616 FXUS65 KPSR 221206 AAA AFDPSR Area Forecast Discussion...Updated National Weather Service Phoenix AZ 505 AM MST Mon Oct 22 2018 .UPDATE...Updated aviation and fire weather discussions. && .SYNOPSIS... Periods of isolated showers and thunderstorms for Phoenix and scattered showers and storms to the south and east of Phoenix will prevail through Tuesday, although only modest rainfall is anticipated for most areas. Temperatures will also cool slightly with readings closer to seasonal normals. Drier conditions will move into the region by the middle of the week with temperatures remaining near seasonal normals before a warming trend into next weekend. && .DISCUSSION.... The upper level trough over the Southwestern U.S. will continue to provide chances for showers and thunderstorms to the northeastern 2/3s of Arizona through Tuesday. Current water vapor imagery shows the low center is situated across western Nevada while several embedded shortwaves rotate through the trough. Atmospheric profiles remain conducive for thunderstorms northeast of a line from Tucson to Phoenix to Las Vegas. This led to a few severe thunderstorms yesterday with severe hail being the main result. Current radar shows the bulk of the shower and thunderstorm activity along the Colorado River Valley north of La Paz County, but the last hour has shown isolated activity beginning again across Pinal and central Maricopa Counties. Fairly cold air aloft will continue to allow for steep lapse rates and relatively unstable atmospheric conditions while shear profiles remain favorable for organized storms. A jet streak moving through Baja early this morning should give support to more showers and thunderstorms to Phoenix and areas east of Phoenix. This activity is supported by the bulk of the CAMs with it lasting into at least early afternoon. These storms should remain fairly isolated to scattered and sub-severe, but we may see some small hail with the strongest storms. Later this afternoon, there should be a lull in the activity due to less favorable jet positioning, but there may still be a few storms that form over higher terrain areas. Tonight also seems quiet for the most part, but slight chances will remain in the forecast as all it would take is a hardly noticeable shortwave to trigger further activity. Temperatures today should drop a couple degrees from yesterday with readings right around seasonal normals. A more significant shortwave is still forecast to affect the region on Tuesday, but the latest model runs have shifted the timing a bit later with it moving through mainly during the daytime hours Tuesday versus during early to mid morning. Under nearly the same atmospheric conditions as we are currently seeing, this should create a better chance for showers and thunderstorms. Environmental conditions should again be conducive for some strong to severe thunderstorms, much like what we had yesterday. Shear profiles do look a bit weaker later on Tuesday, but it should still be sufficient for some discrete longer lasting storms. High res CAMs essentially all agree there will be scattered to widespread showers and thunderstorms Tuesday afternoon across the eastern half of Arizona. This activity should diminish by late Tuesday evening with a few lingering showers or storms into Tuesday night. The shortwave is shown exiting to the east Wednesday morning with drier air beginning to filter in from the west and rain chances coming to an end. Weak troughing will still remain across the Desert Southwest on Wednesday before a building Pacific ridge off the West Coast begins to nudge into the region on Thursday. As this ridge moves over the region Friday into the weekend, temperatures will rise above normals with some deserts likely topping 90 degrees. There is quite a bit of model spread at this time, especially among the GFS members, but for now we are pushing temperatures more toward the more consistent and warmer European. && .AVIATION... South-Central Arizona including KPHX, KIWA, and KSDL: Short wave disturbance rotating northeast through the area this morning will result in isolated showers and thunderstorms. Better bet is for showers but thunderstorms have already been occurring. For now will mention VCTS only at KIWA which is closer to current storms but may have to amend if storms continue and approach the other terminals including KPHX. As wave moves off to the east this morning, shower threat will diminish so VCSH mention will end after 18z. Expect largely BKN decks this morning mainly around 8k feet with cloud decks becoming more scattered during afternoon and evening hours. Cannot rule out CIGs developing again overnight tonight. Winds will favor east/southeast through the afternoon, becoming light variable or light north/northwest late this afternoon into early evening before returning back to the east after midnight. Southeast California/Southwest Arizona including KIPL and KBLH: Generally light winds and virtually no precip chances expected in the western deserts next 24 hours. Winds to be largely light variable at both TAF sites much of the time. Skies genly clear but as the day progresses could see increasing cirrus decks becoming BKN overnight tonight. No real aviation concerns at this time. Aviation Discussion not updated for amended TAFs. && .FIRE WEATHER... Wednesday through Sunday: Dry conditions and gradually lowering humidities will return during the Wed-Sun period as winds aloft become more westerly. Winds should remain at 15-20 mph or less area- wide. Minimum humidities will be on the decrease through the weekend, with values in the 15-50 percent range Wed (lowest over SE CA) dropping into the teens and 20s by the weekend. Expect a warming trend with near normal high temperatures Wednesday rising to above normal readings this weekend. Warmer lower deserts reaching into the low to mid 90s over the weekend. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Kuhlman AVIATION...CB FIRE WEATHER...Hernandez/CB |