Plain-language summary:
It will be rainy in southern areas, heaviest along and southeast of the Appalachians, through Tuesday, while areas to the north experience drier weather with larger day-to-night temperature swings. It will turn wet for everyone on Wednesday before turning cooler and at least partially clearing out Thursday before potentially more rain falls south of the U.S./Canada border next weekend. Though it likely dries out afterward, the weather becomes generally rather uncertain, though widespread summerlike warmth appears less likely than previous forecasts. Frosts and freezes are still possible through mid-May outside urban areas and away from major bodies of water, though afternoons could still be mild to warm given the likely sunnier weather pattern then.
Meteorological discussion:
Showery next few days in southern areas, drier to the north through Tuesday
It is the season of cut-off lows as the polar jet stream weakens and retreats northward as spring progresses. There is currently one cut-off low over the Desert Southwest U.S. and another one over the Ohio Valley, closer to our region, while there is upper-level ridging in between and to the north over the northern U.S. Plains and northern Ontario. As is always the case with these ridge over cut-off low situations, everything is blocked and moving very slowly, with the polar jet stream too far north to push the systems quickly eastward. As a result, there is persistent showery but rather monotonous weather for several days underneath and to the east of the cut off low, where there is moisture transport from the western Atlantic. The northern extent of this wet weather is reaching up to a line from the central Adirondacks to southern Maine this evening, after a wet day yesterday due to a weak disturbance ahead of the cut-off low. Meanwhile, north of the U.S./Canada border, surface high pressure with mostly sunny skies is in control. Due to the sunshine to the north and rain and clouds to the south, daytime temperatures will generally be warmer to the north than to the south, opposite of climatology, though nighttime temperatures will be cooler to the north with a much larger diurnal temperature cycle.
 |
| Source: TropicalTidbits |
Wet everywhere on Wednesday, then at least partial clearing and cooler Thursday and maybe Friday before possibly more rain in southern areas next weekend
The cut-off low currently over the Ohio Valley will slowly push northeastward into Quebec on Wednesday, with rain eventually overspreading most of the region by Tuesday evening, though still mostly south of the U.S./Canada border, heaviest along and southeast of the Appalachians which will also experience upslope enhancement, with up to 3" (75 mm) possible total by Tuesday night. By Wednesday, the cut-off low will interact with a northern stream trough that will be pushing into Quebec, bringing a period of rain to the entire region (even north of the U.S./Canada border), and then move eastward faster and out of our region by later Thursday. The trough will finally push in cooler and drier air, accompanied by a central Canadian surface high pressure system, by late Thursday.
 |
| Source: TropicalTidbits |
However, the aforementioned northern stream trough could itself cut-off into a closed upper-level low as upper-level ridging rapidly develops overtop in central Canada. This closed low would slow down and possibly stall for a couple of days (next weekend), possibly bringing more wet weather to the central Adirondacks to southern Maine. How much rain falls depends on how strong the upper-level low is, which determines the dynamic forcing for lift and also the transport of moisture from the western Atlantic. This is still somewhat uncertain given the trickiness of forecasting slow-moving cut-off upper-level lows that far in advance, and models actually have not shown this second cut-off low much until the past couple of days. It still appears that areas north of the U.S./Canada border will stay mostly dry, like with the current cut-off low.
 |
| Source: TropicalTidbits |
Uncertain long-range outlook, but appears mostly dry with warm weather likely mostly squashed to the southwest, still potential frosts and freezes
It will likely finally clear out more after next weekend, with the cut-off lows likely east of our region, though the long-range outlook is generally uncertain for our region. Upper-level ridging looks to dominate the Midwest U.S. for the foreseeable future, with mostly warm and dry weather, but it is unclear if warmth can push eastward into our region at all after next weekend. Models had shown our region getting into the warmth for the past few days, but have mostly backed off today. To get summerlike warmth, we would need the upper-level ridging to nose into our region, accompanied by a stronger surface high pressure to our south promoting deep westerly to southwesterly flow, but most models are now instead showing the upper-level ridge remaining to our west with repeated upper-level troughs digging into Atlantic Canada. This pattern favors cool Canadian surface high-pressure systems repeatedly nosing into our region, leading to a northerly low-level flow stopping any true warm air mass from entering, though perhaps without the cut-off lows and unsettled weather of the next several days. Our position to the east of the upper-level ridge axis and west of the upper-level trough axis actually favors dry weather synoptically. Some of the air masses could be cool enough to lead to frosts and freezes outside urban areas and away from large bodies of water. Daytime temperatures could still be mild to warm at times given the likely sunnier weather. This is occurring even as areas to our southwest stay persistently warmer. Other than perhaps an occasional day here or there, especially in southern areas, widespread summerlike warmth appears unlikely for the next 10-14 days. I still wouldn't rule it out completely, as models are still disagreeing and flip flopping somewhat, and it might not take very much for the upper-level ridging to indeed nose eastward into our region at times. Amazingly, all these slow-moving weather patterns expected over the next 10 days is occurring with a +NAO and +AO, but after that, both the NAO and the AO will turn negative, which could further squeeze any summerlike warmth to the southern U.S.
 |
| Source: TropicalTidbits |
 |
| Source: Climate Prediction Center |
No comments:
Post a Comment