Weather Synopsis – May 7, 2024

James Murakami

Tue7th66/53Sunny day. Clear evening.
Wed8th68/54Mostly sunny day except chance of some early morning low clouds. Mostly clear evening.
Thu9th70/54Mostly sunny day except chance of early morning low clouds. Mostly clear evening.
Fri10th70/55Mostly sunny day except chance of early morning low clouds. Chance of late evening low clouds.
Sat11th70/56Mostly sunny day except chance of early morning low clouds. Chance of late evening low clouds.


Currently, a northwest wind flow pattern aloft exists in the West (western periphery of a large, upper low pressure located over the Dakotas this afternoon). A semi-“cut-off” low pressure is forecast to form somewhere in the Southwest by Thursday. The low pressure is expected to then meander in the Southwest through the early part to this weekend before heading east. Under some circumstances, such a pattern can promote showery, cooler than normal weather (scenario where low pressure center is close to southern California). However, none of the numerical model forecasts hint at any inclement weather developing in the Southland.

As a matter of fact, some model solutions depict a developing, marginal off-shore flow (as early as tomorrow). This would promote continued, mostly clear skies for the remainder of the week. Depending on how strong the off-shore flow gets (NAM model being the most aggressive), it could get quite warm (west of the mountains) for at least a couple days later this week. Off-shore flow in the western section of the Southland appears most probable (Sundowner winds over Santa Barbara County). However, as I’ve stated in previous synopses, off-shore flow of significance for most of southern California is uncommon by this time of year (more of an autumn-winter phenomenon).

The development of a “cut-off” low pressure in the southern Great Basin states can help support a northerly wind gradient. The low pressure could also end up promoting increasing, surface on-shore flow in some circumstances. Though far from unanimous, today’s model consensus leans toward a brief period of northerly wind flow (best support over Santa Barbara County). Increasing on-shore flow would follow by the weekend. The model consensus favors continued, mostly clear skies and modestly higher temperatures in the coastal plain (a little better warming in the coastal valleys).

The “fly in the ointment” for me is that an intermittent, coastal eddy is forecast for at least the next couple of days. One was present this morning, which promoted patchy low clouds over the coastal waters (about Long Beach area southward). It’s possible that an eddy might support more widespread low clouds (reaching the coastal plain from L.A. County southward). Northerly winds aloft would mostly glide over a shallow marine layer. If this happens, the shallow marine would hinder any potential warming trend in the coastal plain (not getting much warmer than it’s gotten today). Since the usually reliable ECMWF model is leaning in this direction today, I’ve leaned today’s campus forecast in the same direction.

Even if the warmest weather scenario is the right one, temperatures in the coastal plain aren’t likely to exceed the low 80ss (late in the week). Assuming the aforementioned, “cut-off” low pressure weakens and moves east in timely fashion, more local forces should take over the on-shore flow tendency common for spring. In short, seasonable weather should prevail at some point (by the weekend or early next week at the latest). No relevant weather changes are foreseen at this time for next week.

Next issued forecast/synopsis may follow on Thursday, 9 May.