Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 180930
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
230 AM PDT Wed Oct 18 2017

.SYNOPSIS...
A moist warm front will move into the region today and bring an
moderate precipitation to the region today and Thursday. A cold
front will follow on Friday for showers, gusty winds and cooler
temperatures that will last through the weekend and into Monday.
A return to warmer temperatures and drier conditions is expected
next week.

&&

.DISCUSSION...
Today through Friday...The cold front that brought the winds and
showers to the region on Tuesday is now well south and east of
the region, but we are far from done with the active weather. Weak
and short lived high pressure will build into the region this
morning ahead of the next vigorous up stream system. A warm front
will move into the region his morning and stall over the region
through at least Thursday. This will have two effects on the
weather for the next few days. First: The resultant west-
southwest flow will tap into deep Pacific moisture associated with
a significant Atmospheric river moving across the Pacific.
Moisture will increase to well over 200 percent of normal and this
looks like it will remain over the region until a cold front
passage on Friday. Second: the warm front will combine with
several weak waves to provide ample lifting across the region.
This will result in an extended period of precipitation across the
Inland Northwest. The cold front will move across the region
Thursday night and be east into Montana by late Friday mid-day for
drying west to east through the day. Precipitation will turn
showery with the focus over the Cascades and across the eastern
mountains. Showers will likely build back to the west Friday
afternoon with measurable precipitation as far west as the upper
basin.

* Precipitation: It looks like all areas will see measurable
  precipitation. The westerly flow will cause a rain shadow
  downstream of the Cascades Wednesday and Thursday, however this
  system is so wet it will not take much to squeeze up to a tenth
  of an inch of precipitation for the deep basin. Outside of the
  basin the lower elevations will see a half inch or a little more
  and the mountains will see from a half inch to well over an
  inch of moisture. Areas down stream of the Cascade crest and
  across the northeast mountains and the northern Panhandle
  mountains could see 1-3 inches of precipitation. Snow levels
  will be rather high and will only increase with the strong warm
  advection. For today snow levels across the north will be
  4500-5000 feet but will increase to well over 7000 feet by this
  afternoon. So precipitation will be as rain with snow only at
  the highest elevations, and even there it will turn to rain by
  late afternoon. Snow levels will drop quickly behind the front
  down to 4500 feet again. But by this time the precipitation is
  beginning to subside. Still the higher elevation will likely
  pick up a good shot of snow.

* Temperatures and winds: Temperatures will be in the 40s to mid
  50s and on the cool side of normal. Winds have decreased
  substantially from Tuesday afternoon but will remain
  breezy/gusty at times today and Thursday. The winds will be on
  the increase Thursday night and Friday with the cold front
  passage with gusts 25-35 mph likely Friday. Tobin

Friday night through Sunday: A very wet zonal flow will be over
the area over the weekend as an atmospheric river of subtropical
moisture becomes aimed at the area. The leading edge of the
precipitation will arrive in the form of a warm front on Saturday.
Sufficient isentropic ascent should bring rain and mountain snow
to all areas on Saturday. The strongest lift with the passing warm
front occurs Saturday afternoon and evening. Once the front
passes...precipitation will likely become more confined to the
Cascade crest and Idaho Panhandle as strong downslope flow kicks
in east of the Cascades with 850mb winds out of the west-
southwest at around 50 kts. Snow levels increase to 6000-7000 feet
Saturday night behind the warm front. Overall impacts from snow in
the mountains should not be significant as warm air will be quick
to enter the region. Model qpf values Saturday and Saturday night
near 1-2 inches in the Idaho Panhandle Mountains and 3-5 inches
along the Cascade crest. The abundance of precipitation along with
snow melt Saturday night into Sunday will lead to rises on area
streams and rivers but no flooding is expected.

Pressure gradients become tight Saturday night over SE Washington
into the Camas Prairie area...which may lead to windy conditions
with local gusts of 40-50 mph. On Sunday models show some
differences with how quickly the atmospheric river sags south of
the area but the latest consensus keeps the highest rain chances
over SE Washington into the Central Panhandle Mountains as the
atmospheric river begins to shift south. 850mb winds of 35-50 kts
remain over the region on Sunday so locally windy conditions are
possible.

Monday and Tuesday: An upper ridge builds for a warming and drying
trend. Will likely have to contend with overnight/morning fog for
the northern valleys and Idaho Panhandle given the abundance of
low level moisture that will be around after the weekend soaking.
JW

&&

.AVIATION...

06Z TAFS: The next Pacific storm system will begin to impact the
region today. The effects from this storm system will stretch over
the next few days. The warm front will push across today. Clouds
will thicken over the region tonight. Light rain will pick up in
the afternoon. Strong westerly flow should result in a rain shadow
in the lee of the Cascades with KEAT and KWMH seeing little precip
if any at all. Not much rain is expected at KPUW either and KLWS
will likely be shadowed out by the Blue Mtns. Confidence is high
that the Spokane/Coeur d`Alene corridor will see rain beginning
right around noon then decrease Wednesday evening. VFR conditions
are expected as cigs will remain above 4-6 kft agl and rain
shouldn`t be heavy enough to drop vis below 6 SM. /SVH


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        54  48  53  42  51  36 /  90  80  90  90  50  20
Coeur d`Alene  55  46  55  41  49  36 /  90  80  80  90  50  30
Pullman        59  48  58  43  50  37 /  30  30  50  90  50  40
Lewiston       67  49  66  47  58  40 /  20  10  10  90  30  20
Colville       53  45  54  41  52  34 /  70  60  80  80  40  40
Sandpoint      51  44  52  38  48  33 / 100 100 100 100  70  40
Kellogg        53  43  56  40  45  35 /  70  60  40 100  80  70
Moses Lake     60  48  59  39  58  35 /  50  30  60  30  10  10
Wenatchee      56  45  58  41  55  37 /  20  10  50  40  10  20
Omak           54  42  58  36  56  32 /  40  40  80  40  30  10

&&

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

&&

$$


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