John Homenuk

Widespread severe weather possible on Thursday

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The Storm Prediction Center has placed the area in a rare “Moderate Risk” on the Day 2 Outlook, valid for Thursday July 26 2012, mentioning the

Storm Prediction Center Day 2 Outlook for Thursday July 26, 2012. Categorical (left) and probabilities of severe weather within 25 miles of any point (right).

potential for widespread and significant damaging winds with strong and severe thunderstorms. The Moderate Risk line runs through North-Central New Jersey from southwest to northeast, including the NYC Metro Area. Points to the south of this line are included in a “Slight Risk” (more typical for our area), with the risk of severe thunderstorms dropping off somewhat as one heads into Central and Southern New Jersey. However, to the north over Northern New Jersey, Southeast New York (including NYC Metro) and Connecticut, the potential exists for a more significant severe weather episode, characterized by the potential for strong and damaging wind gusts as well as isolated tornadoes. The Storm Prediction Center also mentions the potential for a “Derecho”, which produces damaging winds in excess of 60 miles per hour over a large area The next few paragraphs will dive into some more advanced meteorology, so if you’re not looking to hear the down and dirty details, just skip below.

The potential for such a widespread severe weather episode in the Northeast  is being driven by an approaching cold front over the Ohio Valley, but the exact processes behind the severe thunderstorms remain incredibly complex. To start, forecast models agree on a decaying MCS (system of thunderstorms) moving east across New England along a warm frontal boundary early Thursday morning. The models are struggling with the exact track of this feature, and where it ends up will ultimately iron out a ton of details in regards to the second round of storms Thursday PM. Several models keep the morning activity to the north, while a few also bring it into our area. Wherever it tracks, the potential exists for some isolated severe weather reports (mainly some hail in elevated convection). Regardless, a plume of extremely impressive kinematics will be involved…with forecast models indicative of effective shear over 40 knots by Thursday afternoon. A surface low developing near Albany will also bring enhanced low level shear along a gradient near NYC.

NAM Model’s forecast for Thursday PM, showing the thunderstorm event. 500mb heights/vorticity (left), mean sea level pressure (center), and 3 hour precipitation (right).

By afternoon, forcing along the mid level height gradient will develop storms over North-Central PA and Central New York, that will begin to slide eastward. Well back to our west, activity will also fire along the cold front. But along the gradient, which runs from North-Central PA to near NYC and Northern NJ, is the best juxtaposition of instability and shear parameters. Here, the potential exists for a developing thunderstorm complex which could eventually mature into a Derecho .. and produce strong damaging winds over a large area. Where this gradient sets up will be critical to storm development.

One potential caveat to this severe weather potential will be, as mentioned above, the exact positioning of the gradient and baroclinic zone. Forecast models have been ticking this farther north during the day today — which could eventually place the best gradient for the MCS just to the north of the NYC area. If this is the case, the widespread damaging winds could develop and track from Northern PA through Southeast New York and possibly into Western New England.

In summary, the potential for a high-end severe weather event is definitely there. The Day 2 Moderate Risk from the Storm Prediction Center certainly reflects that potential. However, the threat is not very clear cut at all. In fact, forecast uncertainty is extremely high at this point, with the event expected to transpire beginning with the activity moving through New England late Wednesday Night into Early Thursday morning. So, we urge you to stay tuned both tonight and into Thursday. We’ll be activating our Live updates page, and will continue to update via Facebook and Twitter. We’ll also have a new blog post out around 2am with details on the new Day 1 Outlook from the Storm Prediction Center.

 

John Homenuk

Storms roll through, airmass remains warm

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Showers and thunderstorms rumbled through the area from Monday afternoon and were continuing to impact isolated areas on Monday evening, but the airmass behind them won’t be much cooler than the one

User submitted photo of a rainbow behind a thunderstorm in Northeast New Jersey on July 23rd, 2012.

which preceded them earlier on Monday afternoon. In fact, the airmass is expected to get warmer with time this week. Temperatures in the low to mid 90’s are expected on Tuesday, with upper 80’s to low 90’s again expected on Wednesday. The warmer air will come with more humidity, so a generally uncomfortable mid-week is on the way. By the end of the week, more storms (possibly strong and severe once again) are expected on Thursday and Friday, with a warm and cold front interacting near the area. First, organized storms are possible Thursday near a warm front and surface low. Finally, with a cold front ready to sweep through the area on Friday, more organized storms will remain a possibility. The Storm Prediction Center mentions in the Days 4-8 outlook that a “considerable amount of convection” is possible from the Great Lakes into the Northeast towards the end of this week. We’ll certainly be keeping an eye on it, so stay tuned!

Mondays storms offered severe weather mainly over New Jersey, with the shear direction and marine layer keeping New York City and coastal areas safe. 1.25″ diameter hail was reported in parts of New Jersey with a complex of storms that  moved through Monday afternoon. Stay tuned for further updates on the severe weather threat which may develop later this week!

John Homenuk

Surge of big heat will kick off Summer 2012

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The seasons first burst near-dangerous level heat is likely to arrive rapidly by Wednesday afternoon throughout the forecast area. A ridge in the mid and upper levels of the atmosphere is expected to rapidly build beginning Tuesday, beginning the advection of the warmest air the area has seen so far this season.  Tuesday will likely end up near average with high temperatures ending up in the mid 80’s, ending a streak of normal to slightly-below normal temperatures which began almost a week ago. By Wednesday, the playing field will be completely change as the pattern will re-adjust setting the stage for big heat. High temperatures on Wednesday are expected to rise into the mid to upper 90’s throughout most of the area, with the potential for a few near-100 degree readings in New Jersey. With low temperatures in the upper 70’s to near 80 Wednesday Night into Thursday, temperatures will be off to a fast start once again. Highs on Thursday could reach the upper 90’s to near 100 in more than a few locations. Although it will, of course, be cooler near the shore…a big sea-breeze is not expected. West winds off the hot and dry land to our west will end the threat for the ocean-influence away from Eastern Long Island.

The National Weather Service has issued Excessive Heat Warnings for parts of New Jersey (likely to include NYC by Tuesday evening). The aforementioned heat, coupled with dew points in the 60’s will lead to Heat Index values over 100 in many spots during hte afternoon hours on both Wednesday and Thursday, which are near-dangerous levels. Remember, strenuous outdoor activities or prolonged exposure to the sun without hydration in such temperatures can lead to heat-stroke. Plan ahead and plan carefully — but most all, if you can, enjoy the beautiful summer weather which is on the way. Summer officially begins this Wednesday June 20th, 2012 during the summer solstice, which occurs at 7:09pm.

John Homenuk

Warm up, then heat wave loom this week

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Forecast models are beginning to come into better agreement on what looks to be a gradual warmup towards above average temperatures to start the new work week, followed by several days of heat with temperatures over 90 degrees in many locations. A large ridge in the mid levels of the atmosphere and high pressure at the surface is to blame, as a south-westerly flow in the atmosphere will advect in some of the warmest air of this years warm season to date. The humidity will be on the rise as well, with models pinning upper 60’s F dew points combined with 90+ F temperatures beginning Wednesday and likely continuing on Thursday and Friday. It remains to be seen exactly how long the heat will last (a typical heat wave around our area lasts around 3 days), before thunderstorms become a threat with any trough or cold front that approaches the heated/unstable atmosphere Regardless, the weather looks to take a summery turn this week. Early-forecast high temperatures for the middle and end of the week (Wednesday) are in the mid 90’s with some warmer readings likely inland and a few cooler readings near the shore.

If you’re looking to head to the beach this week, we’ll have a full forecast out Monday morning. There may be a seabreeze in some locations along the shore during the heat wave – but early indications are that the seabreeze may be strongest on Friday. We’ll keep you posted on the best beach days as the heat draws closer.