Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/24/17


Area Forecast Discussion
National Weather Service Phoenix AZ
850 PM MST Sun Apr 23 2017 .SYNOPSIS... High pressure will remain situated over the region today keeping desert high temperatures well above seasonal normals. Some of the warmer deserts may approach 100 degrees today. After today, a gradual cooling trend will begin lasting through the end of the week. Periods of mainly high clouds can be expected along with breezy or even windy conditions during the afternoon hours each day. There will be little if any chance for rain this week outside of higher terrain areas mainly east of Globe. && .DISCUSSION... Close, but not quite sums up this afternoon, as the high of 99 at Sky Harbor fell just short of the first triple-digit day of the year. A patch of high cloudiness that moved over the region this afternoon likely kept us from reaching 100. Global model output continues to show a shift to a broad upper-level trof over the western CONUS this week, with a series of embedded shortwaves bringing a trend towards significantly cooler weather as the week progresses. Thus, it looks more-and-more likely that the calender will roll into May before Sky Harbor (and most of the lower deserts of our cwa) will hit 100. For the short term, the main concern for the rest of the night will be gusty winds over parts of SE CA, with the latest NAM 3km forecast soundings showing 30 kt winds at 850mb continuing until early tomorrow morning. Thus, will allow our wind advisory for extreme Southwest Imperial County to continue. Outside of some minor modifications to the hourly temp/dewpoint/wind grids, inherited forecasts are still looking good. && .PREVIOUS DISCUSSION... Upper ridge heights have transitioned eastward into New Mexico this early afternoon, with cirrus trailing as far south as the Baja Peninsula ahead of the upper vort max swinging through the Great Basin this afternoon. Regional 500mb heights are trended a bit lower than morning model forecasts, with aircraft soundings indicating heights may have already fallen into the mid to upper 570s over the 580s still drawn across the length of the forecast area. Broken to overcast high level cirrus (trailing cirrus ID`d above) bisects the forecast area with clear skies either side of SW AZ and the Lower Colorado River Valley. Cirrus field having little effect on surface temperatures so far today, with readings 3 to 5 degrees warmer than obs this time Saturday across southeast CA as well as the south-central AZ deserts. Still some limited potential to see daytime mixing peak temperatures (especially at the ASOS sensor at KPHX) at the 100F mark, but an occurrence of it would be short-lived with many desert sites ambient warmed into the upper 90s. By this evening, winds will begin to increase through the lower atmo layers with 20 to 30 kts at 925mb. This will result in locally windy conditions through the Superstition Hills and Coyote Mountains in southeast Imperial County, CA. Gusts through the early evening and into the early morning may crest 40mph at times and as such, a wind advisory has been issued for that corner of Imperial Co. Operational runs of the GFS and ECMWF as well as GEFS ensemble output continue to agree that we will see the development of a very large and broad upper trof over much of the western and central CONUS this week. Initially the flow aloft becomes stronger and rather zonal, and with time flow becomes more northwesterly, as a series of disturbances move through the flow and across mainly northern Arizona. All of this will result in a cooler airmass, allowing high temperatures to fall off early this week, with even more significant cooling to occur starting Friday and continuing into the weekend. Most of the disturbances that pass by the area will stay mostly to the north of the lower deserts and any chance for precipitation will be confined to higher terrain areas north and east of Phoenix - especially areas to the east of Globe. One such disturbance will race southeast and across the 4 corners area Tuesday, bringing the first shot of much cooler air to the area and lowering high temps into the upper 80s over the central deserts. Behind the exiting wave Wednesday into Thursday high temps will rebound and return to the low to mid 90s. The final push of cool air begins Thursday night as the upper trof deepens even further and a closed low center dives south towards the 4 corners area, and a cold front swings into southern AZ. As this low center moves through the four corners, a slight chance for showers will develop over the higher terrain east of Phoenix with best rain chances (such as it is) occurring on Friday. High temps over the south central deserts will lower into the mid 80s for the most part with the cooling persisting into the weekend. The far western deserts (including far SE California) will stay a bit warmer, mostly in the upper 80s and low 90s. There will be breezy conditions over the area during the afternoon hours pretty much every day this week as low/mid level gradients tighten, but some of the strongest wind will likely occur Thursday and Friday associated with the continued deepening of the main upper trof. It is possible that wind advisories may be needed at some point and there may be fire weather impacts as well, especially if humidities drop low enough. We will be monitoring the potential for dangerous fire weather during the days to come. && .AVIATION... South-Central Arizona Including KPHX, KIWA, and KSDL: Southeast California/Southwest Arizona Including KIPL and KBLH: Westerly winds will become breezy this afternoon across south- central Arizona, with gusts to around 20 kt possible through 02-03Z. A band of cirrus will move across the area 21-00Z, but should remain AOA 20 thousand ft. Otherwise, winds will follow typical diurnal patterns, shifting out of the east between 08-10Z. Stronger winds are expected across southeast California and along the lower Colorado River Valley. Southwesterly winds will gust up to 25 kt into the late evening at KBLH, and persist into early Mon morning across KIPL. Wind gusts should decrease in frequency and intensity overnight, but sustained speeds should hover around 12 kt. Wind gusts will pick up once again tomorrow, likely by 18Z. Periods of thin high clouds may occur, but skies will generally be mostly clear. Aviation discussion not updated for amended TAFs. && .FIRE WEATHER... Tuesday through Saturday: Temperatures will continue to hold above seasonal averages, but not at readings as warm as the weekend. After Wednesday, a gradual cooling trend will settle into the region as mostly dry storm systems sweep through the Great Basin and down through the Southwest. Outside of a remote chance at some light showers over high terrain of Gila County Thursday, widespread dry weather will cover the districts. Dry afternoons with 5-15% will be common with overnight humidities varying between mostly fair to good. Active storm track through the West will keep afternoons breezy for the district, with upslope west winds and occasional gusts possible through week`s end. While widespread areas of fire danger due to the low humidities and winds look unlikely, some localized pockets of elevated fire danger may be realized Thursday. && .CLIMATE... First Hundred Degree Day Facts for Phoenix and Yuma: PHOENIX Average First 100F (30 yr Normal Period 1981-2010): May 2nd Earliest (Period of Record 1895-2016): March 26, 1988 Latest first occurrence (1895-2016): June 18, 1913 YUMA Average First 100F (30 yr Normal Period 1981-2010): April 29th Earliest (Period of Record 1876-2016): March 12, 1916 Latest first occurrence (1878-2016): June 13, 1971 && .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed through the middle of next week. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...Wind Advisory until 5 AM PDT Monday for CAZ562. && $$ Visit us on Facebook, Twitter, and at weather.gov/phoenix DISCUSSION...Percha/Nolte/CB AVIATION...Rogers FIRE WEATHER...Nolte CLIMATE...AJ/Nolte