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Thursday, 11:59 a.m.
The past couple of days I have been focusing in on the raging (model) debate over temperatures this weekend from the middle of the country on East, as well as getting more and more into the impending storm for later this weekend into next week. The battle lines have been drawn all week long, with the European and Canadian models coming down with a warm solution, while the NAM and GFS have been noticeably cooler. That really hasn't changed a lot over the past 24 hours since I last wrote, though you could make an argument that the gap between the two has narrowed.
The 12z April 24 models are just rolling in, so I won't have time to decipher them all in great detail. However, from what I have seen so far, there really isn't an awful lot that has changed with the NAM and the RGEM models. The lead cold front will be moving off the coast Saturday morning as a low pressure area scoots by south of New England. The 48-hour NAM surface forecast clearly shows this:
Right on the heels of this lead disturbance will be the upper-level low, which the NAM depicts as rolling through southern New England Saturday night. Interestingly, the European model doesn't really look much different. Here's the 500mb forecast for Saturday night:
You would think that would mean a well mixed atmosphere on Saturday from the Ohio Valley on into the mid-Atlantic states, with temperatures getting as high as they can given the air aloft. The question will be how warm will the air be aloft? The NAM and GFS are notably cooler than the European at 850mb, and I tend to side with the warmer idea. It would appear that the wedge of warm air will hold its ground pretty well from Kentucky and southern Indiana and southern and central Illinois on south, as the surface high over Hudson Bay may simply be too far north to push the cold air as far south as the NAM and GFS have been suggesting.
One thing is certain: it will be fascinating to verify the model forecasts from earlier in the week!
Meanwhile, the storm coming into California will not just mean rain for California, but it will mean wet weather across virtually the entire country! Surface pressures will begin to lower tomorrow afternoon and tomorrow night in the lee of the Rockies, and by Saturday a full-fledged surface storm will have developed. It will gradually deepen later Saturday and Saturday night into Sunday, but it won't move eastward very fast. As the heights lower over the eastern Rockies and Plains, more and more rain will break out from eastern Colorado up into eastern Montana, as well as out across the Dakotas into Minnesota and Wisconsin. By late Sunday, strong to severe thunderstorms are likely from eastern Kansas and Missouri into East Texas and western Louisiana.
The threat of severe weather will march slowly eastward Monday and Monday night into Tuesday across the Ohio and especially the Tennessee valleys into the Deep South, and maybe parts of the East on Wednesday.
At the same time, there will be a lot of rain with embedded thunder from the central Appalachians on west into the Midwest, rain that could total 3 to 5 inches by the time this storm finally winds down late next week. This means flooding is a real threat from the eastern Rockies and northern Plains all the way to the East Coast and down to the Gulf Coast. Eventually the cooler air coming down into the Rockies Saturday night and Sunday will spread out across the Plains Monday and Tuesday and should move into the East by Thursday. Once it reaches a given location, expect it to be much below normal few several days before steady warming going into the first weekend of May.
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