Spring Wx

When Will The Warmth Be Here To Stay?

Miguel Pierre Long-Range Discussions, Spring Wx

So far, this Spring in the Tri-State Area, we have seen more cooler weather, dominate and warmer periods more transient. Last week was another example with Tuesday and Wednesday will very cool, with east winds bringing marine air off the ocean. While Thursday we saw temperatures warm into middle to upper 70s, away from immediate coast. According to a tweet from the National Weather Service in Upton, NY, January to April 2014 averaged below normal for Central Park. The last four-month period to do that,was from April to July 2003. Later this week, looks like more swings with temperature, with the warm front position each day very important. So when will the warmth be here to stay for good?

First we need too look at what has been causing all this huge swings temperatures. The first, most persistent feature, are the above normal sea-surface temperatures in the Northeast Pacific. This enhances a stronger ridge over parts Northeast Pacific Basin, usually ahead of deep trough or low positioned near the Aleutian Islands. This pattern is known as EPO (Eastern Pacific Oscillation), in its negative phase. This is a feature that has been there, since the late fall of 2013.

Warm SST anomaly across the Northeast Pacific
Persistent pool of warm SST anomalies over the Northeast Pacific Ocean

The -EPO ridge often shifts east into West Coast of North America. However, with the lack of sustained blocking on the Atlantic side the pattern remains somewhat progressive. The -EPO ridge shifts east into west coast of North America transforming into +PNA pattern. Then when the next Pacific storm moves in Aleutians/Bering Sea, the -EPO ridge reloads  with enhancement from the warm sea-surface temperatures over the Northeast Pacific.

500mb mean height anomalies from January-April 2014 showing an -EPO pattern dominating over North America
500mb mean height anomalies from January-April 2014 showing an -EPO pattern dominating over North America

A moderate to strong, El Nino is forecast later this summer. The means we are likely looking at a warm East Pacific Chances are this warm SST anomaly will also persist through the summer and beyond. So the -EPO likely won’t be going away for good, anytime in the near future.

CFSv2 forceast for
CFSv2 ensemble forecasting sea-surface anomalies +1K to +2K for Nino 3.4 region

Warmer than average temperatures over also in the lower stratosphere has supported the -AO/-NAO blocking to develop. This has resulted keeping deeper trough over SE Canada or the Northeast for much of this Spring. Although there has been a tendency for the -AO/-NAO blocking to be transient, because there has been a parade of Pacific storms crashing into West Coast. So were not able to lock cooler than normal pattern over the Eastern CONUS either. Instead, we see more volatility with huge swings in temperature.

70mb temps in lower stratosphere are currently above average
70mb temps in lower stratosphere running above average, late March/early April

The models show the AO/NAO rising next two weeks. So that will allow the for another intense, warm surge late this week for Eastern US. However, models now trending stronger with trough over SE Canada. This trough will produce confluence or high pressure over New England and likely force the warm front to stall to our south on Thursday. Keep most of the area in cool, marine airmass with chance of a showers.

GFS showing the warm front remaining south of the Tri-State area on Thursday.
GFS showing the warm front remaining south of the Tri-State area on Thursday. Temperatures in 50s over Northern New Jersey, New York City, and Long Island.

The trough will start shifting east on Friday. Allowing the warm to make more progress northward. We could see big difference in temperatures and sky conditions from SW to NE across the area. More widespread 70 or 80 degree temperatures are more likely this weekend. With a little more sunshine and showers and thunderstorms more widely scattered.

The MJO is now active and will be propagating into phase 2 next week. Which supports another period cooler and wetter weather over the Eastern US, sometime between May 15- 20th period. Beyond that, MJO might get into phases 5 and 6. Which supports longer period of above normal temperatures for much of Central and Eastern CONUS for late this month. With El Nino growing the summer, the MJO is likely to be more active and have some influence on our weather pattern.

15-day ECMWF ensemble forecast for MJO propagate into phases 2 and 3 next week into phases 4 and 5, the following week
15-day ECMWF ensemble forecast for MJO propagate into phase 2 next week.

As we go later in Spring and Summer, the cold impacts of -EPO/-AO/-NAO gradaully decrease. The supply of cold air begins to run out. The configuration morphs into a pattern that supports warmer west-down slope flow in our region. So will probably warm periods will last longer. However, we still have monitor for troughs over SE Canada or New England to force warm front to stall south of region or to push backdoor cold front in our region. Until mechanisms producing -EPO/-AO/-NAO  patterns from to time start to change.

 

Heavy Rainfall & Minor Coastal Flooding Through Tonight

Miguel Pierre Spring Wx ,

As I discussed in the previous post, a large cut-off low that brought severe weather with tornadoes to our Central US is now bringing periods of rain to us.  Lifting and moisture will increase through the today as the warm front slowly approaches from the southwest. So more waves of rain, moderate to heavy at times mare expected for today. East winds gusting at times to 35mph will also keep us in very cool marine airmass. Temperatures will struggle to get out 40s. These winds will also cause some areas of minor coastal flooding during high tides this morning and early this afternoon. Especially along the shores of New Jersey and Western Long Island sound.

Tonight, a strengthening southerly low-level jet and an increasing precipitable water values will enhance moisture convergence for more widespread heavy rainfall. Elevated instability in form of MUCAPE will also be increasing for some embedded thunderstorms with torrential downpours. Rainfall totals between 2 to 4 inches are expected for most of the area. A few areas that receive more thunderstorms, could see higher totals.  This rainfall can cause flooding in the low-lying and poor drainage areas and flooding near small streams and rivers. Winds turning southeast early tonight, will cause more widespread minor coastal flooding during high tides. For these reasons, the National Weather Service have issued Flood Watches for the entire Tri-State area today and tonight. As well as Coastal Flood Advisories for areas around Western LI sound, New York Harbor for early tonight.

6z GFS showing heavy rainfall and embedded thunderstorms tonight over the region.
6z GFS showing heavy rainfall and embedded thunderstorms over the region tonight

Any rain and thunderstorms should come to end early tomorrow morning, as the warm front lifts north of the region. Some sunshine will break out between clouds later in morning and during the afternoon with winds turning more southwest. Causing temperatures to rise into lower to middle 70s, away from immediate coast. Which will be a big difference from what we are experiencing today. Some scattered showers and thunderstorms are possible late tomorrow afternoon with passage of a weak cold front. Friday still looks drier and slightly cooler, as the entire system weakens and lifts to our north.

I will have more updates on the storm, if there any significant changes. Check the 7-day Forecast and Forecast Summary for more updates later today.

Cut-Off Low to Bring Heavy Rainfall Midweek

Miguel Pierre Spring Wx

Hope you enjoyed today’s weather. A large, slow moving cut-off low will bring cooler and wetter beginning tomorrow. This is part of the same storm system that also causing severe weather with tornadoes to our West. Severe weather is not expected for the Tri-State area, due to onshore winds bring stable marine airmass over our area. But periods of rain likely to begin Tuesday afternoon and last into Wednesday. Then that rain will become steadier and heavier at times by Wednesday night. As a warm front approaches from southwest, with a 50kt+ low-level jet and precipitable water amounts 1.50″+. This will result in strong moisture convergence and elevated instability, enhancing heavy rainfall and isolated thunderstorms. Total rainfall totals from this storm are likely to range between 2 to 4 inches, for the most of the area. Some spots could receive more. Some flash flooding may occur in the typical poor-drainage areas. Some small stream or river flooding may also occur. Minor coastal flooding may also occur with easterly winds and astronomically high tides with the new moon. Especially for areas around New York Harbor and Western Long Island sound, Wednesday night.

12z GFS showing strong low-level jet at 850mb (5000ft)
12z GFS showing strong low-level jet at 850mb (5000ft)
12z GFS showing precipitable water values at 1.50 inches and higher, Wednesday night.
12z GFS showing precipitable water amounts of 1.50 inches and higher, Wednesday night.

The cut-off low will gradually weaken and move north of the area late this week. The warm front is forecast to lift well north of the area on Thursday. Some sunshine will break out between clouds, causing temperatures to rise into the 70s away from immediate coast. However, this may also cause more instability, for more scattered showers and thunderstorm to develop with an approaching cold front in afternoon and evening hours. Friday is looking cooler but drier. More disturbances coming from the northwest may bring scattered showers and thunderstorms this weekend and early next week. But there will be some sunshine as well.