18-Day Weather Analysis – June 22 through July 9

By: Scott Borgioli Weather Ag Chief Meteorologist

General Summary

Generally, and at this time, above-normal high and low temperatures are expected throughout this forecast period. Just about all data suggests fluctuations of +5° to + 10° for high temperatures and lows 0 to +8°. The typical summertime “North Pacific Subtropical High Pressure” is in place in the Pacific and is expected to remain in place during this forecast period (which is normal). Meanwhile, low-pressure systems will periodically pass through the far PacNW with just about no impacts here.

Strong high pressure is present across much of the U.S., including Colorado westward into California. Low pressure in and high-pressure way east of AZ will cause some subtropical moisture to spin into SoCal (south of L.A.) through Sunday, but there will be no effects here in the valley other than maybe a few passing clouds.

EXCEPTION: Thurs/Fri/Sat (June 27-29): Early Thursday morning, a weak and dry low-pressure frontal system will pass through. This will cause slight cooling with temps within 0-4° of the seasonal average. Temperatures respond upward and will then peak back into the ranges listed in the summary above.

Around July 7: Some data signals exist that high pressure in the Pacific may weaken and move more west for 4-10 days. This could result in temperatures dropping to within 0-4° of the normal mean.

Valley Rainfall: None expected at this time.

North American Monsoon: Is expected to fully kick in starting around mid-July with early data indications that such may be above average this year. At this time, it’s a wait-and-see game that will determine if an above-average monsoon will have any effect on the valley in terms of slightly reduced temperatures (periodically) due to any debris cloud cover over the valley.

Precipitation Probabilities

  • July: Average
  • August: Average
  • Sept-Nov: 40-70% of average due to expected “weak” or “moderate” strength La Nina
  • Dec-Jan: 60-80% of average due to expected “weak” or “moderate” strength La Nina
  • Feb/Mar/Apr 2025: 80-110% of average due to expected weakening and/or dissipation of La Nina (conditional on La Nina dissipating during February 2025)

Temperature Anomaly Probabilities

  • Odds favor +4° to +8° of average mean temperatures (as a whole) for July* (*see around July 7 above)
  • Odds favor +4° to +8° of average mean temperatures (as a whole) for August (conditional, preliminary)
  • Odds favor 0 to +5° of average mean temperatures (as a whole) for Sept (conditional, preliminary)


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