LAS VEGAS (KTNV) — MORNING: A warm start in the upper 80s and low 90s around Las Vegas with sun and light winds. August begins this weekend, and if the forecast verifies on Saturday, we'll tie the August all-time record high. The heat risk rises to "extreme" this weekend and beyond; an Extreme Heat Warning begins today at 10 a.m. and runs through Sunday at 8 p.m.Overnight lows rise from the upper 80s this week to the low 90s this weekend and early next week. Forecast pollen levels are "low" this week, with ragweed, grasses, and chenopods listed as the predominant pollen types. The air quality forecast is "moderate" today and tomorrow due to ozone.