At the very beginning of June, New England experienced a few days of intense, well above average heat. Temperatures soared 10-15 degrees above average on June 1st and 2nd for most of the region. Then came June 3rd. A very strong cold front dropped through New England, knocking temperatures way down and bringing a chilly rain. Temperatures dropped over 30 degrees in places from the afternoon of June 2nd to 3rd.
Boston dropped 26 degrees. High temperatures on June 3rd and 4th were stuck in the 50s. The city went from 15 degrees above average to 20 degrees below average in one fatal swoop. Since then, the weather has generally been cool, cloudy and unsettled across most of New England. Boston has seen 15 days below average from June 1st-23rd versus just 4 days above average (and 4 average days) as of June 23rd. The city did not break out of the 60s from June 17th-June 22nd.
Being on the coast, Boston's June weather is often influenced by a sea breeze, keeping things cooler, but further inland has not done too much better. Manchester, NH has seen 14 below average days with only 4 above average. Burlington, VT has done slightly better, with 10 below average days and 8 above average days. Mt. Washington has seen the snowiest June on record.
This has been the case for about three weeks now, and the pattern is not showing signs of changing quite yet. New England is starting to warm up in the last week of the month, but the active, unsettled weather is once again picking up after a brief break. This mostly stagnant weather has been the case across the entire county, although different parts of the country have been stuck with different weather.
This blocked up pattern is thanks to an extremely persistent "Omega Block". This type of block causes a large ridge in the middle of the country with troughs in the east and west. Blocking patterns block (hence the name) low and high pressure systems from moving quickly. In the east, a parade of cut off low pressure systems (which is a low that has separated or cut off from the main flow) has brought generally cool, wet weather. These low pressure systems become cut off thanks to the blocked up pattern.
Even further south along the east coast has seen some cooler weather. Charlotte, North Carolina has seen 13 below average days as opposed to 2 above average days so far this June (with the rest being around average).
Areas on the west side of the ridge have been ever cooler. Denver has seen 19 below average days with just one above average day. Blizzard conditions occurred in mid-June on Pikes Peak. Snowfall at Beaver Creek Ski Resort derailed the opening weekend of summer operations. Of course, snow in Colorado's Rocky Mountains in June isn't overly unusual.
In the middle of the country, where a massive ridge has resided for most of the month, has seen the opposite conditions. Minneapolis, Minnesota has seen 17 above average days with 2 below average days. A shift in the pattern is looking to bring Minneapolis a break from the constant heat this upcoming week. Even in a very persisent block, shifts can still happen, bringing temporary change. A shift in the pattern this past week allowed northern New England to warm up to the mid to upper 80s, but the overall pattern remains in place.
On the south side of the ridge, a heat dome that was sitting in Mexico has shifted north. The heat dome (which is a ridge of high pressure that traps heat around it) is now sitting in Texas. This blocking pattern is keeping this heat dome stuck right where it is (just like how the pattern forces low pressure systems to get stuck over the east coast).
Heat alerts have been in effect in south Texas for over a week now. This heat is not going anywhere for at least another week or so. High temperatures in the upper 90s to low 100s combined with dew points close to 80 in eastern Texas and Louisiana has led to heat index values in the 110s, and in some places closer to 115-120. This heat will continue and actually re-intensify in places heading into the final week in June.
There are some signals that show the high pressure sliding further to the east by early July, so the heat dome would be focused more over the southeast, but the general pattern really isn't showing strong signs of ending.
What really needs to happen to get this pattern broken is for a large trough to dig into the west. This would force the ridge in the middle of the country to move eastward. This would help the east get into prolonged summer weather while giving the middle of the country a break from the sweltering heat.
A good indication of whether the west will be in a ridge or trough is looking at the Pacific/North American (PNA) Index. Here at New England Storm Center, we look at North American Oscillation (NAO) Index to determine troughing or ridging in the east. The same can be done with the PNA Index for the west. Here's a look at the forecast:
You can see the PNA stays in a positive phase through at least early July, but does slide toward "neutral" conditions. A positive phase supports more ridging in the west while a negative phase supports troughing.
There's no doubt America's weather has been generally stuck in an unseasonable blocking pattern. These patterns are much more typical of spring time, but it's officially summer now. When this anomalous block breaks down (and what causes the breakdown) is still very much up in the air.