Nov 16, 2013: Some Rain, Wind Monday Morning

[notice]A new poll has been added to the right regarding the wording of the 7-day forecast. The second example (Highs between 50-55 degrees) has been used for today’s outlook as an example.[/notice]

Forecast Highlights:

nam-hires_namer_036_sim_reflectivityWarmer than average temperatures returned to the region today as temperatures reached the low 60s across the area, with warmer temperatures expected for Sunday and Monday as a cold front approaches, bringing a narrow line of rain/wind through the area on Monday morning with rain amounts less than 1/4 to locally 1/2 inch. The progressive pattern continues into next week as a transient cool down is followed by another late week warm up, with the next rain potential towards next weekend.


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Friday, November 15 Observations:


A relatively mild air mass remained in place over the region following the departure of the midweek cold temperatures, but with increasing cloud cover especially by the evening and overnight hours as an area of scattered showers approached New Jersey from the southwest; high temperatures generally reached the mid to upper 50s across the area. The highest temperature was 59 degrees in Montgomery, NY, and the coolest high temperature was 53 degrees in JFK airport.




Tonight – Monday: Warmth Continues; Quick Rain/Wind Monday Morning

Storm Analysis: A strong shortwave trough currently over the western US will become negatively tilted as it quickly lifts northeast into Canada, with a strong surface low pressure rapidly developing and intensifying over Wisconsin and Michigan on Sunday before moving into Canada. Dynamics are supportive of widespread severe weather over Illinois, Indiana and Ohio, with relatively high instability for this time of the year, strong surface-500mb bulk shear and a strengthening low level jet, and favorable mid level lapse rates. The primary risk with these storms is strong to damaging wind gusts, with tornadoes possible as well with any discrete severe cells in the afternoon-evening hours.

As the low pressure tracks into Canada, the cold front will steadily track east overnight into Pennsylvania, where both a shift in the strongest forcing further north into New York state and a more stable environment will result in storms weakening as they enter the region, with the strongest storms north and west of the area, towards New York state and western Pennsylvania. As the cold front reaches the NYC area early on Monday morning, a weakening narrow line of moderate-locally heavy rain is expected to move through, with little or no thunder. The low level jet will intensify overhead with 925mb winds up to 60-70 knots; some of these winds could mix down closer to the surface with any locally heavy rain shower, with gusts up to 30-40 mph expected, highest north and west of NYC. Rain amounts are expected to be generally light, up to 1/4 inch for most, locally up to 1/2 inch towards NW NJ and SE NY; should Central Park reach 1/4 inch, it would be the 3rd most significant rain event this fall. After the cold front moves through on Monday morning, a breezy west wind will develop, with highs surging into the mid to upper 60s in the early afternoon before cooling down by the mid-late afternoon due to strong cold air advection.

Forecast for NYC Area: Mostly cloudy skies will continue tonight into Sunday, with high temperatures on Sunday surging into the low to mid 60s across the area, locally over 65 degrees near or southwest of NYC. Scattered showers are possible in the afternoon mainly well north/west of NYC. With a breezy southwesterly flow overnight along with widespread cloud cover ahead of an approaching cold front, temperatures will slightly fall on Sunday evening before rising into the low-mid 60s by Monday morning. A quick moving narrow line of moderate-locally heavy rain is expected to move through between 4-7 AM west of NYC and 7-9 AM east of NYC, with little to no thunder expected; wind gusts up to 30 mph are likely, locally up to 40 mph north/west of NYC with any convection. Rain totals of up to 1/4 inch are expected for most, locally 1/2 inch inland. Clearing skies are expected for the rest of the day with highs peaking in the mid to upper 60s in the early afternoon before falling, with a breezy west wind at 10-20 mph.


Tuesday – Next Weekend: Temperature Swings Continue; Weekend Rain?

The progressive flow aloft continues through next week as a transient cold air mass moves through on Tuesday, with 850mb temperatures near -6C, but quickly moves out by Wednesday as weak ridging returns into the region in response to lowering 500mb heights over the western-central US. Temperatures on Tuesday are expected to reach the upper 40s to low 50s, falling slightly to the mid to upper 40s on Wednesday with mostly to partly sunny skies. Cloud cover is expected to increase by the late week as temperatures likely return into the low to mid 50s range.

The main uncertainty in the outlook is towards next weekend, as some of the medium range model guidance hints at a potential weekend storm affecting the region. There is a large spread regarding the exact setup of any storm, with some of the latest GFS and ECM runs hinting at heavy rainfall, which given the recent pattern would be questionable considering the medium range models frequently exaggerated rain potentials this fall; 55 days have passed since the last rain event over 1 inch, or more specifically 1/4 inch, when 1.17″ fell on September 21-22, marking the beginning of an unusually long stretch of dry conditions. While at least some precipitation is expected to affect the region around the weekend and/or early next week, the setup is still uncertain, with indications at this time suggesting any organized low pressure would likely track north/west of the area. There is higher confidence of at least a transient cool down behind this potential storm, however. Stay tuned for more information on next weekend’s outlook.

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