796  
FXUS65 KTWC 222225  
AFDTWC  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE TUCSON AZ  
325 PM MST SUN APR 22 2018  
   
SYNOPSIS
 
EXPECT DRY CONDITIONS ACROSS MUCH OF THE AREA AND  
UNSEASONABLY WARM DAYTIME TEMPERATURES THIS WEEK. THE EXCEPTIONS ARE  
A FEW LIGHT SHOWERS POSSIBLE SOUTHEAST OF TUCSON THIS AFTERNOON, AND  
A FEW AFTERNOON THUNDERSTORMS NEAR SOME EASTERN MOUNTAINS THE  
SECOND HALF OF THE WEEK.  
 

 
   
DISCUSSION
 
AS EXPECTED, THE WEAK LOW WE'VE BEEN LOOKING AT  
FROM THE EASTERN PACIFIC HAS OPENED UP AS IT MOVES THROUGH  
NORTHERN MEXICO AND SOUTHERN ARIZONA. LOWER LEVELS HAVE REMAINED  
DRY WITH SURFACE DEW POINTS IN THE TEENS TO 20S AND MOST OF THE  
MOISTURE AT 500MB ON THE 12Z SOUNDING. THAT SAME SOUNDING ALSO  
SHOWED AN INCREASING TREND BETWEEN 700-500MB THOUGH, AND CURRENT  
SATELLITE ESTIMATED PRECIPITABLE WATER IS UP TO AROUND .65 INCHES  
(FROM 1/3 OF AN INCH YESTERDAY AFTERNOON AND 1/2 INCH THIS  
MORNING). THE ACCAS AROUND THE AREA JUST AFTER SUNRISE TOLD A  
STORY THAT HAS EVOLVED INTO PLENTY OF VIRGA TODAY, AND EVEN SOME  
SPRINKLES TO LIGHT SHOWERS. CURRENT DEVELOPMENT IS NOTED SOUTHEAST  
OF TUCSON IN COCHISE COUNTY WHERE WE HAD GOOD SOLAR INSOLATION.  
HRRR TRENDS CONTINUE TO SUGGEST SOME ENHANCEMENT NEAR THE  
CHIRICAHUA MOUNTAINS OVER THE NEXT FEW HOURS. STILL WOULDN'T BE  
SURPRISED BY A LIGHTNING STRIKE OR TWO THERE WITH A SMALL BULLSEYE  
OF 250 MUCAPE NEAR THERE.  
 
OTHERWISE, STEADY AS SHE GOES WITH THE WARMING TREND INTO EARLY  
THIS WEEK WITH DIRTY AND LONG PERIOD RIDGING. ANOTHER LOW HAS  
SPLIT FROM THE NORTHEAST PACIFIC AND INTO A POSITION WELL OFF THE  
COAST OF BAJA. AS IT COMES THROUGH, THIS WILL MAKE WEDNESDAY AND  
WEDNESDAY EVENING A LOT LIKE TODAY. AFTER WEDNESDAY, WE'LL  
CONTINUE TO SEE ENOUGH MID LEVEL MOISTURE WITH WEAK DISTURBANCES  
EMBEDDED IN THE FLOW TO BRING A FEW THUNDERSTORMS TO THE EASTERN  
MOUNTAINS LATER IN THE WEEK. FRIDAY LOOKS PARTICULARLY INTERESTING  
WITH INCREASING GFS/ECMWF H7 THETA-E TRENDS FROM CENTRAL THROUGH  
NORTHWEST MEXICO.  
 
MODEL DIVERGENCE AT THAT POINT WITH A MORE PROGRESSIVE GFS  
SHUNTING STORM CHANCES EAST OF OUR AREA NEXT WEEKEND, WHILE THE  
ECMWF IS LESS AGGRESSIVE IN RECONSOLIDATING THE FLOW SOUTH AND  
SOUTHEAST OF THE GULF OF ALASKA AND IS THUS SLOWER.  
 

 
   
AVIATION
 
VALID THROUGH 24/00Z.  
ISOLATED -SHRA POSSIBLE NEAR THE NEW MEXICO STATE LINE THROUGH  
23/03Z. OTHERWISE, FEW-BKN CLOUDS 10K-15K FT AGL WITH SCT CLOUDS  
ABOVE 20K FT AGL FOR THE REST OF THE AFTERNOON BEFORE GRADUALLY  
DECREASING IN COVERAGE THROUGH LATE EVENING. SKIES WILL BE MOSTLY  
SKC BY MONDAY MORNING. SFC WINDS WILL REMAIN LIGHT AND TERRAIN  
DRIVEN AT GENERALLY LESS THAN 10 KTS FOR THE FORECAST PERIOD.  
AVIATION DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.  
 

 
   
FIRE WEATHER
 
A FEW LIGHT SHOWERS WILL BE POSSIBLE ACROSS  
EASTERN ZONES THIS EVENING, WITH THE MAIN FOCUS BEING IN SOUTHERN  
COCHISE COUNTY. DRY CONDITIONS WILL RETURN FOR MONDAY AND TUESDAY  
BEFORE A SLIGHT CHANCE OF THUNDERSTORMS DEVELOPS ACROSS THE EASTERN  
MOUNTAINS DURING THE AFTERNOON HOURS WEDNESDAY THROUGH SATURDAY. ANY  
LIGHTNING WOULD ENHANCE FIRE INITIATION CONCERNS AND GUSTY OUTFLOWS  
MAY ALSO OCCUR. ABOVE-AVERAGE TEMPERATURES WILL CONTINUE FOR THIS  
WEEK ALONGSIDE GENERALLY LIGHT AND TERRAIN DRIVEN WINDS, WITH A FEW  
AFTERNOON GUSTS DUE TO DAYTIME HEATING.  
 

 
   
TWC WATCHES/WARNINGS/ADVISORIES
 
NONE.  
 

 
 

 
 
MEYER/PEGRAM  
 
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