Climatological Report (Monthly)
Issued by NWS Boise, ID

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CXUS55 KBOI 011733
CLMBOI

CLIMATE REPORT
NATIONAL WEATHER SERVICE BOISE ID
1127 AM MDT SUN OCT 1 2017

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

...THE BOISE ID CLIMATE SUMMARY FOR THE MONTH OF SEPTEMBER 2017...

SUMMER ABRUPTLY CHANGED TO FALL FOLLOWING A COLD FRONT ON THE 14TH,
A WEEK BEFORE THE FALL EQUINOX. TEMPERATURES AVERAGED NEARLY 10
DEGREES ABOVE NORMAL DURING THE FIRST TWO WEEKS OF THE MONTH, AND
NEARLY 6 DEGREES BELOW NORMAL FOR THE REST OF THE MONTH.
PRECIPITATION WAS CLOSE TO NORMAL.

SMOKE FROM NUMEROUS WILDFIRES PLAGUED THE REGION FOR THE FIRST HALF
OF THE MONTH.

HIGHS RANGED FROM 99 ON THE 3RD TO 52 ON THE 22ND. LOWS RANGED FROM
69 ON THE 9TH TO 36 ON THE 23RD AND 24TH, WHEN FROST WAS OBSERVED AT
MANY LOCATIONS AROUND THE VALLEY. AT BOISE THE AVERAGE DATE OF THE
FIRST 36 DEGREE LOW IS SEPTEMBER 25, AND THE AVERAGE DATE OF THE
FIRST 32 DEGREE LOW IS OCTOBER 10.

THE LOW OF 69 ON THE 9TH SET A RECORD FOR THE DATE, BREAKING THE OLD
RECORD OF 68 IN 1969. THE LOWS OF 67 ON THE 4TH AND 8TH, AND 66 ON
THE 13TH, TIED RECORDS SET IN 1998, 1967, AND 2011 RESPECTIVELY.

THE FIRST HALF OF THE MONTH WAS DOMINATED BY A STRONG AND VERY WARM
HIGH PRESSURE RIDGE OVER THE WESTERN U.S. AND SOUTHWEST CANADA. AT
ITS STRONGEST DURING THE FIRST WEEK OF SEPTEMBER, THE RIDGE EXTENDED
AS FAR NORTH AS NORTHERN B.C. AND ALBERTA.

BY THE 12TH, WESTERLY FLOW ALOFT ACROSS SOUTHERN CANADA HAD ERODED
THE NORTH PORTION OF THE RIDGE, AND TEMPERATURES IN OUR AREA COOLED
TO NEAR NORMAL BY THE 14TH, AHEAD OF AN UPPER LEVEL TROUGH WHICH WAS
DEEPENING AND DRIFTING SOUTH FROM B.C.

AS THE TROUGH CONTINUED TO DEEPEN, IT PUSHED A COLD FRONT ACROSS
EASTERN OREGON AND SOUTHWEST IDAHO DURING THE EVENING OF THE 14TH.
THE TROUGH BEGAN A STRETCH OF UNSEASONABLY COOL FALL-LIKE WEATHER
WHICH WAS TO LAST THROUGH THE 25TH, INTERRUPTED BRIEFLY ON THE 17TH
BY WARMER AIR AHEAD OF A SECOND EVEN COLDER TROUGH WHICH ORIGINATED
WEST OF ALASKA.

THAT SYSTEM BROUGHT SHOWERS, GUSTY WINDS, AND THE COOLEST
TEMPERATURES OF THE MONTH. AS IT EXITED TO THE EAST, TEMPERATURES
MODERATED TO NEAR NORMAL BY THE 26TH.

FROM THE 27TH THROUGH THE 29TH AN UPPER LEVEL RIDGE PROVIDED CLEAR
SKIES AND SLIGHTLY ABOVE-NORMAL TEMPERATURES. BUT DURING THE NIGHT
OF THE 29TH, ANOTHER PACIFIC COLD FRONT CROSSED THE AREA, FOLLOWED
BY MORE COOL, SHOWERY, AND BREEZY WEATHER TO END THE MONTH.


CLIMATE NORMAL PERIOD 1981 TO 2010
CLIMATE RECORD PERIOD 1875 TO 2017

WEATHER         OBSERVED          NORMAL  DEPART  LAST YEAR`S
                 VALUE   DATE(S)  VALUE   FROM    VALUE
                                          NORMAL
.............................................................
TEMPERATURE (F)
HIGHEST            99   09/03
LOWEST             36   09/24
                        09/23
AVG. MAXIMUM     78.5              78.8    -0.3
AVG. MINIMUM     53.9              51.0     2.9
MEAN             66.2              64.9     1.3
DAYS MAX >= 90      9
DAYS MAX <= 32      0
DAYS MIN <= 32      0
DAYS MIN <= 0       0

PRECIPITATION (INCHES)
RECORD
 MAXIMUM         2.93   1986
TOTALS           0.56              0.58   -0.02
DAYS >= .01         7
DAYS >= .10         2
DAYS >= .50         0
DAYS >= 1.00        0
GREATEST
 24 HR. TOTAL    0.25   09/18 TO 09/19

DEGREE_DAYS
HEATING TOTAL     131               103      28       89
 SINCE 7/1        131               121      10
COOLING TOTAL     175               100      75       63
 SINCE 1/1       1341               934     407
..............................................................

WIND (MPH)
AVERAGE WIND SPEED              6.6
RESULTANT WIND SPEED/DIRECTION   0/273
HIGHEST WIND SPEED/DIRECTION    29/330    DATE  09/15
HIGHEST GUST SPEED/DIRECTION    40/310    DATE  09/15

SKY COVER
POSSIBLE SUNSHINE (PERCENT)   MM

AVERAGE RH (PERCENT)     46


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

$$


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