lakeville weather journal

Wow...I wanted to title this entry "Deja Vu", but I think I used that title last July. But, weather history...like all history...does has a tendancy to repeat itself. I think that we are all hard pressed to think the repetition here is due so soon. And, in case you didn't hear it all over the news today, yes, the pattern is scary reminiscent of January 1982 when there were two back-to-back storms each dumping 17" of snow on the Twin Cities.

So, I waited until I could study the 00Z model runs tonight to make my "preview" predictions and analysis. Others were very intrigued by the 18Z runs this afternoon, which coupled up the jet structure very nicely on this system, and progged vigorous cyclogenesis as the bulk of the storm energy rolled across KS. GFS has been relatively consistent at pointing out a similar track to the main sfc low as this past weekend storm, putting the metro and surrounds back under the gun. 00Z GFS still tracking like this, but it seems that NAM might have taken a slight departure tonight. 18Z NAM was running the storm track pretty consistent with the other models, and decided to go a bit farther north with the 00Z run, and lacked some other consistency with the previous version. GFS on the other hand is almost carbon-copy. GFS still has the best track record for these Pac-gen'ed winter cyclones, in my opinion. MOS from it at station KLVN has been extremely reliable as well.

Near term concern (or, "Round One") is warm air advection begining tomorrow AM, with H70 flow especially running up from the Gulf of Mex by just afternoon, and with already high relhum in place...low lev atmos is 'primed', which could aid dendridic growth in the low-mid level stratus that will end up rolling over the area through the day. Looks like GFS places precip beginning in earnest over SW MN at first around noon Wednesday, and then progresses NE quickly...with Twin Cities being in height of snowfall around the PM rush hour. Most commercial progs tonight called for 2-4" around the metro by 1800 CST, and I would concur with that given this synopsis. I would expect snow to taper a bit after 06Z Thurs, and redevelop for round two.

Round two comes after the main low moves from KS to northeast IA by 00Z Friday (18C Thurs) and has a central pressure of 980mb or less...very powerful height falls will preceed as a result, and per the GFS, I think we will see heavy snow bands develop between 18Z and 22Z Thurs, and like the last storm will develop and propogate from southeast MN towards the northwest. GFS precip bullseye is focused over SE MN, and pushes the 1" accum Pwat mark...translating on the 10:1 rule for snow as 10".

Here is where I may not totally toss the NAM...as stated before, the 00Z NAM run put that 980 low further north...but NAM develops the upper low and closes it off over the Badger State from 00Z Fri-12Z Sat...quite the stall-out. As a result, precip progs for NAM favor heavy initial snowbands acrs EC MN and WC WI, then changing over to a more "steady" and sustained -SN event into early Sat MN.

Turning to MOS for the period, GFS categorical snowfall outputs show 6-8" through 06C Thurs, and 8"+ from then through Fri AM. I will also point out that the GFS temps run warm tomorrow night...just hovering at if not slightly above freezing. This is a good indication we will see some mixing possible in the precip during the rush hour.

WINTER STORM WARNING Noon Wed-Noon Friday
Wednesday...Cloudy, High 34, snow and/or sleet or snow pellets move in after 4pm. Wind ESE 5-10. All snow after dark. Total accumulation 5-7". Low 25.
Thursday...Cloudy, light snow in the AM possible with 1-2" accum possible. Then heavy snow developing after 4pm. 8-12" possible. Gusty ESE winds 15-20 mph. High 32, low 25.
Friday...Cloudy, snow tapering off after noon. Total storm accumulation 12-17" possible. Blustery and cooler, High 23. Low 19.

Posted by pierre at 11:16 PM | Permalink

Last night right before midnight, and at the height of the snowfall intensity yesterday, we measured 4.5" at lakevilleweather.com, and again this morning as we began digging out, added another 4.5" from the overnight snowfall, bringing the crop to 9" total (so far). At this time, light snow continues to fall, and along with all other forecast thinkers out there, we expect another 1-2" before all said and done with this system.

Core of the system - 990mb Sfc Low is now about 50nm north of the Quad Cities (KMLI) and on relatively slower than what yesterdays models first progged, and due to partial blocking to the NE as mentioned in previous post. 12Z NAM run init'd a tad better than GFS, showing excellent sfc feature placement and capturing other dynamic features in the mid and upper levels that are easy to correlate with rad/sat imagry. A great example is the dry surge behind the storm, now maxing acrs the MS delta up towards and along the Upper OH river valley. This matches a H30 and H70 coupled jet structure that has a max streak moving zonally acrs the TX plains and then wrapping up around the SE quad of the system. 990 low begins to weaken as it stalls out over So. Lk MI and ends up getting moisture flow cut off by the dry inflow. Hum levels increase in wake due to snowpack, and upper level low will continue to trigger -SN showers and flurries through early Monday.

Next system comes in from the PacNW again, but both NAM and GFS do not portray nearly the amount of dynamic digging of the trough as it moves over the Rockies as our currently departing system did. Nonetheless, again very zonal setup will feed the system initially with Pac moisture, and GFS paints a typical track (like this last one had). However, Gulf moisture still not progged to be tapped nearly as much, and dewpoints do get progged at higher levels for the mid-MS valley states, but much of this might be related to melting evap in the prog?

For now we will continue to dig out and look ahead to what might be a stormy beginning to March.

Posted by pierre at 12:43 PM | Permalink

Much of today saw warm air advection and overrun continue. FZRA and PL throughout much of the day as result, changing all over to -SN to SN by 21Z. 12Z models and 18Z MOS avail to me attm show trend of SN through the night. MPX WSR-88D now showing western metro with heaviest band of SN. National NEXRAD comp paints more moisture moving north, while sat imgry showing dry fetch moving into TX and OK on the SW flank of the H8 low. MADIS confirms drier dewpts in this area. GFS had really reinforced the WAA and moisture conveyence on the eastern flank of the storm through the night, wrapping right into EC MN/WC WI. In fact, LLJ max exits over the TC metro on the GFS, and to punch the energy quotient, H3 jet steak exits over KMLI, with some coupling potential with the LLJ.

This would all support redev of conv and snow bands over SE MN/NE IA, with motion either NW or N of the bands. MPX WFO wrote this afternoon that they reinforce the 12-15" pops acrs the area. KARE-11 has progged 6-9" as of 1700 CST, WCCO "around 10", and KSTP went way down to 2-4". Thinking on the later was that storm track of main sfc low is too far south. Still not convinced that this will pan out, as the southerly fetch of drier air from NM and TX will kick it north a bit, and that both NAM and GFS paint a bit of a rex block to the east and north.

I am going with a 9-10" hunch now for the sundown-sunup period for Lakeville and the SE metro. Stay tuned!!

Posted by pierre at 5:38 PM | Permalink

Winter storm predictions are easy to bust, and amidst the commercial wx hype and media attention, local TV forecasters were quick to embrace a relenting 00Z model run last night. 00Z runs painted a better picture for the Friday overnight, and renewed forecast discussions and statements tentatively backed off the 3-5" or -6" progs for the overnight snow event. Primary view from the 00Z runs was a slowing low pressure center in SE CO, as well as a very warm overrun that was setting up off the LLJ. The only forecast hints that were stymied was the baroclinic wrinkle that emerged over the KRGK-KONA river valley and gave rise to some elevated convection which moved SE overnight. This pumped 3-8" of snow from Prescott, WI down to KMSN.

Focus this morning turned to how the models handled the convection signatures in the 12Z runs. MPX-WFO tossed out the 00Z GFS in their early AM shift discussion, but I think that the model had some even points to grab at. Init and matchup with NAM features were good, and I think that GFS still has some better handling of the pressure gradients that are setting up troughs that spoke out from the low. Along with the trowaling comes the convective setups...and rad/sat imagry has confirmed the higher tops signature of the elevated convection acrs NE and IA this early AM. Law enforecement spotter reports this morning in these areas have indicated "thunder sleets" and FZRA acrs IA that have downed power lines.

Dewpts from TX on up into the center of the low are high, and even extend into srn NE, and model Pwat vals are consistently high in same area as well, so moisture is in place. Overrun effect still in place it seems, as sleet taps my windows at present. Radar echoes show first band of moderate to heavy precip just along I-90 attm. KULM and KRWF are now obs -SN, and my gut is that the colder air aloft is starting to seep into the north side of the system. This sets our area up for the heaviest snow potential this afternoon. Redevelopment of snow bands will depend on whether or not convection redevs to our south, and how the low track goes through the day.

For now, my concurrence is with general thinking that we get 4-7" today by sundown, with potental of 4-5" more after dark. May start as sleet/heavy wet snow and then all snow by mid-late afternoon.

Posted by pierre at 8:42 AM | Permalink

Yes, I know, the absence has been long...but I really had nothing to sink my teeth into, ya know? We had a protracted and severe cold snap as the polar jet moved way into the central plains a couple weeks back, and the polar jet has now receded back to its "normal" home near the Arctic Circle. In its place the subtropical jet has moved up from the mid lats and has ushered in the great peace of zonal flow for the last couple days...bringing a nice fetch of Pac air to warm us to 40's the last couple days...a 60 degree swing since two or so weeks back with temps in the -10's and -20's. A clipper pushed through yesterday cooling things back off for today, which was seasonal at mid-lower 30's. Temp grids are still low and a few inches more of snowpack remaining in South Cent MN has helped keep the air at the surface colder...and primed for the upcoming storm.

So...here it is, "The Preview" of what our local Commercial weather folks are calling the storm of the season. PacNW low scooted over the Cascade range, southeast to lower ID early this AM, and now has settled into the Bitteroot Valley of western MT. As a matter of fact, the 00Z model runs nailed the 06Z position of the 996mb low over Dillon, MT...with good initialization elsewhere, as confirmed by spot on surface as well as RAOB checks. The models are tight...both NAM and GFS very close to each other in addition to their prog checks.

Sfc low is progged to slip east-south-east over Yellowstone Park overnight, and slide down the front range from the Bighorns to the Tetons south to near Denver by mid-afternoon. Drawing strength from subsidence left by the high pressure Chinooks that had winds off the front range yesterday gusting over 60 kts, the low will stabilize as the H50, and eventually H30 upper lows will begin to form up over the Rockies. Ahead of this is a dramatically deveoping LLJ streak from the Gulf of Mex straight up the mid-MS valley states...going to a 70kt jet max at H85 by noon saturday. It is this low level flow that will kick off precip for the Lakeville area tomorrow night.

SE-Southerly flow tomorrow will continue to increase precipitable water values and hum through Saturday. As this moisture runs over our cold air surface stratas, we will see the isentropic precip begin to fall sometime close to sundown tomorrow, mainly as snow. Meanwhile, the system stacks up over KS, and moves out by late Saturday...both NAM and GFS track the low as a stacked system (no more tilt like prev models) and moves to central MO/IA border by 0600 am Sunday. This is when I think we will see the next big precip wave hit the area, and the pressure gradient would suggest some very windy conditions developing with the system along with the revived snowfall.

Models track low over Chicago by 6am monday, and still strong wrap-around dynamics will affect us as we see back-side effects from the storm. Snow should then taper by mid-late Monday. This storm almost seems prolific, as it covers a ton of area very slowly and purposefully. MOS categoricals on the snowfall chances are 4-6" between Friday and Saturday AM, and then 8"+ for late Sat into Sunday, and then another 2-4" from late Sun through Monday. No disagreement between NAM or GFS MOS for these stats either...so I think the following approach is valid: get ready for snow!! My mark on Lakeville storm total (Friday through Monday) is at 16"...a bit on the heavy side for some, but I think this has the markings of a whopper.

Posted by pierre at 12:43 AM | Permalink