May 20

May 20, 2015: Coastal Low Approaches on Thursday

Forecast Highlights:

gfs1What was originally forecast to be a sunny ending to the week has trended increasingly cloudier, as a coastal low will make a close approach but likely remain offshore on Thursday, followed by a frontal passage on Friday accompanied by isolated thunderstorms. Sunshine and seasonable conditions will return for the weekend, but will remain short lasting as a significant ridge results in very warm, humid and occasionally stormy conditions throughout most of next week.

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May 18

May 18, 2015: Temperature Swings Continue

Tonight – Tuesday: Scattered T-Storms Expected

northeastOne of numerous quotes attributed to Mark Twain is “If you don’t like the weather in New England, just wait a few minutes.” While a few minutes may not be long enough in reality, one day may be sufficient as each day has brought a different air mass into the tri-state area; Saturday was generally overcast and seasonable, Sunday was warm and humid with partial sunshine, after which a backdoor cold front pushed through the area last night ushering in areas of drizzle, fog, and substantially cooler temperatures in the mid to upper 60s. To the west of the backdoor cold front, widespread showers and thunderstorms developed over Pennsylvania as depicted in the radar imagery to the left from the National Weather Service, but are generally weakening as they progress east into the more stable air mass over the tri-state area.

The backdoor cold front, stalled to the south of the tri-state area, will slowly retreat northward tonight into Tuesday morning as the wind direction turns more southerly ahead of an approaching cold front. Warm air advection aloft and marginal elevated instability may maintain some of the convective activity over Pennsylvania as it approaches NYC on Tuesday morning, with scattered showers and thunderstorms likely, mainly before 10-11 AM. Rain totals are somewhat uncertain, with high resolution models such as the NAM and HRRR depicting little rain extending into the area, although given high precipitable water values, showers may produce locally heavy rain especially north and east of NYC.

18z 4k-NAM hour 27, valid at 2100 UTC Tuesday, 5/19 (5 PM EDT), depicting NJ and NYC in the warm sector with temperatures in the low 80s, while CT and LI remain in the upper 60s and 70s. Image from PSU e-Wall.

temp27Most model guidance depicts the frontal boundary surging north of NYC by the early afternoon, ushering in a warm and moist air mass from the south with temperatures quickly rebounding into the low 80s in NYC and New Jersey by the late afternoon, while Long Island and Connecticut remain north of the front with temperatures in the upper 60s to mid 70s range. There is some question as to how far north the warm front will extend, as model guidance is often notorious for exaggerating the northward extent during similar springtime setups, although in the event the front does quickly progress through as modeled, the spike in temperatures and humidity would be sufficient to result in much higher CAPE values upwards of 1000 J/kg, indicative of a moderately unstable air mass ahead of the approaching cold front. Despite a relative lack of moisture, weak forcing along with increasing vertical wind shear may allow for the development of isolated thunderstorms along the cold front, capable of producing strong wind gusts and small hail. The highest risk of these storms is primarily north of the area, but may extend into northern New Jersey and southeast New York.

The temperature swings continue into Wednesday, as temperatures will return into the low 70s but with noticeably lower humidity and a strong northwesterly wind, gradually trending calm with more sunshine by Memorial Day Weekend. Tuesday’s post will feature more information on the outlook for the remainder of the week through Memorial Day Weekend.

May 17

May 17, 2015: Drier, Cooler Week Ahead

Forecast Highlights:

ne_f30Heat and humidity make a brief return today as temperatures have warmed into the 80s away from the coast, along with dew points in the 60s. A backdoor cold front will push through tonight, resulting in an easterly flow with cooler temperatures and widespread cloud cover lasting through Tuesday, when a frontal passage accompanied by limited shower activity will usher in a drier air mass with more sunshine and seasonable temperatures through Memorial Day Weekend.

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May 16

May 16, 2015: Scattered T-Storms This Evening

Forecast Highlights:

rad4After a streak of 23 consecutive days of no measurable rain at Central Park, a weak surface trough aided by additional forcing from a shortwave trough aloft produced scattered strong to severe thunderstorms over Pennsylvania and western New Jersey this evening, which will gradually weaken as they progress into the area. Some rain is expected through Sunday and again on Tuesday, however, but is unlikely to be enough to offset the recent dry anomaly as dry conditions and seasonable temperatures return for the second half of the week. (Image credit: PSU e-Wall)

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May 08

May 8, 2015: Subtropical Storm Ana Develops, Warm & Humid Next Week

Forecast Highlights:

vis0-laloAnother day of warm and dry conditions is expected, with temperatures peaking in the low to mid 80s for most locations. A marine air mass will spread inland over the weekend, producing areas of fog and drizzle with cooler temperatures, but with a brief increase in heat and humidity next week as a significant midlatitude cyclone over the Plains approaches, producing a major severe thunderstorm outbreak in the Plains and a major snowstorm over South Dakota, at the same time that subtropical storm Ana, the earliest-forming named storm in the Atlantic basin since 2003, likely makes landfall near the South/North Carolina border.

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May 03

Blog Notice


With the exception of significant weather events, such as severe thunderstorms or unusual heat, no updates will be posted through Friday, May 15. Updates will resume beginning on Saturday, May 16.


Apr 25

April 25, 2015: Chilly Ending To April

Forecast Highlights:

na_f0A strong upper level low continues to persist over the region, accompanied by below normal temperatures and even some snow and graupel in interior locations on Thursday, but with temperatures slowly moderating as the upper level low gradually departs. Temperatures will return into the 60s and possibly 70s again by the mid week, but another approaching trough will keep any significant warmth suppressed to the south through at least next week.

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Apr 22

April 22, 2015 Brief Update

Afternoon Update: T-Storms, Gusty Winds Possible This Afternoon

As mentioned during the previous forecast update, a significant low pressure system developed on Sunday before affecting the tri-state area on Monday, producing a swath of very heavy rainfall on Monday morning which amounted to as much as 1.20 inch of rain in just 3 hours at Caldwell, NJ. Much of this heavy rain can be attributed to strong upward vertical motion aloft, particularly due to strong frontogenesis, related to the strengthening of the temperature gradient.

Drier conditions resumed on Tuesday, but with another rain event expected to affect the tri-state area today as a line of precipitation forced by a strong vorticity maximum rotating through New York state and Pennsylvania around the cutoff upper level low. This shortwave trough has noticeably trended slower over the last two days on the model guidance, allowing for an extended duration of sunshine in the morning hours resulting in warmer temperatures than expected, having surged into the upper 60s and low 70s in the immediate NYC area.

15z RAP Skew-T valid at 1800 UTC (2 PM EDT) this afternoon, depicting a vertical profile of the atmosphere with height in vertical coordinates, temperature in the red line, dewpoint in green, and the surface-based air parcel temperature in blue. Image from College of DuPage.

15_RAP_003_40.89,-74.1_skewt_SBThe warmer temperatures are only accompanied by marginal instability, however, with Convective Available Potential Energy (CAPE) values near 250-500 J/kg and Lifted Index values near -1 degree Celsius. A look at model-derived soundings, such as the 15z RAP sounding valid at 1800 UTC this afternoon posted to the left, from the College of DuPage, further supported by current surface observations and the SPC mesoanalysis, reveals a very deep mixed layer approaching the 750 hPa pressure level, as indicated by the nearly constant decrease of temperature with height following the dry-adiabatic lapse rate at -9.8 C/km. Such a deep mixed layer would also be expected to feature dry conditions near the surface, as is currently the case with dew points only in the 30s and relative humidity values below 35-40%. CAPE is defined as the region of positive buoyancy in the atmosphere, or where the temperature of an air parcel lifted from the surface is warmer than that of the environment; this is represented in the Skew-T to the left by areas where the blue line is to the right of the red line, with high CAPE where this difference is very large. There is a swath of positive CAPE, although very narrow, suggesting relatively minimal CAPE approximately near 500 J/kg which may be sufficient for some thunder but not conducive for a widespread severe thunderstorm event.

Latest regional radar, from the National Weather Service.

northeastOnce the rain to the west arrives into the area towards 3-6 PM from west to east, the boundary layer will moisten up with temperatures decreasing and dewpoints rising. This will also allow some of the stronger winds aloft to mix down to the surface, potentially allowing for wind gusts near or above 40 mph to accompany the heavier showers. Any stronger thunderstorm that develops may be capable of producing small hail, although at this time the risk of stronger wind gusts appears to be the highlight of today’s event, with a lack of sufficient moisture and forcing to produce heavy rain amounts over 1/4 inch for most locations. As synoptic forcing decreases to the east of NYC with the shortwave trough passing to the north of the area, along with a more stable air mass to the east, any thunderstorm is likely to weaken in intensity towards Long Island and Connecticut with a lower risk of strong wind gusts and likely lower rain totals.

Apr 19

April 19, 2015: Warm Weather Transitions to Stormy Pattern

Forecast Highlights:

nam4km_ref_neus_9The last two weeks have been relatively inactive, but featured a much warmer pattern with temperatures frequently in the 60s and 70s. Yesterday marked the peak of this warm pattern, however, as cooler temperatures return on Monday with a heavy rain event, while a return of high latitude blocking will result in a powerful upper level low stalling over the region with a return to cooler than average temperatures through the remainder of next week (Image from Tropical Tidbits).

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Apr 12

Blog Statement on the Recent Lack of Updates

April 12, 2015 Blog Statement:

Over the last several months, updates to the blog have been increasingly sporadic. This is due to a multitude of factors, including an increasingly busy schedule restricting the hours I can dedicate to providing a high-quality, detailed analysis of the forecast on a daily basis, as well as work on various projects which in the long term would serve to benefit the blog with a larger quantity and improved quality of products, such as model guidance plots, which are well under way at this time. I will not be able to resume daily updates immediately, although updates will be posted as frequently as possible, especially during any major weather event; a forecast update for this evening is currently in progress. I apologize for any inconvenience resulting from the current lack of updates, as progress continues on long term projects for the blog with a focus on continuing to provide high-quality forecast analyses.


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