Aug 18, 2013: Scattered Showers Today

Forecast Highlights:

northeastA weak wave of low pressure spread north of the forecast, with scattered showers expected to cover the area throughout the day along with chilly high temperatures. The temperature cool down will be brief, however, as a warmer and more humid air mass gradually returns, with temperatures back into the mid 80s to low 90s range for Tuesday through Thursday with a cold front moving through on Friday, bringing a temporary cool down for next weekend.



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Saturday, August 17 Observations:

8.17.13A high pressure gradually passed to the east of the region as a frontal boundary in the southern US slowly spread north, bringing more widespread cloud cover into the area especially in the afternoon and evening. The slow warming trend since the mid week continued, with temperatures slightly warmer than Friday, peaking in the low to mid 80s across most of the area with some upper 70s for interior and coastal areas. The highest temperature was 84 degrees in Teterboro, NJ and Central Park, and the coolest high temperature was 79 degrees in multiple locations.




Today – Monday: More Clouds, Scattered Showers

northeastAs of this morning, a weak 1018 mb wave of low pressure was situated over southeast VA along a frontal boundary, and will continue to move northeast today. A high pressure over New England will keep most of the rain suppressed to the south, although despite this, rain from the storm has advanced north of the forecast this morning, and in some cases significantly north of the models; compared with the latest radar posted to the left, the 6z NAM hardly has any rain anywhere in the region and keeps the showers suppressed in southern Virginia. The GFS was the northernmost model and did depict rain spreading into the majority of NJ and eastern PA, but was too far north with the precipitation shield, spreading it way north into northern Massachusetts, and too heavy with precipitation with over 1/4 inch for NYC and Long Island. Although more widespread precipitation is expected, any rain is expected to remain light with under 0.1 inch for most of the area, locally higher south of NYC. The 5-Day Forecast has been added to reflect more widespread and increased light rain probabilities with high temperatures lowered a few degrees especially inland.

The wave of low pressure will move out overnight, with more sunshine and dry conditions returning for Monday with highs returning into the upper 70s to low 80s, peaking in the mid 80s near NYC. A weak mid level shortwave is likely to move through the region with some models showing increased mid level relative humidity and scattered showers over the region and area; at this time I am siding with a drier outlook with showers staying west and partly cloudy skies over the area, but as with today this setup will be watched in case changes need to be made to the outlook later today.

Tuesday – Next Weekend: Warm, Humid For A Few Days

Following the departure of the frontal boundary, a weak high pressure will build into the region again with a southwest flow at the surface bringing in a warmer and more humid air mass from the Gulf of Mexico, which along with mostly sunny skies and 850 mb temperatures warming up to about 16-18C will result in the most significant heat in almost a month, with a minor heat wave for parts of the region. Temperatures will start out in the mid to upper 80s on Tuesday with partly sunny skies, increasing on Wednesday and Thursday with more widespread upper 80s and some low 90s in the immediate NYC area, with mostly sunny skies likely.

As ridging sets up over the central US, the region will be placed under a NW flow aloft, which will keep the region under a somewhat fluctuating pattern between warmth surges and cool downs. A strong trough will dive southeast from Canada into the region on Friday with a surface cold front expected to move through; the models remain divided with the specific details, as the GFS shows widespread rain and thunderstorms while the ECM and CMC depict a dry frontal passage with light rain staying north. The GFS is slower with the frontal passage, which is interesting to note given its occasional progressive bias with cold fronts. As Friday is now in the 5-day forecast range, I sided with a lower chance of showers especially north of NYC, but with the outlook subject to change.

Behind the front, a cooler air mass will return for next weekend, with highs likely back into the upper 70s to mid 80s range across the area with lower humidity. Another warmth surge may attempt to build in early the following week, although based on the current pattern, any warmth surge should remain relatively long lasting and followed by another frontal passage. Stay tuned for more information on the longer range outlook.

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