258  
FXUS65 KPIH 261936  
AFDPIH  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE POCATELLO ID  
136 PM MDT THU APR 26 2018  
   
SHORT TERM
 
TONIGHT THROUGH SUNDAY. A RIDGE OF HIGH PRESSURE  
CONTINUES TO EXPAND ACROSS THE REGION EARLY THIS AFTERNOON AHEAD OF  
A LOW PRESSURE SYSTEM APPROACHING THE NRN CALIFORNIA/OREGON COAST.  
IT LOOKS AS IF WE PEAK FRIDAY AFTERNOON WITH FALLING TEMPERATURES  
ANTICIPATED THROUGH THE WEEKEND AS THE UPPER LOW GRADUALLY MOVES  
ONSHORE AND ACROSS THE REGION THROUGH TUESDAY. LITTLE IN THE WAY OF  
ANY SUBSTANTIVE CHANGES WERE MADE TO THE GOING FORECAST OTHER THAN  
TO ALIGN BETTER WITH NEIGHBORING OFFICES AND/OR NUDGE PRECIPITATION  
POTENTIAL AND AMOUNTS HIGHER WHERE NECESSARY. HUSTON  
   
LONG TERM
 
SUNDAY NIGHT THROUGH NEXT THURSDAY NIGHT. 500MB  
LONGWAVE FORECAST IS FOR WEAK NORTHWESTERLY FLOW TO TRANSITION ON  
TUE NIGHT TO A RIDGE OVER THE FORECAST AREA, WHICH SHOULD MEAN  
WARMER AND DRIER BY MID-WEEK. AND THAT IS BROUGHT OUT IN THE DETAILS  
AS WELL. THE MAIN FORECAST PROBLEM FOR THE PERIOD IS HOW MUCH AND  
WHERE THE FOCUS MAY BE IN THE FORECAST AREA. THE HIGHEST POP OCCURS  
SUN NIGHT AND AGAIN TUE. SUN NIGHT LIKELY POPS IN THE CENTRAL IDAHO  
MOUNTAINS, CHANCE ELSEWHERE. TUE IS SOLID CHANCE ACROSS THE BOARD,  
EXCEPT THE SOUTHWEST CORNER OF THE FORECAST AREA. THERE ARE LARGE  
DISPARITIES IN AMOUNTS OF PRECIPITATION BETWEEN THE GFS AND ECMWF;  
TRIED TO SPLIT THE DIFFERENCE IN THE OPERATIONAL FORECAST. BY THE  
VERY END OF THIS PERIOD, STRONG UPPER LEVEL RIDGING SHOULD BE  
LEAVING SKIES CLEAR AND A RETURN TO ABOVE NORMAL TEMPERATURES FOR  
WED/THU. SNOW LEVEL AND TEMPERATURES ARE SOMEWHAT WARMER FOR THE GFS  
COMPARED TO THE ECMWF, AND THIS IS MAINLY BECAUSE THE ECMWF IS  
WETTER. BOTH THE SUN/SUN NIGHT TROUGH AND THE TUE TROUGH COULD BRING  
SOME WIND, POSSIBLY ADVISORY-LEVEL. BUT CONFIDENCE IN ACTUAL TIMING  
FROM SUN NIGHT THROUGH TUE AFTERNOON IS FAIRLY LOW AND EXPECT LARGE  
SWINGS ARE POSSIBLE FROM MODEL RUN TO MODEL RUN. MESSICK  

 
   
AVIATION
 
HIGH PRESSURE WILL KEEP CIGS AND VSBYS UNLIMITED UNTIL  
FRI NIGHT. EXCEPT FOR GUSTY WIND IN THE EASTERN MAGIC VALLEY (KBYI),  
WIND SHOULD BE LIGHT NORTHEASTERLY TO EASTERLY, EXCEPT FOR DIURNAL  
SLOPE/VALLEY WIND AT KSUN. MESSICK  

 
   
HYDROLOGY
 
WARMER TEMPERATURES TODAY AND FRIDAY WILL CONTINUE  
TO SUPPORT ENHANCED SNOWMELT. LOWER REACHES LIKE THE PORTNEUF AND  
BLACKFOOT MAY BE SEEING THEIR SUPPLY DWINDLING RAPIDLY AND THUS THE  
FINAL PEAKS FOR THEM THIS SEASON. A CHANCE OF SHOWERS THROUGH THE  
WEEKEND AND INTO EARLY NEXT WEEK WILL ADD TO RUNOFF WHILE  
ACCOMPANYING COOLER TEMPERATURES SHOULD HELP TO RELIEVE SOME RUNOFF  
PRESSURE. FOR NOW, IT LOOKS AS IF THE PORTNEUF, BIG LOST, HENRY'S  
FORK AND SNAKE RIVERS WILL ALL SEE HIGH FLOWS EITHER DUE TO  
SNOWMELT OR DAM OPERATIONS CONTINUE INTO EARLY NEXT WEEK. HUSTON  

 
   
PIH WATCHES/WARNINGS/ADVISORIES
 
 
FLOOD WATCH FOR HENRYS FORK NEAR REXBURG FOR SATURDAY EVENING.  

 
 

 
 
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