Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 250353
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
853 PM MST SAT JAN 24 2015

.DISCUSSION...THERE IS A GREATER POTENTIAL FOR FOG IN THE TREASURE
VALLEY TONIGHT-SUNDAY MORNING THAN LAST NIGHT DUE TO A STRONGER
INVERSION AND LESS CLOUDS. THE VISIBILITIES ARE ALREADY STARTING
TO LOWER...ALTHOUGH THERE ARE NO REPORTS OF DENSE FOG YET.
CURRENT FORECAST SHOWS PATCHY FOG LATE TONIGHT THROUGH SUNDAY
MORNING ACROSS THE TREASURE/WESTERN MAGIC VALLEYS AND IN THE
NORTHERN VALLEYS WHICH APPEARS TO BE ON TRACK. INVERSION WILL
CONTINUE TO STRENGTHEN THROUGH SUNDAY AS A VERY STRONG AREA OF
HIGH PRESSURE ALOFT MOVES INTO THE REGION. TEMPERATURES WILL BE
MILD IN THE HIGHER ELEVATIONS AND COOLER IN THE VALLEYS DUE TO
THE INVERSION. NO UPDATES.

&&

.AVIATION...ISOLATED MVFR/IFR STRATUS NEAR KONO THIS EVENING
BECOMING LIFR/IFR STRATUS/FOG FROM KBKE THROUGH THE TREASURE AND
MAGIC VALLEYS LATE TONIGHT THROUGH AT LEAST NOON SUNDAY. COULD SEE
SOME IMPROVEMENT TO MVFR STRATUS SUNDAY AFTERNOON. VARIABLE
SURFACE WINDS UP TO 10 KNOTS. WINDS ALOFT NEAR 10K FT MSL...
NORTHWEST 20-25 KTS DECREASING TO 10-20 KTS FOR SUNDAY.

&&

.AIR STAGNATION...THE INVERSION WILL STRENGTHEN BELOW 5KFT MSL
THROUGH SUNDAY DUE TO WARMING ALOFT ASSOCIATED WITH AN AREA OF
STRONG HIGH PRESSURE. A WEAK SYSTEM WILL MOVE UP THE WEST COAST
FROM BAJA CALIFORNIA AND ACROSS THE FORECAST AREA TUESDAY NIGHT
INTO WEDNESDAY. THIS SYSTEM MAY TEMPORARILY WEAKEN THE
INVERSION...BUT AN UPPER RIDGE IS EXPECTED TO BUILD OVER THE
PACIFIC NORTHWEST BY THE END OF THE WEEK.

&&

.PREV DISCUSSION...
SHORT TERM...TONIGHT THROUGH MONDAY...A STRONG RIDGE OF HIGH
PRESSURE IS NOW BUILDING IN FROM THE SOUTHWEST AS A WARM FRONT
MOVES NORTH OF THE FORECAST AREA. TEMPERATURES ALOFT ARE WARMING
AND WILL CONTINUE TO WARM THROUGH SUNDAY AFTERNOON. SUBSIDENCE
ALOFT WILL ALSO BE ENHANCED AS THE CENTER OF THE UPPER LEVEL HIGH
PRESSURE MOVES OVER SOUTHERN IDAHO AND THE GREAT BASIN. TEMPERATURES
ARE ALREADY IN THE LOW 60S NEAR BEND OR AND PENDLETON OR. LOW
STRATUS IS KEEPING TEMPERATURES COOL LOWEST ELEVATIONS OF IDAHO
AND NORTHEAST OREGON NEAR BAKER CITY AS THE INVERSION CONTINUES TO
STRENGTHEN. TEMPERATURE FORECAST WILL BE DIFFICULT AND IS
CONTINGENT ON THE STRATUS FORMATION OVERNIGHT. LACK OF SNOW COVER
SHOULD IN TREASURE AND MAGIC VALLEYS SHOULD ALLOW STRATUS TO
BREAK UP DURING THE AFTERNOON BUT NOT ENOUGH TO MIX OUT INVERSION.
VALLEY TEMPERATURES WILL LIKELY REMAIN COOL AND NEAR AVERAGE UNDER
THE INVERSION WHILE THE TERRAIN ABOVE THE INVERSION APPROACHES
RECORD WARMTH FOR THIS TIME OF YEAR. AIR QUALITY WILL CONTINUE TO
DETERIORATE THROUGH MONDAY.

LONG TERM...MONDAY NIGHT THROUGH SATURDAY...LONGWAVE UPPER LEVEL
RIDGE OVER THE NW U.S. THROUGH THE END OF JANUARY WILL BE
INTERRUPTED BY 2 SYSTEMS. AVERAGE TEMPERATURES WILL BE MUCH ABOVE
NORMAL IN THE MOUNTAINS AND NEAR TO ABOVE NORMAL UNDER THE INVERSION
ACROSS THE SNAKE RIVER PLAIN/I-84 CORRIDOR. PRECIPITATION IS
EXPECTED TO BE BELOW NORMAL TO ROUND OUT JANUARY 2015.

THE FIRST IMPULSE LOOKS TO HAVE THE MOST AFFECT. IT LIFTS SSW TO NE
WITH PRECIPITATION LIKELY SPREADING NORTH ACROSS THE NV BORDER
TUESDAY AFTERNOON. THE MODEL BLEND BRINGS A SLIGHT CHANCE OF
PRECIPITATION TO THE MOUNTAINS OF BAKER COUNTY AS WELL AS THE WEST
CENTRAL AND BOISE MOUNTAINS LATE TUESDAY AFTERNOON AND THIS MAKES
SENSE WITH OROGRAPHIC LIFT. TIMING AND PLACEMENT OF THE EC/GFS
PRECIPITATION TUESDAY NIGHT THROUGH WEDNESDAY EVENING ARE IN
BETTER AGREEMENT - MOISTURE LIFTS MAINLY ACROSS THE S HALF OF ID -
SO TRENDED OREGON POPS DOWN WEDNESDAY. THIS STILL LOOKS TO BE A
RELATIVELY WARM SYSTEM /FOR JANUARY/ WITH SNOW LEVELS GENERALLY
AROUND 5200 TO 6500 FT.

THE SECOND SYSTEM IS A BIT COOLER UPPER LEVEL TROUGH EMBEDDED IN THE
NW FLOW THAT BRINGS A SLIGHT CHANCE OF SNOW SHOWERS /RAIN BELOW 5K
FT/  ACROSS CENTRAL IDAHO FRIDAY /FASTER AND WETTER IN THE GFS.

BY SATURDAY JANUARY 31ST THE UPPER RIDGE REMAINS STRONG OVER THE
PACNW AND IDAHO BUT LOWER HEIGHTS RETURN TO THE BAJA AREA...FOR
SPLIT FLOW ACROSS WESTERN CONUS...AND PROBABLY A BLOCKING RIDGE OVER
IDAHO...WHICH ACT TO SHUNT THE STORM TRACK INTO SE AK.

&&

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

&&

$$

WEATHER.GOV/BOISE

DISCUSSION...BW
AVIATION.....JS
AIR STAGNATION...KA/BW
PREV SHORT TERM...KA
PREV LONG TERM....VM/WH


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