textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES

- Temperatures hovering around 3 to 8 degrees above daily normals will result in widespread Moderate HeatRisk with isolated pockets of Major HeatRisk through the middle of next week.

- An increase in moisture through the weekend will lead to slight chances for showers and storms with better chances focused during morning and overnight time frame.

- Overnight low temperatures will be noticeably warmer as a result of the increased humidity with many of the typically warmer lower desert locales struggling to cool below 80 degrees.

SHORT TERM /TODAY THROUGH SUNDAY/

Goes mid-level WV imagery shows the Eastern Pacific remaining under broad ridging with two troughing features on either side. One well defined system in the Gulf of Alaska, while the second feature is centered well over Canada, however affecting the bordering states (ND, MN, WI & MI). Meanwhile, here in the Desert SW, the upper level low continues to track northwards along the Baja Peninsula with ample moisture. This system, to the region's SW, is what brought some sprinkles early this morning across the Phoenix Metro and will continue to bring spotty activity throughout the weekend. Currently isolated thunderstorms can be seen on radar over Yuma County, and thanks to an 18Z balloon launch out of Yuma we can take a closer look at the conditions that helped fuel the activity this afternoon. As of the 18Z sounding, PWATs were at 1.48", and MUCAPE was at 457 J/Kg, enough for convection to continue the development of some isolated storms. However, with CIN at -300 J/Kg and very dry lower atmosphere continued development will struggle to really blossom, albeit not impossible, as the afternoon progresses. Across western Maricopa County and south central AZ a band of activity can also be seen on radar that originally developed just south of Maricopa County and is streaming overhead moving to the NE in the form of mostly virga showers. Due to this most of the areas can expect to receive no measurable rainfall throughout the rest of today.

By Saturday PWATs remain elevated with most of the lower deserts expecting values between 1.2-1.5" or roughly 200-250% of normal, and with 1000-700 mb mixing ratios floating between 8-10 g/kg across Southwest and South-Central AZ. Additionally, the ECMWF deterministic shows another pocket of vorticity moving SW to NE across the state early Saturday morning. This can be enough to set of another round of early morning virga showers with areas of isolated showers. Unfortunately, similar to Friday morning accumulation totals are expected to be near if not at zero in the lower deserts and the Phoenix Metro. By the afternoon hours activity is expected to shift further eastwards into the foothills and the Northern AZ high terrain.

Temperatures over the weekend will remain in the mid 100s to upper 100s by Sunday as the subtropical high begins to inch closer to the region. Current H5 heights are sitting between 589-590 dam and expected to climb slightly by Sunday heading into next week to near 590-591 dam. Overnight low temperatures will also be above normal over the weekend, by 5F-8F, putting overnight lows in the upper 70s to mid 80s across the lower desert areas. This has lead to widespread Moderate to localized Major HeatRisk. With the absence of much overnight/ early morning relief from the heat ensure to stay hydrated and follow heat safety precautions.

LONG TERM /MONDAY THROUGH THURSDAY/

Although uncertainty remains in the upper level pattern next week and especially by the end of the week, ensembles continue to advertise H5 height aloft remaining fairly stable through at least the first half of the week and dry (albeit weak) westerly or northwesterly flow being maintained. Temperatures may warm a few degrees Tuesday and/or Wednesday under slightly drier conditions and a period of stronger subsidence, as suggested by deeper midlevel inversions in model soundings, resulting in slightly higher coverage of Major HeatRisk for a day or two. Extreme Heat products may need to be considered for this timeframe, but confidence is currently lower than usual on the temperature forecast, as it has been fluctuating a few degrees up or down with each run over the last few days. Regardless, temperatures 3F-8F above normal will persist through at least the middle of next week, and Moderate HeatRisk will be widespread.

AVIATION

Updated at 0505Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The potential for isolated SHRA and unusual wind shift timing and directions will be the main weather concerns through Saturday night under periods of mid/high cigs. Confidence is good the typical nocturnal easterly wind shift will either be delayed or absent overnight/early morning and wind directions may just become variable. Isolated SHRA may sweep through the area through Saturday morning; while most activity will be virga or limited duration SHRA, this may create a period of erratic wind directions in the morning before reverting back to a west direction by afternoon. Models continue to suggest SHRA/TSRA well north of the terminals late afternoon sending an outflow boundary south into the Phoenix metro. Models are less resolute with this outcome, and confidence is very low, but KSDL and KDVT would be the most likely to experience an abrupt wind shift from this outflow Saturday evening.

Southeast California/Southwest Arizona including KIPL and KBLH: No major weather concerns should exist through Saturday night under mostly clear skies. Confidence is good that a southerly wind component with occasional gustiness will be maintained at KBLH while directions oscillate between SE and SW at KIPL. Some stronger 20- 30kt sundowner gusts will be possible at KIPL Saturday evening, though confidence is only low to moderate.

FIRE WEATHER

Temperatures 3-8 degrees above normal will prevail with lower desert highs near 110F in some of the hotter spots, especially over the weekend. Improved humidity levels will prevail through the weekend, with afternoon minimums between 15-20% and overnight recoveries in a poor to fair category, with values as low as 25% in the far western districts and between 35-50% for most other areas. With the increasing moisture will also come slight chances for isolated shower and thunderstorm activity. There is a slight chance of isolated showers Saturday morning across southcentral AZ but chances will then become almost entirely confined to the high terrain of the eastern districts by Saturday afternoon. Rainfall potential will be limited, so locally gusty outflow winds and dry lightning potentially leading to natural fire starts are the main concerns. The overall wind pattern will remain diurnal with speeds at or below 15 mph and afternoon/early evening upslope and upvalley gusts up to 25 mph.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...None.