Area forecast discussion...updated
National Weather Service Pendleton or
400 PM PDT Tuesday Jun 18 2013
Updated aviation discussion
Short term...tonight through Friday. The Pacific northwest will be
influenced by a large vertically stacked low through the short term
period. The low is offshore and will be tracking inland tonight then
east of the Cascades Wednesday morning. The low will continue to
spin over Washington/or/ID through the remainder of the period. The NAM was
the outlier of all the models by pushing the closed low eastward
Thursday night and was disregarded in the forecast.
There is an extensive cloud cover over the forecast area that is
limiting the amount of surface heating. Several weak embedded
thunderstorms have developed over central Oregon. Water vapor shows
a wave over northwest California that will swing northeast this evening and
should bring scattered thunderstorms across our eastern zones. A 50
knot middle level jet and strong shear will provide middle level ascent
for organized convection. Current forecast...hazardous weather
outlook...and graphical weather stories highlight the potential for
penny to nickel size hail and isolated gusts to 50 miles per hour in eastern
Grant, Union, and Wallowa counties. Isolated to scattered
thunderstorms will continue in this area even after midnight.
It will be cool and showery Wednesday through Friday. Afternoon
temperatures will be about 10-20 degrees below seasonal averages.
Snow levels will lower to around 6000-6500 feet. A Special Weather
Statement was issued to alert campers and hikers of snow in the
higher terrain of the Cascades and The Wilderness regions of eastern
Oregon. The cold upper low will also bring isolated to scattered
thunderstorms. All areas in our County Warning Area have a potential to observe
thunderstorms on Wednesday...and the threat will mainly be in our
eastern zones Thursday through Friday. Thunderstorms are not
expected to be strong or severe but should produce small hail. Wister
Long term...Friday night through Tuesday...mid/upper level low
still lingering over Idaho/Montana thus keeping western flank of low
and attendant wrap around moisture streaming across mountains of southeast
Washington and NE Oregon Friday evening for a chance of showers.
Probability of precipitation decrease overnight and Saturday as the low finally eases
eastward into central Montana with a middle/upper level ridge of high
pressure building over forecast area on Saturday for dry conditions.
Sunday. Saturday night/Sunday the next upstream middle/upper level
Pacific trough moves to coast and pushes a cold front with
increasing moisture east of Cascades for chance of showers mainly
along east slopes of Cascades and in Blue Mountains. Monday and
Tuesday a large middle/upper level low in NE Pacific causes flow aloft
to back to the southwest thus bringing a moist middle level air mass
into forecast area which becomes marginally unstable in the
afternoon/evening on Monday and Tuesday for a slight chance of
afternoon/evening thunderstorms over the eastern mountains. Polan
&&
Aviation...00z tafs...generally VFR conditions will prevail until
around 8 PM. Conditions will deteriorate late this afternoon by
virtue of the moist air mass being marginally unstable. A middle/upper
level disturbance in the southern flank of the offshore low will has
moved into south central Oregon this afternoon and will move into
central and east central Oregon early by 6pm this evening. Dynamic
lift associated with the disturbance will combine will orographic
lift over mountains to produce scattered showers and isolated
thunderstorms (ts) this afternoon and tonight...especially between
until 07z. Any ts that move over a taf site will likely lower
conditions to MVFR or possibly even brief periods of IFR. IFR/LIFR
will occur along the aviation Route over the Blue Mountains from
kpdt to kbke for the next 18-24 hours due to low ceilings and reduced
visible in showers, which will become more numerous over the Blue
Mountains tonight. Some isolated ts are also possible along thick
kpdt-kbke Route. The potential exists for a few thunderstorms to
become strong or even borderline severe from the Blue Mountains
eastward. The strongest ts are expected in Union, Wallowa, and Baker
counties this afternoon and this evening. Cannot rule out a stray ts
in those counties producing hail of 1/2 inch to 1 inch and wind
gusts of 35 to 45 kts. Otherwise, winds near any ts will be gusty
and erratic.
Surface winds of 5 to 10 kts will occur tonight, mainly in central
Oregon north to kdls and east to the lower Columbia Basin and the
Blue Mountain foothills. West-west-northwest surface winds at klgd will be 15-20
kts this afternoon and through tonight. Polan
&&
Preliminary point temps/pops...
PDT 51 65 48 66 / 60 60 40 40
alw 54 65 52 66 / 60 70 50 40
psc 55 70 53 69 / 60 50 40 40
ykm 53 69 51 65 / 50 40 40 40
hri 55 69 52 69 / 60 50 40 40
eln 51 66 51 63 / 50 40 40 40
rdm 41 60 37 66 / 60 50 30 20
lgd 48 56 44 60 / 70 80 60 40
gcd 47 54 40 61 / 60 70 50 30
dls 54 67 52 69 / 50 50 40 30
&&
PDT watches/warnings/advisories...
or...none.
Washington...none.
&&
Threat index
Wednesday : green
Thursday : green
Friday : green
Green: none or limited need for watches, warnings, or advisories.
Yellow: a few watches, warnings, or advisories possible or in effect.
Red: numerous watches, warnings, or advisories possible or in effect.
For additional weather information, check our web site at...
www.Weather.Gov/Pendleton
$$
85/99/99
