Dry Pattern About to Change

It's been nearly a week and a half since any measurable rain has fallen.   That's about to change this week and could come as early as Tuesday.

High pressure that was over the Midwest and Great Lakes over the weekend and late last week will move off the East Coast this week and remain stationary.  What this will do for our weather is keep a southerly flow from the Gulf of Mexico pointed over the Plains and Midwest, increasing our humidity and rainfall outlook this week.

While not a complete washout, there is a daily rain and storm threat in the forecast all week. 

Pinpointing the exact time and day for the higher probability of rain may be a little more difficult.  The moisture (instability) in the atmosphere will be in abundance, especially by the middle of the week.  However, the trigger to get thunderstorms to develop becomes a little less clear and will rely mostly on when upper level lows move through the jet stream.  As of Monday evening, it looks like the best timing for rain arrives Tuesday afternoon/evening (40%), Wednesday afternoon (50%) and Thursday night into Friday (50%).  The downside to this type of forecast is it makes trying to plan something for outdoors a little more complicated.

As for rainfall amounts we will have copious amounts of moisture in the atmosphere beginning Tuesday night and Wednesday with PW values (precipitable water values) over one and a half inches.  What does that mean?  Think of the atmosphere like a sponge that you've just soaked in a sink full of water.  When you wring out that sponge you try to wring out as much water as you can to get it out of the sponge.  The atmosphere works in the same way.  When storms move into an area that has high PW values, it's going to wring out as much moisture it possibly can.  This in turn can lead to heavy rainfall.

The latest weekly rainfall forecast from the Weather Prediction Center suggests close to 2" to 3" of rain could fall between now and Saturday.  That's quite a bit when you think about it.  So at least we'll be making up for the deficit, and then some, before the month is over with.

As for stronger to severe thunderstorms, the threat is there and could arise Wednesday afternoon.  A lot of that depends on whether or not we get any convection Wednesday morning.  Stay tuned!