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WxChallenge 2013-14


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I have absolutely no good feeling about tomorrow...

 

39/27/17/0.26

 

Excluding the notoriously over-wet NMM, most models are spitting out 0.30" to 0.40" of liquid tomorrow, but I just can't get over the fact that the forcing for precip is so weak.  And man it's hard to forecast precip like that when you're looking at a 19 F Td currently.  I've got a gut feeling we'll end up only being in the single digits in the precip column before 06z or something, but I don't have enough confidence to actually go for it.

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I'm in a tough position today as on Wednesdays I have to forecast from class.

High: 40 : Heck it hit 43 at noon today when it was 23 this morning, the models that are 39 or below are hard to believe. Should get enough sunshine tomorrow morning before the clouds move in.

Low: 29 : High clouds tonight should limit the LWR to an extent. The LWR last night dropped the low 15 degrees, 48-15 = 33. So if it doesn't get to 29 tonight, the snow should fall at a good enough rate to get it there anyway at 6z.

Wind: 14 : Shouldn't be too far off, though I also said that to myself today :yikes:

Precip: 0.35: NWP and CYS AFD seemed in good agreement/confident that 3-5 inches would fall with the PV anom. swinging through, the 12 and 18z GFS also had some really strong omega around 3z-6z. I wish I had the time to really dig into this day, but I'm in class. Oh well. :/

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I have absolutely no good feeling about tomorrow...

 

39/27/17/0.26

 

Excluding the notoriously over-wet NMM, most models are spitting out 0.30" to 0.40" of liquid tomorrow, but I just can't get over the fact that the forcing for precip is so weak.  And man it's hard to forecast precip like that when you're looking at a 19 F Td currently.  I've got a gut feeling we'll end up only being in the single digits in the precip column before 06z or something, but I don't have enough confidence to actually go for it.

Upslope flow will get the job done for precip. 

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Upslope flow will get the job done for precip. 

Predicting/modeling upslope flow is notoriously tricky though.  Not exactly the same thing, but I've chased eastern CO/southeastern WY for years and I've seen how subtle changes in wind speed/direction make or break convection, and I assume that uncertainty carries over into the cold season.

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40/30/16/0.22"

 

I undercut guidance QPF a tad but went near guidance in general which was around a quarter inch or a tad more. I think they should hit at least 40 tomorrow...am hoping on clouds/snow moving in early enough to keep from exceeding that. Undercut guidance a bit for lows tonight with clear skies at least to start...may also get there tomorrow evening if it snows hard enough. Went a bit above most guidance for winds. We'll see.

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39/30/16/0.27"

 

Looks like I'm on the warm end of the bell curve with the low. Hopefully that doesn't end up being a mistake--the temperature is plunging tonight already. Models seemed to agree on somewhere around 0.20-0.40" of precip. So many ways for this forecast to fail.

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Down to 34 at 5z with a dew point of 22. Still clear and KFEW just a mile or so west of KCYS is allegedly at 26 right now. Winds have stayed up at 5-7 knots this evening but temps have still fallen off nicely. Mid-high clouds look to be an hour or two out, so will be curious to see how much more cooling can occur. Looks like the national consensus on the low was 28 so as long as it doesn't get colder than 29 I won't be loosing ground due to the low. We'll see.

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As long as it's still snowing and cloudy it should't drop off too much...hopefully...

 

Meanwhile, the wind is already 15 kt.

 

I guess it depends what the dew point does. Of course, it will come (back) up once the snow starts, but it should fall off after that. I also expect it to be cooler this afternoon than modeled (maybe 36-37 for a high), so we won't have far to fall.

 

With steady snow and dropping dew points, I definitely expect the temperature to fall. Not confident with my 27F, but at least into the upper 20s I think.

 

 

EDIT: Then again, the temperature seems to be coming up just fine so far, and the dew points are quite a bit higher than I expected at this time.

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I agree that 28-29 seems likely before midnight. The question is--how much more will it drop after that? Especially since the clouds should stick around until sunrise.

 

The after midnight precip issue is another thing. And the high tomorrow with the fresh snow cover. Not to mention the strong winds.

 

Yikes.

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This is more interesting than tracking convective precipitation for two weeks...lots of variables that will be affected by the snow cover tomorrow...not to mention we won't know the final precip number for today until 6z. 38 for the high before the snow moved in, 31 for the low thus far but that may change and a max sustained wind of 16 knots thus far.

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Probably going to go with 0.02 or something low on precip tomorrow. Models always seem to over do how long the snow will last...at least that's what my limited experience has told me...

 

Looks like this storm is going to bring about 0.20" or more for the Cheyenne area.  But the snow will fly before midnight. So that may be a reason increase the QPF for today, and keep QPF lower for tomorrow. Actually the snow will fly by 1853z

 

KCYS 171853Z 34004KT 4SM -SN FEW017 BKN039 OVC047 03/M01 A3009 RMK AO2 SNB28 SLP195 P0000 T00331011

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37/24/22/0.06"

 

Lots of things that can go wrong here. Undercut MOS by several degrees for highs figuring fresh snowcover and CAA at least initially will hold down temps. Went a bit warmer than MOS and closer to the slightly warmer raw GFS/NAM data for the low tonight with clouds through much of the night...but we'll see as some CAA will occur. Went a bit higher than most guidance on wind...except for Tuesday I believe guidance has been a bit low on wind...given decent CAA will be occurring into the morning have no issue going a bit over guidance for wind. For precip...welp...looks like I'm a tenth of an inch under the National Consensus for tomorrow. GFS/Euro both spit out 0.10" or a few hundredths more after 6z but the higher resolution models, that may be able to better resolve a situation like this including downsloping likely developing not too long after 6z, show less. We'll see!
 

Up to 0.11" for today and pretty decent echoes nearby right now.

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