ATP6, COX1, COX2, ND4, and ND4L exhibit incomplete stop codons. Phylogenetic reconstruction supports a monophyletic Subfamily Nymphalinae, Tribe Junoniini, and genus Junonia. The phylogenetic tree places Junonia iphita and J. stygia as basal mitogenome lineages sister to the remaining Junonia sequences.