• Category Archives AO
  • Warmth Dominates Now, But A Cold & Wintry Pattern Is Lurking For The Holidays…

    The short-term weather pattern will continue to be dominated by rather “boring” conditions for this time of year, along with much milder than normal air.  A weak frontal system will swing through here Thursday and while a light shower is possible, that’s really the only significant (if you want to call it that) weather feature through the upcoming 7-10 days.

    In addition to the rather quiet weather, relative warmth will dominate as we open December.  When “normals” feature lows in the upper 20s and highs in the lower 40s, actual overnight lows will only fall into the low-mid 30s and highs will reach the middle to upper 50s.

    When we look ahead, the shelf life of this warmth is certainly limited.  The GEFS showcases this shift in the pattern from a warm open to the month towards a much colder pattern very nicely.  The GEFS has other model support, as well.

    This is the type of dramatic shift in the overall pattern that not only threatens to “lock in” a colder than average regime, but potentially lead to plenty of wintry mischief to boot, and just in time for the holiday season.

    There’s teleconnection support for the wintry shift, as well, leading to further confidence of a significant move towards cold, and potentially snowy/ icy, conditions as the true holiday and Christmas season approaches.

    To summarize, while unseasonably quiet and mild conditions will rule in the short-term, Mother Nature sure seems to have an attitude of making up for “lost time” in the medium to longer range.  This is the type pattern that we’ll have to monitor the potential of some sort of leader-follower scenario as the transition from warm to cold takes place, and given the blocky nature of the pattern, it sure seems like we’re heading into a busy time of things from a wintry perspective mid and late month.

    Perhaps this will be the scene as Christmas time nears across the Mid West, including central Indiana?  Time will tell…


  • “Block Ready To Rock?” Cold Pattern Developing Around Thanksgiving…

    Model data continues to suggest a Greenland block will develop as we progress into late-November.  This kind of pattern creates a “log jam” of sorts in the weather pattern and is the type pattern notorious for unseasonably cold regimes across our region.  The overall agreement between various models raises our confidence in this pattern unfolding as Thanksgiving nears.

    Such a pattern illustrated above, per the European ensemble (image 1) and the GFS ensemble (image 2), would help drill a tongue of unseasonably cold air through the northern Plains, into the Mid West, and across the East.

    A look at the 00z teleconnections this morning shows 3/4 “big boy” drivers going to that cold look for late-November, as well:

    We’ve been discussing early snow cover across Canada and the northern tier for weeks and how models would have to “correct” colder as they realize the air masses traveling over the snowpack won’t be able to modify as they normally would without that snowpack.  The differences between this November and last are startling and show how the early snowpack is beginning to “feedback” on itself leading to early-season cold air.

    2016 snowpack and temperatures anomalies through the first week of November:

    2017 snowpack and temperatures anomalies through the first week of November:

    Given the overall look to the pattern downstream, I anticipate the cold will continue to “press” and eventually overwhelm the pattern east as we progress through the second half of the month.

    To close, we expect a developing Greenland Block to help drive an unseasonably cold late-November, including the Thanksgiving holiday.  This is the type pattern that can also help generate early season wintry “fun and games,” however it’s far too early to be specific with any sorts of potential wintry events that may eventually come in this pattern.  Stay tuned.


  • Shift Back To A Cold Pattern Awaits; What About Winter Storm Potential?

    December-to-date is running colder than normal (to the tune of 2.2 degrees at IND), but the past (7) days has seen a flip in the frigid 1st half of the month.

    December temperature anomalies, courtesy of Weatherbell.com.
    December temperature anomalies, courtesy of Weatherbell.com.
    Temperature anomalies the last 7 days. Courtesy of Weatherbell.com.
    Temperature anomalies the last 7 days. Courtesy of Weatherbell.com.

    The “relaxation” is temporary.  Modeling continues to advertise the recent “thaw” will give way to increasingly bitter times as we get deeper into the New Year.  By New Year’s Day we note the positive heights continuing to establish themselves across Alaska and Greenland (cold and stormy signal).  We also note the southeast ridge present, though to a lesser degree than over the past week.

    jan1By Day (10), the cold pattern is well established over the Lower 48.  This is a coast-to-coast cold signal (heart of the cold centered over the west and central) depicted by the European ensemble, along with other modeling.

    day10

    ecmwf-ens_t850amean_namer_6Teleconnections support a cold pattern returning.

    epowpo122916

    aonao122916

    pnaThe agreement amongst teleconnections is nice to see and ups confidence in the overall direction of where this pattern is heading in regards to colder than average times looming.  The negative PNA correlates nicely with the SE ridge that continues to make itself heard from time to time over the next few weeks.  It should also be noted that the phases of the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) become more of a factor for mid and late winter.

    As far as storminess goes, we’ll have to handle those as they come.  The overall pattern screams towards the idea of an active Ohio Valley to interior Northeast storm track as we move forward (continuing deeper into mid and late winter, as well).  That doesn’t mean one or two storms won’t bypass our local region to the south, due to strong, cold high pressure north, but the mean storm track should put areas through the Ohio Valley in the “sweet spot” from a snow perspective throughout the majority of January, and the rest of winter, for that matter.  Depending on the position and strength of the Greenland Block will have a lot to say about things.  Needless to say, storms cutting NW into the central Lakes should be few and far between after the New Year.  Speaking of storms, we have to continue to keep an eye on the second half of next week.  At the time of this discussion, the threat is still beyond the 7-day period, but circle late next week and weekend for the potential of wintry “mischief.”


  • A Word (Or Two) On Where We Think This Pattern Is Going…

    Before we get into the updated thinking on the pattern, lets review what we have out:

    • Step-down process to cooler/ colder weather begins in mid-November.
    • Thanksgiving-Christmas period, as a whole, turns wintry and is snowier than average.
    • Our complete 2016-2017 Winter Outlook can be found here.

    The first week of November has featured an incredibly warm start to the month. (Image courtesy of MRCC).

    month-tdevSpeaking of warmth, 2016 has been a very warm year.

    ncep_cfsr_t2m_anom_ytd(The cold of 2014 seems so long ago…)

    ncep_cfsr_t2m_anom_2014Back to present.  We’ve targeted the middle part of November to finally beginning “bucking” the recent warm trend.  This won’t happen overnight and will be a battle of back and forth, initially.  Thus, the “step-down” label.  To be clear, November, as a whole, will finish much warmer than average.  It’s virtually impossible to counter the incredibly warm start.  That said, we do anticipate “jabs” of colder air working in here over the next couple weeks. For instance, this weekend will feature lows in the 20s for most and highs not making it out of the 40s Saturday afternoon.  (The average low and high at IND Saturday are 37 and 54).

    Despite being in a weak La Nina, the pattern is taking a while to respond.  Remember, we’re coming off one of the strongest El Ninos on record.  Until we slow the PAC jet, significant, long-lasting, changes won’t occur.  We can lean on the AAM (Atmospheric Angular Momentum) forecast for clues as to when this may occur.  You can read more about the AAM here.  My fellow local weather compadres, Michael Clark, Ed Valley, and Kirk Hinz have also written/ blogged extensively about the AAM and resulting impacts.

    gfsgwo_1

    gfs1When we look at the AAM forecast (above), we note the westerlies may begin to slow (indicative of the negative values) in the 8-10 day period.  This is crucial and, simply put, has to happen for the pattern to begin shifting into more of a position to allow sustained cold to enter the equation.  We want to reiterate that this, in and of itself, doesn’t create the cold, but instead allows the pattern to begin shifting away from the Nino-like (warm) regime into more of a La Nina pattern, as a whole.  – Hey, you have to start somewhere.

    If we can finally get the westerlies to slow, other elements are in play that could (and should) lead to a colder pattern as we move forward.  Our (3) big teleconnections are in a position favorable for cold for mid/ late November, into early Dec.

    cw5yrrsxaaefhiy-jpg-largeAdditionally, the EPO is forecast negative off the GEFS and EPS. (Images courtesy of Weatherbell.com).

    eps_epo_bias

    gefs_epo_12Again, this is a cold signal. (Image courtesy of Madusweather.com).

    eponew_neg_11novThe ensemble data is also beginning to key-in on higher heights (blocking) developing over the top.  Notice the significant changes in the overall look to the pattern between now and days 11-16. (Images courtesy of Weatherbell.com).

    cw5qrw0wgaaphxr-jpg-largeIn summary, and in the face of *most* seasonal data that is screaming warm, warm, warm, we still don’t have any significant changes to our overall thinking of “step-down” mid-November giving way to more sustained wintry-like conditions in the overall sense from the Thanksgiving-Christmas period.  Time will tell and only the Good Lord knows what the future holds, but we’ve done far too much work and research to throw the “game plan” in the trash before the game even begins…


  • Overwhelming Evidence On Mid Month Cold…

    The step-down cold pattern early January is ongoing, but we’ve been clear with our thinking of even colder air invading around mid month (Jan 10th-20th time period). We wanted to show the data that continues to come in supporting this idea.

    All three major teleconnections (AO, NAO, PNA) are aligning in a fashion that supports cold weather for our particular part of the country.

      
    The MJO suggests mid month cold rolls right through the next several weeks, as noted here.

       
     
    Ensemble data continues to support the cold idea.

       
        
     
    While individual storm systems with wintry potential will have to be dealt with as they come, it’s very easy and clear to see the shift towards a downright wintry feel in the days and weeks ahead…


  • A Word About What Lies Ahead…

    No need for model data or fancy graphs with this post, but instead we just wanted to level set with you on where we think we’re heading as we rumble into 2016 and deeper into winter.

    In short, we have zero change in our thinking since fall that though this winter would open warmer than normal in December, we would, in fact, have a winter to contend with (back loaded). Our reasoning behind this thinking has been laid out time and time again in our winter outlook and archived posts so there’s no reason to bore you again with those thoughts. 

    We think early January shifts colder from where we’ve been, but we’ve been saying it’s not until mid month where things can really lock in and crank. Though colder, the first half of January is likely to still be a bit transient. (By the way, there’s potentially a significant storm system waiting on deck week 2 that may be plenty capable of producing wintry mischief). That storm is the one that should precede the whole sale pattern shift to more sustained cold and snow across the Ohio Valley and Mid West region that carries us through the back half of the 2015-2016 winter.

     

    Week 2 shows an active southern stream and developing negative AO. Source: Tropicaltidbits.com

    To sum things up, we have absolutely zero changes to our ideas on the winter from back when we initially released our winter outlook. Winter is coming this year, despite what you may be hearing :-). 

    The transient 1st half of January will likely turn progressively colder in more sustained fashion for the 2nd half of the month. In the meantime, if you’re someone who likes to review each and every model suite as they come, have the dramamine handy, as wild swings will continue with operational model runs. Instead, we suggest leaning more towards the ensemble data as we work through this pattern transition (always tough on model data). 

    Much more later! As always, you can follow us on Twitter @indywx!