Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 220245
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
845 PM MDT SUN SEP 21 2014

.DISCUSSION...UPPER LOW MOVING NE THROUGH MAINLY THE SE HALF OF
THE CWA THIS EVENING AND WILL BE EAST OF THE AREA BY SUNRISE. A
BAND OF SHOWERS HAS BEEN SLOWLY ROTATING NORTHWARD ON THE NORTH
SIDE OF THIS LOW...DROPPING VERY LIMITED AMOUNTS OF PRECIP IN THE
SE HALF OF THE AREA. WILL KEEP THE FLASH FLOOD WATCH UP AS STORMS
MAY STILL MOVE NORTH OUT OF NE NV INTO OWYHEE COUNTY AND SRN TWIN
FALLS COUNTY THIS EVENING. BUT IT IS BEGINNING TO LOOK UNLIKELY.
NO CHANGE IN EXPECTATIONS FOR TOMORROW SO NO CHANGES AT THIS TIME.

&&

.AVIATION...SHOWERS ALONG AND EAST OF A LINE FROM KREO TO KMYL
OVERNIGHT. MOSTLY SCATTERED COVERAGE...EXCEPT SCATTERED TO NUMEROUS
EAST OF KMOU WITH LOCAL MVFR CONDITIONS. THUNDERSTORMS POSSIBLE
ESPECIALLY AROUND KTWF. SHOWERS WILL RETRACT MOSTLY TO THE WEST
CENTRAL AND BOISE MOUNTAINS DURING THE DAY MONDAY. SURFACE
WINDS...EAST TO SOUTHEAST 10 KTS OR LESS OVERNIGHT...THEN WESTERLY
UP TO 15 KTS MONDAY. WINDS ALOFT... EASTERLY UP TO 20 KTS AT 10K FT
MSL OVERNIGHT...THEN NORTHEAST UP TO 15 KTS MONDAY.

&&

.PREV DISCUSSION...
SHORT TERM...FLASH FLOOD WATCH IN EFFECT THROUGH THIS EVENING IN
SRN-MOST IDAHO ZONES EXCEPT THE OWYHEE MOUNTAINS.  UPPER LOW HAS
BECOME WELL-DEFINED IN NEVADA AS IT MOVES NORTHEAST.  AT 2 PM MDT
KCBX RADAR SHOWED AN AREA OF SHOWERS IN S-CENTRAL IDAHO MOVING
TOWARD THE WNW.  MORE SHOWERS ALONG THE ID/NV BORDER WERE ALSO
MOVING WESTWARD AND GRADUALLY EXPANDING NWD INTO OWYHEE COUNTY.
NO HEAVY RAIN SO FAR THAT WOULD CAUSE FLASH FLOODING BUT DEEPER
MOISTURE IN NEVADA HAS YET TO REACH OUR CWA.  UPPER LOW IS NOW
FORECAST TO MOVE NEWD INTO SRN IDAHO THIS EVENING THEN TURN EWD
ACROSS SRN IDAHO TONIGHT AND INTO WYOMING MONDAY MORNING.  SHOWERS
ARE EXPECTED TO STAY MAINLY ALONG AND EAST OF THAT TRACK.
MEANWHILE...A FRONTAL BAND CAN BE SEEN ON SATELLITE OFF THE NW
COAST ALONG 132W AT 20Z.  MODELS TAKE IT INLAND MONDAY AND DEVELOP
SHOWERS ACROSS OUR NRN OREGON ZONES MONDAY NIGHT BEFORE DISSIPATING
IN NRN IDAHO TUESDAY MORNING.  AT THE SAME TIME THE MAIN UPPER RIDGE
TO OUR SOUTH WILL BUILD NWD INTO OUR CWA BRINGING CLEARING AND
WARMING TUESDAY.

LONG TERM...TUESDAY NIGHT THROUGH SUNDAY...MODELS CONTINUE TO SHOW
A PROGRESSIVE PATTERN WITH AN AMPLIFYING UPPER LEVEL RIDGE EXITING
TO OUR EAST AS A DEEP UPPER LEVEL TROUGH APPROACHES FROM THE WEST.
SOUTHWEST IDAHO AND SOUTHEAST OREGON WILL BE BETWEEN THESE SYSTEMS
THROUGH THURSDAY...AND TEMPERATURES WILL CONTINUE ABOVE NORMAL
AHEAD OF THE SLOW MOVING COLD FRONT IN ADVANCE OF THE TROUGH. NO
PRECIPITATION IS EXPECTED TUESDAY NIGHT THROUGH WEDNESDAY
EVENING...THEN SHOWERS WILL SPREAD ACROSS EASTERN OREGON INTO THE
WEST CENTRAL IDAHO MOUNTAINS ON THURSDAY. WE CAN EXPECT SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS ACROSS MOST OF OUR AREA ON
FRIDAY...DECREASING TO SCATTERED MAINLY MOUNTAIN SHOWERS OVER THE
WEEKEND. MODELS HAVE COME INTO BETTER AGREEMENT ON TIMING THE COLD
FRONT AS IT CROSSES OUR AREA ON FRIDAY. FOLLOWING THE FRONT THE GFS
BRINGS THE UPPER LEVEL TROUGH INLAND A BIT FASTER THAN THE ECMWF
WHICH MAY REFLECT GFS SPEED BIAS IN THE LONGER RANGE. NEVERTHELESS
BOTH MODELS SHOW SIMILAR COOLING WITH MAX TEMPERATURES AROUND 5
DEGREES BELOW NORMAL BOTH FRIDAY AND SATURDAY. FOR SUNDAY CONFIDENCE
IS MUCH LOWER AS MODEL SOLUTIONS DIVERGE.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...FLASH FLOOD WATCH UNTIL MIDNIGHT MDT TONIGHT IDZ014>016-030.
OR...NONE.

&&

$$

WEATHER.GOV/BOISE

DISCUSSION...SP
AVIATION.....TL
PREV SHORT TERM...LC
PREV LONG TERM....JT/WH


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