Area Forecast Discussion
Issued by NWS Spokane, WA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45
000
FXUS66 KOTX 301702
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
1002 AM PDT Tue Aug 30 2016

.SYNOPSIS...
An approaching weather system will slowly cool the region through
Thursday and bring an increasing potential for showers and
thunderstorms as the week wears on. This upper level trough will
move into the region late in the week, ushering in cooler
temperatures and showery conditions for the beginning of the
holiday weekend.


&&

.DISCUSSION...
Morning update: We have made some changes, mainly to cool
temperatures today and adjust timing/placement of showers and
t-storms for latter today. We are monitoring a shortwave tracking
toward Bend, OR at this hour which will lifting into Ern WA and N
ID latter today into tonight. First off, we are seeing a lot of
cloud cover moving into the region ahead of this which will keep
temperatures cooler than previously thought and temperatures were
adjusted downward.

As for thunder, showers, and potential for gusty winds: The large
scale setup is favorable for a gusty wind event but not all
ingredients appear to be lining up. The morning balloon data
indicated steep lapse rates through much of the atmosphere but
also a lot of dry air. Despite the increased cloud cover, models
are only indicating saturation from 600mb and above. Looking at
upstream observations, nearly all METARS are showing clear skies
(not the reality) but this implies ceilings are at or above 15,000
ft. Additionally, the Salem balloon data indicated very dry air at
700mb. As the lift from the shortwave comes through, looks as if
the bulk of the midlevel CAPE will come from parcels ascend from
600mb which is only squeezing out around 100 J/kg of CAPE. As a
result, nearly all Hi-Res models are only showing echoes near 20
dbz or less for much of northern Oregon and southern WA. This will
be in the form of sprinkles or brief light showers with little to
no QPF and should produce little to no lightning. As this falls
into the inverted V boundary layer, gusty winds are likely but
speeds should not be intense given the depth of the convection.
Will keep a small mention of thunder across SE WA and the lower ID
Panhandle but confidence is low and showers look to be more
prevalent. Under showers, wind gusts near 25 mph will be possible.
Timing for these areas will be closer to 4PM.

Now as the wave tracks further north into NE WA and N ID, the
instability will be a touch greater given the presence of the
thermal trof. Hi-res modeling indicates stronger cells with a
better chance for isolated lightning strikes. Stronger wind gusts
will also be possible due to deeper convection but timing is later
and there is some uncertainty whether the inversions will setup.
Overall, the risk is still low given earlier reasoning but
something to monitor for the evening hours. The wave and any
chance for wind or lightning will lift north out of the region
by midnight.  /sb


&&

.AVIATION...
18Z TAFS: Mid and high level clouds will spread across all
terminals today and depart tonight. An accompanying shortwave will
supply lift to squeeze out light showers and a few lightning
strikes. Best chance for lightning will be across NE WA and N ID.
The air mass below will be very dry and any shower or t-storm
activity will present the risk for brief gusty winds and this
should be the main aviation focus outside lightning strikes.
Expect this activity to cross KPUW/KLWS 3-5PM...KGEG-KCOE
5-8PM...and depart arnd 11PM. High based shwrs will track vcnty
KEAT/KMWH 4PM-7PM. /sb



&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        84  59  81  56  73  52 /  10  20  10  10  10  50
Coeur d`Alene  85  56  81  54  74  51 /  10  30  10  10  10  50
Pullman        82  53  80  51  73  48 /  20  20  10  10  10  50
Lewiston       88  60  87  59  79  55 /  20  20  10   0  10  50
Colville       87  53  83  51  75  47 /  10  30  10  10   0  20
Sandpoint      84  52  81  50  73  48 /  10  30  10  10  10  50
Kellogg        84  53  81  51  73  47 /  10  30  10  10  10  40
Moses Lake     85  55  83  54  76  51 /  20  10  10  10   0  10
Wenatchee      84  61  81  58  74  53 /  20  10  10  20  10  20
Omak           87  56  85  52  77  50 /  10  20  10  20  10  20

&&

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

$$



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.