textproduct: NWS Phoenix

KEY MESSAGES

- Extreme Heat Warnings are in effect through this evening for Western Imperial County as well as along the Lower Colorado River Valley as heat indices are forecast to peak between 110 and 120 degrees.

- Deeper moisture will provide favorable conditions for daily shower and thunderstorm activity to materialize across the area through the middle of the week, along with noticeably cooler temperatures.

- Thunderstorm chances will decrease noticeably by the end of the week into next weekend as drier air filters in.

SHORT TERM /Today through Tuesday/

High pressure remains positioned over the Four Corners region continuing to bring easterly to southeasterly flow aloft over Arizona. With easterly flow in place moisture will continue to be advected into the region with model projecting PWATs this afternoon/evening climbing upwards of 1.5" with the 18Z sounding already measuring a PWAT of 1.45". Models are in good agreement in another round of thunderstorms will development in the northeastern AZ high terrain, and especially in southern AZ, late this evening/tonight. With any thunderstorm development in these areas outflows are very likely with the HREF showing up to a 70% chance of winds above 35 mph in the higher terrain and southern AZ, with a 30- 50% chance of winds above 35 mph surviving into NW Pinal County and Maricopa County. Similar to last night, these outflows will have the potential of triggering storms in the lower deserts, however the location of where exactly storms are likely to develop in the lower deserts is where model agreement begins to fall apart. As mentioned previously, development is still favored for tonight as the atmosphere continues to see similar conditions to last night. Hi-res models continue to show CIN eroding to below 100 J/kg and MLCAPE climbing near to slightly above 1000 J/kg this evening. With these conditions, strong downburst wind gusts and locally heavy rainfall will continue be the main hazards across the lower deserts of south- central AZ, to include portions of the Phoenix area. There will also be a potential for areas of blowing dust to materialize as well in the dust prone areas. Atmospheric conditions will not vary much on Tuesday, especially in the eastern higher terrain, however, depending on this evening's activity Tuesday could turn out to be more of a down day for the lower deserts.

Otherwise, afternoon high temperatures today will continue to be above normal, ranging between 105-110 degrees, resulting in widespread Moderate HeatRisk. Out west the dew points will remain quite high, in the mid 60s to mid 70s, resulting in heat indices peaking between 110-120 degrees this afternoon. Due to this the Extreme Heat Warning remains in effect through this evening along the Lower Colorado River Valley and the Imperial Valley. By Tuesday temperatures "cool" slightly back near normal, and the HeatRisk becoming widespread minor to localized Moderate, with Moderate mostly across the western lower deserts.

LONG TERM /Wednesday through Sunday/

Model guidance continues to be consistent in indicating another more active period materializing Wednesday into the first half of Thursday. The flow by Wednesday is forecast to shift out of the south as the subtropical high shifts into Texas and a upper-level low meanders off the California coast. This southerly flow is likely to bring additional moisture northward from Mexico, with projected PWATs increasing to 1.7-2.0" and low-level mixing ratios increasing to 12-13 g/kg. In addition, there will likely more favorable upper- level forcing from the aforementioned upper-level low in the form of divergence aloft as well as the potential of an easterly wave moving into the region from Mexico as indicated by both the GFS and ECMWF. The more favorable upper-level forcing is likely to enhance the convective activity, with flash flooding becoming more of a threat given the deeper moisture profiles that will be in place. The latest NBM PoPs for Wednesday through the first half of Thursday remain elevated, ranging between 40-60% across much of south-central and southeast AZ.

Heading towards the end of the week and next weekend, the guidance is in good agreement in showing the subtropical high relocating towards the Gulf Coast Region while the aforementioned upper- level low remains situated off the west coast. This pattern configuration will cause the flow to shift more out of the southwest, bringing in a drier airmass as PWATs drop under 1.2-1.3". As a result, an overall downtrend in thunderstorm activity is expected, with afternoon activity limited to the eastern third of AZ.

Temperatures during the middle to latter half of the week will run slightly below normal as afternoon highs will top out in the low 100s across the south-central AZ lower deserts to the mid 100s across the western deserts. In fact, with the potential for abundant cloud cover as well as lingering rainfall activity, afternoon highs on Thursday may struggle to reach the triple digits across the south- central AZ lower deserts. Temperatures will gradually rebound Friday and into next weekend but remain near seasonal levels with no extreme heat in sight for at least the next seven days.

AVIATION

Updated at 1800Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The primary aviation concerns this evening will once again be the potential for gusty outflow winds, blowing dust, and reduced vsby due to TS at the metro terminals. Over the next several hours, westerly winds around 10-11 kts are expected with gusts into the teens to around 20 kts developing during the afternoon. Confidence in the wind forecast decreases considerably this evening with many discrepancies still existing from the arrival of potential outflow boundaries. Thunderstorms are expected to again form over the high terrain to the north and east of Phoenix and in southeast AZ. Both complexes of storms will be capable of producing long-lived outflows which will push towards the terminals by this evening. The northeasterly outflow may briefly cause an easterly shift, but the southerly outflow is likely to be the stronger of the two. These outflows could carry some blowing dust, especially the southerly outflow and then may be followed by TS development in the Phoenix area mainly between 04Z-06Z tonight. Amendments will likely be needed to the current TAF as conditions evolve.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns are expected through the next 24 hours under periods of FEW-SCT mid to high cloud decks and otherwise mostly clear skies. At KIPL, winds will primarily stay southeasterly with a switch to westerly by this evening. There is a low chance (10%) for an isolated strong TS within the vicinity of KIPL this afternoon, which could cause an abrupt wind shift (likely out of the southwest) and strong gusts. At KBLH, winds will generally fluctuate between SSE and SSW. Overall, wind speeds should generally remain AOB 12 kts.

FIRE WEATHER

Gradual cooling temperatures to near to slightly below normal levels can be expected throughout the week. Elevated moisture will maintain afternoon MinRHs between 20-30% each afternoon along with good to excellent overnight recoveries. The chances for shower and thunderstorm activity as well as wetting rainfall will remain elevated through the middle of the week, especially across the eastern districts. The chances for showers and thunderstorms will decrease noticeably by the end of the week through next weekend as drier air filters in. Outside of gusty and erratic winds due to thunderstorms, winds will follow the familiar diurnal trends, with typical afternoon upslope breeziness around 20 mph.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST this evening for AZZ530-532.

CA...Extreme Heat Warning until 8 PM PDT this evening for CAZ563-566- 567-569-570.