Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 221657 AAA
AFDPDT

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
956 AM PDT Tue May 22 2018

Updated aviation discussion

.SHORT TERM...Clear skies over the region this morning with light
winds. Weak instability over central and northeast Oregon combined
with upper low to our south will result in isolated thunderstorms
developing later this afternoon into early evening. Storms should
be from the Blues and Wallowa county to the John Day highlands.
Remainder of the forecast area sunny today with highs in the upper
70s and 80s. Winds becoming northerly 5-10kt. 94

&&

.AVIATION...18Z TAFs...VFR conditions will prevail through the
period. Upper level high pressure will keep the weather dry at all
TAF locations. A few afternoon and evening showers and possibly a
thunderstorm will develop over the mountains, but should not affect
any TAF sites.  Winds will generally be less than 10 kts.  Earle

&&

.PREV DISCUSSION... /issued 428 AM PDT Tue May 22 2018/

SHORT TERM...Today through Thursday...Upper low over the Great
Basin will lift newd through Wednesday in response to a more potent
upper low offshore that will approach the California coast on
Thursday. As this transition occurs the flow aloft will turn
southerly with increasing moisture across the interior NW. For today
expect a similar day compared to Monday with a few showers and
isolated thunderstorms during the afternoon and evening. Activity
could extend just a bit farther west today but should still be most
focused over the eastern mountains. The storms are not expected to
be organized or severe. For Wednesday scattered to numerous showers
and isolated thunderstorms are expected especially over the higher
elevations in Oregon with the activity continuing into the evening.
There is some potential for the storms to congeal into a general
area of moderate rain during the evening and overnight hours but the
latest models don`t agree on where that may occur. On Thursday as
the height gradients tighten in association with the approaching
upper low...vertical wind shear will increase. This may support more
organized thunderstorm activity during the afternoon over central
and northeast Oregon provided sufficient daytime heating can occur.
It will be warm through the period with highs mostly in the 80s
lower elevations and 70s in the mountains. 78

LONG TERM...Thursday Night through Tuesday...Models continue to
have significant run to run changes and detail variations so
confidence in not high from Thursday night into Saturday. Thursday
night models show an upper low along the Northern California coast
sending a very moist southerly flow into the area. The GFS and the
NAM show a very strong tightly wrapped up low while the ECMWF and
Canadian have a weaker low. Thursday evening will have a chance of
showers and a slight chance of thunderstorms across the Oregon
portion of the area. Overnight and Friday a chance of showers will
continue in Oregon while a slight chance of showers in expected in
Washington. Friday afternoon and evening will see a slight chance of
thunderstorms in central Oregon and the Eastern Oregon mountains.
Rainfall amounts were a challenge. The stronger GFS and NAM were
putting well in excess of an inch of rain into central Oregon and
the Ochoco-John Day Highlands Thursday evening through Friday
evening. The NAM reached 2 inches in places. The ECMWF, Canadian and
models blends had much more modest (and probably more realistic)
values. Went with the more modest values and have 4 to 6 tenths of
an inch in the southern portion of the area and lighter amounts
further north. Models have the low moving ashore in northern
California Friday night and into Nevada Saturday, weakening as it
goes. This will keep a chance of rain showers over the area Friday
night and a slight chance on Saturday with a slight chance of
thunderstorms over the eastern Oregon mountains on Saturday
afternoon. The low will drift slowly east to the Utah/Nevada border
Sunday and a slight chance of showers will continue in the mountains
with a slight chance of thunderstorms in the northern Blue Mountains
and Wallowa County while the lower elevations will be dry. Monday
and Tuesday the low will move very slowly east but will be weakening
as a ridge starts building over the area. The area will be dry with
just a few showers over Wallowa county. Temperatures through the
long term period will remain a few degrees above normal with highs
in the mid 70s to mid 80s and in the mid 60s to mid 70s in the
mountains. Perry

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  84  57  85  60 /  10  10  20  20
ALW  86  59  87  61 /  10  10  20  20
PSC  89  59  90  63 /   0  10  10  20
YKM  89  56  90  60 /   0  10  20  20
HRI  89  58  90  62 /   0  10  10  30
ELN  87  54  87  57 /   0   0  20  20
RDM  82  51  81  52 /   0  10  40  60
LGD  79  50  79  54 /  30  30  40  40
GCD  78  51  78  54 /  30  30  60  50
DLS  89  59  87  60 /   0  10  20  20

&&

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

$$

94


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