Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
677 FXUS65 KTWC 180935 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 235 AM MST Tue Jun 18 2024 .SYNOPSIS...After a mild decrease in temperatures today, high temperatures heat back up again Thursday and Friday. Moisture should begin to increase late this week which would bring the potential for thunderstorms late in the week into the weekend. && .DISCUSSION...The upper air pattern is characterized by a longwave trough over the western portion of the U.S. and strong high pressure over the eastern U.S. This will put Arizona under dry westerly flow through the middle of the week with temperatures around normal today and a few degrees above normal Wednesday. Winds will also be elevated today, especially along the international border. By Thursday the area of high pressure over the eastern CONUS begins to build back into the Southwest shunting the trough into Canada. Shortwave troughing will be present to the west over California. This will bring temperatures back into the moderate and major heat categories for portions of southeast Arizona Thursday and Friday. Tucson will make another run at 110 degrees with the NBM giving a 60 percent chance to hit 110 Thursday and 26 percent chance Friday. Because of this an Excessive Heat Watch is in effect both days. Along with the heat the position of the high will help turn the mid-level flow to the east southeast. This easterly flow will extend all the way to the surface thanks to surface high pressure over the plains creating a fairly strong east-west pressure gradient. This will lead to fairly strong winds Thursday, especially in the Gila River Valley where sustained winds of 20 to 30 mph will be possible. This will lead to fairly strong moisture advection from the Gulf of Mexico, aided by a possible tropical system hugging the Texas coastline. Moisture arrives Thursday afternoon mainly along the AZ/NM border where there will be a 15-20 percent chance of mainly dry thunderstorms. Friday into the weekend moisture increases with mean ensemble PWAT values ranging from 1.2 to 1.5 inches by Saturday. Surface dew points also look to reach the mid 50s from Tucson eastward Friday into the weekend. This surface moisture will likely be aided by outflows generated from convection in New Mexico Wednesday and Thursday. By Friday into the weekend expect isolated to scattered thunderstorms each afternoon and evening mainly from Tucson south and eastward. The main threats will likely be strong outflow winds and lightning, with possibly localized and brief heavy rain if the boundary layer has moistened enough later in the weekend. Temperatures moderate some over the weekend thanks to the moisture. Early next week the moisture looks to stick around with continued afternoon and evening thunderstorms with high pressure centered over Arizona. && .AVIATION...Valid through 19/12Z. SKC through the forecast period. Surface winds less than 10 kts this morning becoming southwesterly 10-15 kts with gusts to 25 kts this afternoon and early evening. Winds decease again below 10 kts a couple hours after sunset. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Temperatures are expected to heat back up by Thursday and Friday after the brief few degrees of cooling today and tomorrow. Through Wednesday expect minimum relative humidities of 8 to 15 percent with overnight recoveries between 25 to 40 percent. Afternoon breeziness out of the southwest can be expected through Wednesday with gusts to around 20 to 25 mph. Starting Thursday, surface winds turn to the south to southeast, which also begins to open the door for increasing low and mid-level moisture. The Gila River Valley could see sustained southeast winds of 20 to 30 mph Thursday and 15 to 25 mph Friday. Chances for mainly dry thunderstorms east of Tucson arrive on Thursday and then as far west as Tucson by Friday into the weekend. Min RH values will also increase to 15 to 30 percent. && .TWC WATCHES/WARNINGS/ADVISORIES... Excessive Heat Watch from Thursday morning through Friday evening for AZZ501>506. && $$ Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson