Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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942 FXUS65 KPSR 241150 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 450 AM MST Tue Sep 24 2024 .UPDATE...Updated Aviation Discussion. && .SYNOPSIS... Record high temperatures are expected for at least the Phoenix area during the latter half of the week and possibly into next week. This is all due to an unseasonably strong high pressure system that is currently building over the region and could even strengthen further this weekend. Early to mid June like high temperatures are forecast for much of the area starting Wednesday, lasting through at least the weekend. An Excessive Heat Warning has been issued for the Phoenix area for Wednesday through Sunday. Dry air will also remain entrenched over the area well into next week with mostly clear skies persisting. && .DISCUSSION... Even though we are now into the fall season, temperatures and humidities through the rest of the month are expected to be more like what we would expect during the month of June. An unseasonably strong high pressure ridge is already pushing into our region from the northwest, setting up what will become a strong blocking pattern by late week as a pair of cut-off lows develop on either side of the ridge. The high center is currently over Oregon, but it is forecast to quickly shift southeastward into New Mexico over the next day or so. H5 heights over our region have already risen to around 585dm, but will rise further to 588-590dm by Thursday and likely even higher over the weekend as guidance continues to push heights and temperatures higher with each model run over the last couple of days. Guidance now shows H5 heights reaching into the 90th percentile of climatology through the weekend, while also showing record or near record 700mb and 850mb temperatures for the period. The blocking high is now also favored to persist into at least early next week, probably longer. We now have high confidence this fall heat episode will last through the weekend and medium confidence through early next week. Starting today, high temperatures are expected to top 105 degrees over the majority of the lower deserts before rising another few degrees over the south-central Arizona deserts starting Wednesday. Since we are now into early fall and normal highs have dropped nearly 10 degrees from their summer peak, these temperatures will more easily reach Major HeatRisk. Areas of Major HeatRisk begin to develop today before becoming fairly widespread on Wednesday, focused more over south-central Arizona due to the high center setting up over the eastern portion of the region. The Excessive Heat Watch for the Phoenix area has now been upgraded to a Warning and extended out through Sunday. Forecast highs starting Wednesday will mainly top out between 105-110 degrees across the lower deserts with the hottest days likely falling from Friday- Sunday. NBM forecast highs for Phoenix Sky Harbor are now eclipsing daily records each day from Wednesday through Monday with the peak highs of 111 degrees on Friday and Saturday. It is a near certainty that Phoenix Sky Harbor will see its latest 110 degree day ever as the previous latest 110 degree day was September 19 in 2010. Temperature records for Yuma and El Centro are around three degrees warmer than Phoenix, but now the NBM is showing anywhere from a 20-60% probability of tying records for those locations. Needless to say, do not underestimate the upcoming heat and keep practicing proper heat safety. I wish I could definitively say long range models are showing this unseasonably strong ridge weakening or getting displaced at some point next week, but so far there are no strong signs of either one happening. In fact we may be dealing with record or near record temperatures through the rest of next week, time will tell. && .AVIATION...Updated at 1150Z. South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns are expected through the TAF period. Winds will overall favor light, diurnal tendencies with extended periods of variability. There is uncertainty in regards to whether or not winds this afternoon will make a definitive westerly switch. As of now, expect light and variable winds to prevail while favoring a light westerly component at times this afternoon. Clear skies will persist. Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns are expected through the next 24 hours. Winds will generally favor the west at KIPL and NNE at KBLH with extended periods of light and variable winds throughout the period. Clear skies will continue. && .FIRE WEATHER... Strong high pressure will settle over the region today and remain in place at least through the weekend. This will result in well above normal temperatures and continued dry conditions. Lower desert highs temperatures are likely to reach 9-13 degrees above normal by Wednesday and stay there through the weekend. MinRHs will continue to dip down to around 10% over the lower deserts to 15-20% over higher terrain areas through the rest of the week, while winds remain light generally following diurnal wind patterns. && .CLIMATE... Record highs this week: Date Phoenix Yuma El Centro ---- ------- ---- --------- Sep 25 108 in 1989 112 in 1963 110 in 2015 Sep 26 108 in 1989 111 in 2010 110 in 2010 Sep 27 107 in 2009 111 in 1963 111 in 2009 Sep 28 108 in 1992 108 in 1994 109 in 2009 Sep 29 107 in 2003 110 in 1980 110 in 1969 && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning from 10 AM Wednesday to 8 PM MST Sunday for AZZ537-540>544-546-548>551. CA...None. && $$ DISCUSSION...Kuhlman AVIATION...Smith FIRE WEATHER...Kuhlman CLIMATE...18