• Category Archives AO
  • Saturday Morning Rambles: Periods Of Heavy Rain Early Next Week…

    I. A weak weather maker will help spread a mixture of light rain and snow across the state later today, particularly this afternoon and evening.  Precipitation amounts will remain light and insignificant, but serve as a nuisance as you go about your weekend plans.

    II.  We’re hopeful for much needed sunshine Sunday as we’ll be in between storm systems, however any sun that we see won’t last long.

    A rather ominous setup for heavy rain will take place Monday into Wednesday.  This will include a combination of ingredients as a strong southeast ridge will prevent much forward motion of a “wavy” front that will drape itself across the Ohio Valley region.  Additionally, the subtropical jet will transport moisture-rich air northward into the area (true Gulf of Mexico connection).

    While this is an unseasonably warm pattern (we forecast highs of 50°, or above, 5 out of 7 of the upcoming days, and at least 2 60°+ days), it’s one that will likely result in periods of heavy rain not only next week, but in waves over the upcoming 10 days.

    Widespread 10-day rainfall numbers of 3″ to 4″ will be likely in this setup, including locally heavier amounts of 5″ to 6″ in spots.  Certainly, if you live near waterways we suggest having a plan in place as it’s not a matter of if, but when flooding takes place in spots across the region with such a setup.

    III. Longer-term, we still need to be wary of the potential of a colder pattern returning as we get into March.  That forecast deep negative arctic oscillation (AO) has to raise an eyebrow for the possibility of making up for lost time in the cold weather department before we can signal “all clear” on winter…


  • Wednesday Morning Notebook: Thursday Storm Threat; Heavy Rain Next Week…

    I. Scattered light showers will impact the southern half of the state today, but these won’t be a big deal and more of just a nuisance for our Valentine’s Day.  Temperatures will remain in the 40s for most of the afternoon before rising overnight.

    Forecast radar today at 3p shows scattered light showers around.

    II. A cold front will drop in Thursday evening and this will deliver more widespread heavier rainfall and even a couple of thunderstorms Thursday night.  In general, we expect 0.50″ to 1″ of rain to fall.

    III. We’ll turn briefly colder to close the work week. A couple of light snow showers are possible Friday morning and a wave of low pressure will “try” to push moisture into the cold air Saturday.  As of now, we remain unimpressed with the prospect of impactful wintry weather Saturday, but have included the potential of wet snow in our Saturday forecast.  Precipitation appears to be very light.  Nonetheless, we’ll continue to keep an eye on things.

    IV. The pattern continues to scream and warm and wet next week as a big ole southeast ridge remains in place.  This will direct the steering current into the TN and OH Valley regions and multiple waves of rain, occasionally heavy, will result beginning early next week and continuing into the middle and latter portions of the week.  Widespread 2″ to 3″ totals with locally heavier amounts seems to be a good bet next week.

    We note a true Gulf connection and precipitable water values that will exceed 300% of normal at times.  Parts of the Ohio Valley will deal with flooding, but it’s premature to get more specific than that from this distance.  If you live near waterways, plan to keep a close eye on future updates and forecasts.

    V. We note data continues to suggest a colder period looms as we close out the month of February and head into March. Note how the GEFS and EPS continues to tank the Arctic Oscillation (AO).  Winter’s not over, not by a long shot…


  • Bet On The Cold…

    During wholesale pattern transitions, operational data will struggle at times, including some wild run-to-run swings.  Earlier this week, the European wanted to put early next week in the lower 50s.  At the same time, the GFS suggested lower single digits.  Precisely, it was a difference of 46° between the two models for a high?!  🙂

    We note the teleconnections (in particular, the EPO) are aligning in a manner conducive for widespread cold.

    The GEFS might be a bit quick on dropping the arctic hammer, but the consistency of the model is impressive.  Meanwhile, the European (even it’s ensemble data) has been much less consistent and has really been struggling the past couple of winters, overall, as a whole.

    While we can argue as to just how cold it’ll get through the early part of February, the overwhelming message is that a prolonged colder than normal pattern will develop during this time period.

    Let’s also keep in mind that the initial cold onslaught is coming in the face of the MJO still rumbling through the warm phases.  We note the European is consistently having to correct towards a more “amped up” MJO- swinging into the cold phases as we approach mid-month.  And it’s mid-February that continues to have us concerned for the potential of truly nasty, severe cold.

    As for snow, it’ll come in this pattern.  Again, don’t get caught up in the operational output, but understand that the pattern over the upcoming 7-10 days favors numerous fast-moving snow systems.  While most of these will be light, we’ll have to keep a close eye on things as the potential exists for one of these waves to spin up a moderate event.

    As we look ahead to Week 2, the potential is there for a more widespread significant phased interior threat prior to the dumping of the bitterly cold air for mid-month.

    As it is, both the GEFS and EPS “mean” paint a bullish signal for piling snow up over the next couple weeks…


  • Transition Begins Back To A Prolonged, Sustained Wintry Pattern…

    The January “thaw” has taken hold the past 7-10 days.

    Despite the milder air over the past week, January, as a whole, is still running 4° below average at Indianapolis- a byproduct of just how frigid the first half of the month was.

    While the January thaw has been nice, times are changing and winter sure seems to be reloading for a very active second half.

    Initially, we think it’s the storminess that will be most impressive as a “fight” develops between resistance from southern ridging and a new mean trough pushing southeast.  The end result should be multiple snow and ice makers from the southern Plains into the Ohio Valley and northeast over the upcoming couple of weeks.

    Once we get a snowpack laid down, arctic highs oozing southeast will likely lead to bitterly cold air.  Recall our expectation for this pattern to yield at least (1) night of double-digit below zero lows, but it’s more towards mid-month that we think the severe cold takes hold.

    Teleconnections are lining up and in overall agreement of cold, wintry times returning.

    The Madden-Julian Oscillation (MJO) is forecast to rotate into the colder phase 8 as we rumble from early to mid February.  Given the amplitude of the MJO, it should continue to rumble right through the cold phases of 1,2, and 3.

    All of these moving pieces that lead up to extended periods of cold, wintry conditions are part of a bigger outcome low solar, easterly QBO winters deal up.  What we should experience with this setup is a 6-7 week period of wintry conditions, including times of severe cold.  It appears to be a snowier version of what we went through late-December through mid-January.  Hang in there, spring will come…eventually.


  • 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…