Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 03/13/21

Area Forecast Discussion
National Weather Service Phoenix AZ
509 PM MST Fri Mar 12 2021 .UPDATE... Updated 00Z aviation discussion. && .SYNOPSIS... A slow moving weather disturbance will impact the region through the first part of Saturday evening with periods of scattered showers, locally gusty winds, and the possibility of an isolated thunderstorm. Precipitation amounts are not expected to be very heavy with the greatest chances and highest accumulations over elevated terrain areas of south-central Arizona. Temperatures will hover around 10 to 15 degrees below normal before moderating starting Sunday. A separate, faster moving weather system may create a period of breezy to locally windy conditions on Monday. Warming conditions are likely for the latter half of next week with above normal temperatures likely by next Thursday. && DISCUSSION... The upper air pattern depicts pronounced southwesterly flow aloft with an H5 jetstreak along a slightly dryer slot axis. This pattern was just ahead of the slow-moving Pacific low pressure circulation centered over S CA and NW AZ as seen on afternoon WV imagery. The low pressure system is maintaining elevated WV levels and clusters of PVA anomalies/vort lobes rotating around it. The overnight radar loop depicted an area of scattered showers that moved east across Maricopa county and the Phoenix metro before moving exiting the metro and tapering off earlier this morning. Rainfall totals so far have been more on the modest side, ranging from 0.04-0.08 in the west valley to 0.01-0.3 in the N and NE valley, and mostly about 0.04-0.12 in N Pinal cty and south of Phoenix. Sky Harbor picked up a total of 0.12" since Thursday night with most of that amount falling in the pre-dawn hours. Clearing skies by early to mid morning to the w-sw-nw of Phoenix allowed for some extra heating, the development of a morning cu field and the resumption of isolated to scattered showers and and an isolated thunderstorm by early afternoon. The latest afternoon radar was depicted a pronounced area of light to moderate showers extending from near Gila Bend to s-central to E and NE Metro valley. There were also some isolate showers in SE CA/E Riverside Cty. CAMs and HREF members indicate periods of scattered to isolated showers this afternoon and again late tonight across S-Cent AZ and the Phoenix Metro. The latest ACARS sounding showed an increase PW from 0.40 to 0.57 due to and increase in BL and mid-level moisture, although there was a stable and dry layer near H5. SBCAPE had also increased to the low 300sj/kg. range. Valley convective outflow boundaries combined with PVA forced ascent and weak instability will help maintain on-and-off shower activity for the next several hours, again tonight with mostly modest rainfall amounts continuing. On Saturday as the low pressure center and cold core slowly moves across N-Central AZ and the region, CAMS are in good agreement on another round of isolated to scattered showers with the E Valley and higher terrain areas to east favored. Snow levels are expected to fall to near 5Kft tonight and 3.5K ft on Saturday so accumulations of 1-3 in. are possible for those higher terrain areas. && .PREVIOUS DISCUSSION... Temperatures through Saturday will be unseasonably cool with highs 10-15 degrees below normal, but increasing high pressure beginning Sunday should bring temperatures back to near normal. After a brief upper level ridge Sunday into early Monday, models generally agree in a deepening, but progressive upper level trough affecting the region Monday into early Tuesday. The consensus track of the system brings the low center mostly along the Arizona/Utah state line and any potential precipitation chances remaining across northern Arizona. The main forecast concern for this next system will be strong westerly winds Monday afternoon affecting much of the area, particularly southeast California. Advisory level winds definitely seem possible across at least across Imperial County. After a brief cool down on Tuesday resulting in highs slightly below normal, gradual warming is expected through the rest of next week as the bulk of the ensemble members show a large ridge forming across the western U.S. Median NBM temperature guidance currently shows highs topping 80 degrees by next Thursday and potentially reaching into the 85-90 degree range for the following weekend. && .AVIATION...Updated at 0008Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Periodic rain showers and associated low ceilings and erratic winds will be the main aviation weather impacts through Saturday. Although East Valley terminals and KPHX should experience a brief lull in shower activity through about 02-03Z, showers will likely persist at West Valley terminals and KDVT through the evening hours. More scattered to widespread shower activity affecting all terminals should occur between 03-07Z as the upper level low moves overhead before gradually tapering off overnight. Another round of convection is expected Saturday morning, but confidence on timing is low so only VCSH was included at this time. Very isolated thunderstorms capable of producing small hail and lightning will be possible at any time, though chances are too low to include VCTS in the TAFs at any time. Winds will generally be westerly this evening and southerly overnight through the morning hours before becoming westerly again tomorrow afternoon. Isolated gusts up to 20 knots are possible with shower activity through Saturday morning, with widespread gusts up to 20 knots Saturday afternoon. Southeast California/Southwest Arizona including KIPL and KBLH: Aside from gusty westerly winds on Saturday afternoon, minimal aviation concerns are expected through the TAF period. Isolated showers will be possible through early evening, particularly at KIPL where VCSH is expected through 02-03Z. Otherwise, shower activity will be ending from west to east as the upper level low pushes east of the region during the evening and overnight hours. Winds will generally favor westerly components at 10-15 knots through Saturday morning before gusting up to 20-25 knots during the afternoon hours. A brief period of marginal low-level wind shear is also possible at KIPL just prior to sunrise, but confidence is too low to include it in the TAFs at this time as W-NW winds aloft will probably remain below 30 knots with winds near 10 knots at the surface. && .FIRE WEATHER... Sunday through Thursday: High pressure will be dominant through most of the period with one mostly dry weather system tracking across northern Arizona late Monday into early Tuesday. Near normal temperatures early in the period will quickly warm starting Wednesday with highs reaching the lower 80s by Thursday. After modest daytime breezes on Sunday, stronger winds are expected on Monday with gusts approaching 25 mph across south-central Arizona to 30-35 mph across the western deserts. Minimum afternoon humidity levels in a 15-25% range are expected for Sunday and Monday, lowering to 10-15% starting Tuesday. Overnight recoveries early in the period will mostly reach 40-55%, before dropping to 30-40% by the middle of next week. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...Wind Advisory from 9 PM this evening to 10 PM PST Saturday for CAZ562. && $$ DISCUSSION...Sawtelle PREVIOUS DISCUSSION...Kuhlman AVIATION...Hopper FIRE WEATHER...Kuhlman