The Official 2009-2010 Denver winter weather thread

[Dencolo]

http://www.crh.noaa.gov/bou/include/sho ... duct=wrkf6

Check out column 5 - temperature departure from normal. Every day in October has been below normal, and right now we are standing at 14 degrees below normal for this month.

[PTPatrick]

Tomorrow will will be far cry from the records low highs and record lows of a week ago. Projected high is 82 for Denver. Record is 84. Pretty warm for mid-to-late October. New Orleans, LA is project to be some 20 degrees cooler than Denver tomorrow. Quite an extreme pattern....

[SCMedic]

The Tuesday front and low look to be slowing, strengthening and cooling with each run. Upslope looks decent too for some late Tues snow mixing down.

For now, I'll enjoy the hot October weather with a nice BBQ!

[Dencolo]

If it's cold enough for snow Tuesday night, we would be talking about up to a foot or more of snow accumulation. Right not, the NWS is calling for it to fall as rain, with some snow mixed in Wednesday morning. Quite a change from the nice weekend.

From this afternoon's AFD:

THE GFS AND ECMWF SHOW MOST LOCATIONS GETTING BETWEEN A HALF INCH TO ONE INCH OF PRECIPITATION.

[SCMedic]

They're swinging back to all snow in the foothills and over the Palmer. Mentioning snow after midnight on Tues for the western plains. Good QPF for both areas. If that temp is 2 degrees one way or the other, it could be the difference between 6" and nothing.

[Dencolo]

Some minor accumulation on the south side. Snow was coming down at around a quarter inch per hour. I'd like to get a couple inches before it's all done.

[Dencolo]

Based on the cameras, some decent accumulations are starting on the South and West sides of town. Downtome it's a rain and snow mix with no real acculations, even on grass.

[vbhoutex]

Here are some Denver area webcams http://www.dickgilbert.com/denvercams.htm

[SCMedic]

Still coming down here at DIA. Has been since I came into work at 2. Solid snow coming down, warm ground, warm temps and no accum. I also drove to Vail this morning at 6am. Sloppy on the west side of town, and all the way up 70 till the divide, then foggy and dry.

Forecast has some small disturbances rotating through through the weekend. Nothing amazing. Sunday and Weds have pretty large, deep lows spinning through. Could be interesting. Already mentioning chances, and snow at 5 days out.

[Dencolo]

Driving from downtown to Littleton was interesting after work. Went from no accumulation to 2-3 inches and still coming down at about 1/4-1/2" per hour at the house. And the roads are pretty slushy now also. It looks pretty neat outside right now.

And check out the snow totals! Up to 6" in Parker (Southeastern suburb of Denver)

REGIONAL TEMPERATURE AND PRECIPITATION SUMMARY
NATIONAL WEATHER SERVICE DENVER CO
819 PM MDT WED OCT 21 2009

MOST REPORTS ARE FOR THE 24 HOURS ENDING AT OBSERVATION TIME.
AIRPORT LOCATIONS ARE TODAY`S HIGHS AND LOWS.


.BR DEN 1021 M DH19/TX/TN/PP/SF/SD


: STATION ELEV DAY/ SNOW SNOW
: NAME FEET HOUR HIGH LOW PCPN FALL DEPTH

...NORTHERN COLORADO FRONT RANGE...

EAGC2: AURORA/EAGLECREST :: 2107: M / 32 / .29 / .5 / T
BRIC2: BRIGHTON 3S :: 2107: M / 33 / 0.19 / 0 / 0
APA : CENTENNIAL AIRPORT :: 2118: 36 / 32 / 0.37 / M / M
CMMC2: COMMERCE CITY 2NE :: 2107: M / 35 / .32 / 0 / 0
DEN : DENVER INTL AIRPORT:: 2118: 37 / 33 / 0.32 / M / M
DUAC2: DENVER STAPLETON :: 2106: M / 32 / 0.22 / 0.1 / T
DVNC2: DENVER WATER DEPT :: 2107: M / 30 / 0.35 / T / T
WUDC2: ENGLEWOOD 2SSE :: 2107: M / 35 / .30 / T / T
ENLC2: ENGLEWOOD 1SSE :: 2107: M / 33 / .29 / .2 / T
HLRC2: HIGHLANDS RANCH 2SE:: 2107: M / 31 / .44 / 1.5 / 1
NRTC2: NORTHGLENN :: 2108: M / 33 / 0.26 / T / T
PKKC2: PARKER :: 2117: 41 / 31 / 0.67 / 6.0 / 5
THNC2: THORNTON 5NNE :: 2107: M / 31 / .25 / T / T
CSLC2: CASTLE ROCK 1NE :: 2107: M / 33 / .20 / 2.5 / 3
CASC2: CASTLE ROCK 3NE :: 2107: M / 29 / .20 / 2.5 / 3

[Jag95]

Just wondering...how do you guys read the long range models in Denver when trying to anticipate snow? At sea level a lot of people around here start getting excited when the 850 mb 0 degree isotherm drops down. At 5600+ ft I imagine that changes. Isn't there generally something like a -3 degree drop for every 1000 ft in altitude? I know there are a lot of variables, but what's the general feature to watch when predicting snow in Denver?

[Dencolo]

I'm not much of a model expert. I can tell you in Denver it's pretty much all snow November through March. I know in the AFDs their mainly interested in the elevations of the wet bulb temperatures to determine P-type.

Anyway, the 06z GFS is very interesting. Check out the 36 hr precip total for days 5 and 6. If that plays out, that would be our first big storm of the season. The snow in my yard from the snow a couple days ago should melt of today.

Note: Click under 36 hr precip at hour 144.

http://www.nco.ncep.noaa.gov/pmb/nwprod ... el_l.shtml

[PTPatrick]

Yeah...I was actually just going to post that DEN! My downtown snow has been gone since early yesterday . apparently still some good snow cover over douglad county. Sounds liek Centennial/Aurora have melted though. Anywho...

based on the amount of precip in that model, for that whole period ( I looked at the 48 hr period), GFS is painting over 1.25 inches of precip. Based on this thicknesses that will undoubtedly be all snow. In fact, thickness get pretty low and cold next week during that period, which could suggest a higher than typical snow to liquid ratio. Even with the normal 10:1 though that would still be over a foot of snow. I suspect much will change between now and then. But something to look forward to. If it does materialize it should be quite the early season storm. CMC has much of the precip up over the cheyenne ridge, but Euro looks very similar to GFS in the position of the low(cant seem QPF on the Euro model). GFS and EURO agreement is good

Incedentally, saturday and sunday on NAM is showing a few inches of snow for the area too. GFS doesnt agree with that.

[PTPatrick]

Still not much concensus in the models on the Tuesday to thursday time frames...to quote the NWS DISC:

WILL NOT CHANGE THE FORECAST FROM TUESDAY NIGHT ON DUE LARGE RUN TO
RUN INCONSISTENCIES AND LARGE DIFFERENCES BETWEEN THE MODELS. THE
GFS PUSHES THE TROUGH THE AREA BY WEDNESDAY WITH A NORTHWEST FLOW
BEHIND IT. BY THURSDAY THE GFS HAS RIDGING OVER THE AREA. THE ECMWF
DIGS THE TROUGH OVER THE FOUR CORNERS AND CLOSES IT OFF. IT THEN
SLOWLY PROGRESSES EAST AND THEN NORTHEAST CREATING A LARGE SNOW
STORM FOR THE AREA WEDNESDAY AND THURSDAY. DIFFICULT TO BELIEVE ANY
SOLUTION AT THIS TIME AND WILL RIDE WITH THE BELOW NORMAL
TEMPERATURES AND LOW POPS THE CURRENT FORECAST HAS.
My analyisis...
12z GFS seems a little deeper and less progressive with this trough/storm than previous runs but still abut 6-12 hrs faster than the 12z NAM and 12z CMC... 0z Euro seemed a little MORE progressive than its 12 z run yesterday so it may be coming off the wild solution from yesterday. 12z GFS would have about .8-1.2 inches for most of the metro resulting in 8-12 inches. Time frame is shorter than CMC and EURO for snow, as GFS has it starting Tuesday night late, peaking wednesday rush hour and the tapering through the evening. 0 Z EURO still shows a pretty decent storm and slow moving(compared to GFS), I dont have access to the models QPF details and 12z isnt out yet. CMC 12 Z is deeper and slower than the 12 z GFS run Shows roughly the same QPF amounts only instead of concentrating them in the Tuesday night to wednesday night time frame they are spread out until Friday morning. In fact, CMC would have almost continuous moderate to light snow from Tuesday night to Friday morning. Clearly still some bugs to work out. THe QPF differences at this point are inconsequential I think. The models even while coming to a generally slower pattern with the storm lingering over the 4 corners longer are going to have difficulty with exact QPF this far out. The important thing is the pattern. If this storm does linger from later Tuesday to Friday morning we will likely, regardless of whether the amounts are epic or not, have a fairly cold and snowy period. Will post an update later on what I see with the 12z euro when it comes out

[VoodooCadillac]

rut-roh! Flying out of DIA 1:00 PM Wednesday.

It would be OK with me if the system slowed down just a tad.

[PTPatrick]

Wont regurgitate what all was said above...but I looked at 12 z EURO and it doesnt look all that different from the 0 z. 18 z GFS is also in agreement with its 12 z run, so there is still a split. EURO(and Canadian for that matter) close the low off in the desert SW swinging slowly up into the plains by Friday morning. Per Euro the best position of it for precip (again QPF amounts not available) would be the wednesday to thursday night time frame taking the low roughly from about NW NM at 0z Thursday to SE SD 0z Friday In fact, Euro is basically on board with CMC in keeping precip in the area from Tuesday through Friday morning. The afternoon DISC mentions that nogaps has this solution too. So far it seems like GFS is the fast/progressive outlier and even IT produces at least 3 quarters of an inch of precip for the tuesday night-wednesday time frame resulting in probably a least 6-8 inches around the metro. Right now the NWS seems to be leaning more toward the EURO solution as well.
Excerpt from the discussion...
THE NEXT UPPER TROUGH TO AFFECT THE STATE WILL BE DROPPING DOWN FROM
CANADA ALONG THE ROCKIES. THIS SYSTEM HAS BEEN DIFFICULT TO GET A
HANDLE ON AS MODEL CONSISTENCY AND AGREEMENT HAVE LACKED FOR THE
LAST SEVERAL DAYS. HOWEVER JUST RECENTLY HAS THERE BEEN SOME
AGREEMENT INTO TWO DIFFERENT SOLUTIONS. THE GFS HAS BEEN CONSISTENT
WITH ITSELF IN BRINGING THE TROUGH DOWN TO THE FOUR CORNERS REGION
EARLY WEDNESDAY MORNING THEN QUICKLY MOVING IT TO THE EAST INTO
KANSAS BY WEDNESDAY NIGHT. THE ECMWF...CANADIAN AND NOGAPS ARE
SHOWING THE OTHER SOLUTION OF DIGGING THE TROUGH INTO ARIZONA TO
BECOME A CUTOFF LOW THEN MOVING IT EAST THURSDAY. IN TERMS OF TIMING
OF THE ASSOCIATED COLD FRONT...THE LATEST GFS SLOWED TO THE EC
SOLUTION...THEREFORE SLOWED THE CURRENT FORECAST BY ABOUT 6 HOURS.
MOISTURE WILL BE INCREASING WITH RAIN AND SNOW STARTING TUESDAY
MORNING AND THE COLD FRONT TO PASS TUESDAY NIGHT. A COLD AIRMASS
WILL FOLLOW THE COLD FRONT SETTLING IN OVER THE STATE AND ONLY
ALLOWING MAX TEMPERATURES TO REACH INTO THE 30S WEDNESDAY. BOTH
MODELS HAVE THE POSSIBILITY OF SIGNIFICANT PRECIPITATION...BUT
DEPENDING ON WHAT MODEL IS FOLLOWED FOR GUIDANCE...IT COULD LAST
THROUGH WEDNESDAY EVENING AS THE GFS SHOWS OR ALL THE WAY THROUGH
FRIDAY MORNING SHOWN BY THE EC. LEANED A LITTLE MORE TOWARD THE EC
BY CARRYING POPS THROUGH THURSDAY NIGHT.
OVERALL...LOOK FOR TEMPERATURES BELOW NORMAL WITH ABOVE NORMAL
PRECIPITATION FOR THE WEEK.

[SCMedic]

Looks like we should see at LEAST 6-8" on the low end for the Tuesday night/Weds time frame. If the slower models pan out, we could be talking epic October storm. 20"+. Should get ugly too with winds developing after the front and blowing snow. Here's to hoping!

[Dencolo]

06z GFS now showing up to 2" of precip for parts of the Denver area. This clearly has the potential to be a significant storm.

From the latest AFD:

THE GFS IS THE WEAKEST AND MOST PROGRESSIVE IN HANDLING THE
TROUGH. THE ECMWF...NAM12 AND THE GEM CLOSE OFF THE TROUGH OVER THE
DESERT SOUTHWEST. THIS LOOKS REALISTIC WITH THE LARGE TEMPERATURE
GRADIENT THAT WILL BE OUT THERE.

From this morning's Hazardous Weather Outlook:
THERE IS A CHANCE THIS SYSTEM COULD DEVELOP INTO A STRONG WINTER STORM AND BRING HEAVY SNOW TO THE REGION

[PTPatrick]

12z GFS backed off from 06z's 2 inches a bit but still pretty wet with about 1.5 inches. Of course with air as cold as it would be would could see more than 15 inches snow if it gets fluffy. The difference is a slightly less favorable position for QPF for our area in the thursday evening time frame. GFS and EURO BOTH now try to eject the system pretty quickly NNE from around south E Colorado up into ND in the Thursday morning to evening time frame which would turn us to downsloap pretty quick on thursday evening. It would almost be like a sling shot if it moved that fast on thursday but I guess its possible. The general track of the low is slightly more north on the latest runs too, which doesnt take away our storm but it makes it less big. We need it to go across the CO.NM border really slow then lift north gently throught he OK panhandle into central KA and NB to get epic snow...right now Euro and GFS are just north of the border and lift from SE CO into Wester Nebraska so that the system is NE of us by friday early morning and good upsloap thursday cuts off afternoon. Its all a very complex dance these weather systems make and Denvers nook here in the elbow of Palmer Divide and the Front Range make these things difficult. Dont get me wrong, both Euro and GFS still have a big storm for us, but looks like it may not be as big. These low track difference are fairly minor and still in the 3+ day time frame so lots will change. The good news is the 12 z Canadian looks slightly better than the GFS and EURO for us.

[PTPatrick]

Local disc this afternoon seems pretty much down with the idea of a snowstorm but the devil is still in the details. It could be a big one for WY and not so much CO, or a big one for both, or just CO, depending on which model track you follow. The 18 z NAM and GFS couldnt look much different. 18z nam has the low over NE CO at 06z thursday, with nil precip through 84 hrs. Basically in that track upsloap never gets going good because the storm goes over us instead of south of us.At 84 hours NAM only has .5 inches of precip, and nothing in southern CO. Meanwhile, 18z GFS has shifted back south has the low down in the vicinity of the panhandles, a MUCH better spot for upsloap for Denver... As a result it paints 3 inches of QPF by the time it winds down on Friday early AM!!! I heart the 18z GFS with its 20+ inches of snow. I WISH. So now we have the NAM/EURO camp and the GFS/Canadian camp.