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TO RAIN OR NOT TO RAIN...

It's been nothing but blue skies around the Midwest the majority of this week. The only rain was confined to a short window Tuesday evening and at least half of the area missed out on that. For some the quiet weather conditions have been too much of a good thing. Abnormally dry soil conditions have expanded over much of my western and northern counties. Here's the latest drought index. Around the Midwest dry soils increased from 9.44% last week to 24.77% this week.

In the graphic below you can see that with the year nearly half gone, Iowa City's yearly precipitation is approximating 1955 which is the driest year there since 1893. That year only 22.06 inches of precipitation was recorded. A far cry from 1993 when 62.89 inches fell.

Dubuque is in a similar situation rivaling its driest year 1894 when only 19.35 inches fell.

Here's the yearly departures so far thanks to the Iowa Mesonet. Most of my western and northern counties are running 3.5 to 5.5 inches below normal.

Where I live, the yearly deficit is over 5 inches and the grass is burnt, brown, and crunchy. A good soaker is really needed as we head into what is typically the hottest time of the year. Hopefully, some will find its way to those in a similar situation this weekend. Here's the break down of prospects.


FRIDAY

A couple days ago this period held promise but recent trends have shown the rain with this initial disturbance remaining well to the southwest of the region. Thus, Friday will be another dry day.


FRIDAY NIGHT/SATURDAY MORNING

Another wave of energy will ride a ridge and form a convective complex in Nebraska Friday evening. That is shown spreading east into western Iowa as the low level jet intensifies after dark. With time it should reach eastern Iowa by daybreak and then cross the river into Illinois early Saturday. While some rain is likely, the concern is that the complex will be in a decaying state with instability and the low level jet weakening late night and early morning. How that evolves will determine how much (if any) rain accumulates. Eastern Iowa has better chances of seeing storms as dynamics are likely to be stronger there than further east as the weakening process unfolds. SPC does indicate a marginal level 1 risk of severe storms Friday night in my counties west of the Mississippi.

SATURDAY AFTERNOON AND EVENING

This period remains low confidence for rain and storms due to it's reliance on what happens with Saturday morning's convective complex. If clouds and precipitation lingers into early afternoon, that limits heating and restricts the growth of instability necessary for new storm development. That scenario exists late Saturday or Saturday evening ahead of a cold front entering from the northwest. The mesoscale details discussed are unknown and will remain that way until they show their hand Saturday. Thus the low confidence in whether or not storms form and if they do, in what location.


Assuming atmospheric recovery takes place Saturday afternoon, CAPE reaches sufficient levels for moderate to strong instability. The 3k NAM (a convective allowing model) is very bullish with CAPE of 3-4,000 j/kg.

Here's what the 12K depicts.

The GFS

The EURO

With the aid of such instability, the 3K NAM shows storms firing by 5:00pm Saturday. The focus being over the SE half to two/thirds of my area. The speed of the cold front will dictate how the process transpires. Two hours slower and areas further NW are involved. Two hours faster and only the SE gets in on the action.

The supercell composite on the 3k is significant indicating sufficient shear for surface based updrafts that would likely support strong winds and heavy downpours were storms to develop. At least for the time being, (probably due to the uncertainty of morning convection on potential instability), the Storm Prediction Center shows only a marginal level 1 risk of severe weather. At some point that could be elevated to a slight risk in parts of my area.

In terms of rainfall, here's what various models are projecting for totals. Consistency is lacking and far lower than I would like to see in my area, most of what you see comes in the period late Friday night through Saturday evening. The screaming message is the potential is there for some needed beneficial rains but if and where they occur is far from certain. I have concerns that poor timing will cause the first batch of rain Friday night to fall west of the region while the second batch later Saturday just catches my southeastern counties. We'll see how our luck is running Sunday morning when this is all said and done. Here's those rain projections.


The EURO

The GFS