Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 211105 AAA
AFDPDT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
405 AM PDT SUN SEP 21 2014

UPDATED AVIATION DISCUSSION

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT...AN UPPER LEVEL RIDGE
WILL MOVE EAST INTO IDAHO TODAY. TEMPERATURES WILL BE A LITTLE
WARMER TODAY THAN YESTERDAY DUE TO SUBSIDENCE FROM THE DEPARTING
RIDGE. WINDS WILL BE GENERALLY LIGHT AS WELL. A CUTOFF LOW IN
CENTRAL CALIFORNIA THIS MORNING WILL MOVE NORTHEAST INTO NEVADA BY
AFTERNOON. SOME MID/HIGH LEVEL MOISTURE FROM THE LOW IS MOVING INTO
SOUTHERN OREGON THIS MORNING AND WILL SPREAD NORTH DURING THE DAY.
AT THIS TIME EXPECT TO SEE SOME BATCHES OF HIGHER BASED CLOUDS DRIFT
INTO PORTIONS OF THE AREA BUT DO NOT EXPECT ANY PRECIPITATION
THROUGH TONIGHT. UPPER LEVEL FLOW WILL BECOME SOUTHWESTERLY BY
MONDAY, AND REMAIN SOUTHWEST THROUGH THE REST OF THE SHORT TERM
PERIOD. MODELS ARE SUGGESTING PRECIPITATION FROM A WEAK FRONT MONDAY
MORNING ALONG THE CASCADES. I THINK THE MOISTURE ADVECTION IS TOO
FAST A TRANSITION FROM A DRY RIDGE TO PRECIPITATION. SOUNDINGS SHOW
THE MOISTURE IS MAINLY ABOVE 14 KFT AT 12Z. SHOWERS MAY DEVELOP
MONDAY AFTERNOON OVER EASTERN OREGON AND WASHINGTON AS THE WEAK COLD
FRONT STALLS. THERE WILL BE ENOUGH INSTABILITY IN THE WARM AIR TO
TRIGGER A FEW THUNDERSTORMS AS WELL. VERY LITTLE PRECIPITATION WILL
OCCUR WITH THIS SYSTEM BECAUSE THE LOW LEVELS WILL BE VERY DRY
INITIALLY. A SLOW TRANSITION INTO COOLER WETTER WEATHER WILL
CONTINUE TUESDAY AS ANOTHER FRONT APPROACHES THE COAST. THIS SYSTEM
APPEARS STRONGER ON SATELLITE AND MODEL FORECAST BUT IT WILL BE SLOW
TO MOVE INLAND WITH WINDS NEARLY PARALLEL TO THE FRONT. COONFIELD

.LONG TERM...WEDNESDAY THROUGH SUNDAY NIGHT...A MATURE LOW PRESSURE
SYSTEM WILL BE LOCATED OFF THE PACIFIC COAST ON WEDNESDAY WITH A
COLD FRONT JUST WEST OF THE CASCADES TO START THE FORECAST PERIOD.
THE PROGRESSION OF THIS COLD FRONT COMPARED TO PRIOR MODEL GUIDANCE
HAS BEEN SLOWED SOMEWHAT...WITH THE FRONT EXPECTED TO MOVE ACROSS
THE TWO STATE AREA BY THURSDAY NIGHT.  THIS SLOWER EASTWARD
PROGRESSION WILL PLACE THE AREA UNDER A STRONG SOUTHERLY FLOW...WITH
ADJUSTMENTS MADE TO THE GRIDS TO INCREASE DAYTIME HIGHS ON WEDNESDAY
AS WELL AS SOUTHERLY WINDS AHEAD OF THE FRONT.  HAVE ALSO SLOWED
DOWN EASTWARD PROGRESSION OF THE ANTICIPATED MOISTURE BAND WITH THE
FRONT AND INSTEAD HAVE THE ENTIRE CWA BEING UNDER A CHANCE OF
SHOWERS.  THE STEEPENED LAPSE RATES ARE STILL EVIDENT ON LATEST
FORECAST SKEW T SOUNDINGS...THEREFORE HAVE LEFT A SLIGHT CHANCE OF
AFTERNOON THUNDERSTORMS ALONG THE NORTHEASTERN OREGON MOUNTAINS
THURSDAY AFTERNOON.  THE MAIN TROUGH AXIS WILL SLOWLY MOVE EASTWARD
OVER THE AREA BY FRIDAY...WITH A GOOD CHANCE OF WIDESPREAD SHOWERS
POSSIBLE OVER THE ENTIRE CWA.  THERE IS SOME QUESTION AS TO WHETHER
THERE IS ENOUGH INSTABILITY ON FRIDAY FOR AFTERNOON THUNDERSTORMS
ALONG THE NORTHEASTERN OREGON MOUNTAINS...BUT IN CONSULTATION WITH
NEIGHBORING OFFICES...HAVE HELD WITH A SLIGHT CHANCE OF
THUNDERSTORMS FOR NOW.  ON SATURDAY...MODEL SOLUTION DIFFERENCES ARE
EVIDENT AS TO THE POSITION OF THE EVENTUAL UPPER LOW AT THE BASE OF
THE TROUGH AXIS.  ALL MODEL GUIDANCE SOLUTIONS PLACE THE REGION
UNDER WESTERLY OR NORTHWESTERLY FLOW...WHICH WOULD ALLOW FOR A
GRADUAL END TO PRECIPITATION IN THE LOWER COLUMBIA BASIN WHILE
CONTINUING ALONG THE HIGHER ELEVATIONS OF THE CWA.  HAVE OPTED TO
DECREASE POP CHANCES IN THE LOWER COLUMBIA BASIN FOR SATURDAY
AFTERNOON AND EVENING GIVEN THOSE SOLUTIONS.  TEMPERATURES DURING
THE FORECAST PERIOD WILL START ABOVE NORMAL FOR THE CWA AND WILL
TREND TO NEAR OR JUST SLIGHTLY BELOW SEASONAL NORMS STARTING ON
THURSDAY.  BIEDA

&&

.AVIATION...12Z TAFS.  CIRRUS CLOUDS WITH CIG AOA 25K FT AGL ARE
SPREADING INTO THE AREA FROM THE SOUTH THIS MORNING DUE TO AN UPPER
LOW TO OUR SOUTHEAST.  AFT 21/18Z...ALTOCUMULUS CLOUDS WILL DEVELOP
ALONG HIGHER TERRAIN WITH SCT CIG AOA 10K FT AGL.  NO SIGNIFICANT
WEATHER IS EXPECTED AT THIS TIME WITH VFR CONDITIONS.  WINDS AOB 15
KTS WILL CONTINUE THROUGH THE TAF PERIOD.  BIEDA

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  87  57  85  57 /   0   0  10  10
ALW  88  63  86  63 /   0   0  10  10
PSC  89  56  88  58 /   0   0  10  10
YKM  92  56  87  55 /   0   0  10  10
HRI  90  54  88  55 /   0   0  10  10
ELN  93  57  85  55 /   0   0  10  10
RDM  90  48  81  47 /  10   0  10  10
LGD  88  54  84  53 /   0   0  20  20
GCD  91  51  86  53 /  10  10  20  20
DLS  90  59  84  57 /   0   0  10  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
&&

FOR ADDITIONAL WEATHER INFORMATION, CHECK OUR WEB SITE AT...
WWW.WEATHER.GOV/PENDLETON

$$

76/98/98





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