Climatological Report (Monthly)
Issued by NWS Boise, ID

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CXUS55 KBOI 011728
CLMBOI

CLIMATE REPORT
NATIONAL WEATHER SERVICE BOISE ID
1027 AM MST TUE DEC 01 2020

...................................

TEMPERATURES AVERAGED CLOSE TO NORMAL. PRECIPITATION WAS ABOVE
NORMAL, RANKING AMONG THE WETTEST 30 PERCENT OF NOVEMBERS.

THE TOTAL SNOWFALL OF 4.3 INCHES EXCEEDED THE 30-YEAR NOVEMBER
AVERAGE OF 2.6 INCHES.

A STRONG UPPER LEVEL HIGH PRESSURE RIDGE OVER THE INTERMOUNTAIN
REGION ON THE 1ST AND 2ND WEAKENED ON THE 3RD, BUT ABOVE-NORMAL
TEMPERATURES CONTINUED THROUGH THE 6TH AHEAD OF A PACIFIC COLD FRONT.
THE HIGH OF 76 ON THE 5TH BROKE THE PREVIOUS RECORD FOR THE DATE OF
73 SET IN 1914.

THE COLD FRONT PASSED THE BOISE AREA DURING THE AFTERNOON OF THE 6TH
WITH NO PRECIPITATION. THE COLD UPPER-LEVEL LOW PRESSURE TROUGH
BEHIND THE FRONT DRIFTED SOUTH OVER CALIFORNIA BEFORE SETTLING OVER
THE GREAT BASIN ON THE 7TH. AT THE SAME TIME, A SECOND TROUGH FROM
ALASKA WAS DEEPENING OVER WESTERN CANADA.

IT INITIALLY BROUGHT ONLY LIGHT SNOW TO BOISE ON THE 7TH, BUT
HEAVIER SNOW WAS TO FOLLOW AS IT JOINED FORCES WITH THE GREAT BASIN
TROUGH. BY THE MORNING OF THE 8TH, 2 INCHES WAS ON THE GROUND AT THE
AIRPORT. IT WAS THE FIRST TIME SINCE FEBRUARY 6 THAT BOISE RESIDENTS
SAW SNOW COVER IN THE VALLEY. THE TOTAL OF 2.7 INCHES EXCEEDED THE
OLD RECORD FOR THE 8TH OF 0.3 INCH SET IN 1911.

YET ANOTHER TROUGH, THIS TIME FROM THE GULF OF ALASKA, ARRIVED OVER
THE NORTHWEST U.S. ON THE 10TH WITH ONLY LIGHT SNOW AT BOISE.
MEANWHILE, A BAND OF WESTERLY FLOW ALOFT, AKA THE JET STREAM, WAS
STRENGTHENING SOUTH OF THE ALEUTIANS. ITS ARRIVAL OVER THE NORTHWEST
COAST ON THE 13TH WAS PRECEDED BY A VERY ACTIVE WEATHER DISTURBANCE
WHICH DELIVERED AROUND HALF AN INCH OF PRECIPITATION TO THE BOISE
AREA IN THE FORM OF MORNING SNOW AND AFTERNOON RAIN.

ON THE 15TH COPIOUS PACIFIC MOISTURE ACCOMPANYING A WARM FRONT
BROUGHT MORE RAIN. THE .46 INCH ECLIPSED THE OLD RECORD FOR THE DATE
OF .42 INCH SET IN 1911.

TEMPERATURES HAD BEEN BELOW NORMAL SINCE THE 7TH, BUT AN UPPER-LEVEL
HIGH PRESSURE RIDGE FOLLOWING THE WARM FRONT RAISED TEMPERATURES
ABOVE NORMAL ON THE 16TH.

ON THE 17TH A COLD UPPER-LEVEL LOW PRESSURE TROUGH, WHICH HAD BEEN
DEEPENING OFF THE B.C. COAST, GENERATED A STRONG COLD FRONT WHICH
PUSHED RAPIDLY INLAND. THE FRONT, ENERGIZED BY THE JET STREAM, WAS
ACCOMPANIED BY THUNDERSTORMS WITH ABUNDANT LIGHTNING AS IT ROARED
ACROSS THE BOISE AREA DURING LATE AFTERNOON ON THE 18TH.

STORM REPORTS INCLUDED BRIEF HEAVY SHOWERS WHICH DROPPED FROM A
QUARTER TO A HALF INCH OF PRECIPITATION, SMALL HAIL COVERING THE
GROUND AT SOME LOCATIONS, AND WIND GUSTS EXCEEDING 40 MPH.

THE COLD FRONT CAUSED ONLY SLIGHT COOLING, AND TEMPERATURES REMAINED
ABOVE NORMAL THROUGH THE 19TH UNDER SOUTHWEST FLOW ALOFT.

THE NEXT SEVERAL DAYS WERE MUCH LESS DRAMATIC AS A SERIES OF
RELATIVELY WEAK TROUGHS AND RIDGES CROSSED THE AREA. DURING THE
MORNING OF THE 25TH, A BETTER ORGANIZED TROUGH BROUGHT WET SNOW. ONE
INCH WAS MEASURED AT THE AIRPORT. MOST OF IT MELTED DURING THE
AFTERNOON.

BY THE 27TH A HIGH PRESSURE RIDGE HAD BUILD OVER THE NORTHERN
INTERMOUNTAIN REGION. AS IS TYPICAL OF THIS TIME OF YEAR, THE WARM
AIR ALOFT AND NIGHTTIME COOLING IN THE VALLEY RESULTED IN AN
INVERSION WHICH KEPT TEMPERATURES AROUND 5 DEGREES BELOW NORMAL FROM
THE 28TH THROUGH THE 30TH.

ON THE 30TH A WEATHER DISTURBANCE PRODUCED ONLY VERY LIGHT SNOW, AND
IT WAS NOT STRONG ENOUGH TO BREAK THE INVERSION.


...THE BOISE ID CLIMATE SUMMARY FOR THE MONTH OF NOVEMBER 2020...

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           76   11/05
LOWEST            21   11/30
AVG. MAXIMUM    48.8               48.2     0.6
AVG. MINIMUM    31.3               31.9    -0.6
MEAN            40.0               40.0     0.0
DAYS MAX >= 90     0
DAYS MAX <= 32     0
DAYS MIN <= 32    18
DAYS MIN <= 0      0

PRECIPITATION (INCHES)
RECORD
 MAXIMUM        4.43   1874
TOTALS          1.71               1.35    0.36
DAYS >= .01       11
DAYS >= .10        4
DAYS >= .50        0
DAYS >= 1.00       0
GREATEST
 24 HR. TOTAL   0.51   11/14 TO 11/15

SNOWFALL (INCHES)
TOTALS           4.3
SINCE 7/1        4.3
GREATEST
 SNOW DEPTH        2   11/08
 24 HR TOTAL      MM

DEGREE DAYS
HEATING TOTAL    743                748      -5      720
 SINCE 7/1      1111               1255    -144
COOLING TOTAL      0                  0       0        0
 SINCE 1/1      1087                942     145
..............................................................

WIND (MPH)
AVERAGE WIND SPEED              7.3
HIGHEST WIND SPEED/DIRECTION    28/110    DATE  11/13
HIGHEST GUST SPEED/DIRECTION    37/120    DATE  11/13

AVERAGE RH (PERCENT)     67


-  INDICATES NEGATIVE NUMBERS.
R  INDICATES RECORD WAS SET OR TIED.
MM INDICATES DATA IS MISSING.
T  INDICATES TRACE AMOUNT.

$$


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