Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/15/20

Area Forecast Discussion
National Weather Service Phoenix AZ
452 PM MST Mon Sep 14 2020 .UPDATE...Updated Aviation Discussion. && .SYNOPSIS... Slightly above normal temperatures are forecast this week with the elevated haze from wildfire smoke gradually decreasing through at least tomorrow evening. The warmest days will be during the latter half of the week with high temperatures topping out between 106-109 degrees across the bulk of the lower deserts. Overall dry conditions are expected, but slightly elevated moisture early this week will support a slight chance of isolated afternoon showers and thunderstorms mostly well east and south of Phoenix. && .DISCUSSION... A sprawling high pressure system has strengthened and shifted further east and is now centered over the west-central US with a ~593 dam H5 center. A weak mid level closed low circulation and thermal trough axis is positioned over E-NE AZ with light winds aloft. Early afternoon ACARS sounding indicated a PW near 0.7" and maintained slightly elevated moisture near 600 mb with easterly component flow from the BL through about H5. Early afternoon satellite imagery showed very substantial thinning out of the regional smoke-haze layer aloft with less smoke advecting in. Towering cu and very isolated showers were also seen across the Mogollon Rim and the far outlining areas from Phoenix. With abundant insolation today`s high has already reached 104 degrees by early afternoon at Sky Harbor with regional temperatures running a few degrees warmer than yesterday in the upper 90s to low 100s. A gradual increase in regional tropical moisture from the southeast will continue from now through Tuesday morning with PWs climbing just shy of 1" or slightly above seasonal norms. Combined with the weak UL low pressure disturbance and weak vorticity expect a few relatively modest isolated showers and thunderstorms across high terrain areas and the distant deserts to the south today and possibly Tuesday. The latest HREF CAMs guidance are in good agreement on keeping most of the convection during those periods rather isolated and short-lived. Isolated gusty afternoon and evening outflow winds/dust and isolated dry lightning will be the main concern. Models remain in good agreement on maintaining the strong high pressure system over the Southwest and West CONUS for much of the week with the previously noted developing low centered east to southeast of the region. Northerly and easterly flow aloft will continue to help mitigate the smoke-haze at least in the next day and a half or so. The persistent regional high pressure will also combine with a drying trend beginning by midweek to support a warm-up as models trend slightly warmer. Highs are expected to be several degrees above normal for much of the week. Highs in and around Phoenix could reach 106-109 by mid week and possibly a couple of degrees warmer for SE CA to SW AZ and impose large areas of moderate heat risk and isolated areas of high heat risk. The wildcard could be the state of the haze-smoke layer for late Wednesday through Friday. Late this week and into the weekend a progressive low pressure system passing to the north will flatten the ridge and shift it east and south. Expect a slight cooling trend this weekend and into early next week as heights gradually relax. Mostly dry west- southwesterly flow aloft will also manage to keep conditions mostly dry along with some occasional breeziness. && .AVIATION...Updated at 2350Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Evening storm activity has remained over the Mogollon Rim and southwestern Arizona with minimal impact to the terminal area. Right now, winds are variable but headings continue to favor an easterly direction, and should do so through tonight. There are indications of possible LLWS tomorrow morning between 15/09Z and 15/14Z with nearly 80 degrees of directional shear and 20-25 kts of speed shear between the surface and FL030. Otherwise, lofted smoke is much less noticeable today compared to recent days. Southeast California/Southwest Arizona including KIPL and KBLH: There are no major aviation weather concerns as surface winds transition to a westerly direction this evening. Speeds should remain fairly light, AOB 6 kts. There may also be periods of a very light/calm wind and variable directions. Lofted smoke is considerably less noticeable today compared to recent days. && .FIRE WEATHER... Thursday through Monday: A warm and dry weather pattern is anticipated during the period. Above normal temperatures will gradually decrease to slightly above normal from this weekend through early next week. Mainly light to occasionally moderate winds will favor normal diurnal patterns through most of the period. Daily min RH values near 10% will improve slightly to the mid teens percent range by Saturday. Overnight recovery around 25% will steadily improve every night beginning on Friday night. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Sawtelle AVIATION...AD FIRE WEATHER...Sawtelle/Kuhlman