lakeville weather journal

As hoped for, convection overnight and new modeling of the synoptic disturbance out west is giving a better picture of convection chances this afternoon through tonight. LLJ is hoisting more warm air advection into southern MN as progged by all previous modeling. This provided a nice push of CAPE between midnight and 2am in front of the shortwave mentioned in the previous post. Heavy rain and some small hail affected the TC Metro with the resultant squall line. As that line developed into an MCS over western WI, debris clouds/trailing stratus deck evolved over SC and SE MN. That deck is now slowly but surely eroding as we move past noon, hampered only by continually increasing moist advection from the south.

MADIS surface reports clearly depict warm front now advancing more rapidly northbound. Boundary traces back to a triple-point low centered over SD at 1000mb. North-northeast disecting southwest through the low is the cold boundary. NAM and latest RUC model runs agree on low moving along the cold boundary as warm front advances northeast, while another shortwave rolls off the CO front range and into the Sioux Empire by early this evening. Meanwhile, warm sector heating will build in earnest with highs well past 90°F acrs SW MN and NW IA. Resultant CAPE progged by RUC is well in 3000-4000J/kg range over central MN. Mid-level capping from WAA flow will most likely break from mixing and forcing efforts as warm front and shortwave move in unison across the area. Models suggest the cap break to occur between 21-23Z and in area from MOX-AXN-HCD-MOX, and then expanding southwesterly.

This grants some validity to MPX-NWS grids targeting the I-94 corridoor as init area for most severe storms. However, as shortwave pushes in, initiation will trend more to the southwest. Morning satellite loop showed cumulus streaks breaking out over SW MN inhibited from outflow of WI MCS. This indicates the cap is still in place, but that low-mid layer CAPE is building. Also, along the cool boundary that runs from PIR-JMS-FAR-BJI, some deeper sheer is occuring. Will expect TRSA development to continue along and around this area, but as it is outside of warm sector, severity will be limited. Effect of any storms evolving along that portion of the boundary will be to reinforce the front with cool outflow, and as it ejects into warm sector will reinforce the continued nocturnal development tonight.

Given the limited confidence on the cap actually breaking, I will introduce my forecast with a slightly lower potential grid, and will keep it on the short-term as this situation is in flux.

Lakeville forecast for rest of Monday...Mostly cloudy with a 50% chance of thunderstorms after 5pm. Some storms could be severe with large hail, heavy rain, and damaging wind. Then an 80% chance of showers and thunderstorms after 8pm. High 82. Low 62. Rain ending after 1am.

Posted by pierre at 2:00 PM | Permalink

The MN State Fair is in full swing this week. Invariably, fairgoers at some point will encounter a thunderstorm at the fair, and tomorrow looks like it could ripen for the chance. Warm southerly flow today and tomorrow is ushering in moisture and instability. Tonights late 00Z NAM run paints a very volatile picture with CAPE values surging to 4500J/kg and PWATs to the 2" range by 00Z tomorrow. This is all kept in check by CIN values in the mid-layers of the atmosphere well into the -1000's. That type of inhibition is borne of the H70 temp progs, which show that layer warming to over 15° C by late afternoon. The capping will only be broken by airmass forcing along the frontal boundary or by a shortwave ripple across the still very zonal upper jet. NAM seems to favor former scenario, as it now paints best precip bulleyes along the frontal zone through the forecast. This is contrasted to the 18Z run where it figured an early afternoon initiation timeframe.

Speaking of shortwave ripples, this is the only other variable that needs watching and waiting. Currently one of these energy ripples is spreading from the Sioux Empire into SWern MN. Just before sundown, mid-layer cumulus clouds were developing across this area. Present infra-red imagery indicated the clouds continue to build in this area. Should lifting continue overnight, we could see an early-AM round of thunder shaking us from bed near dawn.

At current time, will advise that 50/50 chance of thunderstorms in NWS grid for lakeville looks reasonable, but remainder of forecast will depend on just what happens with overnight convection chance, and affect (if any) on convective chances Monday. Will update in the AM.

Posted by pierre at 11:11 PM | Permalink

The unsettled pattern, previously thought to be exiting the area today, has stuck around and continues to plague southern MN with rain and the threat of hail and wind. The zonal flow of the upper level jet continues to streak across the MN/IA border, and little airmass transgression has occurred. Therefore, stubborn warm/stationary front remains over the border and is still the focus of main forcing and genesis for convective weather.

Currently (1700 CDT hour), SPC is watching area of initiation that broke some modest capping in srn MN today. Surface indications and RUC modeling indicates vorticity and surface heating pooled in SW MN and has kicked up some elevated convection, and is pushing ENE bound towards the TC Metro. Slight MCS characteristics are forming with this cell cluster as well, as it rides up on strong southerly low level advection and gets an upper jet steer associated with another shortwave ripple in the mid-layers. This increases hail threat with these storms and WW issuance is likely.

The SW MN MCS will propagate ENE and then easterly into WI tonight, with outflow wake carrying along with the shortwave and pushing the frontal boundary a bit further south overnight. This should spell some breathing room for clearing tomorrow over much of MN. After low stratus and fog burns off late morning, temps should rebound nicely. This will reset the stage for convective development again late Wednesday into Thursday AM, as yet another shortwave pushes in from the Sioux Empire and precedes a more significant cold front that should eject from Saskatchewan Thursday. Models are still struggling with the coupling of features from the stubborn corn belt front and the Canadian front, but hopefully the latter spells some drying for the region late this week and weekend. Your Lakeville Forecast...

Tonight...Thunderstorms likely after 5pm. Chance of rain 70%, and some storms could be severe with hail and damaging winds. Then fog develops after dark, with a low of 65 and light wind from the northeast 5 mph

Thursday...Thunderstorms ending by noon. Wind shifts to the NW 5-10mph by 2pm. High 75. Low 56.

Posted by pierre at 5:07 PM | Permalink

Rain, rain, go away? Now that a "good soaking rain" has turned into "worst flood in history" for southeastern MN, people want a reprieve. We have been, in comparison, lucky in our neck of the woods. Rainfall totals for Lakeville over the last two days have totaled 2.28" here at our station -- compare that with Witoka, MN which has seen 20"+, and major flooding, mudslides, and fatalities from this wet and stormy pattern.

The TC Metro is now shrouded in fog and mist as things to our south and west "regroup" a bit. Strong low pressure is troughing over the Rockies and will push out over the plains this afternoon. Meanwhile, the surface front associated with this system will push across Dakota and occlude the warm/stationary front now running along I-90 in southern MN. As this occurs, the warm front will translate slightly north and east producing showers and thunderstorms through the day today for the southern half of MN. Once we enter the "warm sector" overnight tonight, the atmosphere will reprime again, albeit quickly, for another round of storms that should push through our area by mid-Tuesday morning.

Variables to consider in this forecast are all over the spectrum, and the various computer models are hindered by the sloppiness and complexity of it all -- 12Z, 18Z, and 00Z runs yesterday for NAM and GFS all lacked continuity. So, generalization has remained in the forecast grids for many WFO's...and the common theme has been "you will get wet"!

For all intents and purposes here at LakevilleWeather.com, are greatest concern, and threat, from the remainder of this unsettled pattern will be rainfall amounts and severe weather. I will address the latter first:

Current regime of cooler temps and densely-clouded atmosphere will provide little convective potential for severe-level storms today. However, partial clearing is occurring behind current squall line moving across SW/Srn MN, with greatest clearing west of SUX at this time. W-SW of here surface temps and dp's are rapidly climbing through the 70's, and if cloud cover is limited, should hit 80's for certain by midday. This will provide best CAPE scenario for squall/MCS development as the long wave trough and cold front pushes into this airmass. Convective inhibition values, however, are also being progged with high marks by both RUC and NAM runs for forecast periods through tonight. Basically, this is due to very warm wide-area advection flow from the south-southwest that will persist until CFP. Capping will prevail unless some other element breaks the potential free. Long-story-short: severe potential - at least for the Lakeville area - seems minor at this time.

Rainfall amounts, however, remain a big challenge. Precip. water values and "nature of the beast" type history of our current system could spell more "training" type showers through today. As front approaches, however, we are tasked with the assumption that an MCS/squall event that will have cells in latter-mature/dissipation stage will pass through our area late between midnight tonight and noon Tuesday. Given the vast amount of moisture in the system, the latter event could spell some heavy downpours that cause flash flooding in our area. Topsoil is saturated, and runoff in urban areas will be street-borne as storm sewers struggle to keep up.

In summary, it would be best to tune into local news and weather forecasts this evening as the "main event" for our area will not shape up until the overnight hours. Here is a quick crack at the forecast for Lakeville:

Rest of Monday - Fog and drizzle persist until afternoon. Then a 50% chance of showers and thunderstorms. High 67. SE wind 5-10 mph.

Wednesday - Partly Cloudy. High of 80. Northwest wind 5-10 mph.

Posted by pierre at 9:13 AM | Permalink

After a summer of drought, the prayers and exhortations of many MN residents are finally being realized as a very stubborn frontal boundary and active upper level system has brought soaking - and unfortunately flooding - rains to southern MN. Albeit to late for this rain to arrive for many farmers and gardeners, this rain will finally true-up the area's rainfall totals to normal. 1.2" have fallen Saturday alone, bringing our total to 4.97" for August (so far).

The synopsis lies in a warm front now lined up along, or just north of, I-80 in Central IA. South of and near this boundary in IA, highs soared into the upper 80's today, while cloud cover and showery precip over southern MN up towards the TC Metro kept the atmosphere cooled into the 60's. Across the front is a steady low level moisture flow borne on southerly H85 winds. Moderate shortwave impulses moving through the H70 and H50 layers of the atmosphere along the front are giving enough vorticity to produce a continual train of showers and thunderstorms along and just north of the front, and this is what threatens southern MN through the morning hours.

Lakeville sits on the northern periphery of the bulk activity, so we can expect passing showers and thunderstorms through at least 4am Sunday. A slight break may occur during church hours of the morning, and then more TSRA will develop mainly mid-afternoon. At this time, only decent modeling avail is 00Z NAM which nailed tonights training storms across srn MN. GFS also blobbed precip max's over srn MN, but with more trending for SE'rn MN...which is fine as flash flooding is a major concern over that part of the state and along the MS River and its tributaries in that region. 00Z GFS also seems to trend a bit of an MCS signature tomorrow afternoon in SE MN/NE IA. That might be a stretch, but 50/50 pops in MOS seem pretty fair for both models. Wind profiles suggest a bit more vorticity might be on tap later Sunday as well.

After this front sags a bit further south and then translates into a stationary boundary Monday afternoon across MO, eyes of WFO's in the area have also turned to the mid-week period when two major weather-affecting events affect the North American continent: Hurricane Dean bound for the Yucatan, and possibly affecting srn TX, and a unseasonably deep Pac-NW cyclone bound for the intermountain west. GFS paints the latter more like a spring storm, dropping out of Alberta along the front ranges, and into the high plains of CO and NE as it triggers off a short-wave cold front to push across the area sometime Wednesday night. As for Dean, if the NHC forecast holds, landfall will be about 100 miles south of TX on Wed night...however Gulf moisture will pump more rapidly up the LLJ ahead of the system we will experience as a result of Dean's influence. If Pwats and DT's rise as a result, we could see quite another potent round of thunder and rain mid week.

Posted by pierre at 12:00 AM | Permalink

It has been quite a while since the last entry...but it has been quite a while since any significant weather (other than the pervasive drought) has affected the area. I don't think I needed to give significant analysis day-after-day about the lack of rain -- you know all about it.

Lucky for Lakeville, things have shifted this weekend. A shortwave trough with an unseasonable pressure drop and an associated frontal boundary has provided the energy needed to develop some real rain makers for the Twin Cities Metro. Between 0300-0430 CDT this morning, a well formed MCS pushed ESE from the frontal boundary across central MN and into the TC Metro. Straight-line wind damage was reported across the state from Alexandria to St. Paul, and the classic "derecho" bow-shaped echo was noted on radar returns from that system. Torrential rainfall also occurred, with flash flooding reported across the area. LakevilleWeather.com's SKYWARN spotting team, amateur radio station KD0ASB, went out into the rain to report flooding in the Apple Valley and Lakeville areas. We reported 18" of standing water in the intersection of Co Rd 42 and Pennock, as well as several other areas with 2-3" of water standing or running over the roads. We recorded 1.75" here at lakevilleweather.com.

This afternoon, the scenario has "reset". As noted in the depiction above (Mesoscale Discussion #1725 from the SPC), the atmosphere is re-priming for another round of thunderstorms this afternoon and evening as the front re-approaches the area. Ahead of the front, dewpoints are tagging 76-78°F in western MN. The MPX sounding this morning showed some slight capping, however, that feature is diminishing with the retro-expansive outflow from this morning's re-development of elevated convection from FBL-RST-LSE. Now, focus on initiation will be cues from NEXRAD and satellite imagry. At this time (21Z) some TCU's popping in central MN behind of small area of cumulus streeting acrs the central MN River valley. Would guess best initiation from these cues and RUC modeling at this hour would be across Stearns, Becker, and northern Wright Co's, with a squall lining up to move from NW to SE metro between 1700-2000 CDT. Best chance for severe development will remain on the western flank of the line, which will remain in best potential shear and CAPE. Also expect some training, or possible secondary development to occur right along the front as it sweeps through, with CFP around 00Z tonight.

Please check back for warnings and advisories posted live as they are issued here on lakevilleweather.com, and stay tuned to local TV and radio broadcasts for updates.

Posted by pierre at 4:00 PM | Permalink