Climatological Report (Monthly)
Issued by NWS Boise, ID

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CXUS55 KBOI 251123
CLMBOI

CLIMATE REPORT - RESENT WITH NARRATIVE
NATIONAL WEATHER SERVICE BOISE ID
422 AM MST SAT FEB 25 2017

JANUARY WAS COLD, SNOWY, AND UNUSUALLY FOGGY.

IT RANKED AS THE 9TH COLDEST JANUARY AT THE AIRPORT AND THE 16TH
COLDEST SINCE RECORDS BEGAN IN 1865. HIGHS REACHED 32 DEGREES OR
HIGHER ON ONLY 12 DAYS. LOWS FELL BELOW ZERO ON 5 NIGHTS. THE HIGH
OF 6 ABOVE AND THE LOW OF 11 BELOW ON THE 6TH SET NEW RECORDS FOR
THAT DATE.

THE LOWS OF 11 BELOW ON THE 6TH AND 10 BELOW ON THE 7TH WERE THE
COLDEST TEMPERATURES SINCE THE 25 BELOW ON DECEMBER 22, 1990. SINCE
THEN TEMPERATURES DIPPED TO ZERO OR BELOW ONLY 5 TIMES. THE COLDEST
READING DURING THE 1991-2016 PERIOD WAS 7 BELOW ON DECEMBER 9, 2013.

IT WAS THE SNOWIEST MONTH SINCE DECEMBER 1983, WHEN 26.2 INCHES
FELL. THE SNOWIEST MONTH ON RECORD WAS JANUARY 1929, WITH 27.0
INCHES.

THE .45 INCH PRECIPITATION ON THE 4TH SET A NEW RECORD FOR THE DATE.
IT CAME IN THE FORM OF 6.5 INCHES OF SNOW.

THERE WAS FOG ON 26 DAYS, 6 OF WHICH HAD DENSE FOG, WITH
VISIBILITIES A QUARTER MILE OR LESS.

ON THE 1ST AN UPPER LEVEL HIGH PRESSURE RIDGE OVER THE GULF OF
ALASKA EXTENDED NORTH OVER ALASKA, ENABLING NORTHERLY FLOW ALOFT TO
TRANSPORT WEATHER SYSTEMS AND COLD AIR SOUTH FROM ALASKA AND THE
WESTERN CANADIAN ARCTIC.

FROM THE 1ST THROUGH THE 5TH AN UPPER LEVEL TROUGH, WHICH ORIGINATED
OVER THE GULF OF ALASKA, RESIDED OVER THE PACIFIC NORTHWEST STATES.
IT BROUGHT BOISE 9 INCHES OF SNOW, INCREASING THE SNOW DEPTH TO 15
INCHES ON THE 5TH, AS ARCTIC AIR MOVED INTO THE REGION FROM BRITISH
COLUMBIA.

THE COLDER AIR, ALONG WITH CLEARING SKIES AND FRESH DEEP SNOW,
PROVIDED IDEAL CONDITIONS FOR RADIATIONAL COOLING AND SUBZERO
TEMPERATURES.

ON THE 8TH SOUTHWEST FLOW BROUGHT A PERIOD OF RELATIVELY MILD
WEATHER. WINDS WERE STRONG ENOUGH AT ALL LEVELS TO PREVENT AN
INVERSION FROM FORMING, AND TEMPERATURES ACTUALLY AVERAGED ABOVE
NORMAL FROM THE 8TH THROUGH THE 11TH.

THE COLD PATTERN RETURNED ON THE 12TH AS AN UPPER LEVEL TROUGH
DEEPENED OVER THE REGION. THE TROUGH DEPARTED FOR CALIFORNIA AND
BAJA ON THE 13TH, BUT COLD AIR REMAINED TRAPPED IN THE TREASURE
VALLEY AS AN UPPER LEVEL RIDGE BROUGHT WARMING ALOFT, FORMING A
TEMPERATURE INVERSION. THE 5 INCHES OF SNOW COVER HINDERED DAYTIME
WARMING AND GUARANTEED COLD OVERNIGHT TEMPERATURES. IN THIS
"HOMEMADE" ARCTIC AIR, HIGHS WERE ONLY IN THE TEENS AND LOWS WERE
NEAR ZERO FROM THE 15TH THROUGH THE 17TH.

MILDER WEATHER RETURNED FROM THE 19TH THROUGH THE 22ND UNDER
SOUTHWEST FLOW ALOFT, THANKS TO AN UPPER LEVEL LOW PRESSURE SYSTEM
OFF THE NORTHWEST COAST.

AS THE LOW MOVED INLAND ON THE 23RD, IT BROUGHT, IT BROUGHT BOISE 3
MORE INCHES OF SNOW ALONG WITH COLDER AIR, WHICH AS USUAL BECAME
TRAPPED IN THE VALLEY. ANOTHER TEMPERATURE INVERSION FORMED AND
INTENSIFIED AS AND UPPER LEVEL RIDGE BUILT OVER THE NORTHWEST U.S.
VALLEY TEMPERATURES WERE NOT AT COLD AS EARLIER IN THE MONTH, BUT
STILL AVERAGED ABOUT 10 DEGREES BELOW NORMAL.

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

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

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            45   01/08
LOWEST            -11   01/06
AVG. MAXIMUM     28.4              37.8    -9.4
AVG. MINIMUM     14.3              24.7   -10.4
MEAN             21.3              31.3   -10.0
DAYS MAX >= 90      0
DAYS MAX <= 32     21
DAYS MIN <= 32     29
DAYS MIN <= 0       5

PRECIPITATION (INCHES)
RECORD
 MAXIMUM         5.29   1875
TOTALS           2.96              1.24    1.72
DAYS >= .01        14
DAYS >= .10        10
DAYS >= .50         1
DAYS >= 1.00        1
GREATEST
 24 HR. TOTAL    1.14   01/09 TO 01/10

SNOWFALL (INCHES)
TOTALS           21.5
SINCE 7/1        35.5
GREATEST
 SNOW DEPTH        15R  01/05
 24 HR TOTAL      6.5   01/04 TO 01/04

DEGREE_DAYS
HEATING TOTAL    1345              1046     299      966
 SINCE 7/1       3534              3361     173
COOLING TOTAL       0                 0       0        0
 SINCE 1/1          0                 0       0
..............................................................

WIND (MPH)
AVERAGE WIND SPEED              5.8
RESULTANT WIND SPEED/DIRECTION   2/146
HIGHEST WIND SPEED/DIRECTION    31/280    DATE  01/09
HIGHEST GUST SPEED/DIRECTION    37/280    DATE  01/09

SKY COVER
POSSIBLE SUNSHINE (PERCENT)   MM

AVERAGE RH (PERCENT)     81


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

$$



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