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fxus66 kpqr 222326 

Area forecast discussion
National Weather Service Portland or
324 PM PST Wed Feb 22 2017

Synopsis...a cold upper level trough dropping down from the Gulf of
Alaska will bring showers to the region through this evening, and
again on Thu. Snow may mix down to the lower elevations during the
nighttime and early morning hours. Also, due to the low freezing
levels, small hail may mix into heavier showers at any time. A
surface low will drop down along the coast on Fri, bringing a little
better chance for accumulating snow at the lower elevations. After a
break on Sat, another upper level trough will drop south on sun. This
will bring more showers, with snow levels hovering around 1000-1500
ft. Expect some showers lingering into early next week, but the trend
appears to be toward drier weather toward the middle of the week.


Short term...tonight through Saturday...a cold and showery air mass
is moving into the pac northwest today and will remain through the rest of
the week. Snow levels will hover around 1000 ft through Thu. Snow may
mix down into at lower elevations at times during heavier showers,
particularly during the nighttime and early morning hours when
surface temps will be at a minimum. However, expect little to no
impact to travel.

A cold upper level trough is moving toward the pac northwest from the Gulf
of Alaska today. Showers picked up over the coastal waters and at the
coast this morning, aided by increased lapse rates driven by the
relatively warmer ocean temps. Diurnal showers have picked up over
the interior this afternoon as well, as surface temps have now mostly
warmed into the mid 40s after a chilly start to the day. Showers also
may be getting some energy from a weak shortwave trough that is
moving into the region. A few of the showers have a bit more
vigorous over the past couple of hours, and we have had several
reports of pea, to even dime-sized hail, reaching the surface. Even
though there hasn't been any lightning detected so far, will hold on
to a slight chance of thunder for the coast and coastal waters into
this evening as the colder air arrives aloft. With 850 mb temps
around -6 to -7 c today and tomorrow, snow levels will be quite low,
potentially low enough to impact the interior lowlands at times. Any
showers that linger into later this evening or overnight may mix some
snow flakes down close to the valley floor, as surface temps will be
dropping closer to freezing. Light accumulations are possible, mainly
for elevations above 1000 ft, but in general expect little impact to

Shower activity to drop off considerably over the interior later this
evening and overnight as we lose the diurnal element to the showers
and a shortwave trough axis pushes east of the region. Expect clouds
to scatter, with areas of fog and low stratus again forming over most
of The Lowlands going into Thu morning. In general, expect Thu will
be a pretty close repeat of today. The fcst models indicate that 850
temps are a bit cooler, closer around -7 to -8 c. However, the period
of heavier shower activity will again be during the afternoon and
early evening, when surface temps again be well up into the 40s,
which will several limit the potential for any snow impacts at the
lowest elevations. However, any heavier showers could again bring wet
snow flakes, graupel, or small hail down to sea level.

The time period of greatest concern with respect to low elevation
snow appears to be late Thu night into Fri. The fcst models are
suggesting that an upper level shortwave will dive south along the
b.C. Coast on Thu, then push offshore and move south along the
Washington and Oregon coast Thu night and Fri. An attendant weak
surface low also rides along the coast, bringing a little more
organized precipitation to the region than we will see today or Thu.
850 mb temps remain around -7 c Fri morning, so snow levels will
again be flirting with the lowest elevations. The best chances for
impacts appear to be over the northwest portions of the cwa, where the
precip is expected to be focused during the early morning hours when
surface temps will still be down closer to freezing. Am skeptical
that accumulating snow will occur down near the valley floor, or at
the coast, as there will be an increasing southerly wind developing
in response to the approaching surface trough to the north. However,
it's not out of the question that some spots could pick up an inch or
two of snow, especially around 1000 ft and above. Can't rule out some
light accumulations below this, which would have the potential to
impact the morning commute. Confidence in the fcst details are not
high, but have issued a Special Weather Statement (spspqr) to
highlight the potential impacts.

Precip will spread southward through the fcst area during the day Fri
and Fri evening. Chances for sticking snow will decrease during Fri
afternoon as surface temps begin to warm, but can't rule out a quick
burst of snow if any heavier bands develop. The precip drops off Fri
night as the low moves south of the region. The trend is then toward
drier weather on Sat as a shortwave upper level ridge move over the
pac northwest. Pyle

Long term...Saturday night through Wednesday...the longwave upper
level trough will be shifting over the central U.S. Over the weekend.
However, one last shortwave will rotate around the backside of the
trough on sun. This will bring another round of precip. Snow levels
will remain on the lower side, likely around 1000-1500 ft, with
additional decent accumulations for the Coast Range and Cascades. The
upper level flow will be northwesterly and slightly cyclonic going
into early next week, which will likely allow for some lingering
shower activity, mainly over the higher terrain. However, the trend
will be toward drier weather as we get into the middle of next week.
A broad upper level ridge over the NE pac will build toward the pac
northwest. Pyle


Aviation...locally dense morning fog has given way to mainly VFR
conditions outside of showers. Some of the heavier showers could
briefly put down a stray lightning strike or two, as well as some
brief small hail or graupel. Showers are primarily being driven
by weak instability caused by the heating of the day, so coverage
should decrease this evening...with some clearing overnight. Fog
is expected to develop again in the valleys overnight, possibly
becoming dense and somewhat stubborn again to burn off Thu

Kpdx and approaches...VFR conditions likely for the afternoon,
though a few showers may briefly reduce cigs/vsbys in rain, hail,
and/or graupel. Showers decreasing this evening, with some
clearing likely as well. Dense fog should develop again later
tonight similar to Tue night/Wed morning. Fog may reduce vsby to
<1/4 sm at times after 08z...with fog lingering until 18z-20z
Thursday. Weagle


Marine...quiet marine weather through the period with 6 to 8
foot seas for the next 7 days and winds likely to remain below
Small Craft Advisory criteria. Instability over the waters will
cause some squally showers at times...with gusty winds and some
potential for lightning. There will be a chance for Small Craft
Advisory-level winds on Friday night/Saturday as a surface low
tracks south along the Washington coast, but there is still some
uncertainty how closely this surface low will track to the or
coast which will impact the winds on the waters. A similar low
pressure system is expected to drop down the pac northwest coast sun/Sun


Pqr watches/warnings/advisories...


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