071
FXUS66 KPQR 021749 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1049 AM PDT Tue Jul 2 2024

Updated Aviation Discussion

.SYNOPSIS...Warm and dry conditions persist through mid week
before a drastic warmup starts late Thursday. the high pressure
ridge intensifies through the week leading to potentially
dangerously hot temperatures over the weekend. The ridge will
shift eastward as a broad trough stemming from the Gulf of
Alaska dips into the far northeastern Pacific. While not
impactful to the area, could see a return of onshore flow.


&&

.SHORT TERM...Now through Wednesday Night...Continued zonal
onshore flow persists on Tuesday and Wednesday which will lead
to warm, but not exceptionally warm conditions. The high
pressure ridge is continuously building but will not reach it`s
peak until later in the week. Looking at the mesoscale level,
the pressure gradient between Troutdale and the Dalles is around
3-5 mb which is consistent with breezy westerly flow,
especially through the Columbia River Gorge near Hood River, and
the east- west aligned valleys in the Cascades. Along the coast
and the Willamette Valley, a weak thermal trough will cause
localized northerly winds to dominate. Overall, weather is not
impactful.

  -Muessle
.LONG TERM...Thursday through Monday...A much more active
pattern in store towards the end of the week as high pressure
intensifies over the entire West Coast. There is a digging broad
scale trough over the Gulf of Alaska, which, when paired with a
trough over the northern Plains, is creating an Omega Blocking
pattern. These tend to be the most amplified of the ridging.
This high pressure ridge will be coupled through all levels of
the atmosphere which supports significant warming. For example
around the Salem area, which is trending to wards being a hot
spot, 850 mb (5000 ft) temperatures are around 25 deg C. This is
matched at 500 mb (18,000 ft) where temperatures are around -4
deg F. The depth of this warm air will enhance the surface
temperatures and provide little relief. While still different
than the heatwave in 2021, this is not dissimilar in the overall
structure.

Let`s dive into the numbers. Based on the most recent model data
(07Z NBM and 00Z Global Model suite), there has been little
movement in the probabilities for the maximum temperatures on
July 4-7th. However, between the ensembles, there is still a
decent amount of disagreement. For example, in Salem, the
global models are showing around a 35% chance of temperatures of
105 deg F or greater, and in Eugene around 17% on Saturday. In
contrast, the NBM is closer to maximum temperatures of 105 deg
F is around 75% in Salem, 65% in Eugene, and 50% in Hood River.
The probability of temperatures greater than or equal to 110
deg F are around 20-40% with the highest probability along the
I-5 corridor and near Hillsboro. There will be a slight east
wind during this time which will help usher in warmer and drier
air from east of the Cascades. While the wind may provide some
relief in theory, a hot wind is not necessarily that helpful in
the way of cooling.

Of nearly as high of concern are the overnight temperatures as
relief is truly needed in order to keep HeatRisk low. On Friday
morning, there is around a 50% chance of temperatures dropping
below 65 degrees in the urban areas between Aurora and Corvalis.
Interestingly, some of the peaks of the Coast Range will remain
warm - likely due to sitting in a warm pocket aloft which can be
see in forecast soundings. On Saturday morning though, those
probabilities plummet - even along the coast. Around Portland-
Vancouver it is around 20-35% chance of temperatures below 65
deg F, 40% in Hood River, and in the 30-40% range from
McMinnville southward. Ultimately, without the overnight relief,
those without access to methods of cooling may experience
impacts from the heat.

Heat risk remains elevated with areas of Major heat risk popping
up around the northern Willamette Valley and the valleys of the
Cascades on both Friday and Saturday. A major HeatRisk means
anyone without effective cooling and/or adequate hydration will
be impacted, especially those who are particularly sensitive to
heat. Be sure to do everything you can to stay cool during the
upcoming heatwave, and don`t forget to check on your neighbors
and loved ones from time to time. If you must work outdoors
avoid doing so during the peak heating timeframe (12-5 PM).
Lastly, never leave pets or people inside a hot car, and ensure
your pets stay cool during this heatwave as well. Walking your
dog in the afternoon will not be a good idea as their paws may
easily burn.

Sunday into Monday will bring a slight degrease in
temperatures, but will still remain elevated in the 90s. One
thing to note is the impact that marine stratus may have. It is
common that marine stratus will move in with the onshore flow
following a drastic warmup like this. The stratus will aid in
keeping conditions cooler and more moist. -Muessle


&&

.AVIATION...High pressure continues, with weak onshore flow.
Terminals north of the KTMK to KPDX line continue to marine
stratus which is resulting in MVFR conditions. VFR conditions
could return to some of these terminals around 00Z Wednesday.
Otherwise, expect predominately VFR conditions. Northwest winds
will persist with gusts up to 25 kt along the coast and up to 20
kt for inland locations through 07Z Wednesday.

PDX AND APPROACHES...Lingering marine stratus is resulting in
MVFR conditions. Conditions should improve to VFR around 00Z.
Northwest winds persist with gusts up to 20 kt possible through
07Z Wed. /42

&&

.MARINE...Weak high pressure over the northeast Pacific with lower
surface pressure over California and the Great Basin will persist
through the week. NNW winds across all waters as high pressure
strengthen. Winds will generally peak in the afternoon and
evening hours each day with gusts up to 25 kt. Small Craft
Advisory still on track, and likely to continue through much of
the week. Because the thermal surface low will strengthen through
the middle of the week, will likely see (75%-90% probability)
northerly wind gusts up to 30 kt for zones PZZ272, 273, 252 and
253 by the middle of the week. Seas are becoming more wind driven
and building towards 7 to 9 ft, remaining around that level
through the week. /42

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Excessive Heat Watch from Thursday afternoon through Sunday
     evening for ORZ104>125.

WA...Excessive Heat Watch from Thursday afternoon through Sunday
     evening for WAZ202>210.

PZ...Small Craft Advisory until 11 PM PDT this evening for
     PZZ251>253-271>273.

&&

$$

www.weather.gov/portland

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