000 
FXUS65 KBOI 140400
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
900 PM MST SUN JAN 13 2008

.DISCUSSION...STRATUS AND FOG UNDER DEEP INVERSION REMAINS THE
MAIN FORECAST CHALLENGE THIS EVENING. 03Z SURFACE ANALYSIS PUTS
CENTER OF 1037 MB HIGH OVER CENTRAL IDAHO. THUS...LITTLE TO NO
WINDS IN THE VALLEY HAVE ALLOWED STRATUS DECK TO DESCEND 200 TO 300
FEET IN THE LAST 4 HOURS. AVERAGE STRATUS DECK HEIGHT IN THE
VALLEY IS AROUND 300 FEET ABOVE GROUND. STILL DIFFICULT TO PIN
DOWN DETAILS OF WHERE FOG WILL BE DENSE. HOWEVER...THE OVERALL
LOWERING OF THE STRATUS DECK IN THE VALLEY GIVES MORE CONFIDENCE TO
AT LEAST AREAS OF DENSE FOG. MODELS GUIDANCE STILL UNSURE OF
WHERE DENSE FOG WILL SETUP WHICH IN PART SEEMS TO BE DUE TO THE
INCREASING SOUTHEAST WINDS FORECAST FOR EARLY MONDAY MORNING WITH
APPROACH OF PACIFIC COLD FRONT. BELIEVE THE MODELS ARE OVERDOING
THE WINDS WITH THE SYSTEM...FOR MONDAY MORNING...WHICH IS STILL
WELL OFF THE NORTHWEST COAST. THUS...HAVE DECIDED TO ISSUE DENSE
FOG ADVISORY FOR ENTIRE TREASURE VALLEY...WESTERN MAGIC VALLEY AND
BAKER COUNTY OREGON THROUGH 16Z. EXPECT FOG TO LIFT TO STRATUS
FROM WEST TO EAST AS SURFACE PRESSURE GRADIENT INCREASE IN
RESPONSE TO PACIFIC COLD FRONT...HOWEVER AN EXACT TIMING OF THIS
WILL BE DIFFICULT. MID LEVEL WINDS WILL INCREASE BY EARLY
AFTERNOON WITH 700 MB WINDS INCREASING TO 20 KNOTS. THIS SHOULD
HELP BREAK UP THE STRATUS DECK MIXING DRY AIR DOWNWARD...EVIDENT
ON 00Z BOI SOUNDING...AND WEAKENING INVERSION. COLD FRONT COMES
THROUGH EARLY ON TUESDAY WHICH WILL BE ENOUGH TO BREAK UP THE
INVERSION.

&&

.AVIATION...IFR/LIFR IN FOG AND LOW STRATUS WILL PERSIST IN THE 
VALLEYS OF SW IDAHO AND SE OREGON THROUGH MON MORNING. WINDS AT 
SURFACE AND ALOFT WILL INCREASE MON...HELPING TO MIX OUT LOW CLOUDS 
AND FOG. WILL SEE MVFR/VFR OVER MOST OF THE TREASURE AND MAGIC 
VALLEYS BY 21Z MONDAY. LAST AREA TO LOSE THE LOW STRATUS AND FOG 
WILL BE THE LOWER TREASURE VALLEY....WHERE IT MAY PERSIST INTO TUE.


&&

.PREV DISCUSSION...
SHORT TERM...VALLEY FOG AGAIN TONIGHT BUT IT WILL BEGIN TO ERODE 
AFTER MIDNIGHT AS SURFACE HIGH PRESSURE MOVES TO OUR EAST AND SE 
WINDS BEGIN TO INCREASE.  BY MONDAY AFTERNOON THE FOG SHOULD BE
GONE.  FOR THIS EVENING WILL INDICATE ONLY WHERE FOG WILL BE MOST 
PREVALENT BUT DETAILS OF WHERE IT WILL BE DENSE WILL BE DIFFICULT 
TO PIN DOWN.  FOR NOW WILL INDICATE PATCHY DENSE FOG IN ALL ZONES.  
NO ADVISORY TO BE ISSUED AT THE OUTSET OF THIS PACKAGE.  

NEXT UP IS A VIGOROUS SHORT WAVE TROUGH AND ASSOCIATED SURFACE COLD 
FRONT DUE TO MOVE THROUGH OUR CWA FROM NW TO SE LATE MONDAY NIGHT 
AND TUESDAY MORNING.  THIS FRONT WILL BRING GUSTY W-NW WINDS WHICH
WILL COMPLETELY SCOUR ANY REMAINING FOG.  TUESDAY WILL BE BLUSTERY 
AND THEN COLDER LATE IN THE DAY.  THE FRONTAL PASSAGE WILL BRING A 
CHANCE OF SNOW SHOWERS TO OUR NORTHERN AND CENTRAL ZONES BUT ZONES 
SOUTH OF THE SNAKE RIVER WILL PROBABLY HAVE NONE. 

LONG TERM...TUESDAY NIGHT THROUGH SUNDAY...UPPER RIDGE OVER THE 
NORTHERN PACIFIC WILL KEEP AREA UNDER NORTHERLY FLOW THROUGH THE 
EXTENDED PERIOD. CONTINENTAL SOURCE OF COLD AIRMASS WILL BE DRY WITH 
LITTLE CHANCE OF PRECIP THROUGH THE WEEKEND. GROWING MODEL CONSENSUS 
OF RIDGE AMPLIFYING OVER THE WEEKEND WHICH WILL TAP INTO COLDER AIR 
OVER NORTHERN CANADA. TEMPERATURES THROUGH THE PERIOD WILL BE AT OR 
BELOW NORMAL.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...DENSE FOG ADVISORY UNTIL 9 AM MST MONDAY FOR IDZ012-IDZ014-
     IDZ016.
OR...DENSE FOG ADVISORY UNTIL 9 AM MST /8 AM PST/ MONDAY FOR ORZ062-
     ORZ064.
&&

$$

WEATHER.GOV/BOISE

DISCUSSION...JS
AVIATION.....SP
PREV SHORT TERM...LC
PREV LONG TERM....DG/DD