Howard Goldstein wrote:
In the following AFD snippet the forecasters uss a phrase "BETTER TD
GRAD IS FARTHER NORTH". Are they likely talking about a temp/dewpoint
gradient here or is there another kind of relevant TD gradient?
Thanks in advance for enlightening very much an amateur meteorologist
with questionable qualifications and dubious talent.

**********************
FXUS62 KTBW 260709
AFDTBW

WEST CENTRAL AND SOUTHWEST FLORIDA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAMPA BAY AREA - RUSKIN FL
205 AM EST WED NOV 26 2003

.CURRENTLY...SFC ANAL SHOWS LEADING EDGE OF FRONTAL BOUNDARY FROM
ABOUT PGD TO VRB. HOWEVER...BETTER TD GRAD IS FARTHER NORTH FROM
TPA TO MCO/ORL. BKN TO OVC LOW CLOUDS N OF TPA...AND SCT-BKN CLOUDS
CENT AND S FA. FOG IS STILL VERY PATCHY...BUT SUSPECT IT WILL GET A
LITTLE MORE WIDESPREAD...ESPEC TPA SOUTH WHERE CLOUDS ARE MORE
SCATTERED.

[...]


Generally, T (alone) is temperature and TD is dewpoint (alone). In
scientific notation it would be T with a subscript lowercase d.

Dewpoint gradient is an important front-locating parameter, and he is
mentioning the discrepancy between where the front has been shown, and
where a significant dewpoint gradient actually exists.

Howard,
You are correct. The "TD" mentioned in the AFD is the temperature/dewpoint
gradient. Its not listed in the NWS acronyms and abbreviations
(http://www.crh.noaa.gov/dtx/glossary/acronyms.htm) list, but that is what
is being referred to in this message.
Regards,
Declan


"Icebound" wrote in message
ogers.com...
Howard Goldstein wrote:
In the following AFD snippet the forecasters uss a phrase "BETTER TD
GRAD IS FARTHER NORTH". Are they likely talking about a temp/dewpoint
gradient here or is there another kind of relevant TD gradient?
Thanks in advance for enlightening very much an amateur meteorologist
with questionable qualifications and dubious talent.

**********************
FXUS62 KTBW 260709
AFDTBW

WEST CENTRAL AND SOUTHWEST FLORIDA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAMPA BAY AREA - RUSKIN FL
205 AM EST WED NOV 26 2003

.CURRENTLY...SFC ANAL SHOWS LEADING EDGE OF FRONTAL BOUNDARY FROM
ABOUT PGD TO VRB. HOWEVER...BETTER TD GRAD IS FARTHER NORTH FROM
TPA TO MCO/ORL. BKN TO OVC LOW CLOUDS N OF TPA...AND SCT-BKN CLOUDS
CENT AND S FA. FOG IS STILL VERY PATCHY...BUT SUSPECT IT WILL GET A
LITTLE MORE WIDESPREAD...ESPEC TPA SOUTH WHERE CLOUDS ARE MORE
SCATTERED.

[...]


Generally, T (alone) is temperature and TD is dewpoint (alone). In
scientific notation it would be T with a subscript lowercase d.

Dewpoint gradient is an important front-locating parameter, and he is
mentioning the discrepancy between where the front has been shown, and
where a significant dewpoint gradient actually exists.

On Thu, 27 Nov 2003 00:13:54 GMT,
Howard Goldstein , in
wrote:
+ Declan, Icebound, thanks for the explanations. I found the 1AM
+ surface analysis at
+ http://www.hpc.ncep.noaa.gov/sfc/lrgnamsfc06bw.gif but probably not
+ for much longer.

[0600Z 26 Nov 2003 surface analysis]

Ugh. Oh, that's ugly. A "front" wandering semi-aimlessly thru a ridge?
Oy. Messy situation, tho. Not well defined. Probably constrained by
continuity, too.

+ If the person who put the front there shouldn't have
+ then where did it belong? Was it enough it was labeled diffuse? Seems
+ the front is smack dab in the middle of a line that was fitted between
+ the temp/dewpoint=1 stations.

Actually, it looks like the analyst followed the 65F isodrosotherm.
Unless continuity called for it, I would have dropped that part of the
front in its entirety. I would not be surprised if it was dropped in
the next analysis.

I eyeballed in a 1018 isobar, and that provided -no- help whatsoever.

James
--
Consulting Minister for Consultants, DNRC
I can please only one person per day. Today is not your day. Tomorrow
isn't looking good, either.
I am BOFH. Resistance is futile. Your network will be assimilated.

On Fri, 28 Nov 2003 12:09:00 GMT,
Howard Goldstein , in
wrote:
+ On 27 Nov 2003 01:54:00 GMT, I R A Darth Aggie wrote:
+ : On Thu, 27 Nov 2003 00:13:54 GMT,
+ : Howard Goldstein , in
+ : wrote:
+ : + Declan, Icebound, thanks for the explanations. I found the 1AM
+ : + surface analysis at
+ : + http://www.hpc.ncep.noaa.gov/sfc/lrgnamsfc06bw.gif but probably not
+ : + for much longer.
+ :
+ : [0600Z 26 Nov 2003 surface analysis]
+ :
+ : Ugh. Oh, that's ugly. A "front" wandering semi-aimlessly thru a ridge?
+ : Oy. Messy situation, tho. Not well defined. Probably constrained by
+ : continuity, too.
+
+ Is that last element, i.e. preserving a feature through subsequent
+ analyses even when it's really tough to find, a common practice?

It's standard. On the time/space scales involved, the atmosphere can
be considered continuous. Things don't magically (dis)appear. In this
particular instance, you grabbed the analysis where they're in the
process of disapating the front out of the analyis.

+ I think I see (but with the proviso that I lack most qualifications to
+ render opinions here at all) a preference towards consistency would
+ make tons of sense for features with a lot of diurnal variation, and to
+ help smooth out stuff like sampling errors.

Or things like shift changes...

+ : Actually, it looks like the analyst followed the 65F
+ : isodrosotherm.
+
+ (Thank you for the new word)

It's one of my favorites... :-)

+ Could I have found the isodrosotherm contours plotted somewhere on
+ the HPC site or elsewhere? ISTR seeing
+ model outputs with isodrosotherms but not an analyses product.

You might. I'm not familiar with any surface analysis products
(outside of model analyses) that carry that analysis, tho.

+ A couple of articles back Icebound talked about dewpoint gradient as
+ useful for placing fronts.

Indeed. Fronts are the boundaries between air masses. Temperature and
moisture are two easily measured and analyzed characteristics of air
masses. Find where the temperatue and moisture characteristics change,
and you're well on your way to finding the front. Additional guides
are weather, changes in wind direction and speed, and the pressure
field. By definition, the front lies in a trough of pressure.

Keep in mind that the wind and pressure gradients are related.

+ I found an example of an isodrosotherm
+ contour plot here
+ http://ww2010.atmos.uiuc.edu/(Gh)/guides/maps/sfcobs/cntr/dros.rxml

Intriguing example. Easy enough to come up with the right answer, but
some gotcha's for the unwary. For instance, Green Bay is a gotcha.

+ Two graphics the page, the second one is confusing (to me) since it
+ overlays a red/blue line through the region of densest gradient. Are
+ they depicting a front there but in such a way they're not committing
+ to the type of front?

No, they're calling it a stationary front. The winds in the colder air
mass are parallel to the front, and it is the motion of the cold air
that determines whether you have warm, cold or stationary. Since the
winds are mostly parallel, the frontal boundary isn't moving a lot.

+ : I eyeballed in a 1018 isobar, and that provided -no- help whatsoever.
+
+ I really hate to ask such beginners questions. So much of this is
+ art.

In truth, it's experience. In this case, if I really needed to know
what was going on over the SE USA, I'd probably have analysed the
pressure field every 1 mb. But that also wouldn't be a standard
synoptic surface analysis, either.

And in this case, I doubt that would have helped a lot.

+ Are there any good printed materials a beginner might use to
+ help learn the process from those who've gone before so as to develop
+ one's own skills?

The USAF has a series of technical report/manuals addressing this
issue. I would be very surprised if you can't obtain them on the web
in PDF files. NWS should also have a technical library. Try googling
for them.

James
--
Consulting Minister for Consultants, DNRC
I can please only one person per day. Today is not your day. Tomorrow
isn't looking good, either.
I am BOFH. Resistance is futile. Your network will be assimilated.

On 29 Nov 2003 00:28:34 GMT, (I R A Darth
Aggie) wrote:

On Fri, 28 Nov 2003 12:09:00 GMT,
Howard Goldstein , in
wrote:
+ On 27 Nov 2003 01:54:00 GMT, I R A Darth Aggie wrote:
+ : On Thu, 27 Nov 2003 00:13:54 GMT,
+ : Howard Goldstein , in
+ : wrote:
+ : + Declan, Icebound, thanks for the explanations. I found the 1AM
+ : + surface analysis at
+ : + http://www.hpc.ncep.noaa.gov/sfc/lrgnamsfc06bw.gif but probably not
+ : + for much longer.
+ :
+ : [0600Z 26 Nov 2003 surface analysis]
+ :
+ : Ugh. Oh, that's ugly. A "front" wandering semi-aimlessly thru a ridge?
+ : Oy. Messy situation, tho. Not well defined. Probably constrained by
+ : continuity, too.
+
+ Is that last element, i.e. preserving a feature through subsequent
+ analyses even when it's really tough to find, a common practice?

I had looked at a satellite animation and it appeared to me that the
front probably should have been drawn out to the east.
snip/snip
In truth, it's experience. In this case, if I really needed to know
what was going on over the SE USA, I'd probably have analysed the
pressure field every 1 mb. But that also wouldn't be a standard
synoptic surface analysis, either.

And in this case, I doubt that would have helped a lot.

+ Are there any good printed materials a beginner might use to
+ help learn the process from those who've gone before so as to develop
+ one's own skills?

The USAF has a series of technical report/manuals addressing this
issue. I would be very surprised if you can't obtain them on the web
in PDF files. NWS should also have a technical library. Try googling
for them.

James

One item - Weather Station Operations has a section on "Depiction"
http://www.e-publishing.af.mil/pubfi...fman15-125.pdf

Some other tech manuals/reports at
http://wx.erau.edu/reference/

Many should be available at the Air Force Combat Climatology Center
http://www.afccc.af.mil/
because they are releasable to the public but I haven't tried.

Jim

Howard,
Check out the mesoanalysis graphics at:
http://www.srh.noaa.gov/mlb/ldis/ldis_realtime_top.htm
Declan


"Jim" wrote in message
news.com...
On 29 Nov 2003 00:28:34 GMT, (I R A Darth
Aggie) wrote:

On Fri, 28 Nov 2003 12:09:00 GMT,
Howard Goldstein , in
wrote:
+ On 27 Nov 2003 01:54:00 GMT, I R A Darth Aggie
wrote:
+ : On Thu, 27 Nov 2003 00:13:54 GMT,
+ : Howard Goldstein , in
+ : wrote:
+ : + Declan, Icebound, thanks for the explanations. I found the 1AM
+ : + surface analysis at
+ : + http://www.hpc.ncep.noaa.gov/sfc/lrgnamsfc06bw.gif but
probably not
+ : + for much longer.
+ :
+ : [0600Z 26 Nov 2003 surface analysis]
+ :
+ : Ugh. Oh, that's ugly. A "front" wandering semi-aimlessly thru a
ridge?
+ : Oy. Messy situation, tho. Not well defined. Probably constrained
by
+ : continuity, too.
+
+ Is that last element, i.e. preserving a feature through subsequent
+ analyses even when it's really tough to find, a common practice?

I had looked at a satellite animation and it appeared to me that the
front probably should have been drawn out to the east.
snip/snip
In truth, it's experience. In this case, if I really needed to know
what was going on over the SE USA, I'd probably have analysed the
pressure field every 1 mb. But that also wouldn't be a standard
synoptic surface analysis, either.

And in this case, I doubt that would have helped a lot.

+ Are there any good printed materials a beginner might use to
+ help learn the process from those who've gone before so as to develop
+ one's own skills?

The USAF has a series of technical report/manuals addressing this
issue. I would be very surprised if you can't obtain them on the web
in PDF files. NWS should also have a technical library. Try googling
for them.

James

One item - Weather Station Operations has a section on "Depiction"
http://www.e-publishing.af.mil/pubfi...fman15-125.pdf

Some other tech manuals/reports at
http://wx.erau.edu/reference/

Many should be available at the Air Force Combat Climatology Center
http://www.afccc.af.mil/
because they are releasable to the public but I haven't tried.

Jim

On Sun, 07 Dec 2003 12:24:36 GMT,
Howard Goldstein , in
wrote:

+ Awesome. These products seem to have everything quantitative one
+ needs for short term stuff.

Indeed. Of course, that's the purpose.

+ Is the nws deploying ldis everywhere?

Doesn't look like it (yet). Looks like a joint project between
Melbourne and Houston NWS space flight meteorology group.

+ Would you recommend I attempt to get a comfortable and more complete
+ grasp of analysis methodology (awkward working, distilling
+ observations into airmass and frontal boundary classifications) first
+ before trying to hone my forecasting skills?

It's hard to prognosticate the future if you don't know what the
present is, and what the past was.

James
--
Consulting Minister for Consultants, DNRC
I can please only one person per day. Today is not your day. Tomorrow
isn't looking good, either.
I am BOFH. Resistance is futile. Your network will be assimilated.