Area Forecast Discussion
Issued by NWS Phoenix, AZ

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS65 KPSR 201308 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 608 AM MST Tue Mar 20 2018 .UPDATE...Updated aviation and fire weather discussions. && .SYNOPSIS... A warming trend continues this week with high temperatures reaching the mid 80s to 90 by Thursday. A weak weather system moves across the region from late Thursday through Friday bringing our next chance of showers together with modest rainfall totals. Cooler and drier conditions will accompany this system with near normal temperatures expected through the weekend. && .DISCUSSION...
-- Changed Discussion --
Current satellite shows mostly clear skies across region with a large area of thick cirrus climbing over a building West Coast ridge. Cool and dry conditions with light to calm winds are being observed across the deserts with temperatures now in the mid 40s to mid 50s. Low dewpoint temperatures, as low as the single digits in the deserts, together with pronounced radiational cooling will support another chilly morning with lows dropping into the 40s to near 50. With mostly clear skies, expect temperatures to warm nicely today into the seasonably pleasant upper 70s. Plenty of WAA through the column ahead of a strong Pacific Basin low pressure system is helping to build the west coast ridge at a significant pace. As the warming trend continues, highs in the low to mid 80s are anticipated for Wednesday as the West Coast ridge axis moves across the region. Although the ridge axis shifts off to the east by Wednesday evening, heights and thicknesses will continue to increase over the area to near 581-583 dam and 568-569 dam respectively by Thursday. This is due to the ridge dramatically increasing in amplitude as it moves out over the Plains. As a result, expect the highest temperatures so far this year on Thursday with highs reaching the upper 80s to 90 in Maricopa and Pinal counties, and the low to mid 80s elsewhere. The middle of the week will also feature mostly cloudy skies and high cloud decks associated with the upper level moisture field ahead of and with the next weather system. This may help to moderate the forecast high temperatures on Wednesday and Thursday. The models are now in good agreement on the next weather system bringing chances of light rain showers late this week with the best chances for the Phoenix area coming very late Thursday night and early Friday morning through Friday afternoon. The best rain chances for out west and SE CA occur on Thursday evening. This represents a later arrival time than model runs from earlier this week. This fast- moving, filling, shortwave disturbance from the west is expected to produce very modest rainfall accumulations for the region. Its associated IVT/AR weakens as it moves inland with the rain shadow effect taking its toll. Short-lived mixing ratios are expected to peak around 6 g/kg with PWs near 0.75-1.05 in. on Friday morning. POPS remain near 30 percent for Friday from Phoenix eastward and 10-20 percent elsewhere. Expect low rainfall totals, generally less than a tenth of an inch around the Phoenix metro. Expect much cooler temperatures on Friday as well. By next weekend expect cool and dry conditions with near normal high temperatures in the upper 70s. For early next week a chance of breezy to windy conditions are expected in SE CA and SW AZ as a low pressure system moves in.
-- End Changed Discussion --
&& .AVIATION... South-Central Arizona including KPHX, KIWA, and KSDL and Southeast California/Southwest Arizona including KIPL and KBLH: Strong high pressure aloft will continue to build over the area today into Wednesday resulting in continued light wind and dry conditions. Expect increasing high cloud to spread across the area from the west with CIGs developing at the terminals later today. Bases to be genly aoa 20k feet but some SCT decks down to 15k feet or so may develop over the western deserts by late afternoon/early evening. Winds in the greater Phoenix area will be light diurnal next 24 hours with speeds mostly below 8kt. Aviation Discussion not updated for amended TAFs. && .FIRE WEATHER... Thursday through Monday... Expect warm and dry conditions today ahead of a weather system that will pass across the region later today into Friday with drier air returning by the end of the week. The weather system will bring isolated showers to the western and central deserts tonight and scattered showers to south central Arizona on Friday. High temperatures today reaching as high as 90 over portions of south central Arizona will drop back down into the upper 70s to low 80s by Friday. Min RH`s of 15-25% today will climb mostly into the 20s Friday and then drier air will spread in over the weekend, dropping minimum RH values into the 10-17% range. Breezy southwesterly winds gusting in excess of 25kt from SE CA to SW AZ are also expected today ahead of the approaching system. Otherwise winds will be rather light and favoring typical diurnal tendencies mostly favoring west to northwest during afternoon hours. Generally fair overnight recoveries should improve to fair to good by Wednesday night and Thursday night. Little change is expected Monday as compared to Sunday. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Sawtelle AVIATION...CB FIRE WEATHER...CB is the U.S. government's official web portal to all federal, state and local government web resources and services.