April 29, 2012: Some Warmth To Return

Forecast Highlights:


- Rainy Tuesday expected; at least 1/4 inch possible
- Back door cold front keeps Wednesday and Thursday seasonable
- Brief warmth surge possible on Friday, may be accompanied by storms
- Cooler pattern may develop towards longer range


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The May outlook has been posted this morning in the Long Range Forecasts page.


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Yesterday's Observations:

Yesterday (Saturday, 4/28) brought increasing clouds across the region as a wave of low pressure approached, remaining to the south of the area overnight. Due to the cold air mass in place, a widespread frost was observed inland, where temperatures dropped into the upper 20s to lower 30s in the far north/west suburbs of NYC. Places closer to NYC, including the city itself, saw low temperatures in the 30s, which is quite chilly for this time of the year; Central Park's 38 degree low was 11 degrees below the average low, and was 4 degrees short of breaking the record low for that date, set in 1934. High temperatures generally ended up in the upper 50s to lower 60s.

With the low pressure moving out, cloud cover has cleared for most places, and mainly sunny skies are expected through the rest of the day, with clear skies resulting in another frost potential tonight for interior parts of the area. A weak wave of low pressure will move through on Tuesday, bringing rain especially in the morning hours as a back door cold front moves through, keeping seasonable temperatures in place through Thursday as southern and western parts of the Northeast region surge into the 70s and 80s. Depending on the development of a potential Greenland block and the back door cold front, the surge of warmth may briefly reach the area on Friday; should it do so, temperatures may surge above 80 degrees, and thunderstorms may come back into the picture.


Today And Monday's Outlook:


Mainly sunny skies are expected to continue through today, with high temperatures reaching the upper 50s to lower 60s across the area again, getting close to 65 degrees in the immediate NYC area. A light NW wind is expected.

With clear skies tonight, cold temperatures are expected again with an inland freeze; temperatures will drop into the upper 20s for NW NJ, interior SE NY and possibly the colder areas of central/eastern Long Island, lower to mid 30s for southern CT and the rest of SE NY/northern NJ, mid to upper 30s for the immediate north/west suburbs of NYC, and the upper 30s to lower 40s in NYC.

Mostly sunny skies are expected for Monday morning, although cloud cover will increase by the late afternoon and evening hours as the next low pressure approaches. Temperatures will also reach the upper 50s to lower 60s for highs, getting close to 65 degrees in the immediate NYC area, with a light north wind in the morning becoming a light south wind by the afternoon.


Tuesday - Wednesday: Some Rain, Seasonable Temperatures

A weak wave of low pressure will approach the region on Monday, producing locally strong thunderstorms in western PA on Monday evening. The rain is expected to begin affecting the area after 12-2 AM, with scattered showers expected to last through at least 12 PM on Tuesday. Locally heavy showers are possible as well, with rain totals likely ending up close to 1/4 inch. Due to the cloud cover, occasional showers and an east/SE wind, chilly temperatures are expected, likely reaching the mid 50s in southern CT and Long Island, upper 50s to lower 60s in NYC, lower to mid 60s in the north and west suburbs of NYC, and the mid to possibly upper 60s towards NW NJ/Orange county. There is still uncertainty with the exact temperatures, the models continue to show different solutions, as the morning NAM run had highs in the mid 50s in NYC while the latest run has upper 60s, although given typical model trends, it is possible that the next update to the forecast may slightly increase high temperatures.

With the low pressure moving out, a back door cold front will be stuck close to the area, keeping New England chilly while the Mid Atlantic and western PA/NY end up with warmer temperatures. The area is expected to be in between this boundary, with temperatures ending up in the 60s for most places, possibly in the upper 50s towards southern Connecticut and in the lower 70s towards western NJ. Partly to mostly cloudy skies are expected on Wednesday, while scattered thunderstorms, locally strong, will take place towards Pennsylvania and the Mid Atlantic.


Thursday - Weekend: Brief Warm Surge / Storms Possible


Warmer temperatures may return on Thursday as a warm air mass moves into the region. While temperatures especially further east will still be influenced by an onshore flow, the western parts of the area are expected to reach and pass 70 degrees, with mid 70s possible towards western NJ. Isolated thunderstorms are also possible west of NYC; the best risk of scattered thunderstorms, however, is in Pennsylvania and New York, where storms could end up locally strong.

Depending on a developing block near Greenland, discussed in more details in the next paragraph, and the location of the warm sector, a one day warm surge may be possible on Friday, focusing in the western and southern parts of the region while also affecting parts of, if not most of the area. In locations where winds end up switching to the southwest/WSW with at least partly sunny skies, temperatures are likely to easily surge well into the 80s, getting close to 90 degrees southwest of NYC. At this time, I am thinking that temperatures in the area end up in the mid 70s to lower 80s, with eastern areas the coolest, although places west of NYC, in the warmer case scenario, may also surge well into the 80s. In places that end up in the warm sector, more instability is expected, and the risk of strong thunderstorms may be there in parts of the region, although exactly where this potential ends up is still uncertain. Stay tuned for more information on the late week outlook.

By the end of the week, strong ridging will push towards Greenland, with a Greenland block developing for the first time this season as a result. During the winter, a Greenland block would provide the East with below average temperatures and snow potentials, as observed during the winter of 2010-2011, although with shorter wavelengths as summer approaches, the impact won't be the same. A colder than average pattern is unlikely, especially as observed throughout April when despite some relatively strong troughs moving into the region, temperatures still ended up near-slightly below average as opposed to below-well below average. A persistently warm pattern, however, is unlikely as well, and as mentioned in my May outlook posted in the Long Range Forecasts page, most warm spells under this pattern are likely to end up relatively short lived, with slightly more frequent troughs keeping temperatures closer to average. More information will be posted on the May pattern as details become clearer.