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fxus66 kpqr 151638 

Area forecast discussion
National service Portland or
938 am PDT Mon Jul 15 2019

Updated the aviation discussion

Synopsis...showers have already developed along much of the coast
and across portions of SW Washington early this morning. A weak
frontal system will gradually spread these showers southeast this
morning, likely reaching the Portland Metro later this morning.
Scattered showers will linger into the afternoon, favoring areas
north of Salem. Thick low clouds will move in tonight, with
occasional drizzle or light showers Tuesday...again favoring northern
portions of the forecast area. Expect an increasing chance for rain
again Wednesday as a somewhat stronger front arrives, followed by
decreasing showers and less humid weather Thursday and Friday. Warmer
and drier conditions are expected by the weekend.


Short through Wednesday...weak low pressure off the
Oregon coast is over performing expectations by quite a bit this
morning when it comes to shower activity, with precipitation reported
as far south as Newport as of 3 am. Measurable rain has also been
reported as far inland as Toutle and Kalama. Despite how weak this
system is, it apparently is producing just enough lift to take
advantage of our neutrally stable or weakly unstable air mass shown
aloft by 06z NAM model soundings. Looking at 850-700 mb Theta-E
fields, it appears there is some weak isentropic lift happening ahead
of the warm frontal portion of this system. The 06z GFS suggests this
isentropic lift will end by midday, which may bring a lull in the
shower activity. However, a humid air mass left behind will probably
allow more showers to develop this afternoon, especially if a few
sunbreaks develop and contribute to surface-based instability. The
air mass aloft looks to be just barely to warm to allow deep
convection or thunderstorms, but more sunbreaks than expected today
may change this. We decided to leave thunder out of the forecast, as
odds of any particular location getting a thunderstorm appears to be
in the 5 to 10 percent range. However, it is notable that Storm Prediction Center
included inland portions of our County Warning Area in a general thunder threat

NAM model time-height relative humidity plots continue to suggest a very moist
low-level air mass tonight and Tuesday morning, which will lead to
cloudy skies throughout the forecast area to start Tuesday. Expect
occasional drizzle and/or a few showers later tonight into Tuesday,
especially for the coast and the northern half of the County Warning Area. It appears
there is a better chance for sunbreaks Tuesday afternoon, which could
in turn drive shallow instability and some more shower development
across the north.

Latest runs of the GFS have slowed down the midweek front a little,
bringing it more in line with what the European model (ecmwf) has been suggesting for
a while. Thus we backed off our pops a bit for Wednesday, especially
for the southern part of the forecast area. It does appear rain will
be likely for our north coastal zones by Wed night, with rain chances
spreading south and east later that night and into Thursday morning.

Temperature forecasting for the next few days is fraught with
uncertainty, due to the subtle features in play and the impact of the
strong July sunshine if sunbreaks occur. Obviously, the more
sunbreaks, the warmer our highs will be. For example, there is an
impressive 9 degree spread amongst MOS members for today's high
temperature forecast for Portland, ranging from 68 degrees by the 06z
mav and 77 degrees by the 06z met. Given that it is very difficult to
hold inland temps below 70 degrees this time of year, we leaned
toward warmer guidance options for today with lower to mid 70s. High
temps trend upward into the mid 70s to around 80 Tuesday due to the
expected increase in sunbreaks. Now that the GFS seems to be on board
with the slower progression of the next front, temps may approach 80
degrees Wednesday, especially Salem southward. The coast will
generally remain cloudy and a little on the muggy side with highs
generally in the upper 60s to near 70 through the period. Weagle

Long term...Wed night through Saturday...models appear to be coming
into better alignment in suggesting the best chance for rain with our
next front will be Wed night for our north coastal zones, spreading
south and east Thursday morning. There is good agreement that there
will be a noticeable air mass change behind the front, with cooler
and less humid conditions developing Thursday. Still, a few showers
will linger into Thursday afternoon and evening, especially in the
higher terrain. Cooler temperatures will be most noticeable at night
due to the drier air mass, and some outlying areas may dip into the
upper 40s. However, building high pressure is expected to bring a
warming trend with continued dry weather heading into the weekend.


Aviation...expect a break in showers this afternoon with
improvement to VFR. An upper trough moving over the area tonight
will likely squeeze some drizzle or showers out of a deep moist
layer late tonight through early Tuesday. This will likely return
MVFR conditions overnight with possibly IFR for the coast.

Kpdx and approaches...showers are becoming less frequent late
this morning, and should end this afternoon. MVFR with patchy
drizzle is possible overnight tonight into Tuesday morning. ~Tj


Marine...a trough will move through the waters today with high
pressure rebuilding Tuesday. Models still indicating a slightly
stronger front affecting mainly the northern zones Wed. So winds
could reach marginal Small Craft Advisory criteria with gusts 20
to 25 kt. Will be keeping an eye on this and see if these winds
will manifest. Otherwise, winds will generally be 15 kt or less
through the forecast period. High pressure offshore should return
late in the week, but there will be weak fronts moving into b.C.
That should temporarily weaken the high pressure. Seas start in
the 2 to 4 ft range, then build to around 5 to 7 ft towards the
end of the week. /Mh


Pqr watches/warnings/advisories...


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