Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pendleton or
300 PM PDT Sat Aug 1 2015
Short term...tonight through Tuesday. High pressure continues to
dominate the areas weather with dry conditions and above normal
temperatures. Afternoon highs are expected to remain around the century
mark into Sunday and the heat advisory will continue for the
remainder of the weekend mainly over and near the Columbia Basin.
Meanwhile moisture was moving into central Oregon and the John Day
Highlands which could produce isolated thunderstorms and rain into this evening. As the
high pressure slowly slips east...additional moisture will move
north and the area of thunderstorms and rain will expand to include the Washington/or Cascades
Sunday night. This area of precipitation are expected to migrate eastward
into the remainder of our area Monday. Afternoon temperatures will only climb
into the 90s on Monday but will still remain above normal. A weak
disturbance will accompany the moisture and will increase precipitation
chances over the John Day Highlands along with the blue/Wallowa Mountains
Monday night. As the disturbance and bulk of the moisture drifts
away from the two state area...drier conditions will advect into the
region on Tuesday. However lingering moisture will combine with
daytime heating to produce isolated thunderstorms and rain over central Oregon and
blue/Wallowa Mountains Tuesday afternoon.
Long term...Tuesday night through Saturday night...the long term
starts off with a chance of lingering showers and thunderstorms
mainly over the southern and eastern mountains as an upper level
disturbance moves eastward through the area Tuesday night. The
latest guidance is now in much better agreement for the remainder of
the extended period...which allows for a higher confidence forecast.
Heading into Wednesday and Thursday a potent upper trough/low is
forecast to drop through central b.C. And into southern Alberta
leaving our County Warning Area on the drier southern side of the system under a
west to northwest flow. Therefore lowered probability of precipitation to slight chance or
less over the forecast area during this time...as much of the region
is now looking likely to stay dry. Conditions may also turn breezy
Wednesday afternoon and evening with westerly winds between 10-20
kts with higher gusts possible. On Friday the latest guidance is
indicating a transient upper level ridge working its way through the
area...helping to continue the dry and seasonable weather. Friday
night through Saturday night an upper level trough begins to develop
over the interior pacnw...and this combined with increasing moisture
on a southerly flow will lead to chances of showers and
thunderstorms over parts of the region.
Temperatures for Wednesday through Saturday are expected to be much
cooler than we have been experiencing recently...but still near to
slightly above average each day. This translates into high
temperatures in the middle 80s to lower 90s in the lower elevations
with mainly 70s to low 80s in the mountains. Overnight lows will be
in the 50s to lower 60s for the valleys/basins with 40s in the
mountains most nights. 77
Fire weather discussion...upper level ridge remains centered over
the area today into Sunday. The airmass is very dry and humidities
will remain low. Minimum relative humidity values during the day will be 5-20
percent for most locations. Recoveries at night will also be poor.
Haines index today is 5/6...with a 5 on Sunday. Temperatures will be
well above normal with highs in the 90s to near 105. Moisture moving
into the region from the south may generate a few thunderstorms late
this afternoon and evening over the southern portion of the
district...mainly 610 611 640 and 642. Thunderstorm coverage could
be a little further north Sunday...possibly up the Oregon Cascades.
An upper level trough moving into the Pacific northwest Monday will
start a cooling trend which will continue into middle week. Humidities
will begin to rise. Westerly winds will increase some Monday as the
trough moves into the area.
Previous aviation discussion...18z tafs...VFR conditions are
expected at all taf sites except kpsc through the period. There is
an area of low level smoke moving south at about 10 miles per hour which may
affect kpsc beginning around 01/18z. This smoke layer could reduce
visible/ceilings into the MVFR category for a time late this morning and
into the early afternoon. Once the inversion breaks the smoke should
begin to mix out and lift into a haze or smoke aloft layer...right
now the best estimate for this to happen is near 01/20z. At the
remaining taf sites expect just a few or scattered high clouds between 15-
25k feet above ground level with diurnal and terrain driven winds at or below 15kts. However
at kbdn there is also the possibility for a few vcsh late this
afternoon and early evening... very similar to yesterday afternoon.
Preliminary point temps/pops...
PDT 64 101 69 96 / 0 10 10 20
alw 70 102 73 95 / 0 10 10 20
psc 62 104 69 98 / 0 0 10 20
ykm 64 100 68 94 / 0 0 0 20
hri 62 103 69 96 / 0 0 10 20
eln 62 101 65 94 / 0 0 0 20
rdm 57 98 59 88 / 10 20 20 30
lgd 55 99 55 90 / 10 10 10 20
gcd 56 101 60 92 / 10 10 20 30
dls 66 101 71 96 / 0 10 20 20
or...red flag warning until 10 PM PDT this evening for orz639-640-642.
Heat advisory until 9 PM PDT Sunday for orz041-044-507.
Washington...red flag warning until 10 PM PDT this evening for waz639-641-643.
Heat advisory until 9 PM PDT Sunday for waz024-027>029.
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