textproduct: NWS Phoenix

KEY MESSAGES

- A backdoor sfc front will progress through central AZ late tonight, resulting in strong easterly winds with gusts approaching 40-50 mph across the foothills and high terrain areas east of Phoenix.

- Unseasonably hot temperatures will continue to challenge daily records through this weekend.

- The late morning through early afternoon hours may be dangerous, especially for any strenuous outdoor activities without proper hydration and frequent breaks in the shade, or air conditioning.

- The dominant ridge of high pressure should finally begin to break down and push east of the region by Sunday, promoting a cooling trend heading into next week.

SHORT TERM /TODAY THROUGH SATURDAY/

The unseasonably strong ridge of high pressure which has brought record breaking heat to our region is still the predominant feature over the Desert Southwest today. Despite an ewd shift in the ridge axis, the western periphery of the ridge is still robust over AZ as 500 mb hghts remain between 584-586 dam. This will result in another afternoon of record breaking highs in the upper 90s to lower 100s across the lower deserts of AZ and southeast CA. So far Phoenix has seen 12 record highs that were tied or broken this month and we could see at least 3-4 more record highs through this weekend.

Heading into tonight, a particularly strong surface high (1037- 1040mb) moving through the Southern Plains will push a backdoor front through eastern and central AZ. The front will likely reach the eastern portions of the Phoenix Metro by midnight. Gusty post- frontal winds up to 30-35 mph will be possible across the lower deserts and even as high as 45-50 mph in the adjacent foothills and high terrain of E Maricopa and S Gila Counties. A Wind Advisory has been issued for much of the high terrain east of Phoenix from 11 PM MST tonight to 11 AM MST Saturday. The Wind Advisory also includes portions of the lower deserts including N Pinal County where blowing dust channels could cause reductions in visibilities below 3 miles at times. The sfc gradient will gradually slacken through Saturday afternoon, allowing winds to quickly diminish.

In addition to the gusty winds Saturday, there will be an initial push of boundary layer moisture into the region from the east and south in the morning, however dew points are only expected to climb into the mid 30s. Unfortunately, the backdoor front will have little affect on temperatures Saturday afternoon as highs are still expected to reach the mid to upper 90s across southcentral AZ and the lower 100s along and W of the Lower Colorado River Valley. Therefore daily records will likely be reached again in Phoenix, Yuma, and El Centro.

LONG TERM /SUNDAY THROUGH THURSDAY/

Heading into Sunday a better push of moisture into the region is expected as high pressure shifts further east to the Gulf States and southerly to southwesterly flow taps into some subtropical moisture from the south. Ensemble members continue to show PWATs increasing to around 200-250% of normal across AZ by late Sunday into Monday. The increased cloud cover in combination with the high shifted further east will result in further cooling temperatures. The caveat of coming out of a wave of historical heat is that even a little bit of cooling will still result in near record temperatures. Afternoon high temperatures are forecast to be in the mid to upper 90s across the lower deserts both on Sunday and Monday and may still tie or break daily record highs. The influx of moisture late this weekend and early next week will also result in some low-end shower and thunderstorm chances, with best chances across the AZ high terrain to the north and east of the Phoenix Metro. NBM PoPs remain quite low for the lower deserts of central and southwest AZ, generally under 10%, despite the abundance of moisture. With the unseasonably hot temperatures, the lower troposphere and PBL will still be pretty dry. So, showers that do develop may mostly fall as virga. Additionally, the forcing will be very limited Sunday through Monday. There is at least some guidance support for some mid-level confluence and convergence that could better the chances for scattered showers or a band of light showers. Most global ensemble guidance has the best instability Monday (few hundred J/kg of CAPE), but with the minimal forcing it may be difficult to realize any instability to get thunderstorms. With the dry sub-cloud air, any convective or stronger shower or storm that develops will be capable of producing gusty outflow boundaries, but the hope of outflow boundaries generating new activity is pretty low given LCL heights likely remaining fairly high for this time of year.

Beyond Monday, ensemble guidance continues to show an East Pacific trough moving through the region during the middle of next week. There are still uncertainties regarding the exact track and strength of this system. However, it currently looks to drop H5 heights into a 570-575dam range during the middle of the week. As a result afternoon high temperatures are forecast to fall back into the 80s by Wednesday, which is near to slightly above normal for this time of year. The last time our region saw afternoon high temperatures in the 80s was on March 11, which will have been 3 weeks by next Wednesday. Additionally, this trough will bring additional shower and storm chances to the region, but as of now primarily favoring northern AZ. The NBM currently has the best rain chances (20-30%) across the higher terrain to the north and east of Phoenix. The latitudinal progression of the trough through the region will influence whether the rain chances increase across the southern deserts (a deeper southerly track) for the beginning of April. Stay tuned for future updates.

AVIATION

Updated at 1740Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The primary aviation concern during the TAF period will be elevated E/SE winds picking up overnight and becoming gusty at times Saturday morning. Winds will generally follow diurnal tendencies through today with a period of southerly winds late this morning into the afternoon, a briefer than usual westerly switch this afternoon, then an earlier than usual shift back to east this evening. Sustained speeds between 7-15 kts will become common overnight, then widespread gusts into a 20-25 kt range will become common Saturday morning shortly after sunrise. Anticipate gusts to subside and speeds to gradually relax Saturday afternoon. The strongest winds will likely occur at KIWA. Slantwise visibility reductions cannot be ruled out due to lofted dust/haze from the elevated winds. SCT to at times BKN mid and high cloud decks will fill in this evening and persist through Saturday.

Southeast California/Southwest Arizona including KIPL and KBLH: The primary aviation weather concern during the next 24 hours will be lower than usual confidence on wind directions. Winds will remain light and variable at times with directions settling out of the S at KBLH later this afternoon. Winds will eventually turn out of the W at KIPL and SW at KBLH during the evening. Confidence on exact wind directions then decreases tonight into Saturday morning, though a prevailing SE direction is expected at both terminals towards the end of the current TAF period. Skies will remain mostly clear until high cirrus move in this evening and then FEW-SCT decks as low as 15 kft AGL enter the region overnight into Saturday.

FIRE WEATHER

Unseasonably hot temperatures with very dry conditions will continue through at least this weekend. MinRH values will bottom out around 5-15% today before increasing to 10-20% starting tomorrow. MaxRHs will follow a similar uptrend with readings close to 20-40% the next few mornings before rising up closer to a 40-60% range by the beginning of next week. Moisture levels will be highest Sunday into Monday and Wednesday with some moisture fluxes into the region. Winds will be light for the rest of today and follow typical diurnal tendencies. However, strong easterly winds (gusts 25-35 mph) are expected to materialize late this evening, across southcentral AZ as a cold front encroaches on the region. The front will continue to progress through central AZ late tonight through Saturday morning. The strongest winds will reside across the foothills and high terrain areas east of Phoenix where gusts will reach upwards of 40+ mph. Winds should gradually subside from midday through the afternoon Saturday, but will remain out of the E-SE. Although minimum RH values are forecast to stay above the critical threshold (15%) most of the day, there may still be a period of elevated, to near critical, fire weather conditions Saturday due primarily to the widespread breezy easterly winds and unseasonable hot temperatures. There will be at slight chances for rain (10-30%) Monday through Wednesday, but the CWR will be under 10%. Any showers that do develop will be capable of producing gusty and erratic outflow winds, which could impact any existing fires.

CLIMATE

Daily record highs through this week:

Date Phoenix Yuma El Centro ---- ------- ---- --------- 3/27 98 in 1986 100 in 1986 99 in 1988 3/28 95 in 2015 98 in 2015 98 in 2015 3/29 97 in 2015 100 in 1897 97 in 1969

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Wind Advisory from 11 PM this evening to 11 AM MST Saturday for AZZ547-549-551>553-555>558-560>563.

CA...None.