776
FXUS65 KBOI 211637
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
937 AM MST SAT DEC 21 2024
DISCUSSION
SATELLITE AND REGIONAL RADAR COMPOSITE IMAGERY
SHOWING AN ELONGATED TROUGH SWINGING INTO THE PAC NW THIS
MORNING WITH A BROKEN LINE OF PRECIPITATION CROSSING OREGON.
AREAS OF LIGHT PRECIPITATION WILL TRANSIT ACROSS THE REGION
FROM LATE MORNING THROUGH THIS EVENING AS THE TROUGH ADVANCES
INLAND. INITIALLY PRECIPITATION WILL BE FOCUSED NORTH OF A LINE
FROM BURNS-MOUNTAIN HOME-SUN VALLEY, BEFORE SHIFTING SOUTH AND
EAST THIS EVENING. ACCOMPANYING SNOW LEVELS WILL RUN BETWEEN
4000-6000 FEET WITH UP TO AN INCH IN MTN VALLEYS AND 2-4 INCHES
EXPECTED ABOVE 6000 FEET THROUGH TONIGHT. BREEZY E-SW WINDS
WILL BE GUSTY ACROSS HIGHER TERRAIN TODAY AND HELP WITH MIXING
DOWN WARMER AIR FROM ALOFT. CURRENT FORECAST IS ON TRACK FOR
TODAY.
AVIATION
MAINLY VFR WITH EXTENSIVE MID AND HIGH CLOUDS.
PATCHY FOG THROUGH 18Z TODAY. LIGHT VALLEY RAIN AND MOUNTAIN
SNOW WILL MOVE WEST TO EAST ACROSS THE AREA ALONG A COLD FRONT
THIS AFTERNOON AND EVENING. PERIODS OF MVFR TO LIFR CONDITIONS
IN PRECIPITATION WITH SNOW LEVELS GENERALLY 4000-6000 FT MSL.
MOUNTAINS OBSCURED. SURFACE WINDS: SE-SW 10-20 KT, EXCEPT
LIGHTER IN SHELTERED VALLEYS. GUSTS 25- 35 KT SOUTH OF KBNO THIS
AFTERNOON. WINDS BRIEFLY BECOMING W-NW ALONG AND BEHIND THE
COLD FRONT. WINDS ALOFT AT 10KFT MSL: SW 25-45 KT. AREAS OF LLWS
TODAY.
KBOI...VFR. RAIN SHOWERS WILL MOVE THROUGH LATE THIS AFTERNOON
THROUGH EARLY EVENING, BUT CIGS SHOULD REMAIN VFR. SURFACE WINDS
LIGHT AND VARIABLE THIS MORNING, BECOMING SE 5-15 KT THIS
AFTERNOON. WINDS BRIEFLY BECOMING NW 5-10 KT WITH THE SHOWERS
TODAY.
SUNDAY OUTLOOK...PATCHY LIFR FOG IN VALLEYS SUNDAY MORNING.
SCATTERED LIGHT RAIN AND SNOW SHOWERS WILL MOVE THROUGH SUNDAY
BEFORE WIDESPREAD RAIN AND SNOW ARRIVES SUNDAY NIGHT. SNOW
LEVELS GENERALLY 4000-6000 FT MSL. MOUNTAINS OBSCURED. SURFACE
WINDS SW-SE 5-15 KT.
PREV DISCUSSION
SHORT TERM...TODAY THROUGH MONDAY NIGHT...A SERIES OF UPPER
TROUGHS AND RIDGES IN THE NORTH PACIFIC WILL BRING RAPID
DAY-TO-DAY CHANGES THE NEXT SEVERAL DAYS, WITH EACH TROUGH
BRINGING PCPN TO OUR CWA. AN UPPER RIDGE THIS MORNING WILL
EXIT EAST THIS AFTERNOON AS A PACIFIC UPPER TROUGH MOVES CLOSER
TO THE COAST. A SURFACE COLD FRONT JUST OFF THE COAST AT 12Z
WILL MOVE ACROSS EASTERN OR MIDDAY AND WESTERN ID LATE THIS
AFTERNOON/EVENING WITH LIGHT RAIN AND SNOW (EXCEPT IN SOUTH-
CENTRAL ID), AND BRIEFLY GUSTY WINDS AT HIGHER ELEVATIONS.
CLEARING OVERNIGHT AND EARLY SUNDAY AS THE NEXT PACIFIC UPPER
RIDGE COMES RAPIDLY INLAND. THEN ANOTHER TROUGH SUNDAY AND
SUNDAY NIGHT, WETTER THAN TODAY'S TROUGH, WITH LIGHT TO MODERATE
PCPN IN ALL AREAS. CLEARING FROM THE WEST MONDAY MORNING AS THE
NEXT UPPER RIDGE MOVES INLAND, THEN MORE PCPN IN EASTERN OREGON
LATE MONDAY NIGHT WITH THE NEXT TROUGH. TOTAL PCPN THROUGH NOON
MONDAY SHOULD BE .25 TO .50 INCH IN NORTHERN AREAS AND .10 TO
25 INCH IN THE SOUTH. TOTAL SNOWFALL 3 TO 6 INCHES IN THE
HIGHER NORTHERN MOUNTAINS, 1 TO 3 INCHES NEAR 5000 FEET, AND
LITTLE OR NONE BELOW 4000 FEET.
LONG TERM...TUESDAY THROUGH SATURDAY...ACTIVE WEATHER WILL
CONTINUE THROUGH THE EXTENDED PERIOD. A PACIFIC TROUGH AND COLD
FRONT WILL MOVE INLAND ON TUESDAY, BRINGING A 60-90% CHANCE OF
RAIN AND SNOW AND LIGHT TO MODERATE PRECIPITATION AMOUNTS.
TEMPERATURES WILL BE MILD AHEAD OF THE FRONT WITH HIGHS AROUND
10 DEGREES ABOVE NORMAL. SNOW LEVELS WILL START OUT AT 4500-6500
FEET MSL, THEN LOWER TO 3500-4500 FEET BEHIND THE FRONT. THIS
WILL RESULT IN RAIN IN THE LOWER VALLEYS, WHILE SEVERAL INCHES
OF SNOW WILL FALL IN THE MOUNTAINS. CHRISTMAS DAY WILL BE DRY
AND COOLER AS THE TROUGH MOVES EAST. WINDS WILL BE BREEZY
TUESDAY INTO WEDNESDAY AS THE FRONT PASSES THROUGH.
DRY CONDITIONS WILL BE SHORT-LIVED AS A DEEP UPPER LOW IN THE
GULF OF ALASKA WILL BRING ABUNDANT MOISTURE AND A SERIES OF
SHORTWAVE TROUGHS INTO THE PACIFIC NORTHWEST THURSDAY THROUGH
SATURDAY. ENSEMBLES ARE IN GOOD AGREEMENT ABOUT THIS PATTERN,
LEADING TO HIGH CONFIDENCE THAT PERIODS OF WIDESPREAD
PRECIPITATION WILL OCCUR FROM EACH PASSING SYSTEM. MODERATE TO
HEAVY PRECIPITATION TOTALS ARE EXPECTED FROM THIS PATTERN, WITH
HEAVY SNOW LIKELY IN THE MOUNTAINS. SNOW LEVELS ARE EXPECTED TO
START OUT JUST ABOVE VALLEY FLOORS AT 3000-4000 FEET ON
THURSDAY, THEN RISE TO 5000-7000 FEET BY SATURDAY AS WARMER AIR
MOVES IN UNDER WEST TO SOUTHWEST FLOW ALOFT. TEMPERATURES ARE
FORECAST TO AVERAGE AROUND 5 DEGREES ABOVE NORMAL ON THURSDAY,
THEN RISE TO AROUND 10 DEGREES ABOVE NORMAL BY SATURDAY. THE
PASSING FRONTAL SYSTEMS WILL RESULT IN BREEZY WINDS THROUGH THE
PERIOD.
BOI WATCHES/WARNINGS/ADVISORIES
ID...NONE.
OR...NONE.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.TWITTER.COM/NWSBOISE
DISCUSSION...DG
AVIATION.....SP
SHORT TERM...LC
LONG TERM....ST
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