• Category Archives High-latitude Blocking
  • Times Are Changing, Or Are They?

    January-to-date is running milder than normal across the region- to the tune of 3.3 degrees (F).  This is after a frigid open to the month, as you recall.

    conus_mtd_t2max_anom_2017The second week of the month warmed significantly and continues, overall, for the next week.

    ncep_cfsr_noram_t2m_week_anomThe mid-January warmth is attributed to a roaring PAC jet which is currently helping flood the country with temperatures much more like spring than the dead of winter.  We continue to forecast 60+ this weekend across central IN.

    Winter lovers, have no fear as changes appear to be in the offing as we go through the last few days of January and head into February.  The winter so far has featured conflicting signals that continue to try and compete with one another to take hold of the pattern.  Can we get these drivers to align in a way that would pull a more persistent trough into the east for the second half of the winter and, ultimately, set-up a sustained cold pattern helping make up for lost time in the snowfall department?  Time will tell, but we do note the following late month:

    • (+) PNA pattern
    • Sudden stratospheric warming event
    • High latitude blocking

    All are encouraging for a shift back towards a wintry regime.  As always, the devil is in the details and we’re skeptical as to the longevity of these signals.  “Cautiously optimistic” would be the way to sum up our current feel longer-term into the month of February, but we’re not as bullish on lock and hold cold, wintry conditions at this time as what you may hear from some of our national compadres.  Understanding that various drivers can have a different impact mid and late winter as opposed to early is one thing.  It’s also important to note that long term modeling has been abysmal as of late and we want to tread through the next couple of weeks with caution to see whether or not the cold drivers can finally take hold.

    Needless to say, at least through late month, one can see the significant changes take place at 500mb.

    Thursday:

    ecm_eps_z500a_noram_2This Weekend:

    ecm_eps_z500a_noram_5Next Thursday:

    ecm_eps_z500a_noram_9Next Weekend:

    ecm_eps_z500a_noram_11The pattern begins in the short-term with a look that will power anomalous warmth through the weekend, along with renewed rain chances Thursday night into Friday (another 1″+ for most), but begins to shift next week towards the colder look.  The 2nd (weekend) storm system will be significant and poses a severe risk to the southeast region.  Modeling has backed away on the heavy rain threat Sunday, but showers will be around early next week along with very windy conditions (40+ MPH gusts).  Blocking is forcing the low south.  By the time we get to next weekend, the pattern has done a 180 and in a position to drill unseasonably cold air back into the central and eastern portions of the country.

    As far as storms go later in the period, it’s far too early to discuss specifics, but the pattern seems to be one that will promote the chance to get into the act on high-ratio producing clippers.  It’s the first time we can say that this year.  Time will tell…


  • Snowy; Increasingly Cold December Expected…

    The 2016-2017 IndyWx.com Winter Outlook was posted on October 30th. If you haven’t had an opportunity to see it, you can here.  Right out of the gate, we remain bullish on the prospects of a snowy holiday stretch this year, including above average snowfall for the month of December (average December snowfall at IND is 6.9″).

    We continue to undergo that “step-down” process within the pattern, but there are growing signals that suggest the pattern takes on a very “blocky look” as we rumble into December.  When we talk about a blocking pattern in this instance, we’re specifically talking about high-latitude blocking.  Essentially this is when high pressure sets up in the high latitude regions (Greenland or northern Canada, for example).  Textbook blocky patterns feature high pressure that sustains itself and is very persistent, leading to a “log-jam” of sorts in the weather pattern, and playing a pivotal role in locking cold, stormy weather in for lengthy periods of time across the Lower 48.  Many times this is a “feedback” type scenario, meaning the early period of blocking patterns initially turns stormy and then grows progressively colder as the snowpack is laid down further and further south.

    When we look at the medium-range and longer-term model data, we note the blocky pattern developing as we wrap up November and rumble into December.  The European, Canadian, and GFS ensemble data all shows the stormy look evolving.epsblockgefsblockgepsblockThe Weeklies also show this pattern in the longer-term.  While we can’t show the European data here (due to licensing), we can show the JMAs.  Again, note the high-latitude blocking.

    jmaweekliesblockActive times are ahead as a busy storm track develops.  Perhaps the scene for many will look a little something like this as we push into the Christmas season…

    2d8dc26454216c3ca978614ecc98faa4In the meantime, gas up the snow blower and sharpen the snow shovel.  If our idea is correct, a snowier than average December will come out of this blocky pattern.