Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 251730 AAA
AFDPDT

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
1030 AM PDT Sun Jun 25 2017

Updated AVIATION Discussion

.SHORT TERM...Today through Monday night...Have raised today`s
temperatures 1-3 degrees north of a line from Madras to Pendleton
to Dayton based upon 0zSun-0zMon temperature increase in the
HRRR/NAM models in the lower and mid levels. Many sites likely to
set daily record. Watching a band of moisture moving slowly north
at about 15 mph over northern CA just about to enter southwest
OR. There were thunderstorms with this band on Saturday and
overnight. Current speed would put this band of moisture into
southwest Deschutes County in late afternoon/early evening. So
current forecast of isolated thunderstorms along east slopes of
Oregon Cascades and central Oregon after 5 pm looks good. As ridge
moves east and upper level trof enters the area on Monday,
chances for thunderstorms will spread to the east and temperatures
will retreat 5 to 10 degrees due to extra clouds and cooling
aloft. There will also be a push of marine area beginning in areas
near the Cascades.

&&

.AVIATION...18Z TAFs...VFR conditions will prevail through the next
24 hours, though there may be cumulus buildups this afternoon over
the mountains and in Central Oregon. Tonight there will be
increasing mid and high clouds ahead of a trough moving NE and
approaching the northern California coast. Winds will be light and
generally less than 10 kts. Polan

.FIRE WEATHER...Hot and dry conditions will prevail today, with highs
100 or higher expected across the lower elevations, along with
minimum RH`s of 8-15 percent. With a high Haines index of 6 across
much of the area today, will continue the Red Flag Warning for the
lower elevations. Isolated thunderstorms will likely develop across
Central Oregon this evening, but with coverage limited and RH`s
increasing by the time any convection does develop, a significant
fire weather threat is unlikely. On Monday, scattered thunderstorms
will develop in Central Oregon and across the Oregon mountains in
the afternoon. Abundant lightning combined with outflow winds from
storms may create rapidly spreading wildfires. A Fire Weather Watch
remains in effect from Monday afternoon through Monday evening for
Oregon fire weather zones 640 and 644. Additionally, breezy winds
with continued low humidity expected on Monday and Tuesday
afternoons, though the humidity will be a few percent higher than
this weekend, may create fire weather concerns as well. Confidence
is not there at this time for a watch and models today have trended
lighter with winds, so will opt to keep an eye on that situation for
now.

&&

.PREVIOUS DISCUSSION... /issued 252 AM PDT Sun Jun 25 2017/

SHORT TERM...Today through Monday night...An upper level ridge over
the Pacific Northwest will shift slowly east today as an upper low,
currently near 34N/134W, pushes towards the region. Will still see a
hot and dry day today with a few locations possibly nearing record
high temps. The approaching upper low and eastward shifting upper
ridge will cause the flow aloft to become increasingly southerly
today. As such, will see a gradual increase of mid and high level
moisture into central Oregon late today and this evening. This
moisture is expected to interact with instability induced by daytime
heating, causing the development of stray, high based showers or
thunderstorms over central Oregon this evening. A few high based
showers and possibly a thunderstorm or two look to linger through
the overnight hours from south-central Washington south to central
Oregon. On Monday, these isolated high based showers or storms
should spread over a larger portion of the area during the morning.
The weakening upper low will push through the region Monday
afternoon and evening. The energy and increased moisture associated
with this system will cause isolated to scattered showers and
thunderstorms over a good portion of the area during this time
frame. Shear will be relatively strong from central Oregon to
northeast Oregon, and strong wind gusts will be possible from
thunderstorms. SPC has a marginal risk of severe thunderstorms
indicated for portions of the area Monday. High temps Monday will be
a bit cooler due to increased cloud cover. Areas in the lee of the
Cascades will see further cooling due to an increasing intrusion of
marine air Monday afternoon. Winds will be breezy in the Gorge
Monday, with these winds working into the Columbia Basin late in the
day and the evening. 90

LONG TERM...Tuesday through Sunday...High pressure aloft will
dominate the weather in the extended period. There will be breezy to
windy conditions over a good portion of the forecast area on Tuesday
behind a departing upper trough and weather system. After Tuesday
high pressure will rebuild back over the region with another warming
trend...though it will be slow. Winds through this period will be
generally light (Wednesday through Sunday). Temperatures will start
out in he mid 70s to mid 80s in the lower elevations on Tuesday and
will gradually warm to the mid 80s to around 90 by Sunday. It will
be dry and stable through the extended period. 88

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT 102  64  93  59 /   0   0  20  30
ALW 103  69  94  64 /   0   0  20  30
PSC 103  66  97  62 /   0   0  20  20
YKM 103  67  97  59 /   0  10  10  10
HRI 104  66  96  60 /   0   0  20  20
ELN 103  64  91  56 /   0  10  10  10
RDM  99  58  88  48 /   0  20  40  10
LGD  96  56  92  56 /   0  10  20  50
GCD  99  62  93  55 /   0  10  50  50
DLS 104  68  89  61 /   0  20  20   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Monday morning through Monday evening
     for ORZ640-644.

     Red Flag Warning until 11 PM PDT this evening for ORZ640-641.

WA...Red Flag Warning until 11 PM PDT this evening for WAZ641-675.

&&

$$

79/99/90/88



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