Funnel Cloud in Washington, May 16, 2019

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
1056 AM PDT Thu May 16 2019

Updated aviation discussion

.UPDATE...Upper low along the northern California coast will spread
abundant moisture and rain showers northward today and tonight.
Rainfall amounts will likely exceed 1 inch over the Blue and
Wallowa Mountains and could also exceed 1 inch along the east
slopes of the Washington Cascades. Because of this flood watches
are in effect for these and adjacent areas. The potential for
thunderstorms today will be tempered by the already extensive
cloud cover. For now have kept the thunder chances confined to the
northern half of the forecast area but will fine tune if
necessary during the day based on convective trends. 78

&&

.AVIATION...18Z TAFs...Low pressure to our south will send
significant rain showers through the area for much of the next 24
hours. Moderate rain will be possible at times, especially late this
afternoon and evening. Have generally kept ceilings at MVFR levels
but occasional MVFR ceilings and visibilities will be possible with
the heavier rain showers. There is enough instability for a few
thunderstorms over the northern portions of the area this afternoon
so have added TEMPOs for TSRA from 22Z-02Z to KPSC, KYKM, KALW and
KPDT. Do not expect thunderstorms at other TAF sites. Winds will
remain below 12 kts through this afternoon but will begin increasing
after that reaching 10 to 20 kts with gusts to 20 to 30 kts after
06Z. Perry

&&

.PREV DISCUSSION... /issued 245 AM PDT Thu May 16 2019/

SHORT TERM...Today through Saturday...Very wet weather pattern with
the potential for flooding across portions of the forecast area
over the next 24 to 48 hours.

An upper level low pressure system off the coast of California and
Oregon with abundant moisture associated with it will slowly move
inland and impact the forecast area with some heavy rainfall through
Friday night. A surge of moisture working its way north will lift
across the forecast area today and then stall over Washington and
northeast Oregon overnight and into Friday. An eastward flow into
the Washington Cascades could produce one to two inches of rainfall
late today through Friday morning. Meanwhile, precipitation over
northeast Oregon and southeast Washington will continue into Friday
night before tapering late. The potential is there for 1 to 3 inches
of rainfall by Saturday morning. In addition to the prolonged
rainfall, there is the slight chance of slow moving thunderstorms
this afternoon which themselves could produce some locally heavy
rainfall issues. The remnants of the upper level low will be exiting
the forecast area Friday night and Saturday with a temporary ridge
of high pressure build over the region. The next weather system
will set up another low pressure system off the Oregon coast late
Saturday. Southerly flow ahead of it could bring some rain back into
the forecast area Saturday afternoon but for sure Saturday night.

LONG TERM...Saturday night through next Friday...Another deep
closed low will form off the Oregon coast by 00Z Sunday (Saturday
afternoon). This will put a deep southerly flow over the forecast
area with a significant fetch of Pacific moisture with a warm front
into the Pacific Northwest. Thus rain showers will be likely, and
some of the showers could be moderate to heavy. The upper low will
move inland into the Great Basin by late Sunday or Sunday evening.
The overall trough where this upper low will exist will have a
negative tilt to it which will increase upper level diffluence. As
such there may be some significant rainfall amounts during that
period. The main threat will be a rises on small rivers and streams
for possible small stream flooding. There will be some marginal
instability as well, but with the cloud cover am not too confident
for thunderstorms on Sunday and will not include them in the
forecast. Then the low over the Great Basin will move to the
southeast and another upper low will move into the region from the
northwest. This will keep showery and unsettled conditions with cool
temperatures over the forecast area through next week. As the upper
low moves over the forecast area the atmosphere will have steepening
lapse rates. However, am not confident for thunderstorms that far
out due to model to model inconsistency, and will not include them
in the extended forecast for now. It will be occasionally breezy
through the extended period, especially on the ridge tops. 88

HYDROLOGY...Excessive rainfall is possible over Washington and
northeast Oregon over the next 24 to 48 hours with the potential for
flooding. A flood watch has been issued for the Washington Cascades
as well as for the Wallowa and Blue Mountain regions. Small streams
coming out of the mountains will likely rise rapidly over the next
couple of days resulting rises on the large rivers. Those living in
flood prone areas should pay close attention to river levels.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  64  48  59  44 /  90  80  90  10
ALW  69  51  59  46 /  90  90 100  30
PSC  71  55  66  49 /  70  90  90  10
YKM  68  51  64  44 /  80  90  60   0
HRI  68  50  65  45 /  80  80  80  10
ELN  66  49  55  41 /  80  90  70  10
RDM  63  39  60  34 /  60  50  30  10
LGD  62  44  53  39 / 100  90 100  30
GCD  60  43  54  38 /  90  80  80  20
DLS  70  50  64  45 /  70  50  40   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Flood Watch from 2 PM PDT this afternoon through Saturday
     morning for ORZ049-050-502-507.

WA...Flood Watch from 2 PM PDT this afternoon through Saturday
     morning for WAZ029-030.

     Flood Watch from 2 PM PDT this afternoon through late tonight
     for WAZ026-520.

&&

78/91/83