Rain Update and Comments on Weekend Storm

If current modeling hold true, we have a ways to go before drier weather returns to the forecast area. We'll be tracking showers and storms each day this week, with the potential for a more significant widespread precipitation event to impact the region this Mother's Day weekend.

Latest precipitation analysis from the last three days shows pockets of very impressive precipitation totals, with the western Palmer Divide taking the lead. Note this map was published 12z May 5, so rainfall today is not included. With light to moderate rain continuing all day today across eastern Colorado, these numbers will continue to increase before the next analysis is done Wednesday morning.

NWS precipitation analysis | WeatherBell Analytics

Expect to rain to continue into Tuesday night for much of the metro area, but overall the intensity should be on the decrease. Latest HRRR forecast through 5am shows pockets of heavier totals across the eastern Plains, and some good moisture pushing into the Western Slope as well.

Precipitation forecast HRRR | Weather5280 Models

Wednesday we'll be a bit drier and warmer than today, but will again see a good chance for showers and storms across eastern Colorado by the afternoon. A similar story will be true for Thursday and Friday as well, with 40 to 50% chances for showers and storms through the end of the work week, and temperatures in the 50s and 60s for highs.

Mother's Day weekend storm?
Beyond Friday our focus turns to the weekend, and what could be another potent system headed for the region, meaning another widespread precipitation event, and a good chance of rain and snow for the state.

Weather5280 Models

In this week's State of the Atmosphere we discussed the GFS hinting at something bigger and colder for this coming weekend. Both the Canadian and EURO have since taken over, narrowing in on what would be a pretty significant precipitation event, with >5" of liquid in some of the grids across northeast Colorado.

For Denver, the 12z EURO produced 4.85" QPF between today and Sunday night, with much of that coming this weekend. With a monthly average of 2.12" of precipitation in May for Denver, it's clear how significant this would be. Outlined in the image below is the weekend QPF (cumulative) forecast for DIA, a total of 3.14". Also note in the "2 M TMP" and "850 TMP" columns temperatures dropping to near 0 (Celsius) Sunday, and possibly below freezing Sunday night.

European QPF forecast Denver

Which leads us to yes... the chance for another Mother's Day snow for the second year in a row. While the CMC and EURO have both been producing a significant snow for Denver (>10") over the last handful of runs, for the time being I like the GFS a bit better. Temperatures/sun angle are a HUGE issue as we get into mid May, so a more conservative snow-line estimate (>7,000 feet) for now seems sufficient. Nevertheless, with enough cold air advection we could see snow levels pretty low for mid May with this system, so something to watch.

Here's the 18z GFS snowfall forecast through the weekend. It tries to produce a bit for Denver, while keeping the significant accumulation west of town at higher elevations. The bigger issue for ranchers could be the heavy snow it paints across eastern Wyoming, western South Dakota, and northwest Nebraska. Many ranchers are in the middle of calving season, and this type of storm would certainly threaten livestock. From an agricultural perspective the moisture is great, but the threat it could produce to very expensive baby calves needs to be taken seriously.

GFS Snowfall Forecast | Weather5280 Models

The last item to address with this weekend storm is the severe weather threat. Today's analogs produce a pretty impressive severe weather outbreak across the region, with many severe (and tornado) reports showing up for eastern Colorado, Kansas (all), northern Texas, and Nebraska. This is the type of storm that combines a lot of ingredients (lower level and upper level) that are necessary for a significant severe weather outbreak. While the details are yet to be decided, this system certainly has the potential to produce a nasty outbreak.

Severe weather analogs | CIPS

Still a ways to go, but the SPC is already highlighting some areas for severe weather potential on day 4 and 5 (Friday and Saturday):

SPC severe weather outlook

Uncertainty remains
For the time being, I think the 'bust index' is highest for the Denver area for both rain and snow this weekend, given still some uncertainty with track, and really how realistic some of the snowfall totals models are producing actually are. That being said, regionally this looks like a pretty significant event, with severe weather likely and possibly a pretty nasty snow on the back side.

Despite the uncertainty we wanted to get you all a heads up as snow and severe potential this time of year can have big impacts both in the city with new vegetation, and across eastern Colorado for farmers and ranchers. A long ways to go yet, but certainly one to watch if you live in the Wyoming/Colorado/Nebraska/Kansas area. Additionally, should high-end QPF verify, flooding concerns will continue into the weekend for many.

If you're not subscribed to Weather5280 now is a great time to do so. We'll be offering plenty of updates here and on Twitter and Facebook through the rest of the week, keeping a close eye on this weekend's system.

Overall this is shaping up to be a very wet and memorable first 10 days of May. Stay tuned!

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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