National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS66 KPDT 162304
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
404 PM PDT Tue Apr 16 2024

Updated Aviation Discussion

.AVIATION...00z TAFs...VFR conditions expected. Breezy winds will
decrease this evening, and with a drier, colder airmass moving
in, clearing will take place across all sites through the
overnight hours. By tomorrow, winds will be light less than 12
kts, primarily out of the NW/N, with mostly clear skies. Evans/74

&&

.PREV DISCUSSION... /issued 303 PM PDT Tue Apr 16 2024/

SHORT TERM...Today through Thursday Night...

Key Messages:

1. Breezy conditions through this evening.

2. Cold temperatures tonight into Wednesday morning.

Current radar and visible satellite imagery showing spotty, light
returns across the Snoqualmie Pass area and along the west slopes of
the Cascades as ribbons of high level cirrus clouds pass through
Central Oregon, with mid-level clouds present through the northern
Blue Mountains and foothills. This is in response to the upper level
trough continuing to drop through Washington and into northeastern
Oregon later tonight. This synoptic feature has attributed to
tightening pressure gradients along the Cascades and northwest flow
aloft to provide breezy conditions through the Kittitas Valley.
Pressure gradients from Seattle to Pasco are currently 4.2 mb as
gusts of 32 mph are occurring at Ellensburg.
While the NAM is initializing the best, the RAP, SREF, and the GFS
all show continued gradient tightening through 4 PM before slowly
slackening through the remainder of the evening. The NAM is
advertising a 1.7 mb increase in the pressure gradient between
Seattle and Pasco from now until 4 PM, and keeping it above 5 mb
until 8 PM. These values correlate to wind gusts between 40-50 mph
as the peak nears 6 mb around 4PM - indicative of gusts near 50 mph.
The tight gradient along the Cascades has also brought breezy
conditions along the Eastern Gorge and the northern Blue Mountain
foothills of Oregon, but gusts are expected to stay sub-advisory and
between 30-40 mph. Confidence in these wind gusts is moderate to
high (70-80%) as guidance is in agreement on gradient enhancement,
and the NBM showcases a 61% chance of Ellensburg experiencing
gusts of 47 mph or greater before 8 PM.

Clouds will slowly clear west to east across the region this
evening as northwest flow aloft continues to pipe in colder air.
These clear skies will allow effective radiational cooling to
occur, which will drop temperatures quickly. However, the areas
that are expected to clear out the fastest, the Yakima/Kittitas
Valleys and the Eastern Gorge, will still exhibit breezy winds as
the pressure gradients slowly slacken. This will keep the lower
levels of the atmosphere mixed, slowing down the efficiency of
cooling. Broken mid-to high level clouds have been lingering
across the northern Blue Mountain and foothills through the day
today, which is expected to increase this evening and overnight as
the incoming trough`s axis drops into eastern Wallowa county.
This should keep mid-level clouds present across the northern
Blue foothills which will inhibit effective radiational cooling.
Both of the above mentioned processes should keep temperatures
above freezing over these areas, with the exception of protected
areas over the Yakima and Kittitas Valleys - where winds will have
a tough time mixing to lower levels. Confidence in these areas
not experiencing widespread freezing temperatures is moderate to
high (60-80%), as the HREF advertises a 20% and 0% chance of
temperatures of 32 or less at Ellensburg and Yakima respectively.
However, the NBM does hint at slightly better chances of
temperatures reaching 32 degrees or less Wednesday morning, with a
65% and 44% chance for Ellensburg and Yakima respectively. The
primary reason for these varying probabilities relates to winds,
in that the HREF has initialized better in terms of wind speeds
and gusts than the NBM, which has trended lower than what has been
observed through the day. This means that the NBM suggests mixing
will not be as efficient, leading to more enhanced radiational
cooling and overall cooler temperatures expected - which is why
the HREF probabilities are preferred.

Dry conditions continue through the remainder of the period as the
upper level trough broadens over the northern CONUS and a weak
upper level ridge nears the coast late Thursday. Temperatures will
slowly warm through Thursday, with highs bumping up 2 to 6
degrees Tuesday to Wednesday and another 3 to 7 degrees Wednesday
to Thursday. This warming trend will eventually bring highs into
the low to mid-60s across the Basin on Thursday, which is near
average values for this time of year. Morning low temperatures
will continue to stay 2 to 6 degrees below normal as clear skies
Wednesday and Thursday will keep efficient overnight cooling
occurring with morning temperatures staying in the low to mid-30s
through the Basin. 75

LONG TERM...Friday through Tuesday...Models in fair agreement
through the period. However, they do differ in their timing of an
upper level ridge moving through the area early in the period. By
early next week, general southwest to west flow is expected to
develop as an upper trough/low spins over the Gulf of Alaska.
Overall, ECMWF ensemble mean is drier and warmer for next week while
the GFS ensemble mean is a little wetter and cooler.

A weak shortwave behind the exiting ridge should spread some light
precipitation over the Washington Cascades Saturday into early
Sunday. There is a moderate chance (40-50%) we`ll see 24 hour QPF
totals of 0.10 inch along the crest, but these values drop off
quickly from west to east. Another weak shortwave is expected to
move through the general southwest flow producing some showers over
our northeast mountains and cascades Monday afternoon/evening and
possibly again Tuesday afternoon/evening. However, the signal is
pretty weak (15-20%) at this time. Overall, most locations will
remain dry.

Daytime highs are expected to remain near to above normal through
the period. Earle/81

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  32  56  32  61 /  10   0   0   0
ALW  36  58  36  64 /  10   0   0   0
PSC  38  63  37  66 /  10   0   0   0
YKM  32  61  34  64 /   0   0   0   0
HRI  34  62  34  66 /  10   0   0   0
ELN  33  58  33  61 /   0   0   0   0
RDM  24  53  26  61 /   0   0   0   0
LGD  29  51  28  58 /  10  10   0   0
GCD  28  52  28  60 /   0   0   0   0
DLS  37  62  38  66 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Wind Advisory until 8 PM PDT this evening for WAZ026.

&&

$$

SHORT TERM...75
LONG TERM....81
AVIATION...74