478
FXUS66 KOTX 191210
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
510 AM PDT Sun May 19 2024

.SYNOPSIS...
Cool and unsettled weather will continue through the weekend.
Patchy frost, especially in the northern mountain valleys, will
again be possible by early this morning. A brief break between
weather systems Monday into Tuesday. Then a wet low pressure
system is expected Late Tuesday night and Wednesday, lingering
Thursday. The series of cold upper level low pressure systems
through the week will keep temperatures below normal.

&&

.DISCUSSION...

Today: A cold, unstable upper low pressure system continues over
the Inland northwest. Instability continued to and center trough
to drive showers overnight from Deer Park-Sandpoint into the
central Idaho Panhandle. This area of showers will continue to
move east into the early morning hours.

Showers will once again develop late morning into afternoon.
Latest convective models suggest a better chance of thunderstorms
with 300-500 Joules of Cape as the airmass destabilizes rapidly
under a mid-May sun and cold temperatures aloft. Thunderstorms
will have a general northwest to southeast drift into the late
afternoon hours on the east Washington side. A few strikes of
lightning, and brief, heavy showers can be expected so be on the
lookout for darkening skies this afternoon for passing
thunderstorm showers.

Sunday night: Once the evening shower activity dies down weak
high pressure builds into the region. We would expect clearing
skies from the west with lingering clouds in the Idaho Panhandle.
There`s some indication at least the northern mountain valleys of
northeast WA could see some patchy frost early Sunday morning for
2 to 3 hours until the sun comes up. These cool temperatures
around 36 have a roughly 25% chance of reaching typically colder
pockets as far south as Davenport, Cheney and even Pullman, WA if
the clouds clear out sufficiently. The other wildcard is some
valleys will see some patchy fog to help moderate temperatures. It
doesn`t hurt to be covering plants until we can get out of this
cold airmass pattern or get some cloud cover in here like we will
Monday night.

Monday into Monday night: Overall these will be drier days except
for a 20 percent chance of mountain showers in the Idaho
Panhandle. Expect temperatures solidly in the 60 to middle 70s in
the Central Basin, Wenatchee and Omak areas. With high clouds
building in low temperatures late Monday night are expected to be
40 degrees and above in all if not most lower elevation locations. /TC

Tuesday to Saturday: Much of the Inland NW will turn wetter as we
head into the middle of the week as a strong low pressure system
move into the region. This is followed by a decrease to more
scattered showers toward the end of the work week, before another
system moves in toward Friday night and Saturday. This latter
system currently looks similar to the midweek system in terms of
trajectory, but there are some disagreement and it does not look
quiet as wet.

First in the 24-hour period between 12Z Tuesday and 12Z Wednesday
the center of a deep low pressure drops from northern British
Columbia to northwest Washington (somewhere near Puget Sound to
the Olympic National Park). The leading warm front gradually
pivots into the region through Tuesday. Shower chances come to the
Cascades in the morning, starting to increase over central and
northeast WA and the ID Panhandle through the afternoon. It is
Tuesday night into Wednesday when the low drops in and moisture
deepens, tapping a a PWAT fetch of around 0.60 to 0.80 inches (or
120-150% of normal), that the steadier precipitation expands. The
potential starts to increase in the evening, but really ramps up
overnight into Wednesday morning over much of northern and eastern
WA and the ID Panhandle, persisting near the Cascade crest too.
The lower lee of the Cascades and deeper basin will see more
limited rain chances. Heading into Wednesday afternoon the center
of the low moves from northwest WA to northeast Oregon; then
between Wednesday night into late Thursday morning it tracks
toward the Yellowstone area near the MT/ID/WY border. Moisture
wrapping into the low will continue to provide modest
precipitation chances, though the focus starts shift toward the ID
Panhandle and southeast WA as we progress into Wednesday night
into Thursday morning.

* Rain amounts: This system will bring a good chance of moderate
  to heavy precipitation to some of the area. Ensembles show the
  24-hour probabilities for wetting rain between 70%-100% over all
  but the lower lee of the Cascades and deeper Columbia Basin.
  This latter region includes place like Wenatchee and Moses Lake,
  where the wetting rain potential is around 25-50%. If we bump
  amounts up to 0.25 inches, the probabilities are around 70-90%
  over the Cascade crest, the northern mountains, the east third
  of WA and the ID Panhandle. Amounts of to 0.50 inches have
  probabilities around 60% over the Cascade crest, northeast WA
  and ID Panhandle mountains, but there is even a 20-30% chance
  even over the lower east third of WA. Also the EFI table show
  this to be anomalously wet system and the signal for that has
  only increased in the past couple days. So, yes this system
  appears will bring a good soaking to much of the area (except
  south-central WA, which does not have as high a risk, sorry.)

* Hydrology: With all the rain projected, some main stem rivers
  across far eastern WA and ID show rises heading into the mid to
  later week time frame, but none of them are projected to rise to
  even action stage much less flood stage at this point. However
  some of the smaller creek/streams will need to be monitored
  (Paradise Creek is on the more prominent ones that comes to
  mind, but right now it isnt forecast to reach action stage, but
  it will be monitored. There could be some ponding of water on
  roads and some debris or mudslides, especially in the steeper
  terrain. The main potential for any of this is over north-
  central through eastern WA and the ID Panhandle.

* Snow: I would be amiss if I did not mention the snow risk with
  this system. Yes overall it is tiny. But models are showing
  some snow around the higher mountains. The risk for anything
  measurable is low, but I would not be surprised to see some
  around Stevens or Sherman Pass. The exception is Washington
  Pass/North Cascades Highway Mountain Pass along SR 20; many
  ensemble show the 24-hour potential for 1 inch between 50-60%
  with the 48-hour potential higher. Some guidance, such as the
  ECMWF right now shows 2 inches of more, but 24/48 hour
  probabilities are at around 35% and 45%, respectively. With all
  the said, road temperatures are generally not conducive to much
  accumulation this time of year.

* Thunderstorms, winds, temperatures: There is a limited chance
  for some embedded t-storms, mostly Wednesday afternoon over
  northeast WA and the ID Panhandle, but those chances are only
  around 10-15%. So this will not be a big threat by any means.
  Winds will be a little bit breezy between Tuesday and Wednesday,
  with most models pointing to the lee of the Cascades and central
  WA as having the highest potential with gusts near 20-25 mph.
  Elsewhere gusts near 15-20 mph will be possible. Lastly
  temperatures: Tuesday will be relatively mild with highs in the
  mid-60s to near 70, but Wednesday those milder readings will be
  mostly held to south-central WA as the clouds and rain
  elsewhere which have highs struggling to get out of the 50s, if
  not even the lower 50s.

For Thursday, secondary weak upper impulses drop in from the
north, keeping the potential for showers alive. The highest
chances will be found over the northeast WA and the ID Panhandle
in the afternoon. The overall potential wanes heading into
Thursday night and Friday morning. Then the next low starts to
approach later Friday into Saturday, leading to another increase
in the precipitation potential. Marginally afternoon breeziness
remains each afternoon, particularly over central WA. Temperatures
will be held back on Thursday over the eastern third of WA and
ID, with highs still in the 50s to mid-60s, while upper 60s to low
70s are seen closer to lee of the Cascades. Temperature recover a
little bit Friday into Saturday, but remain below normal. However
at this point I do not see any significant threat of morning lows
being cold enough for frost in this period. That is at least true
outside of the mountains; so if you are heading into the
mountains be aware the could be some low temperatures near
freezing, especially the higher elevations Cascades. /Solveig

&&

.AVIATION...
12Z TAFS: A closed low circulation from KCOE to KPUW will track
east through central ID Panhandle with with local MVFR
conditions and showers near higher terrain. We generally expect
TAF sites to remain VFR but the cirulation itself will enhance
cloud cover this morning. With lingering instability today and
another wave moving south from Canada there will be another
round of scattered showers with a potential for a few
thunderstorms. There looks to be a better chance for
thunderstorms across northeast WA into the far north ID
Panhandle to start around 20Z with a slow migration of cells
southward. Most areas will experience VFR conditions however
passing showers will create short periods of MVFR conditions.
Short burst of wind from approacing showers could gust to 25
mph. Shower activity willdiminish after 02Z.


FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
Showers after 20Z have the best chance of impacting KCOE, KSFF
and KGEG in that order. Confidence is low that showers will
directly impact any one of those TAF sites. TC

-----------------------

Confidence descriptors:
Low - Less than a 30 percent chance
Moderate - 30 to 70 percent chance
High - Greater than a 70 percent chance

For additional probabilistic information for NWS Spokane airports,
please refer to the Aviation Dashboard on our webpage:
https://www.weather.gov/otx/avndashboard

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        62  38  69  43  66  45 /  50  20  10   0  10  80
Coeur d`Alene  57  38  65  41  64  46 /  60  40  20   0  10  90
Pullman        56  36  63  41  63  44 /  30  10  10   0  10  80
Lewiston       64  44  70  46  72  50 /  20  10  20   0  10  70
Colville       63  33  69  38  66  41 /  60  40  20   0  30  80
Sandpoint      55  36  62  40  63  44 /  80  60  50  10  20  80
Kellogg        52  40  60  43  62  47 /  70  50  50  10  20  80
Moses Lake     68  41  75  44  68  45 /  10  10   0   0  10  30
Wenatchee      66  44  73  49  65  48 /  10  10   0   0  20  30
Omak           69  40  75  44  68  45 /  30  20   0   0  30  60

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...None.
&&

$$