HPC: Eastern Trough likely permanent through Fall

[Derecho]

http://www.hpc.ncep.noaa.gov/preepd/preepd.html


PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
800 AM EDT SUN JUL 18 2004



...THIS TROUGH WILL AMPLIFY...
ENCOMPASS A GOOD PORTION OF THE CENTRAL US AND EVENTUALLY PROGRESS
DOWNSTREAM INTO THE ERN US BY THE END OF THE FCST PERIOD WITH
AGAIN WELL BELOW NORMAL HTS AND H85 TEMPS. MODEL RUN OUT OF GFS
INDICATES THE MEAN TROF WILL PERIST FOR THE FORESEEABLE FUTURE.

ANALOGS BASED ON THE UPCOMING PATTERN AT D+8 AND D+11 ARE YEARS
1990/1956/1981/1994/1975/1973. ALL OF THESE EXCEPT 1973 KEPT UP
A PERSISTENT PATTERN FOR A MONTHLY AVERAGE THRU LATE SUMMER AND
EARLY FALL OF MAINTAIN A CENTRAL TO ERN TROF AND WRN RIDGING.
ONLY 1973 REVERTED TO A ERN RIDGE/ROCKIES TROF.....


All analog years were devoid of East Coast hurricane landfalls, tons of early CV recurvers, and very light on any landfalls at all of hurricanes, other than Eloise...interesting

[Stephanie]

That is very interesting. Thanks for sharing.

My main concern now is with the ridge out west - those people need rain!!

[Rainband]

Looks like a GOM year!! Things can change though so we shall see.

[Trader Ron]

Looks like a VERY quiet year....We'll see..

[Weatherboy1]

I just don't see how this kind of trof can persist for a long period of time in late July/early August. It's just so climatologically "out of whack" that a normal pattern has to return, doesn't it? And from what I can remember of past recent seasons, we tend to "flip flop" from west coast ridge/east coast trof and back again, usually every few weeks. That's what happened already this season ... we had a strong ridge/Bermuda high for several weeks in June and early July ... now, we've flipped into the opposite pattern, with a strong trof. My guess is we will eventually flip back. But then again, any of this long-term forecasting stuff is really just guesswork anyway. Anything's possible...

[KatDaddy]

If the trough remain persistent TX will be protected by uncommon Summer Westerlies associated with the E US trough

[Stormsfury]

http://www.hpc.ncep.noaa.gov/preepd/preepd.html


PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
800 AM EDT SUN JUL 18 2004



...THIS TROUGH WILL AMPLIFY...
ENCOMPASS A GOOD PORTION OF THE CENTRAL US AND EVENTUALLY PROGRESS
DOWNSTREAM INTO THE ERN US BY THE END OF THE FCST PERIOD WITH
AGAIN WELL BELOW NORMAL HTS AND H85 TEMPS. MODEL RUN OUT OF GFS
INDICATES THE MEAN TROF WILL PERIST FOR THE FORESEEABLE FUTURE.

ANALOGS BASED ON THE UPCOMING PATTERN AT D+8 AND D+11 ARE YEARS
1990/1956/1981/1994/1975/1973. ALL OF THESE EXCEPT 1973 KEPT UP
A PERSISTENT PATTERN FOR A MONTHLY AVERAGE THRU LATE SUMMER AND
EARLY FALL OF MAINTAIN A CENTRAL TO ERN TROF AND WRN RIDGING.
ONLY 1973 REVERTED TO A ERN RIDGE/ROCKIES TROF.....


All analog years were devoid of East Coast hurricane landfalls, tons of early CV recurvers, and very light on any landfalls at all of hurricanes, other than Eloise...interesting

Analogs are used for good reason and can give a general idea of a seasonal overall pattern ... and analogs can shed some insight on future weather patterns/predictions, etc. As Derecho pointed out, the CV storms that developed in these years had a tendency to recurve early.

Also, let's point out that MOST all these years also were in a period of less TC activity with the exceptions of 1956, and 1990. There are no absolutes ... something could slip through the cracks, so to speak, but Rainband also brings up a good point about the GOM.

SF

[elw]

And SF, the Water temperature profile in the North Pacific Supports the continuation of a Western Ridge/Eastern US trough for some time.

Remember back in June when we had the monster ridge in Western North America and all the record heat in Alaska and the Yukon?

[Stormsfury]

If the trough remain persistent TX will be protected by uncommon Summer Westerlies associated with the E US trough

Not necessarily ... and that also is in regard to the East Coast as well ... varying degrees of the strengths of the ridge and trough, and the minute wavering of the placements of these features one way or another will take place, and a wrongly (or rightly, depending of one's perspective of things) timed storm hitting a weakness (channel) can occur even in an area protected by a trough 5½ months out of the 6 months in the Tropical Atlantic Season.

Although, just about every year, you generally see a hurricane channel or corridor in regards to track overlays (or principal storm tracks in a given tropical season), but there are always aberrations amnd other systems that do not follow that rule, etc..

In 2002, the channel targeted Lousiana ...


In 2001, the channel was around 65W in the Central Atlantic.


In 1999, there were 2 apparent channels for storm tracks ...


Just examples ...

[Dean4Storms]

A question that arises in my mind is how many of these past analog years had a neutral El Nino in place as well?

[LarryWx]

SF and others have made some good points here.

PERHAPS there will be a persistent protective eastern US trough for the heart of the season, which I'd agree would probably significantly reduce the threat on the east coast from what otherwise had been the case. Then again, who the heck knows at this VERY early stage? And even with that, one can still slip in between the cracks.

My opinion about analogs is that one should not assume too much statistical credibility with analogs in general. I have a couple of reasons for saying this. First, the atmosphere is far too complex to allow for high stat. cred. The forecaster has mentioned a handful of analog years as opposed to, say, 50-100 years, which would have had a much higher stat. cred. Also, coming up with any one analog year is a SUBJECTIVE process. Another forecaster could easily come up with different analog years. There are no set in stone ways to determine analog years for all met.'s.

For day 11, I'm assuming they are putting a lot of weight on the day 11 accurate GFS and its accurate ensemble mean. If that is the case, knowledgeable weather people should imo know better. Furthermore, have we really been in a persistent eastern trough pattern for a long time?

I'm not making too much of this NCEP discussion whatsoever because I feel it amounts to a shot in the dark. Whereas I think that analogs are a useful tool, I also feel they are often overrated. By the way, people familiar with the typical tone of my posts will hopefully think of me as objective and not anything close to either a wishcaster or the opposite extreme.

[Stormsfury]

A question that arises in my mind is how many of these past analog years had a neutral El Nino in place as well?

Source (CPC ENSO impacts on the U.S.)
1956 -- Strong La Niña
1973 -- Strong El Niño transitioning to Strong La Niña
1975 -- Strong La Niña
1981 -- Neutral ENSO
1990 -- Strong El Niño
1994 -- Moderate El Niño

SF

[LarryWx]

A question that arises in my mind is how many of these past analog years had a neutral El Nino in place as well?

Source (CPC ENSO impacts on the U.S.)
1956 -- Strong La Niña
1973 -- Strong El Niño transitioning to Strong La Niña
1975 -- Strong La Niña
1981 -- Neutral ENSO
1990 -- Strong El Niño
1994 -- Moderate El Niño

SF

Bingo! Here already is a good example illustrating why to realize my point that choosing analog years is such a subjective process. IF ENSO had also been considered, all but 1981 could have easily been eliminated.

Also, if only 1981 were considered an analog, the credibility would be next to zero due to the sample size being miniscule (only one year).

[Stormsfury]

Bingo! Here already is a good example illustrating why to realize my point that choosing analog years is such a subjective process. IF ENSO had also been considered, all but 1981 could have easily been eliminated.

Also, if only 1981 were considered an analog, the credibility would be next to zero due to the sample size being miniscule (only one year).

And the factors this year vs. 1981 in regards to the PDO/ATL thermaline circulation are totally different.

1981 featured 15 EPAC TC's that year, vs. 1981's 12 TC's ...





Now, notice something very interesting about 1981 in the ATL ... NO GOM activity, whatsoever.

SF

[Guest]

Analog shmanalog!!! These "analogs" go back 100 years or so which is very little to go on when you consider weather has been happening for billions of years.I think a few hundred years need to go by before we can take these analogs more seriously & by that time we will all be long gone.Just because 53,69,80 were so called analog years does not mean the same exact wx patterns,tracks,etc will happen this year.As far as the EC Trough being "permanent",nothing is permanent.It will fluctuate from ridge to trough.We'll have to wait & see where the storms are in relation to these ridges/troughs.Are troughs always a saving grace??? NO! If there is a Allen or Gilbert in Caribbean when this trough digs in well then some one better lookout on the EC or GOM.If this trough hangs around till Sept & then lifts for a week just as a hurricane is arriving on the scene north of the Caribbean then what.

Its all about timing.

[ameriwx2003]

Agreed.. its about timing ..Also,,, doesn't the warmer waters in the Western Atlantic help support a ridge???Could be a interesting battle ground:):)

[LarryWx]

[And the factors this year vs. 1981 in regards to the PDO/ATL thermaline circulation are totally different.

1981 featured 15 EPAC TC's that year, vs. 1981's 12 TC's ...

Now, notice something very interesting about 1981 in the ATL ... NO GOM activity, whatsoever.

SF

OK, what the heck, now we can eliminate 1981. Oh no, we have zero analogs!! What now?

By the way, I clearly remember the 1981 season and its high level of activity off of the east coast especially in early September. On 9/12, there were 4 TC's on the map simultaneously: Emily, Floyd, Gert, and Harvey. I do remember met.'s repeatedly mentioning that the persistent eastern trough and its attendant W to WNW flow was safely keeping everything offshore. (No, I'm not saying this to make fun of Rainstorm's often mentioned protective WNW flow. There really was persistent W to WNW flow throughout that Sept not giving anything a chance to hit.) On the other hand, I remember Savannah getting some of the effects of TS Dennis with some decent rain and pretty gusty winds in late August of '81. That was an example of one that "slipped through" even though it wasn't a bad storm. Of course, it slipped through in late Aug., or before the eastern US trough became strong in early Sept.

[rainstorm]

If the trough remain persistent TX will be protected by uncommon Summer Westerlies associated with the E US trough

the whole us is safe. so much for jb, and dr gray

[Rainband]

the whole us is safe. so much for jb, and dr gray

Can I see your crystal ball??

[LarryWx]

If the trough remain persistent TX will be protected by uncommon Summer Westerlies associated with the E US trough

the whole us is safe. so much for jb, and dr gray

Rainstorm, saved by the WNW flow again?