Aviation AND MARINE DISCUSSIONS BELOW,
Periods of high cloud coverage are expected to continue into Monday. The pressure gradient is trending more onshore compared to noon yesterday with the pressure gradient -1.1 mb from SAN-DAG. The trend is expected to continue to skew more onshore, which may allow for patchy low clouds and fog to develop tonight into Monday morning. One potential hiccup to fog development could be how widespread the high cloud coverage is. More widespread high clouds will lessen fog chances and less will increase them. If fog develops, it may be locally dense. The most likely place for dense fog to develop is near higher coastal terrain. Low clouds and fog are expected to remain present each night and morning for much of this week but a deepening marine layer will limit chances for coastal dense fog.
Highs on Monday are expected to be a few degrees cooler across the area due to a passing shortwave trough. Breezy westerly winds may develop over the mountains and locally into the deserts, but no impacts expected. Weak ridging will build over California on Tuesday, which will bring a degree or two of warming to some inland locations. The ridge will quickly be pushed aside on Wednesday as stronger troughing sets up over the Eastern Pacific.
There remains quite a bit of uncertainty in the ensemble guidance in regards to the timing of the low's passage and expected precipitation amounts. Overall, timing of the onset of precipitation has trended later, but members of the GEFS are still showing a quicker passages of the low with the bulk of the precipitation centered on Friday/Saturday, while the majority of the ensemble members of the ECMWF are showing a slower progression and the bulk of the precipitation centered Saturday/Sunday. Both of the global models have quite a bit of spread in precipitation amounts as well. NBM probabilities of 48 hour rainfall totals (5 am Friday-5am Sunday) exceeding 0.50" are highest in the mountains at 50-60 percent and around 20 percent for the coast and valleys. The High Desert has about a 10 percent chance with less than 5 percent chance for the low desert. In addition to timing of rainfall, the forward progression of the low will influence when the strongest winds and coldest conditions will occur. Some snow is expected out of this system but there still remains considerable uncertainty in snow levels. The spread in snow level guidance from the NBM ranges from 7000-9000 ft on Friday and 6500-7500 ft on Saturday and Sunday.
Patchy fog may develop tonight into Monday morning along the coast, with the potential for locally dense fog on the coastal mesas. Low clouds and fog will continue most nights and mornings this week, but the marine layer will become deeper, lessening the chances for dense fog. Temperatures will fluctuate a few degrees each day through mid- week, but mostly stay above average for this time of year. Pattern change expected for the end of next week, with cooler, windier, and wetter conditions expected.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, UPDATED 00Z AVIATION AND MARINE DISCUSSIONS BELOW,
Periods of high cloud coverage are expected to continue into Monday. The pressure gradient is trending more onshore compared to noon yesterday with the pressure gradient -1.1 mb from SAN-DAG. The trend is expected to continue to skew more onshore, which may allow for patchy low clouds and fog to develop tonight into Monday morning. One potential hiccup to fog development could be how widespread the high cloud coverage is. More widespread high clouds will lessen fog chances and less will increase them. If fog develops, it may be locally dense. The most likely place for dense fog to develop is near higher coastal terrain. Low clouds and fog are expected to remain present each night and morning for much of this week but a deepening marine layer will limit chances for coastal dense fog.
Highs on Monday are expected to be a few degrees cooler across the area due to a passing shortwave trough. Breezy westerly winds may develop over the mountains and locally into the deserts, but no impacts expected. Weak ridging will build over California on Tuesday, which will bring a degree or two of warming to some inland locations. The ridge will quickly be pushed aside on Wednesday as stronger troughing sets up over the Eastern Pacific.
There remains quite a bit of uncertainty in the ensemble guidance in regards to the timing of the low's passage and expected precipitation amounts. Overall, timing of the onset of precipitation has trended later, but members of the GEFS are still showing a quicker passages of the low with the bulk of the precipitation centered on Friday/Saturday, while the majority of the ensemble members of the ECMWF are showing a slower progression and the bulk of the precipitation centered Saturday/Sunday. Both of the global models have quite a bit of spread in precipitation amounts as well. Nbm probabilities of 48 hour rainfall totals (5 am Friday-5am Sunday) exceeding 0.50" are highest in the mountains at 50-60 percent and around 20 percent for the coast and valleys. The High Desert has about a 10 percent chance with less than 5 percent chance for the low desert. In addition to timing of rainfall, the forward progression of the low will influence when the strongest winds and coldest conditions will occur. Some snow is expected out of this system but there still remains considerable uncertainty in snow levels. The spread in snow level guidance from the NBM ranges from 7000-9000 ft on Friday and 6500-7500 ft on Saturday and Sunday.
052340z, Generally VFR with BKN-OVC clouds AOA 15k ft through tonight, not as widespread on Monday. Confidence is moderate on low clouds 1200-1800 ft MSL impacting coastal TAF sites after 10Z tonight. Highest chance for low clouds is across San Diego County. Vis restrictions 2-5 SM over higher coastal terrain. Any low clouds near the coast that form will begin to scatter out 16-18Z Monday.
No hazardous marine conditions expected through Thursday. Winds and seas may increase late week due to an incoming weather system. Low confidence in details at this point.
Ca, None. PZ, None.
