Sunrise 5:17 AM   Sunset 7:35 PM Moonrise 2:29 AM   Moonset 3:43 PM

  Print   HELP   Reset   Save   Recall  New

FXUS65 KPSR 022018 AFDPSR

Area Forecast Discussion National Weather Service Phoenix AZ 118 PM MST Sun Jun 2 2024


SYNOPSIS
Slightly above normal temperatures are expected through Tuesday before high pressure builds across the western United States, resulting in hotter temperatures during the middle to latter portions of the upcoming week. Excessive Heat Watches are in effect Wednesday and Thursday across most of south-central AZ as well as for portions of Riverside and Imperial Counties in southeast CA as high temperatures approach 110 degrees. Cooler temperatures are then expected by next weekend as a weak disturbance moves across the region.

DISCUSSION
The overall weather pattern continues to remain similar to what has been observed during the past several days with the Desert Southwest remaining in between the sub-tropical high over Mexico and cyclonic flow over the northwestern U.S. through southwest Canada. This will continue to result in a dry, quasi-zonal flow through Tuesday. As a result, temperatures will remain nearly unchanged as highs will range between 100-105 degrees across the lower deserts, which is just slightly above normal for this time of the year.

By later Tuesday into Wednesday, the overall synoptic pattern will undergo a significant change as the sub-tropical ridge off the eastern Pacific will be amplifying across the majority of the western U.S., while simultaneously a cutoff upper-level low will develop and sit off the central Baja Peninsula. With the amplifying ridge, 500 mb height fields are forecast to rise from the current 582-585dm to 589-593dm beginning on Wednesday, resulting in hotter temperatures. The latest NBM guidance shows highs over the lower deserts on Wednesday between 106-110 degrees, increasing a couple of degrees further on Thursday to between 108-112 degrees. The forecasted high for Phoenix Sky Harbor for Thursday is currently sitting at 112 degrees, which if it would come to fruition, would break a daily record high of 111 degrees last set in 2016. Given the increasing temperatures during the middle to latter portions of the week, the overall HeatRisk will be elevated to moderate areawide with areas of Major Heatrisk materializing, especially across south-central AZ as well as across portions of eastern Riverside and western Imperial Counties in southeast CA. As a result, an Excessive Heat Watch is in effect for these areas for Wednesday and Thursday.

The aforementioned upper-level low off the Baja Peninsula is expected to eventually make its way northward through our region heading into next weekend. However, the latest guidance has trended slower with progression of this feature into our region in the last couple of iterations and thus it is appearing more likely that the ridge will still be in full control through Friday, resulting in the continuation of excessive heat conditions. This overall trend is being reflected in latest NBM guidance, which is a couple of degrees warmer with highs ranging between 106-111 degrees across the lower deserts. Thus, it is very possible that the current Excessive Heat Watches in effect may very well extend through Friday.

By next weekend, as the upper-level low finally migrates through the region, temperatures will be on cooling trend with highs retreating back to near normal, between 100-105 degrees across the lower deserts. Moisture advection from the progression of the upper-level low northward will likely result in PWAT values to rise to around 150-175% of normal, which may be enough to spark some afternoon convection across the eastern AZ high terrain, where the NBM currently has slight PoPs.

AVIATION
Updated at 1720Z.

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

No aviation concerns are expected during the TAF period. Winds over metro Phoenix sites will follow diurnal trends with moments and variability during directional shifts and occasional afternoon gusts near 20 kts. Familiar late afternoon/evening breeziness is likely (>90%) at IPL with gusts 20-25 kts, with daytime gusts near 20 kts expected at BLH. A FEW high clouds will filter in over the region during the forecast window, but skies will be mostly clear otherwise.

FIRE WEATHER
Little to no change in the weather pattern will keep seasonably dry and hot conditions in place through Tuesday. 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...Excessive Heat Watch from Wednesday morning through Thursday evening for CAZ563-566-567-570.

Full Color Weather Map

Link to Loop


Other links: GEOS-West     Contential US     Full GOES-East

Phoenix, AZ,