Area Forecast Discussion
Issued by NWS Spokane, WA
FXUS66 KOTX 031142
Area Forecast Discussion
National Weather Service Spokane WA
442 AM PDT MON AUG 3 2015
The ongoing drought combined with high heat and low humidity will
contribute to high fire danger throughout the Inland Northwest.
Temperatures on Monday should be a few degrees cooler with an
increase in clouds. Cooler temperatures and locally breezy winds
are expected mainly Monday through Wednesday following the arrival
of a cold front. Another threat of showers and thunderstorms
arrives next weekend.
Today and Tonight: An upper level ridge of high pressure across
the Rockies will keep the region under southerly flow through tonight.
Water vapor satellite imagery shows a shortwave disturbance
pushing across northern CA and into OR. Moisture at mid levels
will increase out ahead of this wave, but models do not show much
cooling taking place aloft to result in any substantial steepening
of the mid level lapse rates. The weak instability is resulting in
shallow convection with not enough charge separation to generate
lightning. This trend will continue as the disturbance pushes
north through this morning and into the afternoon. Thunderstorms
were removed from the forecast for the most part. The only
exception is over the higher mountain peaks in ID near the border
of MT. All other areas are expected to see plenty of mid and high
level cloud cover with passing very light showers or sprinkles.
Winds will also increase through the Cascade gaps today. Low
levels remain very dry and this will not change even with the
increasing moisture at mid levels. Although temperatures will be
cooler today compared to over the weekend, relative humidity will
be at critical levels with rapid fire spread possible as the winds
increase. The Fire Weather Watch for the central and northern
Cascade valleys remains valid, which covers both Monday and
Tuesday: The upper level low pressure system currently spinning
over northwest BC early this morning will drop into central BC. A
cold front will also sweep across eastern WA and is denoted by the
darkening on the water vapor imagery northwest of Vancouver
Island. The darkening on water vapor is indicative of more dry air
approaching the region behind the front. This dry air will likely
keep much of the region free of showers. Best chances will be
near the Canadian border. Winds will continue to be breezy through
the Cascade gaps on Tuesday as well. /SVH
Tuesday night through Monday...The models are showing some differences
out towards the end of the run. But mostly they are in very good
agreement showing an upper level low moving through southern B.C.
Tuesday through Thursday. Then another low pressure system looks
to move into B.C. again Saturday and Sunday.
Tuesday night through Thursday...The upper level low will track
through the region. Lingering moisture and weak instability will
combine with up-sloping flow for a low end chance of showers and
thunderstorms Tuesday evening. Behind the front much drier air
will move into the region. This will put a cap on any additional
convection and all the chances for showers were taken out of the
forecast. A second wave will move through the low Wednesday night
and Thursday. Again this wave will be moisture starved and models
are showing little if any instability south of the Canadian
border. As such pops were lowered and any chance for thunderstorms
were taken out as well.
There is much better confidence in temperatures cooling off into
the low to mid 80s on Wednesday and upper 70s to low 80s on
Thursday. This may be as much as 10 degrees below normal on
Thursday. Southwest winds will be on the increase as the surface
gradient across the Cascades tightens up. Winds speeds of 10-20
mph with gusts 20-25 mph will be coming through the Cascade gaps
and likely on to the Waterville Plateau and into the deep Basin.
As mentioned earlier much drier air is progged to move in behind
the front dropping relative humidity down into the teen to lower
20s. This combination will be a good set up for fire weather
concerns Wednesday afternoon.
Thursday night through early Saturday a transient ridge of high
pressure will track through the region resulting in a short lived
warm up with another round of low relative humidity.
Saturday night through Monday...the models begin to break down on
the timing of the next upper level low. The GFS/Canadian model
bring the low through the quickest as an open wave which would
give the northern zones another glancing blow of showers and
possibly thunderstorms. The ECMWF is much slower, deeper and
further south. This pattern would be much wetter and cooler for
the region and is a perfect set up for thunderstorms. Consensus is
to lean in direction of the faster moving system. This would
result in isolated to scattered showers near the mountains. And
continued warm and dry for the remainder of the forecast area.
12Z TAFS: Wildfire smoke will continue to reduce visibilities to
between 3-9 miles over much of the region...with greater
restrictions around Chelan. A weak weather disturbance passing
through today and tonight will result in mainly mid and high level
clouds...with a few sprinkles possibly reaching the surface. /SVH
.PRELIMINARY POINT TEMPS/POPS...
Spokane 93 66 87 59 82 57 / 0 10 10 10 10 10
Coeur d`Alene 94 62 87 57 82 54 / 0 10 10 10 10 10
Pullman 92 57 86 54 82 52 / 0 10 10 10 0 0
Lewiston 97 68 95 63 90 61 / 10 10 10 10 10 10
Colville 97 60 89 56 86 54 / 10 10 10 10 10 10
Sandpoint 90 57 85 51 80 49 / 0 10 10 10 10 10
Kellogg 95 58 86 54 81 52 / 0 20 20 10 10 10
Moses Lake 97 62 92 59 88 58 / 10 10 0 0 0 0
Wenatchee 94 69 90 66 88 64 / 10 10 0 0 0 0
Omak 96 62 92 58 88 57 / 10 10 10 10 10 10
WA...FIRE Weather Watch from Noon PDT today through Tuesday evening
for East Washington Central Cascade Valleys (Zone 677)-East
Washington South Central Cascade Valleys (Zone 676).