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FXUS65 KPSR 021140 AFDPSR

Area Forecast Discussion National Weather Service Phoenix AZ 440 AM MST Sun Jun 2 2024

UPDATE
Updated 12z Aviation Discussion.

SYNOPSIS
A stagnant weather pattern will keep hot and dry weather conditions over the region for most if not all of the upcoming week. Expect slightly above normal temperatures through Tuesday before hotter temperatures are likely starting Wednesday. An Excessive Heat Watch has been issued for Wednesday and Thursday for much of south-central Arizona with highs potentially reaching 110 degrees across portions of the lower deserts. Temperatures should then trend back toward seasonal normals next weekend as a weak weather disturbance passes through the region.

DISCUSSION
Current satellite imagery showing clear skies and upper level objective analysis is virtually unchanged from what we have seen the last several days. The Desert Southwest remains positioned in between a progressive wave pattern across the Northwestern U.S.
and Southwest Canada and the sub-tropical high over Mexico. This will continue to provide dry westerly flow and slightly above normal temperatures through around Tuesday before the pattern finally shifts.

As we have mentioned in previous AFDs, the main forecast concern will be the even hotter temperatures for the latter half of this week. By Tuesday, guidance shows the sub-tropical ridge building over the east-central Pacific before quickly moving eastward over the Southwestern U.S. on Wednesday. At the same time, a weak cut- off low is expected to develop west of central Baja and this disturbance should eventually move through our region at some point Friday into next weekend.

H5 heights are forecast to rise from the current 583-585dm to around 590dm on Wednesday before peaking at around 592dm over the eastern half of Arizona on Thursday. These heights would just reach into the 90th climatological percentile for early June, while giving a decent boost to temperatures starting Wednesday.
The latest NBM forecast temperatures shows highs over the lower deserts between 106-110 degrees Wednesday before peaking at 107-112 degrees Thursday. These expected highs would mostly fall a few degrees short of daily records with the exception of the 111 degrees which is the current record high for Phoenix on Thursday.
According to the NWS HeatRisk, some locations would reach into Major HeatRisk, especially on Thursday across south-central Arizona. Given this threat, we have issued an Excessive Heat Watch for much of south-central Arizona on Wednesday and Thursday. By Friday, guidance shows the cut-off low starting to move northward up the Gulf of California which if the timing holds would begin to bring some slight cooling to our area. If the cut-off low is slower, excessive heat conditions could extend into Friday.

As the cut-off low starts to approach our area from the south later this week, some weak moisture advection into our region is expected to occur. There has also been a notable uptrend in potential moisture over the past several model runs, but it is still of fairly low confidence due to considerable differences among ensemble members. The GEFS is the most bullish on the moisture with PWATs increasing to 175% of normal by Saturday, but even these anomalous PWAT values would still only represent fairly limited moisture given this is our driest time of year. NBM PoPs have likely yet to reflect this increase in moisture as the lower deserts are still at 5% or less while the high terrain is upwards of 10-15% for Friday and Saturday. Given the time of year, getting decent rain chances is extremely unlikely, but it is definitely something that will be monitored over the next several days.

AVIATION
Updated at 2310Z.

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

No significant weather issues will exist through this afternoon under clear skies. Wind trends will again follow a near persistence forecast around the Phoenix metro, albeit with more frequent westerly gusts up to 20 kt through early evening. Periods of variable directions will be common during directional shifts.
For SE California terminals, sundowner gusts at KIPL in the late afternoon and evening hours should be around 20-25 kts, with occasional daytime gusts around 20 kt at KBLH.

FIRE WEATHER
Little to no change in the weather pattern will keep seasonably dry and hot conditions in place over the next few days. Expect lower desert highs between 100 and 105 degrees, or 3-5 degrees above average each day. MinRH values will continue to run between 5-10% across the majority of the area each day, while overnight recoveries will continue to range from poor to fair at around 25-40% over the eastern districts to 35-50% over the western districts. Winds will remain fairly light following diurnal tendencies with periodic afternoon gusts of 15-20 mph. The latter half of the week will see even hotter temperatures with potential for highs around 110 degrees Wednesday through Friday over portions of the lower deserts. There will also eventually be a slight improvement in humidities by next weekend along with a low end chance of some isolated thunderstorms over the Arizona higher terrain.

PSR WATCHES/WARNINGS/ADVISORIES
AZ...Excessive Heat Watch from Wednesday morning through Thursday evening for AZZ534-537>546-548>555-559>562.

CA...None.

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