GFS Leans Snow as Weekend Forecast Continues to Evolve

We're continuing to track what looks like an active weekend of weather for the region as a large, upper level low will move into the southwestern United States and bring rain, snow, and severe storms to Colorado, Texas, Oklahoma, Kansas, Nebraska and Wyoming over the course of several days.

Tuesday morning models
A review of today's 6 am models tells us several things. To begin with, there is still a great deal of uncertainty surrounding this system and what its eventual impacts on the state will be. Despite how things may look on paper at times, models struggle a great deal with these large, slow-moving cutoff lows (storm system that is organized but is cut off from the main storm flow), and as we've seen time and again, the difference in track by just a few hundred miles can mean all the difference between a high-impact event, and a miss. So, while models have generally converged on a very wet solution for the entire region at this time, it's worth noting there's still plenty of time for things to change as we continue to work out the details.

Another notable aspect of today's morning runs was that the GFS, which has thus far shown only rain at lower elevations, came in much colder than its previous runs. For the first time it is now also showing snow for the greater Denver area and northeast Plains, as the Canadian and European models have for some time now.

GFS model showing much colder air for the region as compared to its previous runs (left). For the first time this week it is showing snow at lower elevations | Weather5280 Models

This morning, the EURO continued to lead the way with a high-impact rain and snowfall event for the entire region Friday through early next week. That's not to say there weren't some shifts in its modeling too – namely a western jog and broadening of the 500mb Low compared to its previous runs. In some respects, this better matches what the GFS looks like for the same period, rather than tracking the low pretty far east along the Colorado/New Mexico state line:

ECMWF 500mb forecast for Saturday evening (left) from last night's run, and early Sunday (right) from today's run | Weather5280 Models

It clearly didn't affect its precipitation outlook – but should this become a trend, it's something we'd need to watch. A more western track will inevitably dry-slot someone east of the mountains, which would greatly reduce rain/snowfall totals for wherever that may be. Nevertheless, the EURO has stayed very steady and continues to show pretty big snowfall at lower elevations, as well as the potential for several inches of liquid. The latest run for Denver produces over 2.5" of water (blue bars), with the ensemble mean (green) in good agreement.

WeatherBell Analytics

Severe storms
Another aspect of this system will be the potential for severe storms. The greatest likelihood of seeing severe weather in Colorado will come Friday, with the main focus likely being along the dry line across southeast Colorado extending into western Texas and Kansas. That's not to say we can rule out the potential for severe storms across northeast Colorado just yet – this will be a very dynamic spring storm, and it's likely any convection across the northern forecast area could produce some severe weather as well.

SPC day four (Friday) severe weather outloook

CIPS analogs also show the potential for severe weather across the far eastern plains on Friday, with the greatest potential showing up south and southeast of the state:

CIPS analogs

A prolonged event
In the event we see high-end snowfall totals across the region (or even rainfall for that matter), it won't come all at once. With the main system spinning for several days over the southwest, we would likely see a couple rounds of heavier precipitation and snow over a three (or four?) day period. All models are showing a good round of precipitation (whether rain or snow) Friday into Saturday, and again Sunday night into Monday. Heck, the Canadian keeps rain/snow in the forecast through Wednesday of next week.

It's madness out there
Look, it's April in Colorado, we can handle a spring storm, can't we? It's VERY common for us to see snow in Denver in April – it's the city's second snowiest month on average!

We fully understand the excitement that comes when tracking a system like this... but, there's been a LOT of really bad information being thrown around in recent days. Folks following meteorologists (or otherwise) on social media should use caution when they see a EURO snowfall map producing 50" of snow across the Plains. First of all, it's against WeatherBell's terms of service to share these maps, and second... it was, is, will be a HIGHLY unlikely forecast from ONE model that we are now spending time answering questions about days later.

Please, everyone, take a step back and let's just see how this thing ends up evolving. There's still a decent chance most locations at lower elevations see mostly rain from this storm or worse yet (maybe better yet?) it stalls over Arizona and we get nothing but dust in the eye.

Deep breaths everyone!

TL;DR

  • We'll see beautiful weather Wednesday and Thursday with highs in the 70s across eastern Colorado
  • Friday changes arrive, first in the way of severe storms and heavy downpours, with a better chance of rain and or snow across the entire region by Friday night and Saturday.
  • Rain and snow looking like a good bet off and on throughout the weekend and possibly into early next week.
  • The POTENTIAL exists for a heavy, wet, and likely damaging (see all the leafed trees) snowfall across the region. Certainly that potential is greater for higher elevations (foothills, Palmer Ridge), but many models are showing snowfall across the metro areas as well.
  • This is a slow moving system with lots of unknowns. There is plenty of time to track how this system will eventually evolve, and with that, we can continue to narrow in on the details as the week progresses.
  • At the moment, our biggest unresolved questions are:
    • Will the western shift continue, will it stall out too far west?
    • How cold temps will actually be, and where does the rain/snow line set up?
    • Someone gets dry slotted – but who?
    • Does convection out east across the Plains and on into Nebraska and Kansas end up hurting precipitation totals back west along the I-25 corridor?

Brendan Heberton

Brendan is founder of Weather5280. He is co-founder of FreshyMap, and develops software for geospatial data analysis and visualization.

Denver, Colorado
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