THE WAVE TRAIN IS ROLLING
Make no mistake about it, the weather trains are on the track and set to roll. At 500mb, you can see at least 5 distinct short waves within the long wave pattern plowing east off the Pacific. This represents an energetic storm track that is bound to make for some interesting times across the country in coming days.
The satellite depiction shows the individual waves of energy traveling the energetic jet they are embedded within.
When the short waves are bunched like this, the pattern gets noisy and models often struggle with the resolution of energy within the flow. Models can look substantially different from day to day as they attempt to resolve how the atmosphere will respond. Guidance is especially vulnerable to change when the energy is concentrated over the Pacific, where data grids are limited compared to what's available over the U.S. I'm anticipating some challenging forecasting, especially once colder air returns to the pattern next week. So far I'm not seeing any major storms locally, but that is subject to change.
One of the things I'm watching closely is the potential for an intrusion of Arctic air in roughly a week or so. In the animation below showing 850mb temperatures, there's essentially no readings colder than freezing over the bulk of the continental U.S. at the beginning of the loop. That's verified and quite unusual for the end of December. In fact, the 850 temperature in the Quad Cities are pegged at +5 Friday morning.
At the end of the animation January 8th, the 850 reading is down to -24 in the Quad Cities. That is frigid Arctic air that is certain to get your attention. Add a little wind and it will be harsh. Of course, this is predicated on the model verifying. It may be too aggressive, but I do think the idea of cold in the period January 3rd-11th has merit.
In fact, looking at teleconnections, there is reason to believe this is a plausible solution. First and foremost, the MJO is cycling from phase 8 into phase 1.
That matters as the temperature analogs for phase 8 and 1 in January are both cold, especially 1 which we would be in at that time.
The phase 1 500mb heights in January indicate high heights in Canada. When heights are high, that's indicative of strong high pressure that allows cold air to be displaced into the NC United States. It's also a look that suggests storminess in the southern edge of the cold, wherever that sets up.
The mean of the Arctic Oscillation (AO) is shown on the GFS being negative for much of January. That's a cold signal if the GFS is correct.
The negative phase of the NAO (North Atlantic Oscillation) is also rearing its head, which is a strong signal for winter weather over the central and eastern U.S.
Certainly, the signs are there for a pattern change that has the potential to be impactful at times. Details and timing are still up in the air, but the evolution is in its early stages. We will monitor it closely to see if trends hold in coming days.
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DECEMBER RAIN...
The short term concerns are fog and rain that will be players entering the weekend. Fluctuating pockets of dense fog remain a possibility in most areas early Friday, which may cause travel restrictions, especially in the northern half of my area (roughly I-80 north). As the morning progresses, the fog should ease, especially in the south where the first disturbance (of several to come) arrives along with rain. It looks to spread from south to north as the morning unfolds. With a weak surface low traveling through eastern Iowa, that should keep the heaviest of the rain more in central Iowa. With the rain will come a sluggish warm front that is likely to cut the fog significantly with its passage. Unfortunately, that may not take place in the north to scour out the fog until late afternoon or evening, although the rain should help to disperse it some when it arrives. Temperatures will range from the low 40s far north to the mid to upper 40s elsewhere, the warmest south of HWY 34.
As for rain totals, models suggest amounts in the range of .25" to .50" across most of the area. Some local spots west of the river in eastern Iowa could see a bit more. Even further west, amounts will be heavier in central and far NE Iowa.
The EURO
The GFS
Saturday the rain is gone, and it's looking like a very mild day, with the potential for the majority of the region to reach highs of 50–55 degrees. In fact, enough dry air could be found to at least provide some breaks from the clouds. With the short days and low sun angle, this might be a big ask, but at least it's a hope. If we do pull it off, that could allow even warmer temperatures. Here's what the GFS indicates Saturday.
Saturday night and Sunday is low confidence at this time with the EURO dry but the GFS showing some additional rain. This is due to how each handles an amplifying short wave that curls into the Ohio Valley. I prefer the drier solution of the EURO, but I will qualify that there is a slight chance that a few showers could clip the far southeast. This should be clearer later Friday. Temperatures Sunday will be somewhat cooler with E/NE winds circulating around the system to the southeast. Still, they will remain mild in the mid 40s north to the low 50s south.
The next system of concern arrives later Monday night or Tuesday. While the surface low takes a good path for snow, cold air is lacking, and it seems as precipitation will come as rain. There is a chance that enough cold air could arrive just in time for a brief change to snow before it ends. Anyway, this will get more focus later as data improves, and we get closer to the event.
Well, with lots of weather on the table, I could go on, but you should at least have an idea of where things are heading. Happy Friday and roll weather....TS
