086  
FXUS65 KPSR 222148  
AFDPSR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PHOENIX AZ  
245 PM MST FRI FEB 22 2019  
   
SYNOPSIS
 
 
A MAJOR WINTER STORM WILL QUICKLY EXIT THROUGH EASTERN ARIZONA THIS  
EVENING WITH RAIN AND SNOW TAPERING OFF ACROSS THE AREA. CLEARING  
SKIES WILL RESULT IN A FEW CHILLY MORNINGS, HOWEVER DRY WEATHER AND  
MUCH WARMER TEMPERATURES WILL FINALLY RETURN TO THE REGION NEXT  
WEEK. TEMPERATURES WILL STEADILY RETURN TO NEAR AVERAGE LEVELS  
WITH WELCOME HIGHS REACHING BACK INTO THE MIDDLE AND UPPER 70S.  
 

 
   
DISCUSSION
 
 
A DEEP PV ANOMALY HAS PROPAGATED INTO SOUTH-CENTRAL ARIZONA THIS  
AFTERNOON WHILE THE STREAM OF MORE PRONOUNCED ISENTROPIC ASCENT AND  
MIDTROPOSPHERIC FRONTOGENTICAL FORCING HAS SHIFTED INTO NEW MEXICO.  
HOWEVER AHEAD OF THE TROUGH AXIS THROUGH WESTERN ARIZONA AND UNDER  
AN IMPRESSIVE AND CLIMATOLOGICALLY RARE COLD CORE (12Z KNKX H5  
TEMPERATURE SAMPLED AT -34C IS ONE OF THE COLDEST 500MB TEMPERATURES  
EVER RECORDED AT THIS UPPER AIR SITE), VERY STEEP LAPSE RATES WERE  
SUPPORTING SBCAPE UP TO 250 J/KG AND LOW TOPPED CONVECTIVE SHOWERS  
(TROPOPAUSE CURRENTLY BELOW 20K FT WILL LIMIT ANY FURTHER VERTICAL  
DEVELOPMENT TO THESE SHOWERS). GIVEN THE VERY LOW FREEZING LEVELS,  
ANY MORE ROBUST SHOWERS WILL SUPPORT A FEW LIGHTNING STRIKES AND  
SMALL HAIL/GRAUPEL. COVERAGE SHOULD BE FAIRLY NUMEROUS THOUGH THE  
SMALLER SIZE OF SHOWERS AND RAPID PROPAGATION SHOULD SIGNIFICANTLY  
LIMIT ANY FLOODING IMPACTS.  
 
CONCEIVABLY, HEAVIER CONVECTIVE ACTIVITY COULD BRING SNOW LEVELS  
DOWN MUCH LOWER LOCALLY, HOWEVER THE RESIDENCE TIME OF ANY OF THESE  
QUICK MOVING SHOWERS WILL HAVE A MUCH MORE DIFFICULT TIME IN  
DYNAMICALLY COOLING THE ATMOSPHERIC COLUMN VERSUS YESTERDAY.  
NEVERTHELESS, OVERALL SNOW LEVELS WILL REMAIN AROUND 3000 FT AND  
WITH SHOWERS PERSISTING INTO SOUTHERN GILA COUNTY BEYOND SUNSET, THE  
WARNING IN THE SOUTHEAST PART OF THE CWA WAS EXTENDED A FEW HOURS.  
THE COMBINATION OF LOSS OF DAYTIME HEATING AND PASSAGE OF THE TROUGH  
AXIS WILL QUICKLY BRING RAIN/SNOW TO AN END BY LATE EVENING AS  
SUBSIDENCE AND DRY AIR ENVELOP THE ENTIRE REGION.  
 
WITH CLEARING SKIES AND DRIER AIR MOVING INTO THE AREA, FREEZING  
TEMPERATURES WILL BE A DISTINCT POSSIBILITY TONIGHT - EVEN AT LOWER  
ELEVATIONS OF SOUTH-CENTRAL ARIZONA. THE TYPICAL SHELTERED VALLEYS  
SHOULD FALL INTO THE UPPER 20S/LOW 30S. ANY LOCATION THAT DOES HAVE  
SNOW COVER (I.E. FOOTHILLS AND HIGHER ELEVATIONS) WILL DEFINITELY  
FALL EVEN COLDER. HOWEVER GIVEN THE UNUSUALLY COLD PERIOD OF WEATHER  
THIS MONTH AND COMMON, WIDESPREAD FREEZING TEMPERATURES VERY  
RECENTLY, NO FREEZE HEADLINES SEEM NECESSARY AT THIS TIME. THE  
GREATEST HAZARD HEADING INTO SATURDAY MORNING WOULD BE RE-FREEZING  
OF ICE ON LESS TRAVELED ROADS OUTSIDE OF MAJOR POPULATION CENTERS.  
 
THE TROUGH AXIS FINALLY EXITS WELL TO THE EAST OF THE AREA 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. LOCATIONS WITH LINGERING SNOW  
COVER WILL BE NOTABLY COLDER FOR THE NEXT SEVERAL DAYS. OVERNIGHT  
LOWS SATURDAY NIGHT WILL AGAIN BE CHILLY, LIKELY ONLY A COUPLE  
DEGREE IMPROVEMENT OVER TONIGHT NEAR OR BELOW 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  
TUESDAY WITH HIGH CLOUDS POTENTIALLY KEEPING TEMPERATURES IN THE LOW  
70S ON WEDNESDAY BEFORE WARMING INTO THE MID 70S BY THURSDAY AND  
FRIDAY.  
 

 
   
AVIATION
 
 
SOUTH-CENTRAL ARIZONA INCLUDING KPHX, KIWA, AND KSDL:  
THE STRONG WINTER STORM IMPACTING THE REGION WILL CONTINUE TO  
PRODUCE WIDESPREAD LOW CIGS THROUGH THE AFTERNOON, GENERALLY  
RANGING FROM 2 KFT TO 4 KFT. CIGS AOB 1 KFT WILL BE POSSIBLE AT  
TIMES WITH ANY RAIN SHOWERS THAT MOVE THROUGH. VCTS WILL BE  
POSSIBLE OVER THE NEXT FEW HOURS, BUT CONFIDENCE IS TOO LOW TO  
MENTION IN THE TAF. A FEW GUSTS WILL BE POSSIBLE THIS AFTERNOON  
FROM THE W/SW.  
 
RAIN CHANCES DIMINISH BY 02Z WITH CIGS SCATTERING OUT LATER THIS  
AFTERNOON INTO THE EVENING AS DRY NORTHWESTERLY FLOW ALOFT BEGINS TO  
DOMINATE. MOSTLY CLEAR SKIES WILL THEN PREVAIL THROUGH THE REMAINDER  
OF THE TAF PERIOD. MOSTLY CLEAR SKIES OVERNIGHT WILL ALLOW FOR  
OPTIMAL RADIATIONAL COOLING TO OCCUR, PROVIDING THE POSSIBILITY OF  
FOG DEVELOPING EARLY TOMORROW MORNING. CONFIDENCE IS NOT HIGH ENOUGH  
AT THIS TIME TO INCLUDE IN THE TAFS.  
 
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:  
THE STRONG WINTER STORM THAT HAS BEEN IMPACTING THE TERMINALS HAS  
NOW MOVED TO THE EAST WITH DRY NORTHWESTERLY FLOW SETTING IN.  
MOSTLY CLEAR SKIES ARE EXPECTED TO PREVAIL THROUGH THE REMAINDER  
OF THE TAF PERIOD. BOTH TERMINALS WILL FAVOR WINDS OUT OF THE N/NW  
THROUGH THE AFTERNOON BEFORE FAVORING A WESTERLY COMPONENT AFTER  
02Z. GUSTS UP TO 25 KTS WILL BE POSSIBLE THROUGH THE AFTERNOON  
BEFORE WINDS DECOUPLE THIS EVENING. WINDS WILL THEN WEAKEN TO AOB  
10 KTS THROUGH THE REMAINDER OF THE TAF PERIOD.  
 
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.  
 

 
   
FIRE WEATHER
 
 
SUNDAY THROUGH THURSDAY:  
DRY CONDITIONS ARE EXPECTED THROUGH THE FIVE DAY PERIOD, ALONG WITH  
A WARMING TREND AS HIGH PRESSURE STARTS TO BUILD INTO THE AREA.  
INITIALLY HIGH TEMPERATURES WILL BE WELL BELOW NORMAL; DESERT HIGHS  
SUNDAY WILL BE IN THE LOW TO MID 60S AND NEARLY 10 DEGREES BELOW  
NORMAL. AFTER THAT STEADY WARMING WILL OCCUR WITH HIGHS BACK INTO  
THE LOW 70S AND NEAR NORMAL BY TUESDAY. HIGHS WILL BE ABOVE NORMAL  
BY THURSDAY WITH MID 70S HIGHS. HUMIDITY LEVELS WILL STAY ELEVATED  
EACH DAY, WITH THE DESERTS TYPICALLY RUNNING 20 TO 30 PERCENT EACH  
DAY. WINDS WILL ALSO 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 THIS AFTERNOON FOR AZZ545-  
557.  
 
WINTER STORM WARNING UNTIL 8 PM MST THIS EVENING FOR AZZ558-  
560>563.  
 
CA...NONE.  

 
 

 
 
DISCUSSION...MO/HOPPER/PERCHA/KUHLMAN  
AVIATION...SMITH  
FIRE WEATHER...CB  
 
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