Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 301951
AFDPIH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO ID
152 PM MDT THU JUL 30 2015

.DISCUSSION...TONIGHT THROUGH NEXT THURSDAY. A HIGH PRESSURE RIDGE
WILL CONTINUE TO EXPAND ACROSS THE GREAT BASIN THROUGH SATURDAY.
SATELLITE IMAGERY WAS SHOWING SEVERAL FEATURES ROTATING NORTH ALONG
THE WRN PERIPHERY OF THE HIGH WHICH WILL HELP TO INJECT SUB-TROPICAL
MOISTURE INTO SRN IDAHO. THE MODELS CONTINUE TO SHOW SOME INFLUX OF
THIS MOISTURE AS EARLY AS SATURDAY AFTERNOON AND TO A GREATER EXTENT
STARTING SUNDAY AFTERNOON AND CONTINUING THROUGH THURSDAY. IN
ADDITION TO THE INFLUX OF MOISTURE...A LOW PRESSURE SYSTEM IS
EXPECTED TO SHIFT SLOWLY SOUTH ALONG THE CANADIAN COAST SUNDAY
THROUGH THURSDAY...GRADUALLY SHUNTING THE UPPER RIDGE AXIS EAST OF
THE DIVIDE BY MONDAY WITH ILL TIMED DISTURBANCES EMBEDDED IN THE SW
FLOW ALOFT HELPING TO TRIGGER PERIODIC THUNDERSTORM ACTIVITY. I HAVE
NO ILLUSION THAT THE GFS MODEL ACTUALLY HAS THE TIMING OF THESE
PASSING WAVES CORRECT AT THIS POINT BUT THE OVERALL PATTERN CHANGE
IS ALSO REFLECTED IN THE ECMWF. SO FOR NOW...HAVE BEGUN TO BUMP THE
PRECIPITATION/THUNDERSTORM CHANCES UPWARD STARTING MONDAY COINCIDENT
WITH THE BREAK DOWN OF THE UPPER RIDGE. HUSTON
&&

.AVIATION...CIGS/VSBYS UNLIMITED AND LIGHT WIND UNDER HIGH PRESSURE
CONTINUES. MESSICK
&&

.FIRE WEATHER...WARMING AND DRYING CONTINUES THROUGH SAT WITH LIGHT
WIND UNDER STRONG HIGH PRESSURE. THE HIGH WILL ENTRAIN SOME UNSTABLE
AIR...POTENTIALLY STARTING AS EARLY AS SUN AFTERNOON. THE AREA
AFFECTED WOULD BE THE EXTREME WESTERN EDGE OF THE FORECAST AREA. ON
MON...THE THUNDERSTORMS WILL SPREAD ACROSS ALL ZONES FOR THE
AFTERNOON...WITH THE MOISTURE CONTENT...KNOWN AS PRECIPITABLE
WATER...INDICATING DRY MIXED WITH WET AS MOST LIKELY. THIS IS
ESPECIALLY TRUE AFTER THE EXTENDED DRY PERIOD. THE MAIN FORECAST
PROBLEM UNTIL THEN IS THE EXTREME DRYNESS AT 10000 FT AND THE
UNSTABLE AIR WHICH IS PUSHING THE HAINES INDEX TO 6 IN WIDESPREAD
AREAS. FORTUNATELY WIND IS LIGHT EVEN WITH THE HIGHER ALTITUDE WINDS
REACHING DOWN TO THE SURFACE. THE HIGHLIGHT FOR THE EXTENDED IS THE
THUNDERSTORM ACTIVITY...POTENTIALLY DRY...FOR MANY AREAS THAT HAVE
HAD STRONG CURING THESE PAST SEVEN TO NINE DAYS. MESSICK
&&

.PIH WATCHES/WARNINGS/ADVISORIES...NONE.
&&

$$


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