California Polytechnic State University, CA 93405 Weather

Synopsis

29/235 AM.

Gradual cooling will continue through the week as will coastal flooding issues due to very high tides. The next storm system is expected to bring rain to the area from as early as Friday through Sunday, likely peaking Saturday evening into Sunday morning.

Short term (tdy-sun)

29/1255 PM.

For the short term, main focus remains on rain chances across the district. Models continue to be on the same broad synoptic page, but differ in the details. An upper low will continue to spin off the Pacific Northwest coast through Saturday, before moving inland on Sunday. This will result in a very sharp trough, or a weak upper low, impacting the area this weekend.

Overall, the last couple of model runs have trended a bit "drier" and further south with this storm, but ensembles, especially the ECMWF suite, still indicate a decent number of moderate to heavy rainfall members. So, at this time, there is high confidence in widespread rainfall across the area, but only moderate confidence in amounts through the Halloween weekend.

Today through Saturday morning, there will be some scattered light showers just about anywhere with a deep moist layer in place across the area. Rainfall totals, if any, through Saturday morning will be on the order of a few hundredths of an inch. By Saturday afternoon/evening, the main storm will move eastward towards Southern California, moving inland during the day on Sunday. As alluded to above, the heaviest rainfall Saturday night and Sunday looks to remain south of LA county. Current rainfall totals look to generally be in the 0.25 to 1.00 inch range across the area with locally higher amounts (up to 2.00 inches) possible across favored mountain slopes. Given the continued uncertainty between models, there still is a 20% chance of amounts about double the expected totals and a 20% chance of amounts about one half of the expected totals.

As for rain rates, the best instability looks to remain south of LA county. So, rainfall rates are expected to be in the 0.10 to 0.33 inch/hour range. Additionally, any thunderstorm threat looks to be minimal (under a 10% chance).

Long term (mon-thu)

29/1255 PM.

For the extended, latest models are exhibiting good synoptic agreement through the period. At upper levels, ridge will develop over the area Monday/Tuesday then will shift eastward as a upper low sweeps northeastward across northern California on Wednesday and Thursday. At the surface, weak offshore flow will prevail on Monday/Tuesday with a return of weak onshore flow by Wednesday and Thursday.

Forecast-wise, the above synoptic pattern will result in benign weather for the area. With the ridge overhead and weak offshore pressure gradients, Monday and Tuesday will be dry and warmer with high temperatures topping out in the upper 60s and 70s. There will be some northeasterly winds, due to the offshore pressure gradients, but any winds are expected to remain below advisory levels.

For Wednesday and Thursday, a slight cooling trend can be expected with some increase in high clouds. With the upper low moving northeast into northern California, there will be a low chance (less than 20%) of some light showers across the Central Coast.

Aviation

29/2313Z.

At 2212Z at KLAX, there was a deep moist layer to 5500 feet. marine layer was 5000 ft deep. The top of the inversion was at 8000 ft with a temperature of 10 C.

High confidence in VFR TAFs for KPMD & KWJF.

Moderate to high confidence in TAFs with VFR cigs for remaining sites, with infrequent periods of 020-030 MVFR cigs. Additionally, there is 10-25% chance of -DZ or -SHRA from late tonight through the TAF period.

KLAX: Moderate to high confidence in TAF. VFR cigs likely with infrequent periods of BKN020-030 cigs. 15-25% chance of -DZ or -SHRA from around 30/06Z through the period. Any east wind component is expected to remain under 8 kt.

KBUR: Moderate to high confidence in TAF. VFR cigs likely with infrequent periods of BKN020-030 cigs. 10-20% chance of -DZ or -SHRA from around 30/06Z through the period. No wind issues expected.

Marine

29/142 PM.

Conditions are expected to remain below Small Craft Advisory (SCA) levels through Saturday. Southwest flow aloft will produce chances for drizzle and isolated light rain showers Today & Friday.

A storm system is expected to impact the coastal waters this weekend. However, guidance continues to shift to the south with some solutions showing the bulk of showers only as far north as the Channel islands. Regardless, there will be some gusty SCA NW winds behind the system on Sunday.

Watches, warnings and advisories

CA: Coastal Flood Advisory in effect until 2 PM PDT Friday for zones 87-340-346-349-350-354-362-366. (See LAXCFWLOX). PZ: NONE.