Category Archives: Jet Stream Discussion

Running the Gamut; Looking Ahead to April…

We’ll apologize in advance for the long-winded post tonight, but there’s a lot to cover. Not only do we have the accumulating snow on deck, a couple of strong storm systems this weekend into the middle of next week, but the long range pattern is set to turn cold (again) after a mid-month respite. We also want to look ahead to our early thoughts towards April…

Let’s take things one at a time:

Thursday-Friday Snow

While we don’t have major changes to our ongoing snowfall forecast, we have “sagged” the swath of 1″ to 3″ snow south just a hair given the latest computer model guidance. Steadiest snow should fall Thursday night into the predawn hours Friday. We’d anticipate a slick Friday morning commute through the heart of central Indiana.

Snow should exit off to the southeast around, or just before, lunchtime Friday. As always, your ground-truth reports are welcome (feel free to send to us on Twitter or via e-mail).

Warmer Side Of Things

The ‘mean’ trough position will shift to the west (temporarily) and lead to an overall milder time of things for the mid-month stretch. Unfortunately, the milder air will come with a wetter pattern.

This milder, wetter pattern will be highlighted by (2) storms:

I. Saturday, 3/10

II. Tuesday-Wednesday, 3/12-3/13

Both storm systems will be capable of producing locally heavy downpours and embedded thunder. Greatest chances of severe will remain south of central IN with this weekend’s storm, but may be further north next week. We’ll keep a close eye on things and issue Client Briefs if need be as we get closer.

A combination of the GFS and European computer models print-out rainfall totals between 1″ and 2″ over the upcoming 10-days and this seems reasonable given the fact both storm systems will be able to tap into Gulf of Mexico moisture.

From a temperature perspective, the brutal cold will come to an end behind our late week snowmaker. While “transient” chill will follow both of the upcoming storm systems, we’re heading into a much milder pattern, overall, through the mid-March stretch. Mildest air will come directly in front of the storm systems, highlighted by a couple of 60 deg. + days the middle of next week.

Positive PNA takes over

Unfortunately (for lovers of spring), the mid-month warm-up will be only a “tease” as we’re set to trend cooler, relative to normal, for the last 10 days of the month. The reason? A developing positive PNA.

To no surprise, we see the cooler pattern returning on the computer models:

Not only will we turn colder to close the month, but Thursday likely won’t be our last accumulating snow of the season…

Looking Towards April

Despite the late-March “set back” to a chilly time of things, we continue to think a more sustained “stick and hold” spring pattern looms around the corner. In fact, we agree with the latest CFSv2 delivering a warmer than normal pattern for April, as a whole, to the eastern portion of the country.

Note that as we go, the model is getting warmer for April with each passing day. As things stand now, we think the trough will pull back to the west with a more sustained ridge in place across the eastern portion of the country in April. With this, a wetter than average regime likely awaits, including an uptick in severe chances further north into the region.

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VIDEO: All-Access Long Range Update…

This evening’s long range video update discusses the pattern drivers behind the late-March weather pattern…

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All-Access Long Range Update: Walking Through March…

Recently, a “transient” pattern has dominated. This has kept any sort of long-lasting cold at bay and resulted in above normal precipitation. As we get set to close out February and welcome in a new month, a pattern change is on the horizon.

This overall shift in the pattern will drive a more sustained and significantly colder than normal regime southeast. In short, cold is set to “overwhelm” the pattern through the first couple of weeks of March. In the most extreme case (especially if we can get snow down), we will be able to challenge records at some point during the 1st (10) days of the month.

In spite of a neutral to positive AO and NAO, a significantly negative EPO and MJO rumbling through the cold late Feb and early March phases look to trump the otherwise warm signals. We also can’t forget about the significant SOI crash. Let’s dig into some of the latest data:

CFSv2


Note the modeling spreading the cold out during the Weeks 2-3 time period before gradually modifying things as we move into the middle and latter portion of March. The mean storm track shifts to the east during the first couple of weeks of the month (pattern will likely be dominated by more snow vs. rain events during this time period) before wetter than normal conditions return for the 2nd half of the month.

JMA Weeklies

Week 1
Week 2
Weeks 3-4

Like the CFSv2, the model overwhelms the pattern with cold during the Week 2 time period. Also similar to the CFSv2, the JMA Weeklies bring ridging back into the East and associated warmth by mid-month. While we haven’t included the precipitation anomalies in this post, the model does bring wetter than normal conditions back into the area by mid-March.

European Weeklies

The NEW European Weeklies remain consistent from Monday’s update (and data above) in delivering a very cold 1st half of March. The core of the cold looks to be centered over the upper Midwest and Northern Plains, but temperatures for the balance of the first couple weeks of the month will likely resemble what we’d expect in late January or early February vs. March. While precipitation will likely run below normal (thanks to the cold pattern), the model deliver above normal snowfall during the period. As we move into the 2nd half of the month, warmer (and wetter) conditions are shown to return.

Given all of the above, we expect the primary upper air pattern to feature a central and eastern trough through the 1st half of March before that trough settles into the West during the 2nd half of the month. This will open up the eastern portion of the country for not only warmer air, but a return of moisture-laden storm systems and the potential of strong-severe storms at times.

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Reviewing The Latest European Weeklies And Updated Long Range Thoughts…

We’re growing closer and closer towards the period we’ve been thinking would present one last round of cold, wintry weather (relative to normal) for the ’18-’19 season.

While the stormy idea will likely end up being correct, the significant cold that we thought would “spread out” (as opposed to being confined to the NW and northern Plains) is in jeopardy.

The overall upper air pattern over the upcoming few weeks will likely continue to be dominated by a mean trough position across the central and west, along with the persistent southeast ridge.

This will continue to result in above normal precipitation into the first week to 10 days of March, with a very active storm track.

From a temperature perspective, the baseline of our ideas being centered on the MJO appears to be the error in our forecast. It’s not that the MJO isn’t heading into Phase 8 (it’s officially there now, as noted below), but it appears other teleconnections are “trumping” this cold ingredient.

The combination of the positive Arctic Oscillation (AO) and negative Pacific North America pattern (PNA) are the drivers and are showing no signs of wanting to let go of the wheel.

The AO is forecast to remain strongly positive into early March.

The PNA is forecast to remain negative into early March.

Note how both of the above support that southeast ridge and associated relative warmth.

At one time, it appeared as if the North Atlantic Oscillation (NAO) would dip negative, however, that’s no longer the case.

While the active idea will come to fruition, the cold (at least to the magnitude we thought) will have a difficult time. That isn’t to say that enough cold air won’t get involved with a couple of these storms to result in wintry precipitation of significance, but rather that sustained cold will be tough to come by. Snowfall (of the heavy, wet variety) very well still could end up above normal with these moisture-laden systems over the next few weeks.

European Weekly Update

The new European Weeklies are in and follow the idea above nicely. They forecast a very stormy pattern to persist over the next few weeks with a battle ground between cold to our northwest and warmth to our southeast. We’ll have to be watchful for a couple of storm systems capable of delivering heavy amounts of precipitation. Given the teleconnection states over the next 6 weeks, it continues to look like any sort of significant wintry weather will need to take place before mid-March. Thereafter, warmer than normal times are expected, including true spring-like weather emerging. I know most can’t wait…


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Here Comes March: What We’re Saying (And What We Aren’t)…

2018 is already flying!  As we welcome in March here are the weather statistics for IND (Indianapolis).

  • Average highs start off in the middle 40s on the 1st and rise to the upper 50s on the 31st
  • Average lows are in the upper 20s to begin the month and increase to the upper 30s by month’s end
  • We average 3.56″ of precipitation, including just under 3″ of snow

Before we look forward to March, let’s review where we’ve been in February.  After a very cold start to the month, eastern ridging really flexed it’s muscle and resulted in spring-like conditions for the better part of the past couple weeks.  As we type this up late on the 28th, IND is running 5° warmer than average.  (It’s been a wet month, too, as we’re close to 2.5″ above normal in the precipitation department).

The early spring “fling” has lulled many into believing winter’s finished.  While the worst of the winter is certainly behind us, we continue to think a dose of “reality” awaits as we progress through the better part of the first half of March.  To be more specific, we feel the period March 6th through the 20th will offer up below average temperatures and an active pattern- capable of producing wintry threats.

We note the (2) main drivers this time of year (the AO and NAO) are running negative through mid-month, which favors cold.

Sure enough, modeling is going to the pattern that will produce below normal temperatures (doesn’t appear to be anything particularly frigid, but colder than average, nonetheless) through mid-month.

With blocking in place, an undercutting jet will serve to deliver an active storm track.

Keeping in mind March winter events need multiple items to come together to create impactful situations, it’s also important not to simply “buy in” to the idea that just because it’s been warm lately that winter is finished.  March can be a wild month, as long-time Hoosiers are aware.  The pattern we’re heading into over the next 10-14 days is one that’s been void most of the winter (high latitude blocking in place) and can serve as the player needed to flip a “nuisance” variety late-winter event to one that’s much more significant.  We’ll need to remain on guard for the potential of one or two “more significant” wintry events as we move through the first couple weeks of the month.

Finally, looking ahead, there’s an argument that can be made that we flip the script towards milder times through the last (10) days, or so, of March.  We note (as shown above) the AO and NAO trend neutral-to-positive mid and late March.  Secondly, the EPO is also expected to flip positive for the second half of the month and this is warm signal, locally, as shown.  Majority of guidance also takes the MJO into the “null” phase late month.

The end result is one that should promote colder than average times over the next couple weeks, overall, along with an active storm track.  With blocking in place, the potential of one or two more significant late-winter events are on the table, and we’ll have to fine tune specifics as the individual storms come.  While confidence is high that someone within the Ohio Valley region is likely to still deal with a big-hitter event, there’s no way to get specific until the individual players are on the field.  Thereafter, the pattern should begin to transition to one more conducive for “stick and hold” spring conditions during the latter portion of the month.

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