The Official 2009-2010 Denver winter weather thread

[Dencolo]

That 3" QPF from the 18z GFS would be something else. The NAM wants none of that. I got about 1/2" of the white stuff today. Let's see if we could be measuring this storm in feet by midweek!

THIS STRONG SYSTEM HAS THE POTENTIAL TO
BRING SIGNIFICANT SNOW AMOUNTS TO THE MOUNTAINS...FOOTHILLS AND
PLAINS ALONG WITH COLD TEMPERATURES. THE TRACK OF THE UPPER LOW AS
IT STARTS TO LIFT OUT OF THE FOUR CORNERS REGION IS A LITTLE
UNCERTAIN AS THE MODELS BEGIN TO DIVERGE

[PTPatrick]

0z nam even more dismal...pretty much nothing for the metro area through the end of its run which is Thursday morning. No precip at all wednesday. Now for the 0z GFS. Will post when it comes in. Hopefully it stays on the wet side of guidance. NAM is a downer.

UPDATE: 0z GFS is unchanged from its previous 18z runs with 2.5-3.0 inches in the area. If anything it looks a hair slower. Amazing that GFS and Nam are this different in track still...although I realize 4 days is an eternity in weather day. Its like trying to call a gulf coast hurricane land fall 4 days out. its just folly.

Update: 0z CMC is closer to the GFS but slightly faster with less QPF...still a good storm though. Compared to the previous run it cuts off our precip in the late evening thursday as opposed to eary friday AM. QPFs are hard to read on the Cmc maps but it looks like about 1.5 inches for the event


so there you have the range of the 0z models is 3 inches to zilch.

[Dencolo]

12z GFS still has 2.5" to 3.0" of QPF in an area very close to Denver. The potential is still here.

http://www.nco.ncep.noaa.gov/pmb/nwprod ... 0_102l.gif

[SCMedic]

Model consensus or not, most, if not all are forecasting a major winter storm for Denver and the frontrange. Accuweather alone is calling for 18" of snow over 2 days and they're ending the snow pretty quickly. The amount of QPF around is amazing. The Tuesday night through Thurs morning time frame could be fun!

[PTPatrick]

yeah, I have a habit of reading all the areas neighboring discussions when something is cooking and its funny Denver's disc sounds totally different than the SPrings. Denver's doesnt really analyze much, seems like they are going more with HPC on this. COS says that NAM is a complete outlier, and that the 0z GFS, 0z Euro and 0z Canadian are, and SREF means are all in much more relative agreement compared to anything the Nam is putting forth. GFS backed off the bullseye a bit in NE CO with the 6z run but still over 2 inches is forcast. Denver's guys seem a little more swayed by the Nam. We will just have to wait and see. But make no mistake, every source I read is talking storm.

[SCMedic]

It will snow, no question.


NAM is being discounted, and the ensambles are in line with the GFS. Haven't looked at the new model runs, but hoping for a favorable track. Winter Storm Watch should be up by the morning discussion I would assume.

[SCMedic]

Better agreement and a good looking track!

THIS GENERAL TRACK IS INDEED A FAVORABLE ONE FOR HEAVY SNOWFALL ACROSS NORTHEAST
AND NORTH CENTRAL COLORADO...AND THE SLOW MOVEMENT SHOULD HELP
CONTRIBUTE TO A POTENTIAL SIGNIFICANT WINTER STORM WITH HEAVY
SNOWFALL.

ESPECIALLY BY WEDNESDAY AND WEDNESDAY NIGHT WHEN GULF AIR AND THE WARM CONVEYOR
BELT CONNECT INTO THIS SYSTEM. FINALLY...THERE COULD BE SOME LULLS
IN THE STORM WITH A DRY PUNCH OR TWO ALOFT POSSIBLE...AND THIS
PROBABLY DEPENDS ON THE EXACT TRACK OF THE UPPER LEVEL FEATURES...
BUT DURATION OF STORM WILL HELP OFFSET THOSE LULLS.

THE DURATION OF THIS STORM APPEARS TO BE A GOOD 24-30 HOURS...AND
SUFFICIENT Q-G LIFT AND POTENTIAL FOR GULF MOISTURE AND STRONGER
UPSLOPE ALL SUPPORT A THREAT OF A SIGNIFICANT WINTER STORM AND HEAVY
SNOWFALL. AS A RESULT...HAVE ISSUED WINTER STORM WATCHES FOR THE
MOUNTAINS...FOOTHILLS...AND FRONT RANGE URBAN CORRIDOR STARTING LATE
TUESDAY NIGHT AND CONTINUING THROUGH WEDNESDAY AND WEDNESDAY NIGHT.
IN THE IMMEDIATE DENVER METRO AREA AND PALMER DIVIDE WE WILL HOLD
OFF BEGINNING THE WATCH TIL DAYBREAK WEDNESDAY WHEN BETTER UPSLOPE
IS EXPECTED TO ARRIVE.

[PTPatrick]

Looking good for sure. Despite the great track it isnt looking like that once every 5 or 6 year 20 inch storm that it had been. Either because of the inverted trough or dry air it looks like good upsloap will get cut off midday thursday, which might still allow some flurries for thursday afternoon, but I wouldnt think much accumulation. I think a foot for Denver with 12-18 for the foothills/palmer divide looks about right with this. Not sure if melting will be an issue, so I am saying a foot. Could certainly end up higher if melting doesnt turn out to be an issue and if the storm tracks a hair more westward on thursday then 16 in Denver and up to 2 ft in the foothills and palmer divide. Even the once dismal Nam is now showing about 10 inches... which would make me happy.

[Dencolo]

00z NAM looks about the same. Potentially around 1'. Let's see what the GFS says...

[PTPatrick]

0GFS not too much different. Interestingly enough though, NAM is pretty wet thursday well into the evening. GFS cuts off precip earlier but still manages more precip over the event. It has a small purple area indicating the potential for 1.5 plus QPF somewhere, but majority of the area looks around 1.25 to 1.5. Suspect it wont be cold enough for high ratios so I doubt it will that would fluff up much above 15 inches. Oddly enough these QPF bullseyes with these upsloap storms are always displaced to the east of NE of the foothill/palmer divide. Time is closing in, and models still not really in good agreement on time frame. NAM doesnt get precip going until wednesday night, vs GFS which is tuesday midday.

0z Canadian...looks like it goes somewhere between the NAM and GFS. HPC mentioned GFS was a litte east of everybody else with the lows exit up in to the plains. Either way Canadian looks wet from pretty much 12z Wed to 12 z friday and shows 1.5 -aroun 2.0 inches of precip for the area. So quite a bit wetter than NAM, and a little wetter than GFS. HPC was also mentioning Euro and Canadian had trended together earlier today in the middle of the GFS and NAM spread. So the upper end of the GFS qpf's could wind up being accurate.

[PTPatrick]

WSW is up. Looks like they are going with the 1 and a quater inch QPF average of the models for initial accumulation calls for the metro area. 8-14 plains, 10-16 PD, and 1-2 ft foothills. Sounds right. Still think there is potential for even a little more, esp if the GFS pans out but a little slower. Sounds like they like GFS but want to exit precip slower on thursday evening. NAM still keeps precip in longer on thursday evening. Either way I think we got a storm on our hands folks, albeit probably not a Oct 1997 do over.

[Dencolo]

06z GFS has a bit more than the previous run. Based on the disco's, they see some periods of up to 3" per hour accumulation. If some of those bands move in, we could even exceed the storm totals below. I'm thinking 14" to 16" for the SW suburbs where I"m at. That would be the biggest storm here in quite some time. Looking forward to it!

[Dencolo]

Below is the latest on the winter storm warning for the Denver area. 8-14" (or more) is certainly quite a powerfull storm. 12z GFS shows 1.5" QPF for DIA. That's some cancelled flights for you. Enjoy the next few days!

1131 AM MDT TUE OCT 27 2009

...WINTER STORM WARNING REMAINS IN EFFECT FROM MIDNIGHT TONIGHT
TO 6 PM MDT THURSDAY...

A WINTER STORM WARNING REMAINS IN EFFECT FROM MIDNIGHT TONIGHT TO
6 PM MDT THURSDAY.

RAIN SHOWERS WILL DEVELOP THIS EVENING AND THEN CHANGE TO SNOW
AFTER MIDNIGHT. SNOW WILL CONTINUE ACROSS THE AREA INTO THURSDAY.
SNOW MAY BECOME HEAVY AT TIMES FROM LATE TONIGHT THROUGH
THURSDAY. SNOWFALL ACCUMULATIONS WILL RANGE FROM 8 TO 14 INCHES
WITH HIGHER AMOUNTS POSSIBLE IN SOME AREAS. GUSTY NORTH TO
NORTHEAST WINDS WILL PRODUCE AREAS OF BLOWING SNOW AND REDUCED
VISIBILITIES FROM WEDNESDAY THROUGH THURSDAY.

[srainhoutx]

I would not be surprised to see this system over achieve. There appears to be some mighty cold air associated with this storm and the track is going to offer some forecasting challenges. Enjoy your snowstorm CO folks.

[SCMedic]

I really expect snow totals on the higher end and probably closer to 14-20". I think they're going really conservative with this forecast.


On a different note, I HATE HATE HATE our local mets. They're so scared of being wrong, that they don't forecast anything. They always "wait and see". In fact, 9new said to look for 3-6" for the Denver area this morning? REALLY? They also mentioned that there are two models, and that they have differing tracks, so it'll be a wait and see situation. Where do they get this info? They're terrible.

[Dencolo]

From the AFD.

MODEL QPF
GRIDS GENERATE IN EXCESS OF AN INCH OF LIQUID WATER. AS THE EVENT
MAY EXTEND TO 36-48 HOURS IN LENGTH IT APPEARS THAT SNOW AMOUNTS
ABOVE A FOOT ARE QUITE POSSIBLE ALONG THE URBAN CORRIDOR. AMOUNTS
IN THE FOOTHILLS AND MOUNTAINS MAY EVEN DOUBLE THAT. THE WINTER
STORM WARNING WILL CONTINUE THROUGH THURSDAY AFTERNOON.

[SCMedic]

I'm still thinking that 12" is on the low end by a long shot. Slowing track, and great location of the low puts us in deep upslope for 40+ hours. Barring a dry slot that only the NAM is showing, and it's way out east on top of that, Weds/Thurs should be fun!

[srainhoutx]

WOW. The Warnings are flying with some impressive amounts...

http://www.srh.noaa.gov/nat_hazard.php

[PTPatrick]

well, i am glad the NAM finally laid down the crack pipe. Looks like it has up to around 1.5 inches. HPC is saying slightly higher than 10:1 snow:liquid ration so even on the drier NAM we probably get close to 18 in Denver. GFS is back up to near 2 inches with the bullseye slightly east of the metro(which is probably a model error and should be considered slightly west of the where the mpa shows it. That would certainly give up in the 2 foot range. WSW wording this afternoon is a little dier..."travel will be impossible tomorrow night into thursday" and 1-2 ft of snow expected in the metro. Cant wait


MEANWHILE...the Cow poo smell has arrived in Downtown, which means snow is on the way. NE wind seems to carry it in ahead of any good upsloap event.

[PTPatrick]

Winds are pretty strong right now...already yellow radar echos over the area betwen Denver and Fort Collins. I wonder if the storm getting started early will change anything. Models had not been showing precip that heavy until at least Dawn hours...