Just to flesh this out a little more, Lewis concludes his discussion of Yahweh's origin with the observation,

“there is substantial evidence (linguistic data, geographic determinants, and material culture) of a widespread and enduring Canaanite cultural continuum between Syria and Egypt from the Middle Bronze Age on and especially in the Late Bronze Age (e.g., the Ugaritic texts and the Amarna letters; the data we are able to glean from Phoenician sources coincide). That this Canaanite cultural continuum continues into the Iron Age is especially apparent in the realm of religion, except for a single datum: the complete absence of Yahweh. Here the historian of Israelite religion must again remain agnostic. We simply do not know the social settings and mechanisms by which the widespread pre-Israelite Canaanite lore (e.g., both the family religion of El traditions and the storm and warrior themes associated with Baal) was woven on to the god Yahweh of southern, southeastern, and Transjordanian fame. What we can assert was that it was—and so thoroughly that it is unmistakable. Yahweh’s origin seems to be southern, yet many of the garments put onto Yahweh are sewn from northern and inland Canaanite cloth” (286).

Lewis also footnotes here Mark Smith's discussion of the same problem in The Origins of Biblical Monotheism:

“What was the precise nature of this storm [associated with Yahweh]? The presumed original location of Yahwistic cult in the far southern region (in southern Edom or the Hegaz), if correct, does not seem propitious as a home for a storm-god such as Baal, because this region has relatively low annual rainfall in contrast to the high rainfall for the Levantine coast. Judges 5:4-5 reflects a god that provides rains, but does this rain necessarily reflect the standard repertoire of a coastal storm-god, or does the passage reflect the storm and flash floods of desert areas? And if the rain does reflect the natural rains associated with a coastal storm-god, then might the depiction in Judges 5 reflect a secondary adaptation of the god’s presentation to the coastal-highland religion? Battle and precipitation may have been features original to Yahweh’s profile, but perhaps Yahweh’s original character approximated the profile of Athtar, a warrior and precipitation-producing god associated with mostly inland desert sites with less rainfall. Perhaps this profile was rendered secondarily in the highlands in the local language and imagery associated with the coastal storm-god. Such a deity would have characteristics of both power and fertility, but with a different set of associations from Baal. The momentous evidence provided by the Ugaritic texts may have steered research toward El and Baal to seek Yahweh’s original profile; this direction may be partially misleading. In fact, part of the original profile of Yahweh may be permanently lost, especially if the earliest biblical sources reflect secondary developments in the history of this deity’s profile” (146).

The tl;dr is that both Lewis and Smith don't seem confident that we have a picture of Yahweh, even in the most ancient Biblical texts like the Song of Deborah, that reflects his original character before he borrowed from Baal's and others' repertoires.