"Dirty" brief warmup through Tuesday with clouds and some showers; cooler for rest of week with potential heavy rains southeast of St. Lawrence Valley Wednesday to Friday; drier but still cool next weekend before potential but uncertain gradual warmup following week into mid-May

Plain-language summary:

 

After a cool and dry day today except light rain in eastern Maine, some showers will affect northern areas late tonight before a brief warmup on Monday and Tuesday ensues, but with relatively cloudy skies for most and scattered showers along and northwest of the Appalachians on Tuesday. It will be rather windy on Tuesday, especially in the St. Lawrence and Champlain Valleys. It will then turn cooler for the rest of the week for everyone and potentially very wet southeast of the St. Lawrence Valley for Wednesday through Friday. It turns drier but remains cool next weekend, though pop-up scattered showers are still possible depending on subtle disturbances that are uncertain at this time. It could gradually turn warmer, or at least with pushes of warmth becoming more possible, later in the following week into mid-May, though the extent of the change is uncertain.

 

Meteorological discussion:

 

Cool and dry except light rain in eastern Maine today, then brief warmup through Tuesday with scattered showers and windy conditions for Tuesday

 

The slow-moving storm that I mentioned in the blog post a week ago ended up moving faster and was weaker than modeled back then, with a somewhat less amplified and block weather pattern. It seems like models tend to have a bias for showing very anomalous and blocked patterns in the medium to long range. In any case, that storm is way off to the northeast, but there is still unseasonably cool air in almost the entire eastern North America associated with a classic upper-level ridge/trough pattern in western/eastern North America (+PNA), with the dip in the jet stream in eastern North America aided by high-latitude blocking (-NAO). Actually, another storm is rapidly intensifying off the U.S. East Coast and will bring heavy rain to Atlantic Canada through tonight, with eastern Maine getting overcast skies and light rain on the western edge of the storm. Otherwise, it is mostly dry today though still not particularly sunny given leftover mid-level moisture and the cold air aloft leading to some instability. However, the upper-level trough will reinforce itself over central North America through Tuesday, which is associated with a low-pressure system tracking across northern Ontario into northern Quebec Monday into Tuesday, which will temporarily lead to deeper southwesterly flow and a warmup in our region. It will be a "dirty" warmup with some warm-advection light rain in northern areas late tonight and clouds and scattered showers along and northwest of the Appalachians on Tuesday. On Tuesday, many lower-elevation areas southeast of the St. Lawrence Valley, where there is more sunshine, could surpass 70F (21C). The pressure gradient between the high-pressure system over the western Atlantic and the low-pressure system over James Bay will lead to strong southerly to southwesterly winds on Tuesday, especially in the St. Lawrence and Champlain Valleys, where wind channeling will enhance the winds.

 

Source: TropicalTidbits

 

Cool for rest of the week for everyone, potentially very wet southeast of St. Lawrence Valley Wednesday through Friday

 

However, the warmth will not last, as the broad upper-level trough gradually moves east into our region for the rest of the week and into next weekend. A cold front will slowly pass through the region Tuesday night, but another low-pressure system will track along the front on Wednesday, likely bringing a steady, soaking rain to areas southeast of the St. Lawrence Valley, though models have not agreed on the exact location yet. Yet another potentially stronger low-pressure system will likely follow not far behind as it tracks from Colorado to near the U.S. East Coast from Wednesday to Friday, strengthening as it feeds on the still strong northwest-southeast temperature gradient. However, the trajectory of this storm is even more uncertain, with model runs a few days ago suggesting it could go right into our region, bringing heavy rain and strong winds, whereas most models today show it far enough east for only areas southeast of the St. Lawrence Valley to receive rain, or even close to a total miss for our region. In either case, our region will be on the cool, northern side of the two systems, favoring a cold, steady rain instead of the scattered showers and thunderstorms that are more common in the warm season. If the two storms track over the same area, parts of our region could receive >2" (50 mm) of rain from Wednesday to Friday.

 

Source: TropicalTidbits

 

Source: Climate Prediction Center

 

Drier but still cool next weekend 

 

Once the upper-level trough is right over our region next weekend and any front is pushed south of becomes more diffuse, major storms are less likely, with it still being cooler than average but with less rain. With cold air aloft but no real strong push of low-level cold arctic air anymore, sunshine will still prevent highs from being more than 10F (6C) below average for most, with the daytime heating leading to some instability and cumulus clouds and possibly showers depending on any forcing from subtle disturbances that cannot be foreseen this far out. There could another storm ejecting from the Rockies next weekend and approaching our region early the following week, though the overall blocking pattern and west-northwesterly flow across the region could push the storm entirely to the south.

 

Source: TropicalTidbits

 

Potential but uncertain change to more warmth for mid-May 

 

There are some signs of the persistent cool, unsettled weather pattern slowly breaking down for the following week, though models disagree on the extent of the change. Current projections are for the AO to turn slightly more positive, with the NAO turning closer to neutral heading into mid-May, which would promote a breakdown of the blocking pattern and is less favorable for persistent deep upper-level troughs in eastern North America. There is already a lack of true arctic air, and that will likely continue to be the case, with any cold air mass being able to be quickly modified by the strong May sunshine unless it is continuously reinforced. The PNA will also turn closer to neutral. All of this means that pushes of warmth from the southwest actually become more possible for later in the following week into mid-May, though how much of the warmth reaches our region is questionable, and many models still insist on some upper-level troughing stuck to the northeast of our region that would block some or possibly most of the warmth, in which case the battle could actually lead to yet more clouds and rain, but there is considerable model disagreement on this. I would not be surprised if the models are not persistent enough with the current pattern, and if any change to a warmer pattern is delayed, but time will tell.

 

Source: TropicalTidbits