000
FXUS65 KBOI 290236
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
836 PM MDT THU AUG 28 2008

.DISCUSSION...NEW 00Z NAM SHOWS ABOUT 7F WARMER MAX TEMPS FRIDAY
VIA 850-700 MB THICKNESS TREND...WHICH SUPPORTS OUR AFTERNOON
FORECAST PACKAGE VERY WELL.  CLEAR SKIES...EXCEPT FOR LOCAL SMOKE...
AND LESS WIND ARE ALSO INDICATED THROUGH FRIDAY.  COOLING WILL BEGIN
IN OUR NWRN ZONES SATURDAY AS A DEEP UPPER TROUGH FROM THE GULF OF
ALASKA COMES ASHORE OVER WA AND VANCOUVER ISLAND AND DIGS SEWD.  THE
TROUGH WILL DEEPEN AND CLOSE OFF AN UPPER LOW OVER ERN OREGON SUNDAY
THEN MOVE TO THE ID/NV BORDER SUNDAY NIGHT AND SERN IDAHO MONDAY.
LATEST ESTIMATE OF FROPA ARE NEAR 00Z SUNDAY IN SERN OREGON...
03Z-06Z SUNDAY IN SWRN IDAHO...AND 06Z-12Z SUNDAY IN SCENTRAL IDAHO.
WIND GUSTS WITH FROPA ARE EXPECTED TO STAY BELOW 40 MPH.  WITH 500
MB HEIGHTS LOWERING TO 558DM...SUNDAY AND LABOR DAY WILL BE THE
COOLEST DAYS SINCE LAST JUNE...WITH SNOW POSSIBLE ABOVE 7500 FEET.
WE DON/T EXPECT ANY PLACE IN OUR CWA TO REACH 70F ON LABOR DAY.
HOWEVER...MIN TEMPS WILL BE RELATIVELY MILD DUE TO CLOUD COVER AND
POSSIBLE SHOWERS.  CURRENT FORECAST LOOKS GOOD...NO UPDATES AT THIS
TIME.

&&

.AVIATION...PILOTS REPORTED MVFR CONDITIONS UP TO 10 KFT THIS
AFTERNOON FROM SMOKE NEAR FEATHERVILLE IDAHO...JACKPOT NEVADA AND
PICABO IDAHO. NORTHWEST WINDS HAVE PUSHED SMOKE INTO THE MAGIC
VALLEY CAUSING LOCAL MVFR CONDITIONS BETWEEN 8KFT AND 10KFT ALTHOUGH
SURFACE VISIBILITIES HAVE REMAINED VFR. SMOKE COULD BECOME TRAPPED
IN MOUNTAIN VALLEYS TONIGHT AS INVERSIONS SET UP CAUSING LOCAL MVFR
OR IFR CONDITIONS. OTHERWISE VFR CONDITIONS WILL CONTINUE THROUGH
FRIDAY UNDER MOSTLY CLEAR SKIES. SURFACE WINDS WILL BE LIGHT WITH
LIGHT TO MODERATE SOUTHWEST WINDS ALOFT.

&&

.PREV DISCUSSION...
SHORT TERM...WESTERLY FLOW OF DRY AIR CONTINUES OVER THE AREA
TONIGHT AND FRIDAY AS PACIFIC HIGH PRESSURE CONTINUES TO DOMINATE.
MUCH WARMER TEMPERATURES RETURNING TO THE REGION FRIDAY AS THE
THERMAL TROF REBUILDS ALONG THE WEST COAST AND GRADUALLY SLIDES EAST
DURING SATURDAY. THIS COULD MAKE SATURDAY VERY TRICKY FOR
TEMPERATURES...WIND AND MIN RH WHICH OF COURSE HAS IMPLICATIONS FOR
FIRE WEATHER. RIGHT NOW WE ARE FAVORING SLOWER TIMING TO THE UPPER
TROF AND FRONTAL PASSAGE SATURDAY EVENING AS THE UPPER TROF SHARPENS
UP ALONG THE WEST COAST BRINGING SOUTHERLY FLOW ALOFT INTO THE AREA.
THUS...THE TEMPERATURE SPREAD OF SOLUTIONS FOR SATURDAY IS WIDE
RANGING...BUT WITH A SLOWER EVOLUTION AND EASTWARD PROGRESSION TO
WEATHER FEATURES...A WARMER SCENARIO FOR SATURDAY MAY BE THE MOST
CORRECT. POPS ARE MINIMAL ON SATURDAY AND CONFINED TO KPDT AND KMSO
AREAS AT THIS TIME. A BETTER CHANCE FOR PRECIP STARTS IN THE
EXTENDED PORTION SATURDAY NIGHT AND ESPECIALLY SUNDAY AS
BAROCLINICITY INCREASES OVER THE FORECAST AREA AS THE UPPER TROF
DEEPENS IN THE PACIFIC NORTHWEST AND A BETTER STRUCTURED FRONTAL
SYSTEM TAKES SHAPE.

LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...ACTIVE WEATHER AND
COOLER TEMPERATURES THROUGH THE WEEKEND INTO EARLY NEXT WEEK AS THE
PATTERN SHIFTS TOWARDS A FALL TYPE PATTERN. MODELS REMAIN IN GOOD
AGREEMENT IN BRINGING A DEEP TROUGH INTO THE NORTHWEST EARLY SUNDAY
THOUGH THE LAST THREE MODEL RUNS HAVE BEEN MUCH QUICKER IN TIMING.
TEMPERATURES DROP QUICKLY AS TROUGH MOVES OVER THE REGION WITH
MONDAY EXPECTED TO BE THE COLDEST DAY. HIGH TEMPERATURES SUNDAY WILL
BE 10-13 DEGREES COOLER ACROSS THE ENTIRE AREA FROM SATURDAY IN THE
WAKE OF THE COLD FRONTAL PASSAGE SATURDAY. UPPER LEVEL TROUGH
SETTLES OVER THE CWA ON MONDAY WITH MODELS SHOWING IT WILL BECOME A
CLOSED LOW OVER THE AREA. FALL LIKE TEMPERATURES ON MONDAY AS 556 TO
560 DM 500 MB HEIGHTS OVER THE REGION SUGGEST TEMPERATURES IN THE
MID 60S TO LOW 70S. NOT MUCH IN THE WAY OF MOISTURE WITH THE TROUGH
INITIALLY...UNTIL IT TAPS INTO MONSOONAL MOISTURE FLOWING UP FROM
THE SOUTH ON SUNDAY. MODELS SHOWING A MAJORITY OF THIS MOISTURE WILL
STAY OVER EASTERN IDAHO INTO MONTANA AND WYOMING. NEWER MODEL RUNS
SHOWING MOISTURE FURTHER WEST MAINLY INTO THE CENTRAL MOUNTAINS OF
IDAHO AND SOUTHWESTERN IDAHO MOUNTAINS. HAVE ADJUSTED POPS
ACCORDINGLY BUT FURTHER ADJUSTMENTS MAYBE NEEDED IF MODELS CONTINUE
TO TREND A MORE WESTERLY SHIFT OF MOISTURE. REGION WILL STAY IN
BROAD CYCLONIC FLOW TUESDAY THROUGH THURSDAY AS ANOTHER WEAKER
TROUGH DROPS DOWN FROM CANADA INTO THE BITTERROOT MOUNTAIN REGION.
TEMPERATURES LOOK TO REMAIN AT OR SLIGHTLY BELOW NORMAL MID WEEK.

&&

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

&&

$$

WEATHER.GOV/BOISE

DISCUSSION...LC
AVIATION.....JT
PREV SHORT TERM...GS
PREV LONG TERM....JS/LH