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Medium Range Discussion Summer 2012


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I think the overall cold pattern for the central and eventually eastern 1/2 of the country will persist for at least another 2 weeks. Models tend to be too quick in breaking down blocking patterns, and this one looks to be here to stay. A recurving Typhoon Samba, as well as a couple prospective recuvers further down the line (~a week from now?), teleconnects with further east coast troughing.

Also, MJO has continued to progress quite steadily (albeit weakly) through phases 4 and 5, despite some recent model predictions to slow or stall altogether. I believe it will slow a little, but remains progressive enough to reach phase 1 in 8-12 days. Phases 1 and 2 are both cold phases in the fall, so if the MJO continues to propagate into phase 2 and perhaps continues to slow, we could be talking a fairly long-lived cool spell.

Starting to look more like a temporary MJO stall / weakening similar to what we saw Aug 30-Sep 4 (different phase of course). This may introduce a chance of the Great Lakes getting a warm shot between this weeks' cold spell and a return to cold once MJO does reach phases 1 and 2.

I still think GFS may be breaking down +PNA too quickly and not correctly resolving meridional momentum and enthalpy flux from recurvature of Sanba, so verification may still be cooler in the east than what the 6Z GFS 180 forecast is saying right now.

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Starting to look more like a temporary MJO stall / weakening similar to what we saw Aug 30-Sep 4 (different phase of course). This may introduce a chance of the Great Lakes getting a warm shot between this weeks' cold spell and a return to cold once MJO does reach phases 1 and 2.

I still think GFS may be breaking down +PNA too quickly and not correctly resolving meridional momentum and enthalpy flux from recurvature of Sanba, so verification may still be cooler in the east than what the 6Z GFS 180 forecast is saying right now.

I was noticing that on the GFS also. Seems to want to plow a system into the West coast sometime next week. Then reverse the Ridge to the East and a trough in the West but, that is long range and not to worries about that far out. This front this weekend seems very strong and could bring some first frosts to some area.

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International Falls, MN got down to 20 this morning, shattering the record of 27 from 1918. This is the second year in a row that they've reached very chilly temperatures in September. On 9/15/11, they dipped to 19, by far their coldest temperature so early in the season.

Not a very scientific response... however I surely hope this doesn't mean repeat of last year. :unsure:

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I was noticing that on the GFS also. Seems to want to plow a system into the West coast sometime next week. Then reverse the Ridge to the East and a trough in the West but, that is long range and not to worries about that far out. This front this weekend seems very strong and could bring some first frosts to some area.

Looks like some sort of compromise between what I was advertising last week and what the long-range GFS ensembles were showing will verify. The original GFS idea of an Indian summer / ridging building in for the eastern US no longer looks to verify, with a series of shortwaves (Euro) or single cutoff (GFS) now advertised.

However, the prospect of a continuation of unseasonably cold air busted with my MJO forecast. After what had been an extremely progressive MJO pattern, the signal suddenly stalled / died in phase 6. It appears that a series of westward-propagating near-equatorial waves with 2-10 day periods disrupted the eastward propagation of the MJO.

http://www.atmos.albany.edu/facstaff/roundy/waves/hovsdet/2.5N_12.5N/2012.png

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You're going to have to explain that to me. The 2-10 day waves are easterly waves are they not? How are they disrupting the MJO?

Correct, the 2-10 day waves are easterly waves. You can see two fairly strong easterly waves on the link I posted coinciding with the location of the MJO OLR anomalies between 135 E and 180 E (W/C Pac) over the last week or so. Note the weakening of the MJO as they cross.

While I've heard that it does occur, I'm not an expert on how it occurs. My understanding is that the easterly wave generates enhanced LL convergence "behind" (west of) the MJO as they cross, triggering convection where MJO subsidence should be. Similarly, enhanced easterlies behind the easterly wave also weakens the LL convergence ahead of the MJO, weakening MJO convection. Together, this should cause the MJO to stall/weaken, especially if the easterly waves are strong and the MJO is weak to begin with. Maybe if Mike V sees this thread he can explain it better than I can.

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Correct, the 2-10 day waves are easterly waves. You can see two fairly strong easterly waves on the link I posted coinciding with the location of the MJO OLR anomalies between 135 E and 180 E (W/C Pac) over the last week or so. Note the weakening of the MJO as they cross.

While I've heard that it does occur, I'm not an expert on how it occurs. My understanding is that the easterly wave generates enhanced LL convergence "behind" (west of) the MJO as they cross, triggering convection where MJO subsidence should be. Similarly, enhanced easterlies behind the easterly wave also weakens the LL convergence ahead of the MJO, weakening MJO convection. Together, this should cause the MJO to stall/weaken, especially if the easterly waves are strong and the MJO is weak to begin with. Maybe if Mike V sees this thread he can explain it better than I can.

Is this similar to how easterlies near indonesia associated with La Nina will also prevent further progression of the MJO?

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