Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 161955
AFDPIH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO ID
155 PM MDT TUE SEP 16 2014

.SHORT TERM...TONIGHT THROUGH FRIDAY. SATELLITE IMAGERY WAS SHOWING
A BROAD LOW PRESSURE CENTER SPINNING OFF THE NRN CALIFORNIA COAST
EARLY THIS AFTERNOON WITH A DOWNSTREAM RIDGE POSITIONED OVER ERN
IDAHO. MUCH FURTHER SOUTH...THE REMNANTS OF HURRICANE ODILE WERE
VISIBLE ROTATING NE ACROSS THE GULF OF CALIFORNIA...EAST OF THE
PREVIOUS FORECAST TRACK. THE GFS/NAM WERE BOTH SHOWING ISOLATED
CONVECTION DEVELOPING ACROSS THE REGION THIS AFTERNOON AS WEAK
DISTURBANCES EJECT FROM THE LOW OFF THE COAST AND ROTATE THROUGH THE
RIDGE. A FEW CELLS MAY PREVAIL THROUGH THE NIGHT...BUT BOTH MODELS
WERE MUCH LESS ENTHUSED ABOUT THE POTENTIAL FOR CONVECTIVE ACTIVITY
COMPARED TO YESTERDAYS MODEL RUNS. THE RIDGE IS EXPECTED TO AMPLIFY
SOME AND SHIFT EAST INTO THE DIVIDE WEDNESDAY. ONE WOULD EXPECT AN
INCREASING POTENTIAL FOR CONVECTIVE ACTIVITY...BUT BOTH THE GFS AND
NAM WERE SHOWING JUST ISOLATED ILL ORGANIZED CONVECTIVE ACTIVITY IN
THE ABSENCE OF ANY WELL DEFINED DYNAMICAL SUPPORT. THE MODELS SHOW
THE UPPER TROUGH SHIFTING INTO THE COAST THURSDAY MORNING WITH THE
ASSOCIATED UPPER JET LIFTING NE THROUGH ERN OREGON/NORTH IDAHO WITH
ENOUGH LIFT TO SUPPORT A BROAD BAND OF CONVECTION ACROSS SOUTH-CNTRL
IDAHO WHICH EXPANDS EWRD DURING THE DAY AS THE UPPER TROUGH
CONTINUES TO PUSH INLAND. THE DEVELOPMENT OF A SURFACE FRONT WHICH
ADVANCES INTO/THROUGH SE IDAHO SHOULD ALSO HELP TO PROMOTE ACTIVE
CONVECTION THROUGHOUT THE DAY. IT STILL REMAINS UNCERTAIN AS TO
WHETHER ANY MOISTURE FROM ODILE WILL BE SWEPT NORTHWARD IN THE DEEP
SOUTHERLY FETCH AHEAD OF THE TROUGH. THE NAM APPEARS TO SUPPORT THIS
IDEA WHILE THE GFS KEEPS THE MOISTURE WELL TO THE SOUTH. WITH THE
REMNANTS OF ODILE TRACKING FURTHER EAST OF PREVIOUS PROGS...I AM
LEANING IN THE DIRECTION OF THE GFS SOLUTION. AS THE UPPER TROUGH
PROGRESSES FURTHER INLAND THURSDAY NIGHT...A DEFINITIVE SPLIT OCCURS
WITH THE NRN BRANCH OF THE TROUGH PUSHING FAIRLY RAPIDLY EAST ALONG
THE CANADIAN HIGH-LINE WHILE THE SRN EXTENT OF THE TROUGH SPINS OFF
A CLOSED LOW OVER NRN CALIFORNIA (A BIT FURTHER NORTH THAN
YESTERDAYS PROGS). THE NORTHERLY PLACEMENT OF THE CUT-OFF LOW
COMBINED WITH THE SURFACE FRONTAL BOUNDARY POSITIONED JUST TO OUR
SOUTH HAVE RESULTED IN A BROAD AREA OF PRECIPITATION DEVELOPING IN
THE MODELS AND EXTENDING FROM NE NEVADA ACROSS THE SE HIGHLANDS
THURSDAY NIGHT. HAVE GENERALLY BOOSTED THE PRECIPITATION POTENTIAL
DURING THIS TIME FRAME BUT WITH LOW CONFIDENCE DUE TO RUN TO RUN
MODEL INCONSISTENCIES. BY FRIDAY...THE TAIL END OF THE NRN BRANCH
TROUGH SWEEPS THROUGH THE AREA WITH A DRIER NW FLOW OVERSPREADING
THE REGION. HUSTON

.LONG TERM...FRIDAY NIGHT THROUGH NEXT TUESDAY. AS WAS THE CASE
YESTERDAY...THE MODELS CONTINUE TO STRUGGLE WITH THE POSITION AND
TRACK OF THE CUT-OFF LOW FLOUNDERING OVER CALIFORNIA EARLY IN THE
PERIOD. THE LATEST 12Z GFS LIFTS THE LOW ENE ACROSS NEVADA SUNDAY
AND NRN UTAH SUNDAY NIGHT WITH ACCOMPANYING PRECIPITATION CLIPPING
THE FAR SE HIGHLANDS LATE SUNDAY NIGHT/MONDAY FOLLOWED BY A RETURN
TO DRY CONDITIONS AS THE RIDGE REBOUNDS ACROSS THE AREA. THE ECMWF
ON THE OTHER HAND...RETROGRADES THE LOW OFF THE COAST SUNDAY WHERE
IT REMAINS UNTIL BEING SWEPT INLAND ACROSS CALIFORNIA MONDAY AND
INTO NRN NEVADA TUESDAY. WITH POOR MODEL CONSISTENCY...HAVE
GENERALLY MAINTAINED THE GOING FORECAST WHICH FAVORS THE GFS
TIMING/TRACK. WILL AWAIT BETTER CONSENSUS IN THE MODELS BEFORE
TRYING TO NAIL DOWN ANY CHANGES IN THIS TIME FRAME. HUSTON
&&

.AVIATION...A WEAK SHORTWAVE PUSHING THROUGH UPPER RIDGE IS HELPING
TRIGGER SOME SHOWERS OVER THE REGION. INSTABILITY CONTINUING THROUGH
THIS AFTERNOON MAY KEEP SHOWERS MORE ACTIVE FOR PIH AND IDA...BUT
LOOKS LIKE THIS WILL BE MAINLY FOCUSED OVER THE MOUNTAINS. LOCAL WRF
AND HRRR MODELS INFLUENCED FORECAST AS THEY SUGGEST EARLIER END OF
PRECIP OVER IDA VERSUS THE 12Z NAM. ALL SITES SHOULD REMAIN VFR
THROUGH PERIOD. HINSBERGER
&&

.FIRE WEATHER...SHOWERS AND ISOLATED THUNDERSTORMS WILL CONTINUE
MAINLY OVER THE CENTRAL AND EASTERN MOUNTAINS THROUGH THIS EVENING.
EXPECT RE-DEVELOPMENT OF THUNDERSTORMS AGAIN WEDNESDAY AFTERNOON AS
A DEEP UPPER TROUGH CHANNELS MORE MOISTURE INTO SOUTHEAST IDAHO.
MOISTURE TRANSPORT PEAKS ON THURSDAY AS THE UPPER TROUGH AND SURFACE
COLD FRONT PUSH INTO THE REGION. THIS WILL MEAN INCREASED
THUNDERSTORM COVERAGE FOR THURSDAY AFTERNOON. STORMS WILL BRING
LOCALLY HEAVY RAINFALL WITH THE FOCUS BEING OVER THE SOUTHEASTERN
HIGHLANDS. DRIER WEATHER IS EXPECTED BY FRIDAY AFTERNOON AND SHOULD
LAST THROUGH THE WEEKEND. HINSBERGER
&&

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

$$






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