Area Forecast Discussion
Issued by NWS Pocatello, ID

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804
FXUS65 KPIH 081012
AFDPIH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO ID
312 AM MST MON FEB 8 2016

.SHORT TERM...TODAY THROUGH WED NIGHT. STRONG UPPER LEVEL RIDGING
LEAVES VALLEY FOG/STRATUS AND ITS EFFECTS AS THE ONLY FORECAST
PROBLEM. CURRENTLY THE BOUNDARY LAYER MOISTURE HAS LIFTED IN MOST
PLACES TO A STRATUS. HOWEVER...IT IS STILL EARLY AND THERE IS THE
THREAT THAT IT COULD CONTINUE TO THICKEN AND BECOME DENSE FOG ONCE
AGAIN. BELIEVE THE DENSE FOG ADVISORY SHOULD STAY OUT AT LEAST
UNTIL SUNRISE THIS MORNING...WHEN COOLING/CONDENSATION REACHES ITS
PEAK. NAM BOUNDARY LAYER MOISTURE FORECASTS ALSO POINT TO IT
BEING WORSE TONIGHT AND TUE MORNING...SO HAVE BEEFED UP THE TIME EXTENT
OF THE FOG. THE OTHER FORECAST PROBLEM IS TEMPERATURES. THE
STRATUS WILL LIKELY KEEP THINGS COLD WITH SMALL TEMPERATURE
SPREADS IN THE VALLEYS...WHILE THE RIDGES AND HIGHER ELEVATIONS
WILL HAVE 30 DEGREE SPREADS BETWEEN HIGH AND LOW INSTEAD. NO
CHANGE FOR THE REST OF THE PERIOD...HIGH PRESSURE IS LOCKED IN
PLACE FOR AT LEAST A WEEK. MESSICK

.LONG TERM...THURSDAY THROUGH MONDAY NIGHT. BY THURSDAY...THE
HISTORICALLY STRONG RIDGE HAS FLATTENED SOMEWHAT BUT STILL REMAINS
STRONG ENOUGH TO EFFECTIVELY BLOCK PRECIPITATION TO THE NORTH. THE
RIDGE DOES APPEAR TO STRENGTHEN IN THE FRI-SAT TIME FRAME AS THE
POLAR VORTEX SACKS NEW ENGLAND. THIS SHOULD ENSURE STRONG INVERSIONS
REMAIN IN PLACE...WITH MID AND UPPER SLOPES CONTINUING TO EXPERIENCE
ABOVE AVERAGE TEMPERATURES WITH PERSISTENT FOG AND LOW CLOUD CHANCES
FOR VALLEYS...ALONG WITH DEGRADED AIR QUALITY. A DISTURBANCE IS
EXPECTED TO TRACK EASTWARD ACROSS THE PACNW FOR LATE WEEKEND. THE
GFS AND CANADIAN GEM HAVE WEAKENED THIS SYSTEM CONSIDERABLY...WHILE
THE ECMWF CONTINUES TO HINT AT SNOWFALL POTENTIAL FOR SATURDAY NIGHT
INTO SUNDAY. ENSEMBLES FAVOR THE ECMWF...BUT ARE SLIGHTLY WEAKER
THAN THE DETERMINISTIC ECMWF DEPICTION. THUS WILL LOWER POPS
SOMEWHAT FOR THE LATE WEEKEND PERIOD BUT RETAIN SOME SNOWFALL
POTENTIAL. THIS MAINTAINS CONTINUITY WITH PREVIOUS FORECASTS AS WELL
AS NEIGHBORS. SHOULD LATER FORECAST CYCLES CONTINUE THE WEAKENING
TREND...PRECIPITATION MAY HAVE TO BE REMOVED FROM THE WEEKEND
FORECAST ENTIRELY. AD/MESSICK

&&

.AVIATION...VISIBILITIES HAVE IMPROVED OVER THE PAST 1-2 HOURS AS
FOG HAS LIFTED INTO A LIFR LOW STRATUS DECK AT BYI...IDA AND PIH.
MODEL TIME-HEIGHT AND CROSS SECTION PLOTS ARE SPLIT BETWEEN FOG VS.
STRATUS THROUGH EARLY MONDAY AFTERNOON...MAKING THE FORECAST FOR CIG
AND VIS EVOLUTION A LOW CONFIDENCE ONE. WILL LIKELY SEE CONTINUED
FLUCTUATIONS IN CIG AND VIS THROUGH THE PERIOD...WITH SOME POTENTIAL
FOR IMPROVEMENT AROUND 18Z MON. WILL LIKELY SEE CONDITIONS
DETERIORATE AGAIN AROUND SUNSET MONDAY. KSUN LIKELY TO REMAIN VFR
THROUGH THE PERIOD. AD/MESSICK. &&

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
DENSE FOG ADVISORY UNTIL NOON MST TODAY FOR IDZ019>021.

&&

$$



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