Category: Forecast Models

Feb 02

More Thoughts On Our Next Winter Storm…

As we continue to draw ever closer to our next significant winter storm, we wanted to provide some of our latest thoughts.  This isn’t a post that will hash out snowfall accumulation ideas or precipitation types, but instead will provide details on our expected track and potential liquid equivalent precipitation amounts.  With so much hype and hoopla around this storm for the past couple weeks, lets just sit back and look at the “bigger” picture, as opposed to trying to sort out details that, quite frankly, are still too early to lay out with any certainty as I write this late Friday night

Here’s our (IndyWx.com) expected track of the low Tuesday afternoon to Wednesday afternoon.  We used a blend of the GFS, European, and Canadian operational model data, as well as the GFS and European ensemble data sets.  We think surface low pressure tracks out of northeastern Mississippi (Tuesday evening) through north-central Kentucky (Wednesday morning), and into Pennsylvania (Wednesday night) before a secondary low forms off the northeast coastline.

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This is an ideal track for a winter storm across central Indiana, but specifics such as strength and depth of the cold air, potential southern convection, and forward motion of the storm will have to be sorted out over the next day, or so.  Early indications are that while this storm will take a “good” track for winter weather lovers here across central Indiana, the speed in which the system will be moving may reduce snow and ice accumulations from what they otherwise could be.  That said…early raw numbers suggest .50″ to .80″ amounts (liquid equivalent) could fall in the Tuesday-Wednesday time frame which is significant.  Case in point, a standard 10:1 ratio that would suggest 5 to 8 inches of snow- assuming the form of precipitation fell as snow through the entire duration.  Again, that is far from a certainty at this point.

Ignoring items such as model snowfall forecasts and precipitation types, just looking at the expected track would suggest central Indiana is very much in the game for a potentially significant and disruptive winter storm Tuesday into Wednesday.  We’ll have to fine tune precise amounts and precipitation types in the next day or two.  Additionally, much colder air (below zero once again at night) may blow into the state behind this storm for mid and late week before we gear up for yet another winter weather maker heading into next weekend.  We still have a long way to go in this pattern…

Permanent link to this article: https://indywx.com/more-thoughts-on-our-next-winter-storm/

Jan 31

Accumulating Snow Saturday Night?

In the short term, a wintry mix of sleet, freezing rain, and snow will transition to all rain across the entire region Saturday.  That said, if traveling early Saturday morning, please leave extra time to reach your destination and plan to take it slow on the roads as a mixed bag of wintry precipitation will fall on central Indiana tonight.  Most snow accumulations will range from 1″ or less.

After a cold and damp Saturday, we’ll have to pay close attention to the chance of snow mixing with the rain Saturday evening before possibly turning rather quickly to a heavy, wet snow Saturday night/ wee morning hours Sunday.  A cold front will slip south Saturday evening.  Additionally, a disturbance will move slowly northeast along the pressing front and result in widespread precipitation falling on the back side of the boundary (in the colder air) late Saturday night into Sunday morning.  As of Friday evening, guidance suggests a frontal passage in the city between 6-7 o’clock and cold air will begin to filter back into the region at that time period.

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While we’ll have to keep a close eye on things during the afternoon Saturday, confidence is growing on the opportunity for a stripe of accumulating snow being laid down through central Indiana late Saturday night into the wee morning hours Sunday.  Just how much?  We wouldn’t be surprised if some amounts of 2-3″ are reported by daybreak Sunday, including in, and around, the greater Indianapolis region.  Most of this snow would accumulate within two-three hours so this will be what we call a “thumping” snow.  Stay tuned.

Permanent link to this article: https://indywx.com/accumulating-snow-saturday-night/

Jan 30

Complicated And Complex…

If you have travel plans across central Indiana Friday and Friday night, please make sure you leave plenty of time to get to your destination and prepare for a variety of precipitation types.  In fact, it’s entirely possible (depending on what time of day you’re traveling) that you have to deal with rain across south-central Indiana and snow by the time you arrive into the northern Indianapolis suburbs, complete with an icy mixture “in between.”

Digging through the weather playbook for Friday into Saturday:

A cold front is expected to move through the region Friday morning, allowing a wind shift out of the north to arrive into the city in the early to mid morning Friday. We’ll have to be in “nowcast” mode Friday to determine just exactly how far south the front makes it as this will go a long way into determining precipitation types across central Indiana.

Ultimately, a wave of low pressure will move along the front Saturday, which will help milder air push north and result in a changeover from a wintry mix to all rain during the majority of the day Saturday. In fact, there’s the chance portions of central Indiana may not have to deal with much, if any, precipitation through the majority of the day Saturday- especially south.  Before that, however, we’ll have to deal with a wide variety of wintry precipitation issues Friday and Friday night…  Warmer low level air will be drawn northward and overrun the colder air at the surface Friday and Friday night.  What will initially be a period of snow Friday will transition to an icy mixture of sleet and freezing rain Friday night and all rain Saturday.  That said, we note the milder push will be brief, and colder air will pour back into the region on gusty northwest winds Saturday night. This may result in a brief period of light snow Saturday night (not a big deal).

We think the latest high-resolution, short-term, NAM model (courtesy from the fine folks over at Weatherbell Analytics model suite) has a very good handle on accumulation ideas Friday and Saturday and is in best agreement with our analysis laid out above.  This is a look at forecast snow accumulation between now and Saturday night, but we also note there will be some light sleet and freezing rain accumulation on top of any snow that falls Friday. As far as that snow goes, we think a 1-2″ band is laid down from the city and points north, increasing further as you travel into north-central and northern Indiana.

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Permanent link to this article: https://indywx.com/as-promised-complicated-and-complex/

Jan 29

A Word About Early Next Week…

We posted earlier this morning on the near term (below) and Friday and Saturday remain quite challenging and complicated.  Precipitation type and amounts will have to be resolved as we…

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Permanent link to this article: https://indywx.com/a-word-about-early-next-week/

Jan 29

Wintry Mix Issues Late Week/ Weekend

We’re going to enjoy another day of sunshine, but moderating temperatures (finally) will help being outdoors become a little more tolerable (we think we “warm” into the middle 20s today).  That said, another winter weather maker is brewing and will result in an active Friday-Sunday ahead.

A cold front will sink south Thursday night and could result in a little light snow (not a big deal).  As we move into Friday and Saturday, model data handles our sensible weather differently.  Precipitation type will be highly dependent upon exactly where the cold front stalls.  We want to show you the GFS as it depicts the variety of precipitation types. It should be important to note that the GFS, European, and Canadian, though different in their respected solutions this weekend, are close enough to go with a “blend” of all three models for our official forecast.

We think snow overspreads the region Friday morning and could deposit a quick couple inches across the metro area Friday. It’s as we get into Friday night and Saturday that we’ll note another (stronger) wave moving along the front. In response to this wave of low pressure, warmer air (both at the surface and aloft) will push north.  Exactly how far north is still up for debate as a battle will be established with push back being provided from an area of high pressure across the upper Mississippi River Valley. We feel as if south-central Indiana will get in on some mixing issues with sleet and perhaps a cold rain Friday night into Saturday.  Depending on how strong the wave of low pressure is will determine exactly how far north the rain line makes it.  For now, we think Indianapolis and northern suburbs remain in a wintry mix of snow, sleet, and possible freezing rain through the majority of the day Saturday.  That said, we do note this will warrant tight focus in the days ahead as any deviation from the track of the low or strength of the cold high to our north could greatly impact our weekend weather.1

 

 

 

 

 

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Finally, precipitation will begin to taper late Saturday night as the cold high to our north eventually wins out. It’s possible all of central Indiana deals with a quick pop of accumulating snow as precipitation ends Saturday night/ wee morning hours Sunday.

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We stress that this is still a highly changing weather situation and most likely will require some “fine tuning” as we move forward.  This morning we think heaviest snow (potentially approaching half a foot) falls across north-central Indiana, including Kokomo, Marion, and Lafayette.  A wintry mix of all precipitation types will fall south of there, including the Indianapolis metro.  South of I-70, we think rain will be the predominant precipitation type, with only a light accumulation of snow as precipitation ends.

As stated above, stay tuned…

Permanent link to this article: https://indywx.com/wintry-mix-issues-late-week-weekend/