000
FXUS65 KBOI 201717
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
1017 AM MST THU NOV 20 2008
.DISCUSSION...AREAS OF DENSE FOG ARE PRESENT AGAIN THIS MORNING IN
PORTIONS OF THE LOWER TREASURE VALLEY...ESPECIALLY NEAR THE SNAKE
AND PAYETTE RIVERS. THE FOG WILL DISSIPATE BEFORE NOON AS
SOUTHEASTERLY WINDS INCREASE AHEAD OF AN APPROACHING COLD FRONT.
THE SOUTHEAST WINDS...DOWN SLOPING THROUGH THE SNAKE RIVER PLAIN
WILL HELP BOOST THIS AFTERNOONS TEMPERATURES TO ABOUT 15 DEGREES
ABOVE NORMAL ACROSS MOST OF SOUTHERN IDAHO. COMPOSITE RADAR
IMAGERY SHOWS AN AREA OF RAIN ALONG THE COLD FRONT EXTENDING IN A
NORTH SOUTH LINE THROUGH CENTRAL OREGON. THIS AREA OF RAIN WILL
MOVE INTO EASTERN OREGON THIS AFTERNOON AND INTO THE IDAHO ZONES
THIS EVENING...FAVORING THE BOISE AND WEST CENTRAL MOUNTAINS. RAIN
WILL CHANGE TO SNOW ABOVE 5000 FEET LATER THURSDAY NIGHT WITH AN
INCH OR TWO OF SNOW ACCUMULATION LIKELY ABOVE 6000 FEET. THE
SOUTHERN PORTION OF THE FORECAST AREA IS LIKELY TO REMAIN DRY WITH
ONLY A SLIGHT CHANCE OF SHOWERS WITH THE FRONTAL PASSAGE.
&&
.AVIATION...FOG PRODUCING VIR-VLIFR CONDITIONS THIS MORNING OVER
THE LOWER TREASURE VALLEY WEST OF KEUL AND NORTHERN MALHEUR
COUNTY... INCLUDING KONO. ESTIMATED TOPS ON FOG BETWEEN 200-500
FEET AGL. VFR CONDITIONS ELSEWHERE IN SOUTHWEST IDAHO AND
SOUTHEAST OREGON. GUSTY EASTERLY WINDS UP TO 30 MPH IN THE MAGIC
AND UPPER TREASURE VALLEY EAST OF KMUO WILL GRADUALLY WEAKEN
DURING THE DAY. A COLD FRONT WILL SHIFT WINDS TO THE WEST AFTER
18Z TODAY IN SOUTHEAST OREGON AND AFTER 00Z IN SOUTHWEST IDAHO.
RAIN AND SNOW SHOWERS WILL ACCOMPANY THE COLD FRONT AND WIND SHIFT
WITH LOCAL MVFR AND ISOLATED IFR CONDITIONS OVER BAKER
COUNTY...AND THE WEST CENTRAL AND BOISE MTNS.
&&
.PREV DISCUSSION...
SHORT TERM...UPPER RIDGE OVER THE FORECAST AREA IS FORECAST TO
BREAK DOWN TODAY AHEAD OF A VIGOROUS SHORT WAVE ARRIVING FROM THE
WEST COAST. SOUTHEAST WINDS ALREADY PICKING UP IN THE SNAKE RIVER
VALLEY AND SHOULD CONTINUE TO INCREASE THROUGH THE DAY. INVERSION
INDICES TODAY FALL TO VALUES THAT WILL ALLOW THE INVERSION TO
FINALLY BREAK IN SOUTHWEST IDAHO WITH THE APPROACH OF TONIGHTS
SYSTEM. THUS...TEMPERATURE FORECAST TODAY WILL BE VERY DIFFICULT TO
SAY THE LEAST. HAVE BLENDED TO THE HIGH SIDE OF NUMERICAL GUIDANCE
NUMBERS THINKING THE BREAKUP OF THE LOW LEVEL TEMPERATURE INVERSION
WILL ALLOW ENOUGH MIXING TO BRING TEMPS BACK UP. PLENTY OF SUNSHINE
EARLY IN THE DAY ALSO EXPECTED TO HELP BOOST TEMPS BUT CLOUDS
INCREASE THIS AFTERNOON FROM WEST TO EAST. STRONG SHORT WAVE SWINGS
RAPIDLY ACROSS THE AREA LATE TODAY AND TONIGHT WITH SCATTERED TO
LIKELY POPS OVER THE NORTHERN TIER ZONES. SYSTEM DOES NOT APPEAR TO
BE TAPING HIGH PW OFFSHORE BUT EXPECTING A FAIRLY GOOD OROGRAPHIC
COMPONENT AS IT CROSSES THE MOUNTAINS TONIGHT. SNOW EXPECTED TO FALL
IN THE MOUNTAINS BUT IN THE 1 TO 3 INCH RANGE AND WELL BELOW
ADVISORY CRITERIA. WEST TO NORTHWEST FLOW WILL BRING BACK COLDER
TEMPERATURES TONIGHT AND FRIDAY BUT DRY CONDITIONS EXPECTED ALONG
WITH MUCH IMPROVED AIR QUALITY.
LONG TERM...FRIDAY NIGHT THROUGH THURSDAY...FLAT UPPER LEVEL RIDGE
WILL GIVE WAY TO A WEAK SHORTWAVE PUSHING THROUGH THE PANHANDLE ON
SATURDAY. MOST OF THE MOISTURE WILL REMAIN TO OUR NORTH WITH THE
BEST CHANCES OF PRECIPITATION THROUGH THE MOUNTAINS OF NE OREGON AND
THE WEST CENTRAL MOUNTAINS IN IDAHO. QPF TOTALS WILL BE LIGHT...
GENERALLY A COUPLE HUNDREDTHS UP TO A TENTH OF AN INCH FOR THE
EVENT. A DUSTING OF SNOW IS EXPECTED IN THE HIGHER ELEVATIONS.
MODELS STILL IN GOOD AGREEMENT WITH A HIGHLY AMPLIFIED UPPER LEVEL
RIDGE BUILDING INTO THE WEST BY SUNDAY. HAVE CONTINUED TO DRY OUT
POPS SUNDAY AFTERNOON THROUGH TUESDAY AFTERNOON. HAVE ALSO TRENDED
TEMPERATURES TOWARD AN INVERSION SCENARIO AS THERE WILL BE WARMER
AIR ALOFT THAN AT THE SURFACE. SPLIT TROUGH MOVES INTO THE WEST LATE
TUESDAY INTO WEDNESDAY. ONE PIECE OF THE ENERGY BECOMES A CLOSED LOW
OFF THE SOUTHERN CA COAST WHILE THE OTHER PIECE DROPS THROUGH ID AND
MT. RIGHT NOW IT APPEARS THE BEST MOISTURE WILL BE OVER MONTANA SO
HAVE ONLY BROUGHT POPS UP TO CLIMO WEDNESDAY AND THURSDAY.
&&
.BOI WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
OR...NONE.
&&
$$
WEATHER.GOV/BOISE
DISCUSSION...JB
AVIATION.....DG
PREV SHORT TERM...GS
PREV LONG TERM....DF/DD
