DISCUSSION
Issued at 354 AM CDT Sat Jul 27 2024

Next Seven Days: Heat and Humidity

Over the next week, operational guidance is in very rough agreement that ridging aloft will build first over TX with a shift toward stronger ridging over the intermountain west next weekend. For our forecast area, this should result in heights aloft building through Wednesday before a subtle decrease moving ahead to next weekend.
Heat each afternoon will depend a lot on the details and timing of various shortwaves and associated precip (see below) but GFS/EC suggest heights aloft will be maximized Wednesday afternoon. In any case, most afternoons will feature highs in the mid 80s and, with occasional periods of southerly surface winds expected, 60s and 70s dewpoints look to be the norm. Thus, heat indices in the 90s are favored each afternoon with Wednesday having a small (25%) chance for a triple digit reading in NE IA per latest LREF guidance.

Sunday/Monday and Wednesday/Thursday: Potential for locally heavy rain and a stray severe storm

Sunday, an upper low, currently over the ArkLaTex region, looks to churn northeastward and rejoin the west-southwesterly flow aloft just to our southeast over NW IL. With best forcing for ascent favored to skirt just to our southeast - and progged soundings showing a good amount of capping remaining - am increasingly doubtful precip will occur in the forecast area.

The same cannot be said for Monday as guidance, while differing in exact timing, is in pretty good agreement that a robust shortwave will eject eastward over the forecast area. This should help erode remaining capping, leading to a round of showers and storms. Progged PWATs increase above 1.75", near the 90th percentile of GEFS/ENS model climatology. While widespread risk looks to be limited by the overall progressive nature of the system, could still get a few pockets of locally heavy rainfall given this amount of moisture and storm motion vectors of around 20 knots. Finally, should this shortwave arrive coincident with peak afternoon heating, would have around 1500 J/kg of MLCAPE to work with as deep layer shear approaches 40 knots, so would have a risk for a severe thunderstorm were this to occur, a small possiblity also suggested by LREF joint probabilities (10-15%) and GEFS-based machine learning outlooks (~10%).

While guidance continues to show a variety of solutions moving into the middle of next week, next strong wave looks to approach sometime during the Wednesday/Thursday period. With modeled PWATs again increasing above 1.75" with storm motions of around 20 knots, localized heavy rain would be possible during this period as well.
LREF joint probabilities suggest around a 10-20% chance for sufficient shear and CAPE for a low end severe storm, so will need to keep an eye on this possibility as well.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/
Issued at 557 AM CDT Sat Jul 27 2024

Primary aviation concern is MVFR/IFR stratus this morning at RST/LSE. Expect ceilings to rise and dissipate with time as the sun works its magic but cannot totally rule out occasional MVFR ceilings during the day today courtesy of otherwise fair weather cumulus.

ARX WATCHES/WARNINGS/ADVISORIES
WI...None.
MN...None.
IA...None.