If you have been in Flagstaff for a while, you know that the 4th of July almost always marks the first serious rains of the monsoon season. Humidity should build quickly over the next few days. Along with the humidity, we should start to see thunderstorms start as well. From the dewpoint chart to the right, you can see that the first burst of humidity has busted. By mid-week, dewpoints will be back in the range for thunderstorms.
From the National Weather Service
...MONSOONAL WEATHER PATTERN TO DEVELOP THIS WEEK... THE RECENT PERIOD OF ABOVE NORMAL TEMPERATURES AND GENERALLY DRY WEATHER CONDITIONS WILL END WEDNESDAY AS THE REMNANTS OF AN EASTERLY WAVE USHER A SURGE OF MONSOON MOISTURE NORTHWARD THROUGH ARIZONA...AS WELL AS CENTRAL AND WESTERN NEW MEXICO. ONCE THE MOISTURE ARRIVES...SOUTHERLY FLOW WILL KEEP IT IN PLACE FOR THE REMAINDER OF THE WORK WEEK AND POSSIBLY INTO THE WEEKEND. DAILY ROUNDS OF GENERALLY SCATTERED SHOWERS AND THUNDERSTORMS WILL INCREASE IN COVERAGE TO NUMEROUS AT TIMES IN THE MOUNTAINS AND NEAR NEW MEXICOS WESTERN BORDER. SOME THUNDERSTORMS WILL BE CAPABLE OF PRODUCING LOCALLY HEAVY RAIN AND MINOR FLOODING. WHEN HEAVY RAINFALL DEVELOPS ON RECENTLY BURNED FORESTS...THE LACK OF VEGETATION AND BAKED GROUND CAN EASILY RESULT IN FLASH FLOODING WITHIN AND BELOW THE BURN SCARS. AT THIS TIME...THE RISK FOR BURN SCAR FLASH FLOODING APPEARS TO BE GREATEST WEDNESDAY THROUGH FRIDAY...ESPECIALLY DURING THE AFTERNOON AND EVENING HOURS.