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Dense Fog
12-29-2004, 11:37 PM
Post: #1
Dense Fog
I've been looking for some guidance on how to predict dense fog. Can anyone tell me exactly what circumstances to look for that will generate dense fog and in which model products I can find these readings. I’m assuming it’s more complicated than just looking at the temperature & dew point.

Thanks guys,

Greg
http://webpages.charter.net/littleton/
:guitar
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12-30-2004, 01:34 PM
Post: #2
Dense Fog
IL_Greg Wrote:I've been looking for some guidance on how to predict dense fog. Can anyone tell me exactly what circumstances to look for that will generate dense fog and in which model products I can find these readings. I’m assuming it’s more complicated than just looking at the temperature & dew point.

Thanks guys,

Fog formation is a natural phenomenon that occurs when there is calm wind, high humidity and inversion. Fog generally tends to occur in winter when the heat of the sun is not sufficient to vaporize the fog and lift it. When the ground temperature is much lower in relation to the air temperature, moisture levels are between 60 to 70 per cent and absence of any air movement leads to formation of fog. Air pollution helps in making the fog dense. At times the fog is so thick that it leads to low or zero visibility.
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You might also find this abstract interesting:
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http://137.248.191.94/cost/Nat_Rep_Hungary.pdf
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12-30-2004, 01:58 PM (This post was last modified: 12-30-2004 06:55 PM by Jason234.)
Post: #3
Dense Fog
If you want to see fog go to San Fran in Cali'!!! Beautiful place but get's wicked cold and windy in a flash. I have a picture that my bro' took, an amazing photographer- and it is breath-taking! One day, when we were leaving the hotel (The Radicand) there was 30-40 mph winds coming from the ocean with fog galore, one of the reasons they employed the trolley believe it or not. I urge anyone to go, besides it never actually rains (IN THE SUMMER)-but remember, bring the parka and head out to pier 21!
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12-30-2004, 05:03 PM
Post: #4
Dense Fog
It "NEVER" rains in San Francisco? It's raining there NOW...take a look at ESPN2...they're playing the Emerald Bowl in 3COM Park...and it's raining there... Also, check out the 7 day forecast:

http://www.srh.noaa.gov/data/forecasts/C...+Francisco
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12-30-2004, 06:13 PM
Post: #5
Dense Fog
[Image: rno+bgwv.gif]

FLOOD STATEMENT
NATIONAL WEATHER SERVICE SAN FRANCISCO CA
300 PM PST THU DEC 30 2004

...URBAN AND SMALL STREAM FLOOD ADVISORY WILL CONTINUE UNTIL 800 PM
THIS EVENING FOR MARIN COUNTY AND THE GREATER SAN FRANCISCO AND
MONTEREY BAY AREAS...

THE NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA IS CONTINUING
THE URBAN AND SMALL STREAM FLOOD ADVISORY INTO THIS EVENING. AREAS OF MODERATE TO HEAVY RAIN WILL CONTINUE TO MOVE ONSHORE WITH SATELLITE IMAGERY SHOWING CONTINUED ENHANCEMENT OF CLOUDS AHEAD OF A DEVELOPING LOW CENTER SEVERAL HUNDRED MILES WEST OF SAN FRANCISCO. THE GROUND IS SATURATED AND ADDITIONAL RUNOFF CAN BE EXPECTED. THIS MAY CAUSE SMALL STREAMS AND CREEKS TO REACH BANKFULL AND LOW LYING AREAS SUCH AS UNDERPASSES TO TEMPORARILY BECOME FLOODED.

PERSONS IN MARIN...SAN FRANCISCO...ALAMEDA...CONTRA COSTA...SAN
MATEO...SANTA CLARA...SANTA CRUZ...MONTEREY...AND SAN BENITO COUNTIES SHOULD CLOSELY MONITOR STREAMS AND CREEKS. NEVER DRIVE INTO FLOODED INTERSECTIONS...UNDERPASSES OR AREAS WHERE WATER COVERS THE ROADWAYS. SLOW DOWN WHILE DRIVING AS PONDING ON ROADWAYS WILL CAUSE A LOSS OF TRACTION.
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12-31-2004, 12:57 PM
Post: #6
Dense Fog
I shot Joe Bastardi a email about this and here it is...


"Fog is a very tough thing to forecast. When I go to forecast it I first look at the things that will prevent. Doctor Joel Myers had a theory that when wind averages over for the entire time the sun is up, Fog will not form because there will be enough build up of static electricity on outdoor objects to inhibit fog formation. His education is much more advanced than mine ( B.S. vs PHD) so I am not sure of the physical process that is involved exactly, but with the exception of deep river valleys, that rule has been golden for me.

But obviously he lack of anything to disperse moisture over in an already moist field that has a chance to cool to the dewpoint is important for calm night fog. I say calm night fog, for there is no such thing as "radiation fog" It is all a function of mixing as there is no change in incoming or outgoing radiation due to wind, there is a change in the amount of mixing, and well mixed air on a clear night is night likely to form fog.

As far as advection fog, that is when higher dewpoint air moves over a colder surface capable of cooling the air to the saturation point from below. Very stable soundings are the common denominator in both cases.

One of the more amusing fog stories I have heard is from my Dad. Though one of the great forecasters I have ever met, Dad was involved with obs and research development at Atlantic City back in the 60s. His branch was instrumental in wind shear and fog studies. There were several nights when he was called out with his branch to ride to other eastern airports to measure fog. In one case, it never showed up. In another case a front swept through as they arrived. I guess Fog at Atlantic City was different from Fog elsewhere. In any case it made for amusing stories years later, though I dont think at the time the people getting up for nothing were amused. But it shows the difficulty involved in predicting this ( for instance, sudden mixing at sunrise and fog development then) in what normally will occur in the simplest of weather patterns, and yet how important it is for the disruption it can cause." FROM ACCUWEATHER.COM Joe Bastardi

Hope that helps!
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12-31-2004, 06:53 PM
Post: #7
Dense Fog
Thanks guys, appreciate the help. I’ve always been interested in what the weather was doing but I only recently got into trying to learn the art of forecasting. I thought I was doing pretty well until I woke up one morning to some dense fog and thought, “crap, I didn’t think of this!”

Thanks again,

Greg
http://webpages.charter.net/littleton/
:guitar
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01-02-2005, 12:27 PM
Post: #8
Dense Fog
No problem
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01-02-2005, 09:42 PM
Post: #9
Dense Fog
IL G...yer welcome...BTW, it's still raining in SF...:icon_twis
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01-03-2005, 04:01 PM
Post: #10
Dense Fog
happy bday li phil
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