John Homenuk

Periods of heavy rain, storms possible through Friday

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The NAM forecast model showing heavy rain with embedded thunderstorms throughout the NYC Area on Friday morning, in response to a warm front passing the area.  Courtesy of Penn State University.

A strong upper level low over the Central United States, which produced severe weather from Missouri to Alabama last night, will slowly shift eastward during the day on Thursday and will near the area on Friday. As it does so, increasing moisture owing to a south/southeast flow will bring more humidity and a setup conducive to heavy rain and thunderstorms to the NYC Area. The threat of rain will begin Thursday night, after clouds stream towards the area during the late afternoon hours on Thursday. A strengthening low level jet (strong winds and advection of moisture in the low levels of the atmosphere) on Friday morning will aid in the development of heavy rain and embedded storms, and more storms are possible later Friday afternoon ahead of a cold front.

The most likely timing for the heaviest rain and potential storms is between 6 and 9 am on Friday, with the passage of a warm front and the strengthening low level jet. In addition to the heavy rain and potential storms, the aforementioned low level jet could bring strong southeast winds off the water which will be especially prevalent over the NJ Shore and Long Island. The second round of storms, is expected to be less widespread, with scattered activity Friday afternoon ahead of a cold front after temperatures rise into the 70’s.

Keep reading for potential severe weather impacts and details on the potential hazards…

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John Homenuk

PM Update: Pleasant pattern, but late week storm crashes party

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Typically, in the transition seasons (autumn and spring) the atmosphere is more prone to large mid-level cyclones in the Central and Northern United States. These can include large upper level lows, cutoff lows in the mid levels of the atmosphere, and phasing jet streams. So far this autumn season, we haven’t seen any large low pressure system which feature any of the above. That will change on Thursday and Friday as a large upper level system forms in response to shortwave energy dropping southeast from the Pacific Jet and energy in Northwest Canada. The system will strengthen and slow over the Central US, pushing a cold front towards our area this weekend. Until then, pleasant weather is expected Wednesday Night through Thursday. You can check the details on the storm system by checking out our Technical Feature.

NAM Forecast model showing low temperatures Wednesday Night. Notice the warm air near the coast in response to southeast winds off the ocean.

Tonight: Partly cloudy, pleasant, temperatures in the mid to upper 50’s falling throughout the night. The winds will turn to south and east, bringing in an onshore flow overnight. Coastal areas will see more humidity and temperatures more near the upper 50’s even throughout the night. Cooler inland.

Thursday: Partly sunny, warmer ahead of an approaching storm system over the Central US. Temperatures will reach into the middle 60’s with afternoon sun. Feeling a bit warmer, with increasing dew points. Rain should stay to the west during much of the day, although by early evening we can’t rule out a shower or two across our far western counties in New Jersey and Eastern PA.

Look Ahead: Things take an unsettled turn Thursday Night into Friday. Instability increases and a large storm system approaches from the Central US. Chance of showers and thunderstorms will increase essentially from Thursday Night through Friday evening. The unsettled weather could continue through the weekend until the cold front crosses Saturday PM.

Check out the full forecast through the weekend. Also, if  you haven’t yet, check out our daily posts on Facebook and follow us for live updates and interact with our forecasters on Twitter!

 

John Homenuk

Strong cutoff low will be the main weather story this week

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A strong upper level storm system will cutoff from the main atmospheric flow/jet stream this week over the Central US, becoming the first strong cutoff low of the autumn season. These systems are typically observed in the transition seasons of Autumn and Spring, and can bring a plethora of weather impacts. One of the signature features in a cutoff low is the entrenchment of cold air, especially in northern stream systems which drop south out of the Pacific Jet and/or Canada. This one, coming from Western Canada, will dive south and east into the mean 500mb low over the Central US and briefly cutoff before being lifted northeast by a generally progressive pattern.

ECMWF forecast model showing the strong cutoff low at 500mb (mid levels of the atmosphere). Notice the upper level low is “cut off” from the main atmospheric flow.

Technical Stuff: From a meteorological standpoint, cutoff low events aren’t overly rare. Yet, they remain impressive each time they occur. The strong surface low developing in response to this system is expected to develop and curve northwest over the North/Central US, while the cold air pool dives south of it and brings below normal temperatures and mid-level height anomalies (colder than normal averages). The result will be potential severe weather on the far south and east periphery of the system, and the potential for isolated frozen precipitation on the north/northwest fringes. The 12z Euro from October 17th shows the system very well, with the mid level heights displaying the upper level low cutoff from the main height field.

What’s it mean for us?: In our area, the system will bring a chance of showers and thunderstorms beginning late Thursday Night and continuing through Friday. There is isolated potential for a strong thunderstorm or two, given the very impressive shear from the upper level cutoff low to our west. However, meager instability is expected to generally mitigate the threat. We can’t completely rule out an isolated strong wind gust or maybe a brief spin up/weak tornado if all the pieces fall into place. Either way, the weather will be unsettled from Thursday Night through Friday, and continuing into Saturday before the cold front moves through. Thereafter, the cutoff low is expected to shift North and East away from the area.

Keep reading for more information on the cutoff low, as well as a peek into the winter season…

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John Homenuk

PM Update: Pleasant mid-week weather continues

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Tuesday featured temperatures in the upper 50’s to lower 60’s for highs, with plenty of sun and a breezy northwest wind. Although the wind kept things feeling cooler, along with advecting in a much less humid airmass, the still-warm sun provided the foundation for a beautiful day. It Felt especially good after a rainy and dreary Monday. Tuesday Night will feature cool conditions, without a threat of precipitation. Much of the same is on tap through the end of the week, with moderating temperatures before a cold front crosses on Friday.

NAM forecast model showing tonight’s forecast low temperatures with the coolest readings in the interior/north and west of NYC Metro.

Tonight: Cool, clear, northwest winds. A classic autumn night. Low temperatures in the 40’s in the NYC Metro and surrounding suburbs, with upper 30’s readings possible in the interior and usually cooler spots. Definitely bring a sweatshirt and/or jacket if you’re headed out and about tonight.

Wednesday: A nice day to start — even a little warmer than Tuesday was. High temperatures in the middle  60’s in some spots, with most areas reaching at least the lower 60’s during the afternoon. A little cooler, still, over the interior with high temperatures remaining in the upper 50’s there. Winds will turn from west to south/southeast during the day in response to a changing mid-level atmospheric pattern and a weak disturbance passing near the area will help bring more moisture into the picture. Some clouds are expected to advect into the area by afternoon and evening.

News and Notes: Hurricane Rafael is rapidly accelerating northeastward in the Atlantic Ocean and is not a threat to land…The National Weather Service opened their Center for Weather and Climate Prediction…September 2012 official data is in and the month is tied for the warmest on record for the globe…The Orionid meteor shower peaks this weekend on the morning of October 21st.

Check out the full forecast through the weekend. Also, if  you haven’t yet, check out our daily posts on Facebook and follow us for live updates and interact with our forecasters on Twitter!