Despite plenty of sunshine for most, Saturday likely featured the chilliest temperatures, both daytime and nighttime, until late this fall. A broad high pressure has taken over, and although it initially ushered a chilly air mass from the northwest, the air mass is quickly modifying with the April sun and with the winds lightening and no longer maintaining the cold advection. At this time of year, given the dry source region to the northwest and the lack of evaporation from the cold Great Lakes and leafless trees, the relative humidity quickly drops to very low levels on a sunny day, often <30% and sometimes even <20% in the afternoon. This will occur repeatedly in the region through most of next week as the broad vertically stacked ridge intensifies in the eastern U.S. and takes a while to pass by. This could cause high fire danger in spots, though light winds most of the time should mitigate the threat somewhat.
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| Source: TropicalTidbits |
There are a couple of wrinkles to the warm, dry, and sunny outlook though, especially north of the U.S./Canada border, where the ridge will struggle to push that far north. It is still early April, and it is rare to get a sustained warm spell this early on. On Tuesday, a weak trough will lead to breezy conditions and increased clouds for most. Northern Maine and eastern Quebec will even have some showers Tuesday afternoon and evening, followed by a brief cool down expected for Wednesday, again especially for northeastern areas. This is a big change from a week ago, when there was almost unanimous support for a strong ridge in the Rockies forcing a deep trough in the eastern U.S. for several days, possibly leading to snow. Instead, the ridge in the West and Rockies will be fleeting and not be as strong, a recurring theme of the winter, and the cool down will be minor and very brief.
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| Source: TropicalTidbits |
Source: TropicalTidbits
The ridge will quickly re-intensify on Thursday and Friday. With warming temperatures aloft and strong April sunshine to mix the warmth to the surface, even warmer and possibly record-breaking surface temperatures are likely, especially south of the U.S./Canada border. A
front will stall just to the north and possibly through northern Maine, and
those areas could be cooler and cloudier, especially if the front pushes a
little farther south. Some of the details, such as the exact location of the
front, are of course subject to change. The front could stall there through the weekend, with areas south of it staying unseasonably warm through the weekend,
with afternoon temperatures of 77-86F (25-30C) in lower elevations, especially in areas receiving downsloping warming with the southwesterly flow. This is most likely from the southern Adirondacks to southern
New Hampshire.
The very dry air and mostly clear skies do mean that it will cool off quickly
at night, except closer to the front where it will be breezier and possibly
cloudier. A disturbance from the Gulf of Mexico will increase clouds and humidity by the end of the weekend or the following Monday, likely leading to the first rain in 10 days for southwestern areas that miss the showers Tuesday afternoon and evening.
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| Source: TropicalTidbits |
Source: TropicalTidbits Source: TropicalTidbits
After next weekend, there are indications that a ridge will develop in the western U.S., leading to a trough in the eastern U.S., associated with cooler temperatures, more clouds, and more rain and showery weather. There is even suggestion of higher elevation snows at times. Again though, given the models tendency to overforecast ridges and underforecast troughs in the western U.S. recently in the long-range, and the feedback loop I wrote about a week ago favoring a trough in the western U.S. and a ridge in the eastern U.S., I am a little skeptical for now that it will last more than a day or two.
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| Source: TropicalTidbits |
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