August 2016 Observations and Model Discussion for the Pacific Northwest

[TT-SEA]

Might be an interesting evening here.   Gorgeous afternoon but its about to turn turbulent.

[Phil]

Also, those maps are awkward in that each color represents a wide temperature range, so a fraction of a degree can flip the color code, hence the "range" you have to derive from can be quite unrepresentative.

 

This a huge problem in my area and its why I don't use them.

[Front Ranger]

Might be an interesting evening here.   Gorgeous afternoon but its about to turn turbulent.

 

Flying?

[Deweydog]

No..

You really do struggle with the nuances of our maritime climate.

[Front Ranger]

Interesting that a couple of the spots on the coast that were warmer than almost everywhere else in July have seen that persist, to a lesser degree, in August.

 

And apparently a volcano in NE Nevada.

 

 

[IbrChris]

Marine influence is best seen as a combination of things, first and foremost being onshore gradients. On the models depending on the parameters available you can look at 925 mb RH and winds. Generally if the 500 mb ridge axis is east of the Cascades (implying lower heights/thicknesses over the I-5 corridor vs areas farther east) the thermal trough/low is located east of the Cascades meaning onshore flow is undoubtedly occurring even if weak. This is what I look for at first glance on the model 500 mb progression. For Portland I look at AST-PDX gradients (currently +0.8 so weakly onshore). For Seattle you can look at HQM-SEA which is a similar analog to AST-PDX. If the gradient is positive there's some degree of onshore flow.

In summer absent a thermal trough the flow is almost always onshore west of the Cascades.

http://www.atmos.washington.edu/marka/pd.cgi

[Phil]

You really do struggle with the nuances of our maritime climate.

Translation: "I don't know how to read and/or interpret a sounding, so I have to put on an alpha suit to compensate".

[Phil]

Marine influence is best seen as a combination of things, first and foremost being onshore gradients. On the models depending on the parameters available you can look at 925 mb RH and winds. Generally if the 500 mb ridge axis is east of the Cascades (implying lower heights/thicknesses over the I-5 corridor vs areas farther east) the thermal trough/low is located east of the Cascades meaning onshore flow is undoubtedly occurring even if weak. This is what I look for at first glance on the model 500 mb progression. For Portland I look at AST-PDX gradients (currently +0.8 so weakly onshore). For Seattle you can look at HQM-SEA which is a similar analog to AST-PDX. If the gradient is positive there's some degree of onshore flow.

 

In summer absent a thermal trough the flow is almost always onshore west of the Cascades.

 

http://www.atmos.washington.edu/marka/pd.cgi

Thanks for this, much appreciated.

[IbrChris]

I will say next week continues to look warmer vs 24-48 hours ago, but the 500 mb ridge axis is east of PDX/SEA the bulk of the week (a weak thermal trough may develop as the ridge temporarily spikes on Tue/Wed but my guess is that gradients remain lightly onshore during that time). Persistence of low clouds in the mornings will make a big difference on highs. Currently GFS and Euro ensemble mean are suggesting ~90 Tue and Wed at PDX. This is a situation where the marine layer will likely be fairly shallow so the "Hillsboro Hole" may be in effect esp Tue and Wed mornings (meaning little/no low clouds over the west Portland metro). Looking further ahead the Euro ensemble is clearly the warmest in the late 6-10 and 11-15 day timeframe with GFS and CMCE showing closer to mid 80s (Euro flirts with 90). Above normal temps seem a good bet but there's no consensus on details.

[Timmy Supercell]

Today would have been the next chance of storms but NWS seems pessimistic about it on the AFD.

 

Sheesh, only had 3 t'storms since the start of Meteorological Summer (June 1st). None in the most likely month to have them (July).

 

Not looking good!

[IbrChris]

Thanks for this, much appreciated.

 

Since surface gradients can be tough to deduce on the NCEP maps covering large geographical areas I prefer to look at the 500 mb pattern...the rule of thumb re: 500 mb ridge axis location is pretty reliable as an indicator of the broad transport regime in the lower atmosphere.

 

One could also fairly easily download the GFS output for HQM and SEA and utilize it in calculating the modeled surface gradient over the course of each run. It would be very easy to use a little VBA to develop an Excel-based application that would grab the data, parse it and output the gradients as a function of model hour at the push of a button.

[TT-SEA]

I will say next week continues to look warmer vs 24-48 hours ago, but the 500 mb ridge axis is east of PDX/SEA the bulk of the weak (a weak thermal trough may develop as the ridge temporarily spikes on Tue/Wed but my guess is that gradients remain lightly onshore during that time). Persistence of low clouds in the mornings will make a big difference on highs. Currently GFS and Euro ensemble mean are suggesting ~90 Tue and Wed at PDX. This is a situation where the marine layer will likely be fairly shallow so the "Hillsboro Hole" may be in effect esp Tue and Wed mornings (meaning little/no low clouds over the west Portland metro). Looking further ahead the Euro ensemble is clearly the warmest in the late 6-10 and 11-15 day timeframe with GFS and CMCE showing closer to mid 80s (Euro flirts with 90). Above normal temps seem a good bet but there's no consensus on details.

You to post details like this more often. You are very knowledgeable and seemingly have no agenda on either side.

 

Really appreciated.

[Deweydog]

Translation: "I don't know how to read and/or interpret a sounding, so I have to put on an alpha suit to compensate".

Not a slam, my man. Just a fact. Inversions are our way of life here.

[IbrChris]

You to post details like this more often. You are very knowledgeable and seemingly have no agenda on either side.

 

Really appreciated.

I should add 500 mb height (or thickness) is useful in gauging the relative depth of marine inversions and usually their inland penetration. Heights above 582 dam usually mean a marine inversion will at best be fairly shallow (below 3000 feet usually) and the shallower the inversion the more likely any stratus/stratocu breaks up earlier in the day rather than a situation where it is steadily maintained by weak upslope against the Cascades/Coast Range/Olympics, or a situation where the stratus begins to break up but then the inversion layer is convectively overturned and all you get is high areal coverage stratocumulus that maintains through the afternoon.

[IbrChris]

Not a slam, my man. Just a fact. Inversions are our way of life here.

Yeah look at any summertime sounding and we are rarely convectively mixed (dry adiabatic) from the surface to a height above 700 mb. Whereas places like SLC the sounding is mixed to ~500 mb often (known as an "inverted-V" profile as it resembles the letter V but inverted).

[Phil]

Since surface gradients can be tough to deduce on the NCEP maps covering large geographical areas I prefer to look at the 500 mb pattern...the rule of thumb re: 500 mb ridge axis location is pretty reliable as an indicator of the broad transport regime in the lower atmosphere.

 

One could also fairly easily download the GFS output for HQM and SEA and utilize it in calculating the modeled surface gradient over the course of each run. It would be very easy to use a little VBA to develop an Excel-based application that would grab the data, parse it and output the gradients as a function of model hour at the push of a button.

So, is the longitudinal pressure gradient all you look at? Or would you consider tilt or any meridional bias in the gradient?

 

Mesoscale meteorology isn't my strongest suit, especially out of my own region.

[Jesse]

I will say next week continues to look warmer vs 24-48 hours ago, but the 500 mb ridge axis is east of PDX/SEA the bulk of the week (a weak thermal trough may develop as the ridge temporarily spikes on Tue/Wed but my guess is that gradients remain lightly onshore during that time). Persistence of low clouds in the mornings will make a big difference on highs. Currently GFS and Euro ensemble mean are suggesting ~90 Tue and Wed at PDX. This is a situation where the marine layer will likely be fairly shallow so the "Hillsboro Hole" may be in effect esp Tue and Wed mornings (meaning little/no low clouds over the west Portland metro). Looking further ahead the Euro ensemble is clearly the warmest in the late 6-10 and 11-15 day timeframe with GFS and CMCE showing closer to mid 80s (Euro flirts with 90). Above normal temps seem a good bet but there's no consensus on details.

You could have made this exact same post five days ago, replacing "above normal" with "below normal" and it would have been an accurate representation of models at the time. They have shifted quite a bit the last several days, and there will likely be more shifts in the next several.

[IbrChris]

Here's a classic example of subsidence aloft under a ridge coupled with a shallow marine layer at the surface. Sounding from Vanderburg AFB in coastal southern California. Marine layer is limited to below 950 mb (about 1500 feet elevation) and a sharp inversion exists above that with a much warmer and drier airmass.

http://www.spc.noaa.gov/exper/soundings/16081000_OBS/VBG.gif

[IbrChris]

So, is the longitudinal pressure gradient all you look at? Or would you consider tilt or any meridional bias in the gradient?

 

Mesoscale meteorology isn't my strongest suit, especially out of my own region.

Being that PDX is close to the coast generally AST-PDX or OTH-PDX is a good indicator of onshore flow. Southerly pushes commonly affect Eugene through the coastal gaps, as well as occasionally Corvallis and McMinnville but aren't usually as strong as one driven by W to E onshore gradients. UIL-SEA would be a decent gradient for onshore flow determination for NW Washington and HQM-SEA would be indicative of SW-W boundary layer flow. I think 850 mb winds become a bigger factor when the marine layer is more than 3000 feet deep and are the bigger factor in stratus evolution.

[IbrChris]

You could have made this exact same post five days ago, replacing "above normal" with "below normal" and it would have been an accurate representation of models at the time. They have shifted quite a bit the last several days, and there will likely be more shifts in the next several.

Yep that's why the ensembles look like a bunch of spaghetti most of the time beyond about day 7/8. There's no guarantees outside of GOLU.

[Jesse]

I know exactly what you mean by the Hillsboro Hole. Even before sunrise, Hillsboro can be completely sunny and starting around Beaverton as you head east it's completely cloudly.

I've always chocked that up to some sheltering effects from the extensive easterly reach of the coast range foothills north of the Tualitan Valley, as well as a tendency for the marine layer to bank up against the West Hills.

[IbrChris]

An interesting problem related to wind forecasting east of the Columbia Gorge during the warm season is the timing of diurnal late afternoon/evening westerly surges. Absent a thermal trough west of the Cascades or the presence of convection they occur almost every day from late June through late September and less commonly in May and October. One clue is found in the examination of TTD-DLS and DLS-HRI gradients (cross-Cascade and southern Columbia Basin gradients). When TTD-DLS peaks it's almost always a sign that the westerly surge is on it's way into the Columbia Basin immediately east of the Gorge. The next hour DLS-HRI bumps up and usually within a couple hours it peaks. This allows for better confidence around the timing of westerly surges into a few of the wind parks I forecast for.

[Deweydog]

I know exactly what you mean by the Hillsboro Hole. Even before sunrise, Hillsboro can be completely sunny and starting around Beaverton as you head east it's completely cloudly.

Cloudly. I like that.

[IbrChris]

I know exactly what you mean by the Hillsboro Hole. Even before sunrise, Hillsboro can be completely sunny and starting around Beaverton as you head east it's completely cloudly.

Shallow marine intrusions tend to come either through the gap near Sheridan or down the Columbia. The terrain surrounding the Tualatin Valley is mostly 1000-1500' to the immediate N and NE and over 2000' to the W (Coast Range). If the marine layer is shallow but manages to spill over the west hills usually there's a downslope effect which erodes the shallow stratus keeping it clear over Hillsboro and mostly clear to partly cloudy in Beaverton and Tigard (from my observation). If the marine layer is deeper than about 2000 feet there's no clearing effect most of the time, or the same mesoscale effects are in play that are governing the stratus body over the larger region (NW Oregon/SW Washington).

[Deweydog]

You could have made this exact same post five days ago, replacing "above normal" with "below normal" and it would have been an accurate representation of models at the time. They have shifted quite a bit the last several days, and there will likely be more shifts in the next several.

Tim?

[Jesse]

Tim?

Nice try but no. That was a pretty reasonable statement, and my rhetoric hasn't even approached his lately. Although I know how much you would like me to match his mania. Makes the world feel right to you.

[TT-SEA]

Nice try but no. That was a pretty reasonable statement, and my rhetoric hasn't even approached his lately. Although I know how much you would like me to match his mania. Makes the world feel right to you.

I have not said much of anything about August. July is over. That was the month we got caught up in tracking so closely. Did not expect that to happen by saying that the first part of the month would be cool and the last part would be warm locally.

[Deweydog]

Nice try but no. That was a pretty reasonable statement, and my rhetoric hasn't even approached his lately. Although I know how much you would like me to match his mania. Makes the world feel right to you.

Seemed like a Tim-like rationalization. A trationalization, if you will.

 

Everyone knows models shift and such. And since changing their tune pretty significantly a couple days ago they've been fairly consistent showing a fairly typical mid summer pattern coming up.

[Jesse]

Seemed like a Tim-like rationalization. A trationalization, if you will.

The post was in English too, which is also suspiciously Tim-like. Hmmmm....

[Jesse]

Everyone knows models shift and such. And since changing their tune pretty significantly a couple days ago they've been fairly consistent showing a fairly typical mid summer pattern coming up.

It is late-summer now, thank you very much.

 

Lughnasadh was last week.

[Deweydog]

It is late-summer now, thank you very much.

 

Lughnasadh was last week.

It's a weird year!

 

I already told you guys last week to throw climo out the window!

[Jesse]

Mark's latest 7-day has every day above 85 for the next week...

 

I don't think we've seen a stretch like that yet this summer. Although not sure if it will verify.

[Deweydog]

Mark's latest 7-day has every day above 85 for the next week...

 

I don't think we've seen a stretch like that yet this summer. Although not sure if it will verify.

Sunday looks frigid.

[Jesse]

Gorgeous day. Looks like the last afternoon temps in the comfortable range for several days. Get out and enjoy!

[Anti Marine Layer]

It seems there is a double marine layer inversion in the PAC NW this afternoon with a typical fog layer at the coast and the old, deep marine layer slowly evaporating in some areas west of the Cascades.

Marine layer makes in further inland in the Pac NW than any place in California.

 

Always wondered if marine layer clouds could reach across the whole country if the mountains were to suddenly disappear.

[Deweydog]

Cooling off out there.

[snow_wizard]

Today would have been the next chance of storms but NWS seems pessimistic about it on the AFD.

 

Sheesh, only had 3 t'storms since the start of Meteorological Summer (June 1st). None in the most likely month to have them (July).

 

Not looking good!

The 4 Corners high has been almost non existent due to the dominating GOA ridge. One feature I'm very happy about this summer. Not good for your cause though.

[snow_wizard]

It seems there is a double marine layer inversion in the PAC NW this afternoon with a typical fog layer at the coast and the old, deep marine layer slowly evaporating in some areas west of the Cascades.

Marine layer makes in further inland in the Pac NW than any place in California.

 

Always wondered if marine layer clouds could reach across the whole country if the mountains were to suddenly disappear.

No way.

 

I think the marine layer makes it further inland up here due to lower sun angle and terrain in some cases. Amazingly it makes it east of the Cascade Crest in Kittitas County due to fairly low gaps in the mountains.

[snow_wizard]

Cooling off out there.

Sunday looks frigid.

I think Sunday will be the bust day for his forecast.

[Jesse]

Cooling off out there.

Good. Hoping for 50s tonight.