How is surface pressure extrapolated? / Recon obs question.

[Chris_in_Tampa]

I have a question about the following HDOB from yesterday. Note the area in bold:

URNT15 KNHC 021653
AF303 02DDA INVEST HDOB 02 20070802
164600 1229N 06745W 9842 00238 0113 +239 +231 012009 009 004 008 00
164630 1227N 06745W 9840 00240 0113 +240 +230 019008 009 002 008 00
164700 1225N 06746W 9843 00238 0113 +240 +229 018009 010 002 009 00
164730 1224N 06746W 9840 00241 0113 +240 +230 024010 011 001 009 00
164800 1222N 06746W 9843 00237 0113 +240 +233 027011 011 001 009 00
164830 1221N 06747W 9840 00239 9990 +240 +999 028011 012 001 009 01
164900 1219N 06747W 9842 00238 9990 +240 +999 031011 011 003 009 01
164930 1217N 06747W 9841 00239 9990 +240 +999 031011 011 002 009 01
165000 1216N 06748W 9841 00239 9990 +240 +999 030010 011 003 008 01
165030 1214N 06748W 9841 00239 9990 +240 +999 029010 011 002 009 01
165100 1212N 06748W 9842 00238 0113 +240 +236 032011 012 000 010 00
165130 1211N 06749W 9843 00238 0113 +240 +235 033011 012 003 008 00
165200 1209N 06749W 9841 00239 0113 +240 +236 035011 012 004 008 00
165230 1208N 06749W 9841 00238 0112 +240 +233 039011 011 002 009 00
165300 1206N 06750W 9840 00240 0112 +240 +235 043011 011 005 008 00
165330 1204N 06750W 9841 00237 0112 +240 +230 042011 011 001 009 00
165400 1203N 06750W 9841 00238 0113 +240 +230 038010 010 000 009 00
165430 1201N 06751W 9841 00239 0112 +240 +230 037010 011 002 009 00
165500 1200N 06751W 9844 00236 0112 +240 +229 036009 009 000 010 00
165530 1158N 06752W 9840 00238 0112 +240 +231 036009 009 000 009 00

The section in bold of this recon observation noted that either the air or dew point temperature was suspect. The dew point was probably the only value that may have been suspect since it read as 99.9 degrees Celsius. But during this time the pressure read as 999.0mb.

Now, I know certain parts of the recon observation use 999 values to note that data is missing, but NHOP (http://www.ofcm.gov/nhop/07/nhop07.htm) and the NHC's page about the new format (http://www.nhc.noaa.gov/abouthdobs_2007.shtml) does not mention that this will happen with the dew point or the extrapolated surface pressure.

Can someone tell me if the dew point relates to calculating the extrapolated surface pressure? If the dew point on the aircraft is suspect, should the extrapolated surface pressure be considered suspect? And if there is a relationship, does anyone know if that means the 999 can be considered as a missing value rather than as actually measured, but should be treated as suspect because the air/dew point was suspect.

Despite being in the recon decoding material, if 999 is used as the air temp or dew point, should I consider that the value was in fact missing for those? Obviously, I know it is wrong, but rather than having a real value that seems in line that is suspect, perhaps I should further conclude that the dew point was missing and not that it was measured at 99.9 degrees Celsius and should be considered suspect.

The extrapolated surface pressure is different. 999.0 mb is a possible reading. So if it appears, could it in some cases be what I should consider as a missing value? How would I know? Certainly it should be treated as suspect based on the observations around it in the above HDOB, but there is no specific flag that says it is officially suspect unless the extrapolated surface pressure is used in its calculation.

I suppose this leads me to the question...

How is surface pressure extrapolated?

Thanks for any help.

[pojo]

Its missing data... that's how we notify CARCAH of missing information....I'll check on this when I get back from Leave.

[Chris_in_Tampa]

Thanks. I figured that might be how the temperatures are recorded as missing. I guess I'll have to consider that the pressure might be missing sometimes when reported with 9990.