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COUNTDOWN TO SUMMER...

Thursday afternoon, a storm virtually came together over the region as cool air aloft arriving in the northern stream converged with a potent southern stream disturbance over southern Indiana. The merger literally energized the system, generating strong winds and scattered showers. Even a few thunderstorms popped up due to the cold air aloft and steep lapse rates. At 4:21 pm, lightning strikes were concentrated around I-380 and further east near the Mississippi.



Here's what the system looked like on the late afternoon satellite. Since the showers were driven by instability, the showers were random in nature, with mere sprinkles in spots and brief but heavy downpours in others. In a few locations where banding occurred, amounts greater than 1/2 inch were found. While some areas were getting rain, others were even seeing sunshine. Along with that, I had a 41 mph gust at my place in Dubuque. It was a rather manic day to say the least!


Behind the system Friday, a fairly cool air mass aloft, especially in the morning with 850 temps below zero, will drive gusty winds and cumulus cloud development. Highs will likely remain in the mid to upper 50s. Late in the day, warmer air aloft and a relaxing pressure gradient will decrease winds and clouds, leading to a quiet but chilly Friday night. Lows in the mid and upper 30s are expected.


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BIG TEMPERATURES, BIG BOOMERS?

As you can ascertain in the graphic below, the year is off to an exceptionally warm start. In the Quad Cities, in blue, are the average high and low temperatures from January 1st to April 11th. Plotted in red are the actual temperatures, outside one brief period of cold in January, highs and lows have been consistently above, to much above climatology. Throw out those two weeks of cold and snow in January, and you are left with a remarkably nice winter. Strange but true.



We are going to up the ante even more with an impressive burst of warmth that gets underway Saturday and grows Sunday-Tuesday. The EURO meteogram for the Quad Cities shows 6 consecutive days with highs in the 70s starting Saturday. It would not shock me to see a day or two (Monday orTuesday in particular) where highs near 80 are seen from the Quad Cities south.



The catalyst for the warmth is a powerful 500mb low that rolls into the central Plains Monday and Tuesday. It looks like this on the EURO ensemble Tuesday.


Aside from the warm moist air this set-up brings, there is the added element of active thunderstorms. The first opportunity arrives Monday night, especially north of I-80. Warm air advection is in high gear, and the low level jet powering into it fires convection. These storms would most likely be elevated, with hail and perhaps some wind as the primary threats. Heavy rain is certainly possible as well. The EURO shows the area of concern Monday night.



The next opportunity would be Tuesday afternoon or evening. At that time, the primary energy and surface low is expected to approach from the west. Things get more tricky here, as the position of a warm front could be a major factor in the amount of shear that exists. If winds are backed, a tornado threat is very much on the table. The issue to resolve is, where in the central Midwest will that boundary be located? Even if it's north of my area, the cold front will still have enough shear to produce at least scattered surface based storms capable of strong to severe weather when it arrives later Tuesday.


Already, SPC has issued a 15 percent risk of severe weather 6 days in advance of the event. That means at least a 30 percent chance of severe weather within 25 miles of a point in the yellow shaded area below. That's rare, which means the antennas are up for the big boys on Norman, Oklahoma.


I do stress, it's early and the critical mesoscale details are yet to be defined. However, on a broad scale basis, moisture and instability are currently looking more than adequate. The 500mb jet is approaching 90 kts., while at the 850 level, it's still roaring at 55-60 kts. Being in the left front quadrant of the jet max., there is significant diffluence which is a staple in any severe weather outbreak.

Look at this speed max that EURO shows punching into eastern Iowa at 1:00pm Tuesday.



Throw in the shear factor and the gun is loaded for strong storms (if it all comes together). It sure appears that some part of the central Midwest could be in for severe weather Tuesday. Stay tuned.


Meantime, today looks to be one of those so-so April days with brisk winds and cool temperatures. Outside of a brief shower or sprinkle in the east, it should be a dry day. Then the party begins for our weekend warm-up. Happy Friday and roll weather...TS

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