1/20/06 - 1/21/06 - MIDWEST SNOWSTORM

[Joel Wright]

My computer's been down the last few days getting repaired, so I've been dying to finally look at some model data! (Relying on The Weather Channel leaves a lot to be desired).

Since the storm is just now coming on shore, the next few runs will be pretty important. Even now not all of the storm is on shore, so I think tomorrow's 12z runs will be more telling than tonight's. But, hopefully when the 0z comes out in a bit things will look better.

This morning's runs really speed this thing along, which would severely limit accumulations for whomever ends up in the right track. There does seem to be a lot of moisture available for the storm though.

We are ALL overdue for a good snow, so hopefully one of us can bag a good one with this one, or one soon! 8)

 

[Robert Dewey]

The 18Z GFS didn't look so hot... Trending towards the NAM, though not as extreme. 18Z UKMET keeps continuity with previous runs.

If the 00Z NAM trends back towards a stronger solution, then I would be alot more confident. If both 00Z NAM and 00Z GFS show a weaker system than the 18Z runs, then my confidence will be significantly reduced.

But... Looking at the WV loop, the system looks pretty decent. RUC has a nice jet at 250MB diving down the backside of the trough with decent diffluence downstream. I see no reason why the system should fall apart as rapidly as the 12Z/18Z NAM suggests...

 

[Robert Dewey]

From what I can tell, the 00Z NAM is significantly farther north than the 18Z run, which is a good trend. Also boosting confidence, the 00Z GEM is identical to it's past two runs (12Z and previous 00Z). In addition, the NGM also trended stronger than the 12Z run.

I always like to analyze trends in the models, as I feel that gives the best indication of what is going on. I have average confidence that this system will be AT LEAST as strong as what the 12Z GFS had, though with more QPF. The reason I think we could see more QPF in the north is the fact that the GFS appears to suffer convective feedback along the GoM, dropping as much as 3-5 inches of rain in a 6 hour period over a rather large grid spacing. That could be restricting the northward transport of moisture in the model...

 

[Robert Dewey]

Latest run down...

00Z NAM much further north and stronger than the 12Z runs, but still the farthest south.

00Z GFS a bit stronger and a bit further north than the previous runs. QPF also higher, with super-high QPFs along the GoM gone (still might be overdone down there). QPF axis of 1.15 inches stretches through MI.

00Z RGEM shows the best continuity, but doesn't go past 48 hours. It has a similar look to the GFS though a bit deeper and slower. Produces 1.00 QPF over parts of MO, which might extrapolate into areas further northeast as the precipitation field expands.

00Z GGEM is alot weaker and more progressive. Appears to be the weakest of the models so far with very light QPF amounts.

00Z UKMET is nearly identical to it's previous run... Not much more to say.


Given that, all but one (GGEM) of the models are either continuous or trending slightly deeper. The previous NAM runs appear to be outliers, and I suspect the 06Z and 12Z NAM runs will show an even deeper and further north system. I have above average confidence in a closed 850MB low tracking from central OK through extreme northern OH by FH72. QPF's on the cold side of the baroclinic zone should max out around 1.00 to 1.15 inches with the very intense lift expected. With a slightly deeper solution, I would expect the system to be less progressive, thus owing to the higher QPF values.

HPC Note about the NAM run:

...SYS OVER SW ON DAY 1 AND LIFTING THRU MS VLY DAY 2...
THE NAM IS UP TO 45 M TOO STRONG WITH THE H5 RIDGING IT PLACES
OVER NM/W TX AHEAD OF THIS TROF. THE NAM IS ALSO WEAK WITH THE
H25 WINDS ON THE LEADING EDGE OF THIS TROF...SPECIFICALLY THE NAM
IS 40 KTS TOO WEAK OVER FGZ AND APPROX 20 KTS TOO WEAK OVER BOTH
RIW AND DNR. THE NAM MAY BE TOO WEAK WITH THIS TROF IN THE
FORECAST PD AS A RESULT OF ITS INITIALLY WEAK UPR DYN.

Dewey out.

 

[Alex Lamers]

The reason the models were so unfavorable in the previous 3-4 runs was because of very significant initialization errors and missing observations. Tonight's 00Z GFS initialized wonderfully and the actual piece of energy is now onshore in N CA.

...Alex Lamers...

 

[Robert Dewey]

00Z Canadian Ensembles are in, and the majority hold a wide stripe of +1.00 inch QPF's, dispite what the GGEM shows.

I am now locking the main threat into an area from Quad Cities IA/IL, through southern lower MI, into most of southern Ontario Canada. This looks like it could be a rather significant snowstorm (+12 inches) for some areas given what the current models and trends are suggesting... But obviously too early to pinpoint anything more specific.

FWIW... GFS does kick winds up across lower MI at 12Z SAT to 20-30KNTS, but with the overal weak pressure gradient I'm not too excited for the prospects of a wind driven snow.

 

[Robert Dewey]

HPC noted the NAM was 30-40m too weak with the trough...

Even with that error, NAM has trended slightly stronger and the GFS has trended slightly weaker in the 36-48HR period... RGEM has also trended slightly weaker with the 500MB trough and a touch faster, though the SFC low remains the same intensity at 1010MB. The SREF shows pretty high deviations with the SFC low intensity and 850MB heights. MSLP deviations range in the 3.5-4.5MB range, while 850MB temps are 3.5-4.5 range. The SREF also shows 0.50-0.75 inches of mean QPF with a deviation of nearly 0.50 inches...

As for QPF... RGEM comes in with 25-30mm, or roughly 1.00 to 1.25 inches. NAM has increased QPF in extreme southern lower MI from 0.25-0.50 inches to 0.75 to 1.00 inches. Each run has shown an increase, pushing things further north. The GFS has trended southward and slightly less with the QPF axis, now maxing out at around 1.00 inch across a few places...

Right now, I'll stick with QPF's on the order of 1.00 inch or slighly higher for places in northern IN/OH and southern lower MI, which seems to be the average.

 

[Alex Lamers]

HPC has quite the belt of snow projected...with an update coming in the next hour...but local WFOs seem to be projecting low snow ratios around 9:1 and are concerned that the fast movement of the system will knock down totals. LOT is only going with 2-5 inches as of the morning shift which seems quite low given qpf on most models. Last two GFS runs have shifted slightly south with the main QPF but have not weakened significantly.

...Alex Lamers...

 

[Robert Dewey]

HPC has quite the belt of snow projected...with an update coming in the next hour...but local WFOs seem to be projecting low snow ratios around 9:1 and are concerned that the fast movement of the system will knock down totals. LOT is only going with 2-5 inches as of the morning shift which seems quite low given qpf on most models. Last two GFS runs have shifted slightly south with the main QPF but have not weakened significantly.

...Alex Lamers...

Actually, the NAM has slowed down somewhat... The previous GFS did have a 6 hour period of intense omega at 700MB, but have now extended that to 6-9hrs. Any slowing of the system could really allow things to pile up in a hurry, moreso than what the current models are showing. In addition, things are quite unstable as DTX noted, with theta folding in on itself indicating raw conditional instability (i.e. upright convection will dominate, versus the weaker symmetric stuff). NAM shows a very tight isentropic pressure gradient across southern MI with an overrunning 50-60KNT flow...

But, if the system ends up faster, things would be cut signifcantly... Right now, I'm going for a 12 hour period of light snow, with a 6 hour period of very intense snowfall rates. As for snow ratio, I guess it depends on how tight the baroclinic zone gets... But the system isn't really coming from the deep south, so the ice crystal types in the higher cloud tops might support a higher snow ratio...

I'm still thinking, with the current runs and trends, that someone will end up with over a foot.

 

[Robert Dewey]

12Z WRF NMM Core is quite a bit stronger than the operational NAM...

It outputs 2-3 inches per hour for 3-6 hours, with not much more before or after. The 700MB omega fields are absoluting stunning - more indicative of a strong nor'easter with -15 to -20 ubars/s... The ARW Core on the other hand, is weaker... The NMM is capable of resolving features such as dynamic cooling, thermal circulations, etc..

 

[Robert Dewey]

Just got done talking with Dr. Greg Mann, and he has alerted me to another model run (not available on the web) that actually produces localized regions of -45 ubars/s... I have never seen vertical velocity that high. As he puts it, "fun times"...

Latest 18Z NAM shows increased QPF yet again...

EDIT: I like how this is turning into my personal blog :lol:

 

[Joel Wright]

Looks like the storm is going to lay down some heavy wet snow tomorrow night. I think the heaviest band will set up from southern lake MI into the southern half of lower MI. Should be a solid 7-10" in there somewhere.

Further west for us in WI, IL, and IA... looks like the storm will still be gathering moisture so by the time the best snow bands organize the storm will have vacated our area. Looks like 1-3" for most of eastern IA into NW IL and southern WI. (Maybe a lucky 4" report in there somewhere for someone who gets lucky enough to get caught under a good band). Then, in north-central IL the heavier band will develop on northeastward.


It's amazing that it could be snowing tomorrow in places that are seeing record highs today. It's nearly 60° here right now!

 

[Alex Lamers]

Here's what I have for my forecast area with my afternoon grid suite...

2-4 SC/SE WI
1-3 E IA
3-5 NW IL
5-8 NORTH SIDE of CHITOWN TO IL-WI BORDER
6-10 SOUTH SIDE to JOLIET

I'm likin how the models are falling into better agreement...especially the NCEP ones.

...Alex Lamers...

 

[Robert Dewey]

Man, HPC is going pretty heavy on the QPF... Nearly 1.30 inches. That actually lines up well with the GFS, WRF, RGEM, and UKMET models... Actually the GFS and NAM have the least amount of precip. All models bring in the -3C isotherm at 850MB and an astonishing amount of lift (the strongest omega values I have ever seen on the cold side of a system).

I'm still sticking with the typical 12 to 1 ratio that is usually present with storms that originate in that location... I think snow to liquid ratio has more to do with what kind of crystals are seeding the precipitation than the actual low level thermal profile (unless it's above freezing, obviously). Winds will be light, so that should prevent shearing of snowflakes. In fact, we could probably see some good aggregation if the snow is somewhat "sticky".

Anyway, 1.25 inches at a 12 to 1 ratio spits out 15 inches of snow. DTX is currently calling for 7 inches max (probably to be on the safe side), but if HPC's QPF forecast verifies - that maybe underdone big time. Dare I say it (I say it with just about every event, so here goes): Thundersnow looks like a big possibility... The duration of the event isn't too extended, though the models have been slowing the movement down slightly, while speeding up the actual start time of the system (probably due to a deeper system). But still, if we are able to see 6 hours of 2 or more inches per hour, that could lay down a serious swath of snow.

My only concern at this time would be if things developed a little further to the south and robbed the moisture. Once of the WRF models suggested this, and I wouldn't completely discount the idea.

 

[Aric Cylkowski]

Well, I'm going to be in the thick of it. I'll see about taking some pictures out in Flint and Burton in Michigan (where I'll be staying the night to avoid getting stuck in Davison if the college decides not to have a snow day).

Of course, its a cheap camera, so don't expect too great of detail. Otherwise, you'll probably hear from me sometime Saturday morning or late Saturday afternoon.