Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

101 pm PDT Fri Sep 24 2021

Synopsis

24/1249 PM.

An area of low pressure over southwest Utah will back into the region through the weekend and continue a cooling trend. Instability to the south and east of the area will likely clip the area to bring the possibility of isolated showers and thunderstorms to the mountains and desert. Another area of low pressure will approach the area early next week and keep temperatures on the cool side of normal through the middle of next week.

Short Term

(tdy-Mon), 24/1229 PM.

An upper low is taking an inside slider track from AZ to extreme southern California and northern Baja today. Quite a bit of convective activity is developing in that area today with pwats there in excess of 1.5". However, while stability parameters are decent today, moisture drops off rapidly to the north and chances for convection locally are not as high. Given the northeast flow around the upper low if storms do form over the LA Mountains there's about a 10 percent chance some of that could spill over into the adjacent valleys and possibly even the coast.

Otherwise, today the cooling trend continues with most areas down another 3-6 degrees from Thursday's levels. This is expected to continue through the weekend as the low reverses course and heads back to AZ Sunday. Still a small chance of some convection in the LA Mountains again Saturday but again not a lot of moisture to work with and stability parameters actually a little less favorable than today.

A little high pressure pops up Monday following the passage of the low to the east. However, gradients still trending onshore so while inland areas should warm a degree or two, coastal areas likely will see little change or slight cooling.

Long Term

(Tue-Fri), 24/1248 PM.

Models in pretty good agreement next week indicating a pretty deep trough will move through from the northwest Tuesday into Wednesday. This is expected to rapidly deepen the marine layer, possibly to 4000' or more. High temps expected to 4-8 degrees below normal with possible drizzle in the morning hours.

Following the trough moderate northwest flow will develop and help scour out the marine layer for the remainder of the week. Gusty northwest winds likely across at least the western portion of the forecast areas with some wind advisories possible. Temperatures expected to rapidly warm back up to normal or above normal by Thursday or Friday. Some ECMWF/GFS solutions are showing some offshore flow developing as early as Thursday with very warm temperatures for coast and valleys.

Aviation

24/1758z.

At 05Z, the marine layer depth was around 900 feet deep at KLAX. The top of the marine inversion was around 2800 feet with a temperature near 23 degrees Celsius.

Moderate confidence in the current forecast for coastal terminals. Generally high confidence for valley and desert terminals. Higher confidence in timing. Less confidence in flight categories.

For coastal terminals, IFR conditions will improve VFR category after 19Z to 20Z. An early return of IFR to MVFR conditions should be expected on this evening.

For valley and desert, lower confidence in flight categories for desert terminals due to smoke. It could end up being VFR through the period. There is a slight chance to chance (10-30 percent) of low clouds with IFR conditions for KBUR late tonight into Sat morning.

KLAX, Mostly VFR through early this evening then IFR to MVFR conditions are expected tonight into Sat morning. VFR conditions should develop aft about 21Z on Sat. The timing of the clearing or onset of the lower flight conditions may be off +/- an hour or two.

KBUR, There is a 20 percent chance of IFR conditions between 13Z and 16Z Sat, otherwise hi confidence for VFR conditions thru the period.

Marine

24/1259 PM.

High confidence that winds and seas will remain below Small Craft Advisory (SCA) level through Monday. NW winds will begin to increase Monday evening where there is a 40% chance of SCA level conditions over the outer waters. Much better confidence on Tuesday for widespread SCA level NW winds from the Central Coast to San Nicolas Island and extend through at least Wednesday. There will even be a slight chance (20%) of Gales across the outer waters Tuesday and Wednesday afternoon and evening.

Watches, Warnings, Advisories

Ca, NONE. PZ, NONE.

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