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Short-Term Severe/Flooding Discussion


Quincy
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I also placed this post over on Stormtrack:

 

FYI to anyone chasing today in ND or Canada. The KMBX radar is down and has been down all week. The part was supposed to be here Monday but it still hasn't arrived. The new estimate from the Air Force Base is now tomorrow. The good news is that we have the radar in stand by mode and will be able put it operational when the event starts. There's no telling how long it will last without the new part, however. But we cannot break it further by trying it tonight.

If you are chasing in the area and the radar goes out, we will need reliable spotter reports more than ever! I think I can speak for the GFK office in that regard as well.

 

Thanks!

Looks like they got it fixed. KMBX is detecting a severe thunderstorm right now!

 

 I am back in mid-Iowa. I could make tomorrow a storm chasing day in Nebraska, but I probably won't. CAPE will be very high along my travels on I-80 tomorrow, but I think storms may be very late in the day, such as at 03z. I hope to be done with the trip by 9:00 mountain time.

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Looks like they got it fixed. KMBX is detecting a severe thunderstorm right now!

I am back in mid-Iowa. I could make tomorrow a storm chasing day in Nebraska, but I probably won't. CAPE will be very high along my travels on I-80 tomorrow, but I think storms may be very late in the day, such as at 03z. I hope to be done with the trip by 9:00 mountain time.

No not fixed... We just had it up because they AFB guys had a temp fix that may or may not have failed. Thus far it has held firm but after the event it will be shut down and properly repaired tomorrow.

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Supercell developing near Long Lake, SD might be able to do something if it can right turn and interact with the OFB to its south.

 

Edit:

AT 448 PM CDT...A CONFIRMED TORNADO WAS LOCATED NEAR LEOLA...OR 22

  MILES NORTH OF IPSWICH...MOVING EAST AT 20 MPH.

 

  HAZARD...DAMAGING TORNADO AND GOLF BALL SIZE HAIL. 

 

  SOURCE...WEATHER SPOTTERS CONFIRMED TORNADO. AT 444 PM...A STORM 

           CHASER REPORTED TORNADO ABOUT 5 MILES NORTHWEST OF LEOLA.

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Starting to grow really concerned about western North Dakota Monday afternoon and night. The parameter space along the warm front near the triple point is fairly impressive. In this area it looks like discrete supercells will be possible during the afternoon and then it looks possible that a large destructive MCS could race across central ND overnight along the anomalously strong cold front. Capping could help to really enhance this event. If the NAM solution is close to reality I am very interested to see how SPC evolves in the outlooks.

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And now I'm even more concerned since the guys at the Air Force base still cannot figure out exactly what is wrong with the Minot radar. We will still have it available in standby mode, and will be able to turn it on when the storms start but it's impossible to say how long it will work.

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There is a severe thunderstorm watch for WY/SD/MT, and a few isolated severe storms starting to pop up. There is almost a dryline pushing eastward in Wyoming, although this isn't really the time of year for drylines. There is 40-50kt of 0-6km shear in Wyoming and Montatna now.

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  • 2 weeks later...

Not surprised that the SPC toned up the wording a bit for day 2. Still some mixed signals, but a few signs are there for a potentially enhanced severe weather threat.

 

Both the NAM and GFS show enlarged hodographs and considerable shear, including in the low levels, from far eastern Nebraska into west-central/southwestern Iowa, coinciding with strong instability.

 

Some red flags/uncertainties arise from the high PW values forecast, some warming in the mid-levels, attributing to initially modest mid-level lapse rates and storm mode. While the 4km NAM is actually late with renewed storm development, the GFS shows more of a mass of convection developing over Iowa. I would suspect that the storm model will be fairly messy and if any semi-discrete or discrete storms do fire, they would be HP and merge relatively quickly.

 

Nonetheless, a tornado threat may exist, especially if any storms can fire in the vicinity of strong low-level shear, perhaps near any lingering outflow boundaries from early-day convection.

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These types of events with subtle waves cresting a ridge and neutral/even rising heights during the day are always tricky. I'd lean more towards the messy idea although the dryline does seem to be available for convective initiation this time, which is often the downfall of these kinds of setups where everything south of the warm front is capped.

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Potentially localized big day in SE NE/ NE KS today... SPC is mildly excited as well, but there is uncertainty regarding CI later this afternoon/evening due to the massive MCS encompassing much of eastern Nebraska and Northern Kansas attm. An impressive parameter space will likely exist on the warm side of the boundary evidenced by the the 00Z 12NAM forecast sounding below from Falls City, NE at 00z/ Sunday...

 

ALSO... The 06Z D1SWO from SPC...

 

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1259 AM CDT SAT AUG 08 2015

VALID 081200Z - 091200Z

...THERE IS A SLGT RISK OF SVR TSTMS LOWER MO VALLEY...

...THERE IS A SLGT RISK OF SVR TSTMS BLACK HILLS AREA...

...THERE IS A SLGT RISK OF SVR TSTMS CNTRL HIGH PLAINS...

...THERE IS A MRGL RISK OF SVR TSTMS N-CNTRL STATES...

...THERE IS A MRGL RISK OF SVR TSTMS ERN GULF COAST STATES...

...SUMMARY...
SEVERE STORMS APPEAR MOST LIKELY OVER PARTS OF THE LOWER MISSOURI
VALLEY DURING THE LATE AFTERNOON AND EVENING. TORNADOES...VERY LARGE
HAIL...AND DAMAGING WINDS WILL BE POSSIBLE. LARGE HAIL AND SEVERE
WINDS SHOULD ACCOMPANY A FEW STORM CLUSTERS OVER THE NORTHERN AND
CENTRAL HIGH PLAINS IN THE LATE AFTERNOON AND EVENING.

...LOWER MO VALLEY AREA...
PRIMARY FORECAST CONCERN IS OVER THE POTENTIAL FOR A SIGNIFICANT
TORNADO SETUP ACROSS A LOCALIZED PORTION OF SERN NEB TO SWRN IA
WHERE A 10 SIG TOR PROBABILITY WAS CONSIDERED FOR THIS OUTLOOK.
BUT
WITH PREDICTABILITY RESIDING PREDOMINATELY ON THE MESO-BETA
SCALE...WILL DEFER TO LATER OUTLOOKS FOR POSSIBLE DELINEATION OF AN
ENHANCED RISK PROBABILITY.

ONGOING MCS CENTERED OVER S-CNTRL NEB/N-CNTRL KS SHOULD BE IN A
DECAYING STATE AT 12Z THIS MORNING. REMNANT MCV IS PROGGED TO SHIFT
E THIS MORNING OVER IA AND THEN DAMPEN OVER THE MIDWEST. GUIDANCE IS
HIGHLY CONSISTENT WITH A LACK OF DIURNALLY DRIVEN CONVECTIVE
DEVELOPMENT ASSOCIATED WITH THE REMNANT MCV PERHAPS DUE TO THE
FEATURE OUTPACING THE BUOYANT MOIST SECTOR CURRENTLY ALONG THE MS
RIVER WWD. THE MORE PROBABLE SCENARIO IS FOR RENEWED TSTM
DEVELOPMENT LATE AFTERNOON OR EVENING ACROSS PARTS OF THE LOWER MO
VALLEY WHERE PRONOUNCED DIFFERENTIAL HEATING IS EXPECTED ON THE SRN
EDGE OF RESIDUAL CLOUD COVERAGE/OUTFLOW BOUNDARY FROM THE DECAYING
MCS. A RATHER MOISTURE-RICH BOUNDARY LAYER BENEATH A PLUME OF
MODERATELY STEEP MID-LEVEL LAPSE RATES WILL RESULT IN A CORRIDOR OF
STRONG DESTABILIZATION WITH MLCAPE AOA 2500 J/KG.

UNCERTAINTY DOES EXIST OVER THE TIMING OF TSTM INITIATION GIVEN
CAPPING CONCERNS WITH LARGELY 700-MB SWLYS MAINTAINING WAA. SOME
CAMS SUGGEST TSTMS WILL BE DELAYED UNTIL JUST AFTER SUNSET AS THE
LLJ INTENSIFIES AND PROVIDES NECESSARY FORCED ASCENT. OTHER GUIDANCE
INDICATES LATE AFTERNOON INITIATION PERHAPS AIDED BY A SUBTLE
MID-LEVEL IMPULSE EJECTING FROM THE FOUR CORNERS AREA. SHOULD THIS
OCCUR...RELATIVELY STRONG LOW-LEVEL SRH ALONG THE EARLY-DAY OUTFLOW
BOUNDARY/RESULTANT EFFECTIVE FRONT COULD FAVOR A COUPLE INTENSE
SUPERCELLS /PARTICULARLY GIVEN THAT OVERALL FORCING SHOULD BE
MODEST/. A CONDITIONAL RISK FOR VERY LARGE HAIL AND A STRONG TORNADO
IS APPARENT.
WILL MAINTAIN INHERITED SIGNIFICANT SEVERE
PROBABILITIES /DRIVEN BY HAIL/...BUT MESOSCALE PREDICTABILITY IS TOO
LOW FOR A LOCALIZED UPGRADE TO ENHANCED RISK PROBABILITIES THIS
OUTLOOK. REGARDLESS OF WHEN TSTM INITIATION OCCURS...UPSCALE GROWTH
INTO A LATE EVENING MCS SEEMS PROBABLE WITH A DAMAGING WIND RISK
MOST LIKELY DURING THE EARLY STAGES OF STORM-SCALE MERGERS UNTIL
CONVECTION TENDS TO WEAKEN OVERNIGHT.

post-7962-0-89914800-1439020786_thumb.pn

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The pretty massive MCV over E NE attm is impressive... at least geographically/size speaking. As long as there isn't pestering convection, like there always is in 2015, then today should be pretty good. Main question will be how HP are any supercells that develop going to be and how quickly do they/ do they not form into a messy WF MCS. 06Z 4K NAM shows CI around 23-00z in E NE and almost automatically develops it into a bow-echo by 01Z. Could be a small window in there to get an intense supercell.

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The pretty massive MCV over E NE attm is impressive... at least geographically/size speaking. As long as there isn't pestering convection, like there always is in 2015, then today should be pretty good. Main question will be how HP are any supercells that develop going to be and how quickly do they/ do they not form into a messy WF MCS. 06Z 4K NAM shows CI around 23-00z in E NE and almost automatically develops it into a bow-echo by 01Z. Could be a small window in there to get an intense supercell.

MCC over the central plains. This radar is from 07z. That's quite a large area that got rain, considering that there were just a few isolated storms in Colorado to start off last night.

 

2015_08_08_07z_Radar_centplains.png

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Ironically the first storms to fire are along the "dryline" in W/SW/NC KS along the northern periphery of the southern plains sub tropical ridge. Instability is pretty impressive generally south of the NE/KS border. But shear is pretty underwhelming attm with only 20-30kts of eff. shear across the area. But that should increase as the main-- but subtle-- shortwave rounds the base of the ridge, increasing shear to 35-45kts. Still is some tornado potential later this evening as a 25-35kt LLJ kicks in around the time that shortwave will kick into the area, especially if there is still a discrete storm or two.  Looking pretty linear though in KS already, but doubt that much of that activity will maintain, especially with southward extent due to meager shear.

 

However, even if we were to manage a discrete supercell prior to the MCS... or in front of/away from the MCS... it would still likely be HP given PWAT's of 2-2.5in and unimpressive upper-level winds.

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