HPC Medium Range Discussion...Low Model Confidence

[MWatkins]

Here’s a quick note about the most recent medium range discussion from the HPC…the agency which handles the extended range forecasting beyond the 5 day responsibility of the TPC. For folks who are big model fans who want to figure out which models are handling the synoptic set-up the best…I would strongly recommend reading this outlook every day.

http://www.hpc.ncep.noaa.gov/discussions/pmdepd.html

First…take a look at the coordinated positions of Irene on days 5 and 7:

Day 5:
http://www.hpc.ncep.noaa.gov/medr/day5nav_color.html

Day 7:
http://www.hpc.ncep.noaa.gov/medr/day7nav_color.html

HPC doesn’t make their own forecast…they coordinate with the TPC on the day 6 and 7 positions. Note their comment on the final discussion updated this afternoon:

FINAL MEDIUM RANGE DISCUSSION...

CONFIDENCE IS MARGINAL AT BEST...BUT THE 12Z NCEP ENS MEAN IS
REASONABLY SIMILAR TO THE PREFERRED 06Z GFS SOLN...SO ONLY MINOR ADJUSTMENTS WERE MADE TOWARD THE 12Z NCEP MEAN FOR THE AFTN PACKAGE. PSNS FOR IRENE WERE BASED ON COORD WITH TPC. HOWEVER...WITH THE 12Z GFS NOW KEEPING MORE RIDGING TO THE N OF IRENE AND STEERING IT ON A MORE SLY TRACK...CONFIDENCE IS INCREASINGLY DIMINISHING ON THE SYS TURNING NWD TO THE DEGREE THAT THE COORD TRACK IMPLIES.

Now…what that means…exactly…is still open for discussion. I personally believe the Carolinas are in for a bit of trouble…but I would not let my guard down any place south of there yet. For example, lets take a look at every single model from 18Z yesterday and compare the 24 hour forecast plot to the actual, 22.5N 58.0W at 2PM today:

Code: Select all

 
Forecast Model Positions from 8/9/05 at 18Z verification for 8/10/05 18Z
A90E    23.0N     57.1W
 A98E    23.0N     57.0W
 AVNI    24.9N     57.5W
 BAMD    23.2N     57.5W
 BAMM    23.1N     58.1W
 BAMS    24.0N     58.4W
 CLIP    23.0N     56.6W
 CLP5    23.2N     56.5W
 CONU    24.7N     58.0W
 DRCL    23.4N     57.7W
 DSHP    24.3N     58.8W
 DSNS    24.3N     58.8W
 GFDI    25.1N     58.0W
 GFDL    24.9N     58.6W
 GFDT    24.6N     58.3W
 GFTI    24.8N     58.2W
 LBAR    23.1N     57.3W
 MRCL    23.4N     57.7W
 NGPS    24.1N     59.8W
 NGXI    23.9N     58.7W
 OFCI    24.3N     58.7W
 OFCL    23.4N     57.7W
 SHIP    24.3N     58.8W
 SHNS    24.3N     58.8W
 XTRP    22.7N     55.8W
 GFDN    24.4N     60.1W
 OOPC    24.2N     59.0W


This storm is generating a ton of along-track forecast errors...

MW

[jabber]

Very nice information... just when I was feeling 'out of the woods'

[gatorcane]

so Irene is still a possible FL threat...

[WindRunner]

Carolinas are getting it for certain by the looks of that map.

[deltadog03]

irene is VERY much so a FL threat...just like GA,SC, NC

[gatorcane]

but that is the point he is trying to make.....it is very low confidence at this point so don't concentrate on the exact position based on these models.

[yoda]

Basically everyone from FL to VA should be watching... I know that is a large area... but still.

[tailgater]

thanx for the update and site MW

[WeatherEmperor]

Yes. Most of the models had a northward bias with Irene due to the fact that they were overdeveloping Irene when she actually did not develop as strong as forecast. Due to the fact that Irene remained weak and had a questionable low level circulation at best, she remained west or south of the track. If and when Irene will show signs of better organization and a more evident low level circulation then the models will get right back on track with the WNW to even NW motion they have been hinting at for so long. Until that happens, expect a more general westward motion.

<RICKY>

[gatorcane]

WeatherEmporer, no that was true a few days ago, a real ridge is forecasted to build off the east coast of the US within a couple of days that will steer it west...nothing to do with intensity..

[MWatkins]

but that is the point he is trying to make.....it is very low confidence at this point so don't concentrate on the exact position based on these models.

Thanks Chris...that is exactly the point.

I think the probability is that if this were to threaten the US east coast…NC/SC would be the place to look for a direct impact. However…given the low confidence in all model solutions…nothing that even the southern-most BAM guidance is currently showing a northward bias…the possibility is there for an impact south of NC/SC.

We have a lot of time to watch this system…heck recon is probably another 2-3 days before the first mission on this system. Everyone on the EC should be watching it…

MW

[yoda]

but that is the point he is trying to make.....it is very low confidence at this point so don't concentrate on the exact position based on these models.

Thanks Chris...that is exactly the point.

I think the probability is that if this were to threaten the US east coast…NC/SC would be the place to look for a direct impact. However…given the low confidence in all model solutions…nothing that even the southern-most BAM guidance is currently showing a northward bias…the possibility is there for an impact south of NC/SC.

We have a lot of time to watch this system…heck recon is probably another 2-3 days before the first mission on this system. Everyone on the EC should be watching it…

MW

Good post MW and I agree.

[Anonymous]

I am thinking SC/GA....given it should move more west-northwest under the ridge...I would think.

[WeatherEmperor]

WeatherEmporer, no that was true a few days ago, a real ridge is forecasted to build off the east coast of the US within a couple of days that will steer it west...nothing to do with intensity..

boca-chris even the NHC mentioned this in their discussion. As per their 11am discussion that very same ridge you are mentioning is forecast to have a weakness in it and move towards the east allowing Irene to go more northward. The facts are the facts regardless of what my opinion is or what yours are. But you could be right afterall. Thats why once again the waiting game continues until......the 00Z models come out.... And it has alot to do with intensity because the pro-mets here even agreed with me that had Irene REALLY intensified like it was forecast to do so, it would have gone fishing long time ago.

<RICKY>

[gatorcane]

yes ricky I agree with you...I'm curious how Irene will handle this building East coast ridge...???

[WeatherEmperor]

yes ricky I agree with you...I'm curious how Irene will handle this building East coast ridge...???

By the way, if you end up being right and me wrong your not gonna serve me crow are you?

<RICKY>

[frederic79]

I was noticing the same thing. If you look back at the 11AM position from 2 days ago you'll see that Irene was positioned at the same exact same latitude as today's 11AM postition. What official track EVER forecast Irene to move due west for 48 hours? None. Surely it's based on intensity or lack thereof, but still, forecast track errors are pronounced and therefore, all models should be questioned at this point.

[deltadog03]

hey my forecast did...lol

[gatorcane]

The models are not good when there is no system...in this case we have a marginal system, more likely a wave still. That is the problem.

[TreasureIslandFLGal]

from what I've gathered, Irene missed the initial weakness in the ridge that could have sent her northward -because her intensity was weak at the time she continued more westward.
her strengthening at this point does not necessarily entail an automatic poleward motion as the ridge is now strengthening above her, not weakening, making her have to take the more westerly path whatever her intensification may be from this point on.
there then seems to be 2 options for the ridge in the longer term... my local mets say it stays strong but does lift northward to the point that it straddles the northern part of FL. The other option is that the ridge gets weakened on its left side in the longer term because of what comes cutting across the northeast, affecting the ridge and allowing a weakness that Irene may be able to take advantage of and head poleward.
but...does the weakness even occur, and if it does, how much will it affect the ridge...breaking it down and allowing Irene to "fish" or merely breaking down enough to head to Carolina or points southward?
-time will tell. it looks to me like we need to watch what is happening in the north-central US to see how strong that weather pattern is that is developing, so we can predict how it might affect the ridge in a few more days.