Warming Temperatures on Tap Ahead of Another Slug of Rain

A deep southerly will begin to develop over the weekend, allowing the real warm-up to begin. Widespread highs in the 50s to low 60s are likely on Saturday. Sunday will be the peak of temperatures, when a potent southerly low-level jet begins to build over New England, allowing deep southerly warmth to push into New England. This will allow widespread temperatures in the mid 50s north to mid 60s south. The Merrimack Valley may be the warmest spot, with temperatures in the upper 60s with a decent shot at a couple 70° readings.

Below:Euro showing forecast temperatures Sunday afternoon:

This comes ahead of New England's next storm, which will involve a deep trough moving across the country. The system's primary low continues to look like it will move well north of New England, dragging its cold front across the region after a warm frontal passage. The main slug of rain will occur along a line ahead of the system's cold front. The primary area of low pressure has continued to trend northward, now likely passing over Hudson Bay in Canada with a secondary low pressure forming along the front south of New England.

Southerly winds will begin to increase on Saturday, allowing for a continued upward trend in temperatures. Winds will not be very strong on Saturday and the day will be mainly dry with partly cloudy skies. We only say "mainly" as a couple showers may pop up toward the evening. Sunday will see isolated showers around through the day before beginning to fill in by the late evening.

Below: NAM showing potential weather Sunday evening:

The main slug of rain has been trending a bit later, likely arriving for most, if not all, of New England for the overnight hours Sunday into Monday. This is when bands of moderate rainfall will occur with pockets of heavier downpours. It will remain very mild Sunday night into Monday morning.

Below: NAM showing potential weather around midnight Sunday night (1st image) and early Monday morning (2nd image):

The cold front will slow down on Monday, allowing for periods of rain to continue through the morning and into the afternoon. This will mainly be for eastern New England as Vermont, western Massachusetts and Connecticut will begin to dry out by Monday afternoon as a secondary cold front pushes into the area.

Below: NAM showing potential weather Monday afternoon:

New England is poised to receive a widespread half inch to inch of rainfall. Southernmost New England will stand to see the most rainfall from this one, with over an inch possible. The potential formation of a secondary low pressure south of New England will potentially help boost totals. Northern Maine will likely see the least amount of rain.

The storm will be capable of creating periods of heavy rain Sunday night into Monday as a very strong southerly flow develops. This flow will allow for significant moisture from the deep south to work into New England on basically a conveyor belt working up the eastern seaboard. Precipitable water (PWAT) values may exceed 1" and potentially approach 1.25". This indicates a highly moisture-rich environment.

PWAT is defined as the amount of water vapor contained in a column of air if it were to be condensed and collected. Basically, the higher the PWAT value, the heavier rainfall rates can potentially get. The PWAT value does NOT correspond to how much rain is expected to fall, meaning that a PWAT of 1 to 1.25" doesn't immediately mean 1-1.25" of rain is expected.

Below: PWAT values overnight Sunday into Monday, showing a moisture conveyor belt from the deep south:

The ingredients will be together for significant snowmelt this time around for northern New England. Overall, 1-2.5 inches of runoff from snowmelt will combine with total rainfall. Total runoff across northern New England may come out to around 2-3.5 inches. River ice will continue to rot and break up as well. Rivers in southern and central New England will likely see River ice flushed out, however, the thicker ice across the north may present some ice jam issues as it breaks up.

River rises and ice breakup in rivers are likely. There will be the potential for open water river flooding in addition to potential ice jam issues. Ice jams are more likely across New Hampshire and Maine while open water river flooding is more likely in Vermont. At this point, minor flooding is the most likely outcome for rivers with isolated pockets of moderate flooding possible. Ensemble forecasts on river flooding have been trending downward.

For southern and central New England, this will be more beneficial rainfall as drought conditions persist. Severe drought status was removed from central Massachusetts and Connecticut yesterday, however, a moderate drought remains in place as we continue to chip away from last fall’s bone dry conditions.

Below: Current US Drought Monitor status:

A strong low-level jet of 70-80mph will also cross the region Sunday and Sunday night. Naturally, not all of this wind will make it to the ground, and southerly winds can often have trouble mixing to the surface due to potential inversion issues, which can act as a barrier keeping the strongest winds aloft.

With that said, gusty winds will be likely during this time. They may be at their strongest Sunday afternoon, when mixing is deepest. At this point, maximum gusts of 40-50mph appears to be the most likely outcome, though this could still trend higher or lower given the strong low-level jet and mixing issues working for and against wind gusts.

Below: Winds at the 850 millibar level (about 4,700 feet above sea level) Sunday evening:

Beyond this storm, there’s little indication of any late season chill, with above average temperatures remaining highly favored into next week. Ridging looks to be in charge after this system, allowing for a rather persistent southerly and westerly flow. With that said, spring temperature forecasts can tumble quickly, and subtle changes in a front’s position or the development of an onshore flow can cause what was looking like a mild stretch to become cooler.