Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 11/04/20

Area Forecast Discussion...Updated
National Weather Service Phoenix AZ
440 PM MST Tue Nov 3 2020 .UPDATE...Updated aviation discussion. && .SYNOPSIS... Very warm and unseasonable temperatures will persist through Friday with readings reaching up to 10 to 15 degrees above normal. Afternoon highs should hover at or above 90 degrees for many lower elevation communities and possible record heat Thursday. A drastic cool down is expected this weekend as a cold weather system moves through the region, with 60s and 70s for highs and 30s and 40s for lows. This weekend`s weather system will also bring windy conditions and a slight chance for precipitation. && .DISCUSSION... There has been just enough forcing today to result in isolated convective showers over the lower deserts. Most CAMs have struggled with this activity today and are mostly playing catch up. Aircraft soundings in the Phoenix area depict steep mid level lapse rates, around 8 C/km, and minimal amount of elevated CAPE, around 100 J/kg. A few of the cells that have triggered over the lower deserts have had embedded thunder. Will likely continue to see chances for convective showers through the rest of the afternoon, mainly in Gila county and points north. The subcloud layer is very dry, and with our abnormally warm temperatures, DCAPE is quite high for this time of year. So in addition to occasional lightning, any convective shower through the rest of the afternoon will be capable of producing gusty downdraft winds at the surface. Minimal if any rainfall accumulations are expected. The upper low to the west which has been a primary driver of the clouds and light showers the past few days has become an open wave and is expected to slide east across northern AZ through tonight and push east of the state Wednesday morning, with drier westerly flow in its wake. This has all been occurring within a broad ridge across the west, which has led to well above normal temperatures despite the proximity of the low/wave. As the wave exits though, the H5 height field will rise as high pressure strengthens over the region. Deterministic models show H5 heights reaching 589-591 dm by Thursday. So a subtle and brief warming trend, to the already abnormally warm temperatures, is anticipated through Thursday. The NBM has been highlighting Thursday as the warmest day of the week with potentially record breaking heat. ENS is suggesting 850 mb temperatures will exceed the 99th climatological percentile Thursday. Mid-90s are expected across the lower elevations Thursday. For Phoenix, the latest NBM run has a median of 96 degrees, but given the strong warming, wouldn`t be surprised if this trends closer to 97-98. The record high temperature for the month of 96 will be in jeopardy on Thursday. Heights start relaxing Friday in advance of this weekend`s system. Ensemble and deterministic guidance remain in good agreement that a strong trough will dig into the western U.S. by the end of the week bringing drastically cooler temperatures to our region for the weekend. NBM guidance suggests a nearly 20 degree drop in high temperatures from Friday`s high to Saturday`s as a potent cold front sweeps through promoting strong cold air advection across the Desert Southwest. Lower elevation afternoon highs will go from the low 90s on Friday to low 70s on Saturday. Overnight low temperatures in the higher elevations of southern Gila County and parts of Joshua Tree National Park look to dip below freezing starting as early as Sunday morning and continuing through early next week. Guidance indicates a secondary shortwave disturbance will rotate through the region by the end of the weekend into early next week, which will act to provide a reinforcement of cooler air, with Tuesday currently looking like the coldest day. NBM highs dip into the low to mid 60s across the lower deserts by next Monday, which is about 15 degrees below seasonal normals. Aside from the much cooler temperatures, breezy conditions will increase starting Friday as gradients tighten and winds aloft increase. Model uncertainty this far out still exists with exactly how strong winds will get at the surface. However, it is worth noting that ECMWF EFI guidance show surface wind gusts reaching the upper end of the spectrum Saturday, so we will continue to monitor the potential for conditions potentially reaching Wind Advisory criteria. From a precipitation standpoint, both troughs are expected to bring a chance for rain and higher elevation snow. ECMWF and GFS both show a weak to moderate IVT plume with the initial trough and ensemble means suggest modest PWATs, around 0.4-0.6". Given the current forecast, with the main circulation and dynamics to the north, it may be tough to get much precipitation over the lower deserts. A west to southwest flow over the region supports the idea of the rain shadow effect downstream of the southern CA mountains and better precip chances in the upslope/higher terrain regions of AZ. Latest guidance continues to keep rain chances primarily focused north and east of Phoenix over the higher terrain. For now, PoPs remain in the 20-30% range across southern Gila County while remaining around 10% and lower for Phoenix and areas west. WPC QPF looks good at this time and is generally in accordance with ensemble means, with around 0.5" to a little over 1" possible along and just south of the Rim. QPF drops quickly southwest into the lower deserts with generally around 0.1" currently forecast for Phoenix. && .AVIATION...Updated at 2340Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Isolated showers and/or weak storms associated with a progressive disturbance have moved off to the east of Phoenix and over high terrain so they should not be an issue for this evening going forward. Looking at variable high level cirrus decks aoa 20k feet with only a few high based cu at the terminals through 06z with decreasing high clouds after midnight. By sunrise Wednesday expect skies to be relatively clear. Winds this evening should favor the west but mostly 8kt or less with a shift back to the east starting around 06z. With little support from surface gradients/mixing processes, winds Wednesday should become rather light/variable by midday and should not return to the southwest til 21z or later. Southeast California/Southwest Arizona including KIPL and KBLH: As high pressure begins to build over the western deserts tonight, look for variable high cloud decks diminishing and becoming generally SKC by early morning Wednesday. Winds will be quite light with many light/variable observations at the TAF sites during the next 24 hours. No aviation issues expected for at least the next 24 hours. && .FIRE WEATHER... Friday through Tuesday: Temperatures will remain well above normal through Friday with readings up to 10 degrees above normal. Minimum afternoon humidity levels will begin the period in a 10-20% Friday and then improve this weekend as a cold weather system moves through, with min RHs more around 25-35%. Overnight max humidities increase Friday night and generally remain in the 45-65% range through Monday night, with higher values near bodies of water and at higher elevations across eastern districts. Breezy to windy conditions may develop as early as Friday afternoon, initially out west, and spread across the rest of region Saturday and Sunday. The strongest winds are currently favored from late Friday through Saturday. Considerably cooler conditions are expected with the system along with an increased chance of precipitation. Best chances are currently favored north and east of Phoenix over the higher terrain. && .CLIMATE... Record highs this week: Date Phoenix Yuma El Centro ---- ------- ---- --------- Nov 3 96 in 2009 98 in 1962 98 in 1950 Nov 4 95 in 2001 95 in 1962 93 in 2010 Nov 5 93 in 2007 97 in 1980 93 in 2012 Nov 6 94 in 2007 96 in 1988 96 in 1988 && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Benedict/Smith AVIATION...CB FIRE WEATHER...Benedict/Smith CLIMATE...MO