A Memorial Day Washout 🌧️☂️
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).
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.
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.
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.