Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 051527 AAA
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
827 AM PDT THU MAY 5 2016

.UPDATE...A BUSY DAY IS IN STORE FOR THE CWA. A LARGE UPPER
TROUGH/CLOSED LOW PRESSURE SYSTEM OFF SOUTHERN CALIFORNIA COAST IS
PRODUCING A MOIST AND UNSTABLE SOUTHERLY FLOW OVER THE CWA. THE
THUNDERSTORM THREAT IS HIGHER TODAY THAN ON WEDNESDAY. CONVECTIVE
PARAMETERS ARE VERY FAVORABLE FOR STRONG STORMS AND POSSIBLY SEVERE
STORMS. SPC HAS THE EASTERN PORTION OF THE FORECAST AREA IN A
MARGINAL RISK AREA OF THUNDERSTORMS. THE STRONGEST STORMS WILL BE
OVER EASTERN AND NORTHEAST OREGON/EXTREME SOUTHEAST WASHINGTON.
PLAYED DOWN THE SEVERE WEATHER WORDING IN THE FORECAST A BIT HOWEVER
STILL MENTIONED FREQUENT LIGHTNING...HEAVY RAIN...STRONG GUSTY WINDS
AND HAIL...POSSIBLY LARGE HAIL. THE ATMOSPHERE IS PRIMED FOR
SIGNIFICANT THUNDERSTORMS WITH SOME STORMS HAVING ROTATION AND
ORGANIZATION DUE TO HIGH VALUES OF HELICITY AND SHEAR AND HIGH
MOISTURE CONTENT. SHOWERS ARE ALREADY BEGINNING TO FORM OVER THE
EASTERN CWA AT THIS TIME. SO FAR THERE HAS NOT BEEN ANY LIGHTNING
BUT WITH SURFACE HEATING AND INCREASING CONVECTION LIGHTNING SHOULD
BEGIN BY MID DAY. MADE A FEW CHANGES TO THE WEATHER GRIDS FOR TODAY
AND WILL UPDATE THE FORECAST. 88

&&

.PREV DISCUSSION... /ISSUED 449 AM PDT THU MAY 5 2016/

SHORT TERM...TODAY THROUGH FRIDAY NIGHT...OVERVIEW...ANOTHER BUSY
THUNDERSTORM DAY TODAY AS THE UPPER LEVEL DISTURBANCE TO THE SOUTH
CONTINUES TO SPIN MOISTURE UP TO THE AREA.  WHILE YESTERDAY`S
THUNDERSTORM THREAT FOCUSED WEST OF THE BLUE MOUNTAINS...TODAY WILL
BE THE OPPOSITE. WHILE THERE WILL BE A SLIGHT CHANCE OF
THUNDERSTORMS WEST OF THE BLUE MOUNTAINS...THE MAIN FOCUS FOR STRONG
AND POSSIBLY SEVERE STORMS WILL BE OVER THE GRANT...UNION...WALLOWA
..EASTERN UMATILLA...COLUMBIA...AND EASTERN WALLA WALLA COUNTY.
THERE WILL STILL BE A DECENT CHANCE OVER THE CENTRAL OREGON
AREA...AND SOME OF THESE STORMS COULD BE STRONG...BUT THE BEST
DYNAMICS WILL BE OVER THE AFOREMENTIONED COUNTIES. TOMORROW EXPECT
SHOWERS AND THUNDERSTORMS MAINLY OVER CENTRAL AND NORTHEAST
OREGON...BUT IF THE LOW TRACKS FURTHER SOUTH EAST...THOSE CHANCES
MAY BE LOWERED.  THERE WILL STILL BE LEFT OVER MOISTURE AND
INSTABILITY BUT UPPER LEVEL DYNAMICS WILL NOT BE AS FAVORABLE AS
PREVIOUS DAYS FOR ORGANIZED CONVECTION.  BUT IF THE LOW MAINTAINS
THE CURRENT TRACK THERE MAY BE A FEW STRONG STORMS NEAR OUR CWA
BOARDERS WITH BOISE AND MEDFORD.

TODAY AND TONIGHT BREAKDOWN...SPC CURRENTLY HAS A MARGINAL RISK FOR
SEVERE WEATHER TODAY OVER THE PREVIOUSLY MENTIONED COUNTIES.  THIS
RISK WILL MAINLY FOCUS LARGE HAIL AND POSSIBLY DAMAGING WINDS. HEAVY
RAIN CAN ALSO BE EXPECTED AS PWAT VALUES RANGE FROM 0.80"-1.00". LCL
HEIGHTS BELOW 3000FT...STEEP 850-500MB LAPSE RATES...0-3KM SRH
VALUES 200-300 M2/S2...0-6KM SHEAR 40-50KTS...AND CAPE VALUES FROM
1500-2500 J/KG HELP TO SUPPORT STRONG TO POSSIBLY ORGANIZED
(ROTATING) SEVERE THUNDERSTORMS TODAY.  ALTHOUGH IT MAY BE DIFFICULT
TO SEE ANY IMPULSES THAT MAY MOVE ACROSS THE AREA TO AID IN THE LIFT
FOR INITIATION...WITH LOW LEVELS FAIRLY MOIST...THERE SHOULD BE
SUFFICIENT DAYTIME HEATING FOR SURFACE BASED CONVECTION. IN
ADDITION...THE POSITION OF THE LOW SETS UP A GOOD 500MB DIFFLUENT
FLOW OVER THE AREA OF CONCERN...WHICH WILL AID IN THE UPWARD AIR
ACCELERATION...ONCE STARTED.

ONCE DAYTIME HEATING ENDS...EXPECT THAT MOST STORMS WILL LOSE THERE
FORCING MECHANISM AND THEREFORE WILL DISSIPATE OUT...LEAVING JUST
RESIDUAL SHOWERS.  THUNDER IS STILL POSSIBLE OVERNIGHT WITH AN
IMPULSE DUE TO THE CONTINUED UNSTABLE AIR MASS ALOFT...BUT WILL NEED
UPPER LEVEL DYNAMICS TO KEEP THE LIFT GOING...RIGHT NOW CONFIDENCE
IS NOT HIGH ENOUGH TO MENTION.

FRIDAY AND FRIDAY NIGHT BREAKDOWN...WITH THE LARGE UPPER LEVEL LOW
CENTERED ROUGHLY OVER LAS VEGAS...CENTRAL AND NORTHEAST OREGON WILL
LIKELY BE IN THE DEFORMATION ZONE OF THE LOW...RECEIVING RETURN FLOW
FROM THE EAST. THUNDERSTORM POTENTIAL WILL BE GREATEST HERE DUE TO
PRIMED LOW LEVEL MOISTURE FROM PREVIOUS DAYS...AIDING IN STRONGER
CAPE VALUES OF 1500-2500 J/KG FOR THE AFTERNOON.  AGAIN THIS SHOULD
MAINLY BE TRIGGERED BY DAYTIME HEATING AND STEEP MID LEVEL LAPSE
RATES.  0-6KM SHEAR VALUES ARE NOT AS STRONG 20-25KTS...AND DUE TO
AN EASTERLY FLOW...THESE STORMS WILL LIKELY MOVE FROM EAST TO WEST.
PWAT VALUES STILL REMAIN HIGH AND A FAIRLY MOIST SOUNDING THROUGHOUT
WOULD SUGGEST MAINLY A HAIL THREAT...BUT WONT RULE OUT GUSTY
WINDS...DUE TO THE AMPLIFIED CAPE VALUES AND SOME DCAPE VALUES
REACHING 750 J/KG...SUPPORTED WITH POCKETS OF DRY AIR ENTRAINMENT.
WILL NEED TO KEEP AN EYE OUT FOR THE NEXT COUPLE OF MODEL RUNS TO
SLOWER (LESS THAN 20KTS) TRAINING THUNDERSTORMS MAY BE A PROBLEM.
DUE TO THE NATURE OF SOME AREAS PRONE TO HEAVY RAIN FASTER MOVING
THUNDERSTORMS TODAY...BUT SLOWER POSSIBLY TRAINING THUNDERSTORMS
TOMORROW...AM CONSIDERING A FLASH FLOOD WATCH FOR SOME AREAS. RIGHT
NOW HIGHEST CONCERN MIGHT BE THE CANYON CREEK BURN SCAR. WEBER

LONG TERM...SATURDAY THROUGH WEDNESDAY...THE LARGE UPPER LOW OVER
THE U.S. SOUTHWEST WILL BEGIN TO SHIFT EAST SATURDAY AND SUNDAY DUE
TO A SYSTEM MOVING INTO WESTERN CANADA SATURDAY NIGHT AND SUNDAY. AS
SUCH, WRAP AROUND MOISTURE ASSOCIATED WITH THIS LOW WILL BE PUSHED
OUT OF EXTREME EASTERN OREGON BY MID DAY SUNDAY. WILL CONTINUE TO
ONLY MENTION A FEW SHOWERS OR THUNDERSTORMS OVER PORTIONS OF GRANT,
UNION AND WALLOWA COUNTIES THROUGH SUNDAY MORNING. THIS SYSTEM
MOVING INTO WESTERN CANADA WILL MAINLY CAUSE INCREASED WINDS SUNDAY
AFTERNOON AND EVENING, WITH A FEW SHOWERS NEAR THE CASCADE CREST IN
WASHINGTON. A SECOND WAVE BEHIND THE INITIAL PART OF THIS SYSTEM
LOOKS TO SWING GRADUALLY SOUTHEAST ACROSS IDAHO SUNDAY NIGHT THROUGH
MONDAY NIGHT. THUS COULD SEE A FEW SHOWERS OVER AND NEAR THE BLUE
MOUNTAINS, AND INTO WALLOWA COUNTY. CONDITIONS LOOK TO DRY OUT
TUESDAY INTO WEDNESDAY DUE TO THE RETURN OF HIGH PRESSURE. 90

AVIATION...12Z TAFS...VFR CONDITIONS ARE MAINLY EXPECTED DURING THE
NEXT 24 HOURS. ANOTHER DAY OF ACTIVE CONVECTIVE WEATHER IS EXPECTED
ACROSS THE REGION. AT THIS TIME THE STRONGEST STORMS ARE EXPECTED TO
OCCUR EAST OF ALL OUR TAF SITES. THERE REMAINS SOME THREAT OF
THUNDERSTORMS THOUGH AT KBDN, KRDM, KPDT AND KALW MID TO LATE
AFTERNOON. THERE IS THE POTENTIAL FOR BRIEF MVFR CONDITIONS DUE TO
THESE STORMS, BUT WILL KEEP CONDITIONS VFR FOR NOW. MOST SITES
SHOULD SEE SHOWERS AT OR WITHIN THE VICINITY AT TIMES TODAY. WINDS
WILL GENERALLY BE LESS THAN 15 KTS WITH THE STRONGEST WINDS AT KDLS.
WINDS COULD BE GUSTY NEAR THUNDERSTORMS. 90

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  74  51  80  53 /  50  30  20  10
ALW  75  54  81  54 /  40  20  20  10
PSC  79  55  85  58 /  40  20  10  10
YKM  78  52  86  56 /  30  20  10  10
HRI  76  52  83  55 /  40  20  10  10
ELN  74  49  83  53 /  30  20  10  10
RDM  66  41  75  42 /  70  50  20  30
LGD  72  45  75  47 /  70  60  40  30
GCD  71  48  72  48 /  80  70  50  40
DLS  77  52  86  58 /  40  20  10  10

&&

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

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

$$

88/90/90


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