5.5.11 0z GFS forecast for Tuesday evening with trough slowly progressing east.
Blackwell, OK – Things are somewhat precarious on the storm (or maybe sanity) front, with the promise of at least one chaseable system looming but still far enough out it’s no sure thing.
All along, the idea of a break after the first day (once that day was decided) was a real one. However, it appears that it will stretch longer than hoped and how the streak “breaks” is somewhat undecided. In any event, we’re chewing down days in wait mode.
So far, the traditional Tornado Alley and adjacent states have been largely quiet when it comes to tornadoes this season. While, as noted in a recent post, this is not terribly uncommon heading into May — when storms back into the region from the southeast U.S. – there are at least several large-scale players currently making an active environment more difficult to come by.
Two background issues are the, also previously mentioned, negative trend of the North Atlantic Oscillation and increasingly severe south-central U.S. drought. But, even in a pattern that is less favorable than optimal for severe weather in the Plains and Midwest, there are opportunities. Realistically, it now seems fairly apparent our actual chase days will be limited to only a few to a handful.
Over the next few days a large trough of low pressure in the upper atmosphere will build into the west and then move through the Rockies. As this happens, a series of surface low pressures should form on the lee-side (right side if you’re looking at a standard map) of the range, either remaining relatively stationary or moving northeast only to be replaced by another low pressure.
At the same time, an upper-level ridge of high pressure slowly progresses east through the period. These features will combine to replace the recently cooler than normal weather with hot and humid conditions streaming north. Our 70s are about to be replaced by 90s.
So, low pressure and humid conditions? Sounds good for storms, right? Maybe, and ultimately probably – for a time at least. As the upper trough is slow to progress east, conditions should become generally more favorable for severe weather, including tornadoes, heading into next week.
By Friday, traditional severe weather values – rising instability, moisture, convergence along a boundary (the dryline, then cold front) – will begin to show up in the southern Plains. Initially, it seems that too many ingredients may be stacked against storms to get many or any to fire up. It’s a process though; we have to start somewhere…
One issue, especially early on as the main trough only slowly kicks east, is that warm air is streaming in not only at the surface but aloft, so the atmosphere will tend to be “capped.” In other words, warm air has trouble rising into more warm air compared to when colder air is above and warmth wants to explode upward in the form of a thunderstorm.
Still, there have been many a severe weather outbreak with some initial capping, as it forces storms to go big or not happen at all. There have also been expected outbreaks that have been stifled by such an atmospheric condition because there was no atmospheric “trigger” like a cold front, dry line, and/or mesoscale boundaries like remnant outflow. The question to resolve is if/when the cap will break and where.
The typical dryline, created by dry/hot air coming off the Rockies and clashing with warm/moist air from the Gulf of Mexico, has been stifled for much of this year, likely thanks to much of the region being engulfed in drought. These grounds are typically much wetter than they are now, and evaporation from soil moisture adds fuel for storms in addition to what comes from the Gulf.
Storm Prediction Center severe storm outlook for Sunday-Monday (red) and Tuesday (green).
With the drought in place, even moist air traveling inland can be dried somewhat in the process. At the very least, it makes those looking for Plains storms wish for a southeasterly surface fetch more than usual.
The plan is to watch for the dryline to fire up (even in isolated fashion) prior to the trough ejecting out of the Rockies when a more general severe weather threat probably occurs during the early or middle part of next week.
The Storm Prediction Center has now outlooked the timeframe of Sunday-Tuesday in the extended, highlighting prime Tornado Alley chase territory
BY TUE/D6 INTO WED/D7…FLOW OVER THE PLAINS WILL BECOME
INCREASINGLY MERIDIONAL AS THE UPPER TROUGH BOTTOMS AND BEGINS
MOVING EWD. ALSO AT THIS TIME…A SUBTROPICAL JET IS EXPECTED TO
MOVE NWD AND PHASE WITH THE MAIN TROUGH…INCREASING UPPER LEVEL
WIND PROFILES. ALL THE WHILE…A DRYLINE WILL REMAIN ACROSS THE
CNTRL/SRN PLAINS WITH STRONG INSTABILITY AND AMPLE VEERING SHEAR
PROFILES FOR SUPERCELLS EACH DAY. TUE AND WED APPEAR TO HAVE A
GREATER TORNADO THREAT THAN ON SUN/MON WITH HIGHER THETA-E AIR AND
BETTER HODOGRAPHS. AN ISOLATED STRONG TORNADO MAY OCCUR…ESPECIALLY
ON TUE WHEN A STRONG NOCTURNAL LOW LEVEL JET RESPONSE IS FORECAST TO
OCCUR DURING THE EVENING.
We’re gathering ourselves for a day and hanging out locally in northern Oklahoma (visiting Wakita of Twister fame). Tomorrow we’ll head toward Oklahoma City, perhaps to visit some of the dot-govs. Saturday should begin to feature fairly strong to borderline extreme instability over parts of the region, so we’ll be on the lookout for activity along the dryline by then.
Sunday and beyond could be the real deal – trying not to get hopes up too much though! Sunshine is getting to my head… I may have more later on a few historical outbreak setups and how it compares to what we may see here into next week.