A PATTERN IN FLUX...
Last Thursday the GFS version of the MJO (Madden Julien Oscillation) was showing a steady tour through phases 4, 5, and 6 between February 24th and March 10th. That implies the warmth we are in (and will stay in through Sunday) followed by a colder period next week. In reality that appears to be the sensible weather we'll experience as the temperature forecast is verifying and right on track. Then around the 10th it shows a push into phase 6 which in March is the holy grail of warmth. Just what you would like to see after a long winter.
However that's where things go off the rails. In just 5 days the GFS has changed roads dramatically and is going in a totally different direction. This is the latest MJO forecast from the GFS and it never gets out of phase 4 and actually takes a hard left completely bypassing the warmth of phase 6. Instead, it now heads towards 3, 2 and 1 which are cold phases in March. You can see the temperatures those phases represent by looking at the temperature anomalies to the right.
Unfortunately, this major change of heart by the GFS puts significant mid-month warmth in doubt. (Apparently new sanctions have been issued against entering phase 6). I'm not sure what has caused the shift but it is likely feedback or poor data initialization. Another consideration is sudden shortening of wave lengths which becomes more common in March. Who's to say, maybe the GFS flips again in coming days? Whatever, the case, this indicates the overall pattern is in a state of flux and models (especially the GFS) are struggling to get a grip on energy and the proper trends. In the end, it's going to lead to active weather and challenging forecasts.
WHAT GOES UP...AND WHERE DO WE GO FROM HERE
Tuesday was an absolutely spectacular day. Some would say March came in like a lamb, I would say more like a peach! Highs in most areas were in the range of 55-60 with a couple spots as warm as 63 in the far south. With sunshine and light winds, it was a picture perfect day.
Wednesday will be another mild day with highs again reaching 60 to 65 across the south. The north will hold in the mid 50s with eyes on a cold front that brings a significant change Thursday.
The cold front will blaze a trail through the region Wednesday night and by Thursday a brief but noticeable push of cold air settles over the region. Highs are expected to hold in the low to mid 30s north, low 40s south. As you can see that's a good 30 degrees colder than Wednesday's highs just 24 hours earlier.
With the cold air in place Thursday, a narrow band of forcing sets up ahead of a weak clipper that streaks southeast during the day. There is a chance a small strip of snow could develop along its path but little if any accumulation is currently expected. The EURO shows this for totals late morning and early afternoon Thursday.
As I mentioned, it will be a quick in and out for the cold air as a stronger storm takes shape out west that brings a surge of warm air and perhaps spring like thunderstorms. That's followed by another disturbance that could turn rain to snow as it follows Sunday night and Monday. Here's what the two energy sources look like at 500mb Saturday.
The first storm that spins up looks like this on the GFS Saturday evening. A strong south wind is drawing moisture and warm air into Iowa and Illinois along with scattered showers and thunderstorms.
The GFS depicts highs that could reach 70 as far north as I-80.
Moisture is also significant by early March standards with dew points in the upper 50s.
The moisture and warmth will combine to produce some instability which is measured in CAPE. While it's not high it does exist, and it's likely showers and thunderstorms take off ahead of the surface low and cold front Saturday afternoon and evening.
Despite the relatively small CAPE that's projected, there will be significant shear near the surface low and triple point (wherever that ends up). The high shear low CAPE would still be capable of producing strong thunderstorms so severe weather is not out of the question, especially if we attain the temperatures and moisture levels the GFS indicates. The latest data indicates the best chances may end up just west of my area in central Iowa. As of Tuesday, the Storm Prediction Center does have a slight risk assessment issued for much of Iowa.
With convection involved, a few areas are likely to see some downpours but overall rain numbers from this first wave of energy have come down from where they were 24 hours ago. The reason for that is the storm center today is further west and tracking northeast producing better dynamics out that way. For now, the heavier rains (which are 1/4 to 1/2 inch) are most likely NW of the Quad Cities. Here's what the GFS and EURO currently show for rainfall.