June 18, 2012: 100 Degrees Possible This Week

Forecast Highlights:

– Very Hot Wednesday/Thursday; 95-100 Degrees Expected
– Heat Index up to 105 Degrees Possible
– Chilly Pattern to Return Afterwards
– First cooler than average month in over a year possible


Today’s Observations:

Another mostly cloudy day was observed today with an area of dissipating showers and thunderstorms approaching from the west. Temperatures were similar to those of yesterday, peaking in the upper 60s to low 70s in Long Island/S CT and the lower to mid 70s from NYC and further north/west, which was slightly cooler than expected. A brief yet strong surge of heat will move through the region on Wednesday and Thursday, with temperatures approaching 100 degrees in the immediate NYC area, although the heat will quickly move out, with a chilly pattern returning by next weekend.

Tomorrow’s Outlook:

The last of the chilly days prior to a brief interruption in the colder than average pattern will take place tomorrow, with partly cloudy skies expected and temperatures reaching the mid to upper 70s in Long Island/S CT and the lower to mid 80s from NYC and further north/west. South/SSW winds are expected.

Wednesday – Friday: Hot, Humid; 100 Degrees Possible

The surge of heat currently in the central US will move into the region, resulting in the hottest temperatures of the year until this point. Depending on the pattern for the rest of the summer, it is also possible that this may be the hottest heat surge of the entire year. 850mb temperatures up to 20-22C are expected to move east from the Great Lakes into the Northeast region, with the warmest air mass overhead during Wednesday and Thursday. Both days are expected to bring west winds with mostly sunny skies and dew points close to 70 degrees, which all support the heat and humidity expected for these two days.

Wednesday will start out with temperatures in the 70s in the morning hours, quickly surging into the lower to mid 90s in most of Long Island/S CT and the mid to upper 90s from NYC and further north/west, possibly reaching 100 degrees in some areas just west of NYC. The hottest temperatures are expected in the immediate NYC area. With dew points close to 70 degrees, the heat index is expected to reach the 100-105 degree range across most of the immediate NYC area while getting close to 100 degrees further inland. Temperatures will be slow to decline, and are still likely to be near 90 degrees at 8 PM.

Thursday will be the hottest day, ending up slightly hotter than Wednesday. After mild overnight lows, with temperatures barely dropping below 80 degrees in NYC, temperatures will be quick to rise, already reaching the mid 90s in the immediate NYC area by noon. Temperatures are expected to reach the lower to mid 90s across most of Long Island/S CT, slightly cooler near the coast and hotter closer to NYC, with upper 90s in the immediate NYC area excluding coastal areas and mid to upper 90s further inland. Temperatures may reach 100 degrees again in parts of the immediate NYC area, with the heat index ending up in the 100-105 degree range, possibly a bit higher in some areas. The 18z NAM model posted to the left from the Pennsylvania State University E-Wall (direct link to 18z NAM) shows a set up supportive of temperatures getting close to 100 degrees, with west winds and 850mb temperatures near 20C; the frame posted above for Thursday afternoon shows a small area of 100 degrees in NE NJ.

As with Wednesday, temperatures will be slow to drop in the evening, with 90s still likely in the immediate NYC area by 8 PM. Later overnight, however, a cold front will move through the region, bringing a cooler air mass further southeast, although little shower/thunderstorm activity is expected with this cold front. Overnight lows are expected to end up in the low to mid 70s for most of the area, with temperatures on Friday reaching the mid to upper 80s for most places, possibly getting into the lower 90s in the immediate NYC area.

Longer Range: Cooler Pattern Returns

**First colder than average month since early 2011 possible**

The most recent winter season was accompanied by persistently above average temperatures, well above average in some cases, peaking in March when a record surge of warmth affected a large part of the United States. Since the winter, however, the pattern has flipped, and blocking is gradually becoming more frequent over the northern latitudes, especially near Greenland; during the December-February time frame, there was almost no ridging to be found anywhere near Greenland, yet over the last month positive 500mb height anomalies have been observed along with a strong 576 dm block that remained stationary over Greenland earlier in the month. Blocking patterns in favorable locations, especially over Greenland, tend to result in cold/snowy patterns during the winter while suppressing the heat in some cases during the summer. With the blocking pattern observed this month, along with frequent rain and cloud cover and the lack of sustained ridging as most of the heat was forced to the west and north, staying in the central US and Canada, the entire East Coast is at least slightly cooler than average, with Central Park averaging out 0.5 degree below normal in the June 1-18 time period.

A surge of strong heat is expected for 2-3 days with temperatures as much as 15-20 degrees above average, although with ridging again expected to build into Greenland and Canada, the surge of heat is only an interruption in the pattern as opposed to a pattern change, with the pattern through early July and likely beyond expected to feature more troughs than ridges. There does not appear to be much strong cold air around, meaning that most days for the last 9 days of June will likely end up with temperatures generally close to average, possibly a bit above/below at times, but especially during rainy and cloudy days, as possible with next Monday, larger negative departures are possible. With the heat balancing out the cool days observed so far, June will end up close to average, ending up either slightly warmer or cooler than average, both of which are reasonably possible. Should June end up on the cooler side, it would make this month the first time since early 2011 that a colder than average month has been observed in New Jersey. Stay tuned for more information on the longer range.

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