Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Spokane Washington
446 PM PDT Tuesday Mar 31 2015

Synopsis...
an unsettled and ocassionally showery Spring-like weather pattern
will continue through the week and into the weekend. Widespread
freezing temperatures are possible Thursday and Friday morning.
Then anticipate more seasonal temperatures by early next week.

&&

Discussion...
tonight and tomorrow: a Cool Spring-like upper-level trof will
continue to slide into the region this evening and remain in
place through tomorrow. 500mb temperatures within the core of the
trof are on the order of -30c or cooler which is leading to
steepening lapse rates and potential for showers. Winds this
afternoon are helping to bring drier air in the Lee of the
Cascades and basin which will keep a bulk of the shower activity
focusing on the mountains and adjoining outer reaches of the
basin. So far there has not been a lightning strike in Washington/Idaho (just
across the border in bc) but convection continues to increase and
a few strikes are a strong possibility with the best chances in
the northern and eastern mountains. A Puget Sound convergence zone
has become established and per the hrrr, should continue through
much of this evening into tonight. Depending on where this narrow
bands swings north and south, it looks promising for some snow
accumulations to impact Stevens Pass and possible east into
locations like plain, Coles Corner, and perhaps Leavenworth.
Another feature we are closely monitoring is a second midlevel
circulation or vort Max near 130w. Earlier model runs brought this
feature near the Washington/or border then through The Blues...Palouse
/l-c valley...and into the central Panhandle...but satellite
trends and latest RUC suggest this feature will take a southward
track through Oregon.

Temperatures will be cool overnight with several locations within
the northern valleys dipping below the freezing mark. This includes
locations like Winthrop, Omak, Republic, Deer Park, Ione, and
Priest Lake. Communities along and north of I-90 within the Idaho
Panhandle could also be close to freezing for a short period of
time Wednesday morning but confidence is lower with the potential
for cloud cover.

Following a few hours of warming Wednesday, look for widely scattered
showers to Blossom across a majority of the region. The highest
concentration of activity will focus along and east of a line from
Republic to Pullman but any number of midlevel disturbances coming
across the Cascades could lead to clusters of activity. The
atmosphere will be cooler compared to Tuesday and most shower
activity will fall as a combination of rain and snow pellets. This
lowers the threat for thunder as the thermal characteristics
within the cloud will not be as favorable for charge separation.
There is a small chance for lightning but should be less than
Tuesday...which has yet to materialize. Winds will become low-end
breezy Wednesday but several magnitudes lower than Tuesday. High
temperatures will only warm into the 50s...coming in near to just
shy of typical values for April 1st. /Sb

Wednesday night through Friday night...a typical active Spring
weather pattern will continue for the rest of the work week.
Latest models are in decent agreement in depicting the slow exit
of the current upper level trough through Thursday before a short
wave ridge builds in for an ill defined/less showery break period
Thursday night and Friday followed by the arrival of the next cold
front Friday night.

Thursday will feature slightly cooler than normal high and low
temperatures...probable sunbreaks over much of the area but also
a continuing chance of scattered hit-and-miss showers east of a
line from Omak to Walla Walla with a stray short lived garden
variety Spring thunderstorm thrown into the mix in the northeast
mountains and Idaho Panhandle.

The main threat during this period will be the possibility of
freezing temperatures Thursday morning and again on Friday morning
over most of the region. The lowest elevation locations of
Wenatchee...Moses Lake and the l-c valley will also be at risk for
freezing and ordinarily this early in the year freezes are not
uncommon...however the unusual warmth of the past month has
stimulated some anomalously early budding and blooming in some of
these areas. As the forecast for Thursday morning's low
temperatures is refined on subsequent shifts an early season
freeze warning may be necessary for these low elevation
locations.

Friday will feature the approach of the next trough and while the
cold front will hold off until Friday evening...a weak mid level
warm front is suggested by the models setting up over the
northeastern zones and Panhandle during the day Friday. Not much
actual precipitation is expected but mid level and high clouds
will increase during the day with mid-range chances of light rain
mainly over the north. The actual cold front will pass through
Friday night with a better chance of valley rain and mountain
snow...with breezier conditions behind the front promoting warmer
overnight lows by dawn Saturday. /Fugazzi

Saturday through tuesday: an upper level trough will be main
weather feature for the weekend and into early next week. Both
the GFS and ecwmf are very similar on handling this feature as it
sinks south from the Gulf of Alaska south to the Washington coast
Saturday and Sunday, and then weakens and opens up as it swings
inland for Monday. Broad troughiness lingers into Tuesday. This
will keep temperatures near seasonal normals and showery
conditions through this period. Made some slight chances to the
sensible weather of the forecast. The progress of the upper level
low seems slower than seen yesterday, which would yield to a
slower evolution of the shower development and a slower cool down
of the temperatures. Most showers will be diurnally driven,
peaking in the afternoon and evening hours on Saturday. As the low
digs south, the main brunt of the shower activity shifts south for
Sunday, highlighting the southern Cascades and the Blue Mountains.
Then Monday and into Tuesday, the convection returns to the
diurnal trends concentrating in the mountains. Snow levels will
waffle from the valley floors at night and into the mountains
during the day, so precipitation will switch to snow at night with
minor accumulations possible, to a rain/snow/graupel mix during
the afternoon hours. What this equates to is typically Spring like
weather for the inland northwest. /Rfox.

&&

Aviation...
00z tafs: a cold upper level trof will promote scattered showers
and a slight chance of a thunderstorm mainly this evening and
again Wednesday aft/eve during peak daytime heating. Convection this
evening are expected to be confined mainly in the mountains due to
strong downslope flow off the Cascades. The best chance for an
isolated thunderstorm will be near the Canadian border around
Metaline Falls and Bonners Ferry. Windy conditions will subside
this evening around 02-04z as pressure gradients decrease and
mixing potential decreases. Several type of precipitation are
possible with these showers this evening as well as Wednesday
afternoon...including rain...snow...small hail...and graupel. Jw

&&

Preliminary point temps/pops...
Spokane 33 51 29 52 31 54 / 10 50 20 20 20 20
Coeur D'Alene 31 51 28 50 30 54 / 10 60 30 30 30 20
Pullman 34 49 30 49 32 54 / 20 40 30 20 10 10
Lewiston 37 55 33 54 34 59 / 30 40 20 20 10 10
Colville 33 55 29 55 31 55 / 30 40 20 20 10 30
Sandpoint 31 51 27 50 28 52 / 30 60 20 40 30 40
Kellogg 31 45 29 45 31 50 / 30 60 50 50 30 20
Moses Lake 37 60 30 59 31 59 / 10 20 0 0 10 10
Wenatchee 38 58 34 59 37 58 / 20 20 0 10 10 20
Omak 32 57 30 59 32 58 / 10 30 10 10 10 30

&&

Otx watches/warnings/advisories...
Idaho...none.
Washington...none.
&&

$$

National Weather Service Glossary of Abbreviations