Climatological Report (Monthly)
Issued by NWS Boise, ID
Issued by NWS Boise, ID
000 CXUS55 KBOI 011832 CLMBOI CLIMATE REPORT...CORRECTED TO ADD NARRATIVE NATIONAL WEATHER SERVICE BOISE ID 1133 AM MDT SUN OCT 01 2023 SEPTEMBER WAS SLIGHTLY WARMER THAN NORMAL. TEMPERATURES AVERAGED ABOVE NORMAL ON 20 DAYS. PRECIPITATION WAS CLOSE TO NORMAL. MEASURABLE RAIN FELL ON ONLY 5 DAYS. ON THE 1ST AND 2ND, HIGHS WERE IN THE 80S UNDER SOUTHERLY FLOW ON THE EASTERN FLANK OF A LOW PRESSURE TROUGH OVER THE WEST COAST. THE TROUGH MOVED INLAND ON THE 3RD, BRINGING SHOWERS AND COOLING TEMPERATURES BY AROUND 10 DEGREES. FOLLOWING THE TROUGH, HIGHS WERE BACK IN THE MID 80S ON THE 5TH AND REACHED 90 DEGREES ON THE 6TH UNDER SOUTHWESTERLY FLOW FROM CALIFORNIA. THAT AFTERNOON, AN ISOLATED THUNDERSTORM DEPOSITED .03 INCH OF RAIN AT THE AIRPORT, FOLLOWING A WIND GUST OF 40 MPH FROM THE SOUTHWEST. A WEAK TROUGH APPROACHING FROM THE WEST ON THE 7TH SET OFF ISOLATED THUNDERSTORMS, BUT ONLY A TRACE OF RAIN FELL AT THE AIRPORT. NO MEASURABLE RAIN FELL AGAIN UNTIL THE 22ND. HIGH PRESSURE ALOFT OVER THE WESTERN U.S. KEPT PACIFIC WEATHER SYSTEMS NORTH OF OUR AREA FROM THE 8TH THROUGH THE 12TH. A WEAK COLD FRONT ASSOCIATED WITH ONE OF THESE SYSTEMS CROSSED OUR AREA ON THE 13TH. IT COOLED HIGHS INTO THE LOWER 80S ON THE 13TH AND 14TH, COMPARED TO THE LOWER 90S FROM THE 9TH THROUGH THE 11TH AND UPPER 80S ON THE 12TH. A NEW HIGH PRESSURE RIDGE WAS ALREADY BUILDING INLAND ON THE 14TH, AND DURING THE AFTERNOON OF THE 16TH THE TEMPERATURE HIT 93 AT THE AIRPORT. THAT TIED THE RECORD FOR THE DATE LAST OBSERVED IN 2014. BY THE 18TH, A LARGE HIGH PRESSURE RIDGE HAD BECOME ESTABLISHED BETWEEN ALASKA AND HAWAII. FOR OUR AREA, THE RESULTING PATTERN CHANGE STARTED A COOLING TREND UNDER NORTHWEST FLOW ALOFT. THE FIRST COLD FRONT CROSSED THE BOISE AREA ON THE 19TH, LOWERING HIGHS FROM THE 80S TO THE 70S. ON THE 20TH, A SECOND COLD FRONT PASSED. THE COLD UPPER LEVEL TROUGH BEHIND THE FRONT PREVENTED THE TEMPERATURE FROM RISING ABOVE 66 DEGREES, AFTER A MORNING LOW OF 43. STARTING ON THE 23RD, A HIGH PRESSURE RIDGE BEGAN TO BUILD OVER THE ROCKIES, AND TEMPERATURES WERE ABOVE NORMAL AGAIN FROM THE 24TH THROUGH THE 26TH. MEANWHILE ON THE 24TH, A DEEP TROUGH WAS FORMING OFF THE NORTHWEST COAST. FOLLOWING AN AFTERNOON COLD FRONT ON THE 26TH, THE TROUGH MOVED INLAND ON THE 27TH, LOWERING TEMPERATURES TO NEAR NORMAL. LIGHT PRECIPITATION FELL AT MCCALL, BUT BOISE STAYED DRY. THAT TROUGH WEAKENED AND WAS REPLACED BY A TROUGH WHICH DEEPENED SOUTHWARD OVER THE WEST COAST ON THE 29TH. IT PUSHED INLAND ON THE 30TH, BRINGING A QUARTER INCH OF RAIN. THE HIGH OF 57 WAS THE COOLEST MAX TEMPERATURE SINCE THE 53 ON APRIL 21ST. ................................... ...THE BOISE ID CLIMATE SUMMARY FOR THE MONTH OF SEPTEMBER 2023... CLIMATE NORMAL PERIOD 1991 TO 2020 CLIMATE RECORD PERIOD 1875 TO 2023 WEATHER OBSERVED NORMAL DEPART LAST YEAR`S VALUE DATE(S) VALUE FROM VALUE NORMAL .............................................................. TEMPERATURE (F) HIGHEST 93 09/11 09/16 LOWEST 42 09/28 AVG. MAXIMUM 81.0 80.0 1.0 AVG. MINIMUM 55.4 52.6 2.8 MEAN 68.2 66.3 1.9 DAYS MAX >= 90 5 DAYS MAX <= 32 0 DAYS MIN <= 32 0 DAYS MIN <= 0 0 PRECIPITATION (INCHES) RECORD MAXIMUM 2.93 1986 TOTALS 0.45 0.43 0.02 DAYS >= .01 6 DAYS >= .10 2 DAYS >= .50 0 DAYS >= 1.00 0 GREATEST 24 HR. TOTAL 0.23 09/30 TO 09/30 DEGREE DAYS HEATING TOTAL 49 80 -31 13 SINCE 7/1 49 94 -45 COOLING TOTAL 156 119 37 206 SINCE 1/1 1322 1034 288 .............................................................. WIND (MPH) AVERAGE WIND SPEED 6.8 HIGHEST WIND SPEED/DIRECTION 28/240 DATE 09/06 HIGHEST GUST SPEED/DIRECTION 40/220 DATE 09/06 AVERAGE RH (PERCENT) 41 - INDICATES NEGATIVE NUMBERS. R INDICATES RECORD WAS SET OR TIED. MM INDICATES DATA IS MISSING. T INDICATES TRACE AMOUNT. $$