734 FXUS65 KPSR 161018 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 315 AM MST Sun Jul 16 2017 .SYNOPSIS... Temperatures will moderate during the early parts of this week as moisture and thunderstorm activity increases across the region. Areas of blowing dust and gusty winds will likely accompany any thunderstorms during the afternoon and evening hours. Increasing moisture levels will also lead to greater storm coverage as well as elevating the threat for flooding rains the next several days. && .DISCUSSION... The flow pattern across the SW Conus continues to become increasingly favorable towards general ascent supporting convective development and sustenance through much of the forecast area over at least the next 48-72 hours. The H5 anti-cyclone center over southern NV this morning will slowly translate into Utah later today while a well defined inverted trough bisecting Chihuahua and New Mexico squeezes under the southern periphery of the ridge. The juxtaposition of the midlevel inverted trough and upper divergence fields from a deformed H2 layer appear almost optimal this evening and overnight (and continuing into Monday and Tuesday for that matter) for persistent deep layer ascent. One of the primary forecast uncertainties today deals with the ability for the atmosphere to recover from extensive convection Saturday evening/overnight. 03Z KPSR sounding sampled a somewhat contaminated environment, but nothing completely overturned or prohibitive of rapid destabilization later today. However, there is still question towards the magnitude of clearing today as the convective complex over northern Sonora was only recently decaying with its associated thick cirrus shield. On the other hand, subsidence and clearing were spreading west from New Mexico which should aid in cloud erosion later this morning. Given the evolution of the setup yesterday and recent trends in satellite imagery, feel sufficient clearing and destabilization will occur today though convective initiation may be delayed somewhat versus the past couyple days. One major benefit of the thunderstorms last evening/overnight was the boost in low level mixing ratios as objective analysis shows solid 12-14 g/kg levels now settled through the entire southern half of Arizona. And despite vertical mixing this afternoon, well mixed sfc-800mb 12 g/kg amounts should hold yielding MUCape at least 1500 J/kg in a weakly capped environment. Where as yesterday a subtle shortwave diving SW helped erode capping around H7, no such wave is seen today in WV imagery; and it may be solely on the inverted trough and divergence fields to create ascent, remove capping inhibition, and maintain thunderstorm mode. High resolution models are not necessarily unanimous in congealing storms over the eastern half of the CWA this evening, however SSEO neighborhood probabilities (along with other non-SSEO members) are extremely bullish in bringing mature storms to lower elevations. And many signs remain present indicating this evening might be one of those extremely active monsoon evenings with multiple high impacts for the area. Assuming this evening and tonight are indeed the larger convective periods, Monday would prove to be a more inactive day with a worked over atmosphere. Have kept POPs for most of the daylight hours towards a lower end range for mid July though cannot rule out showers at any point given the greater amounts of moisture advecting into the region. While PWATs near 1.75 inches (per NAEFS mean)are only towards the 90th percentile, actual moisture amounts closer to 2 inches may actually come to fruition. Thus, a better flood threat will begin to materialize starting today and a flash flood watch has been issued through Monday (and could be extended through Tuesday when all is said and done). With the moisture increase and lapse rate reduction, storms will tend to transition more into a heavy rain and flash flood threat (although strong winds will remain a substantial threat). While still relatively low in confidence, there is evidence among operational models that Tuesday morning may provide the ingredients necessary for a nocturnal/morning convective event associated with a more robust shortwave embedded in the easterly flow. The ECMWF has been consistent in presenting this solution and every monsoon season there are 1 or 2 days with this scenario. Will need to maintain a close watch on this period given the potential high impact during an uncommon time of day. The forecast for the second half of the week is still somewhat uncertain, though the trend among operational and ensemble members remains towards maintaining strong positive height anomalies over the central plains with slight retrogression towards the Southwest. Medium range models also still indicate as this transition occurs, drier air will infiltrate and advect westward into the midlevels. This would effectively increase inhibition at lower elevations and return thunderstorm activity/coverage back to a more typical monsoon season level. Therefore, have attempted to depicts POPs closer to a more standard temporal and spatial distribution while also warming temperatures back into a near to slightly above normal range. && .AVIATION... South-Central Arizona including KPHX, KIWA, and KSDL: Another active monsoon afternoon/evening looks to be in store across the region, with scattered-numerous showers/thunderstorms once again developing across the higher terrain to the north and east of the Greater Phoenix Area. Hi-res computer models are in strong agreement that at least a solid outflow boundary will be pushed down into the Phoenix area this evening, with the most likely time of arrival at the terminals being in the 01Z-02Z timeframe. Peak gusts may exceed 30kt. Some blowing dust will likely accompany the winds, with at least minor reductions in visibilities likely. Lighter easterly winds are then expected to prevail through the rest of the night and into Sunday morning. As far as the impacts from the thunderstorms themselves, there is still not enough confidence to mention anything more then VCTS is the tafs at this time. A few lingering showers are possible past midnight and into the early morning hours Sunday and we should see BKN to OVC mid/high cloud decks from the mid evening into the morning hours Sunday with most bases aoa 10k feet. Southeast California/Southwest Arizona including KIPL and KBLH: Thunderstorm chances over the far western deserts, and at the TAF sites, still appear rather low thru the taf period, but we will be seeing more mid and high level cloudiness at the terminals with mid decks 12-15k feet along with variable amounts of cirrus. Winds will continue to favor the south at KBLH and southeast at KIPL over the next 24 hours, with speeds genly below 15kt at both taf sites. Aviation discussion not updated for amended TAFs. && .FIRE WEATHER... Monday through Friday: The early portion of the week looks to be the most active, convectively speaking, as deep moisture will be in place allowing for scattered mainly afternoon and evening showers and thunderstorms across much of the area, especially over south-central Arizona. Minimum RH values will be very high Monday and Tuesday, ranging from 25 to nearly 40 percent. High temperatures will fall well below seasonal normals with some of the central deserts dropping into the 90s. For Wednesday through Friday, convective activity will fall off slightly, becoming more isolated over the lower deserts with the best chances of thunderstorms focused over the higher terrain areas north and east of Phoenix. Minimum RH values will drop slightly but remain elevated, ranging mostly from 20 to 30 percent over the deserts each day. High temperatures will rise but for the most part will stay slightly below seasonal normals. Winds will change little from day to day following typical diurnal patterns with winds favoring the south over the western deserts and the southwest across south central Arizona during the afternoon and evening hours. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Flash Flood Watch from 2 PM MST this afternoon through Monday evening for AZZ534-537>563. CA...None. && $$ Visit us on Facebook, Twitter, and at weather.gov/phoenix DISCUSSION...MO AVIATION...Percha FIRE WEATHER...CB