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Area Forecast Discussion (AFD)

Issued by Pendleton, OR (PDT)

                            
000
FXUS66 KPDT 190518
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1018 PM PDT Sat May 18 2019

.AVIATION...
06Z TAFS....There is a weakening area of showers south of YKM that
should reach there shortly. YKM should remain VFR but will see
some RA. Otherwise, no major changes to previous forecasts. DLS, 
PDT, RDM and BDN will see deteriorating CIGS to MVFR during 
Sunday as low pressure move into northern California. RDM and BDN
will likely see some MVFR VSBY as well. There is a chance that 
those two locations could reach IFR during Sunday afternoon. All 
other locations are expected to remain VFR through the TAF period.

&&

.PREV DISCUSSION... /issued 858 PM PDT Sat May 18 2019/ 

UPDATE...
Latest radar imagery showed an area of showers generally between
(now mainly north of the Dalles) and Hermiston. This area of
showers had some embedded thunder in it earlier, though the
thunder apparently has ended. This area of showers is moving to
the north. High resolution guidance handling of this area has been
mixed. The RAP earlier did not have this feature at all, though
now has seemingly caught on to it. The HRRR has done a much better
job. The global models' performance has also generally been poor.
Both the HRRR and RAP continue to bring this feature northward
over the next few hours into southern Washington, before
eventually weakening it. Therefore, have increased pops over this
area. Also, at least for the next few area, have kept a mention of
thunder. 

Otherwise, made some adjustments to cloud cover, temps and wind. 


PREV DISCUSSION... /issued 155 PM PDT Sat May 18 2019/ 

SHORT TERM...Tonight through Tuesday...It will be cool and wet 
during the short term. A closed low currently centered near 41N/133W 
is rotating precipitation across southwest Oregon this afternoon, 
and precipitation will increase from the south overnight.  The first 
band of showers will bring relatively light amounts of precipitation 
tonight, but the next band of precipitation right at the heels of 
the first one will bring another round of moderate to heavy rain. 
The front on Sunday and Sunday night will be stationary in a NW-SE 
line from The Dalles to Burns, and 24-hour QPF of 0.5-1.5 inch is 
forecast over northeast Oregon. The heaviest accumulations will be 
over the southern Blues and the Ochoco-John Day Highlands. Some 
areas are already saturated from Thursday's rain event, prompting 
the issuance of a Flood Watch. Although flooding is not expected to 
be widespread, the purpose of the watch is to alert those of the 
possibility of rock or mud slides in steep terrain and localized 
flooding. Most of south central and southeast Washington as well as 
central and north central Oregon will have light to moderate rain 
Sunday and Sunday night but less QPF--up to a 0.25 inch for most 
locations.  Will keep the slight chance of thunderstorms for the far 
northern Blues east to Idaho Sunday afternoon, although clouds could 
become overcast and limit instability.

The closed low will travel southeast across the California and the 
Desert SW Sunday night and Monday morning.  Showers on Monday will 
mostly be scattered, but another closed low approaching the Oregon 
coast will bring numerous showers Monday night and Tuesday. Heaviest 
accumulations will be over the Blues and Wallowas and the east 
slopes of the WA/OR Cascades where 0.25-0.5 inch is forecast. Other 
areas will likely receive less than a 0.25 inch of rain. Light snow 
accumulations are possible above 5000 feet on Tuesday.  Wister 
  

LONG TERM...Tuesday night through Saturday...Models in good 
agreement in the short-term with two lows pinwheeling around one 
another over the Northern High Plains through Thursday.  This will 
result in general north to northeast upper level flow over the 
Pacific Northwest. There are minor differences spatially and 
temporally with the lows, but overall scattered showers, mainly 
during the afternoon and early evening, will continue, primarily 
over the Oregon mountains. By Friday the models begin to diverge. 
The GFS shows a disturbance moving down from BC while the ECMWF 
shows the western most low retrograding over Oregon. Either solution 
results in an increasing chance of showers Friday over the CWA, 
mainly over the mountains.  By Saturday, the GFS shows a 
strengthening upper low moving from BC to southern Washington while 
ECMWF shows a more open trough.  Given the discrepancies between the 
two solutions, will continue a mention of afternoon and evening 
showers, mainly over the mountains. In summary, the active weather 
pattern will continue over the Pacific Northwest. Daytime highs will 
remain near to slightly below normal through the period.  Earle 

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  50  60  47  66 /  40  70  60  20 
ALW  51  67  48  68 /  10  60  60  20 
PSC  55  73  51  73 /  20  30  30  10 
YKM  52  70  51  68 /  80  70  30  30 
HRI  52  66  49  71 /  60  60  50  20 
ELN  48  68  47  63 /  70  60  30  40 
RDM  40  59  39  60 /  20  50  50  30 
LGD  44  58  43  60 /  20  90  90  30 
GCD  43  51  42  58 /  30  90  80  40 
DLS  51  63  50  64 /  60  80  60  30 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Flood Watch from 8 AM PDT Sunday through Monday morning for 
     ORZ044-049-050-502-503-505>508.

WA...None.
&&

$$

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