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fxus66 kpdt 260505 aaa 

Area forecast discussion
National Weather Service Pendleton or
1005 PM PDT Tue Jul 25 2017

Updated to end the red flag warnings tonight for fire zones orz611
and orz642

Update...the thunderstorms that developed this past afternoon and
early evening along the southern border of the County Warning Area and in fire
weather zones 611 and 642 have dissipated with only a few isolated
storms remaining, mainly south of John Day. Therefore the red flag
warning has ended for those zones. Otherwise it will continue to be
a quiet evening across the forecast area with just some mid and high
clouds...less as you go north in the County Warning Area. On Wednesday expect
similar conditions except that the penetration northward of moisture
and instability in a southwest flow aloft will be greater. A Fire
Weather Watch will remain in effect for Wednesday in many of the
fire weather zones (see fire weather discussion below for more
details). It will continue to be very warm to hot for the remainder
of the week into the weekend with maximum temperatures possibly
reaching the century mark by late in the weekend. In the mean time
Thursday through Saturday will be dry and more stable. 88


Aviation...06z tafs...VFR conditions will prevail at all taf sites
for the next 24 hours. There may be some thunderstorms in the
vicinity of krdm and kbdn Wednesday afternoon and evening but
ceilings and visibility will remain above VFR minimums. Winds will
be light and under 15 kts except possibly gusty and erratic near
thunderstorms across the southern areas affecting mainly just krdm
and kbdn Wednesday afternoon and evening. Also it will become breezy
in the eastern Columbia Gorge Wednesday evening with wind speeds
from 15 to 25 kts from the west to northwest. 88


Previous discussion... /issued 436 PM PDT Tue Jul 25 2017/

Short term...tonight through Friday...the upper low continues
pumping moisture north into southern Oregon. Another round of
isolated thunderstorms will occur in the southern portion of
Deschutes, Crook, and Grant counties this evening. All models show
the slow moving upper level low near the northern California coast
transitioning to an open wave on Wednesday and moving northeast
across southeast and east central Oregon Wednesday night and
Thursday. As this happens, the chance for thunderstorms will
increase and move north and east into the Blue Mountains and
Wallowa Mountains. Looking at a Fire Weather Watch for mountain
areas south of the Columbia Basin. See fire weather discussion for
additional details. Nearly all of Washington and the Columbia
River counties of Oregon will remain hot and dry. As the wave
moves east, a more westerly flow will bring a drier pattern to
Oregon. This westerly flow will produce gusty winds in the
Columbia Gorge and Kittitas Valley areas Thursday afternoon. This
westerly flow will also drop temperatures slightly on Thursday and
Friday compared to Wednesday.

Long term...Friday night through Tuesday...models in fair agreement
with the overall pattern. However, they differ in position of upper
level high which affects the flow over the Pacific northwest. The
GFS ensemble members show a general ridge over the area with
predominant southwest flow as they keep the high farther south. The
European model (ecmwf) shows southwest flow early in the period becoming more
westerly as the upper ridge builds over central Nevada. At this
time, will lean towards the drier European model (ecmwf) solution as it handled the
current pattern better. With limited low level moisture, the weather
should remain dry and hot through the period. However, there could
be some afternoon buildups over central Oregon and the elkhorns each
late afternoon and early evening, but not expecting them to develop
beyond towering cumulus. Daytime highs will be well above
normal. Earle

Aviation...00z tafs...VFR conditions will continue for the next
24 hours. Isolated thunderstorms may approach central Oregon this
evening, but they are not expected to impact any taf sites.
Thunderstorms will become more widespread Wednesday in central
Oregon, but will leave mention out of krdm and kbdn at this time.
Winds will generally remain 10 kts or less...except kdls 10-15 kts
Wednesday afternoon. Earle

Fire weather...the thunderstorms that developed this past afternoon
and early evening along the southern border of the County Warning Area and in fire
weather zones 611 and 642 have dissipated with only a few isolated
storms remaining, mainly south of John Day. Therefore the red flag
warning has ended for those zones.

Fire weather watches remain in effect for the fire zones across
central and northeast Oregon (or610, or611, or640, or642, or643,
or644 and or645) for thunderstorms producing abundant lightning
Wednesday afternoon and Wednesday night. Confidence is high that
there will be scattered thunderstorms across central and northeast
Oregon, but the uncertainty lies on where the cluster of lightning
strikes will occur. The track of a wave associated with a low
pressure trough over northern California, that gets absorbed in the
southwest flow, is questionable and decisions on what to do with the
watches will be made early Wednesday morning. Due to the high
precipitable water values on Wednesday (approx. 1 inch), believe
some storms could bring a 0.25 inch...possibly 0.5 inch of rain...
that will occur underneath the core of the storms. Despite the
possibility of wetting rains, there will also be abundant lightning.

A weak marine surge on Thursday will cause winds to increase in the
eastern Columbia River gorge, the Kittitas Valley and over portions
of the lower Columbia Basin. The wind and relative humidity threat is marginal and
fire weather highlights may be needed if the marine surge is
stronger than currently advertised by the models.


Preliminary point temps/pops...
PDT 63 96 64 95 / 0 0 10 10
alw 68 98 69 97 / 0 0 0 10
psc 61 99 64 98 / 0 0 0 0
ykm 65 99 65 96 / 0 0 0 0
hri 64 98 66 97 / 0 0 0 0
eln 61 96 63 91 / 0 0 0 0
rdm 57 93 55 92 / 10 30 20 0
lgd 55 94 57 93 / 0 20 20 10
gcd 61 94 60 94 / 10 30 20 10
dls 67 95 66 90 / 0 0 0 0


PDT watches/warnings/advisories...
or...Fire Weather Watch from Wednesday afternoon through late
Wednesday night for orz610-611-640-642>645.



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