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 31 32 33 34 35 36 37
000
FXUS65 KPIH 211637
AFDPIH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO ID
ISSUED BY NATIONAL WEATHER SERVICE BOISE ID
936 AM MST WED JAN 21 2015

.DISCUSSION... SFC OBS ALONG WITH SATELLITE PICS AND WEBCAMS SHOWING
THAT THE DENSE FOG IS LIFTING INTO A STRATUS DECK ACROSS THE VALLEY.
WILL ALLOW THE DENSE FREEZING FOG ADV EXPIRE AT 1100 AM. OTHERWISE
NO BIG CHANGES IN THE FORECAST FOR TODAY AS AN UPPER RIDGE DOMINATES
THE WEATHER PATTERN THROUGH FRIDAY MORNING.

&&

.AVIATION...THE LIFR/IFR IN FOG AND LOW STRATUS ACROSS THE UPPER
SNAKE RIVER PLAIN AND SOUTHERN VALLEYS TO THE NV BORDER THIS MORNING
WILL GRADUALLY IMPROVE TO MVFR OR EVEN SCATTER OUT BY LATE
AFTERNOON. EXPECT FOG AND LOW CLOUDS TO REFILL THE VALLEYS TONIGHT
WITH LOW MVFR AND IFR CONDITIONS RETURNING. SURFACE WINDS LESS THAN
10 KTS TODAY WITH NORTHERLY WINDS ALOFT TO 20 KTS AT 10K FEET MSL.

&&

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT. THE MAIN IMPACT THROUGH
TOMORROW EVENING WILL BE LOW CLOUDS AND FOG. THIS MORNING...WITH A
DOWNVALLEY FLOW WE ARE SEEING DENSE FREEZING FOG UP AND DOWN THE
SOUTHERN/EASTERN FLANK OF SNAKE PLAIN AND MAGIC VALLEY INTO
ADJACENT VALLEYS OF THE SOUTHERN HIGHLANDS. CONDITIONS ARE VERY
POOR VISIBILITY WISE AND SOME SLICK SPOTS ARE LIKELY. ELSEWHERE WE
ARE SEEING SOME AREAS OF VALLEY FOG AND LOW CLOUDS BUT CERTAINLY
NOT AS WIDESPREAD. WE SHOULD SEE CONDITIONS SLOWLY IMPROVE TODAY WITH
THE CURRENT IDEA OF FOG BEING GONE BY AFTERNOON BUT LINGERING
STRATUS IN SOME OF THE MORE HIDDEN/NARROW VALLEYS IN THE CENTRAL
MOUNTAINS AND ACROSS PORTIONS OF THE SNAKE PLAIN AND ADJACENT
SOUTHERN VALLEYS. OTHERWISE...THE MOUNTAINS WILL SEE PLENTY OF
SUNSHINE. WE WILL BE WATCHING FOR MORE LOW CLOUDS AND/OR FREEZING
FOG ACROSS EASTERN IDAHO TONIGHT AND THURSDAY. WE WILL HAVE TO
PLAY THIS BY EAR AND JUST LIKE LAST NIGHT DO MORE TIMELY UPDATES
TO THE FORECAST AND CATCH ITS EVOLUTION. WITH THE
INVERSION...EXPECT 20S TO LOW 30S FOR HIGHS WITH MID AND UPPER
ELEVATIONS BASKING IN ABOVE FREEZING CONDITIONS. IN FACT...SOME
PLACES IN THE CENTRAL MOUNTAINS AND SOUTH OF BURLEY WILL JUMP
ABOVE 40 DEGREES.

THINGS GET A LITTLE TRICKY FOR THURSDAY NIGHT AND FRIDAY. WE WILL
SEE A WEAKENING WAVE MOVE ACROSS EASTERN IDAHO THURSDAY NIGHT.
THIS WILL BRING AN INCREASE IN MID AND HIGH LEVEL CLOUDS.
HOWEVER...THERE WILL LIKELY NOT BE MUCH IN THE WAY OF
PRECIPITATION EXCEPT FOR A FEW SHOWERS NEAR LEMHI COUNTY AND
ISLAND PARK. RIGHT NOW...THIS LITTLE SYSTEM SHOULD NOT BE STRONG
ENOUGH TO FULLY BREAK ANY INVERSIONS OR COMPLETELY SCOUR OUT FOG
OR LOW CLOUDS ESPECIALLY ACROSS THE PLAIN. BY FRIDAY
NIGHT...THINGS BECOME LESS CLEAR. WE DO HAVE ANOTHER SURGE OF
MOISTURE AND A SYSTEM CROSSING THE REGION. HOWEVER...IT LOOKS LIKE
MOST OF IT WILL STAY TO OUR NORTH WITH SOME SHOWERS POSSIBLE
CLOSER TO LEMHI COUNTY AND THE DIVIDE. WE MAY END UP WITH ANOTHER
NIGHT OF LOW CLOUDS AND FOG ACROSS PART OF OUR AREA IF THIS SYSTEM
ISN`T ENOUGH TO MIX THINGS OUT. STAY TUNED. KEYES

.LONG TERM...SATURDAY THROUGH NEXT WEDNESDAY. BOTH THE GFS AND ECMWF
REMAIN IN FAIRLY GOOD AGREEMENT THAT A RIDGE WILL REMAIN ALONG THE
COAST SATURDAY AS A MODEST PAC DISTURBANCE TOPS THE RIDGE AND DIGS
SE THROUGH MONTANA PROVIDING A CHANCE OF SNOW FOR THE
MONTANA/WYOMING BORDER REGIONS. FOR SUNDAY AND MONDAY...THE RIDGE
EXPANDS ACROSS THE GREAT BASIN SHUNTING PAC MOISTURE NORTH AND
ACCENTUATING THE VALLEY INVERSIONS. BY TUESDAY...A PATTERN CHANGE
APPEARS TO BE IN THE WORKS AS THE GFS AND ECMWF BOTH LIFT A CUT-OFF
LOW OUT OF BAJA NNE ACROSS CALIFORNIA/NEVADA AND INTO SRN IDAHO
WEDNESDAY MORNING. THE MODELS SHOW A BROAD TROUGH SETTING UP OFF THE
COAST BY WEDNESDAY WITH THE RIDGE AXIS SHIFTING INTO THE ERN GREAT
BASIN/ROCKIES. THE EWRD POSITION OF THE RIDGE SHOULD OPEN UP
THE REGION TO A MORE ACTIVE SW FLOW. IN RESPONSE...HAVE NUDGED THE
PRECIPITATION CHANCES UPWARD TOWARD CLIMATOLOGY STARTING WEDNESDAY
WHILE SHOWING SOME WARMING. HUSTON

&&

.AVIATION...EARLY MORNING SATELLITE IMAGERY AND OBSERVATIONS WERE
HIGHLIGHTING A FAIRLY NARROW REGION OF DENSE FOG ALONG THE SNAKE
RIVER/HENRYS FORK EXTENDING FROM KIDA SOUTH THROUGH KPIH AND THEN
TRANSITIONING TO AN IFR CIG/STRATUS LAYER ACROSS THE MAGIC
VALLEY/KBYI AREA. NAM MODEL CROSS SECTIONS FAVOR A BREAK IN THE FOG
AT KIDA AND KPIH SOMETIME BETWEEN 8AM AND 11AM WHICH MAY BE A LITTLE
TOO AGGRESSIVE EVEN WITH THE AFOREMENTIONED NARROW COVERAGE. THE
STRATUS LAYER AT KBYI SHOULD BEGIN TO DISSIPATE BETWEEN 11AM AND
2PM. KSUN REMAINS DRY THROUGHOUT THE DAY AND FOR NOW...THE NUMERICAL
MODELS DO NOT SUGGEST A REPEAT EVENT FOR FOG OR STRATUS THURSDAY
MORNING AT ANY OF THE SNAKE PLAIN TERMINALS. THE STATISTICAL
GUIDANCE IS LEANING TOWARD DRIER CONDITIONS AS WELL AT KBYI AND KPIH
BUT IS SPLIT AT KIDA. THUS WILL LIKELY CARRY AT LEAST A MENTION OF
FOG AT KPIH AND PERHAPS SOMETHING MORE SIGNIFICANT AT KIDA THURSDAY
MORNING. HUSTON

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
FREEZING FOG ADVISORY UNTIL 11 AM MST THIS MORNING IDZ020-021.

&&

$$



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