Climatological Report (Monthly)
Issued by NWS Boise, ID

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098
CXUS55 KBOI 011730
CLMBOI

CLIMATE REPORT
NATIONAL WEATHER SERVICE BOISE ID
1124 AM MDT MON OCT 1 2018

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

...THE BOISE ID CLIMATE SUMMARY FOR THE MONTH OF SEPTEMBER 2018...

WITH ONLY A TRACE OF RAIN, SEPTEMBER 2018 WAS ONE OF THE DRIEST
SEPTEMBERS ON RECORD. THERE WERE ONLY 9 OTHERS WITH NO MEASURABLE
PRECIPITATION IN 152 YEARS OF BOISE AREA RECORDS, AND ONLY 5 OTHERS
IN 78 YEARS OF AIRPORT RECORDS.

TOTAL PRECIPITATION FOR THE FOUR MONTHS FROM JUNE THROUGH SEPTEMBER
WAS ONLY.36 INCH. JUNE-SEPTEMBER PERIODS WITH SO LITTLE
PRECIPITATION ARE UNUSUAL, BUT NOT UNIQUE. FOR EXAMPLE:

                               1994   .44
                               1901   .39
                               1898   .37
                               2018   .36
                               1957   .31
                               2012   .31
                               1933   .27
                               1966   .27
                               1935   .19

TEMPERATURES AVERAGED ONLY SLIGHTLY ABOVE NORMAL.

SEPTEMBER BEGAN WITH NEAR NORMAL TEMPERATURES UNDER DRY WESTERLY
FLOW ALOFT. THE FLOW BACKED INTO THE SOUTHWEST ON THE 5TH AS A HIGH
PRESSURE RIDGE BUILT OVER THE NORTHERN ROCKIES. THIS RESULTED IN THE
LAST 90-DEGREE HIGHS OF THE SUMMER ON THE 5TH, 6TH, AND 7TH.

A COOLING TREND COMMENCED ON THE 8TH AS AN UPPER LEVEL LOW PRESSURE
TROUGH FROM THE GULF OF ALASKA APPROACHED THE BRITISH COLUMBIA
COAST. AS THE TROUGH EDGED CLOSER, A DRY COLD FRONT PASSED BOISE ON
THE 10TH, FOLLOWED BY COOLER NORTH PACIFIC AIR. HIGHS WERE ONLY IN
THE LOW 70S FROM THE 11TH THROUGH THE 13TH.

THE TROUGH REMAINED PARKED OVER THE WEST COAST THROUGH THE 18TH,
KEEPING TEMPERATURES A FEW DEGREES BELOW NORMAL. IT FINALLY MOVED
INLAND ON THE 19TH, THEN CONTINUED EAST OUT OF OUR AREA ON THE 20TH.

BRIEF WARMING FOLLOWED ON THE 21ST AND 22ND, WITH HIGHS IN THE LOW
80S, BUT ANOTHER NORTH PACIFIC TROUGH WAS ON THE WAY.

RATHER THAN STALLING OVER THE COAST, THIS TROUGH CONTINUED ON AN
EASTWARD TRACK, PUSHED ALONG BY A BUILDING UPPER LEVEL HIGH PRESSURE
RIDGE OFFSHORE. THE TROUGH WAS EAST OF OUR AREA ON THE 24TH. LIKE
ITS PREDECESSORS, IT PRODUCED NO RAIN IN THE BOISE AREA.

EAST OF THE RIDGE, NORTHWEST FLOW ALOFT OVER THE PACIFIC NORTHWEST
STATES KEPT TEMPERATURES 5 TO 10 DEGREES BELOW NORMAL, WITH HIGHS OF
ONLY 69 ON THE 24TH AND 25TH, THE FIRST HIGHS IN THE 60S SINCE JUNE
17. THE LOW OF 38 ON THE 24TH WAS THE FIRST LOW IN THE 30S SINCE MAY
2.

AS THE EASTERN PORTION OF THE RIDGE EDGED INLAND, WARMER AIR RAISED
TEMPERATURES ABOVE NORMAL FROM THE 27TH THROUGH THE 29TH, WITH HIGHS
IN THE LOW 80S.

DURING THAT TIME, AN UPPER LEVEL LOW WAS DRIFTING SLOWLY EASTWARD
TOWARD CALIFORNIA. BY THE MORNING OF THE 30TH, IT WAS CENTERED OVER
THE OREGON-NORTHERN CALIFORNIA COAST. ITS ONLY EFFECTS ON BOISE WERE
A FEW CLOUDS AND SLIGHTLY COOLER TEMPERATURES.

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

CLIMATE NORMAL PERIOD 1981 TO 2010
CLIMATE RECORD PERIOD 1875 TO 2018

WEATHER         OBSERVED          NORMAL  DEPART  LAST YEAR`S
                 VALUE   DATE(S)  VALUE   FROM    VALUE
                                          NORMAL
.............................................................
TEMPERATURE (F)
HIGHEST            96   09/05
LOWEST             38   09/24
AVG. MAXIMUM     79.9              78.8     1.1
AVG. MINIMUM     51.2              51.0     0.2
MEAN             65.6              64.9     0.7
DAYS MAX >= 90      3
DAYS MAX <= 32      0
DAYS MIN <= 32      0
DAYS MIN <= 0       0

PRECIPITATION (INCHES)
RECORD
 MAXIMUM         2.93   1986
TOTALS              T              0.58   -0.58
DAYS >= .01         0
DAYS >= .10         0
DAYS >= .50         0
DAYS >= 1.00        0
GREATEST
 24 HR. TOTAL       T   09/15 TO 09/15

DEGREE_DAYS
HEATING TOTAL      60               103     -43      131
 SINCE 7/1         67               121     -54
COOLING TOTAL      84               100     -16      175
 SINCE 1/1       1120               934     186
..............................................................

WIND (MPH)
AVERAGE WIND SPEED              6.3
RESULTANT WIND SPEED/DIRECTION   1/297
HIGHEST WIND SPEED/DIRECTION    21/340    DATE  09/23
HIGHEST GUST SPEED/DIRECTION    29/300    DATE  09/23

SKY COVER
POSSIBLE SUNSHINE (PERCENT)   MM

AVERAGE RH (PERCENT)     35


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

$$



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