Climatological Report (Monthly)
Issued by NWS Boise, ID
Issued by NWS Boise, ID
262 CXUS55 KBOI 011940 CCA CLMBOI CLIMATE REPORT...CORRECTED TO ADD NARRATIVE NATIONAL WEATHER SERVICE BOISE ID 1240 AM MST MON JAN 01 2024 ...HIGHLIGHTS... WITH AN AVERAGE TEMPERATURE OF 36.3 DEGREES, DECEMBER 2023 WAS AMONG THE WARMEST 8% OF DECEMBERS AT THE BOISE AIRPORT AND AMONG THE WARMEST 13% OF DECEMBERS AT ALL OFFICIAL BOISE OBSERVATION SITES. THE MONTH`S LOW OF 21 DEGREES ON BOTH THE 24TH AND 25TH WAS THE 3RD HIGHEST DECEMBER MINIMUM AT THE AIRPORT AND THE 4TH HIGHEST AT ALL BOISE SITES. THE HIGH OF 61 ON THE 5TH, A RECORD FOR THAT DATE, WAS THE 4TH HIGHEST DECEMBER MAXIMUM AT THE AIRPORT AND THE 6TH HIGHEST AT ALL BOISE SITES. THE CURRENT "STRONG" EL NINO, WHICH HAD ITS BEGINNINGS LAST JUNE, WAS LIKELY A CONTRIBUTING FACTOR. AT THE BOISE AIRPORT, ABOVE-NORMAL DECEMBER MONTHLY AVERAGE TEMPERATURES WERE OBSERVED DURING 47% OF EL NINOS, 25% OF WHICH ARE CLASSIFIED AS "STRONG" (AVERAGE SEA-SURFACE TEMPERATURES IN THE EQUATORIAL PACIFIC AT LEAST 1.5 DEGREES CELSIUS ABOVE NORMAL). PRECIPITATION AT THE AIRPORT WAS .03 INCH BELOW NORMAL. AT THE AIRPORT (SINCE 1940), ABOVE-NORMAL DECEMBER PRECIPITATION OCCURRED DURING 47% OF EL NINOS, 23% OF WHICH WERE "STRONG". SNOWFALL TOTALED 3.8 INCHES. NORMAL IS 5.5 INCHES. THE GREATEST DEPTH WAS 2 INCHES ON THE MORNINGS OF THE 1ST AND 2ND. AN INCH ACCUMULATED BY MIDDAY ON THE 26TH BEFORE MOSTLY MELTING. TEMPERATURE INVERSIONS PLAGUED THE VALLEY DURING ALMOST HALF THE DAYS OF THE MONTH. THE WORST EPISODE PERSISTED FROM THE 16TH THROUGH THE 22ND. FOG WAS OBSERVED ON 15 DAYS, AND DENSE FOG (VISIBILITY LESS THAN OR EQUAL TO 1/4 MILE) OCCURRED ON 8 OF THOSE DAYS. FOG AND LOW STRATUS LIMITED DAYTIME HIGHS. AT BOISE THERE WAS USUALLY SOME AFTERNOON CLEARING, ALLOWING TEMPERATURES TO RISE ABOVE NORMAL. BUT WITH A HIGH OF ONLY 30, THE 17TH WAS THE ONLY DAY WHEN THE AIRPORT TEMPERATURE FAILED TO RISE ABOVE FREEZING. ...SYNOPSIS... WEATHER SYSTEMS SWEEPING IN FROM THE PACIFIC BROUGHT NEARLY AN INCH OF PRECIPITATION IN THE FORM OF RAIN AND SNOW FROM THE 1ST THROUGH THE NIGHT OF THE 3RD. A HIGH PRESSURE RIDGE BUILT OVER THE REGION ON THE 4TH AND SHIFTED EAST OVER THE CONTINENTAL DIVIDE BY THE 5TH, PUTTING BOISE UNDER SOUTHWEST FLOW ALOFT. THAT PATTERN, PLUS MOSTLY SUNNY SKIES, RESULTED IN THE HIGH OF 61 ON THE 5TH. AS THE RIDGE EXITED EAST OF THE ROCKIES, AN UPPER LEVEL TROUGH PUSHED INLAND ON THE 7TH, PROVIDING BOISE WITH OVER A QUARTER INCH OF RAN AND A TRACE OF SNOW. COLDER AIR FROM THE GULF OF ALASKA FOLLOWED, RESULTING IN A HIGH OF 39 (CLOSE TO NORMAL) ON THE 9TH. ON THE 10TH AND 11TH, A WEAK DISTURBANCE BROUGHT LIGHT RAIN AND SNOW, ALONG WITH SLIGHTLY WARMER AIR. THAT SYSTEM HEADED SOUTH AS A RIDGE BUILT OVER THE PACIFIC NORTHWEST ON THE 12TH. THE RIDGE KEPT OUR WEATHER DRY, BUT WARM AIR ALOFT CAPPING COOL MOIST AIR IN THE VALLEY RESULTED IN THE WEEK-LONG TEMPERATURE INVERSION WHICH STARTED ON THE 16TH. LATE ON THE 22ND, A TROUGH FROM THE GULF OF ALASKA PROVIDED ENOUGH COOLING ALOFT AND WIND AT THE SURFACE TO BREAK THE INVERSION. ANOTHER RIDGE BUILT OVER THE WEST COAST ON THE 23RD AND KEPT SKIES MOSTLY CLEAR WITH TEMPERATURES NEAR NORMAL ON THE 24TH AND 25TH. ON THE 26TH, A WEAKENING DISTURBANCE MOVING INTO THE RIDGE FROM THE WEST WAS DEFLECTED INTO CANADA, BUT IT CAME CLOSE ENOUGH TO GIVE BOISE AN INCH OF SNOW ON THE 26TH. FOR THE REST OF THE MONTH, THE RIDGE SUCCESSFULLY BLOCKED ONCOMING SYSTEMS, ALLOWING ONLY A FEW HIGH CLOUDS TO REACH THE TREASURE VALLEY. TEMPERATURES AVERAGED 5-10 DEGREES ABOVE NORMAL FROM THE 27TH THROUGH THE 31ST. ................................... ...THE BOISE ID CLIMATE SUMMARY FOR THE MONTH OF DECEMBER 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 61 12/05 LOWEST 21 12/24 12/25 AVG. MAXIMUM 42.3 38.8 3.5 AVG. MINIMUM 30.2 25.4 4.8 MEAN 36.3 32.1 4.2 DAYS MAX >= 90 0 DAYS MAX <= 32 2 DAYS MIN <= 32 22 DAYS MIN <= 0 0 PRECIPITATION (INCHES) RECORD MAXIMUM 5.96 1871 TOTALS 1.51 1.54 -0.03 DAYS >= .01 11 DAYS >= .10 5 DAYS >= .50 0 DAYS >= 1.00 0 GREATEST 24 HR. TOTAL 0.46 12/02 TO 12/03 SNOWFALL (INCHES) TOTALS 3.8 SINCE 7/1 3.9 GREATEST SNOW DEPTH 2 12/02 24 HR TOTAL 2.5 12/01 TO 12/01 DEGREE DAYS HEATING TOTAL 858 1020 -162 1102 SINCE 7/1 1845 2231 -386 COOLING TOTAL 0 0 0 0 SINCE 1/1 1342 1044 298 .............................................................. WIND (MPH) AVERAGE WIND SPEED 5.6 HIGHEST WIND SPEED/DIRECTION 24/300 DATE 12/07 HIGHEST GUST SPEED/DIRECTION 33/300 DATE 12/07 AVERAGE RH (PERCENT) 77 - INDICATES NEGATIVE NUMBERS. R INDICATES RECORD WAS SET OR TIED. MM INDICATES DATA IS MISSING. T INDICATES TRACE AMOUNT. $$