Long range forecasts show a huge dip in the jet stream over the East Coast during the early June period which would signal below normal temperatures ( Penn State Ewall )

While May will rank among the warmest on record due to a prevailing ridge in the jet stream over the East, the cold front sweeping through tomorrow (setting off possible severe weather) will trigger a radical reversal in the weather pattern.

Through the first part of June, a big dip in the jet stream promises to prevail over the East. For Washington, D.C., this means highs in the 70s to low 80s.

North Atlantic Oscillation: observed levels since mid-May and projected levels through first half of June (NOAA)

On his Facebook page, Weather Channel meteorologist Stu Ostro notes the NAO’s plunge may be historic:

Per WSI chief meteorologist Todd Crawford, if this model forecast verifies, this will be a record negative value for June! What it means: a persistently cool temperature pattern coming up in the Northeast.

But CWG’s Matt Rogers, who specializes in long-range prediction, says the pattern may flip again in two weeks when the NAO returns to neutral or positive territory (and cold air tends to be locked up to the north).

“There could be another round of heat around mid-June or shortly thereafter,” Rogers said.

For June overall, Rogers expects temperatures will end up close to normal. CWG’s summer outlook called for a warmer than average June - which may be in jeopardy unless temperatures rebound strongly after the initial cool stretch. CWG’s summer outlook lead author, Matt Ross, thinks a late month surge in temperatures is a good possibility.

“The cool start to June does cast some doubt on our prediction of a much warmer than normal month,” Ross said. “However, as the cool spell will last for only the 1st week or so of the month, I still believe that when all is said and done, June will finish above normal.”

Recall that last June, temperatures in early June were miserably hot in the East. In Washington, D.C., it was 90 or higher from June 7-12. On June 9, D.C. reached a scorching 102, matching the record for the date and the hottest temperature so early in the year (since 1871). This year, high temperatures may be some 15-25 degrees cooler.