High Wind Warning after thunderstorms

Blake Allen

I can't recall ever seeing a warning after storms like the one issued in NE Oklahoma tonight.

from http://kamala.cod.edu/ok/latest.wwus74.KTSA.html:


How common is this?

Blake Allen
I actually think there was something similar earlier in the day on Saturday somewhere in NW OK, SW KS, NE TX panhandle (anybody remember???). The winds weren't as strong as the Tulsa winds, but it was pretty much the same situation I think.
The same 'high wind warnings' were posted after storms died out in south western OK earlier this week, before redeveloping into a line across central western oklahoma.
I think it's caused from a small meso high that forms behind the departing MCC. I think this causes a localized, but very tight pressure gradient that can result in these high winds.

I've seen high wind warnings issued before from similar situations around here. I've seen some pretty high winds well after the complex has left the area, which is pretty erie. Although I've never experienced as powerful of winds as what happened down in OK last night.
Yes, it is a very eerie occurence because so often it happens after dark... after the storms move out. I have encountered several occurrences where some stars will be visible and winds will be more than 40mph.

It gives the sense that something big is about to happen.
This happened well behind a bow echo on 13 July 2004, which evolved from the original massive supercell that dropped the Roanoke F4. High winds actually caused some damage in northeast parts of central Indiana as the line itself was actually crossing the Ohio River.
Re: Post T-Storm wind

Originally posted by Glenn Rivers
Blake, this sounds suspiciously like a nocturnal heat burst situation in your case.

Had this been a heat burst, it would have been accompanied by a temperature spike. Here are the obs for KTUL from around that time.

KTUL 050553Z 19008KT 10SM TS SCT040CB SCT080 25/13 A2969 RMK AO2 PK WND 17035/0457 WSHFT 0520 RAE00 SLP045 OCNL LTGIC ALQDS TS ALQDS MOV NE P0000 60001 T02500128 10300 20233 403220233 53018

KTUL 050540Z 22013G20KT 10SM TS SCT040CB SCT080 26/12 A2969 RMK AO2 PK WND 17035/0457 WSHFT 0520 RAE00 PRESRR OCNL LTGIC ALQDS TS ALQDS MOV NE P0000

KTUL 050453Z 16024G34KT 10SM -TSRA SCT040CB BKN080 BKN110 26/12 A2964 RMK AO2 PK WND 18046/0404 SLP029 OCNL LTGICCG ALQDS TS ALQQDS MOV NE P0000 T02560122

KTUL 050353Z 18033G43KT 10SM -TSRA FEW040CB SCT085 OVC150 27/19 A2966 RMK AO2 PK WND 17043/0352 TSB49 PRESRR SLP034 OCNL LTGICCG S-SW TS S-SW MOV NE P0000 T02720189

KTUL 050253Z 16019KT 10SM -RA SCT065 BKN110 OVC150 26/22 A2964 RMK AO2 PRESFR SLP028 CONS LTG DSNT W-NE CB DSNT W-NE MOV NE P0001 60001 T02610217 50000

The obs from KRVS, which is also in the Tulsa area, are similar. I'm a little confused. If the high winds took place between 10:30 and 11:00 PM LST, that would have been between 0330 and 0400 UTC. As you see in the obs above, peak winds from the south of about 46-47 knots were reported. The fact that thunderstorms were reported at and following the time of peak winds would lead me to believe that this was a good old fashioned gust front, and not some special case. In addition, the remark of cumulonimbus distant west through northeast moving northeast at 0253 UTC would indicate that storms were approaching, not moving away, as would the remarks of pressure rising rapidly (PRESRR). I'm a little confused by their assessment of the situation.

However, if this truly was well behind any real thunderstorm activity, I would be more inclined to accept the mesoscale pressure influences suggested by Joel, or to suggest that perhaps a descending rear inflow jet was the culprit.
Nocturnal heatburst interp may be wrong

I must confess that I did not look at the details of Blake's case....maybe it was a classic gust front.

In the other case of July 13 2004 mentioned by Joe, I am inclined to suspect that a RIJ plowed into the ground well behind the convective line after being chilling by evaporating rain in the trailing stratiform region. Interestingly, I don't recall this mechanism being documented in the BAMEX project. Maybe more cases where damaging winds occur in trailing stratiform precip regions behind leading convective lines need to be done.
There was a small increase in temperature about that time. I noticed it on a metogram for the Bixby mesonet site in southeast Tulsa County. I'm not sure if that data is available to the public or not. Also, I was working on my TV station in downtown Tulsa for the severe weather coverage, and our temperature at the station did spike about 5-8 degrees i believe...i know it reach 86...while the high for the day was 90 much earlier in the day.
Although not nearly as dramatic as what happened in OK the other night, we are currently experiencing similar conditions right now. A MCC is departing the area right now, just a bit of rain. The winds are now gusting to almost 40mph from the east. The pressure has dropped from 29.88 to 29.73 in the last half hour. Very interesting.....
Ok, now I am confused. I remember seeing a presentation on this event at the local AMS meeting and it was described as a Wake Low. Going to Milwaukee's website, they are calling it a Derecho.

Wake lows are not the same as derechoes, though I suppose the strength of the wake low may have an impact on overall MCS strength and thus "derecho" classification. From the AMS Glossary:

Derecho—A widespread convectively induced straight-line windstorm.
Specifically, the term is defined as any family of downburst clusters produced by an extratropical mesoscale convective system. Derechos may or may not be accompanied by tornadoes. Such events were first recognized in the Corn Belt region of the United States, but have since been observed in many other areas of the midlatitudes.

Wake Low—1. (Or wake depression.) In meteorology, a surface low pressure area or mesolow (or the envelope of several low pressure areas) to the rear of a squall line; most commonly found in squall lines with trailing stratiform precipitation regions, in which case the axis of the low is positioned near the back edge of the stratiform rain area. 2. (Or wake depression.) In fluid dynamics, a low pressure area on the downstream side of an object embedded in a flow.

Derechoes are essentially MCSs that produce widespread wind damage over a large spatial area (and tend to last for a significant amount of time). The SPC has a good page on derecho case studies.

In either case, the high wind reports weren't from a derecho (I don't recall a well-organized MCS at the time), and I'm not sure I've heard of surface flow associated with wake lows to be that intense. From the METARs posted earlier, I'd tend to think that the high winds were caused by good ole microbursts/macrobursts, though I remember hearing comments that the high winds were located considerably behind the leading edge of the convection (where high winds are most likely in a classic MCS/bow echo fashion).
I encountered winds like this for the first time in the early morning of 5/25/05 in Liberal, KS. The events that morning seem to coincide well with what was described in the case studies of the wake low link above.

The leading edge of a MCS and associated gust front passed through KLBL around 0515Z, moving roughly from N to S. At the time KLBL reported a gust to 40 kt, which I can vouch for because I was attempting to move bags from my car into the local Super 8. As the mesohigh associated with the leading edge passed, the pressure rose to 30.07 in. Hg, and remained above 30.02 for an hour as the precip continued.

When the rain stopped I went back outside to finish bringing in my luggage. To my surprise the wind was even stronger than when the gust front was moving through! Checking the KLBL obs, the wind shifted to the NE and was now gusting to 47 kt! The pressure had also fallen to 29.84 in. Hg. There was a radio tower adjacent to the hotel parking lot, and the wind whipping through the guide wires was making a tremendous howling noise. I took some video of the Super 8 sign blowing back and forth of the wind, and tried to capture the howling noise. The strong wind continued for several more hours until finally subsiding around 0800Z. Very impressive, and very eerie considering it was barely raining.

Thanks to Ben Cotton, here are the surface obs from KLBL for the entire event. You can see the gust front move through, and the strong winds following the passage of the main area of precip. The pressure dropped from 30.07 to 29.84 in 90 minutes, and then rose again.

KLBL 250455Z AUTO 04014G19KT 10SM SCT070 22/16 A2997 RMK AO1 LTG DSNT NW
KLBL 250455Z AUTO 04014G19KT 10SM SCT070 22/16 A2997 RMK AO1 LTG DSNT NW
KLBL 250515Z AUTO 01029G40KT 9SM VCTS SCT024 BKN030 OVC070 18/13 A3004 RMK AO1 LTG DSNT ALQDS TSB06
KLBL 250535Z AUTO 01022G25KT 3SM TS FEW014 SCT021 BKN028 15/14 A3007 RMK AO1 LTG DSNT ALQDS TSB06 P0001
KLBL 250555Z AUTO 02027G32KT 5SM TS FEW001 SCT010 BKN022 15/14 A3006 RMK AO1 LTG DSNT ALQDS TSB06 P0006 60006 10300 20150 52081
KLBL 250615Z AUTO 05027G35KT 3SM TS FEW005 SCT020 BKN031 16/15 A3002 RMK AO1 LTG DSNT ALQDS P0008
KLBL 250635Z AUTO 05032G44KT 7SM VCTS SCT017 BKN044 OVC110 16/15 A2996 RMK AO1 LTG DSNT ALQDS P0010
KLBL 250655Z AUTO 06032G44KT 10SM TS FEW044 16/14 A2992 RMK AO1 LTG DSNT ALQDS P0011
KLBL 250715Z AUTO 07033G47KT 10SM VCTS CLR 16/14 A2984 RMK AO1 LTG DSNT ALQDS TSE0656B13
KLBL 250735Z AUTO 07029G42KT 10SM CLR 16/14 A2988 RMK AO1 LTG DSNT NE TSE0656B13E28
KLBL 250755Z AUTO 06020G34KT 10SM TS FEW110 16/14 A2992 RMK AO1 LTG DSNT ALQDS TSE0656B13E28B51
KLBL 250815Z AUTO 05021G28KT 8SM FEW004 SCT042 BKN095 16/13 A2996 RMK AO1 LTG DSNT E TSE09 P0005
KLBL 250835Z AUTO 05018G32KT 8SM TS FEW002 BKN033 OVC100 16/13 A2997 RMK AO1 LTG DSNT ALQDS TSE09B25 P0010
KLBL 250855Z AUTO 06012G19KT 9SM VCTS FEW032 SCT046 BKN100 16/13 A2999 RMK AO1 LTG DSNT ALQDS TSE09B25 P0010 60021 57024
KLBL 250915Z AUTO 09006KT 8SM FEW037 SCT043 BKN049 16/13 A2999 RMK AO1 LTG DSNT SE TSE05 P0002

That was definately a wake low, probably similar to the one in Iowa Wednesday Afternoon too. High Wind Warnings issued up there. Wake lows can produce severe-criteria gusts. I have been through several already in the MCS-active Great Lakes zone. One produced some 60 mph gusts one morning which caused a lot of tree and powerline hits across the county.

They form behind decaying MCS's....when you see reflectivity and clouds start to wash out rapidly...that is an excellent sign.

Here is a good quote from a Memphis writeup...

Johnson and Hamilton (1988) proposed that wake lows were the result of subsidence warming which was maximized at the back edge of a trailing stratiform precipitation area where there was insufficient sublimation and evaporative cooling to offset adiabatic warming. Stumpf et. al. (1991) also concluded that the trailing stratiform precipitation region of mesoscale convective systems can be dynamically significant, by generating rapidly descending inflow jets at their back edges, producing pronounced lower-tropospheric warming, intense surface pressure gradients and strong low level winds. Similar conclusions were drawn by Zhang and Gao (1989) in a numerical modeling study. Recently, Gallus (1996) found, using a numerical modeling study, that when precipitation rates are prescribed to decrease with time, as might occur with collapsing precipitation areas, microphysical cooling may become sufficiently small as to induce strong subsidence and an intense wake low.

I don't like trying to explain them myself, I always trip all over my words. Bottom line, they occur behind decaying MCS's (although not all the time) and produce several hours of strong winds. I am not 100% sure, but I believe a heat burst and a wake low are different phenomina, which is why you probably didn't see a marked increase in temperatures.

...Alex Lamers...