[NLRS] 2m enhancement from EN24

Tue Jul 11 22:00:42 EDT 2017

This morning my bedroom scanner couldn't hear the local NWS weather 
radio station at about 20 miles due to strong signals from Sheldon or 
Carroll more than 100 miles so there was enhancement here today. The 
enhancement did vary.

73, Jerry, K0CQ

On 7/11/2017 8:50 PM, Dr. Gerald N. Johnson wrote:
>
>
> Weather fronts like we have had the last couple days are often very
> effective at enhancing VHF and microwave propagation. Often there is
> warm air over running cold air and that reverses the normal temperature
> gradient and causes a great deal more refraction. And can trap signals
> to propagate in the front as if in a waveguide.
>
> I saw a strong example of that one Sunday I think about 1976. My TV in
> the kitchen was seeing a Milwaukee WI UHF TV station with just a single
> telecoping rod antenna. That was from a mile south of Gilbert Iowa,
> probably a distance of 300 miles. A strong front that in a short while
> created a super cell and a tornado on the ground a mile in diameter
> located south of Ogden Iowa about 20 miles from Gilbert but visible from
> my back porch. That tornado dissipated and another formed near the tiny
> town of Jordon. The Jordon tornado was also a mile wide and rotating
> reversed to normal tornadoes. Jordon was about 5 miles south and 8 miles
> west of my house. The tornado passed about two miles west of me,
> dropping a side funnel that broke up after draining the Gilbert sewage
> lagoon. It dropped debris about 200 yards from my house. There was
> another side funnel that I didn't see that went past my house about 3/8
> mile east that did damage. The main funnel sometimes lifted over houses
> but in fields it looked like the field had been graded with a mile wide
> grader blade. It went on NNE and lifted up at Story City, damaging the
> tall enclosed tower at the fire department where they dried hoses.
>
> The radio noise from that thunderhead was so great that the county
> deputies couldn't hear their dispatcher in Nevade about 12 miles SE of
> Gilbert. After the funnels had moved on I went into Gilbert to WB0BQV's
> house where he had his generator running and had been supplied a county
> sheriff's radio for such emergencies by the local civil defense
> director. We relayed for the dispatcher for a while, then as the storm
> moved on we learned that the mutual aid radio at the hospital in Story
> City wasn't working so we went to see what was wrong. We climbed up to
> the roof and found 18" of water on the flat roof. The tornado had
> dropped a bunch of tree leaves that blocked the drains. And it had blown
> over the antenna. While Dave fixed the antenna I took off my shoes and
> rolled up my pant legs and waded to the drain and cleaned off the
> leaves. That was a lot of weight on that roof.
>
> The amazing thing for the afternoon that there was only one injury in
> the miles the big funnels were on or close to the ground, an arm broken
> by a falling limb in Story City.
>
> Lots of effects along that front. Contents from some of the damaged farm
> house like books and checks were found 80 or 90 miles NE in a day or
> two.The little town of Jordon is mostly a memory now, most of it was
> blown down by the tornado.
>
> Another very good creator of long VHF and up propagation can be a
> stationary high pressure dome. I've worked 1296 from Gilbert to Dallas
> Texas with 2.35 watts and to Houston on 432 with 100 watts while under
> such a stationary high pressure dome. It also causes a wide area
> temperature inversion preserved by calm winds.
>
> A calm cloudless morning without any other weather features often shows
> enhanced propagation due to a temperture inversion. The inversion is
> cured by breezes mixing the lower atmosphere. The inversion is caused by
> radiant cooling (on a clear night) of the earth's surface often
> significantlly cooler than the air at the NWS standard elevation of 6
> feet. I have software running for decades now at weather.net that
> compares cloud temperature to surface temperature to tell clouds from
> cooled ground and uses the clouds as a mask for radar to mask out odd
> propagation (Anomalous Propagation) echoes. In use its been found that
> the satellite temperature data threshold has to be set as much as 15
> degrees fahrenheit below the official observation dew point sometimes to
> keep from judging the radiant cooled earth surface as a cloud.
> Especially on a calm clear night.
>
> 73, Jerry, K0CQ
>
> On 7/10/2017 8:26 PM, Mary Brown wrote:
>>
>>
>> WD9BGA/b(EN53, 144.296ish) is 5x6 and N0LL/b(EM09, 144.294ish) is 5x2
>> into
>> EN24, as the sun sets conditions may improve with this still air.
>>
>>
>>
>> Mary
>>
>> W0AAT
>>
>>
>>
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