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June 20-21 and June 24-27 Heavy Rain/Severe Threats


Hoosier

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LOT

 


OF GREATER CONCERN STRONG/SEVERE THUNDERSTORMS ARE FORECAST TO   DEVELOP OVER IOWA WEDNESDAY AFTER BEFORE CONGEALING INTO AN MCS THAT   WILL MOVE EASTWARD TOWARD OUR REGION WEDNESDAY NIGHT. SOME REALLY   IMPRESSIVE HEAVY RAINFALL PARAMETERS SHOWING UP IN THE MODELS FOR   WEDNESDAY NIGHT WITH PWATS AOA 2 INCHES AND STRONG MOISTURE   CONVERGENCE ON THE NOSE OF STRONG LOW LEVEL JET WHICH IS PROGGED TO   VEER INTO NORTHERN ILLINOIS OVERNIGHT. CORFIDI VECTOR MAGNITUDES   DROP TO LESS THAN 10KT OVERNIGHT WITH AXIS OF GREATEST INSTABILITY   STILL UPSTREAM OVER THE PLAINS WHICH IS A PRETTY CLASSIC SET UP FOR   HEAVY RAINFALL. PLACEMENT OF THE HEAVIEST RAIN WILL BE DICTATED BY   MESOSCALE PROCESSES THAT ARENT WELL PREDICTED THIS FAR OUT...BUT   OFTEN TIMES MODELS ARE TOO AGGRESSIVE WITH NORTHWARD PLACEMENT OF   ADVANCING WARM FRONTS IN CONVECTIVE SITUATIONS...SO SIDED WITH THE   MORE SOUTHERN PLACEMENT GUIDANCE IN THE GRIDS.     THE KANKAKEE...IROQUOIS...AND ILLINOIS RIVER BASINS ARE WATER LOGGED   AND EXTREMELY FLOOD PRONE. IF HEAVY RAIN FALLS OVER THESE BASINS   WEDNESDAY NIGHT THE POTENTIAL IS THERE FOR MAJOR FLOODING ISSUES. WE   ARE STILL 4 PERIODS OUT AND THERE ARE UNCERTAINTIES WITH REGARD TO   PLACEMENT OF HEAVIEST RAINFALL SO ITS TOO EARLY FOR A FLASH FLOOD   WATCH...BUT WILL ISSUE AN ESF TO HIGHLIGHT THE THREAT AND EXPECT A   FLASH FLOOD WATCH WILL EVENTUALLY BE NEEDED IF GUIDANCE REMAINS   CONSISTENT WITH POTENTIAL HEAVY RAINFALL SCENARIO.     DEPENDING ON HOW FAR NORTH THE WARM FRONT MAKES IT...THE POTENTIAL   COULD ALSO EXIST FOR SOME SEVERE WEATHER WEDNESDAY NIGHT. THE MOST   LIKELY THREAT AREA LOOKS TO BE SOUTHERN CWA...CLOSER TO WARM FRONT   WITH THE PRIMARY SEVERE THREAT (IF ANY) LIKELY TO BE STRONG AND   POTENTIALLY DAMAGING WINDS GIVEN THE EXPECT EVOLUTION TO A LINEAR   MCS BY THE TIME IT ARRIVES EAST INTO ILLINOIS.    GUIDANCE SUGGESTS A CONTINUED THREAT OF SHOWERS AND THUNDERSTORMS   INTO THE DAY THURSDAY...ESPECIALLY SOUTHERN CWA AND HAVE MAINTAIN   POPS ACCORDINGLY. WOULDN'T BE SURPRISED IF PLACEMENT EVENTUALLY ENDS   UP BEING FARTHER SOUTH BUT THAT IS SOMETHING THAT CAN BE DEALT WITH   LATER.  
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Wouldn't be surprised to see the severe threat expanded eastward some on future updates.  There will likely be a sharp instability gradient and surface based instability may be questionable this far east but strengthening wind fields aloft would suggest at least a low end damaging wind threat in any well developed line.

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Have been pondering chasing tomorrow. Target would probably around the OTM-GBG corridor. I have to be out at DKB for something at 8AM, so that would already be part of the trek and factored into the decision.

 

However, given it looks like morning convection will be a significant issue once again and afternoon development may be quick to grow upscale into an MCS, I'm hesitant. 

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I have to re-certify for one of our more important analysis tomorrow, so I'll be stuck at work until at least 4 or 5pm.  Timing is killing me this season.  

 

I wouldn't be shocked if outlook area gets bumped quite a bit to the south again tomorrow if morning MCS activity keeps the effective boundary south.  Seems to happen quite often, so at this point if I were chasing I'd probably plan on heading to south-central, or southwest IA.  

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Impressive late evening severe MCS for Chicagoland on the ARW, not bad on the NMM either. Evening convection holds of until later and effective front really surges north on the strength of the LLJ. Obviously remnants will be an issues but the trend towards a later initiation helps. Needless to say this would be a widespread high-impact solution.

 

hrw-arw_conus_041_sim_radar.gif

 

hrw-nmm_conus_042_sim_radar.gif

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12Z 4K NAM at Des Moines, IA airport tomorrow at 23Z. Pure insanity. 0-1KM SHR at 30kts/SRH at 341m2/s2... and 0-3KM SHR 48kts/ SRH at 703m2/s2. One of the top SARS analogues is OKC on 5/3/99 FWIW.

4K NAM appears to be pretty over the top though with its LLVL wind fields compared to other guidance...  

post-7962-0-17784000-1435085555_thumb.pn

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12Z 4K NAM at Des Moines, IA airport tomorrow at 23Z. Pure insanity. 0-1KM SHR at 30kts/SRH at 341m2/s2... and 0-3KM SHR 48kts/ SRH at 703m2/s2. One of the top SARS analogues is OKC on 5/3/99 FWIW.

4K NAM appears to be pretty over the top though with its LLVL wind fields compared to other guidance...  

 

How? All of the other models are showing very strong low level shear near the warm front with at least 400 m2/s2 0-3 km SRH if not higher.

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Sig changes on the new day 2 outlook with a pretty large enhanced risk area in IA/IL/IN and they mention a possible upgrade to moderate risk.

Just got back from work and am perusing this thread and some svr parameters.  Rinse, wash, repeat.  My cousin up Monon way is ready to cry uncle from a precip standpoint already.

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How? All of the other models are showing very strong low level shear near the warm front with at least 400 m2/s2 0-3 km SRH if not higher.

Im talking purely about the 0-1KM layer. The 4K NAM in this layer shows 300+ m2/s2 of 0-1KM SRH on numerous soundings and 30+ kts of 0-1KM SHR... Meanwhile the NAM and GFS show much less 0-1KM SRH closer to maybe 100m2/s2 maybe up to 200+ on  a few soundings, and 0-1KM SHR about 10-15+kts lower, and on a couple soundings both models may be somewhat closer to the 4K NAM, but overall across the board, they aren't. BUT as far as the 0-3KM  layer goes, i'd agree that they're all pretty close, and in good agreement. 

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Snippet from latest thinking this afternoon from LOT

 

PRECIP SHIELD APPEARS TO BE REMAINING SOUTHWEST OF THE FORECAST AREA
THRU WED MORNING...THEN AS THE INSTABILITY AXIS PIVOTS NORTHEAST WED
MIDDAY/AFTN...PRECIP WILL STEADILY RAMP UP. UNFORTUNATELY THE
DYNAMICS WITH THE SYSTEM WED NGT ARE RAMPING UP AS WELL. SREF BULK
SHEAR VALUES HAVE A HIGH CONFIDENCE OF EXCEEDING 40KT IN THE 0-6KM
LAYER...FORTUNATELY THE ML-CAPE AXIS SHOULD REMAIN POSITIONED WEST
OF THE FORECAST AREA. THE MOISTURE AXIS WILL BE LIFTING NORTH LATE
WED...WITH GUIDANCE POINTING TOWARDS PWAT NEARING 2" AND SETTING UP
ALONG AND SOUTH OF I-88. CURRENT PROJECTIONS ARE THAT SEVERE STORMS
ARE FAVORABLE TO DEVELOP WED EVE...AND COULD BE FOCUSED ALONG THE
FRONTAL BOUNDARY AS IT LIFTS NORTH. WITH THE BOUNDARY BECOMING
ORIENTED ALONG THE CENTRAL FORECAST AREA LATE WED/EARLY THUR...IT
APPEARS FAVORABLE THAT SEVERE STORMS MAY TRANSITION INTO A
HYDRO/FLOOD CONCERN. HAVE BEEN CONTEMPLATING JUST GOING WITH A FLASH
FLOOD WATCH FOR WED NGT/EARLY THUR...AS IT WILL FEED ACROSS AREAS
THAT HAVE ALREADY SEEN HEAVY RAINFALL AND RECENT FLOODING. A COMPLEX
OF STORMS WILL RIDE ALONG THE BOUNDARY WED NGT/THUR...WITH MOISTURE
STEADILY ADVECTING INTO THIS REGION FROM THE SOUTHWEST.

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00Z NAM sounding for KDTX valid at 00z (Im not sure why SHARPpy doesn't tag "NAM" on it, but its from the 00Z NAM) anyways...when you look at the soundings they aren't off by that much really.... Doesn't make much sense that the model output fields show nothing close to the amount of 0-1KM SRH such as in this initialized sounding and several others from around E MI, odd.

post-7962-0-94967500-1435088493_thumb.pn

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