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Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
285 FXUS65 KTWC 182127 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 227 PM MST Tue Jun 18 2024 .SYNOPSIS...After a mild decrease in temperatures today, high temperatures heat back up again Thursday and Friday. Moisture will increase starting Thursday and result in the potential for thunderstorms late in the week and through the weekend. && .DISCUSSION...A relative lull in hot temperatures today across the forecast area as highs this afternoon drop back down to seasonable levels. This is due to broad troughing across the western US. The normal high for Tucson is 102 degrees today. Wednesday: Broad troughing continues, though heights/thickness values nudge upward which will result in a few degrees of warming. Thursday: A very interesting weather pattern starts Thursday as the pattern aloft begins to shift. While heights remains elevated with a ridge axis just to our southeast, a strong low level east push, at least partially attributed to what is now the Potential Tropical Cyclone One in the western Gulf of Mexico, will move into Arizona from the east. A very tight surface pressure gradient will ramp up winds considerably, but most notably near the NM border and in the Upper Gila River Valley. These strong east to southeast surface winds are quite anomalous per the ECMWF EFI and we`ve ramped up the wind forecast east of Tucson Thursday. Some locales, but especially the Upper Gila River Valley may need wind headlines Thursday into Friday, especially if these trends continue. The strong east push will bring with it increased moisture as PWAT values jump to the 1" to 1.25" range Thursday. The western edge of this east push will make it to around the Tucson area Thursday afternoon with a pseudo dry-line/convergence setting up. Still some differences in the ensembles with the GEFS/GEPS pushing the moisture farther west than the ECMWF EPS. This boundary may help to initiate a few mainly dry thunderstorms with little rain but strong and gusty outflow winds (in addition to the background synoptic scale gusty winds). Meanwhile, an Excessive Heat Watch remains in effect from Tucson westward Thursday. Temperature trends have dropped back slightly so will continue to monitor. Friday: The moisture and east push will have made it all the way to the western deserts with ensemble mean PW values ranging from about 1 inch to 1.5 inches across the forecast area. The wind speeds and gradient will remain strong on Friday with continued breezy to windy across the forecast area. Even with the increased moisture, as the high aloft will be nearly overhead with warm mid level temperatures, that will help to limit widespread convection. With that said, still expect at least isolated mainly dry thunderstorms. An Excessive Heat Watch is also in effect Friday but this will need to be re-evaluated over the next day or two as the moisture may help keep temperatures below high heat risk levels, especially for areas near Tucson. Hotter temperatures more likely west of Tucson. Saturday into next week: Once the moisture comes in, it doesn`t appear to be going anywhere per ensemble guidance. That means from a moisture perspective, we are in the monsoon. However, with the mid/upper level high nearby, that will certainly be a mitigating factor. Depending on the strength/location of the high each day, that will drive convective trends but at least a low grade monsoon pattern is expected during this time frame with temperatures a few degrees above normal. && .AVIATION...Valid through 20/00Z. SKC through the forecast period. Surface winds SWLY 10-15 kts with gusts to 25 thru 19/03Z. Thereafter, sfc winds decrease to 10 kts or less into Wednesday morning. Aft 19/18Z, sfc winds become SLY/SWLY 10-15 kts with gusts to 25 kts thru the end of the forecast period. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Temperatures are expected to heat back up by Thursday from Tucson westward after the brief few degrees of cooling through Wednesday. Minimum relative humidity values through Wednesday will be 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 east to southeast and become stronger, especially across Graham/Greenlee/Cochise Counties where sustained 20-ft winds of 20 to 35 mph are expected with stronger gusts. The strongest of these winds will be in the Upper Gila River Valley near Safford. With these east to southeast winds, there will be increased moisture with min RH values in these locales around 20 percent Thursday. So while the winds are at critical levels, RH values will remain just above critical levels but certainly still elevated fire weather conditions due to the strong winds and dry fuels Thursday. Breezy to windy conditions continue Friday, though increased moisture will have overspread more of the forecast area. Some isolated mainly dry thunderstorms are expected starting Thursday from Tucson eastward and then to include the remainder of southeast Arizona Friday. As moisture remains this weekend, isolated thunderstorms will continue each day through the weekend into early next week with a low grade monsoon pattern in place. && .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