textproduct: NWS Phoenix

UPDATE

Updated 12Z Aviation Discussion.

KEY MESSAGES

- Unseasonably hot temperatures will continue to challenge daily records through Monday before noticeable cooling occurs during the middle of the week.

- Isolated showers and potentially a few thunderstorms will be possible over portions of southcentral and southeastern Arizona this afternoon and Monday. Any storm that develops could produce gusty outflow winds.

SHORT TERM /TODAY THROUGH MONDAY/

A slow pattern change is underway with the strong ridge that has brought record temperatures gradually weakening and shifting farther to the east. The repositioning of the ridge has also allowed for some moisture to pool across northwest Mexico where convection has developed over the last couple of days. This moisture is expected to advect northward into far southeast California and southern Arizona today before spreading through the rest of southern and central Arizona tonight into Monday. The south southwesterly flow today will also continue to feed higher level moisture and clouds into the area, but highs this afternoon will again reach well into the 90s across the lower deserts.

The increasing moisture today may be enough to spark off some high-based showers and potentially a thunderstorm or two, focused south of the Phoenix metro. Portions of southern Maricopa county and Pinal county could see some of this activity with gusty downdraft winds possible due to the boundary layer still being quite dry. Also can't rule out outflow winds extending northward into the Phoenix area during the first part of the evening. Localized wind gusts of 35-45 mph will be possible closer to the convection with the stronger wind gust potential diminishing into the Phoenix area. Little if any rainfall is expected with this activity as most will fall as virga.

Better moisture in the lower levels will advect into the area tonight through Monday morning with surface dew points briefly reaching into the lower 60s in southwest Arizona to the mid 50s elsewhere. However, this moisture will be very shallow with drier air aloft quickly eroding the surface moisture Monday afternoon pushing dew points back into the 40s. Isolated afternoon and early convection will again be possible on Monday, but with basically no support aloft and limited moisture the convection should be very sparse and weak. Best chances are likely to be focused over higher terrain areas south and east of Phoenix Monday with PoPs mostly between 10-25%.

LONG TERM /TUESDAY THROUGH SATURDAY/

A mostly zonal westerly flow pattern will set up into mid week with a weak shortwave trough tracking across central California before moving through our region on Wednesday. Drying conditions will continue during this time with low level mixing ratios dropping from the 5-7 g/kg on Monday to 3-5 g/kg starting Tuesday. Conditions on Tuesday present virtually no chance of any shower activity, but with the passing shortwave on Wednesday some high terrain showers may develop. NBM PoPs still seem too high for Wednesday, so we have lowered chances more into the 5-10% range for the lower deserts and 10-20% for the higher terrain.

Temperatures will also finally cool off during the middle of the week with highs falling into the lower 90s Tuesday and into the mid 80s Wednesday. Once the shortwave trough moves to the east of the region Wednesday night, even more dry air will filter in from the northwest. Dry conditions with temperatures on average 3-6 degrees above normal are expected late in the week as a another Pacific trough passes well to our north. Ensemble guidance then mostly agrees a modest ridge is likely to develop off the West Coast late in the week before moving into our region next weekend. This should produce another warming trend with NBM forecast highs back into the 90s by around next Sunday.

AVIATION

Updated at 1110Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Current easterly winds will go westerly around 20-21Z, with speeds remaining around 10 kt or less through the afternoon. Showers and storms developing well south of Phoenix later this afternoon will be capable of pushing outflow boundaries into Phoenix in the evening, likely after 01Z, with around a 10% chance for gusts greater than 30 kts. However, confidence has increased that at least a weak outflow boundary will move into the Phoenix Metro around 02-03Z. Confidence is low on how far north this outflow will go, so a TEMPO group for the southerly wind shift has only been included in the KPHX and KIWA TAFs at this time. Wind speeds with this outflow are expected to be in the 15-20 kt range. Odds of VCSH/VCTS Sunday evening are too low (5-10%) to include in the TAF. VFR conditions are expected through the TAF period with SCT to BKN mid and high clouds staying mostly above 15K ft AGL to as low as 10K ft AGL Sunday evening.

Southeast California/Southwest Arizona including KIPL and KBLH: No major weather issues will exist through the TAF period under persistent mid/high cloud decks. Current light and variable winds will go southeasterly late this morning at KIPL and southerly by mid-morning at KBLH. Wind speeds will generally be around 10 kt or less, but some occasional gusts into the teens will be possible this afternoon and evening.

FIRE WEATHER

Unseasonably hot temperatures with mostly dry conditions can be anticipated through this weekend, however a gradual cooling trend will transpire by early next week. MinRH values will increase from 10-20% today up to 15-20% Sunday and Monday, while MaxRHs will also increase from 20-40% tonight to 40-70% Sunday night. Due to the increase in low-level moisture, there will be at slight chance for rain (10-30%) across southcentral AZ Sunday and Monday, but the CWR will remain under 10%. Any storms that do develop will be capable of producing gusty and erratic outflow winds and dry lightning, which could lead to new fire starts. Winds will continue to taper off below 15 mph through this afternoon and remain out of the E-SE overnight. Winds will resume a diurnal pattern on Sunday with afternoon upslope breeziness expected to increase early next week.

CLIMATE

Daily record highs:

Date Phoenix Yuma El Centro ---- ------- ---- --------- 3/29 97 in 2015 100 in 1897 97 in 1969 3/30 97 in 2004 99 in 1934 101 in 1934

PSR WATCHES/WARNINGS/ADVISORIES

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