FXUS65 KPSR 022116 AFDPSR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PHOENIX AZ 215 PM MST MON NOV 2 2015 .SYNOPSIS... A STRONG PACIFIC LOW PRESSURE SYSTEM WILL BRING MUCH COOLER TEMPERATURES TO THE ENTIRE REGION TOMORROW...AND A CHANCE FOR LIGHT SHOWERS ACROSS CENTRAL ARIZONA TOMORROW AND WEDNESDAY. A RETURN TO DRY CONDITIONS AND A SLOW WARMING TREND WILL OCCUR DURING THE END OF THE WEEK AS HIGH PRESSURE GRADUALLY REBUILDS INTO THE DESERT SOUTHWEST. && .DISCUSSION... DRY RIDGING ALOFT STILL PREDOMINATES OVER THE SWRN CONUS THIS AFTERNOON...HOWEVER PROGRESSIVE DEEP TROUGHING IS VERY EVIDENT ON WV IMAGERY DIVING SOUTH ALONG THE CNTRL CALIFORNIA COAST. IR SATELLITE SHOWS A LARGE SWATH OF SPECKLED CLOSED CELL CONVECTION STREAMING DOWN THE NORTHWEST COAST LINE SUGGESTING THE COLD CORE TRAILING THE INITIAL PV ANOMALY. H5 HEIGHT FALLS OF 5-6DM WERE EVIDENT ON 12Z REGIONAL SOUNDINGS ENTERING THE FAR WRN CWA...WITH MORE SUBSTANTIAL HEIGHT FALLS APPROACHING FROM UPSTREAM. CONCURRENTLY...A LOW LEVEL COLD FRONT HAS ALREADY PUSHED ONSHORE INTO SERN CALIFORNIA THROUGH THE SAN DIEGO AND SAN BERNARDINO MOUNTAINS...WITH A STEEPENED POST FRONTAL SFC PRESSURE GRADIENT FORCING GUSTY WEST WINDS. CURRENT OBSERVATIONS AND MODEL FORECASTS SUPPORT A BRIEF PERIOD OF STRONGER WIND GUSTS WITH FROPA...THOUGH REMAINING JUST BELOW ADVISORY CRITERIA. THIS FRONT WILL REACH THE COLORADO RIVER BY EARLY TUESDAY MORNING...THEN PROGRESSING INTO CENTRAL ARIZONA TUESDAY AFTERNOON. THIS FRONT WILL BE THE DELINEATOR OF OUR CURRENT WARM AIRMASS...AND A FAR COOLER AUTUMN AIRMASS FOR THE REMAINDER OF THE WEEK. DESPITE STEEP FRONTOGENETICAL FORCING ASSOCIATED WITH THIS FROPA...ANALYSIS OF FORECAST SOUNDINGS AND CROSS SECTIONS DEPICT ONLY LIMITED MOISTURE (ABOUT 8 G/KG) IN THE H8-H7 LAYER. IN ADDITION...THIS FRONTAL RIBBON OF SATURATION WILL BE TOPPED BY A WARM LAYER ALOFT...AND THE TEMPORAL DURATION OF FRONTALLY FORCED ASCENT MAY NOT BE SUFFICIENT PUSH CLOUD DEPTHS TO SUPPORT ORGANIZED SHOWERS. THE MOST LIKELY OUTCOME THROUGH TUESDAY AFTERNOON WILL BE ISOLD VERY LIGHT SHOWERS (SPRINKLES) AT LOWER ELEVATION...AND BETTER CHANCES OF A COUPLE HUNDREDTHS OF ACCUMULATION IN OROGRAPHICALLY FAVORED LOCATIONS NORTH AND EAST OF PHOENIX. BY AND LARGE...THE GREATEST OPPORTUNITY FOR ACCUMULATING LIGHT RAIN THROUGHOUT A GREATER PORTION OF CNTRL ARIZONA WILL OCCUR ON WEDNESDAY AS THE MAIN COLD CORE AND PV ANOMALY TRAVERSES THE FORECAST AREA. WHILE H8-H7 MOISTURE VALUES WILL DECREASE CLOSER TO 4- 5G/KG...ADVECTION OF H7 TEMPERATURES NEAR -6C AND H5 TEMPERATURES NEAR -21C JUXTAPOSED WITH BETTER CYCLONIC JET SUPPORT WILL AID IN SCT SHOWER DEVELOPMENT (ESPECIALLY BUT NOT EXCLUSIVELY TIED TO DAYTIME HEATING). CANNOT DISCOUNT SOME EMBEDDED THUNDER WITH ANY OF THESE SHOWERS DURING PEAK HEATING (MUCAPES UP TO 100 J/KG)...THOUGH GIVEN THE PROGRESSIVE ADVECTION OF DRY AIR...COVERAGE MAY BE LIMITED IN TIME AND SPACE. ALSO GIVEN THE SHOWERY NATURE OF THIS ACTIVITY...NOT EVERY COMMUNITY WILL EXPERIENCE RAINFALL AND SREF MEANS SUGGEST A WIDE RANGE OF POTENTIAL OUTCOMES (FROM 0.00 TO OVER ONE HALF INCH). HAVE MADE SOME TARGETED INCREASES TO POPS BASED ON ENSEMBLE OUTPUT DURING THIS WEDNESDAY TIME FRAME. BY THURSDAY MORNING...THE TROUGH AXIS WILL RAPIDLY BE PUSHING EAST OF THE FORECAST AREA WITH LITTLE TO NO CHANCE OF ANY ADDITIONAL SHOWERS DURING THE DAYLIGHT HOURS. FRIDAY THROUGH SUNDAY... DRY CONDITIONS AND A SLOW WARMING TREND IS STILL EXPECTED FOR THIS PERIOD AS HIGH PRESSURE RIDGING ALOFT GRADUALLY PUSHES EASTWARD INTO THE REGION...WITH NEAR-NORMAL TEMPS RETURNING BY NEXT WEEKEND. && .AVIATION... SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...AND SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH... WINDS WILL BE ON THE INCREASE OVERNIGHT FOR THE WESTERN TERMINALS OF KIPL AND KBLH...FOLLOWED BY THE PHX AREA TERMINALS TOWARDS EARLY TUESDAY AM. WIND GUSTS NEAR 30KTS WILL BE POSSIBLE OVERNIGHT FOR KBLH AND KIPL WITH INCREASE HIGH CLOUD COVERAGE...MAINLY REMAINING SCT TO BKN NATURE. WESTERLY AFTN WINDS FOR THE PHX TERMINALS WILL TURN BACK TO SESTRLY FOR THE OVERNIGHT/AM AND INCREASE IN SPEED THROUGH TUESDAY MORNING...POSSIBLY WITH 10-12KTS SUSTAINED. MID- LEVEL CLOUDS WILL INCREASE FROM THE WEST...BECOMING SCT TO BKN BY MID-MORNING TUESDAY. AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. && .FIRE WEATHER... WEDNESDAY THROUGH MONDAY... A RATHER STRONG WEATHER SYSTEM WILL MOVE THROUGH ON WEDNESDAY AND EXIT THE REGION THURSDAY. THIS WILL BRING MUCH COOLER TEMPERATURES AND MINIMUM AFTERNOON HUMIDITY LEVELS OF 25 TO 40 PERCENT. OVERNIGHT RECOVERY WILL BE GOOD TO EXCELLENT DURING THIS TIME FRAME. WHILE A FEW SHOWERS WILL BE POSSIBLE...THE CHANCE OF WETTING RAINS WILL VERY LIMITED (MOST TO HIGHER TERRAIN LOCATIONS). FOR THE END OF THE WEEK AND INTO THE WEEKEND...SOMEWHAT DRIER AND WARMER WEATHER WILL RETURN THOUGH NOT YIELDING ANY FIRE WEATHER CONCERNS. && .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE ENCOURAGED TO REPORT BASED ON STANDARD OPERATING PROCEDURES. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...NONE. CA...NONE. && $$ VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX DISCUSSION...MO/PERCHA AVIATION...NOLTE FIRE WEATHER...KUHLMAN  FXUS65 KPSR 151006 AFDPSR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PHOENIX AZ 305 AM MST SUN NOV 15 2015 .SYNOPSIS... A SERIES OF WEATHER DISTURBANCES WILL AFFECT THE REGION TODAY AND MONDAY BRINGING A CHANCE OF LIGHT SHOWERS TO CENTRAL AND EASTERN ARIZONA. THE STRONGEST WEATHER DISTURBANCE MONDAY WILL USHER IN A MUCH COLDER AIRMASS WITH BELOW AVERAGE TEMPERATURES PERSISTING THROUGH TUESDAY. STRONG AND GUSTY WINDS WILL ALSO DEVELOP MONDAY OVER PARTS OF THE AREA. TEMPERATURES WILL MODERATE DURING THE MIDDLE AND END OF THE WEEK...WITH A RETURN OF AFTERNOON HIGHS IN THE 70S AND 80S. && .DISCUSSION... VERY LITTLE CHANGE IN FORCING MECHANISMS AND THE OVERALL FORECAST REASONING THROUGH THE NEXT 48 HOURS AS TWO DISTINCT WAVES IMPACT SOUTHEAST CALIFORNIA AND ARIZONA. THE FIRST SHORTWAVE EMBEDDED WITHIN THE SUBTROPICAL JET (NEAR 30N 116W EARLY THIS MORNING) HAS OBTAINED AN IMPRESSIVE WV SATELLITE APPEARANCE CROSSING THE BAJA PENINSULA...FULLY ATTENDANT WITH CONVECTIVE ELEMENTS IN MOIST MIDTROPOSPHERIC FLOW. THE SECONDARY KICKER WAVE (NEAR 38N 127W) HAS BEEN RAPIDLY DESCENDING SOUTHEAST TOWARDS THE CNTRL CALIFORNIA COAST WITH COLD CLOSED CELL MARITIME CONVECTION FILLING INTO THE TROUGH BASE. THE FIRST WAVE WILL BE THE IMPETUS FOR LIGHT SHOWERS THROUGH THE SOUTHEAST HALF OF ARIZONA TODAY...WHILE THE LARGER TROUGH SWEEPS THROUGH THE REGION ON MONDAY WITH STRONG WINDS AND MUCH COLDER TEMPERATURES. MIDLEVEL MOISTURE HAS RAPIDLY BEEN ADVECTING INTO SOUTHERN ARIZONA TONIGHT AHEAD OF THE SUBTROPICAL SHORTWAVE...WITH OBJECTIVE ANALYSIS DEPICTING AN IMPRESSIVE LEFT FRONT QUADRANT AGEOSTROPHIC JET CIRCULATION AND DIVERGENCE FIELD. HOWEVER...THE MAIN LIMITING FACTOR TOWARDS MORE EXPANSIVE AND EXPANDING PRECIPITATION HAS BEEN VERY DRY AIR LOCKED IN THE SFC-H7 LAYER. 00Z KTWC SOUNDING DATA SAMPLED ONLY MARGINAL 2 G/KG OF MOISTURE WITHIN THIS LAYER...AND MUCH OF THE ASCENT AND HYDROMETEOR GENERATION ALOFT THIS MORNING WILL BE ABSORBED/UTILIZED INTO THE TOP DOWN SATURATION PROCESS. NEVERTHELESS...MODEL ISENTROPIC LAYER FORECASTS CONTINUE TO ADVERTISE AGGRESSIVE UPGLIDE STARTING AROUND THE 310K LAYER THIS MORNING...THEN WORKING TOWARDS THE 305K-300K LAYERS BY MIDDAY THROUGHOUT CNTRL ARIZONA. HAVE TAILORED FORECASTS TOWARDS THE BETTER PERFORMING AND SIMILAR TRENDING HIGH RESOLUTION MODELS (HRRR...NSSL WRF-ARW...AND NAM-WRF CONUS NEST) TAKING THE INITIAL CORE OF PRECIPITATION INTO PIMA/PINAL/SRN GILA COUNTIES LATER THIS MORNING. LIGHT SHOWERS SHOULD THEN EXPAND NORTH INTO THE PHOENIX METRO MIDDAY AND AFTERNOON WITH THE PERSISTENT ISENTROPIC ASCENT. CONTINUED TO HEDGE ANY RAINFALL ACCUMULATIONS TOWARDS SREF MEANS YIELDING LESS THAN 0.10 INCHES AT LOWER ELEVATIONS AND 0.25 INCHES IN THE MOUNTAINS OF GILA COUNTY THROUGH TONIGHT. TEMPERATURES THIS AFTERNOON WILL BE HIGHLY DEPENDENT ON TIMING OF RAINFALL AND CLOUD THICKNESS...HOWEVER A GENERAL TREND OF JUST BELOW PERSISTENCE IN SOUTHEAST CALIFORNIA AND 5F-10F COOLER THAN SATURDAY ACROSS CNTRL ARIZONA SHOULD HOLD. THE LARGER UPSTREAM COLD PACIFIC WAVE WILL SWEEP THROUGH THE FORECAST AREA TONIGHT AND MONDAY...PRECEDED BY A SHARP FRONTAL BOUNDARY DELINEATING AN ABRUPT AIRMASS CHANGE. THIS FRONT SHOULD CROSS THE SOUTHERN CALIFORNIA MOUNTAINS BY EARLY THIS EVENING WITH LEE MOUNTAIN WAVE ACTIVITY TAPPING/CHANNELING HIGH MOMENTUM AIR (50KT IN THE H8-H7 LAYER) TO THE LOWER ELEVATIONS OF WESTERN IMPERIAL COUNTY. STRONG PRESSURE RISES ALONG COASTAL CALIFORNIA WILL ONLY INTENSIFY THE GRADIENT THROUGHOUT THE DAY ON MONDAY WITH COLD ADVECTION AND DEEP MECHANICAL MIXING TAPPING THE STRONGER UNIDIRECTIONAL WINDS IN THE BACK SIDE OF THE LARGER WAVE STRUCTURE. WHILE MODEL FORECAST APPEARANCE DOES NOT LOOK QUITE AS INTENSE WITH RESPECT TO WIND SPEEDS AS PREVIOUS ITERATIONS...AREAS WITH NWLY 30G45MPH AND BLOWING DUST STILL APPEARS LIKELY THROUGHOUT MUCH OF SOUTHEAST CALIFORNIA NECESSITATING ADVISORIES THROUGH MUCH OF MONDAY. MOISTURE WILL ALSO REMAIN AT A PREMIUM WITH THE FRONTAL PASSAGE AND BEGIN TO SCOUR EASTWARD AS THE COLD CORE PROPAGATES THROUGH CNTRL/ERN ARIZONA. THUS DESPITE FAIRLY WELL ORGANIZED DYNAMICAL FORCING...PRECIPITATION WILL BE SOMEWHAT DIFFICULT TO MATERIALIZE AND BE PRIMARILY FOCUSED IN OROGRAPHICALLY FAVORED LOCATIONS OF EASTERN MARICOPA/SRN GILA COUNTIES. WITH THE PASSAGE OF THE DEEP PV ANOMALY...SNOW LEVELS WILL FALL INTO A 4000-5000K FT RANGE MONDAY AFTERNOON THOUGH MOISTURE AVAILABILITY WILL WANE QUICKLY LIMITING NOT ONLY THE TOTAL SNOWFALL...BUT ALSO THE ELEVATION AT WHICH ANY ACCUMULATION WOULD BE LIKELY. AT THIS TIME GIVEN THE PALTRY MOISTURE...SNOW TOTALS IN A RANGE OF 1-2 INCHES AT AND ABOVE 5000FT WOULD BE MOST LIKELY WITH ONLY A DUSTING/MELTING ON CONTACT AMOUNTS DOWN TO 4000FT. STRONG COLD ADVECTION WILL ALSO SWEEP VERY COLD AIR INTO CNTRL ARIZONA AND ALTHOUGH PRECIPITATION WILL SHUT DOWN MONDAY EVENING...WITH FREEZING LEVELS FALLING TO 3500FT...LOW TEMPERATURES IN THE MIAMI/GLOBE AREA SHOULD FALL INTO THE MIDDLE/UPPER 30S YIELDING THE FIRST HARD FREEZE OF THE SEASON. ON MONDAY NIGHT...THE UPPER LOW WILL SHIFT INTO NEW MEXICO AND THE SOUTHERN PLAINS WITH STRONG SUBSIDENCE OVERSPREADING THE REGION. DESPITE SUNNY SKIES/FULL INSOLATION PREVAILING OVER THE AREA DURING THE DAY ON TUESDAY...LINGERING COLD AIR IN THE BOUNDARY LAYER WILL RESULT IN ANOTHER COOL AFTERNOON. SIMILAR TO MONDAY...HIGH TEMPERATURES MAY ONCE AGAIN BE LIMITED TO THE LOWER/MIDDLE 60S AT LOWER ELEVATIONS OF CNTRL ARIZONA...THOUGH REBOUNDING NEAR 70F IN SOUTHEAST CALIFORNIA. LOW LEVEL PRESSURE GRADIENTS SHOULD RELAX TO SOME EXTENT SO STRONGER WINDS MAY NOT BE AS PROBLEMATIC TUESDAY AFTERNOON THOUGH THE COLORADO RIVER VALLEY (THOUGH STILL ON THE BREEZY SIDE). VERY LITTLE TO NO WEATHER CONCERNS FOR THE REMAINDER OF THE WEEK AS THE HEMISPHERIC FLOW PATTERN BECOMES DOMINATED BY LONGER WAVELENGTH FEATURES...AND SOME MEASURE OF STRONG FLAT RIDGING/QUASI-ZONAL FLOW BECOMES SITUATED OVER THE EAST PACIFIC/SOUTHWEST CONUS. ENSEMBLE MEANS SUGGEST H5 HEIGHTS IN A 576-582DM RANGE THROUGHOUT THE LATTER HALF OF THE WEEK...ONLY BEGINNING TO FALL BY NEXT SUNDAY. HAVE CONTINUED TO TREND FORECAST TEMPERATURES TOWARDS CONSENSUS MEANS YIELDING A NEAR PERFECT FORECAST OF HIGHS IN THE 70S AND LOWER 80S AND OVERNIGHT LOWS IN THE 40S AND 50S. && .AVIATION... SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL... MOSTLY CLEAR SKIES AND LIGHT WIND WILL CONTINUE ACROSS THE GREATER PHOENIX AREA THROUGH 15Z SUN. HOWEVER...INCREASING CLOUDS BECOMING BKN-OVR 6 TO 12 THSD AGL IS EXPECTED AFTER 15Z SUN AND CONTINUING THROUGH 01Z MON...ALONG WITH A SLIGHT CHANCE OF SHOWERS. SOUTHEAST WIND 5 TO 10 KNOTS. SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH... MOSTLY CLEAR SKIES WITH LIGHT WIND UNDER 9 KNOTS EXPECTED THROUGH 12Z SUN. INCREASING CLOUDS BECOMING BKN NEAR 10 THSD AGL FROM 12Z SUN TO 01Z MON...WITH PRE-COLD FRONTAL SOUTHWEST WIND INCREASING 10 TO 12 KNOTS...BECOMING 15 TO 25 KNOTS FROM 22Z SUN TO 01Z MON. AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. && .FIRE WEATHER... MONDAY THROUGH FRIDAY... VIGOROUSLY STRONG UPPER LEVEL LOW PRESSURE AND ASSOCIATED COLD FRONT WILL CONTINUE TO MOVE THROUGH THE REGION THROUGH THE EARLY PART OF THE WEEK. THERE IS A LIMITED WINDOW FOR SOME PRECIPITATION ACTIVITY...MOSTLY ACROSS THE HIGHER TERRAIN TO THE EAST AND NORTH OF PHOENIX. STRONG GUSTY WINDS WILL DEVELOP ACROSS AREA RIDGETOPS EARLY MONDAY BEFORE MIXING DOWN INTO THROUGH TO THE SURFACE...WITH THE STRONGEST WINDS ORIENTED FROM THE NORTHWEST ACROSS SOUTHEAST CA INCLUDING JOSHUA TREE NP. GUSTS APPROACHING 50 MPH ARE NOT OUT OF THE QUESTION. ALONG WITH THE ELEVATED WINDS...A MUCH COOLER AND DRIER AIRMASS WILL FILTER INTO THE REGION INTRODUCING THE POTENTIAL FOR A PERIOD OF TIME MONDAY MIDDAY INTO THE AFTERNOON WHERE CRITICAL FIRE WEATHER THRESHOLDS MAY BE OBSERVED. DECREASED WINDS AND A RETURN TO GOOD OVERNIGHT RECOVERIES IS ANTICIPATED BY THE MIDDLE OF THE WEEK. && .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE ENCOURAGED TO REPORT BASED ON STANDARD OPERATING PROCEDURES. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...FREEZE WATCH FROM MONDAY EVENING THROUGH TUESDAY MORNING FOR AZZ024. WIND ADVISORY FROM 11 AM TO 5 PM MST MONDAY FOR AZZ020. CA...WIND ADVISORY FROM 10 AM TO 4 PM PST MONDAY FOR CAZ031. WIND ADVISORY FROM 4 AM TO 7 PM PST MONDAY FOR CAZ030-032. WIND ADVISORY FROM 4 PM THIS AFTERNOON TO 7 AM PST MONDAY FOR CAZ033. && $$ VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX DISCUSSION...MO AVIATION...VASQUEZ FIRE WEATHER...NOLTE  FXUS65 KPSR 030251 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 750 PM MST Mon Jan 2 2017 .SYNOPSIS... Rather moist Pacific flow will keep periods of thicker clouds streaming into the Southwest for most of the week. There may be occasional light mountain showers on and off throughout the week, but the lower elevation communities will remain primarily dry. Somewhat cool temperatures early this week will moderate slightly by the end of the week, but not vary too far from the seasonal average. && .DISCUSSION... Copious amounts of upper level moisture emanating from the east Pacific continues to stream across the forecast area this evening. While cloud thickness may decrease somewhat, the nearly overcast high deck will persist limiting the magnitude of nocturnal cooling. In all likelihood, morning lows will not fall much more than 5F-10F from the 02Z readings (and only slightly cooler than last night). Only minimal adjustments were made to the evening update mainly to increase cloud cover and strip out any residual slight chance POPs towards the edges of the CWA boundary. && .PREVIOUS DISCUSSION... /231 PM MST Mon Jan 2 2017/ Anomalously strong (99th %) zonal component to the upper level flow will persist through Wednesday resulting in periods of partly to mostly cloudy skies. Models indicate that disorganized areas of vorticity and other forcings will generally not be sufficient to induce enough ascent to generate anything more than spotty/brief light rain or sprinkles. PoPs remain less than 10 percent for most areas. Despite the gradual increase in heights/thicknesses, temperatures will remain at or below normal through midweek. After Wednesday, subtle flat ridging builds northward advecting in a slightly drier and warmer airmass. Prolonged break from the clouds and warmer LL temps, 850 Ts 7-9C, will warm temperatures into the upper 60s and even low 70s for a few spots Thu. Late week forecast solns still remain divergent in their solns, although not as severely different in thermal and moisture profiles as last evening. ECMWF remains one of the cooler solns, but not as pronounced in the arrival of an upper low into the area by Fri-Sat. Upper shortwave may pass through the Four Corners/central Rockies late week and bring some subtle cooling to the airmass. Still maintained a slight blend towards climo PoPs and temps for the upcoming weekend given the challenge the models will have in resolving the blocked atmosphere and strong high pressure ridge over the northeast Pacific/Alaska. All in all, unsettled flow aloft will still be in the vicinity of the region enough that non-zero pops were warranted. && .AVIATION... South-Central Arizona including KPHX, KIWA, and KSDL: Very little to no major aviation impacts through Tuesday afternoon. Occasionally thick high cigs AOA 12K ft will spread through central Arizona, while only a few afternoon cumulus hover over surrounding mountains. A very light east wind will prevail for the majority of the time, though a very late afternoon shift to a light west wind (or variable in nature) is possible Tuesday. Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation concerns through Tuesday afternoon with occasionally thick high clouds spreading over terminal sites. Sfc winds will favor a S/SW direction though extended periods of nearly calm or variable directions are likely. Aviation discussion not updated for amended TAFs. && .FIRE WEATHER... Wednesday through Sunday: For the most part, we can expect a relatively humid period with low chances for rainfall over the 5 day period. A very flat upper ridge will dominate the weather pattern allowing considerable and variable amounts of mid and high clouds to overspread the area day to day. There will be slight chances of showers at times, primarily focused over the higher terrain areas to the east of Phoenix on Thursday, then across the western deserts over the weekend. Humidity values will stay highly elevated through the period, with minimum RH values mostly between 30 and 45 percent each day. High temperatures will stay near or slightly above seasonal normals each day. No consequential winds are expected each day with speeds mostly below 12kt. Overall, there are no fire weather concerns of any kind over the 5 day period. && .SPOTTER INFORMATION STATEMENT... Skywarn Radio Net activation is not expected this week. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ Visit us on Facebook...Twitter...and at weather.gov/phoenix DISCUSSION...MO/Hirsch/Nolte AVIATION...MO FIRE WEATHER...CB  FXUS65 KPSR 210401 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 900 PM MST Thu Jul 20 2017 .SYNOPSIS... The best thunderstorm chances will be limited primarily to higher terrain communities of central and eastern Arizona through the weekend before expanding westward somewhat Monday. While some thunderstorms could affect a few lower elevation areas, coverage and intensity will be less than the past week. And despite the reduction in thunderstorm activity, temperatures should remain near the seasonal average into next week. && .DISCUSSION... It's been another rather interesting day, convectively speaking, over the lower deserts east of the lower Colorado River valley. Huge upper high still in place over most of the CONUS, centered over nrn OK; weak southeast flow aloft on the western periphery of the high was present across Arizona. Moisture values remain elevated with PWAT values in Phoenix/Tucson around 1.6-1.7 inches. Surface dewpoints have not changed much, still running in the 60s across the lower central deserts. Weak disturbances continue move to the north, rotating around the high and adding support for thunderstorms. Despite the presence of the embedded disturbances, one change of note in the flow has been the decrease in the strength of the steering flow - 700-300mb mean winds have dropped below 10kt and is near calm over much of south central AZ. With very weak steering flow, storms will not move very quickly and will typically be bound to the higher terrain where they form. Storms over the deserts will pulse up and then dissipate with little or no storm-relative flow to move them along. Thus the main drivers for convection this evening have been outflow boundary interaction. We saw isolated to scattered storms form north of the CWA this afternoon, and over SE AZ this evening. Boundaries have since moved into the central deserts from the north, the northwest, the south and southeast. New storms and showers have then formed where boundaries interact. Due to cool afternoon highs (Phoenix only reached 103), instability was lowered. Very moist profile in the low layers (as seen in the 00z RAOBs) limited potential for strong outflows due to poor evaporational cooling). All this combines to limit both strength of convection and their corresponding outflow. All this said, previous forecasts underplayed the areal coverage of storms in the lower deserts this evening and have been updated to show 10-20 POPs over much of the lower desert thru midnight. The storms that have developed have proven to be garden-variety, typically well below severe levels. Due to the high moisture, locally heavy rains have occurred but we have yet to see amounts needed for flash flooding. We have issued a couple of SPS and FLS products to cover the evening convection and do not expect further intensification of convection overnight. Will continue to monitor... .PREVIOUS DISCUSSION... Numerous MCV's continue to float around the SW Conus this afternoon within a weakening flow pattern characterized by a pronounced easterly wave lifting north through NW New Mexico and a more subtle anti-cyclone over southern/southwest AZ. Objective analysis already shows H2 jet winds turning westerly across the CWA in response to the aforementioned easterly wave ejecting to the northeast and prevailing strong jet core cutting through central CA/NV. As a result, divergence fields are lifting into northern AZ, as well as developing over far SE Arizona left in the void of the departing easterly wave. The net result later this afternoon will be more confluent flow over the forecast area largely unsupportive for better convective complex organization and sustenance. Adding to the reduced thunderstorm activity (at least compared to the past week) is weaker outflow boundaries given the moist environment and lower T/Td spreads. While distinct outflows are likely to form with higher terrain storms and flow downhill, cold pools will likely be more shallow and probably insufficient to spark strong newer updrafts. Aside from showers already building along the typical terrain features of central AZ, Gila County is most under the gun for storms and locally heavy rain through early evening. Convective activity may be very muted Friday as the combination of confluence aloft and stronger anti-cyclonic subsidence in the midlevels spreads through the forecast area. Naturally, a few storms will likely form over the mountains, yet steering flow would deflect any storms away from the bulk of the CWA. It's probably a better bet that very little of the area experiences rain Friday, and have really limited much in the way of POPs to terrain areas east of Phoenix Friday afternoon/evening. Through the weekend, midlevel flow reconfigures slightly with the center of the H5 anti-cyclone becoming established over southern Utah resulting in northeast flow into central and southern AZ. However as this happens, there is no change in the mostly unsupportive westerly jet winds, so thunderstorm activity may struggle somewhat to maintain integrity trying to propagate into lower elevations (not to mention outflow boundaries that may still be weaker than experienced earlier in the monsoon season). Ensemble probabilities are not very optimistic about any widespread storms over the weekend, and its look more like a typical areal and temporal monsoon storm coverage. Monday through Wednesday... A transition may begin through next week with a potential turn to a more southwesterly component to the flow and a gradual drying trend. However, there is significant uncertainty in this trend as flow may hold at a southerly component with lower level trajectories still from the SE and importing moisture. At some point next week, there will likely be a shortwave partially absorbed in the southerly flow and supportive for organized storms. Pinpointing such a day this far in advance is fruitless, and have continued with modest POPs for the time being. && .AVIATION... South-Central Arizona including KPHX, KIWA, and KSDL: Earlier we were not expecting convection into the greater Phoenix area due to very weak steering flow confining storms to the higher terrain. However, outflow boundaries proved stronger and more persistent than expected; they have moved into the area from the northwest, north, south and southeast and have allowed isolated showers/storms to form and affect the TAF sites. Variable winds up to 25 kt have resulted due to various merging boundaries. Have updated TAFs to add VCTS this evening and even mentioned TSRA earlier at KDSL. Expect isolated convection affecting the TAFs thru around 05z this evening before dissipating and leaving SCT-BKN mid to high decks which will persist into the morning hours. Expect less convection in the central deserts/greater Phoenix area tomorrow due to continued weak and somewhat unfavorable steering winds and a slightly more stable environment. Southeast California/Southwest Arizona including KIPL and KBLH: No convection expected in the western deserts for the next 24 hours as the atmosphere remains relatively stable with very weak winds aloft. Will keep TAFs short as any cloud decks will typically be few- sct with bases mostly aoa 12k feet. Winds continue to favor the SE at KIPL and the south at KBLH with speeds below 15kt. No real aviation concerns over the western deserts or the TAF sites thru Friday evening. Aviation discussion not updated for amended TAFs. && .FIRE WEATHER... Sunday through Thursday: Afternoon and evening thunderstorms will continue next week, although the most concentrated storms will be confined to the higher elevations north and east of Phoenix. Lower elevations of Arizona could still see some storms, but less coverage than the past week while SE CA will struggle to receive any rainfall. Otherwise, minimum afternoon humidity levels will remain generally around 20- 40% range with good to excellent overnight recovery. Typical summertime breezes can be expected except near thunderstorms where erratic gusty winds will be likely. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ Visit us on Facebook, Twitter, and at weather.gov/phoenix DISCUSSION...CB PREVIOUS DISCUSSION...MO/AJ AVIATION...CB FIRE WEATHER...MO/Wilson