1300 EDT 23 JUNE 2012
back the middle of June …I talked about the shift of a pattern in the second and third weeks where the heat dome would be forced to back into the Rockies and Midwest would see an interval of seasonal temperatures over the Midwest. That process is underway right now and will continue for good portion of next week as well.
SUMMARY … However I am still concerned that the pattern is going to enter an interval in the middle of July– specifically after July 5th– that will bring wetter than normal conditions for the Midwest at a very important time for the US corn crop. Exactly “HOW WET? “ this interval will be and “HOW LONG?” it will last I am not certain of but it seems to me at least a week or 10 days seems a good probability. That being said keep in mind that the Midwest area is under a growing and persistent drought so if this ‘wet” interval features conditions that are wetter than it has been….that does not necessarily mean is going to be wether than normal.
Historically the month of July when the MJO moves into quadrant or phase 3 …produces Above and Much Above Normal rainfall over the Midwest . Increasingly more and more of the various MJO Models show the current MJO impulse moving into phase 3 after July 5. It is on that basis that I am forecasting a wetter pattern developing for the Midwest during the middle of July.
This map is from the GFS DAY 10 ensemble mean and it clearly shows the persistent West coast trough… and the East coast trough and the large Heat Dome/ ridge covering the SW states into the Lower Plains and the southeast states. We can also see the high latitude blocking over Greenland and eastern Canada. If that Blocking feature was not there… the Heat would surge be back into position… covering the Midwest and East coast .
By DAY 15… the Heat dome / Ridge is just as pronounced but it is FURTHER SOUTH… than what we have seen over the past 60-90 days. The ridge / dome covers all of the SW states and the Lower Plains into the Delta. Again the powerful Blocking over Northeast Canada — the negative NAO – keeps the dome / ridge SOUTH . When the Dome / Ridge is shaped like this and in this geographical position the pattern supports “ ring of Fire “ Thunderstorms over the Upper Plains into the Upper Mississippi river valley / northern WCB.
of course this is from the GFS ensemble mean which while good… is not that reliable. This next image shows the latest computer forecasted models for the current MJO impulse which has intensified rapidly since JUNE 4. What is important to note here is that all the model data moves the MJO from its current position in quadrant 1 … steadily through quadrant 2 and then quadrant 3 by July 7-10.
This next image is from the CPC– climate prediction center. It shows what the JULY MJO rainfall patterns look like when the MJO moves through the various eight different quadrants. If you take a look at quadrant 3 which is where the MJO is going to AFTER JULY 5-7.. you will see that the Midwest is covered with the DARK GREEN (Above Normal rainfall). And in quadrant 4 portions of the Midwest are still wetter than Normal.