274
FXUS65 KBOI 230320
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
820 PM MST TUE JAN 22 2019
DISCUSSION
SNOWFALL CONTINUES TO MOVE INTO EASTERN OREGON THIS
EVENING. THIS SNOWFALL WILL CONTINUE ITS EASTWARD PROGRESSION THIS
EVENING, IMPACTING CENTRAL IDAHO AROUND MIDNIGHT. SNOWFALL,
ESPECIALLY ACROSS IDAHO AND BAKER COUNTY OF OREGON, WILL CONTINUE
INTO WEDNESDAY. SIGNIFICANT SNOWFALL IS EXPECTED ACROSS THE WEST
CENTRAL MOUNTAINS OF IDAHO WHERE A WINTER WEATHER ADVISORY REMAINS
IN EFFECT. ADDITIONAL LOCATIONS WILL SEE SNOWFALL, POTENTIALLY
INCLUDING THE TREASURE VALLEY. SNOW ACROSS THE VALLEY IS POSSIBLE
INTO THE EARLY MORNING HOURS, THOUGH ACCUMULATION ON ROADWAYS IS
ANTICIPATED TO BE LIGHT AT GENERALLY LESS THAN AN INCH. HOWEVER,
EVEN THESE LIGHT AMOUNTS COULD IMPACT THE MORNING COMMUTE.
ACTIVITY IN THE VALLEY WILL CONVERT TO RAIN BY THE LATE MORNING
HOURS, WITH MOUNTAIN SNOW AND VALLEY RAIN CONTINUING THROUGH THE
EVENING HOURS BEFORE WEAKENING. THE ONLY UPDATE MADE WAS TO
INCREASE PRECIPITATION PROBABILITIES THROUGH THE OVERNIGHT PERIOD
ACROSS THE MOUNTAINS. ADDITIONAL UPDATES ARE NOT PLANNED UNLESS
PRECIPITATION FORMS IN AN UNPLANNED LOCATION.
AVIATION
MVFR/IFR SNOW SHOWERS THIS EVENING MAINLY IN THE HIGHER
TERRAIN OF SOUTHEAST OREGON. SNOW WILL MOVE INTO HIGHER TERRAIN OF
SOUTHWEST IDAHO LATER TONIGHT. KEUL AND KBOI COULD SEE BRIEF SNOW
AROUND 06Z TONIGHT WITH ANOTHER CHANCE FOR RAIN AND SNOW AFTER 15Z
WEDNESDAY MORNING. SURFACE WINDS: LIGHT AND VARIABLE, LESS THAN 10
KTS. WINDS ALOFT AT 10K FEET MSL: WEST 20-30 KTS, INCREASING TO 40-
60 KTS AFTER 23/15Z.
PREV DISCUSSION
SHORT TERM...TONIGHT THROUGH THURSDAY...AMPLE MOISTURE STREAMING
UP AND OVER A RIDGE OFF THE COAST OF CALIFORNIA WILL BEGIN
IMPACTING THE AREA (MAINLY THE IDAHO CENTRAL MOUNTAINS) TONIGHT
THROUGH TOMORROW. A WARM FRONT MOVING THROUGH EARLY TOMORROW WILL
INCREASE SNOW LEVELS, BUT NOT BEFORE MOST AREAS WILL SEE SNOWFALL.
THE FORECAST CHALLENGE IS EXACTLY HOW FAR SOUTH THAT MOISTURE
WILL GO, AND IF IT DOES, HOW EARLY IT DOES SO. THIS WILL DETERMINE
HOW MUCH, IF ANY, SNOW OCCURS IN THE TREASURE AND MAGIC VALLEYS
AND AREAS SOUTH. HOWEVER, CONFIDENCE IS HIGH THAT POPULATED AREAS
IN THE IDAHO CENTRAL MOUNTAINS WILL RECEIVE 2-5 INCHES OF SNOW
THIS EVENING THROUGH TOMORROW AFTERNOON. HIGHER SNOW AMOUNTS WILL
FALL IN THE HIGHEST ELEVATIONS. THE SNOW WILL LIKELY START AS A
LIGHTER FLUFFIER SNOW WITH RATIOS AROUND 14:1, THEN DECREASE TO
AROUND 10:1 PRODUCING A WETTER AND HEAVIER SNOW. A WINTER WEATHER
ADVISORY HAS BEEN ISSUED FOR THE IDAHO CENTRAL MOUNTAINS FOR THE
SNOWFALL AND ITS IMPACT TO TRAVEL AND DRIVING CONDITIONS. HOWEVER,
AS MENTIONED BEFORE, A BIT OF SNOWFALL IS POSSIBLE EARLY TOMORROW
MORNING IN THE TREASURE VALLEY, SO EVEN IF A COUPLE TENTHS OF AN
INCH FALL, IT COULD STILL CREATE IMPACTS TO THE MORNING COMMUTE.
SNOW LEVELS RISE THROUGH THE DAY ON WEDNESDAY, SO MOST VALLEY
LOCATIONS (EXCEPT THE LONG VALLEY) WILL CHANGE OVER TO RAIN
SOMETIME BETWEEN 8 AM AND 11 AM MST. CONDITIONS DRY OUT FOR
THURSDAY UNDER A NORTHWEST FLOW WITH THE RIDGE TO THE WEST
CONTINUING TO BUILD.
LONG TERM...THURSDAY NIGHT THROUGH SUNDAY...DRY NORTHWEST FLOW
CONTINUES AS AN UPPER LEVEL RIDGE BUILDS OFF THE WEST COAST. AS FLOW
SHIFTS NORTHERLY FRIDAY NIGHT, A WEAK SHORTWAVE PASSES ALONG THE
CONTINENTAL DIVIDE, THOUGH ANY THREAT OF SNOW SHOWERS WILL BE
CONFINED TO HIGHER ELEVATIONS IN VALLEY COUNTY. NORTHWEST FLOW
PERSISTS THROUGH SUNDAY, AS CONDITIONS REMAIN DRY AND TEMPERATURES
STAY SEVERAL DEGREES ABOVE NORMAL.
SUNDAY NIGHT THROUGH TUESDAY NIGHT...CLEAR TO PARTLY CLOUDY SKIES
WITH BREEZY WINDS ARE ANTICIPATED ACROSS MOST OF REGION AS DRY,
STABLE RIDGING IS EXPECTED TO DOMINATE. HOWEVER, THE NORTHEAST
QUADRANT IS EXPECTED TO SEE SNOW SHOWERS AS A MOIST TROUGH DROPS IN
FROM THE NORTH AT THE START OF THE PERIOD. THIS TROUGH IS EXPECTED
TO COMPLETELY EXIT THE CWA BY MONDAY EVENING, WHERE CONDITIONS IN
THE NORTHEAST SHOULD IMPROVE AS RIDGING TAKES FULL CONTROL. WINDS
SHOULD ALSO LIGHTEN SOME BY MONDAY EVENING AS THE GRADIENT LOOSENS.
HIGH AND LOW TEMPERATURES WILL MEASURE IN A FEW DEGREES ABOVE NORMAL.
BOI WATCHES/WARNINGS/ADVISORIES
ID...WINTER WEATHER ADVISORY UNTIL 5 PM MST WEDNESDAY IDZ011-033.
OR...NONE.
WWW.WEATHER.GOV/BOISE
WWW.FACEBOOK.COM/NWSBOISE
WWW.TWITTER.COM/NWSBOISE
DISCUSSION...KB
AVIATION.....JS
PREV SHORT TERM...EP
PREV LONG TERM....AL/WH
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