
Next week's forecast, specifically days 5-10 has become more complicated. The ECM and GFS have developed notable inconsistencies in the evolution of the early week storm, as well as the timing and amplitude of the next trough moving into the Pacific northwest. Beyond Sunday the forecast dives into the depths of low confidence.
First, the short term: tomorrow, the heat is on, relatively speaking. High pressure in control with sunny skies and a dry airmass supporting steep low level lapse rates will lift highs into the upper 60's. On Saturday, a short wave will slide south, with a cold front pushing through the region in the afternoon. Clouds will increase after midnight Friday night, with mostly cloudy skies through the day Saturday. High temperatures will be peak early in the upper 50's. Model guidance has started to advertise, with more conviction, low pressure developing along the front and tracking south of New England. With this feature has come an increase in forecasted moisture. Still, considering the extent of the antecedent dry airmass, it will be difficult to get precipitation reaching the ground intially. We could see a couple showers in the evening, with under a tenth inch total. Clouds will keep low temperatures up a few degrees from normal Saturday night.
Sunday, skies clear behind the departing system, however with notably cooler temperatures. 850mb temperatures drop to near -5C, supporting highs around 50.
A storm system will be developing in the southern Plains states Saturday and Sunday. Meanwhile, a short wave will be shifting into southern Manitoba by Sunday evening. (Using 12z guidance) The key difference between the GFS and ECM appears by Monday morning. The GFS shoots the southern shortwave toward the mid Atlantic much faster than the ECM, and develops it as the main system. The ECM phases the two waves along the Mississippi River valley by Tuesday morning, with surface low pressure rocketing northward into the Great Lakes.
So to begin with, the GFS is notably cooler for the Mon-Tue period. It tracks the southern low south of Long Island and over Cape Cod, not unlike a wintertime nor'easter. In fact, taken verbatim, the GFS gives New England north of I90 a light snowfall Monday night. The ECM by contrast, pulls warm air aloft up through northern New England, developing a similar situation to the rainstorms in the past month.
Next, the GFS still has the northern stream low to deal with, and it dives it south into the eastern Great Lakes by Tuesday morning. Short wave out west moves into the Pacific northwest, kicking ridging east. With the southern low out ahead, heights are lowered with high pressure out of the way, and the eastern trough is able to slide on out as quick as it comes. H5 low passes over northern New England Wednesday morning, and inflection point moves through Thursday evening with surface high pressure building in the southeast. This would suggest a quick recovery in temperatures for the end of the week.
The ECM closes off the H5 low over the Great Lakes on Wednesday, with it slowly moving into northern New England on Thursday. Short wave out west has a more positive tilt, so it suppresses western ridging, but doesnt shove it east with the same fervor as the GFS. Ultimately we'd see a continuation of cloudy and cool weather through the end of the week.
Regardless of whichever situation unfolds, the precipitation timing is not all that different. Rain should start up late Monday evening, with the heaviest falling overnight. Showers continue Tuesday, with cloudiness and scattered showers through Wednesday morning.
Temperatures will be on the rise come the following weekend. Despite descepencies in the process, there is a decent consensus for strong ridging over the eastern two thirds of the nation days 8-10.
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