000 FXUS65 KPSR 191150 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 450 AM MST Tue Feb 19 2019 .UPDATE...Updated Aviation discussion. && .SYNOPSIS... Drier conditions will briefly settle into the region today and Wednesday, but well below normal temperatures will lead to freezing or near freezing lows Wednesday morning. A strong winter storm will then affect the region Thursday and linger through Friday bringing moderate to heavy rains to much of the Arizona lower deserts and significant snows to high terrain areas of Arizona. Well below normal temperatures, but drying conditions is forecast for the weekend into early next week. && .DISCUSSION... The first cold trough continues to push east and will completely exit Arizona later today. Current IR satellite shows mostly clear skies across the lower deserts with some leftover clouds over higher terrain areas. With the cold airmass, mostly clear skies, and relatively light winds in place, temperatures have easily dropped into the middle to upper 30s across a good portion of the lower deserts. The coldest deserts spots may see a brief period of temperatures around freezing this morning, but the coldest night will be tonight into Wednesday morning when widespread freezing to near freezing temperatures are forecast. Sunny skies during the day today will hopefully mask some of the unseasonably cool air as highs struggle to reach into the middle 50s. A major winter storm is then anticipated to drop out of the Pacific Northwest on Wednesday, quickly digging south southeastward into southern California by Thursday morning. Model consistency has been quite amazing with this upcoming winter storm, with little changes seen over the past several days. As the center of the trough digs southward Wednesday night into Thursday, the trough is shown deepening and essentially stalling out through Friday morning. Strong low and mid level southwesterly flow will advect moisture off the Pacific on Thursday allowing PWATs of 0.50-0.66" into southern Arizona. The trough will be positioned perfectly on Thursday to put Arizona in an area of strong upper level dynamics and impressive isentropic ascent. Snow levels around 12Z Thursday morning will initially be around 3500-4000 ft when the first rain and snow begins. A Winter Storm Watch has been issued beginning 12Z Thursday, lasting through Friday afternoon for elevations above 3500 ft. Rain and snow should then overtake the majority of the area by late Thursday morning, especially from Maricopa County north and east. A few inches of snow seems possible for areas like Globe Thursday morning before warm air advection raises snow levels closer to 4500-5000 ft Thursday afternoon into early Thursday night. Elevations above 5000 ft will see significant snow accumulations throughout the day Thursday, lasting through at least Friday morning. QPF amounts for Thursday and Friday range from as little as a tenth of an inch over the southwest Arizona and southeast California deserts to upwards of 2" over northeast Maricopa and southern Gila Counties. Rainfall amounts for Phoenix will likely top 1" in many locations with the highest amounts likely falling just north and east of Phoenix. This may lead to some localized minor flooding of washes, but will hold off on any Flood Watches for now as some of the precipitation in the more flood prone areas north of Phoenix will likely fall as snow. The 1.5-2.5" QPF amounts northeast and east of Phoenix should result in heavy snows with snow totals ranging from 6-10" between 4000-4500 ft with much higher amounts above 4500 ft. The highest peaks in the Mazatzals, Superstitions, and eastern Gila County may see more than 2 feet of snow by Friday afternoon. The trough will slowly drift eastward on Friday with the upper level cold core moving over Arizona by Friday afternoon. 1000-500mb thickness are forecast to drop to between 530-536dam as the trough moves through allowing snow levels to drop closer to 3000 ft. Models indicate scattered shower activity Friday afternoon focused across northern Maricopa where elevations down to 2000 ft may see snow or sleet mixing in with rain. Daytime temperatures Friday will be quite chilly with the bulk of the day being in the 40s for much of the deserts. Highs Friday should top out right around 50 degrees, which should end up breaking the coldest daytime high for Phoenix for the date (currently set at 54 degrees). The rain and snow should come to an end sometime Friday evening with the trough finally exiting to the east Friday night. Overnight lows Friday night and Saturday morning will again be quite cold with the coldest desert locations dipping down to around freezing. Drier conditions should then prevail this weekend into much of next week as models generally show the active Pacific low pattern staying to the north of our region. This doesn't mean we are in store for a big warm up anytime soon. Highs will slowly climb this weekend, possibly reaching 60 on Sunday. Further gradual warming is likely next week with highs climbing into the middle 60s by Tuesday. && .AVIATION... South-Central Arizona including KPHX, KIWA, and KSDL: Just a few clouds expected today with bases around 6-7k ft in the wake of a low pressure system migrating eastward into the southern Rockies. Winds will be the primary aviation weather concern with westerly winds occasionally gusting to around 20 kt this afternoon. The stronger than normal westerly flow will also delay the onset of the easterly drainage winds tonight at KPHX and KIWA. Southeast California/Southwest Arizona including KIPL and KBLH: Northwesterly flow will prevail in the wake of a low pressure system across the southern Rockies. At KBLH, wind gusts will reach 20-25 kt this afternoon, before subsiding after sunset. Otherwise, mainly clear skies expected. Aviation Discussion not updated for amended TAFs. && .FIRE WEATHER... Thursday through Monday: A strong winter storm will affect the region Thursday and Friday with widespread wetting rains over the Arizona deserts and mountain snow. Breezy winds on Thursday are likely areawide with continued breezy winds over southeast California and southwest Arizona on Friday. Well below normal temperatures will continue through the weekend with a slight warming trend beginning Sunday. High RH values will occur Thursday and Friday with drying this weekend leading to minimum RHs dropping into the 30s. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Freeze Warning from 11 PM this evening to 9 AM MST Wednesday for AZZ530-533-535>540-542>544-546-548>555-559. Winter Storm Watch from late Wednesday night through Friday afternoon for AZZ545-557-558-560>563. Hard Freeze Warning from 11 PM this evening to 9 AM MST Wednesday for AZZ556-560-562. CA...Freeze Warning from 10 PM this evening to 8 AM PST Wednesday for CAZ569. && $$ DISCUSSION...Kuhlman AVIATION...Hirsch FIRE WEATHER...Kuhlman