910
FXUS65 KBOI 210331
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
831 PM MST WED NOV 20 2024
DISCUSSION
A LARGE-SCALE UPPER-LEVEL LOW CENTERED NEAR 133°W
AND 49°N WILL REMAIN IN PLACE THROUGH THURSDAY EVENING,
SUSTAINING THE ONGOING ATMOSPHERIC RIVER AIMED AT THE FORECAST
AREA. A STRONG MID-LEVEL JET WITH SOUTHWESTERLY WINDS AROUND 50
KNOTS, AS SHOWN ON THE 00Z KBOI SOUNDING, HAS LIMITED
PRECIPITATION ACROSS MUCH OF THE TREASURE VALLEY SO FAR.
WATER VAPOR IMAGERY REVEALS A WEAK EMBEDDED SHORTWAVE MOVING
INLAND OVER WASHINGTON THIS EVENING, WHICH HIGH-RESOLUTION
MODELS INDICATE WILL ENHANCE PRECIPITATION CHANCES ACROSS THE
REGION INTO THURSDAY MORNING. RECENT KCBX RADAR DATA SHOWS
SHOWERS MAKING FURTHER INROADS INTO THE VALLEY, WITH SEVERAL
WEST CENTRAL AND BOISE MOUNTAIN SITES REPORTING MEASURABLE
PRECIPITATION—EVIDENCE THAT THE SHORTWAVE IS HAVING AN IMPACT.
IN THE UPPER TREASURE VALLEY, SHOWERS ARE EXPECTED TO PRODUCE
ONLY LIGHT PRECIPITATION, WITH TOTALS UNLIKELY TO EXCEED A FEW
TENTHS OF AN INCH. IN CONTRAST, MOUNTAIN AREAS REMAIN ON TRACK
TO RECEIVE 0.25 TO 0.50 INCHES OF LIQUID WATER EQUIVALENT BY
THURSDAY MORNING. SNOW LEVELS ARE FORECAST TO STAY NEAR 5,500
FEET OVERNIGHT, WITH NEAR-FREEZING TEMPERATURES AS LOW AS 5,000
FEET. AS A RESULT, WET SNOW IS LIKELY TO PERSIST IN MOUNTAIN
VALLEYS BUT WILL STRUGGLE TO ACCUMULATE SIGNIFICANTLY,
PARTICULARLY ON TREATED SURFACES.
MOUNTAIN VALLEYS AROUND 5,000 FEET ARE EXPECTED TO SEE AN
ADDITIONAL 1 TO 2 INCHES OF SNOW, WHILE ELEVATIONS ABOVE 6,000
FEET COULD RECEIVE 2 TO 4 INCHES. THESE AMOUNTS ARE CONSISTENT
WITH THE CURRENT WINTER WEATHER ADVISORY, SO NO UPDATES ARE
NEEDED. CONFIDENCE REMAINS HIGH (80% CHANCE) THAT SNOW WILL
TRANSITION TO RAIN BELOW 6,500 FEET BY SUNRISE THURSDAY, IF NOT
SOONER.
THE LATEST HIGH-RESOLUTION QPF AND WIND UPDATES HAVE BEEN
INCORPORATED INTO THE FORECAST, WITH ONLY MINOR ADJUSTMENTS.
SLIGHT INCREASES IN WINDS AND QPF WERE NOTED IN MOUNTAINOUS
AREAS ABOVE 5,000 FEET. THE UPDATED FORECAST WILL BE ISSUED
SHORTLY.
AVIATION
MOSTLY VFR. MVFR/IFR POSSIBLE IN PRECIPITATION,
WITH A FOCUS ON HIGH TERRAIN. MOUNTAIN OBSCURATION. SNOW LEVELS
3000-5000 FT MSL TODAY, RISING TO 5500-7500 FT MSL LATE TONIGHT.
AREAS OF LOW LEVEL WIND SHEAR. SURFACE WINDS: S TO SE 15-25 KT,
GUSTS UP TO 30-45 KT. WINDS ALOFT AT 10KFT MSL: SW 40-60 KT.
KBOI
VFR WITH OCCASIONAL LIGHT PRECIPITATION AND CLOUDY
SKIES. LOW LEVEL WIND SHEER POSSIBLE. SURFACE WINDS: SE 15-25 KT
WITH GUSTS TO 25-35 KT.
PREV DISCUSSION
SHORT TERM...TONIGHT THROUGH FRIDAY NIGHT...THE STRONG PACIFIC
LOW WHICH BROUGHT VERY STRONG WINDS LAST NIGHT IS SLOWLY MOVING
NORTHWARD AND WEAKENING. IT IS CONNECTED TO AN ATMOSPHERIC
RIVER WHICH CONTINUES TO FUNNEL DEEP MOISTURE INTO THE REGION,
SUPPORTING WIDESPREAD PRECIPITATION PARTICULARLY OVER THE
MOUNTAINS. OROGRAPHIC EFFECT WILL FOCUS PRECIPITATION OVER
TERRAIN, ESPECIALLY NORTH OF A BURNS-BOISE-FAIRFIELD LINE.
MOUNTAINOUS AREAS CAN EXPECT SNOWFALL TOTALS OF A FEW INCHES,
WITH ACCUMULATIONS EXCEEDING A FOOT ALONG RIDGES AND SUMMITS.
SNOW LEVELS WILL RISE FROM AROUND 5000 FEET MSL TODAY TO 8000
FEET MSL BY FRIDAY MORNING THANKS TO SOUTHWEST FLOW ALOFT AND A
WARMER AIRMASS SETTING IN. THIS WILL SUPPORT RAIN IN LOWER
ELEVATIONS AND A TRANSITION FROM SNOW TO RAIN IN HIGHER
ELEVATIONS EXCEPT FOR THOSE ABOVE 8000 FEET.
MOUNTAINS WILL SEE 1 TO 2 INCHES OF LIQUID EQUIVALENT/RAINFALL
NORTH OF THE AFOREMENTIONED LINE THROUGH THE SHORT TERM. THE
HIGHEST SUMMITS MAY SEE EVEN MORE. THIS AMOUNT OF RAINFALL MAKES
NUISANCE LEVEL PONDING OR SLIDES A SLIGHT CONCERN OVER RECENT
BURN SCARS, BUT NOT ENOUGH FOR A PRODUCT GIVEN THE LONGEVITY OF
THE EVENT. IN LOWER ELEVATIONS DRY AIR NEAR THE SURFACE IS
LIMITING PRECIPITATION EFFICIENCY, BUT WE EXPECT TO HAVE
PRECIPITATION BREAK THROUGH THE DRY LAYER TOMORROW BRINGING A
FEW TENTHS OF AN INCH BY THE END OF FRIDAY. WINDS WILL REMAIN
BREEZY WITH GUSTS UP TO 25 FOR MOST AREAS, HIGHER ALONG RIDGES.
A WINTER WEATHER ADVISORY REMAINS IN EFFECT FOR THE BOISE AND
WEST CENTRAL MOUNTAINS FOR TRAVEL IMPACTS DUE TO SNOW,
PARTICULARLY IN HIGHER TERRAIN. THE ADVISORY LASTS THROUGH 5AM
MST THURSDAY, AT WHICH POINT RISING SNOW LEVELS WILL
SIGNIFICANTLY IMPACT FUTURE SNOWFALL FOR MOST PASSES AND
MOUNTAIN VALLEYS. BANNER SUMMIT WILL CONTINUE TO SEE A FEW
INCHES EVERY SIX HOURS, FOR A FORECAST TOTAL OF 15-20 INCHES
THIS AFTERNOON THROUGH FRIDAY AFTERNOON.
LONG TERM...SATURDAY THROUGH WEDNESDAY...ACTIVE WEATHER TO CONTINUE
AS A TROUGH OF LOW PRESSURE SETTLES OVER THE REGION INTO NEXT WEEK.
THE BULK OF ATMOSPHERIC ENERGY WILL IMPACT THE AREA SATURDAY AS A
COLD FRONT SWINGS THROUGH, LOWERING SNOW LEVELS TO 3500-4000 FEET. A
SERIES OF WEAKER WAVES ARE EXPECTED FOR EARLY IN THE WEEK WITH
ADDITIONAL CHANCES FOR PRECIPITATION. BY WEDNESDAY, ENSEMBLE CLUSTER
ANALYSIS INDICATES SIGNIFICANT UNCERTAINTY IN THE OVERALL PATTERN.
THOSE WITH TRAVEL PLANS SHOULD MONITOR THE SITUATION CLOSELY OVER
THE NEXT SEVERAL DAYS. TEMPERATURES WILL SETTLE BACK TO NEAR
AVERAGE BY EARLY WEEK.
BOI WATCHES/WARNINGS/ADVISORIES
ID...WINTER WEATHER ADVISORY UNTIL 5 AM MST THURSDAY IDZ011-013.
OR...NONE.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.TWITTER.COM/NWSBOISE
DISCUSSION...JDS
AVIATION.....JB
SHORT TERM...JM
LONG TERM....MC
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