651
FXUS66 KPDT 151140
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
440 AM PDT Mon Jul 15 2024

.Updated Aviation.

.SHORT TERM...Today through Wednesday...A large scale ridge of high
pressure continues over the western USA with a dry westerly flow
across much of the Pacific Northwest. One exception is some monsoon
moisture being pulled up into southern and southeast Oregon by the
combined circulation of the high and a small upper level low off the
central California coast. This will lead to a slight chance of
thunderstorms this afternoon and evening mainly from Burns Oregon
southward. This will keep convection just outside of the forecast
area for today. Otherwise, the forecast area will remain mostly
clear with slightly cooler temperatures as the result of some cooler
marine air that spilled over the Cascades Sunday afternoon and
evening instigating the breezy conditions.

On Tuesday the upper level ridge begins to expand further northward
while the small upper level low off the central California coast
begins to lift northward towards the SW coast of Oregon. This begins
to increase the southerly flow into central Oregon in the afternoon
lifting some of the monsoon moisture back into the forecast area.
Combine this with the increased instability provided by the
approaching system and it will produce some isolated thunderstorms
in the late afternoon and evening across central Oregon. The small
low begins moving into western Oregon Tuesday night and then
continues moving across eastern Washington on Wednesday. The forcing
and elevated instability should be enough to generate a few
nocturnal thunderstorms overnight and into Wednesday morning pushing
northward across the forecast area. By midday Wednesday there could
be some lingering thunderstorm activity over the far northern
portion of the forecast area and the eastern mountains which all
comes to an ending by late afternoon as the system exits to the
north.

The high pressure ridge building northward will begin to increase
temperatures again Tuesday and Wednesday. This will keep the
Heatrisk in the moderate range but the Lower Columbia Basin begins
seeing some Major Heatrisk Tuesday and Wednesday with the possible
need of advisories.


.LONG TERM...Thursday through Monday...Ensemble NWP is in excellent
agreement that an upper-level ridge will remain in place over the
West through at least Sunday, albeit with a shortwave passing to the
northwest on Thursday. Subsequently, ensemble agreement in the 500-
mb pattern loosens by Monday, primarily with regard to a Pacific low
and if/when it tracks onshore into the PacNW. In ensemble cluster
space, ~35% of members support the trough moving onshore while the
remainder keep the ridge in place with the trough deflecting into
British Columbia.

In terms of tangible weather, the region will see continued hot and
dry conditions area-wide coupled with breezy to locally windy
westerly gap winds on Thursday and Monday. Winds will be strongest
if the "troughier" solutions materializes.

Heat is forecast to peak over the weekend with near-ubiquitous
Moderate HeatRisk and widespread Major HeatRisk. In terms of
temperatures, NBM probabilities of afternoon highs reaching or
exceeding 90 degrees for our main population centers remain very
high (>90%) through Sunday, only dropping (55-85% chance) on Monday
given the aforementioned uncertainty in the longwave pattern.
Increasing the threshold to 100 degrees, probabilities drop and
highest confidence (40-85% chance) is over the weekend. Plunkett/86


&&

.AVIATION...12Z TAFS...VFR conditions are forecast through the
period for all TAF sites. Cloud cover will consist of FEW-SCT cirrus
accompanied by some haze/smoke from area wildfires. Wildfire smoke
has intermittently impacted surface VSBYs along the foothills of the
Blue Mountains from K9S9 to KPDT early this morning. By mid-morning,
as current nighttime drainage winds veer more westerly and daytime
mixing increases the boundary layer depth, expecting surface VSBYs
to go back to P6SM with surface smoke from the Lone Rock Fire pushed
to the south and east of TAF sites. Diurnally driven winds will
prevail at all sites, becoming locally gusty this morning through
evening. Plunkett/86


&&

.FIRE WEATHER...Fire weather concerns will continue to be elevated
due to the hot and dry conditions. Haines levels will generally be a
5 which is still sufficient to promote plume dominated fires. There
will continue to be some westerly winds of 5 to 15 mph today
especially during the afternoon through evening hours. There will be
some localized 10 to 20 mph winds along the eat slopes of the
Cascades primarily through the Columbia Gorge and Kittitas Valley.
Isolated thunderstorm potential returns to central Oregon late
Tuesday and then spreads north across the forecast overnight through
Wednesday. At this point LAL of 2 is expected with coverage
remaining isolated.


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  95  58  99  63 /   0   0   0  10
ALW  98  63 101  66 /   0   0   0  10
PSC 100  63 102  68 /   0   0   0   0
YKM  98  63 100  70 /   0   0   0  10
HRI  99  61 102  67 /   0   0   0  10
ELN  96  60 100  66 /   0   0   0  10
RDM  94  55  98  59 /   0   0   0  20
LGD  94  56  97  60 /   0   0   0  10
GCD  95  57  99  63 /   0   0   0  20
DLS  97  61 105  69 /   0   0   0  20

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

SHORT TERM...91
LONG TERM....86
AVIATION...86