849  
CXUS55 KBOI 011735  
CLMBOI  
 
CLIMATE REPORT  
NATIONAL WEATHER SERVICE BOISE ID  
1135 AM MDT MON JUN 01 2020  
   
..THE BOISE ID CLIMATE SUMMARY FOR THE MONTH OF MAY 2020
 
 
TEMPERATURES AVERAGED JUST OVER ONE DEGREE ABOVE NORMAL.  
PRECIPITATION WAS 40 PERCENT ABOVE NORMAL.  
 
AN EXTENSIVE UPPER-LEVEL LOW PRESSURE SYSTEM OVER THE NORTHEAST  
PACIFIC WAS THE DOMINANT FEATURE THROUGH THE 17TH. IT WAS  
RESPONSIBLE FOR STEERING WEATHER SYSTEMS INTO WESTERN NORTH AMERICA.  
BETWEEN SYSTEMS, SOUTHWEST FLOW EAST OF THE LOW BROUGHT WARMER AIR.  
 
THE FIRST COUPLE OF WEATHER SYSTEMS, WHICH CAME THROUGH ON THE 3RD  
AND THE 6TH, BROUGHT ONLY LIGHT PRECIPITATION. STRONG WEST WINDS  
FOLLOWED A COLD FRONT ON THE MORNING OF THE 6TH. A GUST OF 48 MPH  
WAS MEASURED AT THE AIRPORT.  
 
THE FIRST SIGNIFICANT PRECIPITATION OF THE MONTH CAME ON THE 14TH  
WHEN .36 INCH OF RAIN FELL AT THE AIRPORT AS A LOW PRESSURE TROUGH  
CROSSED THE AREA.  
 
ON THE 16TH A MUCH LARGER AND COLDER TROUGH FROM SIBERIA WAS NEARING  
THE WEST COAST. BEFORE MOVING INLAND ON THE 19TH, IT HAD DEEPENED  
FAR ENOUGH DOWN THE COAST TO TAP SUBTROPICAL MOISTURE SOUTHWEST OF  
CALIFORNIA. ON THE 20TH IT WAS CENTERED DIRECTLY OVER IDAHO. THAT  
DAY.80 INCH OF RAIN FELL AT THE AIRPORT, BREAKING THE PREVIOUS  
RECORD FOR THE DATE OF.56 INCH IN 1985. OTHER PARTS OF TOWN WERE  
DRENCHED BY EVEN HEAVIER RAIN, INCLUDING 1.31 INCHES AT BSU.  
 
WITH A HIGH OF ONLY 51, THE 20TH WAS THE COOLEST DAY OF THE MONTH.  
THE RECORD COOLEST HIGH TEMPERATURE FOR THE DATE IS 48 IN 1902.  
BELOW-NORMAL TEMPERATURES WOULD CONTINUE THROUGH THE 24TH.  
 
AN UPPER-LEVEL HIGH PRESSURE RIDGE BUILDING OVER THE COAST ON THE  
24TH STARTED A WARMING TREND WHICH WAS BRIEFLY INTERRUPTED BY A  
WEAK PACIFIC COLD FRONT ON THE 26TH.  
 
STARTING ON THE 27TH, TEMPERATURES ROSE EACH DAY AS THE RIDGE  
STRENGTHENED. FROM THE 28TH THROUGH THE 30TH, HIGHS WERE IN THE 90S  
FOR THE FIRST TIME SINCE SEPTEMBER. ON THE 30TH THE HIGH OF 98 TIED  
THE RECORD FOR THE DATE SET IN 1986. AND THE LOW OF 69 BROKE THE  
PREVIOUS RECORD OF 65 SET IN 2015.  
 
A LOW PRESSURE SYSTEM THAT HAD BEEN SPINNING OVER THE SUBTROPICAL  
PACIFIC WEST OF BAJA FINALLY MOVED INLAND OVER CALIFORNIA ON THE  
30TH. AS IT PROGRESSED NORTHWARD TOWARD EASTERN OREGON AND SOUTHWEST  
IDAHO, IT WAS PRECEDED BY HOT DRY WINDY WEATHER AND SCATTERED  
THUNDERSTORMS. PRECIPITATION WAS MOSTLY LIGHT. ONLY A TRACE OF RAIN  
DAMPENED THE AIRPORT, BUT A FEW SPOTS CLOSER TO THE FOOTHILLS GOT  
HEAVY DOWNPOURS.  
 
THE PEAK GUST AT THE AIRPORT WAS 48 MPH FROM THE EAST-SOUTHEAST AT  
5:43 PM MDT. WINDS WERE LIKELY STRONGER ELSEWHERE AROUND THE VALLEY,  
AS THERE WERE REPORTS OF TREES DAMAGED OR BLOWN OVER AND POWER  
OUTAGES.  
 
BY THAT EVENING THE FIRST ROUND OF SHOWERS HAD MOVED NORTH AND EAST  
OF BOISE, AND AT 9:15 PM MDT A COLD FRONT PASSED THE AIRPORT FROM  
THE WEST.  
 
THERE WAS MORE WEATHER TO COME LATER THAT NIGHT, AS THE UPPER-LEVEL  
TROUGH BEHIND THE COLD FRONT WAS STILL ON ITS WAY. THE ARRIVAL OF  
THE TROUGH WAS ANNOUNCED BY A THUNDERSTORM JUST BEFORE 3 AM MDT ON  
THE 31ST. HAIL ONE-HALF INCH IN DIAMETER FELL AT THE AIRPORT, BUT  
THERE WAS ONLY .09 INCH OF TOTAL PRECIPITATION.  
 
THUNDERSTORMS BETWEEN MIDNIGHT AND 6:00 AM ARE VERY RARE IN OUR PART  
OF THE COUNTRY. AT BOISE THE CHANCE IS ONLY 2 PERCENT IN MAY AND 4  
PERCENT IN JUNE.  
   
...............................
 
 
CLIMATE NORMAL PERIOD 1981 TO 2010  
CLIMATE RECORD PERIOD 1875 TO 2020  
 
WEATHER OBSERVED NORMAL DEPART LAST YEAR'S  
VALUE DATE(S) VALUE FROM VALUE  
NORMAL    
..........................................................
 
 
TEMPERATURE (F)  
HIGHEST 98 05/30  
LOWEST 34 05/07  
AVG. MAXIMUM 72.6 71.6 1.0  
AVG. MINIMUM 48.4 46.5 1.9  
MEAN 60.5 59.1 1.4  
DAYS MAX >= 90 3  
DAYS MAX <= 32 0  
DAYS MIN <= 32 0  
DAYS MIN <= 0 0  
 
PRECIPITATION (INCHES)  
RECORD  
MAXIMUM 4.90 1890  
TOTALS 1.98 1.39 0.59  
DAYS >= .01 15  
DAYS >= .10 4  
DAYS >= .50 1  
DAYS >= 1.00 0  
GREATEST  
24 HR. TOTAL 1.02 05/19 TO 05/20  
 
SNOWFALL (INCHES)  
TOTALS 0.0  
SINCE 7/1 15.3  
GREATEST  
SNOW DEPTH 0  
24 HR TOTAL 0  
 
DEGREE DAYS  
HEATING TOTAL 192 226 -34 173  
SINCE 7/1 5102 5449 -347  
COOLING TOTAL 58 41 17 22  
SINCE 1/1 64 44 20    
..........................................................
 
 
WIND (MPH)  
AVERAGE WIND SPEED 7.8  
HIGHEST WIND SPEED/DIRECTION 35/290 DATE 05/06  
35/120 05/30  
HIGHEST GUST SPEED/DIRECTION 48/280 DATE 05/06  
48/110 05/30  
 
AVERAGE RH (PERCENT) 51  
 
- INDICATES NEGATIVE NUMBERS.  
R INDICATES RECORD WAS SET OR TIED.  
MM INDICATES DATA IS MISSING.  
T INDICATES TRACE AMOUNT.  
 

 
 
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