343 
FXUS65 KBOI 221605
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
1005 AM MDT MON APR 22 2013

.DISCUSSION...A SURFACE HIGH PRESSURE OVER WESTERN MONTANA IS
PUSHING A COLD FRONT THROUGH EASTERN IDAHO THIS MORNING. THE
MORNING MODEL GUIDANCE IS SHOWING THIS BACKDOOR COLD FRONT GETTING
INTO THE WESTERN MAGIC VALLEY THIS AFTERNOON. WILL SEE WINDS
SHIFT TO THE N-NE AND AN INCREASE IN CLOUDS AND THE CHANCE OF
SHOWERS OVER THE WESTERN MAGIC VALLEY WITH THE FRONTAL PASSAGE.
EXPECT THE FRONT TO PUSH THROUGH JEROME AND TWIN FALLS AROUND 21Z
THIS AFTERNOON WHICH MEANS HIGH TEMPERATURES WILL BE EARLIER THAN
USUAL AS TEMPERATURES DROP WITH THE FRONTAL PASSAGE. SURFACE
CONVERGENCE AND SHALLOW INSTABILITY SUPPORT DEVELOPMENT OF ISOLATED
TO SCATTERED RAIN SHOWERS ALONG AND EAST OF A LINE STRETCHING
FROM FAIRFIELD SOUTH TO ROGERSON /INCLUDING JEROME AND TWIN FALLS/.
ELSEWHERE THE SURFACE GRADIENT AND WINDS ALOFT WILL WEAKEN THROUGH
THE DAY SO THE STRONGEST WINDS WILL BE REALIZED THROUGH EARLY
AFTERNOON. UPDATES TO THE FORECAST WILL BE TO LOWER THE WINDS FOR
THIS AFTERNOON ACROSS MUCH OF THE AREA...AND INCORPORATE THE
PREVIOUSLY DISCUSSED CHANGES TO THE WEATHER FOR THE WESTERN MAGIC
VALLEY.

&&

.AVIATION...NORTHWEST SURFACE WINDS 15-25 KTS WITH GUSTS OVER 35 KTS 
TODAY WILL GRADUALLY DIMINISH AFTER 00Z AND BECOME LIGHT BY 06Z. 
IN THE KJER/KTWF AREA CONFIDENCE IS NEAR 70 PERCENT THAT WINDS WILL 
SHIFT INTO THE NORTHEAST AND DIMINISH FOLLOWING A COLD FRONT PASSAGE 
AROUND 22Z. WINDS ALOFT WILL BE NORTHWEST UP TO 40 KTS AT 10K FEET 
MSL. VFR WILL CONTINUE EXCEPT FOR ISOLATED MVFR SNOW SHOWERS OVER 
THE CENTRAL IDAHO MOUNTAINS EAST OF KMYL...AND THE HIGHLANDS SOUTH 
OF THE SNAKE RIVER. AFTER 00Z SHOWERS WILL END AND SKIES WILL CLEAR. 

&&

.PREV DISCUSSION...
SHORT TERM...AT 06Z SURFACE COLD FRONT WAS NEAR BKE-IDA LINE... 
FRONT MOVING SOUTH.  LIGHT SNOW SHOWERS HAVE BEEN REPORTED NEAR THE 
FRONT ON THE IDAHO SIDE.  FRONT SHOULD BE IN NRN NEVADA BY 12Z.  
GUSTY NORTHWEST WINDS WILL DEVELOP IN OUR ZONES LATER TODAY...ALMOST 
REACHING ADVISORY SPEEDS IN THE UPPER TREASURE VALLEY AND MAGIC 
VALLEY.  MAX TEMPS WILL ALSO BE 5-10F LOWER THAN YESTERDAY IN THE 
POST-FRONTAL AIR MASS AND UNDER NORTHERLY FLOW ALOFT.  WINDS WILL 
DIE DOWN TONIGHT...SKIES WILL CLEAR...AND DEW POINTS WILL DROP TO 
15-20F ON THE IDAHO SIDE AND 10-15F ON THE OREGON SIDE.  MIN TEMPS 
TUESDAY WILL THEREFORE BE QUITE COLD...20S IN THE IDAHO VALLEYS... 
TEENS TO LOWER 20S IN OREGON AND THE IDAHO MOUNTAINS.   TUESDAY WILL 
BE SUNNY...DRY...AND LESS WINDY WITH MAX TEMPS ABOUT 3F WARMER THAN 
TODAY.

LONG TERM...TUESDAY NIGHT THROUGH MONDAY...NORTHWEST FLOW ALOFT 
CONTINUES OVER THE REGION THROUGH THURSDAY FOR BELOW NORMAL 
TEMPERATURES. MODELS IN BETTER AGREEMENT WITH MORE PROGRESSIVE 
PATTERN SETTING UP THIS WEEKEND. HOWEVER...THEY REMAIN OUT OF PHASE 
WITH REGARD TO TIMING OF THE TROUGH PASSAGES. THE PATTERN BRIEFLY 
DE-AMPLIFIES THURSDAY AND FRIDAY...SHIFTING UPPER LEVEL WINDS FROM 
NORTHWEST ON WEDNESDAY TO WEST ON THURSDAY AND FRIDAY...RESULTING IN 
SLIGHTLY WARMER TEMPERATURES. MOST OF OUR AREA WILL REMAIN DRY AT 
LEAST THROUGH FRIDAY. THE OPERATIONAL GFS MODEL KEEPS THE UPPER 
RIDGE LARGELY INTACT OFF THE WEST COAST OVER THE WEEKEND WITH THE 
UPPER TROUGH REMAINING TO OUR NORTH-NORTHEAST. THIS SOLUTION IS 
LARGELY AN OUTLIER IN THAT THE GFS ENSEMBLE MEMBERS...ECMWF AND 
CANADIAN...SHOW UPPER TROUGH MOVING INTO THE PACIFIC NORTHWEST ON 
SUNDAY. SO HAVE CONTINUED NEAR CLIMO POPS FOR FRIDAY NIGHT THROUGH 
MONDAY...WITH THE BEST CHANCE OF SHOWERS OVER THE CENTRAL IDAHO 
MOUNTAINS AND LITTLE IF ANY PRECIPITATION IN THE VALLEYS. ALSO KEPT 
TEMPERATURES NEAR NORMAL FOR THE WEEKEND.  

&&

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

$$

WEATHER.GOV/BOISE

DISCUSSION...DG
AVIATION.....JT
PREV SHORT TERM...LC
PREV LONG TERM....JDS