August 2016 Observations and Model Discussion for the Pacific Northwest

[snow_wizard]

Yes..."good" being relative. But you have to admit the frequency of strong extratropical cyclones here is much less than the east coast where there are several nor-easters and strong coastal lows each year. We don't see widespread damage very often here and gusts above 60 mph are quite uncommon inland from the coast/NW Interior happening on average less than once every year when considering peak wind gust speeds at SEA and PDX over the last couple decades (and only considering winds associated with lows).

I would imagine high winds inland from the coast are much less common than along the coast on the Eastern Seaboard also. As for the coasts themselves... that would be an interesting thing to look into. I know the WA Coast gets storm force winds pretty often in the winter... gale force almost daily in some cases.

[IbrChris]

I would imagine high winds inland from the coast are much less common than along the coast on the Eastern Seaboard also. As for the coasts themselves... that would be an interesting thing to look into. I know the WA Coast gets storm force winds pretty often in the winter... gale force almost daily in some cases

An objective metric would be central pressure of non-tropical origin lows along both coasts...again we are looking more at frequency than single events. Even then cyclogenesis vs cyclolysis is not tied to the strength of lows but rather whether they are as a rule undergoing intensification or dissipation in a particular geographical area. If a 970 mb low becomes a 975 mb low it has lost strength to some degree (if measured by central pressure), if a 980 mb low becomes a 975 mb low it has gained strength. The one example is cyclolysis and the other cyclogenesis.

[Deweydog]

On a semi-related topic, why does the PNW get more windstorms in the Oct - Dec period than the Jan-Feb time frame?

Jet is typically stronger in early winter, I suppose because thermal gradients are typically more pronounced? Maybe...

[Jesse]

No problem...I think we could get along in an office environment so long as we don't discuss politics.

We probably could even if we did. My current boss is very conservative, and we frequently have good discussions without either of us crossing the line of getting too personal.

[IbrChris]

East coast cities are also closer to the coast (NYC, Boston) than Seattle and Portland. Even Philadelphia and Baltimore/Washington DC have a greater shot at high winds because there's no terrain obstruction between those cities and the coast.

[IbrChris]

We probably could even if we did. My current boss is very conservative, and we frequently have good discussions without either of us crossing the line of getting too personal.

True. This office has every persuasion. Conservative, progressive, libertarian, apathetic...probably some others. Haven't found a royalist yet but we do have a British expat in our group.

 

I will admit my libertarian views have divorced me from the right-left spectrum nowadays. Sure I have conservative views personally that I adhere to in my own life but I don't attempt to push those views onto others. My philosophy is mostly "live and let live" and "don't start none there won't be none." Probably good advice for the forums as well.

[Jesse]

Jet is typically stronger in early winter, I suppose because thermal gradients are typically more pronounced? Maybe...

I think you nailed it. At least at our latitude.

[snow_wizard]

East coast cities are also closer to the coast (NYC, Boston) than Seattle and Portland. Even Philadelphia and Baltimore/Washington DC have a greater shot at high winds because there's no terrain obstruction between those cities and the coast.

Certainly true but that is no fault of the storms.

[snow_wizard]

I think you nailed it. At least at our latitude.

I think that and Chris's idea about more tropical storm remnant potential in early storms.

[Jesse]

I think that and Chris's idea about more tropical storm remnant potential in early storms.

This is true too. I must have somehow missed that post.

[Jesse]

12z Euro ensembles are troughier than the operational days 6-10.

[Deweydog]

Starting to think PDX's all-time high of 107 degrees may be safe for at least another 10 days.

[Jesse]

Starting to think PDX's all-time high of 107 degrees may be safe for at least another 10 days.

The 105+ window quickly closes over the next 10 days.

[TT-SEA]

18Z GFS is very nice.

 

Looks like some great weather ahead.

[Deweydog]

The 105+ window quickly closes over the next 10 days.

Throw climo out the window!

[Jesse]

Throw climo out the window!

But it's closing!

[Deweydog]

But it's closing!

Break the ******* glass if you have to!

 

It's on!!!

[Phil]

I would imagine high winds inland from the coast are much less common than along the coast on the Eastern Seaboard also. As for the coasts themselves... that would be an interesting thing to look into. I know the WA Coast gets storm force winds pretty often in the winter... gale force almost daily in some cases.

Actually, some of the strongest gusts around here (outside the ridge tops) occur inland, downwind of the mountains, vs the coast. West of the Fall Line, we typically get several 60-70mph wind events through a typical November - April period. East of the Fall Line (DC metro, etc), peak gusts are typically ~10mph weaker.

[Phil]

Jet is typically stronger in early winter, I suppose because thermal gradients are typically more pronounced? Maybe...

I think it has more to do with wavelengths juxtaposed on the thermal gradients/TWLs. Otherwise you'd expect more severe windstorms in January-March.

 

We get much stronger windstorms here the February-April period vs the November-January period.

[Phil]

East coast cities are also closer to the coast (NYC, Boston) than Seattle and Portland. Even Philadelphia and Baltimore/Washington DC have a greater shot at high winds because there's no terrain obstruction between those cities and the coast.

We rarely get strong onshore winds though, except during hurricane landfalls. Different story from NYC-northward, though.

 

Our big windstorms tend to occur on the back quadrants of deep lows undergoing cyclogenesis to our north, with downsloping off the Appalachians enhancing the gusts along/west of the Fall Line with a wind gust maximum along/just east of Parrs ridge.

[IbrChris]

Actually, some of the strongest gusts around here (outside the ridge tops) occur inland, downwind of the mountains, vs the coast. West of the Fall Line, we typically get several 60-70mph wind events through a typical November - April period. East of the Fall Line (DC metro, etc), peak gusts are typically ~10mph weaker.

That makes sense and for the most part is true in the higher elevations here as well. Tap into the stronger 925/850 mb wind field.

[snow_wizard]

I think it has more to do with wavelengths juxtaposed on the thermal gradients/TWLs. Otherwise you'd expect more severe windstorms in January-March.

 

We get much stronger windstorms here the February-April period vs the November-January period.

Kind of like the cold normally gets started earlier in the West also. The extreme numbers for Seattle are identical to NYC for November. After that the difference gets progressively larger through Feb.

[snow_wizard]

NOAA actually upper their predictions for the Atlantic hurricane season. Pretty gutsy considering how lame it has been so far and will continue to be for a while yet.

[Jesse]

Guess we'll have to wait another hour and a half to see if PDX hit #7 or not.

[Deweydog]

Guess we'll have to wait another hour and a half to see if PDX hit #7 or not.

Smells like 89.

 

And teen spirit.

[Jesse]

Smells like 89.

 

And teen spirit.

That came out in '91.

 

A preview of Saturday?

[Deweydog]

That came out in '91.

 

A preview of Saturday?

Starting to like 92.

 

92-93.

 

It snowed a lot that winter.

[Phil]

Kind of like the cold normally gets started earlier in the West also. The extreme numbers for Seattle are identical to NYC for November. After that the difference gets progressively larger through Feb.

Was about to comment on that. Seems we generally lag you guys as far as the seasonal progression is concerned.

[Phil]

That makes sense and for the most part is true in the higher elevations here as well. Tap into the stronger 925/850 mb wind field.

Yeah, once east/downwind of the Appalachians, on the typical W/NW winds there's a gust maximum on the Piedmont Slope from the Winchester/Martinsburg corridor to the Germantown/Manchester corridor. Almost all the trees there are shaped to W/NW winds and lean heavily to the E/SE.

[James Jones]

Was about to comment on that. Seems we generally lag you guys as far as the seasonal progression is concerned.

Why is that? November owns March out here as far as winter weather potential, while the opposite is true east of the Rockies.

[BLI snowman]

Why is that? November owns March out here as far as winter weather potential, while the opposite is true east of the Rockies.

November is inversion season, March for all intents and purposes is not. Sun angle simply impacts us more here than back east, where the air masses are much more uniform.

 

The frequency of upper level arctic air masses is pretty similar here at both opposing ends of the cold season. We can still get very definitive continental air masses in March with a similar degree of frequency, they just tend to be extremely mitigated by the sun and low level cold pools are unreliable at best by February 20 or so.

[Front Ranger]

November is inversion season, March for all intents and purposes is not. Sun angle simply impacts us more here than back east, where the air masses are much more uniform.

 

The frequency of upper level arctic air masses is pretty similar here at both opposing ends of the cold season. We can still get very definitive continental air masses in March with a similar degree of frequency, they just tend to be extremely mitigated by the sun and low level cold pools are unreliable at best by February 20 or so.

 

I think there's more to it than that, though. November is simply capable of colder air masses in the PNW.

 

March has never seen anything like Nov 1955, Nov 1985, or Nov 2010. Legitimate Arctic air masses that produced highs well below freezing across the western lowlands, no inversions necessary.

[Phil]

I think there's more to it than that, though. November is simply capable of colder air masses in the PNW.

 

March has never seen anything like Nov 1955, Nov 1985, or Nov 2010. Legitimate Arctic air masses that produced highs well below freezing across the western lowlands, no inversions necessary.

Agree with the bolded. I guess the question is, why?

 

Could be a number of factors.

[snow_wizard]

I think there's more to it than that, though. November is simply capable of colder air masses in the PNW.

 

March has never seen anything like Nov 1955, Nov 1985, or Nov 2010. Legitimate Arctic air masses that produced highs well below freezing across the western lowlands, no inversions necessary.

Actually 1955 had a very legit cold air mass in March also. SEA had a 29-11 day, but that is extraordinary. November is unquestionably capable of longer lasting cold and is aided by inversion potential. The cold in Nov 1985 was nothing short of majestic for so early in the season. 1955 was colder, but 1985 was much longer lasting. 1896 was incredible also.

[snow_wizard]

Models are having huge trouble sorting out the period around day 10. My suspicion is we will revert to a strong GOA ridge / troughing in the NW simply because that has been the default this summer. I'm prepared to be wrong about that though.

[snow_wizard]

Agree with the bolded. I guess the question is, why?

 

Could be a number of factors.

It almost seems the cold is more apt to lock in over the Eastern half of the continent as the cold season progresses. Early in the season the cold that effects us is more from the Yukon / Alaska or Siberia. We do get some really cold Februaries here on occasion, but they are much more common in the East.

[VancouverIslandSouth]

I think there's more to it than that, though. November is simply capable of colder air masses in the PNW.

 

March has never seen anything like Nov 1955, Nov 1985, or Nov 2010. Legitimate Arctic air masses that produced highs well below freezing across the western lowlands, no inversions necessary.

 

I don't think it's just local inversions he's talking about, but also intermountain inversions. During inversion season the intermountain regions of BC can form their own deep bitterly cold air masses so we aren't as dependent on dynamics to align perfectly to pull air masses down directly from the Arctic. When conditions are right at the upper levels, very deep cold air masses can rapidly build up in the BC interior Nov - Jan and the coastal-inland gradients spike. Not the case in March as evident in average temperatures of places like Prince George.

[BLI snowman]

I think there's more to it than that, though. November is simply capable of colder air masses in the PNW.

 

March has never seen anything like Nov 1955, Nov 1985, or Nov 2010. Legitimate Arctic air masses that produced highs well below freezing across the western lowlands, no inversions necessary.

Sun angle and low level cold played a huge part in how those events unfolded, actually. Otherwise, from a strictly upper level standpoint, there have been several very comparable March airmasses to those in the airport era that produced -10c and even -15c or lower 850mb temps over the lowlands. 1955, 1976, and 1989 to name a few.

 

If you look much further back at our climo, then other March events like 1906, 1897, 1896, 1870, 1867, and 1865 all work to disprove the theory that March can't produce significant arctic cold in the lowlands. In fact, from 1850 to 1899, March probably saw more frequent

[snow_wizard]

Sun angle and low level cold played a huge part in how those events unfolded, actually. Otherwise, from a strictly upper level standpoint, there have been several very comparable March airmasses to those in the airport era that produced -10c and even -15c or lower 850mb temps over the lowlands. 1955, 1976, and 1989 to name a few.

 

If you look much further back at our climo, then other March events like 1906, 1897, 1896, 1870, 1867, and 1865 all work to disprove the theory that March can't produce significant arctic cold in the lowlands. In fact, from 1850 to 1899, March probably saw more frequent <35 degree high events around Portland/Seattle than November did. Comparable in terms of airmass frequency but November's cold extremes generally still dwarf March's thanks to the sun angle and fully realized, less well mixed low level cold pools around the region.

Excellent points.

 

I still say the upper level pattern in Nov 1985 was beyond ridiculous though. The duration was insane for so early in the season. I do believe you are correct about March owning November from 1850 at least through 1895. The only notable cold November I can think of in there was 1859.

[BLI snowman]

Excellent points.

 

I still say the upper level pattern in Nov 1985 was beyond ridiculous though. The duration was insane for so early in the season. I do believe you are correct about March owning November from 1850 at least through 1895. The only notable cold November I can think of in there was 1859.

 

Yeah, I don't believe there were any other major November events until 1896.