Area Forecast Discussion
Issued by NWS Pocatello, ID

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
000
FXUS65 KPIH 040835
AFDPIH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO ID
235 AM MDT MON MAY 4 2015

.SHORT TERM...TODAY THROUGH THU NOON. SUBTROPICAL MOISTURE HAS
WORKED ITSELF FROM THE GULF OF CALIFORNIA AND INTO EVEN OUR
CENTRAL IDAHO ZONES. EXPECT SHOWERS WITH AFTERNOON AND EVENING
THUNDERSTORMS FOR THE NEXT THREE AFTERNOONS. THE PATTERN CHANGES
LITTLE EXCEPT FOR A NORTHERN PACIFIC TROUGH SLOWLY BEARING DOWN ON
THE WESTERN STATES. THIS LOW MAKES LANDFALL SOMETIME TUE MORNING
IN SOUTHERN CANADA...BUT FLOW OVER EASTERN IDAHO CONTINUES WEAK
AND WITH ENOUGH SOUTHERLY COMPONENT TO KEEP THE UNSTABLE MOIST AIR
COMING INTO THE FORECAST AREA. BY WED MORNING...THE LOW HAS ONLY
MADE IT TO CENTRAL WASHINGTON AND OREGON. AT THIS POINT...THE LOW
CONTINUES A MORE SOUTHERLY MOVEMENT IN THE GFS AND THE NAM KEEPS
THE LOW IN THE PACIFIC NORTHWEST.

THE MAIN QUESTION IS JUST HOW MUCH MOISTURE WILL BE ABLE TO MAKE
IT NORTHWARD. THERE IS A STRONG DIFFERENCE OF OPINION BETWEEN THE
NAM GUIDANCE AND THE GFS GUIDANCE. THE GFS SEEMS TO BE VERIFYING
BETTER IN THE PRECIPITATION FORECAST SO FAR...SO HAVE KEPT THE
FORECAST SCENARIO CLOSER TO THE GFS COMPARED TO AN UNBELIEVABLY
WET NAM. THE NAM SEEMS OVERLY MOIST IN THE BOUNDARY LAYER...WHICH
LEADS TO HEAVY PRECIPITATION AMOUNTS THAT SEEM UNBELIEVABLE...WIDESPREAD
0.25 INCH OR MORE ON TUE. ITS PRECIPITATION PATTERN ALSO APPEARS
TO BE SUFFERING FROM CONVECTIVE FEEDBACK WITH NUMEROUS BULLSEYES
OF MAXIMUM PRECIPITATION IN ODD PLACES. BY THE END OF THIS
PERIOD...THE GFS AND NAM GET CLOSER IN PRECIPITATION
AMOUNTS...ONLY THE FOCUS OF PRECIPITATION IS IN VERY DIFFERENT
PLACES. SO HAVE PATTERNED THE FORECAST MORE ON THE GFS AND THE
LESS CLOUDY...AND THUS WARMER TEMPERATURE...SOLUTION.
HOWEVER...EVEN THE GFS BRINGS SNOW BACK TO HIGHER ELEVATIONS AS
THIS POWERFUL LOW APPROACHES WED NIGHT. SNOW LEVEL IS STILL
MAINLY ABOVE 7500 FT BY THEN...AND PRECIPITATION AMOUNTS WILL
STILL ONLY GENERATE SNOW LESS THAN 1.5 INCHES IN A 12 HOUR PERIOD.
MESSICK

.LONG TERM...THURSAY AFTERNOON THROUGH NEXT MONDAY. THE GFS/GFSX
AND ECMWF CONTINUE TO DEVELOP A CLOSED LOW CIRCULATION OVER THE NW
WHICH DRIFTS SOUTH THROUGH NRN CALIFORNIA THURSDAY. INCREASING
SPREAD IN THE TRACK AND POSITION OF THE LOW REMAINS A COMMON THEME
IN THE MODEL SOLUTIONS FRIDAY AND SATURDAY WITH THE LATEST ROUND OF
GUIDANCE FAVORING A TRAJECTORY WHICH TAKES THE LOW FURTHER SOUTH
THROUGH CNTRL/SRN NEVADA FRIDAY AND THEN ENE THROUGH THE 4-CORNERS
REGION SATURDAY. A FLAT...MOIST AND UNSTABLE RIDGE FOLLOWS LATE
SATURDAY INTO SUNDAY WITH INSTABILITY SHOWERS CONTINUING ACROSS THE
REGION. BY LATE SUNDAY INTO MONDAY...THE MODELS SHOW A SECOND PAC
DISTURBANCE DIGGING INTO THE NW STATES RESULTING IN A MOIST UNSTABLE
SW FLOW ACROSS THE REGION. AFTERNOON HIGHS ARE EXPECTED TO REMAIN AT
OR BELOW SEASONAL NORMS THROUGH THE PERIOD. HUSTON
&&

.AVIATION...A WEAK UPPER LOW POSITIONED OFF THE SRN CALIFORNIA COAST
WILL CONTINUE TO SUPPLY A PATCHY SOURCE OF MOISTURE ACROSS THE
REGION TODAY. AFTERNOON HEATING IS EXPECTED TO PROMOTE ISOLATED TO
SCT THUNDERSTORM ACTIVITY PRIMARILY FAVORING THE SE HIGHLANDS AND
MACKAY TO ISLAND PARK CORRIDOR FROM ROUGHLY 20Z TO 03Z. WE MAY SEE A
CELL OR TWO SNEAKING OUT INTO THE SNAKE RIVER PLAIN IMPACTING THOSE
TERMINALS. FOR NOW...WE WILL CONTINUE TO ADVERTISE VCTS. HUSTON
&&

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

$$


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.