Tag Archives: heavy rain

NYC Weekend Weather & West Coast Storm – Dec 2, 2014

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It’s been a up and down week for weather in NYC, with Monday starting out in the mid-60s, then a colder mid-week that featured some mixed precipitation and rain. The end of this week will feature rain and slightly warmer temperatures by Saturday, then a return to colder conditions Sunday into next week. I’m also going to point out some of the spectacular weather brought on by a huge Pacific storm that hit California this week.

Thursday – the remainder of today will be pleasant and sunny, though cold with high temps only in the low 40s.

Friday – clouds will begin to build overnight tonight ahead of the a storm system moving in from the Southern Plains to the Ohio Valley. There is a small chance for scattered showers, otherwise expecting a cloudy day with highs in the mid-40s.

Saturday – rain should overspread the area by Friday night into Saturday. This storm system will be drawing on energy and moisture from the Pacific storm that slammed California earlier this week (discussed below). Combined with influx of Gulf moisture, this setup favors a moderate to at times heavy rain event for Saturday. Temperatures will rise steadily ahead of this storm system as it pushes warm air up. High temperatures Saturday should reach into the mid-50s despite rain and clouds.

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GFS model output for overnight Friday into Saturday

Sunday – rain should end overnight Saturday, and high pressure from Canada should quickly build in behind this storm system. The positioning of this high pressure, along with the exiting low, will make for a tight pressure gradient, which should allow for stiff northwest winds perhaps in the 15-25mph range. Temperatures will drop back into the low 40s with the arrival the colder Canadian air.

gfs_namer_084_1000_850_thick
GFS model output for Sunday night

Monday – the storm system from Saturday will move offshore, but it appears from model runs that there’s some chance the storm lingers. As the high pressure from Sunday moves off to the northeast, the clockwise flow behind it may draw this offshore area of low pressure back into the area. This could lead to some rain on Monday. It’ll be a mostly cloudy day otherwise with highs in the low 40s.

Pacific Storm Slams California

Earlier this week, California got slammed by a very strong Pacific low. This storm brought on furious rains that dropped 1″+ in many areas of Northern California, with totals as high as 3-4″ in spots near the Coast Range and Sierra, as well as further south in the mountains east of San Diego. These totals represent more rainfall than had fallen in many of these areas all of last year.

You can see from the map below which overlays drought conditions (the deeper the red, the more extreme the drought, with the darkest red representing extreme/record-breaking drought) with rainfall totals from yesterday. You’ll see that much of the heaviest rain did fall over regions worst affected by drought. Sadly, though this is a case of too much of a good thing, as much of this desperately needed rainfall occurred so quickly, it will simply runoff back into the ocean.

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Map of California with drought condition layer (reds/oranges), and rainfall totals from yesterday

NYC Weather Update – Apr 30, 2014

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Are you wondering why today is so cool with highs barely touching 50, but tomorrow is forecast to have high temperatures in the low 70s? It’s because there’s a warm front currently situated to our south. Let me clarify the two most common types of frontal boundaries:

  1. A warm front delineates a boundary where the airmass behind the front is significantly warmer than the airmass ahead of it.
  2. A cold front, not surprisingly, applies to the reverse situation and delineates a boundary where the airmass behind the front is significantly colder than the airmass ahead of it.

Currently, a warm front sits south of us, causing an onshore flow (easterly winds) off the frigid Atlantic Ocean. Why the easterly winds? Looking at the image below, you’ll see yellow contour lines that demarcate isobars of pressure. In the Northern Hemisphere, air flows counterclockwise around a low pressure center and clockwise around a high pressure center. The counterclockwise flow also applies to the frontal boundaries attached to a low pressure center.

In our present situation, the air flows towards the east (counterclockwise) south of the west-east oriented warm front (in red), and then from the east to west north of it. Hence, we are experience very cool conditions, and the moisture being funneled off the Atlantic Ocean into our region is fueling these steady showers.

Current surface analysis from the WPC with my overlay showing movement of the warm front to our south.
Current surface analysis from the WPC with my overlay showing movement of the warm front to our south.

We should actually see temperatures begin to rise overnight as the warm front pushes through the area. Once this occurs, we will be in what is referred to as the “warm sector”, which is an area that sits behind a warm front and ahead of an advancing cold front. This type of setup is favorable for the development of thunderstorms.

Therefore, Thursday will be a warm, cloudy day with high temperatures in the low 70s and a chance of showers and thunderstorms in the morning.

Friday, with the cold front having passed through, conditions will clear up and we’ll have a nice, sunny day, with temperatures near 70. There will be a chance for afternoon showers.

Saturday continues the trend of nice weather with another day in the upper 60s and mostly sunny skies. Again, there will be a chance for afternoon showers, especially inland where daytime heating can produce enough energy (and instability) to induce those showers.

One other note about today and tomorrow, and that’s the whopping headline numbers for how much rain is forecast to fall, with totals ranging from as high as 3″+ in the western portions of the Tristate to 1.5″+ in the east. This could easily cause flooding in poor drainage areas, small streams, and urban areas.Screen Shot 2014-04-30 at 1.50.54 PM

 

 

NYC Weekend Weather Update – Apr 11, 2014

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We’re going to have a splendid weekend weather-wise in the NYC region. There will be some rain later this evening and into the overnight hours, but things should dry up before sunrise Saturday. High temperatures today will be comfortable in the mid to upper 60s, with western portions of the region possibly topping 70. The south wind will tend to keep inland areas warmer than coastal portions where the wind will be bringing in colder air off the Atlantic where sea surface temperatures are still only in the 40s.

Projected radar reflectivity for about 8PM EST, when we can expect the bulk of the rain for Friday night.
Projected radar reflectivity for about 8PM EST, when we can expect the bulk of the rain for Friday night.

Once the rain lifts out, Saturday is shaping up to be a gorgeous day, with sunny skies and high temperatures in the mid-upper 60s in NYC. Inland areas again will see even higher temperatures with highs near or above 70, while eastern portions of Long Island will see temperatures in the lower 60s due to the continuing cooling influence of southerly winds off the ocean.

Southerly winds will continue to usher in increasingly warm and moist air Sunday with high temperatures in the low 70s inland and in western portions of the region, mid-upper 60s in NYC, and cooler temperatures in the east and coastal CT.

Monday will be the warmest day of the stretch, with highs easily topping 70 area-wide, again with the exception of coastal waters in eastern Long Island and CT. Dense fog may develop overnight Sunday due to the increasingly saturated air mass moving into the area.

Tuesday will be a messy day with a strong cold front moving in from our west. Temperatures will be significantly cooler, with highs probably only in the mid-50s. The Hydrometeorological Prediction Center is forecasting a significant rainfall event. This sharply tilted cold front is associated with a strong low-level jet streak, which will help usher in very moist air from the Gulf.

Note the extremely meridional (north-south) orientation of air flow on Tuesday, indicating a strong frontal boundary
Note the extremely meridional (north-south) orientation of air flow on Tuesday, indicating a strong frontal boundary
Check out the swath of forecast total of 2.5"+ of rainfall Monday-Tuesday in our area!
Check out the swath of forecast total of 2.5″+ of rainfall Monday-Tuesday in our area!

After Tuesday, get ready for a serious cooldown, as temperatures behind this strong cold front will only be in the mid-upper 40s!