087 FXUS65 KTWC 010909 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 209 AM MST Sun Jun 1 2025 .SYNOPSIS...Temperatures cool to below normal as a weather system moves through today and Monday. This system will bring a substantial moisture increase into the region leading to widespread showers and isolated thunderstorms through Monday morning. Slight chance for storms Tuesday then expect dry conditions and warming temperatures thereafter. && .DISCUSSION...Light shower activity has begun west of Tucson as an upper level low currently west of Baja begins to slowly move eastward. Moisture is streaming in from the south thanks to tropical storm Alvin. PWAT values are currently around 1.1" west of Tucson and will increase to 1.3"-1.6" by this afternoon, which is 250-300 percent of normal. A couple lightning strikes have also be detected in the showers. This activity will continue through the morning hours, slowly expanding eastward increasing in coverage and strength late this morning into the afternoon. HREF members show showers and thunderstorms reaching the Tucson area by mid to late afternoon. Then by evening covering most of southeast Arizona. The dynamics brought by the low combined with surface heating could lead to some stronger storms capable of localized heavy rainfall. The 01/00Z HREF paints areas over the Tohono O`odham Nation and Santa Cruz County as the most at risk for heavy rainfall with probabilities for 1" or greater of rain generally 30-60 percent. General rainfall totals are expected to be 0.2"-0.8" for valley locations with localized areas possibly seeing up to 1.25" through Monday. The bulk of this is expected to fall this afternoon and evening. Soils are very dry across the area, so a lot of this rain will quickly runoff and could lead to flooding issues. Because of this and the threat of debris flows over new area burn scars a Flash Flood Watch is in effect Sunday from Tucson westward. Gusty outflow winds will also be a threat before low levels moisten up, especially east of Tucson late this afternoon into the evening. HREF shows probabilities of 30-50 percent for winds in excess of 30 knots east of Tucson. Overnight showers will continue, but rain amounts will be on the lighter side as the upper low weakens and moves northeastward towards the Four Corners. During this time PWAT values also begin to decrease, although they will still be above normal for this time of year. As synoptic scale forcing decreases shower activity will decrease from west to east Monday with additional rainfall amounts up to 0.25". High temperatures today and Monday will be moderated by the moisture and cloud cover with Tucson possibly seeing sub 90 degree highs both days. Tuesday PWAT values will be diminished compared to today, but will still be around 150 percent of normal. Another low will move through Tuesday and will tap into the leftover moisture leading to a slight chance for showers and thunderstorms. Best chances will be in the White Mountains. Thereafter southeast Arizona stays under dry southwest flow with high pressure becoming centered over northern Mexico and shortwave troughing over the West Coast. Temperatures will stay below normal through Wednesday then increase to normal or a few degrees above normal Thursday into next weekend. && .AVIATION...Valid through 02/12Z. Expect BKN clouds 4k-8k ft AGL through the period. -SHRA and isold -TSRA dvlpg west of KTUS this morning and spreading east across the remainder of fcst area this afternoon. Thereafter expect SHRA/TSRA at most terminal locations through the end of the forecast period. Brief MVFR cigs will be possible after 02/03Z in SHRA. SWLY/SLY winds 8-15 kts thru much of valid pd. Isold gusts to 30-40 kts near any TS that develop. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Tropical moisture moves into the area today which will lead to widespread showers and isolated thunderstorms. This activity begins this morning west of Tucson, spreading to cover most of southeast Arizona late this afternoon into the evening. Showers and thunderstorms decreases from west to east Monday. Rain could be heavy at times leading to possible debris flows over new area burn scars. Overall winds remain light but gusty and erratic winds would occur with any thunderstorm activity. Another weather system moves through Tuesday with a slight chance for precip east of Tucson along with breezy winds. Thereafter expect dry and warming conditions. && .TWC WATCHES/WARNINGS/ADVISORIES... Flood Watch from this afternoon through this evening for AZZ503>507-513-514. Flood Watch from 7 AM MST this morning through this afternoon for AZZ501-502-515. && $$ Hardin Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson