Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 020250
AFDBOI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
850 PM MDT SUN MAY 1 2016

.DISCUSSION...A REX BLOCK ALOFT /HIGH PRESSURE TO OUR NORTH AND
LOW PRESSURE TO OUR SOUTH/ WILL REMAIN IN PLACE THROUGH MONDAY
FOR DRY CONDITION AND MOSTLY CLEAR SKIES. GOOD RADIATIONAL COOLING
TONIGHT WITH DRY AIRMASS AND LIGHT WINDS FOR TEMPERATURES IN THE
LOW 40S TO UPPER 30S MONDAY MORNING. MOSTLY CLEAR SKIES MONDAY AND
TUESDAY. NO UPDATES NEEDED AT THIS TIME.

&&

.AVIATION...VFR UNDER MOSTLY CLEAR SKIES. SURFACE WINDS...VARIABLE
10 KTS OR LESS OVERNIGHT...BECOMING EASTERLY 10-20 KTS ON MONDAY.
WINDS ALOFT...EAST TO SOUTHEAST 10-20 KTS THROUGH 10K FEET MSL.

&&

.HYDROLOGY...THE BRUNEAU AND JARBIDGE RIVERS CONTINUE TO RUN HIGH
IN OWYHEE COUNTY. ABOVE AVERAGE SNOWPACK EXISTS IN THE UPPER BRUNEAU
BASIN...PARTICULARLY IN THE JARBIDGE RIVER WATERSHED. WARMER
TEMPERATURES THIS WILL WEEK WILL ACCELERATE SNOWMELT AND KEEP THE
RIVERS RUNNING HIGH. RIVERS AND CREEKS IN THESE BASINS WILL NEED TO
BE MONITORED AS THEY RESPOND TO THE INCREASED RUNOFF.

&&

.PREV DISCUSSION...
SHORT TERM...ABOUT 4 DEGS WARMER MONDAY AND ANOTHER 4 DEGS TUESDAY.
MIN TEMPS WILL RISE MORE SLOWLY...ONLY A DEGREE OR SO MONDAY AND
ANOTHER DEGREE TUESDAY.  DRYING AIR MASS AND LESS WIND WILL ALLOW
BETTER RADIATIONAL COOLING AT NIGHT AND LARGER DIURNAL RANGE.
REX BLOCK HAS FORMED ALOFT WITH HIGH PRESSURE IN SWRN CANADA AND
LOW PRESSURE IN THE SWRN STATES AND EAST WINDS OVER OUR AREA.
THE SWRN LOW WILL EXIT EAST MONDAY LEAVING ONLY THE UPPER RIDGE
OVER THE INTERIOR WEST.  THE RIDGE WILL SHIFT EAST TUESDAY AND
WARMER/MOISTER SOUTHERLY FLOW ALOFT WILL BEGIN AS A PACIFIC TROUGH
NEARS THE COAST.  THIS WILL LEAD TO A SLIGHT CHANCE OF SHOWERS AND
THUNDERSTORMS TUESDAY AFTERNOON IN ERN OREGON AND HIGHER MOUNTAINS
IN IDAHO.  SURFACE WINDS WILL BE LIGHT THROUGH MONDAY NIGHT THEN
BECOME SOUTHEASTERLY AND INCREASE TO 10 TO 15 MPH TUESDAY.

LONG TERM...TUESDAY NIGHT THROUGH FRIDAY...A HIGH AMPLITUDE UPPER
LEVEL RIDGE CENTERED OVER EASTERN IDAHO TUESDAY NIGHT WILL SLOWLY
MOVE TO THE EAST. THE SLOWER MOVEMENT WILL ALSO SLOW DOWN THE TIMING
OF THE NEXT LONG WAVE TROUGH THAT WILL MOVE INTO THE WEST COAST.
MODEL TRENDS WEAKEN THE TROUGH AND THEN SPLIT IT AS IT CONTINUES
TO MOVE TO THE EAST.  THE SOUTHERN SECTION OF THE SPLIT IS FORECAST
TO BE OVER SOUTHERN CALIFORNIA BY FRIDAY. EXPECT SLOWER TIMING OF
PRECIPITATION TO SPREAD OVER THE FORECAST AREA. BUT NOT SLOW ENOUGH
TO MAKE CHANGES TO THE FORECAST. AT THIS TIME LOOKS LIKE PRECIPITATION
WILL SPREAD INTO SOUTHEAST OREGON TUESDAY NIGHT BUT NOT MOVE INTO
SOUTHWEST IDAHO UNTIL LATE AFTERNOON OR EVENING ON WEDNESDAY. WEDNESDAY
NIGHT AND THURSDAY WILL SEE THE BEST CHANCE OF PRECIPITATION AS THE
NORTHERN SECTION OF THE SPLIT CONTINUES TO MOVE EAST AND THE SOUTHERN
SECTION DIGS TO THE SOUTH.  PRECIPITATION WILL DECREASE OVER SOUTHEAST
OREGON THURSDAY NIGHT AND FRIDAY WITH CONTINUED CHANCE OVER SOUTHWEST
IDAHO. MODELS DO DIFFER ON HOW FAR SOUTH THE SOUTHERN SECTION OF THE
SPLIT WILL GO WHICH MEANS WE COULD SEE PRECIPITATION NEAR THE NEVADA
BORDER DUE TO WRAP-AROUND MOISTURE OR WILL WE BE DRY IF IT REMAINS OVER
THE SOUTHERN STATES. WILL KEEP SLIGHT CHANCE POPS OVER SOUTHWEST IDAHO
 FOR FRIDAY DUE TO UNCERTAINTY AS TO THE PLACEMENT OF THE LOW.
TEMPERATURES WILL BE WELL ABOVE NORMAL ON WEDNESDAY DUE TO SOUTHERLY
FLOW AHEAD OF THE APPROACHING UPPER LEVEL TROUGH AND WILL COOL TO A
FEW DEGREES ABOVE NORMAL BY FRIDAY.

SATURDAY THROUGH SUNDAY...PACIFIC LOW STILL SITS TO OUR SOUTH WITH
ASSOCIATED MOISTURE ROTATING AROUND IT AND IMPACTING OUR AREA. A
SLOW PROGRESSION EASTWARD IS SHOWN IN THE MODELS FOR THIS LOW...BUT
LOOKS LIKE THINGS WILL START TO DRY OUT BY SUNDAY AFTERNOON FOR MOST
AREAS. SOUTHERLY WINDS WILL HELP KEEP TEMPERATURES ABOVE NORMAL
THROUGH THE PERIOD.

&&

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

&&

$$

WWW.WEATHER.GOV/BOISE
WWW.FACEBOOK.COM/NWSBOISE
WWW.TWITTER.COM/NWSBOISE

DISCUSSION...JDS
AVIATION.....JT
HYDROLOGY...TL
PREV SHORT TERM...LC
PREV LONG TERM....JA/JC


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