THE LOADED GUN...
Over the past few weeks a strong high pressure has been pulsing in varying degrees of strength over the eastern United States. In a general sense, that's caused a resurgence of summery temperatures, humidity, and rainfall here in the central Midwest. The recent heavy rain event that dumped 1-3" of rain on my area has for the time being knocked the ridge down resulting in a 500mb jet stream flow that looks like this.
Short term this will keep much of the area quiet and comfortable through Tuesday. However, chances for t/storms will be on the increase Tuesday evening when a short wave will send a front quickly southeast. Moisture and instability will be a bit marginal but the dynamics should be sufficient for a line of scattered showers and thunderstorms, especially in Iowa. Low level shear is looking impressive in the low levels and there is a chance that a tornado threat could develop in NC Iowa and SE Minnesota. SPC has a 10% hatched outlook in that area.
They have also upgraded the overall severe weather risk to enhanced for a large portion of central Iowa and SE Minnesota. Something to keep a close eye on.
By the time the front hits the Mississippi, the lack of deep moisture and decreased heating due to nightfall will weaken the line limiting coverage and amounts from there east. Where rain falls amounts are not expected to be heavy on a widespread basis but locally heavy downpours are possible in the stronger updrafts in parts of Iowa and Minnesota. The EURO shows this for totals through Wednesday morning.
Once departed this disturbance will replenish a dry air mass until the ridge blossoms again over the east by the end of the week. It really expands Friday and looks like this on Sunday. That is a highly amplified flow that will send a summery air mass into the eastern half of the nation
These are the forecast temperature departures days 5-10. Extreme warmth with readings 10-20 above normal will dominate the eastern U.S. underneath the ridge.
Extreme cold will be found over the NW third of the nation into SW Canada. Look what that brings. Snow and lots of it! The EURO depicts this for snowfall over the next 10 days.
Here's a tighter perspective.
Get a load of these forecast lows. Montana and Wyoming are in the deep freeze the morning of October 3rd. A minimum of 9 below is shown in the mountains of NW Wyoming. Winter comes early here!
Back in the Midwest by this time the pattern has reloaded and moisture is riding the conveyor belt northward on the west flank of the ridge. Available moisture is going through the roof once again. PWAT's over 2" in NC Missouri and SE Iowa September 30th are exceptional.
In some spots these values are 280% above the standards for late September. These are the anomalies shown on the EURO for September 30th.
It's easy to see the fetch of moisture coming north as it merges from the eastern Pacific and Gulf of Mexico. Due to the strength of the ridge the overall pattern is quite stable and difficult to break. That means a late season ring of fire pattern emerges over the central Midwest. The signals are strong that more heavy rain is in the future over the 6-14 period as we sit in the battle field of the two contrasting air masses.
CPC sees that and has well above normal rain projected in both the 6-10 and 8-14 day outlooks.
The EURO shows many places with an additional 3-5" of rain over the next 10 days.
The Climate Prediction Center (CPC) in light of the evidence shows a high risk of heavy precipitation centered on Iowa in the period October 1-7th. Personally I think the chances are very strong that some part of my area and the central Midwest will have some hydrology issues in the 5-15 day period. Not good news for agriculturel with corn and beans reaching the point where drying and maturation becomes an important consideration.
If nothing else, there are no signs of the cold out west penetrating the Midwest through the first week of October. Thus frost and freezing temperatures do not appear to be an issue yet. If anything, temperatures will be going the opposite direction with CPC showing these temperature departures in the 6-10 period.