textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES

- Strong high pressure will keep temperatures well above normal through the start of next week.

- An unprecedented heat wave for March with widespread triple digits will arrive by Wednesday across lower elevations, and readings near 105 degrees in major metropolitan areas by Thursday shattering daily records by as much as 10 degrees.

- An Extreme Heat Watch has been issued for Wednesday morning for Southeast California, then expanding Thursday morning into southern Arizona.

SHORT TERM /TODAY THROUGH MONDAY/

Satellite imagery shows the expected quasi-zonal flow now set up over the Desert SW as strong ridging begins to build just off the West Coast. However, positive height anomalies still influence the region today through Monday, continuing the above normal high temperatures across the region and especially in the lower desert areas. Today afternoon highs in the lower deserts will be in the low to mid 90s. High temperatures will cool 1-2 degrees on Sunday, then by Monday the core of the ridge begins to move onshore, which will drive temperature back into the low to mid 90s. These temperatures are 10-15 degrees above normal, for this time of year.

Before the aforementioned strong ridge off the West Coast migrates over Western CONUS, a very subtle shortwave trough will pass through the region. This will not only be a reason temperatures cool slightly over the weekend, but it will tighten the pressure gradient over the region causing breezy to locally windy conditions. The strongest gusts are expected to be between 25-30 mph along the Lower Colorado River Valley, but ridge tops can be upwards of 35 mph at times. The main timeframe for the breezy to windy conditions will be Sunday and Monday afternoon into the early evening hours, and will subside after the sunset.

LONG TERM /TUESDAY THROUGH NEXT SATURDAY/

The area of high pressure suppressed and shoved westward by the transient disturbance will rebound and eventually migrate off the Eastern Pacific by Tuesday. As it moves, regional H5 heights will rise markedly, reaching near 588-590dm. However, global deterministic guidance takes things further showing heights aloft peaking near 594-596dm by Thursday. For reference, sounding climatology data for Las Vegas, Flagstaff, and Tucson all show record H5 heights for March are around 590dm and April 591dm, 593dm, and 592dm respectively. With that being said, this high will be near to slightly stronger than any ridge this region has seen in recorded history, not only for March, but for April as well.

This anomalously strong high will translate to record temperatures, not just at the surface, but throughout much of the atmosphere as well. H7-H5 temperatures will reach all-time records for this time of year by Tuesday, with H8 readings joining the fray by Wednesday. These climatological records will not last one day either as forecasts show these abnormal values extending through the end of the work week and even into next weekend. At the surface, lower desert highs by Tuesday will be in the upper 90s to near 100 degrees with values climbing to around 105 degrees for much of the lower deserts by Thursday. If these temperatures are realized, those readings would be 25 to almost 30 degrees above normal.

It should not come as much of a surprise that numerous records are likely to be broken at some point next week with Tuesday likely being the first day when all-time daily MaxTs begin to fall. However, with the lack of movement from the ridge overhead, consecutive days with new record temperatures appear likely. What is also very unusual about how hot this pattern will be is how much high temperatures could potentially best previous records. For instance, the current forecasted high temperature for Phoenix for Friday is 106 degrees. While it is typical to see records beaten by a few degrees at most, this forecast high may beat Fridays record of 96 by 10 degrees. Monthly records are also at risk of falling during this upcoming heat wave. The all-time March records for Phoenix, Yuma, and El Centro are 100, 102, and 101 degrees respectively. All of those values could be tied or eclipsed as early as Wednesday.

The record setting potential doesn't end there. The earliest 100 degree day recorded in Phoenix is March 26, which was observed back in 1988, and is actually the only other time since records began when triple digits were achieved in the month of March for the city. It appears that a new earliest instance of 100 degree will be set as it is a matter of when, not if, it will happen. Current forecasts suggest that will occur on Wednesday the 18th, 8 days ahead of the previous record. Fortunately, the earliest triple digit readings for Yuma and El Centro are March 12th and 15th respectively, so those records are very much safe for at least another year (and hopefully much longer). Nonetheless, the average first 100 degree readings for these locations is late April, so we will be almost a month and half ahead of schedule.

Moderate HeatRisk will develop in response to the upcoming abnormal heat, with even some localized areas of Major HeatRisk not out of the question. Therefore, an Extreme Heat Watch has been issued for the Lower Colorado River Valley and westward starting Wednesday, which will expand to include much of Southern Arizona by Thursday.

AVIATION

Updated at 0500Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT; and Southeast California/Southwest Arizona including KIPL and KBLH:

No major weather concerns will exist through Sunday night under occasional high cirrus decks. Confidence is excellent that an easterly wind component will persist in the Phoenix metro through early afternoon before abruptly becoming westerly. Speeds may exceed 10kt with modest gust prior to sunset and decoupling. In SE California, a W/SW wind component through sunrise should become more northerly later Sunday morning with gusts 20-25kt common at KBLH in the afternoon.

FIRE WEATHER

High pressure will result in temperatures 10-15 degrees above normal today through Monday before increasing to 25-30 degrees above normal by the middle portion of next week. Abnormally hot and very dry conditions will translate to MinRH near or just below 10% with poor overnight recovery as MaxRHs will only be expected to to run near 20- 40%. Increasing breeziness will be observed through this weekend, mainly over the Arizona high terrain and the Lower Colorado River Valley, with the strongest gusts (25-35 mph) focused over the latter area. The breezy conditions, combined with low RH values will result in elevated to isolated areas of critical fire weather conditions. However, with the limited scope of enhanced winds, no fire weather products are needed at this time.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Watch from Wednesday morning through Sunday evening for AZZ530.

Extreme Heat Watch from Thursday morning through Sunday evening for AZZ531>544-546-548>551-553>555-559.

CA...Extreme Heat Watch from Wednesday morning through Sunday evening for CAZ561>570.