Wildfire in Washington, July 30 to 31, 2018

Area Forecast Discussion
National Weather Service Pendleton OR
842 AM PDT Mon Jul 30 2018

.SHORT TERM...Visible satellite imagery shows mid level flow has
become more southerly and smoke from southern Oregon fires is
overspreading the forecast area today. Most of this will be an
elevated layer however central Oregon could have some low
elevation smoke at times. Otherwise strong high pressure over the
region with hot dry conditions. Increasing heights with the
building ridge will result in high temperatures about 2-5 degrees
above yesterday. This will produce highs 95-110 for much of the
area. Models continue to show a cooling trend starting Wed as an
upper level trough moves across the Pacific northwest. 94

&&

.PREV DISCUSSION... /issued 232 AM PDT Mon Jul 30 2018/

SHORT TERM...High pressure continues to dominate the areas
weather with hot temperatures and this will continue into Tuesday.
Afternoon high temperatures are expected to soar above the
century mark and today could be the hottest day of the year
eclipsing some record high temps. The hot temps has prompted an
excessive heat warning into Tuesday. In addition to the heat...dry
conditions should prevail and the only relief could occur
tomorrow. The high pressure drifts slightly east allowing an upper
level low pressure system to inch closer to the coast of wa/or.
This could usher some moisture into the region and combining the
moisture with daytime heating may produce isold tsra along the
wa/or crest and into central oregon towards the blue mountains.
Otherwise the ridge of high pressure weakens some on Wednesday and
slightly cooler temps are expected but afternoon high
temperatures will remain above normal into midweek.

LONG TERM...Wednesday night through Sunday...GFS/ECMWF/NAM differ
on how to handle marginal moisture/instability Wednesday evening
across mainly the eastern mountains. GFS remains the most
aggressive, with sufficient mid level moisture/instability for
perhaps even scattered thunderstorms for the far eastern OR
mountains. NAM/ECMWF have less instability and much less mid level
moisture, keeping all areas dry. Given the differences, will not
change the ongoing forecast much, with a slight chance of showers
and thunderstorms Wednesday evening from the John Day highlands
eastward. Given the very hot and dry conditions recently, any cloud
to ground lightning strikes may spark additional fires. In addition,
breezy winds and low RHs across the Columbia Basin/Gorge may pose
additional fire weather concerns. For Thursday through Saturday,
with the upper ridge to the southeast of the area and a weak trough
to the northwest, mainly dry westerly flow will prevail. Breezy to
locally windy conditions for the Columbia Gorge/Basin Thursday
afternoon/evening along with low RHs may result in fire weather
concerns. GFS does generate some weak instability along the Cascade
crest on Saturday, but with little in the way of deep layer
moisture, do not expect any precip with mainly afternoon cumulus
buildups. Medium range models generally agree Sunday building the
ridge northward east of the region, with the flow aloft becoming
more to the southwest, but still think most significant moisture
will remain to the north and east of the area, so will keep
conditions dry. With westerly flow and more marine influenced air,
expect temperatures within a couple degrees of normal, giving relief
from the recent excessive heat.

AVIATION...12Z TAFs...VFR conditions will prevail for the next 24
hours. Visibilities may be locally reduced due to smoke and haze
from wildfires across the region, but expect conditions to remain
VFR. Light winds this morning will increase to 7-12 KT this
afternoon/evening, with a few gusts to 20 KT, diminishing
overnight.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT 105  68 105  69 /   0   0  10  10
ALW 105  65 105  69 /   0   0   0  10
PSC 106  63 105  68 /   0   0   0   0
YKM 105  66 104  67 /   0   0  10  20
HRI 108  65 107  70 /   0   0   0  10
ELN 105  64 102  65 /   0   0  10  20
RDM 103  61  99  57 /   0  10  20  10
LGD 101  59 102  62 /   0   0  20  20
GCD 102  62 102  64 /   0   0  20  20
DLS 108  69 101  68 /   0   0  10  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning until 11 PM PDT Tuesday for ORZ041-044-
     507-508-510.

     Heat Advisory until 11 PM PDT Tuesday for ORZ049-050-502-503-505-
     506-509-511.

WA...Excessive Heat Warning until 11 PM PDT Tuesday for WAZ024-
     026>029-521.

     Heat Advisory until 11 PM PDT Tuesday for WAZ030-520.

&&

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