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Area Forecast Discussion (AFD)

Issued by Pendleton, OR (PDT)

FXUS66 KPDT 200531

Area Forecast Discussion
National Weather Service Pendleton OR
1031 PM PDT Fri Apr 19 2019

An area of ra extends from BDN newd to ALW and covers a large
portion of Nern OR and a small portion of sern WA. Most of the
guidance has this rain dissipating or lessening overnight before 
additional rain moves in during the mrng. The latest guidance also
now brings MVFR CIGS for PDT, BDN, RDM and ALW. Conditions will 
improve to VFR everywhere later Saturday afternoon as an upper 
trough/cdfnt cross the region, rainfall comes to an end and the 
sky begins to clear out. 


.PREV DISCUSSION... /issued 923 PM PDT Fri Apr 19 2019/ 

An area of rain extended across a large portion of northeastern 
Oregon, and was extending into areas of southeastern Washington. A
portion of this was the thunderstorms of earlier that have since 
dissipated. This rain is in advance of a slow moving cold front.

The high resolution guidance suggests that this rain will
dissipate in the next few hours, while the NAM lingers it longer
than that. Based on radar returns, it is difficult to see how this
will dissipate so quickly, and it seems that the high resolution
models may be underdoing the activity, so have kept higher pops in
most areas through the night.  

PREV DISCUSSION... /issued 525 PM PDT Fri Apr 19 2019/ 

VFR conditions are expected thru the TAF period. However there are
some TSRA over the area that could locally impact the TAF sites
for the next few hours mainly ALW, BDN, RDM. Reduced cigs psbl if
TSRA impacts an individual arpt. SHRA will continue overnight and
decrease durg the mrng and cdfnt moves thru from w to e. 

PREV DISCUSSION... /issued 200 PM PDT Fri Apr 19 2019/ 

SHORT TERM...Tonight through Sunday night...WSR-88D is showing 
increasing returns with showers developing over the southern Blue 
Mountains northeast to Wallowa County.  Few cloud-to-ground strikes 
detected in southern Wheeler County near Mitchell.  Showers and 
scattered thunderstorms are developing ahead of a cold front 
currently moving across central WA and northwest OR. The HRRR has 
been consistent with most thunderstorm activity in Union and Wallowa 
Counties this evening.  MLCAPES around 600-900 J/kg and 35-40 knots 
of bulk shear could mean strong thunderstorms capable of penny size 
hail and heavy rain.

The front will gradually make its way across the forecast area this 
afternoon and evening.  The upper level jet is parallel to the 
front, resulting in a slow-moving system. Keeping this in mind, QPF 
was increased over north central and northeast OR and far southeast 
WA tonight. 0.25-0.5 inch of rain is possible over the Blues and 
Wallowas overnight and up to 0.25 inch of rain elsewhere. Previous 
models indicated the upper level trough moving into Idaho Saturday 
with drier air from the north-northwest, but the timing is slower. 
Therefore, numerous showers will continue Saturday morning 
throughout central and northeast Oregon then tapering off to 
scattered showers in the afternoon and evening. After midnight on 
Sunday morning, the only showers left will be over the Wallowa 
Mountains.  It will be a perfect day for outdoor activities and 
Easter egg hunting on Sunday with mostly sunny skies and highs in 
the mid-50s to mid-60s...near 70 in the Lower Columbia Basin and 
surrounding valleys.  Wister

LONG TERM...Monday through Saturday.  Monday and Tuesday, there 
will be a ridge of high pressure with temperatures about 10 degrees 
above normal and mainly dry conditions.   The ridge is expected to 
flatten slightly on Wednesday with some moisture pushing into the 
Blue Mountains and models indicate some instability, so have kept a 
slight chance of thunder for this area as well.  A trough of low 
pressure will be nearing the coast on Thursday with some moisture 
and instability ahead of it.  Currently, models keep this a little 
further south of the forecast area so I have not mentioned thunder 
at this time.  A large trough of low pressure remains over the area 
on Friday into Saturday with a mainly dry west to northwest flow. 
This will also usher in some cooler air with temperatures cooler to 
near normal levels. 93 

AVIATION...18Z TAFs...Showers will spread across the area this 
afternoon and tonight. There will also be a chance of thunderstorms 
this afternoon and evening over central Oregon and the eastern 
Oregon mountains.  Have opted to leave mention out of forecast for 
BDN/RDM as coverage of storms may be just to east of this area. Cigs 
will be 035-080 with MVFR cigs possible in heaviest showers. Showers 
will continue overnight decreasing from the northwest by early 
morning.  West to northwest winds will increase to 10 to 20 kts with 
higher gusts this afternoon from 20Z-03Z. 93 

HYDROLOGY...Flood Warnings continue for the Grande Ronde river at 
Troy and John Day river at Service Creek as warm temperatures and 
some heavy rain will increase runoff over the next few days.  93


PDT  48  60  40  65 /  70  60  10   0 
ALW  50  61  43  67 /  70  50  10   0 
PSC  52  68  44  72 /  40  30   0   0 
YKM  47  67  41  70 /  40  10   0   0 
HRI  51  66  43  70 /  40  40   0   0 
ELN  42  62  38  66 /  20  10   0   0 
RDM  45  57  35  63 /  70  70  10   0 
LGD  47  53  39  60 /  70  60  30   0 
GCD  46  51  38  61 /  70  70  30   0 
DLS  50  65  43  67 /  40  20   0   0