612  
FXUS65 KPSR 211144 AAA  
AFDPSR  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE PHOENIX AZ  
445 AM MST THU FEB 21 2019  
   
UPDATE
 
UPDATED AVIATION AND FIRE WEATHER DISCUSSIONS.  
 

 
   
SYNOPSIS
 
 
A MAJOR WINTER STORM WILL AFFECT THE REGION TODAY WITH VALLEY  
RAIN AND MOUNTAIN SNOW BECOMING WIDESPREAD BY MID TO LATE MORNING,  
CONTINUING OFF AND ON THROUGH TONIGHT BEFORE TAPERING OFF FROM  
WEST TO EAST FRIDAY. PRECIPITATION WILL BE BEST EAST OF THE LOWER  
COLORADO RIVER VALLEY. SIGNIFICANT ACCUMULATING SNOW CAN BE  
EXPECTED FOR ELEVATIONS ABOVE 3000 FEET WITH VERY HEAVY SNOW ABOVE  
4000 FEET. OTHERWISE, EXPECT MUCH BELOW NORMAL TEMPERATURES  
THROUGH SATURDAY BEFORE A SLOW WARMING TREND STARTS. A RETURN TO  
DRY CONDITIONS ARE FORECAST INTO NEXT WEEK WITH TEMPERATURES  
GRADUALLY WARMING BACK TO NEAR NORMALS BY LATE NEXT WEEK.  
 

 
   
DISCUSSION
 
 
THE STRONGEST WEATHER SYSTEM OF THE WINTER SEASON AND LIKELY OF  
THE PAST FEW WINTERS IS BEGINNING TO AFFECT THE DESERT SOUTHWEST  
EARLY THIS MORNING. A DEEP TROUGH IS CURRENTLY BEING CARVED OUT  
ACROSS THE SOUTHWESTERN U.S. WITH THE TROUGH CENTER OVER NEVADA.  
FURTHER DEEPENING IS ANTICIPATED OVER THE NEXT 12-18 HOURS AS THE  
CENTER OF THE TROUGH SHIFTS SOUTHWARD OVER SOUTHERN CALIFORNIA.  
THE POSITIONING OF THIS IMPRESSIVE LATE WINTER TROUGH WILL PROVIDE  
A NEARLY PERFECT SCENARIO FOR HEAVY SNOW ACROSS THE HIGH TERRAIN  
OF ARIZONA. AS STATED IN PREVIOUS DISCUSSIONS, UPPER LEVEL  
DYNAMICS AND LOW LEVEL UPSLOPE FORCING WILL BE QUITE STRONG AND  
PERSISTENT OVER THE MAJORITY OF ARIZONA THIS MORNING THROUGH MUCH  
OF TONIGHT.  
 
CURRENT OBJECTIVE ANALYSIS SHOWS LIGHT RAIN AND SNOW BECOMING MORE  
WIDESPREAD OVER SOUTHERN CALIFORNIA AND THE NORTHWESTERN 3/4 OF  
ARIZONA. AS THE ATMOSPHERE SATURATES FROM THE TOP DOWN AND  
FORCING INCREASES, RAIN AND SNOW WILL INCREASE IN INTENSITY LATER  
THIS MORNING FOR MUCH OF ARIZONA. LITTLE HAS CHANGED WITH THE  
CURRENT FORECAST PACKAGE WITH HIGH QPF AMOUNTS STILL SHOWN OVER  
ALL BUT SOUTHWEST ARIZONA AND SOUTHEAST CALIFORNIA. THE BEST  
TIMEFRAME FOR MODERATE TO POSSIBLY HEAVY RAIN AND SNOW OVER THE  
EASTERN HALF OF ARIZONA LOOKS TO BE THIS AFTERNOON AND EVENING  
WITH THE HEAVIEST PRECIPITATION SHIFTING SOUTHEASTWARD INTO  
SOUTHEAST ARIZONA BY SUNRISE FRIDAY. THE HIGHEST IMPACTS WILL  
OBVIOUSLY BE THE HEAVY SNOW ACROSS ELEVATIONS ABOVE 3500-4000  
FEET. SNOW LEVELS CONTINUE TO BE A BIT DIFFICULT TO HANDLE WITH  
INITIAL LEVELS AROUND 3000 FT EARLY THIS MORNING AND GRADUALLY  
RISING TO AROUND 4000 FT THIS AFTERNOON BEFORE DROPPING BACK DOWN  
AGAIN ON FRIDAY. SNOW ACCUMULATIONS ARE STILL LIKELY TO OCCUR DOWN  
TO AROUND 3000 FT EARLY THIS MORNING AND ON FRIDAY, CHANGING OVER  
TO RAIN BELOW 4000 FT BETWEEN 18Z TODAY AND 12Z FRIDAY.  
ELEVATIONS AROUND 4000 FT AND ABOVE SHOULD STAY MOSTLY SNOW  
DURING THE BULK OF THE EVENT WITH ACCUMULATIONS ABOVE 1 FOOT,  
POSSIBLY AS MUCH AS 30" OVER THE HIGHEST PEAKS IN THE MAZATZAL  
AND SUPERSTITION MOUNTAINS AND ACROSS FAR EASTERN GILA COUNTY.  
TOTAL RAINFALL OF 1-1.5" IS LIKELY FOR LOWER ELEVATION AREAS FROM  
CENTRAL PHOENIX AND TO THE NORTH AND EAST. THIS WILL LIKELY LEAD  
TO SOME LOCALIZED FLOODING OF WASHES, BUT NO FLOOD WATCHES SHOULD  
BE NEEDED.  
 
THE TROUGH WILL FINALLY BEGIN SHIFTING EAST THROUGH ARIZONA AND  
UTAH ON FRIDAY WITH THE COLD CORE MOVING OVER THE AREA. AT THIS  
TIME, THE MAIN FORCING WILL PUSH TO THE EAST INTO NEW MEXICO, BUT  
STEEP LAPSE RATES UNDER THE COLD CORE AND FORCING FROM A STRONG PV  
ANOMALY OVER CENTRAL ARIZONA WILL AID IN SCATTERED RAIN AND SNOW  
SHOWERS FROM PHOENIX EASTWARD FRIDAY AFTERNOON INTO THE EARLY  
EVENING. THE COLDER AIR WITH THE TROUGH WILL LOWER SNOW LEVELS  
CLOSER TO 3000 FT AGAIN AND WITH THE CONVECTIVE NATURE OF THE  
SHOWERS WE CAN'T RULE OUT RAIN MIXING WITH SNOW OR GRAUPEL AS LOW  
AS 1500-2000 FT ELEVATION. DRIER AIR WILL QUICKLY WORK IN FROM  
THE WEST LATER FRIDAY WITH SKIES BECOMING MOSTLY CLEAR FOR THE  
LOWER DESERTS BY LATE FRIDAY EVENING. AFTER CHILLY DAYTIME  
TEMPERATURES MOSTLY IN THE 40S TO AROUND 50 FOR THE LOWER DESERTS,  
OVERNIGHT LOWS INTO SATURDAY MORNING SHOULD AGAIN END UP AROUND  
FREEZING. THE COLDEST DESERT SPOTS MAY DIP INTO THE UPPER 20S TO  
AROUND 30 DEGREES.  
 
THE TROUGH FINALLY EXITS WELL TO THE EAST BY SATURDAY MORNING WITH  
DRY WESTERLY ZONAL FLOW TAKING OVER THROUGH MONDAY. TEMPERATURES  
WILL BE SLOW TO RECOVER THIS WEEKEND WITH HIGHS STILL ONLY IN THE  
LOW TO MID 50S SATURDAY OVER THE ARIZONA DESERTS TO AROUND 60 IN  
THE WESTERN DESERTS. OVERNIGHT LOWS SATURDAY NIGHT WILL AGAIN BE  
QUITE CHILLY, LIKELY ONLY A COUPLE DEGREE IMPROVEMENT OVER THE  
PREVIOUS NIGHT'S NEAR FREEZING TEMPERATURES. MODELS ARE NOW  
LEANING TO A BIT QUICKER OF A WARM-UP NEXT WEEK WITH A WEAK RIDGE  
BUILDING ACROSS THE WESTERN U.S. TUESDAY INTO WEDNESDAY. THIS  
SHOULD ALLOW HIGHS TO CLIMB TO AROUND 70 DEGREES BY WEDNESDAY AND  
INTO THE LOWER TO MIDDLE 70S FOR THE END OF NEXT WEEK.  
 

 
   
AVIATION
 
 
SOUTH-CENTRAL ARIZONA INCLUDING KPHX, KIWA, AND KSDL:  
 
A POWERFUL WINTER STORM WILL SLOWLY MOVE ACROSS SOUTH-CENTRAL  
ARIZONA TODAY THROUGH FRIDAY BRINGING WIDESPREAD SHOWERS TO THE  
GREATER PHOENIX AREA. IN ADDITION TO PERIODS OF RAIN OR RAIN  
SHOWERS, VERY LOW CIGS CAN BE EXPECTED MUCH OF THE TIME ALONG WITH  
VISIBILITY PERIODICALLY LOWERING DUE TO MODERATE RAIN AND MIST. IN  
AN EFFORT TO KEEP THE TAFS REASONABLY SHORT, TEMPO/PROB GROUPS WERE  
NOT USED AND CONDITIONS IN THE FM GROUPS WERE KEPT A BIT ON THE  
OPTIMISTIC SIDE, WITH SCT DECKS REPRESENTING POTENTIAL FOR LOWERED  
CIGS AT TIMES. THERE ARE REALLY NO "DISTURBANCES" TO TIME INTO OR  
OUT OF THE AREA, A PERSISTENT SHIELD OF RAIN WILL SET UP OVER THE  
AREA AND LINGER INTO FRIDAY AFTERNOON. NOTE THAT THERE MAY WELL BE  
OCCASIONAL EPISODES OF IFR AND LIFR AT THE TAF SITES, WITH CIGS DOWN  
BELOW 1000 FEET AND VIS DOWN BELOW 3SM. ALSO THERE WILL BE TIMES  
WHEN CONDITIONS TEMPORARILY IMPROVE TO VFR. THIS WILL BE A LONG  
LIVED PERIOD OF SIGNIFICANT AVIATION IMPACTS AT THE TAF SITES AND AT  
KPHX. WINDS WILL NOT BE EXCESSIVE AND WILL FAVOR SOUTHEAST TO SOUTH  
THIS MORNING UP TO 15KT OR SO, THEN SWING TO THE SOUTHWEST IN EARLY  
AFTERNOON FOLLOWING A COLD FRONT PASSAGE. EXPECT SOME GUSTINESS IN  
THE AFTERNOON. WINDS TO TAPER OFF THIS EVENING BUT SHOULD MOSTLY  
FAVOR THE SOUTHWEST OVERNIGHT.  
 
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:  
 
A STRONG WINTER STORM WILL SLOWLY MOVE EAST ACROSS THE WESTERN  
DESERTS TODAY INTO FRIDAY BRINGING SCATTERED SHOWERS OR CHANCES FOR  
RAIN TO THE TAF SITES. RAIN MAY BE MODERATE BRIEFLY BUT SHOULD  
MOSTLY BE ON THE LIGHT SIDE. CIGS MAY FALL INTO THE 3-5K FOOT RANGE  
AT TIMES WITH BKN DECKS ABOVE THAT. SOME DECREASE IN CLOUDS AND  
RISING OF CLOUD DECKS CAN BE EXPECTED STARTING THIS EVENING WITH  
CONDITIONS IMPROVING SOMEWHAT OVERNIGHT TONIGHT. WINDS WILL FAVOR  
THE SOUTHWEST TODAY WITH GUSTS TO 25KT POSSIBLE ESPECIALLY AT KIPL.  
LOOK FOR WINDS TO TAPER OFF DURING THE EVENING HOURS TONIGHT.  
 
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.  
 

 
   
FIRE WEATHER
 
 
SATURDAY THROUGH WEDNESDAY: A STRONG WINTER STORM WILL EXIT TO THE  
EAST FRIDAY NIGHT RESULTING IN A DRYING AND GRADUAL WARMING TREND  
FOR THE WEEKEND INTO THE MIDDLE OF NEXT WEEK. DESPITE NEARLY  
CONSTANT WARMING EACH DAY, HIGHS WILL REMAIN BELOW NORMALS THROUGH  
NEXT TUESDAY ALTHOUGH THEY WILL CLIMB INTO MID TO UPPER 60S OVER THE  
WARMER LOWER DESERTS. WARMER DESERTS WILL FINALLY APPROACH NORMAL  
AND REACH THE LOW 70S BY NEXT WEDNESDAY. HUMIDITY LEVELS WILL REMAIN  
ELEVATED THROUGH THE PERIOD WITH DRIER DESERTS STILL MOSTLY ABOVE 20  
PERCENT EACH DAY. WINDS WILL TEND TO BE ON THE LIGHT SIDE DURING THE  
FIVE DAY PERIOD.  
 

 
   
SPOTTER INFORMATION STATEMENT
 
 
SPOTTERS SHOULD FOLLOW STANDARD REPORTING PROCEDURES.  
 

 
   
PSR WATCHES/WARNINGS/ADVISORIES
 
 
AZ...WINTER STORM WARNING UNTIL 5 PM MST FRIDAY FOR AZZ545-557-558-  
560>563.  
 
CA...WINTER WEATHER ADVISORY UNTIL 10 PM PST THIS EVENING FOR CAZ560.  
 

 
 

 
 
DISCUSSION...KUHLMAN  
AVIATION...CB  
FIRE WEATHER...CB  
 
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