0z GFS VERY intresting

[jasons2k]

We got a trace of rain with some lightning and thunder here tonight. Wasn't expected, so it was a pleasant surprise. Hopefully we'll get more in few days.

Yep, looks like the line formed almost on top of you as it moved east. It's frustrating; happens a lot in the Metroplex. Hopefully you'll get some decent rain up there with the upcoming system.

[ETXHAMXYL]

My County (Henderson) is under a Tornado Watch until 2am. Wow Tornados in Jan. ONly in Texas...LOL Well if rains I don't mind a little wind with my rain.
Boy I remember wishing for Snow in JAn. Now I'm just wishing for some Rain. I'll even take some Hail, at least it can melt and keep this dust down around here.

[Extremeweatherguy]

I got about 1/4" rain today. Not bad but can't wait until Monday.

I'm going to New York in February. I hope we'll get a nice storm up there while I'm there, I'd love to see some snow, just not here.

This winter may be a race against the clock. The average low for Houston begins to rise on January 26th (it starts December 25th at 41 degrees). Crazy how this pattern took hold and lasted right through the heart of the winter. I just hope we have a nice, active spring storm season to give us some much-needed rain.

just because the avg. low begins to rise does not mean that winter is over. The coldest I have seen at my house this winter is 27, and Hooks has recorded 28. Record lows for February are in the lower teens in Houston...meaning that there is still a huge gap between 28 and the lower teens. 20s are still quite possible in Feb. and teens do occur. In fact, a few years back there was a recorded 20 degree reading in early March! Also, regarding February, Houston's largest snowfalls have occured during that month. It was in February that we saw the 20-30" snowfall here in Houston over 100 yrs. ago. Also, I mentioned that the record low was in the lower teens...well it was actually even colder. The record of the teens is the record since 1944...in reality (before 44') during the cold snap of 1899, single digits were recorded in this area with some negative readings (Tallahassee, Fl even hit -2)!!! Believe me, winter is not over until March 21st, so do not get your hopes up for spring just yet...though I will be happy myself when it comes (But it will not come yet).

[gboudx]

Two days ago, we had a 50% chance of rain on Monday. Last evening it dropped to 40%. This morning it's down to 30%. I don't like the trend.

[Portastorm]

Have you guys seen the last few GFS runs for this coming mid-week? There's a 534 thickness line well into Texas. If that is true, how in the world is it going to reach 60 degrees for a high here in Austin???!!!

No way, if this verifies ... the NWS high temps will bust badly.

[Donwx]

The latest 12z GFS shows a LOT of rain and severe weather over us and it also shows behind the low rap around moisture with the 540 line in Southeast Texas.(Wintry Precip??) Edit: I must note the 6z run shows the same thing...


http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_078s.gif


http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_084s.gif


http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_090s.gif


http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_096s.gif


http://www.nco.ncep.noaa.gov/pmb/nwprod ... p_102s.gif


http://www.nco.ncep.noaa.gov/pmb/nwprod ... p_108s.gif


http://www.nco.ncep.noaa.gov/pmb/nwprod ... p_114s.gif

[Johnny]

Well AFM, what do you have for us today concerning the cold and precip. chances next week?

[jkt21787]

The latest 12z GFS shows a LOT of rain and severe weather over us and it also shows behind the low rap around moisture with the 540 line in Southeast Texas.(Wintry Precip??) Edit: I must note the 6z run shows the same thing...


http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_078s.gif


http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_084s.gif


http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_090s.gif


http://www.nco.ncep.noaa.gov/pmb/nwprod ... n_096s.gif


http://www.nco.ncep.noaa.gov/pmb/nwprod ... p_102s.gif


http://www.nco.ncep.noaa.gov/pmb/nwprod ... p_108s.gif


http://www.nco.ncep.noaa.gov/pmb/nwprod ... p_114s.gif

The 540 line is NOT a rain/snow line!!! I have thicknesses of 534 and 850 temps of -4 right now, and guess what, its 42 and raining!! So remember that the next time the 540 line is over your area with green on the GFS. It does not mean snow at all.

[Tyler]

It does indicate very cold air aloft though with this system. Looks like alot of rain for the Houston area next week.

[Extremeweatherguy]

Latest NWS forecast has highs in the 50s next Tuesday...but looking at the latest model runs, we may struggle to even get there. Also, the thickness and 850mb temps. are showing signs of this severe outbreak possibly ending as snow flurries (that would be weird!). I do not currently think that this will happen, but we should continue to watch this closely.

[Air Force Met]

The 540 line is NOT a rain/snow line!!! I have thicknesses of 534 and 850 temps of -4 right now, and guess what, its 42 and raining!! So remember that the next time the 540 line is over your area with green on the GFS. It does not mean snow at all.

Exactly...it's just a tool. What's making the thickness low in this particular instance is the deep 500mb low. That is gobbling up the thickness values.

Remember Donwx...all the 1000/500mb thickness is is a measurement of how thick the atmosphere is b/w the 1000mb pressure and 500mb pressure contours. If the pressure at the sfc is really high...or the pressure aloft is really low...you can have a low thickness value and still be above freezing well into the air column...which is why jkt has rain. IN this case...it's the every deep 500mb low of 540dm (which is really deep this far into Texas) that is skewing the thickness values and making the column appear colder than it is.

For instance, when the GFS is putting Houston in 543 thickness at 18/00z and 540 at 18/06Z...the actual forecast skew-t from the GFS shows 5C at the SFC and above freezing all the way up to 800mb (6000') at 00z, and dropping to 900mb (about 3000') at 06Z.

What this means is a cold rain and nothing more for the Houston area. Again as I have spoken about before...540 does NOT mean snow...it's a head's up tool...nothing more. It's a light that goes off that should make you look at other things...like meteograms and skew-t's so you can see how deep the cold air is and where the warm air is.

[Air Force Met]

Latest NWS forecast has highs in the 50s next Tuesday...but looking at the latest model runs, we may struggle to even get there. Also, the thickness and 850mb temps. are showing signs of this severe outbreak possibly ending as snow flurries (that would be weird!). I do not currently think that this will happen, but we should continue to watch this closely.

I wish I could get you off the 850 mb temp. and get you to understand there is much more to the atmosphere than just what there is at 850 and the thickness

The freezing level...at least as far as what the GFS is putting out now...is going to be ~3000' when the precip stops and the drying out starts. In order for snow to make it to the sfc in a moist environment with an air temp in the mid 30's (which we will be a little warmer than that) you have to have a freezing level in the 1000-1200' range at max...no more. The 850 mb temps could be -50C and if your freezing level is over 1200' AGL...you are not getting anything reaching the sfc.

The only time 850 temps matter as far as snowfall is concerned is:
1) When you live in Denver!
2) When it comes to heavy snow....you usually find the heaviest snowfall rates around the -5C 850 isotherm...assuming you have the rest of the column below freezing and it's snowing.

[Portastorm]

I knew it ... I knew it ... I knew it .... Air Force Met shows up and rains on the parade ... dang professional meteorologists ... what are they good for?



One of these days, I'm hoping to see AFM post something like "am concerned about potential wintry weather in central and southeast Texas." etc, etc, etc. Until then ... I'm going to bang my head against the 540 thickness line.

[Extremeweatherguy]

Latest NWS forecast has highs in the 50s next Tuesday...but looking at the latest model runs, we may struggle to even get there. Also, the thickness and 850mb temps. are showing signs of this severe outbreak possibly ending as snow flurries (that would be weird!). I do not currently think that this will happen, but we should continue to watch this closely.

I wish I could get you off the 850 mb temp. and get you to understand there is much more to the atmosphere than just what there is at 850 and the thickness

The freezing level...at least as far as what the GFS is putting out now...is going to be ~3000' when the precip stops and the drying out starts. In order for snow to make it to the sfc in a moist environment with an air temp in the mid 30's (which we will be a little warmer than that) you have to have a freezing level in the 1000-1200' range at max...no more. The 850 mb temps could be -50C and if your freezing level is over 1200' AGL...you are not getting anything reaching the sfc.

The only time 850 temps matter as far as snowfall is concerned is:
1) When you live in Denver!
2) When it comes to heavy snow....you usually find the heaviest snowfall rates around the -5C 850 isotherm...assuming you have the rest of the column below freezing and it's snowing.

This afternoon's run of the JMA has temps. below 0C at 200mb, 500mb, 700mb, 850mb and 900mb in 120 hrs. What would this mean? I just hope that we either get a good shot of cold next week, but if not, then I hope the severe threat for Monday plays out. I need to see SOME kind of extreme weather to keep me going. This boring dry, sunny, warm weather has been here for too long.

[Air Force Met]

One of these days, I'm hoping to see AFM post something like "am concerned about potential wintry weather in central and southeast Texas." etc, etc, etc. Until then ... I'm going to bang my head against the 540 thickness line.

OK...how's this: I am looking...thinking that a pattern that is favorable for the discharge of arctic air into the southern US is going to set up in about 2-3 weeks. First of all, I am finally starting to see some cold temps in Ak/Yukon. Right now there are some -40F/C temps up there. Looking at the ensembles, by next week (late), it loks as iff the upper pattern becomes more favorable for Siberian air to blled across the poles and into AK and that should reinforce the stuff that is already there. I don't see any big shots coming down before that to empty what is there, so it should build.

Now...the long range GFS does not show any big outbreaks at the end of the period, but I think it's wrong. I think near the end of the period the pattern may be setting up...providing the air up there doesn't get tapped.

The main reason we haven't gotten anything so far is the upper air pattern has sent all the really cold stuff into China and Japan....but in the next couple of weeks...it should start to send it back into our source regions and that could start our setup into an arctic outbreak...maybe like the Feb 1989 outbreak...first week in February....some ice due to overrunning in College Station....lot's of cold...HUGE arctic high slides out of Alaska. Probably not THAT cold as that set a lot of record min max's...but it was chilly.

Anyway...that's my take on it...I think there is a pattern change in a couple of weeks with some building arctic air in Alaska and across the poles (disclaimer: AS LONG AS IT DOESN'T GET TAPPED AND IS ALLOWED TO BUILD).

Happy now?

[Air Force Met]

This afternoon's run of the JMA has temps. below 0C at 200mb, 500mb, 700mb, 850mb and 900mb in 120 hrs. What would this mean? I just hope that we either get a good shot of cold next week, but if not, then I hope the severe threat for Monday plays out. I need to see SOME kind of extreme weather to keep me going. This boring dry, sunny, warm weather has been here for too long.

Well...the day our temps at 200 are above 0C is the day all life on this planet ceases

500mb temps below 0C is always occuring except at rare instances in the heat of summer...

700mb...normal freezing level in the winter...

850mb is 5000' and 900mb is 3000'. You have to know what is going on in the lower 100mb or so to be able to determing the snow layers. Actually...you have to know the entire column...not just layers.

1000mb:-2.3c
925mb:-0.2c
850mb:-0.3c
800mb:-1.4C
700mb:-5.7C

Looks like it should snow, right? But you still can't tell because in this example, you could have a layer from 900mb-855mb above freezing. That would be thick enough to melt the snow and give you sleet or freezing rain. That's why you have to look at a forecast skew-t.

A good place to do it (when you don't have DoD programs or NWS programs) is at teh ARL.

http://www.arl.noaa.gov/ready/cmet.html

Go to the link, type in your ICAO (3 letters for US...like IAH, HOU) or Lat/Long...click Continue....choose sounding...GFS or whichever model...and go from there.

That way you can get the exact profile of the atmosphere and you will know if it supports snow.

Remember:
1) If freezing level is >1200' AGL...rain or freezing rain (depending on sfc temp)
2) If layer (if below freezing at sfc and above sfc...but a layer is above freezing aloft) is 700-1200' thick but temp not greater than 3C in the layer...snow or snow grains are likely. If layer is 700-1200' thick and temp is greater than 3C within the layer, complete melt is likely and you will get sleet if there is a freezing layer of 2000' of so beneath the warm layer. Otherwise it falls as freezing rain.
3) If the warm layer is <700' thick and temp is greater than 3C, snow grains, if lower than 3C, likely to remain snow.

There are other rules but there are good guidlines.

[southerngale]

One of these days, I'm hoping to see AFM post something like "am concerned about potential wintry weather in central and southeast Texas." etc, etc, etc. Until then ... I'm going to bang my head against the 540 thickness line.

OK...how's this: I am looking...thinking that a pattern that is favorable for the discharge of arctic air into the southern US is going to set up in about 2-3 weeks. First of all, I am finally starting to see some cold temps in Ak/Yukon. Right now there are some -40F/C temps up there. Looking at the ensembles, by next week (late), it loks as iff the upper pattern becomes more favorable for Siberian air to blled across the poles and into AK and that should reinforce the stuff that is already there. I don't see any big shots coming down before that to empty what is there, so it should build.

Now...the long range GFS does not show any big outbreaks at the end of the period, but I think it's wrong. I think near the end of the period the pattern may be setting up...providing the air up there doesn't get tapped.

The main reason we haven't gotten anything so far is the upper air pattern has sent all the really cold stuff into China and Japan....but in the next couple of weeks...it should start to send it back into our source regions and that could start our setup into an arctic outbreak...maybe like the Feb 1989 outbreak...first week in February....some ice due to overrunning in College Station....lot's of cold...HUGE arctic high slides out of Alaska. Probably not THAT cold as that set a lot of record min max's...but it was chilly.

Anyway...that's my take on it...I think there is a pattern change in a couple of weeks with some building arctic air in Alaska and across the poles (disclaimer: AS LONG AS IT DOESN'T GET TAPPED AND IS ALLOWED TO BUILD).

Happy now?

I think you made a lot of people happy with that possibility.

[Extremeweatherguy]

One of these days, I'm hoping to see AFM post something like "am concerned about potential wintry weather in central and southeast Texas." etc, etc, etc. Until then ... I'm going to bang my head against the 540 thickness line.

OK...how's this: I am looking...thinking that a pattern that is favorable for the discharge of arctic air into the southern US is going to set up in about 2-3 weeks. First of all, I am finally starting to see some cold temps in Ak/Yukon. Right now there are some -40F/C temps up there. Looking at the ensembles, by next week (late), it loks as iff the upper pattern becomes more favorable for Siberian air to blled across the poles and into AK and that should reinforce the stuff that is already there. I don't see any big shots coming down before that to empty what is there, so it should build.

Now...the long range GFS does not show any big outbreaks at the end of the period, but I think it's wrong. I think near the end of the period the pattern may be setting up...providing the air up there doesn't get tapped.

The main reason we haven't gotten anything so far is the upper air pattern has sent all the really cold stuff into China and Japan....but in the next couple of weeks...it should start to send it back into our source regions and that could start our setup into an arctic outbreak...maybe like the Feb 1989 outbreak...first week in February....some ice due to overrunning in College Station....lot's of cold...HUGE arctic high slides out of Alaska. Probably not THAT cold as that set a lot of record min max's...but it was chilly.

Anyway...that's my take on it...I think there is a pattern change in a couple of weeks with some building arctic air in Alaska and across the poles (disclaimer: AS LONG AS IT DOESN'T GET TAPPED AND IS ALLOWED TO BUILD).

Happy now?

I'm happy. February 89' was quite cold according to NWS records. Houston had a high of 28 on the 4th, 30 on the 5th, 30 on the 6th and 32 on the 7th. Lows, however, were not too terribly cold. They did reach the lower to middle 20s though. If a repeat or even a close repeat of this were to happen, it would be Houston's coldest air in a long time. Also...according to the weather research center, a trace of snow fell in Houston on February 6th, 1989. If a similar scenario were to occur..I would be happy.

[Tyler]

AFM,

Thank you for you analysis about the upcoming pattern and about the models. I am beggining to actually understand them now. Wow, I've learned alot now from this thread!

[jasons2k]

Anyway...that's my take on it...I think there is a pattern change in a couple of weeks with some building arctic air in Alaska and across the poles (disclaimer: AS LONG AS IT DOESN'T GET TAPPED AND IS ALLOWED TO BUILD).

Happy now?

No...I keep staring at my pool wanting to jump in.