Area Forecast Discussion
Issued by NWS Boise, ID

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000
FXUS65 KBOI 211500
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
900 AM MDT SUN SEP 21 2014

.DISCUSSION...UPPER LOW IN WRN NEVADA IS MAKING STEADY NEWD PROGRESS
TOWARD OUR CWA.  LATEST SATELLITE IMAGERY SUGGESTS A MORE DIRECT HIT
THAN MODELS INDICATE.  MODELS FAVOR A TRACK TO THE SWRN CORNER OF
IDAHO THIS EVENING THEN ENE ACROSS SRN IDAHO TONIGHT.  OUR SERN-MOST
ZONES INCLUDING TWIN FALLS COUNTY REMAIN THE AREA OF GREATEST
CONCERN FOR POSSIBLE FLASH FLOODING AS AIR MASS IN ERN NEVADA IS
VERY MOIST.  WFO ELKO STILL HAS A FLASH FLOOD WATCH FOR NERN NEVADA
FOR TODAY AND THIS EVENING.  HPC NOW INCLUDES SWRN IDAHO AS WELL AS
NERN NEVADA FOR AN ELEVATED RISK OF EXCESSIVE RAINFALL.  WE ARE
CONSIDERING A FLASH FLOOD WATCH FOR LATE TODAY AND THIS EVENING BUT
NOT AS FAR NORTH OR WEST AS HPC SUGGESTS.  DECISION WILL BE MADE
LATER THIS MORNING AFTER REVIEW OF ALL 12Z GUIDANCE. REST OF CURRENT
FORECAST LOOKS GOOD FOR NOW.

&&

.AVIATION...SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS SOUTH OF A
KREO-KMUO-FAIRFIELD LINE BY 18Z. AFTER 18Z WIDESPREAD SHOWERS SOUTH
OF A JORDAN VALLEY-KMUO-FAIRFIELD LINE...LOCALLY HEAVY SOUTH AND
EAST OF KMUO WITH MVFR-IFR CONDITIONS AND TERRAIN OBSCURATION...
SPREADING OVER THE BOISE MOUNTAINS EAST OF IDAHO CITY BY 00Z. AFTER
06Z SCATTERED SHOWERS DECREASING TO ISOLATED MAINLY OVER HIGHER
TERRAIN BY 12Z. SURFACE WINDS...VARIABLE 10 KTS OR LESS. WINDS
ALOFT...NORTHEAST UP TO 15 KTS AT 10K FT MSL.

&&

.PREV DISCUSSION...
SHORT TERM...TODAY THROUGH MONDAY...RADAR ECHOES WERE ACROSS NW NV
TO EAST CENTRAL NV AT 3 AM. THUNDERSTORMS WERE EVEN FARTHER SOUTH
NEARER THE UPPER LOW CENTER WHICH WAS OVER CENTRAL CA PER WATER
VAPOR IMAGERY. HRRR RUNS UNAVAILABLE SINCE 20Z. GFS AND NAM BRING
SHOWERS N OF THE NV BORDER TODAY WITH THE NAM EXTENDING THE SHOWERS
TO CHALLIS...THE OWYHEE MTS...AND KLAMATH FALLS THIS EVENING AND
OVER IDAHO TONIGHT THEN NE OREGON AND IDAHO MTNS MONDAY. THE GFS WAS
A BIT SLOWER AND FARTHER S AND W. LIMITED INSTABILITY WAS ALSO
PRESENT IN THE GFS/NAM SO HELD OFF ON THE THUNDERSTORMS...GREATEST
COVERAGE IS EXPECTED OVER THE ID MTNS SOUTH OF THE SNAKE RIVER.
TEMPERATURES WILL BE A LITTLE COOLER TODAY BUT STILL ABOVE NORMAL
THEN RETURN TO 5-10 ABOVE NORMAL FOR TONIGHT /DUE TO CLOUDS/ AND
MONDAY DUE TO MILD W TO SW FLOW ALOFT.

LONG TERM...MONDAY NIGHT THROUGH SATURDAY...MODELS STILL SHOWING A
PATTERN CHANGE FOR LATE IN THE WEEK TO COLD AND WET. HOWEVER...THE
MODELS CONTINUE TO SLOW THE NEXT TROUGH TILL LATE THURSDAY NOW ON
THE 00Z RUNS.  THEREAFTER THE MODELS DIVERGE GREATLY...THUS
CONFIDENCE REMAIN LOW FOR NEXT WEEKEND. AHEAD OF THE UPPER TROUGH...
TEMPERATURES WILL REMAIN WELL ABOVE NORMAL IN THE UPPER 80S TO LOW
90S IN THE LOWER VALLEYS. ON THURSDAY...THE UPPER LEVEL TROUGH WILL
MOVE ONSHORE BRINGING MOISTURE BEHIND A COLD FRONT. AHEAD OF THE
FRONT THE AIRMASS REMAINS DRY...ESPECIALLY ACROSS SW IDAHO WHICH
WILL LIMIT SHOWER AND THUNDERSTORM DEVELOPMENT. FRIDAY HAS THE BEST
CHANCE FOR SHOWERS ACROSS MOST OF THE REGION. THE MODELS DIVERGE
BEGINNING FRIDAY WITH THE 00Z GFS SLOWLY MOVING THE FRONT EASTWARD
ACROSS THE AREA AND INTO EASTERN IDAHO FRIDAY NIGHT. THE ECMWF
STALLS THE FRONT OVER SW IDAHO ON FRIDAY AS A CLOSED LOW FORMS OVER
RENO ON SATURDAY. BOTH MODELS SHOW PRECIPITATION OVER THE REGION
THROUGH SATURDAY THOUGH THE AMOUNTS AND DURATION VARY GREATLY WITH
THE ECMWF BRINGING MONSOONAL MOISTURE FROM THE SOUTH AND GFS
BRINGING MOISTURE /FAR LESS AT THAT/ FROM THE PACIFIC. FOR NOW...
ABOVE CLIMO POPS AND NEAR CLIMO TEMPERATURES SEEM REASONABLE GIVEN
THE UNCERTAINTY.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
OR...NONE.

&&

$$

WEATHER.GOV/BOISE

DISCUSSION...LC
AVIATION.....JT
PREV SHORT TERM...VM
PREV LONG TERM....JDS



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