Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 291544
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
944 AM MDT FRI AUG 29 2014

.DISCUSSION...UPPER TROUGH AND ASSOCIATED COLD FRONT MOVING INTO
THE REGION TONIGHT AND WILL BE THE PRIMARY FOCUS FOR CONVECTION.
HOW FAR WEST AND HOW EARLY CONVECTION INITIATES WILL DEPEND
GREATLY ON THE SMOKE LAYER WHICH IS ACROSS MUCH OF SE OREGON AND
SW IDAHO THIS MORNING. 12Z BOI SOUNDING SHOWED AN INCREASE IN
MOISTURE /PW OF 0.74 INCHES/ FROM YESTERDAYS SHORTWAVE.
ALSO...EVIDENT ON THE SOUNDING IS A STABLE LAYER AROUND 500 MB
WHICH MAY PROVE DIFFICULT TO BREAK UNTIL THE FRONTAL PASSAGE THIS
EVENING. THICK SMOKE PLUME FROM FIRES IN W/SW OREGON IS EVIDENT
ON SATELLITE IMAGERY...BASICALLY SOUTH OF A BURNS-ONTARIO-LOWMAN
LINE WITH MORE SMOKE MOVING IN FROM THE WEST SHOULD LIMIT SURFACE
HEATING POTENTIAL TODAY AND THUS CONVECTIVE POTENTIAL AHEAD OF
THE FRONT. THERE IS EVIDENCE OF THAT FROM YESTERDAY AS CU FAILED
TO DEVELOP OVER PARTS OF SW IDAHO WHERE THE SMOKE PLUME WAS
LOCATED. THUS...THINK CONVECTION WILL INITIATE LATER THAN NORMAL
ACROSS THE AREA PROBABLY JUST A FEW HOURS BEFORE THE FRONTAL
PASSAGE OR TO AREAS OUTSIDE THE SMOKE PLUME. THE FRONTAL TIMING
REMAINS ALMOST UNCHANGED REACHING BAKER CITY/BURNS AROUND
02Z...BOISE AROUND 06Z AND TWIN FALLS/JEROME AROUND 11Z.
IN THE TREASURE VALLEY...THE BEST CHANCE FOR THUNDERSTORMS WILL
BE LATER THIS EVENING...AFTER 9 PM TONIGHT. NORTHWEST WINDS
BEHIND THE FRONT 10 TO 15 MPH OVERNIGHT INCREASING TO 15-20 MPH
WITH GUSTS TO 30 MPH SATURDAY AFTERNOON. UPDATED POP/WX FORECAST
FOR TONIGHT. UPDATE WILL BE OUT SHORTLY.

&&

.AVIATION...VFR. SMOKE LAYERS ALOFT IN SOUTHEAST OREGON AND
SOUTHWEST IDAHO. MOSTLY CLEAR THEN INCREASING MID-HIGH LEVEL CLOUDS
AFTER 18Z. ISOLATED SHOWERS AND THUNDERSTORMS DEVELOPING OVER THE
MOUNTAINS AFTER 18Z. LIGHT AND VARIABLE SURFACE WINDS...EXCEPT GUSTS
TO 30 KNOTS IN THE VICINITY OF THUNDERSTORMS. WINDS
ALOFT...SOUTHWESTERLY 10-20 KNOTS UP THROUGH 10K FEET MSL.

&&

.PREV DISCUSSION...
SHORT TERM...TODAY THROUGH SATURDAY...BROAD AREA OF MOISTURE FROM
THE QUEEN CHARLOTTE`S SW TO 40N 140W IS WITH A COLD FRONT DUE IN
TONIGHT. FRONT IS NEARING NW WA AT 3 AM. SCATTERED TO THIN BROKEN
HIGH CLOUDS ACROSS WA AND THE ID PANHANDLE WILL EXPAND OVER THE
AREA TODAY. ANOTHER AREA OF MOISTURE WAS NEAR THE NV BORDER AND
THAT IS EXPECTED TO LIFT ACROSS THE AREA AS WELL. PREFRONTAL LIFT
AND VERY WARM TEMPERATURES ARE EXPECTED TO COMBINE WITH MOISTURE
FOR ISOLATED LATE DAY THUNDERSTORMS. EXPECT INCREASING CHANCES OF
SHOWERS AND THUNDERSTORMS AS THE FRONT CROSSES THE AREA /BOISE
AROUND MIDNIGHT AND TWIN FALLS BY 6 AM/ THROUGH EARLY SATURDAY.
INSTABILITY PARAMETERS AND CALIBRATED SPC GUIDANCE SUPPORTED
NOCTURNAL THUNDERSTORMS /WHICH WERE ADDED/ SO THAT WAS THE MAIN
CHANGE THIS PACKAGE. COOLER AND LOCALLY VERY WINDY CONDITIONS ARE
EXPECTED AS THE ASSOCIATED UPPER LEVEL TROUGH CROSSES THE AREA
SATURDAY.

LONG TERM...SATURDAY NIGHT THROUGH THURSDAY....NORTHWEST FLOW ALOFT
OVER THE FORECAST AREA SATURDAY NIGHT THROUGH MONDAY NIGHT WITH MAX
TEMPERATURES 5-10 DEGREES BELOW NORMAL...ALONG WITH DRY CONDITIONS.
WESTERLY FLOW ALOFT WILL DEVELOP OVER THE FORECAST AREA TUESDAY AND
TUESDAY NIGHT AS AN UPPER LEVEL TROUGH DIGS SOUTH ALONG THE CANADIAN
WEST COAST.  THE SHIFT TO WESTERLY FLOW WILL BRING TEMPERATURES BACK
TO NEAR NORMAL...ALONG WITH DRY CONDITIONS.  WEDNESDAY UPPER LEVEL
FLOW SHIFTS TO THE SOUTHWEST AS THE AXIS OF THE UPPER LEVEL TROUGH
MOVES INTO THE PACIFIC NORTHWEST.  MAX TEMPERATURES WILL REMAIN NEAR
NORMAL WEDNESDAY WITH A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS
OVER THE WEST CENTRAL AND BOISE MOUNTAINS WEDNESDAY AFTERNOON.  AXIS
OF THE UPPER LEVEL TROUGH WILL BE JUST TO THE NORTH AND WEST OF THE
FORECAST AREA THURSDAY WITH MAX TEMPERATURES COOLING TO AROUND 5
DEGREES BELOW NORMAL AND CONTINUED SLIGHT CHANCE OF SHOWERS AND
AFTERNOON THUNDERSTORMS OVER THE WEST CENTRAL AND BOISE MOUNTAINS.

&&

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

&&

$$

WEATHER.GOV/BOISE

DISCUSSION...JDS
AVIATION.....BW
PREV SHORT TERM...VM
PREV LONG TERM....JA


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