Chad’s WLFI Weather Blog

Updates

July 26th, 2014 at 7:25 pm by under Chad's WLFI Weather Blog

9:30 p.m.

Storms have exited.  Winds gusted 30-45 mph in our eastern/southeastern counties.

This bowing line of storms has not reached derecho status.

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8:15 p.m.

Mesoscale analysis still show considerable CINH (surface capping) that storms are fighting.  So, storms are still a bit elevated.  Downstream of the line, temperatures are 75-80 with dew points of 70-75.

Winds may gust to 50 mph with line moving northeastward through Tippecanoe, Clinton & Montgomery counties.

Tyler reported gust of 50 mph at West Lafayette golf course & witnessed 2″ diameter limb coming down.

Thorntown united just gusted to 51 mph.

Jamestown INDOT unit just reported sustained winds at 30 mph & gust to 41 mph.

I-65 & 28 INDOT unit is reporting sustained winds at 25 mph.

Estimated gust of 40-45 mph southwest of West Lafayette.

WLFI gusted to 40 mph, Purdue Airport 38 mph.

No warnings in effect as of 8:18 p.m.

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8 p.m.

It is a pretty ragged comma head with main organized bow of storms in southern Indiana & southeastern Illinois.

Severe T’Storm Warning in effect for southern Montgomery County.

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MEASURED T’STORM GUSTS:

M35 mph  Covington

M35 mph  Attica

M36 mph  Crawfordsville

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7:25 p.m.

Gusts of 60 mph have been reported from Vermilion County, Illinois (south of Danville).  Trees & large limbs are reportedly down in Urbana, Illinois.

Downtown Danville gusted to 41 mph.

Severe T’Storm Warning for southern Fountain & central & southern Montgomery counties until 8 p.m.  Gusts to 60 mph are possible.

T’Storm Watch is in effect until 2 a.m., but it will likely only last until 10 p.m. in our area.

+2″/hour rainfall rates are likely.

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6:37 P.M. Update

July 26th, 2014 at 6:36 pm by under Chad's WLFI Weather Blog

Storms are becoming surface-based as MCV & widespread storms erode capping in east-central Illinois.  However, much of the viewing area is still very much capped near the surface.

The storms have reportedly broken large limbs off trees in Coles & DeWitt counties in east-central Illinois.

Thinking T’Storm Watch likely soon, given environment downstream (especially if cap erodes).

Again, even if we do not get bow/derecho apex, comma head may still produce widespread damaging straight-line winds over part of our area given potential of the cap to erode away with approach of the storms.

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5:30 P.M. Update

July 26th, 2014 at 5:29 pm by under Chad's WLFI Weather Blog

Strong cap continues over area with stratus deck trapped beneath.  Cap is such that even strong winds only 2500′ above surface cannot mix down, so winds are quite light.

It is warm & muggy, however.  As of 5:30 p.m., temperature is 82 at WLFI with a dew point of 74.  There is quite a reservoir of CAPE (energy) above cap & some below it.

Bow of strong in comma head of MCV have blow up in central Illinois, but they are a bit elevated above capping issue.  It has been hard to get severe gusts to the ground, since they are rather elevated above the capping inversion.  Thinking that MCV would be strong enough to completely eliminate cap & completely access 5000-6000 J/kg of surface CAPE.

Think of the storms as a person at a restaurant buffet & you are really hungry.  The good fried chicken & mashed potatoes are underneath glass in the buffet & not accessible.  However, above the glass there are lots of rolls & salad to eat.  That’s good, but that not the really good stuff to fill you up.  Caps near the surface do the same thing with storms.  You want it gone, so the storms will completely root near the surface & have access to all CAPE & all dynamics, rather than rooting above the good, good stuff.

Or think of a clay soil with a hard pan.  The plant roots grow atop the hardpan & cannot penetrate it.  They wilt with water & nutrition deficiencies despite rich soil & moisture being underneath hardpan (fragipan).

It is also heard to get intense wind gusts to the ground with inversion to have to deal with, though the wind may be very strong even at 1500′.

Should the cap completely erode & these wind fields/shear continue to increase then our projected derecho will definitely develop.  It has what it needs to become a long-lived, damaging wind event, if you take away the strong cap near the surface.

With upper 70s dew points approaching, torrential +2″ per hour rainfall rates are possible.

Regardless, storms with wind & heavy rainfall threat will arrive this evening in the 7-10 p.m. time frame.

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3:15 P.M. Update

July 26th, 2014 at 3:25 pm by under Chad's WLFI Weather Blog

Temperatures are now 98 at St. Louis & as far northeast as Champaign, Illinois they are in the mid 80s.  Upper 70s dew point are pushing northward from Arkansas, southeast Missouri, southern Illinois to as far north as Springfield & Champaign.  It is highly unstable in this region with surface CAPE approaching 5000 J/kg in places.

Here, low stratus is trapped under strong cap, though stratus has eroded some in our northern counties.  At WLFI, it is 79 with a muggy dew point of 73, while Morocco is now 82 with a dew point of 72.

MCV with developing t’storms is now in western Illinois & will serve as impetus for storms to blow up into derecho over next few hours.  Meanwhile, along warm front, glancing southeastern Ontario shortwave, substantial deep-layer shear & sun has popped supercells with large hail in northeastern Indiana & northwestern Ohio.  Watch is likely for that area soon.

Here, we will watch Illinois.  Even with our low stratus, it is very hot & unstable in Illinois.  That, with holes in our stratus should allow severe storms to form & then go linear with largely a wind threat.  Again, if they are discrete longer, then large hail may be an issue.  Isolated tornadoes cannot be ruled out & even if man apex of bow is south of us, comma head will still bring severe weather.

7-10 p.m. time frame seems reasonable, given fact that MCV is now coming into western Illinois.

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1:22 P.M. Update

July 26th, 2014 at 1:23 pm by under Chad's WLFI Weather Blog

Low stratus deck trapped under inversion or cap is complicating forecast.  As of 1:15 p.m., it is 77 with a dew point of 71 at WLFI.  Around 1500 J/kg of surface CAPE is found across the viewing area.  However, up to 3500 J/kg of CAPE are found above the cap or lid (stratus).

Where the sun is out in west-central Illinois, up to 4500 J/kg of surface CAPE exists & sun in our southwestern counties is pushing surface CAPE values to nearly 3000 J/kg.  St. Louis was 92 at 12:54 p.m.!  Central Illinois is rising into the upper 80s with dew points in the 70s.  Dew point at Springfield is 76!

All this said, forecasts are being based on the temperatures getting well into the 80s to near 90 today & we are not warming up as much due to stratus deck.

Regardless, severe storms are approaching western Iowa & have been going strong since South Dakota.  New t’storms are forming on remnant circulation (MCV) from storms yesterday in the western High Plains.

Shear/wind fields still look good for derecho/severe this evening-night.  Sun coming out would make severe event/outbreak forecast more concrete, but the CAPE & approaching stronger wind fields aloft are pretty  impressive west of here.

Though main apex of expected bow may be just south of our area, again, the comma head may get a chunk of the area with widespread wind/isolated tornadoes.

Again, if storms remain more discrete for a longer period of time, large hail threat will be higher.

This is a complete now-casting situation.  This stratus deck needs to be monitored, as does the stronger wind fields aloft approaching, high surface CAPE to the west, evolution of storms coming into Iowa, then developing storms in Missouri & whatever might start to pop in Illinois.

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9:50 A.M. Update

July 26th, 2014 at 9:58 am by under Chad's WLFI Weather Blog

Scattered showers & storms are in the process of exiting the viewing area as of 9:50 a.m.  These should weaken pretty rapidly to our southeast over the next 1-2 hours as low-level jet weakens and veers.

Isolated hail of 0.25-1″ diameter occurred with 1″  hail reported at Covington, 0.50″ hail at Kingman & 0.75″ near Waveland and 0.50″ hail south of Waynetown.

The 0.02″ of rainfall at WLFI is the first measurable amount of rainfall since July 14.

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Supercells will blow up likely in Iowa, Illinois & Missouri this afternoon with large hail (some to 3.00″ diameter), wind & a few tornadoes.  However, thinking these will go linear relatively quickly & form derecho that will race east/southeastward & pass in the 7-10 p.m. time frame.  This would cause the main threat to shift to widespread damaging straight-line winds.  However, looking at the speed shear, even with complete linear situation, a few isolated tornadoes/gustnadoes cannot be ruled out.

Torrential rainfall of up to +2″ an hour is possible.

Timing still looks to be generally 7-10 p.m.

Two potentially blurry elements are in the equation:

1.  If storms do not go linear as quickly, then our large hail risk will go up & threat of a couple of tornadoes will exist.

2.  Some models indicate the main bow of derecho hitting areas south of us from Terre Haute to Indianapolis, southward to Vincennes, Bloomington.  Although this is not out of the question, the comma head of it would still pivot through at least part of our area with a widespread damaging straight-line wind isolated tornado threat.

 


Saturday Evening/Night Derecho

July 25th, 2014 at 11:25 pm by under Chad's WLFI Weather Blog

Potential derecho is still there Saturday evening-night.  It looks to pass 7-10 p.m. with widespread, damaging straight-line wind threat.

Wind fields, shear & surface instability all point to severe weather outbreak with wind.

It will likely take on a backwards “C” shape with a comma head as it matures with passage over area.


Scattered Showers/Storms Later Tonight-Saturday Morning……..Isolated Hail Possible

July 25th, 2014 at 9:46 pm by under Chad's WLFI Weather Blog

Scattered showers & t’storms will develop after midnight west of our area, then will move in overnight-early Saturday morning as lift increases north of the warm front. 

Some storms may produce large hail in eastern Iowa, southern Wisconsin & northern Illinois, given the 4000-6000 J/kg of surface CAPE being thrusted up & over more stable layer in this region.

Low-level jet (strong winds at 5,000′ racing north & northeast from the Gulf area) will advect or push higher elevated CAPE values up & over warm front & stable layer nearer to ground into our area overnight-early morning.  Current elevated CAPE values are as high as 500 J/kg in our area (ZERO surface CAPE….. it is cool & stable in the lower levels……the CAPE for storm will need to be pushed in).  However, models show up to 2500 J/kg of elevated CAPE by 6 a.m.

That said, 40-45% coverage of storms looks good & I do feel the need to insert an isolated hail wording, perhaps marginally severe, given such a thrust of CAPE into a colder zone aloft.

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Derecho Looking Increasingly Likely Saturday Evening/Night

July 25th, 2014 at 6:25 pm by under Chad's WLFI Weather Blog

With up to 5000 J/kg of surface CAPE projected over area & up to 65 kt. flow at 500 mb & 700 mb.  Even at just 925 mb, flow is up to 45 kts.  All levels have strong winds from 2500′ to 50,000′.  Flow is unidirectional with strong speed shear.

Deep layer shear

This is very favorable with a substantial to significant derecho with some gusts exceeding 75 mph.

In terms of timing, it would be after 6 p.m.  & before 12 a.m.  Hourly timing will be lined out with 00z run coming out by 10:30 p.m.

Stay tuned for updates.

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Another Record Low at the Ag Farm! Coolest July Since 2009…..Will Rank Up As One of the Top 10 Coolest Since 1887

July 25th, 2014 at 3:30 pm by under Chad's WLFI Weather Blog

The temperature dropped to 50 (49.6) at WLFI this morning & 51 at the airport, but the Purdue Ag Farm reached 47!

This breaks the record low of 50 set in 1909 & marks the second record low this month.  The low of 48 on July 17 broke the old record of 49 set in 1985 at the Ag Farm.

We have gone from pretty typical cool spell in mid-July to more unusual month with multiple cool spells & now two daily record low temperatures.

We are also reaching a threshold where this will likely make this one of the top 10 coolest Julys on record, dating back to 1887.  It will likely be the coolest since 2009.

If we have another record low temperature next week, it would mark the first time we have officially had 3 record low temperatures in July since 1988.

Oddly, 1988 was an extremely hot, dry summer, but the first 3 days of July saw record cool temperatures, including a 43, which is only one degree shy of the all-time record July low of 42 (set on two days in 1972).

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