textproduct: NWS Phoenix

UPDATE

Updated Aviation Discussion.

KEY MESSAGES

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

- Isolated showers and potentially an embedded thunderstorms will be possible over portions of south-central Arizona this afternoon and Monday producing gusty outflow winds.

SHORT TERM /Today through Tuesday/

The Conus flow pattern has become far more zonal in nature with subtropical ridging becoming dampened equatorward while fast moving, low amplitude features remain north of the forecast area. Early afternoon WV imagery reveals a weak cyclonic signature and vorticity center along the southern CA/Baja coast creating local southerly flow tapping better deep moisture profiles aided by convective overturning across the international border. Confidence is increasing via objective analysis and HREF output that 7-8 g/kg mixing ratios will advect north with weak ascent mechanisms sparking isolated deep convection across portions of southern Arizona. Locations along I-8 near the Table Top Wilderness appear most poised for late afternoon convective initiation tapping ~500 J/kg MLCape. However, rainfall prospects will be quite remote and isolated given the predominant inverted-V soundings and large T/Td spreads, and instead will yield DCape values in excess of 1200 J/kg promoting enhanced downdraft winds and organized outflow boundaries. The preponderance of HREF output suggests outflow winds 30-40 mph capable of producing areas of blowing dust in the I-8/I-10 vicinity late afternoon/early evening with residual stronger winds/gusts entering the Phoenix metro before quickly subsiding during the mid evening.

While slightly better quality moisture continues to advect into south-central Arizona Monday morning, flow trajectories will steadily turn more westerly during the day eroding moisture depth and magnitude resulting in a somewhat more convectively hostile environment. Some modest instability will exist across the eastern forecast area Monday afternoon, however weaker ascent structure and notable CinH will likely constrict deep convection to isolated orographic locations. Similar to today, outflow winds will be more preferred than actual accumulating rainfall given the thermodynamic profiles, and any activity should quickly wane with loss of daytime heating. By Tuesday, moisture will be scoured even further with deepening westerly flow precluding any additional POPs. Otherwise, H5 heights retreating from near 582dm today to around 574dm Tuesday will force a modest cooling trend with temperatures still challenging record highs today falling closer to a +10F anomaly Tuesday afternoon.

LONG TERM /Wednesday through Saturday/

A mostly zonal westerly flow pattern will continue midweek with a weak shortwave trough tracking across central California before moving through our region on Wednesday. Drying conditions will persist during this time with low level mixing ratios dropping 3-5 g/kg, but also with the passing shortwave on Wednesday, some high terrain showers may develop. NBM PoPs still seem too high for Wednesday, so 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 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 0001Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Primarily aviation weather impact and forecast challenge through the TAF period will be timing and intensity of outflow winds from the south this evening. An outflow is expected to move through, reaching terminals as early as 02-03Z, with wind gusts in excess of 20 kts and a 10% chance for peak gusts greater than 30 kts. The outflow may bring lofted dust into the area and reduce slantwise visibility, with a low potential to reduce surface visibility below VFR. VCSH/VCTS is not expected at any of the terminals, with chances under 10%. East winds develop by around midnight tonight and then an early W/SW wind shift is expected Monday, by 16-17Z with speeds up to 7-12 kts and afternoon gusts up to 15-20 kts. An outflow is less likely Monday afternoon and no VCSH/VCTS are expected. SCT to BKN mid and high clouds will continue to pass over the area.

Southeast California/Southwest Arizona including KIPL and KBLH: No major weather issues will exist through the TAF period under persistent mid/high cloud decks. Winds will remain predominantly southeasterly at KIPL and southerly at KBLH through tonight. 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.