Area forecast discussion
National Weather Service Spokane Washington
426 PM PDT Wed may 22 2013
Synopsis...
a cool and wet period awaits the inland northwest care of a cold
upper level low. Occasional showers are expected each day through
the end of the week with cooler than normal temperatures. Snow
will also be possible over the mountains. Conditions could
moderate a bit by the weekend as the low moves out of the area
but it will be replaced by another cool low sometime early next week.
&&
Discussion...
tonight...large closed low centered near Yakima this evening will
move northwest towards Seattle overnight. Models show the Theta E
ridge axis which has brought heavy rain over the north Idaho
Panhandle and north Pend Oreille County shifting east into western
Montana this evening. A Flood Advisory remains in effect through
this evening for this area. The closed low position tonight will
result in south-southeast flow over central and eastern
Washington and north Idaho with showers rotating around the low.
Laps data from this afternoon also has cape values of around 200
j/kg from Wenatchee through Hanford and the Blue Mountains which
could spark a stray thunderstorm. All models show a wedge of drier
air coming up from the south tonight which should dry most areas
out once evening showers die off with the loss of daytime heating.
However closer to the Cascades showers may persist overnight given
close proximity to low center.
With the drier air skies will have an opportunity to become mostly
clear or partly cloudy for eastern Washington overnight. This
combined with a cool start with afternoon temperatures only in the
mid 40s over most areas will result in a cool night. Freezing
temperatures are expected for most locations on the Palouse and a
freeze warning has been issued. A tougher call for the northern
valleys where abundant boundary layer moisture may allow for more
fog or stratus to develop which would keep lows near or slightly
below freezing. With lower confidence opted to not include the
northern valleys, but colder spots like Republic and Deer Park
will have a good chance of reaching 30-32 degrees f. Jw
Thursday through Saturday...cold upper level low will remain
the dominant feature through this period. Model solutions are
exhibiting very good agreement with the movement of the low and
the placement of the associated deformation band of precipitation.
The current deformation band which is responsible for the
widespread band of precipitation extending from NE Washington into
the central Panhandle...is expected to track east-NE overnight and
and move into northwest Montana by late-morning or early afternoon. Drier
and more stable air is expected to move in its wake which will
likely bring a brief drying trend across much of the inland northwest at
least through the morning. The atmosphere is expected to
destabilize in the afternoon due to diurnal heating...and
scattered showers could develop over the eastern half of the
forecast area. Farther west...the presence of the low near the
mouth of the Columbia will result in weak upslope easterly flow
into the Cascades and keep more persistent shower activity fixed
over that region. Temperatures should moderate quite a bit
compared to today as a bit more sunshine is expected with the core
of the upper level low shifting the coldest air to our west.
By Thursday night into early Friday the low is expected to wobble
into central Oregon before heading north-northeast. This should
result in drying conditions for most locations. By Friday
afternoon...the models continue to exhibit great consistency by
showing the upper level low will wandering into NE Oregon with the
atmosphere over the inland northwest exhibiting a rapid destabilization.
Showers will likely become plentiful as model cape values climb
into the 250-500 j/kg range with no convective cap. Given the
southerly mid-level flow...the most abundant activity will cluster
along the northern forecast zones adjacent to the Canadian border.
Thunderstorms look like a possibility given the stability
parameters...however the lack of strong ascent aloft the coverage
will be underwhelming.
For Saturday...the low will meander back west of the Cascades...
with the best chances of precipitation focusing over the northern
and western portions of the forecast area...near the Canadian
border and Cascades. Once again the instability parameters suggest
a small chance of thunderstorms...however most of the upper level
ascent will remain focused west of the Cascades. Temperatures will
continue to moderate through the period with highs climbing into
the mid 60s to lower 70s for most valley locations. Fx
Saturday night through Wednesday...long-wave trof continues to
influence the western United States through this time
interval...therefore this interval remains marked with below
normal temperatures...lower than usual snow levels at times...and
moderate pops and amounts of precipitation at times. The flow
does become westerly enough and void of disturbances to allow for
some intervals of drying between shortwave passages but as far as
shortwave features traversing through there are just enough timing
differences in passing each one through (and there appears to be
about four or more) that there isn't enough confidence to modify
any timing of each feature in the forecast...so the end result
syntax wise is a forecast cluttered with generally chance pop
wording. /Pelatti
&&
Aviation...
00z tafs: an upper level low pressure area centered in the vicinity
of the aviation area allows for a cluttered forecast of primarily
showers at various times, either surface based or the elevated
forced type in the forecast for most of the time interval through
00z Friday. These showers may produce MVFR ceilings at times.
Additionally some late night and early morning fog near rivers and
northern valleys could produce brief MVFR visibilities along with
some frost as temperatures drop below freezing for a brief spell
near kpuw, kdew...and other more favorable aviation locations.
Additionally a very small potential for thunder exists near
Cascades and vicinity klws and portions of north Idaho Panhandle.
/Pelatti
&&
Preliminary point temps/pops...
Spokane 36 60 42 60 42 64 / 20 20 20 40 30 30
Coeur D'Alene 35 59 39 60 40 64 / 20 20 20 40 40 30
Pullman 32 59 39 57 40 64 / 20 20 20 40 20 30
Lewiston 38 66 45 64 45 71 / 20 20 10 40 20 30
Colville 35 63 39 68 41 69 / 70 30 30 50 40 40
Sandpoint 35 58 38 62 39 64 / 80 30 20 50 50 40
Kellogg 34 55 40 56 41 61 / 40 30 30 50 50 40
Moses Lake 39 66 43 69 45 72 / 20 20 20 30 20 10
Wenatchee 41 63 44 66 47 69 / 60 40 30 30 20 20
Omak 35 65 39 68 42 69 / 50 30 30 40 30 30
&&
Otx watches/warnings/advisories...
Idaho...freeze warning from 2 am to 7 am PDT Thursday for Idaho Palouse.
Washington...freeze warning from 2 am to 7 am PDT Thursday for Washington
Palouse.
&&
$$
