421
FXUS65 KBOI 201655
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
955 AM MST FRI DEC 20 2024
DISCUSSION
HIGH CLOUDS ARE STREAMING IN TODAY AHEAD OF A
WEAK SYSTEM THAT WILL BRING VALLEY RAIN AND MOUNTAIN SNOW LATE
TOMORROW MORNING INTO THE EVENING. THIS WILL KICK OFF A SERIES
OF WEAK SYSTEMS THROUGH NEXT WEEK, WITH INTERMITTENT PERIODS OF
RAIN AND MOUNTAIN SNOW. SNOW LEVELS LOOK TO REMAIN AROUND
5000-6500 FEET THROUGH SUNDAY, WITH MINIMAL ACCUMULATIONS OF
SNOW/RAIN ON SATURDAY AND SUNDAY. PATCHY FOG WILL BUILD IN
TONIGHT IN SHELTERED VALLEYS, ALTHOUGH INCOMING CLOUDS WILL
REDUCE COVERAGE. NO FORECAST UPDATES NECESSARY.
AVIATION
PATCHY LIFR FOG IN LOWER VALLEYS THIS MORNING SHOULD
DISSIPATE BY 11 AM. OTHERWISE, OVERCAST MID TO HIGH CLOUDS TODAY.
SURFACE WINDS: VARIABLE LESS THAN 10 KT, EXCEPT EASTERLY 10-20 KT
NEAR KJER/KMUO. WINDS ALOFT AT 10KFT MSL: W-SW 15-25 KT.
KBOI...GENERALLY VFR. HIGH CLOUDS TODAY. SURFACE WINDS LIGHT AND
VARIABLE.
WEEKEND OUTLOOK...LIGHT VALLEY RAIN AND MOUNTAIN SNOW WILL MOVE WEST
TO EAST LATE SATURDAY. A BRIEF BREAK IN PRECIPITATION IS EXPECTED
LATE SATURDAY NIGHT INTO SUNDAY MORNING BEFORE MORE RAIN AND SNOW
ARRIVE LATE SUNDAY. MVFR TO LIFR IN PRECIPITATION WITH SNOW LEVELS
GENERALLY 4000-6000 FT MSL. MOUNTAINS OBSCURED. SURFACE WINDS:
GENERALLY SW-SE 5-15 KT EACH DAY, WITH GUSTS 25-35 KT ACROSS
PORTIONS OF SE OREGON. LOW LEVEL WIND SHEAR POSSIBLE SATURDAY.
PREV DISCUSSION
SHORT TERM...TODAY THROUGH SUNDAY NIGHT...INVERSION AND
AREAS OF FOG ARE IN THE VALLEYS UNDER HIGH PRESSURE ALOFT.
BUT THE CURRENT DENSE FOG ADVISORY LOOKS DUBIOUS AND WE MAY
CANCEL IT BEFORE ITS 11 AM MST EXPIRATION TIME. THE TREASURE
VALLEY HAS NOT BEEN AS COLD IN THIS INVERSION AS IT WAS IN THE
PREVIOUS ONE, BUT THE CAMAS PRAIRIE HAS BECOME MUCH COLDER THIS
TIME WITH YESTERDAY'S HIGH TEMP AT FAIRFIELD BARELY ABOVE 20
AND CURRENT TEMP NEAR ZERO. A WEAKENING PACIFIC TROUGH WILL
BRING CLOUDS BUT NO PCPN TO OUR CWA ON SATURDAY. A STRONGER
PACIFIC TROUGH WILL BRING LIGHT PCPN TO NORTHERN AREAS SATURDAY
AND MIXING WINDS TO SOUTHERN AREAS, POSSIBLY STRONG ENOUGH TO
SCOUR THE'INVERSION. AFTER BRIEF CLEARING SUNDAY MORNING A
WETTER PACIFIC SYSTEM WILL COME INLAND WITH WIDESPREAD VALLEY
RAIN AND MOUNTAIN SNOW AND FURTHER LOW-LEVEL MIXING. A COLD
FRONT WILL FOLLOW LATE SUNDAY NIGHT WITH MORE PCPN.
LONG TERM...MONDAY THROUGH FRIDAY...AN ACTIVE PATTERN IS
EXPECTED DURING THE EXTENDED PERIOD. A BREAK IN PRECIPITATION
WILL ARRIVE ON MONDAY AS AN UPPER LEVEL TROUGH MOVES EAST AND
A RIDGE OF HIGH PRESSURE MOVES INLAND. THE BREAK WILL BE
SHORT-LIVED AS ANOTHER PACIFIC TROUGH MOVES INLAND ON TUESDAY.
THIS WILL BRING A 70-90% CHANCE OF RAIN AND SNOW TO THE AREA,
WITH MODERATE PRECIPITATION AMOUNTS EXPECTED. SOUTHWEST FLOW
ALOFT AHEAD OF THE SYSTEM WILL BRING MILD AIR INTO OUR REGION,
PUSHING SNOW LEVELS UP TO 5000-7000 FEET. HOWEVER, MUCH OF THE
PRECIPITATION IS EXPECTED ALONG THE COLD FRONT, WITH SNOW LEVELS
FALLING TO 3500-5500 FEET. PRECIPITATION SHOULD BE MOSTLY RAIN
IN THE LOWER VALLEYS, WITH SEVERAL INCHES OF SNOW POSSIBLE IN
THE MOUNTAINS. HIGH TEMPERATURES MONDAY AND TUESDAY WILL AVERAGE
AROUND 10 DEGREES ABOVE NORMAL WITH BREEZY WINDS ON TUESDAY AS
THE FRONT MOVES THROUGH THE AREA.
DRIER, COOLER, AND BREEZY CONDITIONS ARE EXPECTED CHRISTMAS DAY
AS THE TROUGH MOVES EAST. HOWEVER, A DEEP UPPER LOW IN THE GULF
OF ALASKA WILL BRING ABUNDANT MOISTURE AND A SERIES OF SHORTWAVE
TROUGHS (POSSIBLY AN ATMOSPHERIC RIVER EVENT) INTO THE PACIFIC
NORTHWEST THURSDAY AND FRIDAY, LIKELY CONTINUING INTO THE
FOLLOWING WEEKEND. MODERATE TO HEAVY PRECIPITATION TOTALS ARE
EXPECTED FROM THIS PATTERN, WITH A CONTINUOUS 60-90% CHANCE OF
PRECIPITATION THURSDAY THROUGH FRIDAY, WHICH IS HIGH THIS FAR
IN ADVANCE, AND IS A LONG DURATION TO MAINTAIN HIGH POPS. THIS
SYSTEM WILL BE COOLER THAN THE SYSTEM EARLIER IN THE WEEK, BUT
NOT QUITE COLD ENOUGH TO FAVOR SIGNIFICANT VALLEY SNOW, AS SNOW
LEVELS ARE PROJECTED TO BE 3000-4500 FEET. HOWEVER, HEAVY
MOUNTAIN SNOW WILL CERTAINLY BE POSSIBLE LATE NEXT WEEK INTO
THE FOLLOWING WEEKEND. TEMPERATURES ARE FORECAST TO AVERAGE
AROUND 5 DEGREES ABOVE NORMAL WITH BREEZY WINDS THURSDAY AND
FRIDAY.
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...SA
AVIATION.....JDS
SHORT TERM...LC
LONG TERM....ST
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