Jul 22

**Limited Blog Updates July 22-August 2, 2014**

** BLOG NOTICE: Between July 22 and August 2, 2014, updates will be posted less frequently, at least every two days but may vary at times. Daily updates to the blog, along with the 8-day outlook, will resume on Saturday, August 2. **

 

Jul 30

July 30, 2014 Brief Update

Notice

Blog Update: Daily forecasts will resume on Saturday, August 2.

Forecast Overview:

rad_7.30gfs_7.30

Posted above from left to right are the latest available surface analysis and radar composite from the NWS Weather Prediction Center (WPC), and the initialized GFS 500 hPa heights and vorticity from NCEP MAG; both are valid at 12Z Wednesday UTC (8:00 AM Wednesday EDT). Following a strong cold front passage on Monday, which followed heavy thunderstorms on Sunday night in parts of NYC and to the west, south and east, a much cooler air mass returned into the region, with high temperatures on Tuesday only having peaked in the mid to upper 70s. As can be seen in the 500 hPa analysis above, a strong upper level low remains stationed near the southern Hudson Bay; the upper level low will slowly lift north, but with a vort lobe to its west moving through the region on Thursday. Mostly sunny skies are expected to continue today with highs in the upper 70s to low 80s, slightly increasing on Thursday into the low to mid 80s with a risk of scattered afternoon and evening thunderstorms. Similar temperatures are expected on Friday with a risk of isolated evening thunderstorms.

As the strong upper level low departs, strong ridging in the western Atlantic will expand westward closer to the region, with a relatively stationary upper level flow expected by next weekend with a weak trough stuck in the central US and the ridge struggling to expand further west into the region. This will set up for a persistent mid level southwesterly flow, advecting a plume of moisture into the region from the Gulf of Mexico coast with precipitable water values rising to near 2 inches while the stalled frontal boundary offshore retreats west closer to the coast. This is likely to result in a mostly cloudy and occasionally rainy weekend; while the exact timing of rain is uncertain, on-and-off rain is expected during parts of the weekend, which could be locally heavy at times, with high temperatures likely struggling to rise above the mid to upper 70s. A slow trend towards drier and warmer conditions is expected by early to mid next week as temperatures return into the 80s.

Jul 26

July 26, 2014 Brief Update

Forecast Overview:

rad_7.26gfs_7.26

Posted above from left to right are the latest available surface analysis and radar composite from the NWS Weather Prediction Center (WPC), and the initialized GFS 500 hPa heights and vorticity from NCEP MAG; both are valid at 06Z Saturday UTC (8:00 AM Saturday EDT). With a southwesterly flow and increasing temperatures aloft, partly sunny skies are expected with highs in the upper 70s near the coast and low to mid 80s elsewhere; an isolated evening thunderstorm cannot be ruled out north and west of NYC. A significant severe thunderstorm event is expected in the US today and tomorrow as a strong shortwave trough, shown in the 500 hPa analysis above near southern Saskatchewan (north of North Dakota), dives ESE into the Ohio Valley and Pennsylvania as it interacts with a stationary upper level low over central Quebec. This shortwave trough will lead to strong cyclonic vorticity advection over the Ohio Valley and Northeast US, which along with a left exit quadrant of a jet streak is indicative of upward vertical motion as a surface low pressure develops and deepens to nearly 998-996 hPa north of the area. The tighter height gradient south of the shortwave trough will advect a warm and humid air mass into the region, leading to a brief round of heat and humidity on Sunday and Monday along with a risk of thunderstorms.

Thunderstorms will begin late tonight as several weak shortwave troughs move through the region and the surface warm front progresses through the area; this will likely provide sufficient lift to develop and maintain thunderstorms over parts of the area around 6-10am on Sunday. With a moist air mass in place and relatively high precipitable water values, storms could produce locally heavy rainfall, along with strong wind gusts. An area of subsidence is likely behind these storms well ahead of the main shortwave trough, likely providing the area with a period of drier conditions around Sunday afternoon with some breaks in the cloud cover, allowing temperatures to rise into the upper 80s to near 90 degrees away from the coast along with dew points in the upper 60s to low 70s. As the strong shortwave trough and deepening surface low pressure move through the region on Sunday night, another round of rain and thunderstorms is likely but with continuing discrepancies regarding the timing and positioning of the heavy rain and thunderstorms; the highest probability at this time is mainly west of NYC, where storms may be strong or locally severe with heavy rainfall and strong wind gusts.

A chilly air mass will follow behind the cold front on Monday; while the rain will remain to the north, partly sunny skies and a breezy southwesterly wind are expected, warming temperatures up again into the mid to upper 80s. Chilly temperatures are expected on Monday and Tuesday nights, falling into the 50s away from the immediate NYC area and the coast, while daytime highs rise into the upper 70s to low 80s on Tuesday and Wednesday with mostly sunny skies. The upper level trough will lift north of the region, leaving the United States with a weak geopotential height gradient and an overall stagnant pattern, with the only significant changes occurring towards next weekend as the western Atlantic ridge possibly extends westward into the region. A gradual increase in temperatures and humidity is expected through late next week and next weekend, with temperatures rising into the low two mid 80s from Thursday through Saturday as humidity slightly increases.

A few updates may be posted on the blog and on Twitter on Sunday regarding the expected thunderstorm activity, otherwise the next forecast update is scheduled for Tuesday. Daily updates will resume on Saturday, August 2.

Jul 24

July 24, 2014 Brief Update

Forecast Overview:

rad_7.24gfs_7.24

Posted above from left to right are the latest available surface analysis and radar composite from the NWS Weather Prediction Center (WPC), and the initialized GFS 500 hPa heights and vorticity from NCEP MAG; both are valid at 06Z Thursday UTC (8:00 AM Thursday EDT). A cold front moved through the area last night, having previously produced heavy thunderstorms over parts of northern New Jersey, NYC and southeast NY in the evening and early overnight hours. Temperatures peaked in the upper 80s to low 90s away from the coast with humid conditions yesterday. Followed the passage of the cold front, a cooler and less humid air mass is expected through Saturday, with highs in the low to mid 80s.

More significant changes in the upper level flow will occur on Sunday and next week as a strong upper level low, separate from the polar vortex center north of Greenland, becomes stationed over southern Canada due to upper level ridging extending to its north over central-northern Canada and a persistent ridge in the western US, continuing the hot and dry pattern in the West Coast. This will lead to a persistent trough setting up near the central and eastern US, continuing this summer’s trend for a lack of heat in the northeast US relative to the last few years. A potent shortwave trough near Washington state will progress east, reaching Michigan on Sunday while aiding in the development of a surface low pressure. Additional weak shortwaves are likely to approach Pennsylvania on Sunday ahead of the main trough, leading to widespread coverage of rain and thunderstorms. The first shortwave moving through on Saturday night may result in scattered thunderstorms overnight, primarily from NYC and further north and west, with indications of a potential lull in the thunderstorm activity in the afternoon as drier air moves through in the mid levels before the main shortwave trough over Michigan enters the region, providing sufficient forcing to maintain locally heavy rain and thunderstorm activity as it moves through the area between Sunday evening and Monday morning. The possibility of scattered showers remains through at least Monday evening. The exact timing remains somewhat uncertain at this time, and some changes may be possible over the next few days.

A brief surge in warmth and humidity is expected for Sunday and Monday, with highs in the mid 80s away from the coast and dew points likely near the upper 60s, while a southerly wind again keeps coastal Long Island and Connecticut with cooler temperatures in the upper 70s to low 80s. Following the passage of the cold front on Monday, a cool air mass will slowly move through the region with 850 hPa temperatures likely near 8-10C; with the expectation for mostly sunny skies and a downsloping northwesterly flow, however, the latest outlook sides slightly warmer than the model guidance with high temperatures in the upper 70s inland and low 80s elsewhere. Overnight lows may fall into the 50s away from NYC and the immediate coast. Looking into the longer range through the first few days of August, a slow warming trend is expected as the upper level trough lifts north of the region, with increasing humidity likely as well with an overall south-SW flow.

The next full forecast discussion is scheduled to be posted on Saturday. The limited posting schedule will continue through August 2, when updates are scheduled to be resumed on a daily basis.

Jul 21

July 21, 2014: Brief Warmth, Humidity This Week

Forecast Highlights:

temp36Following a cooler than average weekend with highs generally in the mid 70s to low 80s, an increase in warmth and humidity is expected through Wednesday, with highs reaching the low 90s in parts of the area, before a cold front moves through early on Thursday with a risk of thunderstorms. A drier ending to the week is anticipated, but with a continuation of a lack of heat in the region along with a chance of rain through next week (image credit: PSU e-Wall, modeled highs on Tuesday).

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Jul 17

July 17, 2014 Brief Update

Forecast Overview:

rad_7.17gfs_7.17

Posted above from left to right are the latest available surface analysis and radar composite from the NWS Weather Prediction Center (WPC), and the initialized GFS 500 hPa heights and vorticity from NCEP MAG; both are valid at 06Z Thursday UTC (8:00 AM Thursday EDT). The cold front which continued to produce rain through yesterday morning is east of the area, slowly progressing to the east, with a broad area of high pressure to provide the region with mostly sunny skies through Saturday. Daytime highs are expected to peak in the low to mid 80s, while overnight lows are cooler than average, especially inland towards interior northwest NJ, southeast NY and Connecticut away from the coast, where clear skies and light winds should allow temperatures to fall into the mid to upper 50s, falling close to 50 degrees in localized spots.

Otherwise, the weather pattern over the next week is expected to remain relatively inactive compared with recent weeks, with a lack of strong forcing for precipitation except for a weak shortwave trough which may trigger scattered showers on Sunday, and a potential cold front late next week which may produce another round of scattered thunderstorms. Temperatures are generally expected to remain close to average in the low to mid 80s through Monday, gradually warming up next week with increased humidity as temperatures rise into the mid to upper 80s from Tuesday through the late week, possibly reaching the low 90s in spots in the warmer case scenario. Uncertainty increases towards late next week depending on the setup of a strong ridge over the western US with 500hPa heights rising over 600 decameters, with solutions ranging from a persistent trough on the GFS to the western Atlantic ridging expanding westward through the region on the CMC.

Jul 16

July 16, 2014: Drier, Less Humid End To Week

Forecast Highlights:

gfs_7.16A slow moving cold front which produced heavy thunderstorms and localized flash flooding yesterday is currently moving through New York City, with drier and sunnier conditions returning from this afternoon through the rest of the week along with lower humidity. Temperatures are likely to remain in the low to mid 80s through next Monday before a slow warming trend begins.

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Jul 15

July 15, 2014 Brief Update

Today’s Outlook: More Thunderstorms Today

rad_7.15gfs_7.15

Posted above from left to right are the latest available surface analysis and radar composite from the NWS Weather Prediction Center (WPC), and the initialized GFS 500 hPa heights and vorticity from NCEP MAG; both are valid at 06Z Tuesday UTC (8:00 AM Tuesday EDT). With a pre-frontal trough near the area yesterday, along with several weak shortwaves moving through the region, scattered heavy thunderstorms affected parts of the area in the afternoon and evening. The severe thunderstorms set up south of the area, however, with some wind damage towards southern New Jersey and Maryland, along with a nearly stationary cell producing over 5 inches of rain in east central NJ, although the thunderstorms that extended into the area in the evening produced heavy rainfall, locally up to 1-2 inches in parts of Long Island, southwest CT, and northern New Jersey. Since then, the thunderstorm activity from last night dissipated, although the cold front associated with a developing low pressure near Michigan is gradually progressing east towards the region.

As with yesterday, widespread cloud cover is expected to limit instability with CAPE of at least 1500 J/kg, although the region will be placed near the right entrance quadrant of an upper level jet streak, while an approaching 500 hPa jet streak will lead to 0-6km shear increasing to at least 40-45 knots in the western half of the area. The greatest overlap between instability and shear is expected to the south of the area, towards southeast PA into Maryland, where the highest probability of severe thunderstorms exists, although discrete thunderstorm cells may develop in the immediate NYC area and northern New Jersey towards 2-4pm this afternoon, some which may become strong or locally severe with strong wind gusts and downpours producing localized flash flooding. A more organized line of thunderstorms is likely to approach the area towards 5-7pm this evening, but with the main risk primarily from heavy rainfall and flash flooding, along with locally strong wind gusts with the stronger thunderstorms.

More information on the longer range outlook will be included with Wednesday morning’s update.

Jul 14

July 14, 2014: Heavy Rain, Storms Today & Tuesday

Forecast Highlights:

rad11A warm and humid air mass remains in place over the region, with both today and tomorrow featuring heavy thunderstorms, potentially severe, capable of producing flash flooding and strong wind gusts. A cold front will slowly clear the area later this week with dry and sunny conditions returning for Thursday and Friday, but with a trough persisting over the region keeping temperatures near or slightly below average by next weekend into next week along with a risk of rain (image credit: PSU e-Wall, HRRR simulated reflectivity this evening).

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Jul 13

July 13, 2014: Warm, Stormy Start To Week

Forecast Highlights:

t0The recent stretch of seasonable and dry weekends will end for parts of the area on Sunday, as a shortwave trough approaches on Sunday, producing scattered afternoon and evening thunderstorms, while temperatures increase into the mid 80s to low 90s with rising humidity through Tuesday. A slow-moving cold front will produce additional rainfall from Monday through Wednesday, with the potential for strong storms and heavy rainfall, followed by a slight cool down at the end of the week.

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