I pity anyone planning any outdoor activities over the holiday weekend. It's going to be wet, cool and miserable for the most part. The good news is that this rainfall will be great for plants and mitigating our low-level drought conditions. The bad news - besides the obvious - is that this rainfall will likely lead to localized urban flooding.

The Meteorological Set-Up

High pressure has taken hold behind the cold front that just passed. Today, the high pressure is to our north, leading to winds out of the north, which will keep us dry and sunny today (Friday) as moisture gets pushed off shore. The story changes this weekend as that high pressure drifts eastward toward the Canadian Maritimes. This will cause our winds to come out of the east, which will transport cool and moist maritime onto shore. This will lead to the development of low stratiform clouds (when).

EPS (ECMWF model ensemble 00z May 22) surface pressure and height anomalies. Note High Pressure drifting eastward from the Great Lakes to the Atlantic near the Canadian Maritimes.

In the upper levels, however, high pressure causing winds over our region to be out of the southwest. This means all the air sitting over the Gulf States will be transported northeastward into our region.

EPS (ECMWF model ensemble 00z May 22) 250 mb winds. Note the ridge building over the southeastern US with southwesterly winds.

Of course, that air is warm and moist, being fed by an increasingly moist sub-tropical jet stream thanks to the growing influence of the upcoming El Nino event. This will lead to a process called "isentropic lifting" along a warm front that will try to push northward over the weekend. Isentropic lifting is where warm, moist air ascends over denser, cooler air already in place, - it's common along warm fronts and has been the main driving force behind our cloudy and cool spring.

Precipitable water (PWAT) values are forecast to peak around 1.5-1.75," which is quite high for our region. Any values over 1.5" could support a downpour, and we're expected to see elevated PWAT values throughout the weekend.

NAM 12km model (12z May 22) precipitable water anomalies showing significantly above average moisture most of the eastern half of the United States for most of the weekend.

These two features - the high pressure over the Canadian Maritimes and the warm front from the south - will lead to a stationary clash of air masses. We have a tropical airmass (warm and moist) to our south doing battle with a maritime airmass (cool and moist) to our north, and we will be stuck on the battle ground, i.e., the stationary front.

This features will combine quantitatively high precipitable water with strong uplifting mechanisms, a recipe for lots of rain.

The Weekend Forecast

Friday - Saturday AM:

The first half of this afternoon started off quite sunny with high temperatures in the mid 60s, but we're beginning to see increasing cloud coverage. Tonight will be mostly cloudy with temperatures dropping into the lower 50s. Light rain will begin between dawn and noon.

NWS (OKX) 48-Hour Hourly Forecast Plotter: Fri, 4pm - Sun, 4pm

Saturday PM - Sunday AM:

Clouds and precipitation tomorrow will inhibit diurnal heating with temperatures forecast to remain in the 50s all day tomorrow. That's around average for low temperatures but around 20 degrees below our average high temperatures.

Rain intensity will pick up after noon. Expect waves of moderate to heavy rainfall between Saturday afternoon and into Sunday. I can't rule out some low rumbles of thunder and C2C lightning flashes with the heavier downpours. There is no convective or severe risk, but the sheer amount of vertical velocity and moisture could result in updrafts up to 20,000 ft.

Either way, expect a soaking rain with few dry breaks for most of Saturday and Sunday.

NAM 3km (18z May 22) reflectivity showing what the radar might look like 2am Sat - 2am Mon

Sunday PM - Monday PM:

Rain will begin to taper off in coverage by late morning, with scattered showers lingering through Sunday afternoon and evening. A few of these lingering showers could be heavy.

Regardless of rain intensity and coverage, easterly winds will persist and so it will remain mostly cloudy all day on Sunday. However, if we dry out and get some peaks of sunshine, temperatures could break 60°F Sunday afternoon.

NWS (OKX) 48-Hour Hourly Forecast Plotter: Sun, 8am - Tues, 8am

Another shortwave approaching the region is likely to induce a brief rain shower early on Monday - likely in the late morning or early afternoon. But it should dry out in time for evening cookouts and afternoon high temperatures are expected to rebound back to average on Monday, i.e., 70s. Nice!

When all is said and done, over 2" of rain is expected to fall by Monday evening, and some areas could see over 3 inches!

Official Local NWS (OKX) Forecast Total Rainfall This Weekend

Summer Seasonal Outlook

The weather we are experiencing this week will likely be emblematic of our summer ahead: A couple of hot and humid days leading to instability and thunderstorms, followed by several days of cool, grey and unsettled/wet weather. Rinse and repeat.

More often than not, temperatures this summer will be normal to below normal, with more days in 70s and 80s than 90s. We'll get some hot days in the 90s here and there to be sure, but I don't expect any major heat waves.

Humidity will be a feature this summer as El Nino's gains more and more influence as summer wears on, with frequent precipitation events driven by subtropical moisture clashing with cooler maritime and modified continental polar air.

Although the main development region in the Atlantic basin is expected to remain fairly quiet this summer - and NOAA has just released their outlook for a below-average Hurricane Season - we will also have to keep an eye out for "home-grown" tropical cyclones that might form off the coast of North Carolina.

A Final Word to the Wise

Don't go into the ocean this weekend.

The water is cold (around 50-55°F) and rough with rip tides and rip currents. NYC lifeguards are not on duty as official beach season does not begin until next weekend.

A teenager already got swept away and presumably drowned earlier this week.

Honestly, it won't be warm enough anyway, but please be safe out there.

We're in the middle of the first heat wave of the year, but it won't last too much longer. Memorial Day Weekend will see a return of unseasonably cool temperatures, combined with clouds and some unsettled weather (e.g., light rain). In between now and then, we'll see a low risk of evening thunderstorms, which could be strong to severe.

A Heat Advisory is in effect until 8pm on Wednesday. A Heat Advisory is issued when the combination of heat and humidity is expected to make it feel like it is 95 to 99 degrees for two or more consecutive days, or 100 to 104 degrees for any length of time.

All of NYC is under a Heat Advisory until 8pm Wednesday night.

As I write this, temperatures have surpassed 90°F at Central Park and LaGuardia, with Newark Airport all the way up to 97°F! Southerly winds are keeping the south shore cool, leaving JFK at a balmy 77°F and temperatures in the mid-to-upper 80s further inland in Brooklyn and Queens.

NWS Forecast Temperatures (Actual), 11am Tues - 11pm Wed.

Tempratures will be marginally cooler tomorrow, but still dangerously hot, with high temperatures around 90°F. Heat indices (i.e., apparent temperature) will be in the mid-to-upper 90s. especially in the afternoon as the humidity begins to skyrocket.

NWS Forecast Apparent Temperatures (Heat Indices), 11am Tues - 11pm Wed.

These extraordinarily hot temperatures at the surface are creating low-level instability with steep lapse rates in the lower-to-mid levels of the troposphere, yielding between 500-1500 J/kG of CAPE (Convective Available Potential Energy) - more than enough juice to support thunderstorms.

HRRR model (18z May 19) skew-t showing a theoretical vertical profile of the atmosphere at 4pm on Wednesday.

Add in over 1.5 inches of precipitable water in the lower-to-mid levels, sandwiched between drier air aloft and at the surface, this could be recipe for downburst wind gusts or tiny hail. The official meteorologists at NOAA see this too: Today's Day 1 and Day 2 Convective Outlooks put NYC within the "marginal" risk zone for severe weather, namely for severe winds and hail.

NOAA/SPC Convective Outlooks for Tuesday (Day 1) and Wednesday (Day 2) show a marginal risk of severe weather in NYC driven by a 5% risk of severe wind and/or hail.

As far as timing and likelihood is concerned...

The risk for storms tonight is currently low (< 10%) but growing.

• Today (Tuesday): Models have been consistently trending towards no precipitation this evening, but in the past hour, we've gone from clear blue skies to increasing abundance of cumulus clouds. This tells me the atmosphere is mixing and taking advantage of the CAPE. So an isolated shower or thunderstorm can't be completely ruled out, but it is expected to remain dry as the best upper level support remains north of the area and subsidence helps to suppress convective development. Highest odds for rain this evening will be 7-9pm.
• Tomorrow (Wednesday): The risk for storms is meaningfully higher on - closer to 50% along with greater likelihood of severe storms. Based on what I'm seeing in mesoscale analysis, I think the best odds for severe weather will be in central/southern NJ and the Hudson Valley/CT/Long Island, but CAM guidance does support the possibility of thunderstorms in NYC. The best chance for showers and storms will be between 2pm-8pm, which could include isolated downpours, frequent lightning, strong gusty winds, and even tiny hail. However, these storms should be quick moving, which will mitigate the potential for any flooding.

HRRR model (18z May 19) reflectivity showing a theoretical look at the radar (3pm Tues - 2pm Thu)

Light rain showers may linger into Thursday morning's commute, but the day will dry out as high pressure takes control behind the cold front. Temperatures will be 20-30 degrees cooler with morning temperatures in the 50s and afternoon high temperatures expected to top out in the mid-to-upper 60s. Expect a similar story for Friday with high temperatures again only in the 60s.

By this weekend, the high pressure will move off the coast of Maine, creating easterly flow similar to what we saw throughout March and April. This easterly flow will lead persistent cool and unsettled weather conditions throughout the holiday weekend, with low clouds and ample moisture... plus a couple of weak shortwaves passing through the region. I'm not expecting a "wash out" for the weekend, but it will likely be cool, cloudy and drizzly on both Saturday and Sunday. Memorial Day Monday looks to be a little warmer - maybe breaking 70°F - but cloudy with some risk for light rain.

As of now, if you're looking to BBQ this weekend, Monday might be the best bet.

Also, don't expect a lot of heat waves this summer.

I would really love to see Hum tonight, but I don't think I can get to the venue in time to see most of the other bands playing, which is a shame because I've never seen Swirlies or Chapterhouse either.

Would rather not pay full price if I'm not going to see the full show, but if you've got an extra that is otherwise going to be unused and wasted, I'm happy to offset your loss a little bit.

Penn Station gonna be a little quieter