FIRECRACKER SPECIAL...
The first day of July was a typical one around the Midwest with brisk SW winds sending temperatures into the upper 80s and lower 90s. Humidity was tolerable but slowly increasing ahead of a weak cool front advancing from the northwest. All in all, a classic mid summer day.
The aforementioned front has been advancing through the region overnight. That's provided enough forcing for some spotty showers and thunderstorms but dynamics (at least at this time) are not sufficient for widespread coverage. What activity remains will drift out of the south Friday morning as the front sinks into Missouri. It will be a warm muggy day across the south. Much drier air will prevail in the north before before advancing into the far south late in the day. Highs areawide will be cooler in the range of 80-85.
Saturday and Sunday the region comes under the influence of a weak high pressure over the Great Lakes. That is likely to keep any meaningful rainfall out of the forecast both days. There's just a slight chance my southwestern counties get grazed by a storm Saturday night. Southeasterly winds will also see to it that humidity levels remain in check with dew points only in the upper 50s to low 60s (mid 60s worst case in the far south). High temperatures should remain in the mid 80s. As it stands now, the Saturday Sunday portion of the Holiday weekend looks pretty good, seasonal is how I would describe it.
NATURAL FIREWORKS THE 4TH
As I've been advertising for numerous days. beginning the 4th and continuing occasionally the next 10 days, a seasonally supported "Ring of Fire" pattern gets established. It's the by product of a large upper level high pressure system that builds over the south-central U.S. On the northern edge of the heat dome where we reside, instability is high and ridge riding energy will fire thunderstorms, especially at night when the low level jet cranks up and breaks the days storm inhibiting cap.
Here's the set-up at 500mb. Gulf and monsoonal moisture from the southwest is pouring into the upper Midwest around the heat domes circulation.
By the 4th of July that moisture has loaded the gun for thunderstorms with water vapor levels reaching as high as 2.5 inches, more than twice the normal limit.
CAPE (instability) really begins to flourish. On the northern edge of the CAPE gradient is the place to look for active storms. That's a spot my area is located in. Depending on how the day develops, a severe weather scenario is possible the 4th with backed winds on a warm front situated near HWY 20. My northern counties would be favored. The key to the whole day will be the location of the warm front. Too far north we get hot and capped and storms remain north. Further south, the door is open for strong storms and severe weather. Time will tell.
While this type of set-up can breed severe weather, this appears to be a classic MCS set-up where nocturnal thunderstorm complexes rotate along the northern periphery of the heat. All modes of severe weather are possible but wind is the most common threat from large cold pools that form under the complex. This is the classic pattern for flash flooding as back building (or training) of storms is likely as the boundary remains nearly stationary. I can't say where or even if this potential will be realized, but text book signals exist in modeling to support it Monday through Wednesday of next week.
Temperatures will be a challenge as the warm front wavers nearby. North of it readings in my northern counties may hold in the muggie 80s. Further south, it could get really sultry with highs in the 90s and very high dew points. The EURO actually shows highs near 100 in southeast Iowa. Heat index values would approach warning criteria
Needless to say there is the potential for some active and impactful weather beginning July 4th. The position of fronts and mesoscale boundaries from convection episodes will play heavily in the type of weather we end up experiencing. Tweaks in the forecast are likely, especially after the Saturday/Sunday period.
So that's your firecracker special. Have a safe and fantastic holiday weekend. Roll weather...TS
