EVERYTHING BUT THE SINK...
Spring has sprung and with it has come one of the best weeks I can remember for early April. Since Sunday skies have been sunny and temperatures have gone from the 70s to 4 consecutive days in the 80s Tuesday-Friday. Truly fantastic considering a normal high is about 60.
On the topic of above normal temperatures, here's the daily departures for the first 2 weeks of April and outside of 2 days, average highs have been roughly 10-20+ degrees above what's typical.
You can see much of the eastern half of the nation has enjoyed a pleasant start to April
Looking long range, the pattern is turning active again which should mean regular frontal passages that produce precipitation chances and temperature swings. The Climate Prediction Center is now showing below normal temperatures in the 6-10 day period April 20-24th.
Beyond that an east coast trough sets up which allows even stronger NW flow and healthy intrusions of cooler air. CPC has well below normal readings indicated in the period April 22-28th.
Short term we've got another warm day to draw on Saturday before a strong cold front plows through the region Saturday night. The process of change begins with the break down of the upper air blocking pattern that's been in place since Sunday. The transition involves a cold front and wave of low pressure that slowly enters the region Saturday. That finally opens the door to a plume of moisture with dew points up around 60 late in the day.
With highs in the 70s that does allow for a more muggy feel to the air than what we've seen in previous days.
It also develops enough instability for scattered showers and a few thunderstorms but guidance has limited those to later Saturday afternoon or evening due to a slower frontal passage. SPC has pushed its slight risk outlook (level 2 of 5) further northward to include my counties south of I-80. Until then it should be another decent day of weather.
Precipitation should gradually increase in coverage late Saturday night and could continue Sunday and perhaps even Monday morning as a closed 500mb low develops, slows the system down, and wraps moisture into the area.
Again, the most challenging aspect of the weekend forecast is the potential for wet snow to fall in some part of the Midwest. Guidance continues to be bullish on that concern, wrapping cold air and rain into the region on the backside of low pressure that forms along the cold front near or just east of the Mississippi River early Sunday. Not only does this increase precipitation totals, it pulls enough cold air in to change rain to snow (or at least a mix of rain and snow) before the storm departs. Aside from the usual problems with timing any transition, the late season nature of the event will make it difficult to snow unless precipitation comes down fast and furious enabling efficient evaporative cooling. While it may be rare, I've seen it happen a few times this late in the season with the end result being some decent slushy accumulations. Currently, its the NW half of my area that has the greatest threat of seeing the flakes. Timing and amounts are still very much an issue but the window for any accumulating snow is from late Sunday afternoon or evening into early Monday morning.
I wish I could say with great confidence how this turns out but due to the late season nature of the event mesoscale features will be vitally important to the eventual outcome. Those may not be known until Sunday when the snowy side of the storm is about to unfold. This is one of those set-ups where a degree or two could make the difference between a significant snow or a nothing burger. Myself, I think the evidence is strong that snow will fall in some parts of my area and may accumulate on grassy and elevated surfaces by Sunday night. Again, it's the NW half of my area that seems most susceptible to the possibility. Remarkably, models suggest totals like this by April 18th. I do want to stress, this is a low confidence event and none of the models you see are official forecasts. It's all raw model output that will be used to formulate a forecast in the next 24 hours. Here you go.
The Canadian GEM
The 3k NAM
The 12K NAM
Total precipitation from the event appears significant for much of the Midwest. Here's the totals ending Monday.
Once the storm pulls out, plenty of late season cold spills into the Midwest Monday. Readings may have a hard time reaching 40 in the north while the far south shoots for low 50s. Here's the mid-day departures Monday on the EURO.
Check out the wind chills Monday morning. Upper teens to mid 20s. Going in the wrong direction there!
This begins a period of well below normal temperatures that I alluded to in the 6-10 and 8-14 day outlooks from CPC. No more of those 80s for some time to come. They sure were nice while they lasted! The next rain arrives Wednesday. Have a top notch weekend and roll weather...TS