We have a BIG warm up on the way as an extended warm period begins this weekend and extends into next week
The ‘Rex Block’ Pattern
BLOCKING PATTERNS IN THE ATMOSPHERE MATTER because they effectively put the brakes on large-scale weather movement effectively STALLING or DRAMATICALLY SLOWING weather system movement. Look into extended cold or hot spells or extended dry or wet spells and chances are good a blocking pattern has played a role in the extended nature of these weather abnormalities.
A Rex Block weather pattern is a high-pressure system that forms in the upper atmosphere, typically with a warm ridge of high pressure over a cool trough of low pressure below it. In the case of Chicago, when a Rex Block pattern develops, the warm ridge can extend over the region, suppressing the movement of weather systems and creating a stable and warm air mass. This leads to clear skies and a prolonged period of warm weather in Chicago as the high-pressure system prevents cooler air and storms from moving into the area.
REX BLOCKS derive their name from meteorologist Daniel L. Rex who first described the blocking pattern in 1950. REX BLOCKS are sometimes referred to as “HIGH OVER LOW” blocks, since that’s what you see on weather maps.
May be a graphic of map and text that says ‘KGLD 0.5° reflectivity and severe reports 0126 UTC 09 Aug 2023 1926 MDT 08 Aug 2023 40.75 40.25 60 Yuma County 39.75 Record hail report 50 (dBZ) 40 40 factor 30 20 reflectivity 10 equivalent 0 39.25 38.75 -103.75 -103.25 -102.75 -102.25 -101.75 -101.25’ Tom Skilling 14h · Radar image from the KGLD radar at 0126 UTC 9 August 2023 (7:26 pm MDT 8 August), with the locations of severe weather reports indicated (green squares indicate severe hail; red triangles indicate tornadoes.) 
PC convective outlook issued at 10:30am local time on 8 August 2023, showing a 30% probability of severe hail, with a “hatched” region indicating a greater than 10% probability of significant (greater than or equal to 2” diameter) hail over northeast Colorado. 
Comparison of the hailstone photographed by Dan Fitts with a rendering of the stone as it was scanned on 14 August 2023. This illustrates the melting/sublimation that took place between when the hailstone was photographed and when it was preserved at NWS Goodland. Provided by Ian Giammanco of IBHS. 
Comparison of the hailstone photographed by Dan Fitts with a rendering of the existing record hailstone from Bethune in August 2019 (shown in yellow). Provided by Ian Giammanco of IBHS. 
Analysis of the apparent maximum diameter of the hailstone with respect to the caliper measurement, provided by Ian Giammanco of IBHS.
The actual hailstone may have even been larger than reported, said the State Climate Extremes Committee (SCEC) which confirmed the August 8th hailstone in Colorado’s Yuma County:
“The diameter value supersedes the previous record of 4.83 inches, which occurred on 13 August 2019 near Bethune, Colorado. However, the Bethune hailstone will maintain the official record for the other dimensions of weight, volume, and circumference.”
The actual hailstone was preserved for a week before being carefully photographed but is said to have lost mass and size between the time it fell and was measured.
There’s quite a process before records such as this are entered into the books, involving an investigation by multiple agencies—in the case. This is laid out in the report on this hailstone (https://www.ncei.noaa.gov/…/20230926-Colorado-Hailstone…):
WHILE THIS IS THE LARGEST HAILSTONE WHICH HAS BEEN RECORDED IN COLORADO, THE U.S. RECORD FOR LARGEST HAILSTONE was a phenomenal 8″ in diameter and the stone weighed 1.973 lbs. https://www.weather.gov/abr/vivianhailstone
