Nov 17, 2013: Rain/Wind Monday Morning

Forecast Highlights:

0338A severe weather outbreak currently occurring in the Ohio Valley region will reach the region late tonight into Monday morning in a weakened form, with gusty winds up to/locally over 40 mph and moderate rainfall up to 1/4 or locally 1/2 inch in what will be the most significant rain event since late September, almost 2 months ago. Unseasonable warmth will return later on Monday as the trend for significant temperatures swings continues, with highs only in the mid-upper 40s for the midweek, returning to the 50s by the late week and into the 30s by next weekend.

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Saturday, November 16 Observations:

11.16.13Temperatures continued to gradually moderate as a warmer air mass spread into the region, with temperatures returning to above average levels; after isolated early morning showers, generally producing less than 0.05 inch of rain, skies partially cleared during the afternoon with high temperatures rising into the upper 50s in Long Island/coastal CT and the low 60s elsewhere. The highest temperature was 63 degrees in Meriden, CT, and the lowest high temperature was 56 degrees in JFK Airport and New London, CT.




Tonight – Monday: Rain/Wind Tonight, Warm Monday

A severe weather outbreak occurred over the Ohio Valley region today, with SPC having issued a high risk of severe weather over Ohio, Indiana and Illinois. As the mid-upper level trough becomes negatively tilted and quickly lifts northeast, a surface low pressure is currently rapidly intensifying over Michigan, which will continue to track northeast into Canada tonight, bringing its cold front east into the northeastern US region. With less instability and the strongest forcing lifting north into Pennsylvania and New York states, the storms are expected to weaken overnight, with little to no lightning expected. Strong surface-500mb bulk shear is expected to continue, however, which along with a strengthening low level jet is expected to result in a strong wind gust risk extending into the region with the frontal passage on Monday morning. Rain is expected to be relatively fast moving, with up to 1/4 inch, locally 1/2 inch inland, expected, which would make it the most significant rain event since September 21-22 when over an inch of rain fell in NYC, but with wind the main risk, especially north/west of NYC, with gusts up to/locally over 40 mph expected with the heavier rain showers. Rain is mostly expected to fall between 3-6 AM west of NYC and 5-8 AM east of NYC

Cloudy skies and areas of fog will continue tonight as temperatures initially hold steady in the mid to upper 50s before rising late in the overnight hours into the low-mid 60s. Highs are expected to peak early in the afternoon in the mid to upper 60s with clearing skies and a breezy west wind, with decreasing temperatures towards the mid to late afternoon hours.


Tuesday – Friday: Cold Mid-Week, Warmer Late Week

This year’s fall has generally featured a progressive flow in the mid-upper levels, with frequent temperature swings and the storm track remaining well north/west of the area, which resulted in an overall lack of rain and developing drought conditions across the region; this has been evident as the medium range guidance this fall frequently exaggerated rain forecasts, such as on Monday with the models originally indicated the potential for near/over 1 inch of rain. A transient cool air mass will move through on Tuesday and Wednesday, with much colder temperatures, only rising into the mid to upper 40s for highs across the area. Overnight lows are generally expected to fall into the 20s across the area, with low 30s in NYC and the immediate coast. As the cold air mass quickly exits with weak ridging rebuilding into the region, temperatures will rise for Thursday and Friday, returning into the low to mid 50s for highs with partly sunny skies expected.


Next Weekend – Next Week: Some Rain, Then Much Colder

The latest signals indicate a more interesting pattern may be on the way starting next weekend, beginning with a weekend low pressure affecting the region. A cutoff upper level low is forecast to remain stationary over southern California, with more frequent ridging over the western US, which along with various other factors supports troughing downstream into the eastern half of the US. A cold front or low pressure is expected to move through around next weekend; while at least some precipitation is expected across the region, there is some uncertainty regarding whether the rain comes in the form of a relatively moisture-starved low pressure over the US/Canada border bringing a cold front, or a more moist and organized low pressure tracking over the northeast US region but north/west of the area, producing a more widespread precipitation event. Given the progressive pattern and the aforementioned typical model bias of exaggerating medium range rainfall, I am siding at this time with the former scenario, which should produce some showers across the area next Saturday, although the possibility of a more organized and wetter system affecting the region cannot be ruled out.

Behind this cold front, the coldest air mass of this fall so far is likely to enter the region, with the medium range models showing modeled 850 millibar temperatures near -14C to -18C. The models have also exaggerated the intensity of the upcoming midweek cool down from the medium range, and as this is a recurring longer range bias it is also possible the same could be applied in this case, although there is a higher likelihood of much colder temperatures towards the start of next week, with high temperatures likely peaking in the 30s, along with widespread lows in the 20s and 10s inland possible.

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