Area Forecast Discussion
Issued by NWS Spokane, WA
FXUS66 KOTX 220910
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
210 AM PDT Wed May 22 2013
The Inland Northwest will remain under a broad trough through at
least the middle of next week, with disturbances riding in from
the Pacific. This set up means several opportunities for
precipitation. Temperatures are expected to remain cooler than
normal through the end of this week, before some moderation.
Today and tonight: An upper low will continue take hold of the
West with cooler than normal and occasionally wet conditions.
Early this morning the center of low was situated near Redmond,
Oregon. All guidance tracks it into the Columbia Basin by midday,
before its tracks northwest toward the Puget Sound tonight.
Meanwhile at the surface a deformation axis/trough stretched from
the ID/MT border to northeast WA is projected to edge north and
east. For today these two features will provide a high threat of
showers across the central Cascades, portions of the Wenatchee
through Moses Lake zones, and the central and northern Idaho
Panhandle and northeast Washington mountain.
A flood watch continues for parts of northeast Washington and the
northern Panhandle through this evening (06Z Thursday). The region
received some moderate rainfall amounts Tuesday. With
precipitation continuing to train across this region this morning
and more expected through the day, this will make the region
susceptible to flooding. This is especially in the hillier/steep
terrain, low spots and near smaller streams/creeks.
Elsewhere models suggest a migratory precipitation threat. As the
upper low pivots north showers are expected to expand, first over
the east third and north-central WA this morning and second toward
midday/early afternoon into the Okanogan Valley, Waterville Plateau
and northern Cascades. By tonight the low migrates into the
Cascades and eventually western Washington and the deformation
axis near the Panhandle edges northeast, while drier air comes in
from the southeast. The easterly flow will continue to provide
high precipitation chances into the Cascades and across the
northern mountains, but the threat will begin to wane as the night
progresses. The shower threat elsewhere will be dwindling as drier
air comes in.
Some instability around the center of the low, indicated by High
Level Total Totals around 30-38C and low-grade CAPE around 100-150
J/kg, will provide at least an isolated thunderstorm threat near
the Cascades through the Upper Columbia Basin, as well as in the
vicinity of the Blue Mountains.
Snow levels around the upper low are expected to be near the
3000-4000 foot mark much of the period. Snow levels elsewhere
around 5000-7000 feet (highest toward the northern Panhandle) are
expected to lower to between 4000-5000 feet through the day. Thus
some snow or at least a rain/snow mix is likely to be seen around
the Blues, the Camas Prairie and mountain passes. There is the
potential for some snow even around the higher Palouse, including
the Pullman area, this morning.
Temperatures are expected to be held much below normal under the
cool core of the upper low. This means many areas struggling to
get into the 50s today. As for overnight lows tonight into
Thursday morning, we will have to monitor reading for potential
freezing warnings. Possible locations include the Okanogan
Highlands through the northern Panhandle, as well as the Palouse.
Thursday through Tuesday...Model agreement is quite good through
Friday...with some deterioration in detail commonality after
Friday but still display reasonable agreement regarding the over
all flow regime over and near the forecast area.
Thursday through Friday the upper level closed low is firmly
planted over the forecast area. The deformation band of persistent
and frequent showers currently entering the region will be off to
the north over southern BC and Alberta by Thursday morning...but
the forecast area will be under the direct influence of the low
center cold pool aloft with minor vorticity spokes available to
gin up showers in this weakly unstable and moist air mass. This
argues for a cool and showery regime with plenty of clouds and the
possibility of some fairly weak and isolated thunderstorms.
Impossible to nail down these sub-synoptic inter-trough
disturbances at this time...but suffice it to say just about
anywhere in the forecast area will be at risk for a shower or two
each day with the best chance over the mountains ringing the basin.
The holiday weekend harbors no better news for outdoor
enthusiasts. The good news is that the stubborn upper low will
weaken and become less coherent...but the bad news is a general
troffy pattern will remain over the region through the weekend.
Both the latest GFS and ECMWF place the axis of this opening
system/trough off the coast...which implies warmer temperatures in
a pre-trough southwest flow regime. However the area will remain
under cyclonic difluent flow aloft with likely a few sub-synoptic
disturbances rounding this flow Saturday through Monday. This
overall pattern does not suggest a particularly wet period...but
the risk of showers...particularly over the northern and eastern
mountains will present itself each day. Both models hint that the
highest risk of showers associated with a stronger disturbance
will be on Sunday and focused over the southeast and Idaho
Tuesday the flow becomes a bit more progressive...but also brings
the threat of a stronger wave and surface occlusion to enhance
chances of rain once again.
Overall...there is high confidence of a distinctly unsettled and
occasionally showery regime right through the next week with low
confidence in timing any periods of heightened shower activity.
Temperatures will start out below normal Thursday and gradually
achieve seasonably normal values this weekend. /Fugazzi
06Z TAFS: Several bands of rain are expected over eastern Washington
and northern Idaho tonight into Wednesday. One band will remain
nearly stationary over the far NE corner of WA and Nrn ID through
Wed aftn. A second disturbance will bring -shra and isold -tsra to
the KMWH-KEAT area tonight which will linger through much of the day
Wednesday. Showers will also expand into SE WA and Lewiston area
and spread northward toward KGEG-KCOE. Overall...the air mass will
be rather moist and any breaks will lead to periods of overnight fog
or stratus until either winds incr or pcpn returns. This is a low
confidence forecast across the board for timing and reductions in
cigs for most locations. /sb
.PRELIMINARY POINT TEMPS/POPS...
Spokane 50 36 61 44 62 41 / 80 20 20 10 50 40
Coeur d`Alene 48 35 61 41 61 40 / 90 20 20 20 50 60
Pullman 50 34 61 40 58 40 / 70 20 20 20 60 50
Lewiston 58 39 67 46 65 46 / 50 20 20 20 60 50
Colville 54 36 66 41 69 40 / 90 60 30 20 40 50
Sandpoint 49 35 60 40 62 39 / 100 70 30 20 50 60
Kellogg 46 34 56 42 58 41 / 90 40 30 40 60 60
Moses Lake 59 40 67 45 70 44 / 50 20 30 20 30 20
Wenatchee 55 40 65 45 66 46 / 60 40 40 20 30 20
Omak 56 36 66 41 69 42 / 70 50 40 20 30 50
ID...Flood Watch through this evening for Northern Panhandle.
WA...Flood Watch through this evening for Northeast Mountains.