Flash Flood Threats in the Southwest

Flash Flood Threat in Arizona, California, New Mexico as Remnants from Tropical Depression Sixteen-E Spread Heavy Rain into Desert Southwest:

  Tropical Depression Sixteen-E made its second and final landfall in northwestern Mexico Monday morning, about 160 miles south-southwest of the bend in the Arizona-Mexico border. Tropical Depression Sixteen-E then dissipated Monday afternoon over northwestern Mexico. Moisture from the remnants of the depression will contribute to locally heavy rainfall, some of it heavy enough to trigger flash flooding.
  This moisture has already contributed to thunderstorms with very heavy rainfall over the past couple of days in northwestern Mexico. Mazatlan reported 122.5 millimeters (just under 5 inches) of rain in a 24-hour period Wednesday into Thursday morning, and noroeste.com reported flooding of some neighborhoods in Culiacán.

  Now, the combination of upper-atmospheric low pressure near the northern Baja peninsula coast and upper-level high pressure centered over the Rio Grande Valley of Texas is acting like an atmospheric egg-beater, piping deep moisture northward into the Desert Southwest.

  In this setup's case, the upper-level low along with the remnants of Tropical Depression Sixteen-E will track across Southern California and the Desert Southwest early this week, providing added instability and lift in the atmosphere for clusters of thunderstorms.

  Flash flood watches continue for portions of the Southwest, including parts of southern California, Arizona and western New Mexico.

These areas, comprised mostly of deserts and mountains, are most at risk of scattered thunderstorms with brief, heavy rainfall. At this time, it appears the threat of torrential rainfall will stay south of hard-hit southern Utah, and should also stay south of Las Vegas.

Moist Surge Pattern Ahead

Southwest Rainfall Outlook

 Original Article: http://www.wunderground.com/news/southern-california-arizona-desert-southwest-heavy-rain-outlook-sep2015