Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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069 FXUS65 KPSR 132052 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 152 PM MST Thu Jun 13 2024 .SYNOPSIS... Very hot and mostly dry conditions will persist through the weekend, with Excessive Heat Warnings in effect for various parts of the region through Sunday. Weak low-pressure will move over the region later today through early Friday, providing increased cloud cover, breezy conditions, and perhaps a few sprinkles or light showers for areas primarily east of the Colorado River. Temperatures eventually cool towards normal levels during by the start of next week. && .DISCUSSION... The pattern over the past 24 hours has not changed much as high pressure continues build to our east, while the cut-off low mentioned in previous discussion continues to spin of the coast of northern Baja, though the latter feature has begun to advance closer towards the Desert Southwest. This setup has provided our forecast area with enhanced southerly flow aloft, providing us with increased moisture flux which can be observed on WV imagery. This increase in mid-level moisture helped provide increasing cloud cover over south-central Arizona this morning and early afternoon, with a few light virga showers being observed over eastern Maricopa and southwestern Gila Counties. Another plume of moisture will work its way over southwestern and south-central Arizona this afternoon and evening, helping to spark more virga activity. A few sprinkles or light showers reaching the ground cannot be ruled out, but low-level dry air should inhibit chances of seeing measurable rainfall. Hi-res data is also hinting at the the potential (10-30%) of seeing locally gusty winds (>35 mph) associated with this rainfall activity, primarily over La Paz and Yuma Counties. Current mesoanalysis does reveal a narrow area of instability over parts of southwestern Arizona (MUCAPE between 100-250 J/kg), which has led to a few lightning strikes across the area. As this corridor of instability pushes east through the remainder of the day, it would not be surprising to see a few more strikes over western Maricopa and the Phoenix metro this evening and into tonight. Regardless of any rainfall activity, marginally breezy conditions are expected this afternoon and evening as the cut-off low helps to tighten up the regional pressure gradient. Gusts 20-25 mph will be common across the region, with higher gusts (30-35 mph) over the usual breezy spots in Imperial County. Even with the increasing cloud cover and slightly lowering heights aloft due to the closer proximity of the low, temperatures this afternoon across the region will be similar to yesterday, with forecasted highs across the lower deserts between 106-111 degrees. In the past few days, it appeared that Phoenix may potentially flirt with a record high (114 set in 1936) this afternoon, but with temperature forecasts responding to the expected cloud cover and downward trend in heights aloft, it now appears that the old record high is likely to hold for at least another year. Model guidance has the aforementioned low quickly ejecting out of the Desert Southwest, indicating that it will be centered over northern Arizona by mid-day Friday. Heights aloft with the passage of this disturbance will be closer to climatological normals over south-central Arizona, leading a degree or two drop in day-to-day temperatures, with highs Friday over the area between 106-109 degrees. Further west, ridging will quickly fill in behind the low, leading to temperatures over SW Arizona and SE California to be a few degrees warmer, as forecasted highs there range between 108-112 degrees. Positive height anomalies then spread over the remainder of the region by the start of the weekend, resulting in widespread afternoon highs at or above 110 degrees, with above normal temperatures lasting through Sunday. The Excessive Heat Warning that was posted for south-central Arizona has been extended through Sunday in response, while a separate warning is in effect for parts of SE California from Friday morning through Saturday evening. Cluster analysis continues to remain in excellent agreement regarding a deep trough moving over the Intermountain West during the front half of next week. Models have trended deeper with this system, with negative height anomalies reaching as far south as the Desert Southwest. Previous model runs already hinted at the potential for a cooling trend in conjunction with this system, with the main uncertainty being how pronounced it would be. If this more amplified solution were to be realized, noticeable cooling would likely occur, with many areas seeing temperatures right around, to even slightly below seasonal levels. && .AVIATION...Updated at 1710Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Variable and potentially erratic wind directions will be the greatest weather issue through Friday afternoon with 15-20K AGL cigs today giving way to clear skies Friday. Confidence is good that east winds will prevail into the early afternoon, however highly variable directions are probable into the mid-afternoon during the typical transition to a westerly direction. This variability may be exacerbated by isolated, elevated convection resulting in virga and isold SHRA; and west winds may not become truly established until very late afternoon. While coverage and confidence of any more direct impacts are too low to include in this TAF package, low probabilities (~10%) exist of gusty, erratic (up to 30kt) winds during the late afternoon through the evening. Southeast California/Southwest Arizona including KIPL and KBLH: A period of afternoon/evening gusty winds will be the main weather issue through Friday afternoon as midlevel cloud decks stream north along and east of the Colorado River. S/SE winds will be preferred through the early evening with gusts 20-25kt initially materializing at KBLH, then stronger westerly sundowner winds up to 30kt sweeping into KIPL. Confidence is good that wind directions will have the tendency to veer towards a W/SW direction through the overnight, then trending more towards a light and variable character Friday morning. && .FIRE WEATHER... Hot and overall dry conditions will prevail over the next few days. A weak weather system moving through later today and tonight will bring some high based light showers, but much of the rain will not reach the surface due to the very dry lower levels. Some of these virga showers may produce locally gusty winds in excess of 30 mph. Outside of any shower activity, gusts 20-25 mph will be fairly common this afternoon and evening, resulting in locally enhanced fire weather conditions. MinRH values will range between 5-10%, while poor overnight recoveries can be expected with MaxRHs only reaching towards 15-35%. The above normal temperatures will continue through the upcoming weekend, while winds increase further with afternoon gusts of 20-30 mph likely on Sunday and Monday. The combination of the increased winds and low RHs will continue to bring elevated fire danger across the area into early next week. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST Sunday for AZZ534-537>555- 559-560-562. CA...Excessive Heat Warning from 10 AM Friday to 8 PM PDT Saturday for CAZ562-563-566-567-570. && $$ DISCUSSION...RW AVIATION...18 FIRE WEATHER...Kuhlman