Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 271153
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
453 AM PDT WED MAY 27 2015

.SYNOPSIS...
A slow moving low pressure system will bring scattered afternoon
and evening showers and thunderstorms to the Inland Northwest
today. Locally heavy downpours, frequent lightning, and small
hail will be possible. Low pressure will gradually depart by
Thursday, bringing a decrease in precipitation chances, but
chances may increase again by early next week across the region.
Temperatures warm back above normal from Wednesday into the end of
the week, with highs pushing into the 80s Thursday onward.


&&

.DISCUSSION...
Today and Thursday: The upper level low pressure system that has
brought showers and thunderstorms to the region the last few days
is currently circulating over southeast WA. The low will continue
on a southeast trajectory through this afternoon. This is expected
to focus more widespread shower activity over the southeast
portion of the region underneath the cold pool of the upper level
low. This will primarily include the Palouse, over into the
Central Panhandle Mtns and points southward. The boundary layer
will remain fairly moist across much of the rest of the region. We
will not see a situation where there will be an abundant amount of
drier air that filters into the region out of Canada. As such,
daytime heating is expected to result in afternoon convection
across much of the rest of the region as well (especially over the
mtns), but will be more isolated to scattered in coverage further
away from the center of the low.

Models do show fairly good surface based CAPEs over the east
slopes of the northern Cascade Mtns of around 700 J/KG and not
much in the way of CIN needed to be overcome. The atmosphere
itself will also remain on the juicier side with p-wats neat
three-quarters of an inch. Storm motion will be slow on the order
of 10-15 mph to the south-southwest. All these factors will once
again result in some concerns for heavy rain on recent burn scars
from the 2013 and 2014 fire seasons. Satellite imagery does not
show much mid to high level cloud cover upstream of the Cascades
early this morning. This should result in a good amount of
sunshine today with better surface heating expected compared to
the last couple of afternoons. This should make it easier for this
area to achieve there convective potential and realize the 700
J/G of CAPE. There is also the possibility of multiple slow moving
thunderstorms moving over the same area. This would be a worse
case scenario for the burn scar locations. The good news is that
the best instability looks to be a bit west of where the worst
burn scar locations are such as the Carlton Complex and Mills
Canyon burn scars. Confidence is low that heavy rain would lead to
flash flooding or debris flows, but at least a small risk will be
present for this afternoon.

The upper level low will push into Colorado on Thursday. With that
said, dew points will remain in the 40s and low 50s. CIN will be
weaker over the higher terrain and there will be a good chance for
afternoon showers and thunderstorms once again in the afternoon.
The basin will have a harder time getting any convection going
with a stronger cap in place.

Temperatures will see a warming trend over the next couple of
days. Many locations will be up over or near 80 degrees by
Thursday and back above normal for late May. /SVH

Thursday night through Wednesday...Zonal flow across the region
through the weekend as another closed low drops into central B.C.
Thursday and slowly moves east and out of the area on Sunday.
Meanwhile satellite imagery is also showing a deeper closed low
out near 40N/150W. This second feature will be the dominant
weather feature towards the end of the forecast period.

Thursday night through Saturday night...A closed low currently
seen on water vapor imagery just moving into Haida Qwaii will
drop into central B.C. Thursday night and slowly move east well
north of the border through early Sunday morning. This will put
the region into a zonal/westerly flow. This isn`t typically an
overly wet weather pattern for this area. However model guidance
continues to show little in the way of drying as the flow pattern
changes. PWAT`s remain 150% or more above normal. This additional
moisture will add to the normal destabilization process due to
afternoon heating. Several weak waves moving through the forecast
area will be the icing on the cake for late day showers and
embedded thunderstorms. Storm motion is on the low end so the
biggest challenge will be localized heavy rain. However models are
indicating a better shear environment each afternoon so there may
some localized pea sized or slightly larger hail. Temperatures
will be on the increase through the weekend with temperatures in
the 80s and 90s. I did cool off max temperatures Sunday due to
lower 850 temps and increased cloud cover.

Sunday through Wednesday...The previously mentioned low out in the
Pacific will finally make it`s way towards the west coast, again
as a closed low. Models are still having some timing issues but
they all have the low move through the forecast area in some
fashion Monday and Wednesday. This will result in cooler
temperatures and another round of wet, and likely very wet
convection. Interestingly this pattern is typically a good one for
thunderstorms but model guidance is not showing anything but weak
surface based cape and negative LIs for the southeast zones and
the Cascades. Pops were increased accordingly and will go ahead
and hold off on going to wild with the thunderstorm threat at this
time, but stay tuned, certainly there is more to come.
Temperatures will also cool from the very warm weekend with max
temperatures mainly in the 60s and 70s. But this is still above
seasonal averages. Tobin

&&

.AVIATION...
12Z TAFS: An upper level low pressure system will reside over KPUW
and KLWS today. Although there is some mid level clouds wrapping
around the low, there has been enough clearing overnight for low
stratus and fog to form across the northern valleys and may
briefly impact KGEG, KSFF and KCOE with MVFR vis possible through
15Z. Isolated to scattered showers will then develop in the
afternoon across much of the region; KGEG, KSFF, KCOE, KPUW, and
KLWS TAF sites will see the best chances for showers. Isolated
thunderstorms will also be possible at these TAF locations through
the afternoon with confidence a bit higher for thunderstorms at
KPUW and KLWS TAF locations. /SVH

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        75  54  80  56  83  60 /  30  20  20  20  20  10
Coeur d`Alene  74  51  79  54  82  56 /  40  30  20  20  20  10
Pullman        70  49  77  52  82  56 /  60  20  20  10  10  10
Lewiston       76  54  83  58  89  63 /  60  20  10  10  10  10
Colville       80  51  84  54  84  55 /  30  30  20  30  30  20
Sandpoint      74  49  78  51  81  52 /  50  30  40  40  30  20
Kellogg        71  47  77  49  81  54 /  70  40  40  30  20  20
Moses Lake     81  55  87  58  90  61 /  10  10  10  10  10  10
Wenatchee      82  61  87  63  89  64 /  10  10  10  10  10  10
Omak           82  53  87  55  87  55 /  30  30  10  20  20  20

&&

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

$$


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