textproduct: NWS Phoenix

KEY MESSAGES

- Strong high pressure will keep temperatures well above normal through this weekend and the start of the upcoming week.

- Further strengthening of the high will result in an unprecedented heat wave for March with widespread triple digits expected by Wednesday, and readings near 105 degrees 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/

Current objective analysis reveals a generally quiet pattern for the southern tier of the CONUS with quasi-zonal flow stretching from coast to coast. Focusing on the Desert Southwest, high pressure has settled in over the region, setting up continued warmer than normal conditions that were observed to finish out this past work week. Lower elevation high temperatures for this weekend and into the start of next week will range in the lower to middle 90s, a good 10-15 degrees above-normal for the middle of March. Forecasted temperatures during this stretch have actually decreased a few degrees from where they were about 24 hours ago. A glancing trough will dive across the Eastern Rockies, tamping down the ridge enough to keep temps flat to even a few degrees cooler compared observations on Friday.

The above-mentioned trough will not scrape by without impacting more than just temperatures. The tightening of the regional pressure gradient, especially on Sunday, will lead to breezy to locally windy conditions. The strongest gusts look to be focused around the Lower Colorado River Valley where readings 25-30 mph appear likely. Locally higher gusts greater than 35 mph cannot be ruled but should be confined to higher ridge top areas and locations within the river valley where channeling can occur. Even as the shortwave pushes further east, the gradient will remain strong enough to create some residual breeziness for these areas Monday afternoon.

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 0515Z.

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

No weather concerns will exist through Saturday night under periods of high cirrus decks. Trends in wind speeds and timing of directional shifts will be similar to the past 24 hours, though speeds Saturday afternoon in the Phoenix metro should be somewhat stronger than the past few days with modest gusts. Extended periods of light and variable winds will be common.

FIRE WEATHER

High pressure will result in temperatures 10-15 degrees above normal through this weekend 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.