Premium Weekly Outlook: Heavy Rainfall Likely Tuesday and Wednesday

The region has under moderate to severe drought conditions for over past several weeks. But a expansive, complex storm system centered over middle of part of the county, will impact the region Tuesday through Wednesday night, with more widespread, heavy rains likely. A closed upper-level low embedded within larger tough will be moving from the Upper Midwest to Great Lakes. This will cause a mid-level ridge to build over the Eastern US with a mild, moist southerly flow. A couple disturbances with a frontal boundaries will be rotating around the closed upper-level low and trough, causing two rounds of significant rainfall over the region.

The first disturbance arrives tomorrow with a warm front moving through the region. Today an upper-level ridge with high pressure will support sunshine. Then some mid-level warm advection, ahead of this system, will cause clouds to increase tonight. Some showers could break very late tonight or early tomorrow morning. But steadier rain is more likely begin overspreading the region from east to west during the midday hours, more isentropic lift causes by the mid-level warm advection, increases with the warm front moving into the region. Despite clouds and rainfall temperatures will be rising into upper 50s to lower 60s. with southerly winds tomorrow and evening.

The GFS model showing closed low and trough encompassing a large part of the CONUS over with strong 300mbl jet streak, 500mb shortwave , and warm front with over Eastern US on Tuesday.

The GFS model showing closed low and trough encompassing a large part of the CONUS over with strong 300mbl jet streak, 500mb shortwave , and warm front with over Eastern US on Tuesday

A strong southwesterly jet at multiple levels, will move into region, enhancing more low-level convergence and mid-level frontogenesis for some rain to become heavy at times by tomorrow afternoon. There are model differences in placement of heaviest rainfall, tomorrow-likely due some mishandling of some mesoscale dynamics. But high precipitable water values  will support rainfall totals possibly between 1.00 to 1.50” in part of the area. There could lead some from flooding in at least poor drainage and low-lying areas. Instability will be on the low side, but some isolated thunderstorms with even heavier downpours can’t be ruled out.

Southerly winds will be increasing tomorrow as strong low-level jet with moves overhead tomorrow. Some models are showing 850mb-925mb winds, associated with this low-level jet, to around 55kt to 65kts. At this time, we expect winds gusts most common in the 20 to 40mph range throughout the area. Model soundings show low-level inversion or stable temperature profile that would not support stronger winds aloft to mix down to the surface. But any heavy rainfall or isolated thunderstorm could bring down more of these winds by momentum. So will all that considered, we will have to watch for potential for stronger wind gusts, especially closer to the shores.

GFS showing 925mb winds 50kt+ and precipitatable values over over 1.00 " tomorrow.

The GFS model showing 925mb winds 50kt+ and precipitatable values over over 1.00 ” Tuesday afternoon

This system will be a quick hitter though. The warm front lifts north of the area tomorrow evening, with better dynamics shifting that direction. This will lead to a break in at least steadier rainfall tomorrow night and through Wednesday morning. It will remain cloudy with low-levels saturated and some light rain showers or drizzle are possible. Winds will become light and tomorrow night as the thermal and pressure gradient weakens. This will allow for some areas of patchy fog, to develop over the region. Temperatures will be not drop very much through the the 50s, with cloud cover and a mild airmass over the region.

Then a frontal system associated the next disturbance, will bring another round of rain during Wednesday afternoon and evening.  This frontal system will be more organized with one area of low pressure tracking over the Great Lakes and then a weak secondary or triple-point low will forming along another warm front moving northward over the Northern Mid-Atlantic and Southern New England regions. A strong low-level jet with this system may also lead to rain becoming heavy at times especially by late Wednesday afternoon and early evening. This could some flooding again in poor drainage and low-lying areas.

 

The Northeast and Mid-Atlantic region are in right-entrance region of 150kt+ 300mb jet streak where upper-level divergence causes more lift.

The GFS showing the Northern Mid-Atlantic  and Southern New England region are in right-entrance region of 150kt+ 300mb jet streak on Wednesday afternoon, with  divergence causes more rising motion into upper-levels.

High precipitable values will again support additional rainfall totals possible 1.00″ to 1.50″ in parts of the region again. This could lead to some locations seeing over 2.00″ of rainfall from both systems. Which would put some dent in drought conditions.  If the region gets into the warm sector, the airmass may become unstable enough for some isolated thunderstorms again. Winds will be also increasing again out southeast than southwest by Wednesday night. But low-level inversion or stable temperature profile again will likely wind gusts mostly in the 20mph to 40mph range again. Some areas of fog could still be around into the afternoon and evening hours, with stronger warm-air advection. Stay tuned for more updates, on both waves of rainfall over next few days.

Rain will taper off showers and end later Wednesday night, as a cold front moves through region. More clearing will take place on Thursday, as more subsidence in the wave this storm system arrives. High temperatures will be in the middle to upper 50s. Then a more seasonable chilly airmass will arrive for Friday and into the weekend. It will feel like early December with daytime highs in the middle to upper 40s and overnight lows 30s . A few upper-level disturbances passing through region could cause some clouds from time and perhaps a spotty sprinkle or flurry over the Interior locations. But mainly dry conditions with some sunshine are anticipated through the weekend.