Tuesday Severe Weather Chances

Good morning.

Woke up this morning to a low of only 70F with dewpoints as high as 70F in central New Jersey. Moisture content is a lot higher than anticipated, providing some energy to storms moving into the area later. Overcast skies may make it difficult for surface heating and CAPE to build but I’m careful to not underestimate the power of advection of moist and unstable air from our south and west. HRRR simulated radar for 7 PM this evening highlights the threat that needs to be closely monitored.

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Current surface map shows the moisture ridge axis is just to our southwest. This ridge will move northeast slowly, putting eastern Pennsylvania in the optimal location for moisture. High RH near the surface support funnel clouds given sufficient shear. NAM modeled dewpoints are below:

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However, the HRRR is taking into account the cloud shield not allowing for surface heating for significantly high CAPE. This displaces the region most favorable for strong, rotating updrafts to south New Jersey.

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The more south you go, the more favorable CAPE will be and the farther north you go the higher the bulk shear will be. The middle ground will be the most dangerous place for severe storms, which is where New Jersey finds itself. As a result, the sounding for central New Jersey tonight is concerning.

Bulk shear is lacking but directional shear is present, and with the development of a lower level jet being stronger than forecasted, SRH could increase especially in a right moving supercell. Obviously though, shear is the limiting factor for this event and high CAPE is not a certainty either. Note that the NAM is having convective feedback issues, so I am mostly using the NAM for environmental parameters and not precipitation.

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The NAM hi-res radar:

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Rain moving in this evening

Current radar shows rain is about to move into the area:

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It took on a more backbuilding form which led to far more rainfall than was expected. The slow moving rain was due to a slow moving stalled frontal boundary. Rutgers Gardens recorded 0.39 inches of rain and northern areas recorded far more, which is good for the moderate drought conditions.

Monday June 27th Update

Good morning,

A series of shortwaves will begin to move through the area starting tonight as a trough and upper level low moves south from eastern Canada.  This sets the stage for the beginning of a week of unsettled weather due to upper level forcing. On Tuesday we will see moisture surging northward ahead of a cold front bringing in a potent vort max, leading to a marginal risk for severe storms.

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A weak vort max is causing a line of storms to fire up in central Pennsylvania as we speak, which should hold together as it moves eastward into New Jersey. HRRR is flip flopping from model to model on whether or not it actually does hold together. Surface heating ahead of this line meets less than favorable dewpoints in New Jersey.High will be around 86-87F with SW winds. The timing of this rain entering New Jersey would be between 4 PM and 5 PM.anim_nerc.gif

Tonight we will see warm conditions with lows in the high 60s to even still in the low 70s. Following the line of rain we will see a surge of moisture from the south for tomorrow morning and afternoon. Highs tomorrow will be cooler than normal with cloud cover and overcast skies for most of the day. An area of low pressure will form off the south Jersey coast, bringing heavy rain to southern New Jersey for Tuesday morning and afternoon. CAPE will be lacking, limiting the chance for severe weather conditions.

Very heavy rain can be expected tomorrow  throughout much of the state. Western parts of the area will see a chance for some severe thunderstorms firing up along the main cold front to the west of the rain associated with the coastal low. Tuesday night looks like a mess around the area and the models are very messy with dealing with the combination of heavy coastal rains and instability moving in from the west.

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Tuesday night the coastal low moves offshore bringing easterly winds over much of the state on Wednesday, but as the low pressure lifts the chance of rainfall can’t be ruled out with shortwave after shortwave moving in.

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Weekend Forecast

Our weekend will be characterized by a ridge building in the east– ushering in warm and dry conditions. Mostly sunny skies, low dew points, and moderate drought conditions will cause for high temperatures to run higher than forecasted on Saturday and Sunday, despite offshore flow on Saturday.

Modeled average high for Saturday: 83
Winds: East / Northeast
My forecast high for Saturday: 86
Verification: 85F

Modeled average high for Sunday: 84
Winds: east in the morning shifting to south.
My forecast high for Sunday: 89
Verification: 88F

Overall, a very boring forecast as most of the excitement will be west of the ridge that builds in. The bulk of the energy in the atmosphere is out west as seen in this map of 500 mb heights and vorticity.

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A cold front associated with the trough will move in early morning Tuesday and will hopefully bring much needed rain to the region with low chances of severe weather. According to the GFS the bulk of the energy associated with this trough moves in later on Wednesday morning.

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Instability will be very limited ahead of this mid level forcing so no severe weather expected. Windy conditions are expected mid-week as dryer, cooler air (lows in the mid 50s and highs in the upper 70s) moves in. After that, our next chance of rain will be Friday/Saturday.

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The Systematic Destruction of the LLJ

Unfortunately today did not plan out at all like any of the operational models were suggesting. The weak end derecho did form across the Ohio Valley but the low pressure associated with it stalled out over Indiana and did not rapidly strengthen as was suggested. The current surface map shows the weakened low pressure at its current position:

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Precipitation is forming along the stationary and warm front in our area which will bring us a little bit of rain tonight, as opposed to the flash flooding possibilities I discussed earlier in the week.

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CAPE is increasing wildly across the regions to our south and shear is very favorable even despite the LLJ not being as strong as previously forecasted. In our area CAPE is lower but there is enough upper level forcing (500 mb vort max just to our west) in order to support scattered rainfall throughout the evening although nothing severe.

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Dewpoints will remain in the mid to lower 60s so nothing too unstable so rainfall will not be accompanied by hail or lightning.

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Thursday Forecast

Good morning,

Recent model runs have moved the track of the low pressure system to the south and have also weakened it significantly. A blockbuster day for severe storms is unlikely over New Jersey. The more likely scenario is QPF of up to 1 inch with an increased chance for flash flooding throughout the state. For Thursday at 12Z, the surface analysis should look a little like this, with a weak low pressure system crossing the southern half of New Jersey.

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Looking at dew points, we see the southern quarter of the state with surging instability near the triple point as the low pressure moves eastward.

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The limiting factor will be instability as rainfall will occur starting in the morning, keeping CAPE down. Shear will not be a limiting factor as effective SRH will be greater than 300 in many parts of southern New Jersey. However, with every subsequent NAM run, the LLJ weakens significantly. A flooding threat remains over most of the state but the wind damage that was expected to be widespread will be more limited than expected. The main concern with this event is a lot of rainfall over the course of the day.

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Changes to Today’s Chances

As the front makes its way further south it’s pulling dry air down with it, inhibiting central New Jersey’s chances for severe storms. Subsequent model runs of simulated radar have the northern extent of the squall line further and further south. The MLCAPE tells the whole story this afternoon. The resurgence of moisture north is still expected later tonight but not in time for the passage of the squall line out of Pennsylvania.mlcp_sf.gif

Storms have already flared up in south central Pennsylvania along the front which is beginning to stall out, tapping into a ton of moisture.anim_nerc.gif

The SPC introduced a mesoscale discussion for the area that they have recently upgraded to an enhanced risk of severe storms as MLCAPE exceeds 3000 J/kg and bulk shear exceeds 45 kts. Straight line hodographs favor bowing segments but also splitting supercells in the Delmarva area.

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Mid level lapse rates are not so impressive so hail is not the primary threat. Mostly strong winds and isolated tornadoes are the threat moving forward this afternoon. The SPC tornado risk tops out at 5%.

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