Mild to warm, humid, and unsettled week coming up with heaviest rain in northern areas, especially tonight into Monday, and warmest and drier weather in southern areas; sharply cooler late next Sunday into early following week before likely warmer and possibly unsettled again before drier end of April

Plain-language summary:

 

After a somewhat chilly weekend including a freeze last night, most of next week will be rather warm and unseasonably humid for April, especially in southern areas, though also relatively cloudy and unsettled with frequent rains, especially in northern areas. The most substantial rain will likely fall tonight into Monday, especially in northern areas, before it warms up. It cools down modestly in northern areas Tuesday through Thursday with a few rounds of lighter rains before widespread warmth likely with more sunshine dominates Friday and Saturday. After more rain Sunday, it turns sharply cooler for a couple of days, though it likely warms up again afterward, perhaps with more unsettled weather. It could turn drier for the end of April.

Meteorological discussion:

 

Except this morning, mild to warm spring weather to dominate for foreseeable future 

 

Although there are a few occasional chilly days, it is hardcore spring across the region now, with most days in the foreseeable future being mild to warm. This is due to (in addition to the normal progression of spring) a persistent upper-level ridge in the eastern U.S. downstream of a weaker upper-level trough in the western U.S. While there is still a surprising amount of cold arctic air across central and northern Canada, the arctic air masses are weakening quickly finally, and unlike in March, the upper-level ridge position near the U.S. East Coast (as opposed to in the central and southwest U.S. like in March), compounded by a still NAO unfavorable for intrusions of cold air southward into the U.S., will block most of the cold air from penetrating south into our region. Instead, it allows a persistent flow of warm, moist air from the Gulf of Mexico into our region, especially in southern areas, with unseasonably high dew points for a month typically characterized by low humidity outside of storm systems. Actually, it could be among the warmest Aprils on record for the contiguous U.S. after a stunning, record-breaking warm March.

 

Source: Climate Prediction Center

 

 

Mild to warm and unsettled with frequent rains through Thursday, with heaviest rain tonight into Monday, especially for northern areas; warmest and driest in southern areas 

 

That said, we are seeing a relatively chilly surface high-pressure system overhead this weekend that brought a freeze last night, but this is still nowhere near as cold as the arctic air masses in March. This air mass will quickly moderate through Monday as a low-pressure system tracks from the central Rockies to northern Quebec well to the northwest of our region and deep southwesterly flow brought on by the ridge mentioned in the previous paragraph takes over. The warm advection will initially lead to a period of rain, heavy at times in northern areas (>1" or 25 mm in many areas), tonight into Monday before the warm air actually reaches our region. But given all the moisture, it will be a relatively "dirty" warmup with some clouds (though also mixed with some sun outside organized storm systems), limiting just how warm it can get, especially in northern areas closer to the baroclinic zone. A cool surface high-pressure system to the north on Tuesday will sneak in cooler low-level air to northern areas, though this is far from an arctic air mass, and it will still be mild, just not warm. Two weak disturbances/elongated low-pressure systems will bring more rain, again heaviest in northern areas, Tuesday night to Wednesday and again on Thursday. The storminess is the result of being on the northern edge of the persistent warm, moist upper-level ridge across the eastern U.S.

 

Source: TropicalTidbits

 

More widespread warmth and sunshine Saturday before strong cold front brings more rain on Sunday, but likely minimal or no severe thunderstorms

 

The storminess exits on Friday, with the upper-level ridge expanding northward, leading to more widespread warmth with sunshine on Saturday ahead of a slow-moving cold front given the storm track well to the north and deep southerly to southwesterly flow. The amplification of the weather pattern is leading to the cold front being slow-moving, with one or possibly two low-pressure systems riding along the front. While the first one on Saturday will pass well to the northwest of our region, the second one is questionable, as it could be weaker, allowing the front to pass through on Sunday with a brief period of rain, or it could be stronger, allowing the front to slow down and leading to Sunday also being warm before a round of rain possibly heavy at times Sunday evening. A few rogue model runs even show precipitation lingering long enough behind the sharp cold front for precipitation to change to wet snow at the end, mostly for higher elevations, given the perfect setup, though I am skeptical. Either way, it will turn sharply colder behind the front. 

 

Source: TropicalTidbits

 

Before that, one or more days next week could feature temperatures above 77F (25C) in low-elevation locations, especially in southern areas. Although it will be an unsettled week with frequent rain chances, especially in northern areas, rain is unlikely to be heavy or persistent enough to cause flooding, especially given that the snow cover has already melted in almost all of our region, and it will likely be too cloudy to produce the instability necessary for all the severe thunderstorms that are expected over the U.S. Plains and Midwest.

 

Source: TropicalTidbits

 

Cooler for a couple of days early following week, though likely still seasonable to warm most days afterward and perhaps turning unsettled again before drier end of April

 

The upper-level ridge in the eastern U.S. weakens next weekend, and this will allow the strong cold front to at least briefly bring temperatures back below average, perhaps with a widespread freeze, by the following Monday. Still, the lack of any real upper-level troughing in the eastern U.S. and rapidly weakening arctic air masses suggest that any really cold air or snow is very unlikely. Yet another upper-level trough entering the western U.S. will likely pump the eastern U.S. ridge again later the following week, leading to more warm weather, though our region could be near the northern edge of the ridge again, leading to more clouds and rain. 

 

After that, the decreasing AO and NAO may push the jet stream farther south or promote the southern storm track across the central and southern U.S. to be stronger. This would lead to drier weather in our area with cool to mild (not arctic) southern Canadian high-pressure systems dominating our area and storms staying mainly to the south for the end of April. This is a weather pattern typical of El Niño and perhaps the first sign of the atmospheric pattern in our region responding to the developing El Niño. Given the strong April sun angle, daytime temperatures will be mild to warm with any sunny day given the lack of arctic air, though nighttime temperatures could still be cool with the dry air masses and clear skies allowing for good radiational cooling and large diurnal temperature swings. Such a pattern would also prevent unseasonably warm and moist air masses from reaching our region. Such air masses with no Gulf of Mexico moisture tend to be particularly dry at this time of year due to the lakes in eastern Canada being either frozen or quite cold and not providing much moisture to the air, and the still bare trees not transpiring moisture to the air either.

 

Source: TropicalTidbits