tarheelwx Posted February 1, 2014 Share Posted February 1, 2014 There may not be many interested in this topic, but I find it really intriguing. It has to do with significant differences in temperature over relatively short distances. I moved to Colfax in 2001 and live 3.25 miles northwest of the Greensboro airport. I also live in a low spot, maybe 4' above a flat "plain" that has a medium sized stream in it. For all practical purposes, we are at the bottom of the plain. Over the last 12 years, I've been amazed at the difference in temps between here and GSO. About the most I ever see is 10 degrees colder. This past Thursday morning was a good example. GSO had a low of 7 while I hit minus 0.6. Here are some notes in general. temp difference in maximized with clear skies and near calm winds. WIthout both of these, the difference is nonexistence. Max temp difference in summer is maybe 2 degrees In winter before a storm moves in and maybe clouds come in late, we might get 4-6 degrees below GSO temps. Then the clouds move in and my temps slowly climb while GSO remains steady. Eventually, they more or less even out. Winds have a similar impact as clouds. If it is calm (and clear), we can quickly get colder. However, as soon as the wind starts to blow, the discrepancy dissapates. All others things remaining the same (no clouds, precip, etc.). Sometimes when clouds and precip move in quickly but with calm winds, there will still be a bit of a difference - maybe 2-3 degrees. But as soon as the atmosphere saturates, my temp is the same as GSO. I'm not sure where GSO temps are measured, but maybe it is impacted by the new, huge runway they put in 2-3 years ago. How has this impacted GSO's temps compared to the past? Is it fair to depict this as AGW? A few years ago, didn't CLT move thier reporting station? It seemed that for over 20 years, CLT was almost always warmer than GSO. Then, all of a sudden they started reporting cooler temps than GSO on a fairly regular basis. Not all the time, but maybe 20% of the time where before it was 5% of the time. Regardless, I noticed a marked shift. I'll wrap this up by asking if there are any case studies from NC that I can review. Also, does anyone know of someone doing research on this project? Thanks, TW Link to comment Share on other sites More sharing options...
jburns Posted February 1, 2014 Share Posted February 1, 2014 There may not be many interested in this topic, but I find it really intriguing. It has to do with significant differences in temperature over relatively short distances. I moved to Colfax in 2001 and live 3.25 miles northwest of the Greensboro airport. I also live in a low spot, maybe 4' above a flat "plain" that has a medium sized stream in it. For all practical purposes, we are at the bottom of the plain. Over the last 12 years, I've been amazed at the difference in temps between here and GSO. About the most I ever see is 10 degrees colder. This past Thursday morning was a good example. GSO had a low of 7 while I hit minus 0.6. Here are some notes in general. temp difference in maximized with clear skies and near calm winds. WIthout both of these, the difference is nonexistence. Max temp difference in summer is maybe 2 degrees In winter before a storm moves in and maybe clouds come in late, we might get 4-6 degrees below GSO temps. Then the clouds move in and my temps slowly climb while GSO remains steady. Eventually, they more or less even out. Winds have a similar impact as clouds. If it is calm (and clear), we can quickly get colder. However, as soon as the wind starts to blow, the discrepancy dissapates. All others things remaining the same (no clouds, precip, etc.). Sometimes when clouds and precip move in quickly but with calm winds, there will still be a bit of a difference - maybe 2-3 degrees. But as soon as the atmosphere saturates, my temp is the same as GSO. I'm not sure where GSO temps are measured, but maybe it is impacted by the new, huge runway they put in 2-3 years ago. How has this impacted GSO's temps compared to the past? Is it fair to depict this as AGW? A few years ago, didn't CLT move thier reporting station? It seemed that for over 20 years, CLT was almost always warmer than GSO. Then, all of a sudden they started reporting cooler temps than GSO on a fairly regular basis. Not all the time, but maybe 20% of the time where before it was 5% of the time. Regardless, I noticed a marked shift. I'll wrap this up by asking if there are any case studies from NC that I can review. Also, does anyone know of someone doing research on this project? Thanks, TW It all boils down to the simple fact, that left alone(no wind) cold air sinks. It happens all over. My yard is a hill down to a creek. On a clear calm night I can have a 5 or more degree difference from the top of my yard to the creek. Link to comment Share on other sites More sharing options...
tarheelwx Posted February 1, 2014 Author Share Posted February 1, 2014 It all boils down to the simple fact, that left alone(no wind) cold air sinks. It happens all over. My yard is a hill down to a creek. On a clear calm night I can have a 5 or more degree difference from the top of my yard to the creek. Sure. But why is there little or no difference when it is just cloudy? No wind at all but cloudy and the difference is little if any. TW Link to comment Share on other sites More sharing options...
jburns Posted February 1, 2014 Share Posted February 1, 2014 Sure. But why is there little or no difference when it is just cloudy? No wind at all but cloudy and the difference is little if any. TW Radiational cooling stops and things level out. Link to comment Share on other sites More sharing options...
tarheelwx Posted February 1, 2014 Author Share Posted February 1, 2014 I understand that radiational cooling stops, but atmospherically, what happens so that even though temps drop (slowly) with cloudy skies and no wind, there is no drainage of cold air. Why? Why isn't there any separation of colder air at the "bottom" and warmer air higher up? TW Link to comment Share on other sites More sharing options...
nchighcountrywx Posted February 1, 2014 Share Posted February 1, 2014 The Charlotte station is at the same spot at Charlotte Douglas that it has been for quite some years. The AWOS/ASOS site will give you the exact location. These microcilmates exist in quiet a few places in state and are most pronounced on clear calm cold nights. Down near my Dad lived in the coastal plain, there is a RAWS Obs station in the Holly Shelter Game Lands at Back Island in the sandy Angola Bay area. NWS ILM monitors and reports on this site and it has been observed to be as much as 20 degrees colder in ideal low humidity radiational cooling conditions. Link to comment Share on other sites More sharing options...
tarheelwx Posted February 1, 2014 Author Share Posted February 1, 2014 The Charlotte station is at the same spot at Charlotte Douglas that it has been for quite some years. The AWOS/ASOS site will give you the exact location. These microcilmates exist in quiet a few places in state and are most pronounced on clear calm cold nights. Down near my Dad lived in the coastal plain, there is a RAWS Obs station in the sandy Angola Bay area. NWS ILM monitors and reports on this site and it has been observed to be as much as 20 degrees colder in ideal low humidity radiational cooling conditions. 20 degrees sounds suspect. Wouldn't you expect more pronounced differences in varying terrain like the mountains as opposed to near Wilmington? TW Link to comment Share on other sites More sharing options...
jburns Posted February 1, 2014 Share Posted February 1, 2014 I understand that radiational cooling stops, but atmospherically, what happens so that even though temps drop (slowly) with cloudy skies and no wind, there is no drainage of cold air. Why? Why isn't there any separation of colder air at the "bottom" and warmer air higher up? TW Without radiational cooling there is not enough temp difference to make the air rise and sink. It just sits there. Link to comment Share on other sites More sharing options...
NavarreDon Posted February 1, 2014 Share Posted February 1, 2014 Mike Gold (poster in the Mnt. thread) is a part of this precip. project thru Duke. http://iphex.pratt.duke.edu/ Link to comment Share on other sites More sharing options...
downeastnc Posted February 1, 2014 Share Posted February 1, 2014 20 degrees sounds suspect. Wouldn't you expect more pronounced differences in varying terrain like the mountains as opposed to near Wilmington? TW Its legit that location is suspected of going below zero several times, we actually get huge ranges here, here n Greenville the airport is on the "low" sandy north side of the river and has a elevation of 25' most of Greenville is on the south side of the river and averages 50-80' ASL and the airport can be as much as 8-10 degrees colder on a good calm night than my home in south Greenville. When we go hunting our hunting club which is in far eastern Beaufort county can be 5-10 colder than the temp we had in Greenville 45 miles further inland . http://www.erh.noaa.gov/ilm/newnews/2008news/2008textproducts/morninglows_2008jan04.txt Or search this with Yahoo "low temperature near wilmington radiational cooling" and click on the PDF titles "extreme radiational coolng differences due to soil type".....I got a new PC and Windows 8 is kicking my ass Link to comment Share on other sites More sharing options...
tarheelwx Posted February 1, 2014 Author Share Posted February 1, 2014 Thanks Downeast. The NWS writeup was good. A few questions maybe you can answer. If there are 20 degree spreads when there is ideal radiational cooling, over how far of a distance do you have to go to see this? Are sites 2 miles apart, 10 miles apart, 25.........? Also, do you know how cold this spot was this past Thursday morning? How much spread is there in summer? Thanks TW Link to comment Share on other sites More sharing options...
isohume Posted February 1, 2014 Share Posted February 1, 2014 I understand that radiational cooling stops, but atmospherically, what happens so that even though temps drop (slowly) with cloudy skies and no wind, there is no drainage of cold air. Why? Why isn't there any separation of colder air at the "bottom" and warmer air higher up? TW There is...but on a smaller scale. The smaller the temp difference, the more the draining colder air is going to be blocked by relatively lower ridges within the landscape. Link to comment Share on other sites More sharing options...
downeastnc Posted February 1, 2014 Share Posted February 1, 2014 Thanks Downeast. The NWS writeup was good. A few questions maybe you can answer. If there are 20 degree spreads when there is ideal radiational cooling, over how far of a distance do you have to go to see this? Are sites 2 miles apart, 10 miles apart, 25.........? Also, do you know how cold this spot was this past Thursday morning? How much spread is there in summer? Thanks TW Going to work I have to go over the river, the hill down to the river is decent by our standards and the temps can go from 35 at the top of the hill to mid 20's at the bottom and its less than a mile. Link to comment Share on other sites More sharing options...
tarheelwx Posted February 1, 2014 Author Share Posted February 1, 2014 There is...but on a smaller scale. The smaller the temp difference, the more the draining colder air is going to be blocked by relatively lower ridges within the landscape. Regarding the fact that you have much less difference with cloudy skies vs clear skies have anything to do with how rapidly temps fall? Or maybe that with cloudy skies temp fall maybe 10-12 degrees vs clear skies they fall 20-30 degrees. Again, all this assume no wind, no precip, stationary air mass, etc. TW TW Link to comment Share on other sites More sharing options...
nchighcountrywx Posted February 1, 2014 Share Posted February 1, 2014 20 degrees sounds suspect. Wouldn't you expect more pronounced differences in varying terrain like the mountains as opposed to near Wilmington? TW Here in the mountains, the variances are almost always temperature inversions. The ridgeline are the first to cool off when cold air advects in and are also always the first to warm up when warm air advection sets in. Down on the coastal plain at the Back Island site: 20 degrees is common under ideal conditions in that area where the Back Island Obs station is located. Thanks to DowneastNC. He found the exact NWS write up that my Dad sent me in 2008. I noticed it years ago hunting down at Holly Shelter...an 10+ degree variance was common in the deer stands in that area before sunrise or after sunset. Here is the writeup: 00 NOUS42 KILM 042221 PNSILM PUBLIC INFORMATION STATEMENT NATIONAL WEATHER SERVICE WILMINGTON NC 521 PM EST FRI JAN 4 2008 ...COLDEST MINIMUM TEMPERATURES IN ALMOST 3 YEARS... THE COMBINATION OF A CLEAR SKY AND LIGHT WINDS PROVIDED IDEAL CONDITIONS FOR OPTIMAL COOLING LATE THURSDAY NIGHT AND EARLY FRIDAY MORNING. LOWS RANGED FROM THE LOWER TEENS TO MIDDLE TEENS INLAND... TO THE MIDDLE 20S CLOSE TO THE COAST. THE USUAL COLD SPOT IN OUR CWA...BACK ISLAND RAWS...GOT DOWN TO AT LEAST 5. FURTHER INVESTIGATION OF THIS SITE SHOWS THAT THE STATION WAS MISSING 6 HOURS OF DATA BETWEEN 2:18 AM...AND 9:18 AM. THIS WOULD LEAVE ONE TO BELIEVE THAT THIS STATION MAY HAVE GOTTEN COLDER THAN 5 DEGREES...AND PERHAPS APPROACHED 0. AS FAR AS RECORDS GO...NORTH MYRTLE BEACH BROKE THE OLD RECORD LOW OF 17 SET BACK IN 2001. IT WAS ALSO THE COLDEST LOW IN NORTH MYRTLE BEACH SINCE JANUARY 24TH 2003. THE MORNING LOWS OF 16 IN WILMINGTON AND FLORENCE WERE THE COLDEST LOWS SINCE JANUARY 24TH 2005. THE LOW OF 16 IN LUMBERTON WAS THE COLDEST SINCE DECEMBER 9TH 2006. AFTER THE COLD MINIMUM TEMPERATURES OF DECEMBER 18TH...MUCH DISCUSSION HAS COME UP IN THE OFFICE ABOUT THE ACCURACY OF THE BACK ISLAND RAWS SITE OVER THE PAST FEW WEEKS. BACK ON DECEMBER 18TH THE BACK ISLAND RAWS SITE REPORTED A MORNING LOW OF 8. THE BACK ISLAND SITE IS LOCATED IN PENDER COUNTY...TO THE EAST OF BURGAW IN THE HOLLY SHELTER GAME LAND. SINCE DECEMBER 18TH WE HAVE TAKEN A TRIP OUT TO THE SITE AND NOTHING APPEARED TO BE WRONG WITH THE SENSOR. IN ADDITION... CAREFUL OBSERVATION SHOWS THAT THE BACK ISLAND SITE IS DRAMATICALLY COOLER ONLY ON OPTIMAL RADIATIONAL COOLING NIGHTS. COLOR ENHANCED IR SATELLITE PICTURES FROM THIS MORNING DO SHOW A POCKET OF MUCH COOLER SURFACE TEMPERATURES IN EASTERN PENDER COUNTY...ACROSS THE HOLLY SHELTER GAME LAND. FURTHER INVESTIGATION INTO THIS INTERESTING AREA WILL BE DONE IN THE FUTURE. AT THIS JUNCTURE THE VALUES FROM THE BACK ISLAND RAWS SITE APPEAR TO BE ACCURATE. LOCATION MORNING LOW COMMENTS NORTH CAROLINA ...BLADEN COUNTY... BLADENBORO 12 MESONET ELIZABETHTOWN 3SW 12 COOP TURNBULL CREEK 12 RAWS EAST ARCADIA 2NE 13 COOP ELIZABETHTOWN AIRPORT 18 AWOS ...BRUNSWICK COUNTY... LONGWOOD 13 COOP SUPPLY 13 RAWS WINNABOW 14 MESONET SUNNY POINT 19 RAWS SOUTHPORT 21 AWOS SUNSET BEACH 25 CARO-COOPS BALD HEAD ISLAND 32 MESONET ...COLUMBUS COUNTY... WHITEVILLE 7NW 16 COOP WHITEVILLE 16 RAWS WHITEVILLE 16 AWOS ...NEW HANOVER COUNTY... WILMINGTON 16 ASOS (NWS WILMINGTON) WILMINGTON 16 MESONET (KINGS GRANT) WILMINGTON 19 MESONET (OGDEN) CAROLINA BEACH 23 MESONET MASONBORO ISLAND 23 NERRS WILMINGTON 23 MESONET (USGS LORAN STATION) WILMINGTON 23 MESONET (NC STATE PORTS) WRIGHTSVILLE BEACH 26 NOAA NATIONAL OCEAN SERVICE ...PENDER COUNTY... BACK ISLAND 5 RAWS (AT LEAST THIS COLD) BURGAW 4E 12 COOP MOORES CREEK NB 12 COOP SURF CITY 12 COOP TOPSAIL BEACH 24 MESONET HAMPSTEAD 26 MESONET (NEW TOPSAIL BEACH) Link to comment Share on other sites More sharing options...
isohume Posted February 2, 2014 Share Posted February 2, 2014 Regarding the fact that you have much less difference with cloudy skies vs clear skies have anything to do with how rapidly temps fall? Or maybe that with cloudy skies temp fall maybe 10-12 degrees vs clear skies they fall 20-30 degrees. Again, all this assume no wind, no precip, stationary air mass, etc. TW TW Yes that definitely has much to do with the rate of temperature falls under ideal conditions. On cloudy nights the radiating air is absorbed by the clouds and a percentage of radiation is reflected back to the surface, slowing the cooling process. On high RH nights...a very shallow inversion can trap enough moisture for fog or dew to form which release latent heat at the sfc. Link to comment Share on other sites More sharing options...
GaffneyPeach Posted February 2, 2014 Share Posted February 2, 2014 This thread is becoming one of my favorites. I have often wondered about the climate along the I-85 corridor. I used to believe that it was just a map reference, with regard to forecasts and such. I have watched for years as nearly every CAD system has been slowest to erode along (at least) the SC and GA portions of it. It is also a landing zone for down-sloping with NW winds and, in some cases, mixing issues when off-shore lows are at play, with regard to winter wx.Any thoughts or observations?A little research into this and, apparently, 85 was built along an old Native American trading route. It could be as simple as a "path of least resistance" for them and the weather. Link to comment Share on other sites More sharing options...
sctvman Posted February 2, 2014 Share Posted February 2, 2014 Charleston has several microclimates. The temperatures all depend on how close you are to the water. During the winter, nighttime lows are often 10 degrees warmer on Folly Beach than they are inland in Summerville, but the daytime highs are often 10 degrees or more colder. Today is an example. The water temperature is in the mid 40s in the ocean. About the coldest we get all year. Kiawah Island, Folly Beach and the areas right next to the ocean are barely in the lower 50s. You go just inland to James Island, we are 65. Goose Creek is 72 degrees. That's a 20 degree temperature difference in about 20 miles. Even on our hottest days there is a big difference. Summerville and North Charleston can be over 100 on the warmest days while Folly is in the 80s. Link to comment Share on other sites More sharing options...
tarheelwx Posted February 4, 2014 Author Share Posted February 4, 2014 Just curious about you mountain guys. How much spread in temp have you seen before over just a couple of miles? TW Link to comment Share on other sites More sharing options...
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