Severe weather risks have inceased, but the area affected is smaller than in yesterday's forecast (at least in Kansas). The higher risks are from rangeland fire (southwest Kansas, especially, but statewide the risks are elevated), blizzard conditions (Gooodland, Colby and points north), and damaging wind from the rapidly-strengthening low pressure center.
The risks between now and noon Thursday run the gamut. I’m going to try to deal with them by theme. First, severe weather risks/impacts:
An enhanced risk of severe weather has been added to the SPC outlook as of the first issuance today. It covers a small part of Kansas — all of four counties and part of four more. An early-season reminder: this reflects the risk of any severe weather occurrence within 25 miles of any selected point in those counties. The highest risk value posted by SPC is for hail — a 30% probability of a hailstone quarter-size or larger, and a 10% probability of a hailstone of hen egg size or larger.
This morning’s SPC headline and the pertinent dicussion:
A few strong to severe storms with large hail and damaging wind will be possible late this afternoon and into this evening from northern Kansas through the south central and southeast Nebraska vicinity.
Initial development may occur over northwestern Kansas/southwestern Nebraska, but stronger/sustained updrafts appear more likely to initiate a bit later and a bit farther east, into the north-central Kansas/south-central Nebraska vicinity.
While low-level moisture should remain insufficient for substantial tornado risk, one or two long-lived supercells will likely evolve, capable of producing very large hail, and locally damaging winds.
Our risk graphic takes into account the entire state, including the 3/4 of the state which is unlikely to see any severe weather. That’s why I’ve bumped up the wind risk substantially higher than SPC, into the moderate category.
Why, with another very strong cyclone developing overhead and highs in most of the state warmer than 75 degrees, are more of us not seeing a severe weather threat? Bottom-line, not enough moisture in the air. If this system developed one day later, we might have had enough Gulf moisture pulled into the area just in front of the dry line. But models are pretty consistent with best-case dew points in the mid-60’s, and right at the time of peak heating, mid-level dry air from the desert southwest blasts in and much of the state gets dry-slotted. This model forecast for 7pm CDT shows Wichita at a 54-degree dewpoint, while Pratt is at 35, Dodge City at 20, and Liberal at 10 degrees!
If those 62-65 degree dew points in Texas were in the Wichita-Hutchinson vicinity, it’d be game on for severe weather for a couple of hours…but this setup doesn’t contain anything interesting from a chaser’s standpoint until the Phillipsburg to Beloit to Concordia areas and north into Nebraska. The forecaster in Hasting, NE this morning was dubious about any legitimate tornado chance, but you have to acknowledge that in a couple of locations, you could get conditions for a brief spinner.
The severe weather threat Wednesday afternoon/evening will primarily originate near the triple point over north central Kansas with storms lifting northeast from there. Most if not all of the thunderstorms will be elevated with only a small chance at seeing a sfc based storm right near the triple point and even if we do see a sfc based storm it is likely to quickly track north of the boundary and become elevated. Consequently, I hesitate to even mention the possibility of a tornado given the low probability of getting surface based thunderstorms. Any tornadic threat is conditional on getting a storm to form in the warm sector or just ahead of the front, but again this chance appears very low. The warm sector appears at though it will be capped and thus large hail to the size of golfballs will be the primary severe weather threat from the elevated supercell thunderstorms.
Goodland also mentions a brief window for severe weather in their eastern counties:
A west-east or WSW-ENE oriented frontal zone in northwest Kansas may serve as a focus for convective development this afternoon [1pm-7pm CDT] …Large hail assoc/w isolated elevated supercells along/north of I-70 appear to be the primary threat, however, if deviant storm motion increases updraft residence time [near the front] — all severe hazards would be possible.
Here are the graphics from the NWS offices that made enough mention of severe risks (in my opinion) to highlight:
The greatest economic risk all the way around is the wind — not only the damage possible from strong wind on both sides of the system, but the wind’s impact on two conditions at the opposite end of the spectrum: fire and blizzards.
Southwest Kansas is the place of highest threat. With dew points in the teens and low 20’s and wind gusts of up to 55 miles an hour, conditions are ripe for explosive fire growth if something gets started.
There will be two distinct wind impact times any any given location: the warm-side winds this afternoon, bringing in the dry air form the southwest. Most predictions have the highest wind on this side of the system lasting for 4-6 hours or so. Here’s an example from the Dodge City discussion:
The first high wind episode will commence shortly after Noon across far southwest KS first…35 to 40 knot sustained winds are almost a certainty, especially after 20Z (3 PM). The main question is how far north this deep southwest momentum will mix to. It seems as though the models have been trending farther north with each run, perhaps extending as far north as southern Trego-Ellis County. [4pm-6pm CDT]…several 55 knot surface gusts, especially DDC south to LBL corridor.
The second, and potentially higher-impact, wind damage possibility comes as the low starts to move east and even stronger winds ramp up out of the north and northwest. Not only will peak wind likely be higher west of the low, but it’s likely to last several hours longer. Look for this from about midnight in the west to about noon in central Kansas, and another burst of wind for a couple of hours in western Kansas tomorrow afternoon. Don’t look for wind to calm down below 30 mph until Thursday night or even Friday morning in some locations.
With wind like this it won’t take a lot of snow to create extreme to whiteout conditions. In Kansas, this will primarily affect the the six or seven furthest northwest counties. Here’s the key section of the Goodland discussion:
[E]xpect a rapid west-east transition from rain to wet snow late this aft/eve — on the western periphery of the deepening cyclone as it tracks from western->central Kansas. [C]considerable uncertainty persists with regard to precipitation amounts. In general, the greatest potential for accumulating snow appears to be north of I-70 and west of Hwy 283, where a Blizzard Warning is in effect.
It is important to remember that, regardless of snow amounts, this is a dangerous storm that will severely impact travel across the Tri-State area late this afternoon through mid-day Thursday.
Temperature swings are going to be pretty amazing, from highs this afternoon in the 80’s many places, to wind chills in the teens early Thursday. And don’t look now, but there will be a hard freeze out west Thursday night into Friday morning.