Marine Weather and Tide Forecast for Borrego Springs, CA

DISCUSSION
FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES...

AVIATION AND MARINE SECTIONS UPDATED

Marine layer low clouds have spread into the western valleys this morning with mostly clear skies elsewhere. Low clouds will clear towards the coast by late morning as offshore flow develops.
The HRRR has a 60% chance of low clouds and fog returning to the coastal areas tonight into Monday morning, with lesser inland extent as the marine layer becomes more shallow. Surface pressure gradients remain weakly onshore to the local deserts as of 2 AM, but are forecast to transition offshore later this morning as surface high pressure builds over the Great Basin. This will produce locally breezy winds below the passes and on the coastal mountain slopes with gusts to around 25-35 mph. Northeast to east winds continue into Monday, strengthening slightly Monday morning when peak gusts will be closer to 40 mph.

A large upper level ridge of high pressure amplifies off the West Coast and moves slightly eastward today and Monday. This building ridge combined with the offshore flow will begin the warming trend, especially for areas west of the mountains. Today, highs will be as much as 15-20 degrees above normal in the valleys (80-95 degrees), and around 10-15 degrees above normal elsewhere.
For Monday, highs will increase to around 15-25 degrees above normal, with the greatest departure west of the mountains where highs will be in the low 80s along the coast, and mid 80s to mid 90s across the inland coastal areas and valleys. High temperatures in the low desert will approach 100 degrees. A Heat Advisory begins for the coastal areas and valleys Monday morning.

The upper level high slowly shifts eastward through the week, becoming centered over CA Tue and Wed as it continues to strengthen. Ensembles are in good agreement through this period, with high confidence of the warming trend continuing and high temperatures upwards of 20-25 degrees above normal. The upper high then shifts further east towards the lower Colorado River Valley Thursday and Friday, peaking in strength. There are still some discrepancies in how strong the high will get. On the extreme end of the forecast (NBM 90th percentile), high temperatures could exceed 105 degrees in the Inland Empire and 110 in the Coachella Valley on Thursday, and close to 110 in the Inland Empire and 115 in the Coachella Valley on Friday. Current forecast is around the NBM 50th percentile, which exceeds the EC MOS 90th percentile by a few degrees. Given the likelihood of temperatures around 30 degrees above normal and moderate to high HeatRisk, an Extreme Heat Watch was issued for the mountains below 5500 ft and the low deserts for Thursday and Friday. The ridge finally begins to break down Saturday and Sunday, allowing for gradual cooling.

AVIATION
151800Z
Coasts/Western Valleys
Low clouds have cleared the coastal areas and have given way to VFR conditions through this evening. Expecting patchier low clouds around 300-800ft MSL to move in after 06z Monday, spreading up to 10-15 miles inland. Vis restrictions 4-6SM will be possible mainly across coastal mesas and inland valleys. Low clouds will scatter 15-18Z.

Inland Valleys/Mountains/Deserts... Breezy offshore winds are developing on the coastal mountain slopes, through mountain passes, and locally stretching into eastern valleys. North to northeast wind gusts of 20-25 kts expected, locally up to 35 kts in mountain passes. Gusts weaken after 03z Monday, increasing again towards the end of the TAF period.

MARINE
No hazardous marine conditions are expected through Thursday.

SKYWARN
Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions.



SGX WATCHES/WARNINGS/ADVISORIES
CA...Heat Advisory from 10 AM Monday to 8 PM PDT Friday for Orange County Coastal Areas-Orange County Inland Areas-San Bernardino and Riverside County Valleys-The Inland Empire- San Diego County Coastal Areas-San Diego County Valleys- Santa Ana Mountains and Foothills.

Extreme Heat Watch from Thursday morning through Friday evening for Coachella Valley-Riverside County Mountains-San Bernardino County Mountains-San Diego County Deserts-San Diego County Mountains-San Gorgonio Pass near Banning.

PZ...None.