May 30th: Alberto exits, but heat dominates long range

May 2018 Temperature Discussion

May 2018 will likely go down as the warmest May on record for the Continental U.S. and possibly the warmest for southern Illinois. Through May 28th, the Continental U.S. was running 4.09º warmer than normal, which is really a crazy number in terms of averages. It absolutely blows previous records away (of course, there's still three days to add to the month).

2018 May Temperature Anomaly through May 28th

Since 1981, May 2012 is the only year comparable with a temperature anomaly of +2.88º in the Continental U.S.

2012 May Temperature Anomaly

May 2018 Rainfall Discussion

Tropical systems are always a wildcard in the Summer and can sometime tilt the scales to offset drier years. As Alberto moves out, I have a feeling folks in the drier areas of southern Illinois are a little disappointed in the rain they received. A pattern more common in mid to late Summer has dominated the middle of the country through the month of May which has led to big rainfall discrepancies across southern Illinois. Spotty pop-up storms have been the main rain makers in what is historically the second wettest month of the year. Areas that have been hits with the storms are doing quite well with rain, while others are starting to hurt a bit.

Last 60 Days of Rainfall Through May 28th

Rainfall through 8:30AM May 30th from Alberto

LONG RANGE OUTLOOK

With the exit of Alberto, a fast moving "zonal flow" will set up over central U.S. around a large dome of high pressure camped over South Texas and northern Mexico. The northern edge of this dome is going to be active with fast moving storm systems likely resulting in a lot of chances for storms. The concern lies with signs the big ridge in South Texas building into the middle part of the country toward the second and third weeks of June. The key will be how far east the ridge stretches, but this could solidify the heat turning up and the rain turning off. Two potential examples are listed below:

Option 1: Ridge centered over the Central U.S. would spell extreme heat along with potential dry

Option 2: Ridge shifts westward spilling some heat east, but also keeping pattern ripe for storms

This pattern is definitely something that requires some monitoring. Hot and dry was our forecast heading into Summer 2018. Spots that have missed a lot of scattered storms last few weeks could see some serious trouble come late June into July IF that ridge takes hold.

May 24th: Scattered Storms Return, Watching Tropics for Local Impacts

Here at the station, we recorded rain every day between May 15th-21st accounting for about two-thirds of the rain for the month thus far. The pattern through May has been very summer-like with storms that are spotty combined with a lot of warmth this early in the season, a big change from the record cold April.

The first 23 days of May are in the top 3 warmest starts to the month on record

Just across southern Illinois, the difference in rainfall over the last 30 days ranges from 5"+ from Jackson, Union, and Johnson counties, to less than 1" in Wayne County. Rainfall this time of year can be a key for gardeners and farmers, especially later in the summer when the hot and dry kicks on.

Estimated rainfall between April 23rd and May 23rd

LOOKING AHEAD

The brief dry pattern starts to break down on Friday (May 25th) as the upper-level ridge starts to break down and shifts east. That signals the return of the daily isolated to scattered storms with a fast moving pattern that features waves moving through the Upper-Midwest. Pinpointing when and where storms fire has proven to be a challenge in this setup. 

Memorial Day Weekend Pattern Overview

Beyond the weekend, we're keeping an eye on a system in the Caribbean that is expected to move into the Gulf of Mexico later this weekend. It's a system we need to watch for potential local impacts related to rainfall towards the middle of the next week (May 30th). 

A couple different scenarios related too this tropical system that could play out: 

1) System moves on the coast near Louisiana/Mississippi/Alabama and moves north, pushing moisture into the Lower Ohio Valley and delivering heavy rain to parts of southern Illinois. 

Model signaling tropical moisture (red) moving up the Mississippi Valley

2) System moves into the Southeast, setting up a blocking pattern over the middle of the country with moisture streaming into the Tennessee Valley (Tennessee & central Kentucky), while southern Illinois remains dry. 

Tropical systems are always a wildcard in forecasts and with this one being the first of the year in the Gulf, it's one we'll keep an eye on.

May 14th: From a cold April, to a scorching May

From one of the coldest Aprils on record across much of the Midwest, to one of the warmest starts to May. For St. Louis, it's the 2nd warmest start to May in 144 years of observations. For Paducah, it's the warmest start in 69 years of records.

PATTERN BREAKDOWN
A large dome of high pressure over the Deep South has been in control for the last five days, shifting the moisture north across the Upper Midwest and into the Great Lakes and bringing the heat northward. This has been a bit of a blessing for farmers who have struggled to get much corn in the ground up to this point. While the rain has stopped long enough for a lot of planting to get done, the sunshine and warm temperatures have sent soil moisture plummeting, and much of the newly planted grain could likely use a drink.

4" Soil Moisture Trend from April 1st-May 14thth

The big ridge is set to break down as we move towards the middle of the week when a series of weak waves moving through the jetstream will combine with a large storm system in the eastern Gulf of Mexico to suppress the high pressure dome. This pattern is a bit tricky, but will send better rain chances into the Mid-Mississippi and Lower Ohio Valley starting Monday (May 14th) evening and continuing through the end of the week. The big question remains "how much rain"? We're getting to that time of year where storms become more scattered. Some see a lot of rain, while others are left more high and dry, and this pattern enhances that even more. 

Starting Monday night we'll be watching a round of storms diving south and east through northern Missouri. There's some hints these storms could make it into the I-64 corridor late Monday night. Beyond that, there will be daily chances for scattered showers and storms through the end of the week (May 18th), mainly focused in the afternoon and evening. While it's nearly impossible to pinpoint who will see rain and who will not, the set up favors better odds of storms along the Ohio River in southern Illinois and points south and east (western Kentucky & southern Indiana). Anyone who gets caught in these storms should expect very heavy rain in addition to a lot of lightning. 

High Pressure Dome in Control Early in the Week

Storm System Suppresses Ridge Westward While Sending Moisture North

Our overall Summer forecast thoughts have not changed much since the early part of the Spring. A cool, wet Spring was expected, but we feel the rain will shut off and the Summer could end up being quite dry, especially June-August. 

May 7th: Summer-like warmth & humidity on the way

While many gardeners and farmers use April 15th as the average last freeze/frost for southern Illinois, May 7th, 1944 marks the latest freeze on record. On a year like 2018, where the cold seemed it would never go away through the month of April, the pattern has flipped and as we expected, those large troughs pulling cold air out of Canada are becoming a thing of the past. For those that have been clamoring for warmer weather, it's about to go from Spring to feeling a bit like Summer in a matter of days. For those hoping for dry weather, well, the next two weeks are going to be tough.

NEXT TWO WEEKS

Figure 1: Zonal flow (fast moving west to east jetstream pattern)

The jetstream will flatten more than it has in quite some time for the second week of May. (See: Figure 1) Meteorologists call this "zonal flow" and it's characterized by a fast moving, west to east flow pattern. With the lack of north or south push, it usually results in cold fronts trying to move south, stalling in the Mid-Mississippi/Lower Ohio Valley and then retreating northward. Of course, where the two airmasses clash results in showers and storms this time of year. That'll be the case towards the middle of the week with a cold front moving in from the north, sitting near the region before lifting back north.

May 14-18th jetstream. Large ridge on the East Coast deflecting storm systems north

A pattern shift is expected towards the later part of the weekend (May 12-13th) that will put a big ridge of high pressure over the eastern seaboard. The position of the ridge will determine the amount of wet weather for southern Illinois. Typically, when I see this pattern, it screams hot, humid, and nearly daily chances for storms. Beyond May 20th, there are some signs the ridge along the East Coast will strengthen and shift westward a bit, which would lend a hand in prolonged dry weather the last third of May.

April 26th Update: Extended Outlook & Frost Possible This Weekend?

When will the rain stop and the warmth arrive? It's the question I've been hit with the most this Spring. This April has been one for the books. Through Wednesday (April 25th), the mean temperature for the month was 8.6º below normal, an impressive number. In southern Illinois, we've averaged four 80º days in April over the last decade, this year, we'll have zero. Over the same span, we've averaged less than one day with afternoon temperatures below 50º, this year has featured seven.

The pattern of cool weather holds through the weekend. With an unseasonably strong shot of cold air, patchy frost is a possibility on Sunday morning. Winds will be the key, but with high pressure nearby, I won't be surprised to see winds relax enough for temperatures to drop back into the mid to upper 30s with some frost development.

Model Projected Temperatures Sunday Morning

Beyond, the weekend, a pattern shift is in store finally. This time, it appears the pattern will hold for more than just a couple of days. I've been telling my farming friends eager to get corn in the ground, to be patient. There will be a good opportunity with dry weather expected through May 1st, but then the pattern turns VERY wet.

With high pressure positioned over the Southeast and the jetstream streaking across the Plains, it's often a great funnel of moisture from the Gulf of Mexico right into the Mid-Mississippi and Lower Ohio Valley. Heavy rain is a possibility later next week to kick off the month of May.

April 16th: Cold Not Giving Up, Drier Weather Ahead

Wow. The first half of April has been one for the books. If it hadn't been for the stretch of milder days between April 11th and April 14th, it would surely be one of the top 3 coldest starts to April to date on record. The first ten days of the month ranked 3rd on coldest starts to April. In fact, today (Monday April 16th) we recorded a "trace" of snowfall, which comes only two days shy of the latest snowfall on record (April 18th, 1983).

Rain has been another factor plaguing much of southern Illinois for quite some time. Since January 1st, rainfall amounts range from 17-18" along I-64 in Jefferson and Wayne counties to more than 20" of rain in the "Southern Seven". That's a surplus of more than 5" across most of the region and ranks as the 4th wettest start to a year in Cape Girardeau, MO, 7th wettest in Evansville, IN, and 11th wettest in Paducah, KY. Since March 1st, we've recorded rainfall on 22 of 47 days at the station in Carterville, IL.

4" Soil Temperatures Under Bare Soil Morning of April 16th 

LOOKING AHEAD

Pattern continues to show signs of holding onto the cold, with a slight moderation over time. The good news for gardeners and farmers is the drier pattern that appears to be taking hold.

Rain Outlook
As mentioned in last week's post, April 22nd has been a date that was consistent for bringing in a good chance for rain. Though it's only Monday, it looks like that storm is going to be a "southern track" storm system, but close enough to provide some smaller rain amounts generally ranging from less than 0.25" along I-64 to possibly 0.5" along the Ohio River.

The last week of April (23rd-27th) will bring at least five consecutive days without rain as ridging takes hold over the middle of the country. Beyond that, April 28th-29th look to be the next system to bring us rain.

Precipitation vs. Normal Last Week of April

Temperature Outlook
Cooler than normal is still the overall trend that last through the end of month and possibly into the first half of May. There will be warmer days mixed in between storm systems, and naturally, the temperatures will moderate as we get later into the season and the sun angle gets higher in the sky. Coinciding the warm days with the dry days may play out between the 25th-27th. We need to watch for a potential cool spell towards the second week of May, but by that time, we'll be past the date for our last freeze on record, so we're likely talking morning temperatures back into the 40s if it actually occurs. Long-range, there are some signs that the pattern will begin to shift towards the second half of May.

Heading into Spring, our outlook suggested wet and cool, which has played out, but our outlook also revolved around a wet weather shutting off towards Summer. That remains to be seen, but there is the concern that a repeat of 2017 could occur.

April 10th: Brief warm up on the way, but cold still dominant

Good evening! Ten days through April and exactly 100 days into 2018 and many are wondering where the heck Spring is. A persistent pattern has kept the cold air locked in for weeks through much of March and now through the first third of April. A brief pattern break down is expected through the remainder of the week as a strong storm system drops through the Northwest and into the Plains, drawing the warmth many have been clamoring for streaming north into the Midwest. With several days of strong winds and sunshine, combined with the warmer weather, the ground will finally get a chance to dry out a bit. But, is it enough to dislodge the overall upper-level pattern? I don't think so.

Late Week-Weekend Storm System Passes to the North, but Pulls More Cold Air South

The warmth this week appears temporarily, but seasonally cool to chilly weather will likely persist through the remainder of April and possibly even into the early part of May. If there was ever a year we get a late frost/freeze, this could be it. Upper-level blocking pattern will keep waves moving through the Great Lakes into the Northeast and continually pulling cool air southward through the end of the month with only a few warmer days mixed in.

A Strong Signal Last Week of April - First Week of May is Seasonally Cold

After the super soaking rains in February and March, the next couple of weeks will be drier. After the potential for heavier rain late Friday night into early Saturday morning, the next disruptive rain may hold off until the time period around April 21-23rd.