Category: NAO

Dissecting Today’s Severe Potential; Winter Returns & Looking More In-depth At The New JMA Weeklies…

The Storm Prediction Center (SPC) has significantly expanded the “slight risk” area to include a large portions of the state.


While a fresh batch of heavy rain will move into central Indiana later this morning (another 1″ to 2″ is a good bet for most communities), the focus shifts to a window where severe thunderstorms will be possible during the early to mid afternoon.

A warm front will lift north through central IN late morning and this will allow relatively warm and moist air to briefly surge as far north as a Logansport to Fort Wayne line.

Note dew points will spike to 60 to 63 degrees over much of central and eastern IN this afternoon.

It’s during the 1p to 5p window when we’re most concerned for the chance of a few severe thunderstorms ahead of the cold front. Damaging winds are of greatest concern, but anytime you have a warm front hanging around central Indiana with these kinds of setups, the potential of a tornado is in the back of your mind. I don’t foresee this being a major tornado outbreak whatsoever, but parameters do suggest the chance of a quick spin-up tornado is present, as well during this timeframe.

The cold front will crash into Indianapolis between 4p and 5p and you’ll certainly know it.

Strong and gusty northwest winds will blow sharply cold air into the region this evening and tonight. In fact, highs in the lower to middle 60s this afternoon will be into the 20s before midnight. Lows Friday morning will fall into the 10s and highs Friday will only top out in the lower 20s with wind chill values in the single digits most of the day.

After a dry open to the weekend, we continue to monitor the potential of a light wintry event Sunday into early Monday. This doesn’t appear to be a big deal, but the chance is there for an inch or two of snow for portions of the central and northern Ohio Valley during this timeframe.

Additional challenges await early and mid next week, but we’ll save those for updates later this afternoon or evening.

JMA Weeklies

The updated JMA Weeklies are in and in short suggest the southeast ridge continues to put up a fight over the next couple of weeks before getting “squashed” in the Weeks 3-4 timeframe.

This is in line with our thinking of the “transitional” period beginning this upcoming week. We think cold will begin to “push,” but isn’t ready to lock-in as of yet. There will be cold readily available to present more of a wintry potential with storms that track through the region when compared to this week, but we think it’s the period from 2/17 through early March that has the capability of featuring more sustained cold.

That’s a strong signal being painted by the JMA Weeklies in the Weeks 3-4 timeframe for widespread cold. Given that the MJO is forecast to swing into Phase 8 by this timeframe, along with the NAO/ AO looking to dip negative, the widespread cold look is a good idea to us during this particular time period.

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Tuesday Morning Video: Heavy Rain And Looking Ahead To A Wintry Threat Late Weekend For Some…

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Long Range: Cold Pattern Isn’t Going Anywhere Fast…

We’ll save our short-term discussions for the severe and high-impact arctic outbreak on deck and focus our attention in this post to the upcoming several weeks. In short, we don’t expect the cold pattern to break anytime soon. Could there be a day or two of “relaxation?” Yes, but from an overall perspective, confidence is higher than normal on the colder than average pattern continuing through the month of February.

Let’s dig in to the teleconnections:

EPO

AO

NAO

PNA


Given the teleconnections in agreement pointing towards a cold pattern, it shouldn’t come as a surprise that the majority of data is also on the cold train as we flip the page into February:

CFSv2 Weeklies

Weeks 1 & 2

Weeks 3 & 4

JMA Weekly

GEFS

While we aren’t licensed to show the European Weeklies, the new update runs with a cold pattern into early March. This falls in line with the overall consensus of longer range data, backed up by teleconnections.

Though not nearly at the amplitude of a few weeks ago, the MJO (Madden-Julian Oscillation) is forecast to move through Phases 5 and 6 in the coming weeks before going back into the “null” phase.


Phases 5 and 6 this time of year would suggest colder anomalies are more likely around our neck of the woods:

Given the above, we continue to think a colder than average “2nd half” of winter looms for the region. We lean heavily on the NAO, EPO, and AO state(s) this time of year and all would point towards a cold time of things moving forward, overall. The latest European Weeklies are interesting from a couple of fronts- initially very cold and then progressively stormy. The idea here is that we remain quite wintry through February and into early March before this pattern breaks. While we may not see a “repeat” visit of the Vortex, it wouldn’t surprise us to see another major arctic outbreak again this winter (after next week), but that likely comes later, and towards the end of the game before we snap into spring.

Buckle up; we think we have a long way to go this winter…

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Deeper Look Into The Long Range…

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“Pulling The Curtain Back” On The Late December Pattern…

Late December through early January is a critical time period where most folks (even those maybe not normally interested in the weather) are glued in on the forecast.  For some, they’re rooting for a white Christmas, while others are preparing for holiday travel to see loved ones.  The idea here of a transitional pattern remains and this should promote active weather during the holidays this year.

Understanding things can change with respect to timing from this distance (in some cases 2+ weeks out), these are the dates we’re targeting for storm impacts across central Indiana:

  • Dec. 20-21
  • Dec. 24-25
  • Dec. 27
  • Dec. 30-31

Before we talk specifics, it’s important to look at some of the pattern drivers.  Some of these drivers include teleconnections such as the NAO, AO, PNA, and MJO.

Forecast indices with respect to the AO, NAO, and PNA are expected to be more or less neutral through the late month period.  This is what the respective teleconnection “state” would result in the temperature department across the country.

Arctic Oscillation

North Atlantic Oscillation

Pacific North American Pattern

The basis of our late-December forecast is built from the MJO, or Madden-Julian Oscillation.  We note the MJO is expected to rumble through Phase 4 before heading into Phase 5 around Christmas.  Phase 4 (image 2 below) is a warm phase and correlates well to what the week ahead will provide.  However, Phase 5 (image 3 below) is a colder phase and could “up the ante” for the potential of wintry weather around Christmas.

If the MJO amplitude remains, it’ll roll into Phase 6 to close the month and open January.  Here’s how that would correlate in the temperature department:

The upcoming week will run milder than normal- lining up perfectly with MJO Phase 4.

The first of our targeted holiday storm systems will come at the tail end of the warm Phase 4 and will likely deliver a wind-whipped rain in here as early as Wednesday night and Thursday morning.  However, as the storm pulls northeast along the Ohio River, it’ll deepen on its journey into the eastern Great Lakes region.  This will help pull colder air into the region, likely resulting in rain transitioning to snow Friday.  Given the path of the storm, this doesn’t favor some sort of prolonged backlash snow event, but it could be enough to result in accumulating snow across eastern Ohio Valley sections and downwind of the snow belt regions of northern IN, OH, and MI.

The pattern, as a whole, appears to be one of transition to close the month and open January and it’s not really until we get to mid-January where we think all of the drivers “align” to create more of a lock and hold cold pattern.  With that said, a stormy late December pattern can present problems, even in the midst of relatively mild times.  We’ll be here to dissect the storms as they come throughout the holiday season…

Permanent link to this article: https://indywx.com/pulling-the-curtain-back-on-the-late-december-pattern/