textproduct: NWS Phoenix

KEY MESSAGES

- Strong high pressure has quickly built over the region today leading to drying conditions and rapid warming with near record temperatures starting Friday.

- An even stronger high pressure system will build over the region next week, likely pushing daily highs into the triple digits across the lower deserts while breaking daily and monthly high temperature records.

- Widespread Minor Heat Risk is expected through the weekend before increasing to Moderate HeatRisk next week.

SHORT TERM /TODAY THROUGH FRIDAY/

High pressure is quickly building over our region today, with H5 heights ranging from 586-588dm across the CWA. The northerly flow, associated with the high pressure, has allowed for drier air to move into our region. PWATs have gone from 0.5" yesterday down to 0.2" today. Additionally the rapidly strengthening high pressure system has allowed for rapid warming. Temperatures early this afternoon range from mid 80s to low 90s across the lower deserts, which is around 10-13 degrees warmer than they were 24 hours ago. Temperatures are expected to climb even higher today, topping out in the low to mid 90s across the lower deserts and in the upper 70s to mid 80s across the higher terrain. The high will max out tonight prior to weakening slightly and shifting southward tomorrow. Despite this afternoon high temperatures tomorrow are still forecasted to top out in the mid 90s across the lower deserts and in the 80s across the higher terrain. Even with highs in the mid 90s tomorrow daily records may be tied or even broken.

LONG TERM /SATURDAY THROUGH NEXT WEEK/

An unprecedented heat wave for mid March is expected next week across the Western U.S. with widespread temperature anomalies of 20-30F. Model guidance continues to show remarkable agreement through all of next week with model trends over the past couple of days suggesting an even stronger record breaking ridge settling over the Western U.S. by Monday and lasting into late week. This event is likely to break daily records by as much as 10 degrees for many areas and all time March temperature records, especially across the Southwestern U.S. where the largest positive height anomalies are anticipated.

After this first high pressure system shifts southward by this weekend, a weak shortwave trough will move across the Desert Southwest on Saturday, but it will only stabilize temperatures. Highs this weekend will still reach into the 90s with some spots across southeast California and southwest Arizona reaching 95 degrees. By late Saturday, the next high pressure ridge will be developing well off the coast of California, quickly reaching record strength for this time of year on Sunday. Large negative height anomalies developing across the Eastern U.S. will also help drive an increasing amplitudinal pattern quickly expanding the ridge over the Western U.S. by Monday.

Climatological record H2 heights are projected over the entire West Coast and into the Western U.S. by early next week before slowly shifting eastward throughout the rest of next week. A large area of record H5 heights focused across the Southwestern U.S. is also expected to develop by mid week and last through at least next Thursday or Friday. Ensemble mean H5 heights of 588-592dm are shown across the Desert Southwest by Tuesday before peaking as high as 595dm on or around next 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. So, to put this in better prospective the ridge for next week is forecast to be as strong if not a little bit stronger than any ridge this region has ever seen in March or April. Guidance does start to show some weakening of the ridge by next weekend, but that is where model uncertainty increases with some members hanging onto the ridge a bit longer.

Record temperatures are forecast for the majority of next week, particularly from Tuesday-Saturday. As the ridge begins to move into the region on Monday, highs should warm into the mid 90s for Phoenix to as warm as the upper 90s across the western deserts. The first 100 degree temperatures are likely to be seen by Tuesday with NBM forecast highs of 99-103 degrees across much of southeast California and southwest Arizona. Phoenix may also hit 100 degrees on Tuesday which would easily break the earliest 100 degree day on record (currently March 26, 1988). Tuesday should also be our first day of fairly widespread Moderate HeatRisk.

The center of the ridge is expected to move into our region by Wednesday and slowly drift eastward through our region on at least Thursday and likely even next Friday. Guidance shows the ridge reaching its peak strength of 592-594dm around next Thursday, becoming the strongest ridge ever for our region in March and possibly stronger than any experienced during the month of April. Forecast H8, H7, and H5 temperatures are all essentially at record levels for Tuesday through at least next Friday. It is not a question of whether we will get record temperatures next week, the question should be by how much will they be broken. Highs are nearly certain to top 100 degrees each day during the latter half of next week with the hottest readings likely even topping 105 degrees at some point next Thursday-Saturday. NBM 75th percentile temperatures continue to show potential for some spots to even hit 110 degrees late next week. The earliest ever 105 degree day in Phoenix is April 20th and the earliest 106 degree day is May 2.

Widespread Moderate HeatRisk will affect the area during the latter half of next week with at least some potential for localized areas of Major HeatRisk developing across the lower deserts. However, the large diurnal swings may keep this from occurring. Forecast lows are still shown to dip into the 60s for the majority of the area during the entire event which only puts the lows in the Minor category, affecting the calculation of the overall HeatRisk. Either way, this event should easily bring high- end Moderate HeatRisk for several days.

AVIATION

Updated at 1717Z.

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

No aviation concerns are expected throughout the TAF period. Winds will be light and VRB leading into the afternoon hours ahead of the westerly shift. Otherwise diurnal tendencies will continue in the Phoenix Metro, while out at the western terminals, NW to NNW winds will persist. Wind speeds will generally be aob 10 kts with the exception being at KBLH with speeds in the low teens. Skies will be mostly clear, with FEW passing high clouds later in the forecast period.

FIRE WEATHER

High pressure will dominate across the region through next week as temperatures warm to 10-15 degrees above normal starting today before heating up even further(20-30 above normal) next week. Much drier air has also settled into the region today with MinRHs dropping to around or just below 10% and persisting through next week. Overnight recoveries will be poor to fair, dropping to between 25-40%. Winds will remain fairly light, but with periodic afternoon gusts at around 20 mph, especially over the weekend into early next week. As temperatures rise next week and humidities stay unseasonably low, elevated fire danger is likely to become a problem.

PSR WATCHES/WARNINGS/ADVISORIES

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