Some Pattern Thoughts & The Next Few Weeks.

Issued
12-17-2011
Saturday 8:00 AM

It's time for an update, along with some thoughts on this pattern ! Too be honest it really stinks for those who love winter weather and snow. Our fast start to winter is not happening this year and teleconnections continue to be very unfavorable for any sustained cold and snow here in the Eastern US. The main reason for the mild December and no snow so far (Other than the freak late October storm) is due to a + AO and + NAO signal, with no blocking whatsoever !

The PNA which was negative during much of November into the first week of December has switched to Positive and near neutral levels. This Pacific signal going positive is the only help we've had since the 7th/8th in getting some 2-3 day transient cold shots. But with no blocking due to the + AO and + NAO, the troughs are transient and progressive, so the cold air has no staying power. This also allows many systems to cut to the Midwest and G/L's. With this type of storm track being to our west, these storms then bring in a SW flow of milder air ahead of them, along with rain to much of the Eastern US.

As we all know, the past 2 winter seasons, started off fast and furious, with December being quite cold relative to normal, and 2 major winter storms near Christmas time. The pattern now is much different with opposite teleconnections and a La Nina pattern. Often times with a La Nina winter and bad teleconnections, this favors milder than normal temps and less snowfall here in the M/A and NE.

A December Bust ! Ouch
In my Winter Forecast I was expecting these teleconnections to be different here in the month of December or similar to the past 2 years. This is not the case, so my forecasted early start to winter with another cold December Isn't going to work out this time. PHL, PA : December is averaging well above normal with temperatures through mid-month at +5.1 F through the 16th. So with my Winter forecast of -2.0 to -4.0 for Dec it looks like a solid BUST and start to my winter call ! Over the next 2 weeks, I expect temperatures during this period to average near to slightly above normal through the 2 week period. We'll have a few days which could be slightly below normal from near Christmas and during the last week, but some above normal temps occurring during this upcoming week. Normal Highs are in the mid 40's and then drop to the low 40's towards the end of the month. The month of December will probably finish at +4.0 F to +6.0 F with only an outside shot at some snow or a mixed event from near Christmas time to the end of the month.

Ok, now that I've admitted my December bust and explained why, let's move on and talk about where I think We're heading as we progress into January. With teleconnections continuing to be unfavorable through the first week of January and this locked in pattern with no evident blocking, I don't see any sustained cold or major snow events through this period. We could thread the needle, and see some snow (Minor) or a mixed event between 12-25-11 and 1-5-12. Temperature will likely average near to slightly above normal during this period, but I don't expect any more unseasonably warm weather where we hit the 60's. Transient troughs and cold shots will occur, so like I mentioned We'll likely see several days where slightly below normal temperatures occur.

With this pattern and unclear teleconnections heading into the New Year, it's really tough to say what January will bring. I'm being honest this is very tough forecasting this year and La Nina patterns are tricky as our region is usually on the fine line. If January transitions into a colder/snowy pattern we need to see the following things occur.

Our teleconnections need to change !
The AO must head to at least neutral, but a more -AO signal would be ideal to dump the coldest air into the CONUS. With a +AO this very cold air has been locked up to our north in Canada and towards the Pole/Arctic regions. Higher heights near the pole region a (-AO) and blocking is the main mechanism to force the cold air south and east towards the States. So I'll continue to monitor the AO carefully for these possible changes over the next few weeks.

The NAO has also been Positive and this also needs to go negative. This signal is where I look for blocking towards Greenland /North Atlantic and the Davis straights regions. When negative and seeing higher heights (-NAO) this promotes a trough in the east and coastal storm development. This is where we usually get the colder weather and bigger snow events along the east coast. The NAO has been running slightly Positive to near neutral over the past month, this promotes many systems to cut to out west and milder temps here in the East. So this too needs to change and head more negative.

I'll update more on these teleconnections and the overall pattern towards the New Year and see where we stand to further my thoughts into the month of January !

For now expect no sustained cold weather or any major snowstorms through January 5th. A thread the needle minor snow or mixed event is possible between Christmas and January 5th, with only a few days seeing below normal temps. I expect only transient cold shots and troughs moving through with overall temps being near to slightly above normal.

Take Care,
Ruggie