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Area forecast discussion 
National Weather Service Portland or
321 am PDT sun Jul 5 2015

Synopsis...the heat is on across inland southwest Washington and
northwest Oregon...and will remain on through midweek. A stagnant
pattern remains in place across the region with a ridge of high
pressure aloft remaining dominant. A brief cooldown is possible
tonight and Monday for Eugene as a southwest surge of marine air
pushes through the adjacent Coast Range. Otherwise onshore flow will
be weak and ineffective at bringing much relief from the heat inland
through Wednesday. An upper low off California may drift far enough
north Tuesday/Wednesday to bring thunderstorms up the Cascade crest to Lane
County by midweek. Relief from the heat may come later this week as
the upper ridge breaks down enough to allow stronger onshore flow.

&&

Short term...today through Tuesday...the prolonged heat wave of 2015
continues across SW Washington and northwest Oregon...with little change in
the overall weather pattern which has rendered onshore flow weak and
ineffective for all but the immediate coast. Upper level ridge axis
remains stretched from Texas/Four Corners region through Oregon and
into the NE Pacific. The upper ridge continues to compress the marine
layer such that onshore flow is robbed of its cooling influence by
the time it reaches more than a few miles inland.

Onshore pressure gradients are weakening this morning as a clipper
system moving through British Columbia and Alberta turns the flow
more northerly across Washington/north or. High pressure building behind the
associated cold front will likely push thermal low pressure offshore
today...further limiting onshore flow or even turning it a little
offshore across western Washington. With any vestige of a marine inversion
eliminated...temperatures will likely heat up a few degrees today versus
Saturday despite similar 850 mb temperatures in the +20 to +21 degree c range.
This will bring high temperatures close to 100 today for many inland valley
locations...including the pdx metropolitan and Salem.

With thermal low pressure being shoved off the Washington coast and weak flow
aloft...an ideal setup will be in place for the development of a
southerly surge of marine air to develop and push up the coast
tonight. Depending on how deep this push of marine air can get...it
has the potential to bring some decent cooling to the central Coast
Range and even the Eugene metropolitan. Decided to end the heat advisory for
these zones this evening...as 4 km WRF-arw and NAM guidance suggest
cooling SW winds pushing into the S Willamette Valley tonight. Some
models are so bullish with this marine push that they even bring some
low clouds into the Eugene area Monday morning...suspect this is a
little overdone.

Areas further north are a different story...as it is doubtful the
marine push will be strong enough to affect areas Salem northward.
With little change in air mass...and onshore flow mitigated due to
low pressure/weakened high pressure offshore...expect a few more hot days
with highs reaching well into the 90s through Wednesday. A weak flow
pattern will keep nights warm. GFS/European model (ecmwf) ensemble guidance show
excellent agreement that little change is likely through Wednesday...so we
decided to extend the heat advisory through Wednesday evening. Hopefully
this will be as far as we need to go with it...as models show good
agreement on our upper ridge breaking down/shifting east by late
week.

Meanwhile...upper level low pressure will be nearly stationary off
the California coast. Models suggest it will remain too far south to
spread enough moisture/instability far enough north to induce a
thunderstorm threat for the Lane Colorado Cascades. Some debris cloudiness
is possible from time to time due to convection to our south...but it
appears thunderstorms are unlikely until at least Tuesday/Wednesday unless the upper
low wobbles further north than currently expected. Weagle

Long term...no changes. Previous discussion follows...
Tuesday night through Saturday...Rex block remains in place through
middle-week with continued hot and dry weather across the area. Models
continue to suggest Rex block over the West Coast starts to break
down later this week as an upper-level trough pushes the ridge of
high pressure off to the east. There is still some disagreement on
when this will actually break down...but ensembles suggest a good
chance that the blocking pattern breaks down by Friday. This should
bring temperatures down some for Friday and Saturday with a chance
for some cloud cover as well. There is a slight chance for a
thunderstorm or two later this week in the Lane County Cascades as
the upper-level trough moves through...but elsewhere looks to remain
dry into next weekend. -McCoy

&&

Aviation...IFR stratus and fog developed along the immediate
coast. Ceilings are generally under 800 feet with some locations in fog
with visible less than 1/2 mile. The stratus and fog should clear by
17z Sunday. A southerly wind reversal will develop along the
coast from south to north during the day today. This will bring
stratus will return to the coast by late afternoon on the central
coast and tonight for the South Washington coast. VFR conditions
prevail inland through early Monday.

Kpdx and approaches...VFR will continue through early Monday. /26

&&

Marine...the pressure gradient will continue to weaken over the
waters today as a thermally induced low moves offshore. The
thermal low will expand off of the Oregon coast today resulting
in a southerly wind reversal. Southerly winds will develop first
for the central Oregon coast in the afternoon...then for the
Washington coast tonight. A weak pressure gradient will continue
through at least Wednesday keeping surface winds light...less than
15 knots. The thermal low will weaken by Thursday with west-northwest winds
returning.

Seas will gradually subside today and remain below 6 feet through
Thursday. The very strong morning Ebb will likely result in rough
bar conditions so a Small Craft Advisory will be issued. /26

&&

Pqr watches/warnings/advisories...
or...heat advisory until midnight PDT Wednesday night for central
Columbia River gorge-central Willamette Valley-greater
Portland metropolitan area-lower Columbia-northern Oregon Cascade
foothills-Upper Hood River Valley-western Columbia River
gorge.

Heat advisory until 6 PM PDT this evening for Cascade foothills
in Lane County-central Coast Range of western Oregon-south
Willamette Valley.

Washington...heat advisory until midnight PDT Wednesday night for central
Columbia River gorge-Greater Vancouver area-I-5 corridor in
Cowlitz County-South Washington Cascade foothills-western
Columbia River gorge.

Pz...Small Craft Advisory for rough Columbia River bar in effect
until 9 am PDT this morning.

&&

$$

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This discussion is for northwest Oregon and southwest Washington
from the Cascade crest to 60 nautical miles offshore. The area is
commonly referred to as the forecast area.

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