Hail in Oregon, July 21, 2024

Area Forecast Discussion
National Weather Service Pendleton OR
230 PM PDT Sun Jul 21 2024

.SHORT TERM...Tonight through Tuesday...An upper level ridge over
the region continues to bring hot temperatures across the forecast
area this afternoon. However, smoke form area wildfires and cloud
cover associated with a passing system has certainly reduced the
heating potential this afternoon, resulting in many locations
a few degrees cooler than expected. Meanwhile, an upper level
trough associated with a low in the Gulf of Alaska is beginning to
push towards the PacNW while an upper level shortwave is riding
north along the coastline. The shortwave passage through tonight
will continue to aid in the development of scattered showers
with isolated thunderstorms across the Cascade east slopes,
central OR, and the eastern mountains. While winds have already
picked up through the Gorge, the gradual approach of the upper
trough offshore will trigger a marine push that will result in
breezy winds developing through the Cascade gaps into the Columbia
Basin this evening.

Monday, the upper ridge will push east into the Northern Rockies
while the upper trough offshore begins moving into the PacNW. this
will reinforce the marine push, resulting in cooler temperatures
across central OR and through the Cascade gaps, as well as higher
RHs across much of the forecast area. However, the combination of
the marine push and the tightening of the cross Cascade pressure
gradient will result in breezy to locally gusty conditions through
the Gorge, Simcoe Highlands, and the Kittitas valley, with
winds generally 20-30mph and gusts 35-45mph. Portions of the
Columbia Basin will also see breezy winds develop in the
afternoon, with winds 15-25mph and gusts up to 40mph. Elevated
instability and lingering shortwave energy aloft will also bring
isolated thunderstorm chances across the eastern mountains Monday
afternoon in the early evening.

By Tuesday, the forecast area will mostly be under the influence
of the upper trough, with cooler temperatures across the forecast
area. Winds will have decreased through the Cascade gaps by
Tuesday morning, though locally breezy conditions will redevelop
in the afternoon. Lawhorn/82

.LONG TERM...Wednesday through Sunday...Models in good agreement
through the period with the exception of the position of a weak
cutoff low over northern California Friday and Saturday. A slow
moving upper level low pressure system will consume a large portion
of the extended making its way across central BC.  Although much of
its energy will remain over Canada, there is a small threat for
convection over our eastern mountains late Wednesday
afternoon/evening. At this time, moisture and instability appear
limited so we may not see anything. However, given time of year and
the threat of lightning will continue with low chance PoPs.  The
deterministic models show a weak cutoff low making its way across
northern California Friday into Saturday. They differ greatly in
their position of this feature. The GFS shows it moving into
southeast Oregon Saturday afternoon but weakening while the ECMWF
keeps it south of the Oregon border. If the GFS pans out, we'll need
to add some thunderstorm chances over portions of our eastern
mountains of Oregon Saturday afternoon/evening. At this time,
confidence is low (10-15%) the GFS's solution will be correct with
the position of the weakening low over southeast Oregon.

Breezy afternoon/evening winds are expected over portions of the
Columbia Basin, Columbia River Gorge, and Kittitas Valley Wednesday
and Thursday.

Daytime highs will begin above normal Wednesday, but will be near to
slightly below normal through the rest of the extended. Earle/81

&&

.AVIATION...Previous discussion...18Z TAFS...VFR conditions will
prevail through the period. However, isolated/scattered
thunderstorms are expected to develop this afternoon over central
Oregon and move northeast before dissipating this evening. KRDM and
KBDN may see a storm nearby. Gusty winds can be expected in the
vicinity of these storms. Winds will be 5-15 kts with higher
afternoon/evening gusts, except KDLS 15-25 kts and gusty. Winds will
decrease overnight. Earle/81

&&

.FIRE WEATHER...Red Flag Warnings for hot, dry, and unstable
conditions will continue through this evening across Fire Weather
Zones OR642 and OR644, and Red Flag Warnings for abundant lightning
will continue through this evening for Fire Weather zones OR611
and OR640. A weak shortwave moving along the coast will continue
to support the development of isolated thunderstorms along the
Cascade east slopes, portions of the eastern mountains, and
central OR through this evening. The shortwave will also produce
unstable conditions over eastern Grant, southern Umatilla, and
Union/Wallowa counties through this evening. Elevated fire weather
concerns remain tomorrow with another round of isolated
thunderstorms over the Blues and Wallowas, increased winds through
the Cascade gaps, and unstable conditions over the eastern
mountains.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  64  96  56  91 /  10  10   0   0
ALW  69 100  61  95 /  10  10   0   0
PSC  70 100  61  95 /  10   0   0   0
YKM  68  99  58  93 /  20   0   0   0
HRI  68  98  59  95 /  10   0   0   0
ELN  65  92  57  91 /  10   0   0   0
RDM  57  92  48  93 /  20  10   0   0
LGD  63 100  57  95 /  10  20  20   0
GCD  63 102  57  99 /  30  20  20   0
DLS  65  86  58  93 /  20   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning until 10 PM PDT Monday for ORZ041-044-049-
     050-502-503-505-507-508.

     Red Flag Warning until 11 PM PDT this evening for ORZ642-644.

     Heat Advisory until 8 PM PDT Monday for ORZ506-510-511.

     Red Flag Warning until 10 PM PDT this evening for ORZ611-640.

WA...Excessive Heat Warning until 10 PM PDT Monday for WAZ024-026>030-
     521.

     Heat Advisory until 8 PM PDT Monday for WAZ523.

&&

SHORT TERM...82
LONG TERM....81
AVIATION...81