lakeville weather journal

Frontal movement has still remained on track, with southern and western slope of front now pushing across southwest MN. SPC has just published a Mesoscale Discussion and a Severe Thunderstorm Watch. Satellite now shows clear-cut convective development running parallel and just ahead of the front, and radar confirms with a line of cells, becoming more MCS and squall-like in the north-eastern and north-central portions of MN.

Closer to home, some cells have fired over the MN River Valley near Jordan and LeSuer. All of the activity is moving east at 20-30 mph. Will have to keep a close eye on situation, as these more local cells could have potential to intensify rapidly. Main threat for these storms are damaging wind and hail.

Lakeville can expect these storms to roll through between 1430-1600 this afternoon.

Posted by pierre at 1:58 PM | Permalink

At time of this writing, many changes are possible to SPC and local WFO grids and forecasts, so I will keep this brief on the synoptical side. Heat Idx is currently over the century mark at Lakeville, as temps over 88 and dewpoints over 70 have built quickly since sunup. The rHum outside is 62%, and it is being felt in earnest, as air conditioning is the rule everywhere across town. Skies are sunny to boot, and warm instability will continue to build in advance of a cold front now lined up from KBDE to just west of KGPZ and then arching back to KAXN and KATY. Associated 1010mb low is now up over Lake of the Woods, and not progged to deepen much more. Nonetheless, height falls should increase during the day for our area as front approaches and diurnal heat aids the differential. CAPE values are in the 2000-3000J/kg range and possibly some 4000J/kg pockets mixed in, and lifting indicies are between -6 and -10! The amount of convection will be regulated, however, by the weakening of the CAP, which has been in place now for the better of 72 hours. H70 temps on recent balloon launches remain at 15°C over our area. However, some models have suggested a rapid cooling of the mid-layers of the atmosphere. Should this be the case, our area could see +TSRA with an intense large hail threat, not unlike last week.

Right now, best guesses are the 1pm-3pm time frame for initiation. Morning progress of the front suggests that this is a on-time guess. Still waiting for new RAOB data to confirm the erosion of the CAP. Best clue so far will be satellite imagry which is beginning to show some instability CU's building just ahead and in vcty of the front.

SPC has us under slight risk for severe weather on the Day 1 Outlook for this system, and new Day 1 is due in 1/2 an hour. Will update as day progresses.

Posted by pierre at 11:00 AM | Permalink

Well, since our last severe weather outbreak -- just over a week back -- Lakeville and the surrounding region has enjoyed an early summer. Today things have turned almost tropical, with a current Temp and DP of 88/65. Between breeze rushes, that brings the heat index to about 100. And, although the southerly breeze is helping keep things somewhat bearable outdoors, it has also ushered in the moisture and heat needed to fuel severe convection. Now we need the other elements - lift, maybe a bit of spin, and some cooler air aloft to allow the storms to grow.

Currently, that is the only stymie for a convective eruption - capping is present at the mid layer of the troposphere from the central Dakotas eastward towards the Great Lakes. That is rapidly changing attm for a couple reasons now evolving on both a meso- and synoptic-scale. First, mesoscale analysis over the region of frontogenesis (currently western SD, NE, and eastern WY) shows a very abrupt dryline has formed from the Black Hills southwestward over the NE panhandle. Temps are at or near the century mark, but there is a 30 degree F drop in dewpoints over a span of 50 miles in the region. Add to that evidence that the cap over SoDak is weakening as shown in the 18Z RAOB from ABR. And now convection has fired from the SoDak badlands southwest along the dryline.

Frontogenesis should wrap up behind this line, and push east through the evening hours. Currently, it looks as though gut instinct is going to have to weigh in heavilly on system timing for our area. Supposing that the cap continues to weaken ahead of the system, and supposing that the upper jet flow remains in its swift zonal pattern until the trough arrives, we are looking at a fropa of mid-monday AM. Most WFO forecast grids have been focusing on that timeframe with earlier model runs as well. The next factor in handicapping this system is whether or not a MCS/and or squall line forms ahead of, or along the frontal boundary.

I am going to hedge my bets towards "ahead and possibly along"...and here is why: should the cap continue to weaken tonight from west to east, we could see impulse initiation over western to central MN by midnight. Then is is a matter of propogation, and with TD's in the mid-60's, PWats in the 1.5" to 2" range in all previous modeling available, propogation should be easy enough. We then move to supercell indicies...which are at high levels across the rapidly destabilizing central Dakotas. This area should move east, and if conditions hold tonight, we could see round one glance the metro around 3am and round two -- a more substantial round possibly -- just in advance of the front between 7am and 10am.

For some reason, models are not publishing fully on normally available internet sources, so this near-term outlook is all I can muster for now. MPX just published a short and generalized FD, and may be due to other activity now cropping up in Nrn MN (WW410 was just issued for the northern 1/3 of MN til midnight, and a tornado touched down near Crookston about 20 minutes ago). Will have to keep watching conditions as the night wears on...

Tonight...Warm and humid. Partly turning mostly cloudy, 40% chance of thunderstorms after 1am. Low 72. Winds south southwest 10-15mph, gusting to 30.

Tuesday...Sunny and dry with a high of 76. Northwest wind 5-10 mph.

Posted by pierre at 4:30 PM | Permalink

As noted in this AM's post, dryline was focus for initiation of severe cells. The first fired over Goodhue county just to our SE, and moved rapidly NE towards St. Croix and Pierce Co's in WI. Tornado warnings were issued in conjunction with this storm. Dynamics were easily read from both MADIS sfc plots and most recent RUC modeling...drying in SWrn MN continues, and dry slot is clearly evident on sat imgry. Dewpoints have dropped almost 10 degrees in the last 4 hrs here at Lakeville, proving the point. SPC now has carved out the TC Metro from the greatest risk areas.

Meanwhile, low pressure center deepens in Dakota, and has been inching NEbound. Steep lapse rates and height falls in vcty of the low triggered SPC to issue Tornado Watch 357 for the WC, NW and Nrn parts of MN. That watch now houses some cells that have reached severe levels, particularly around the confluence MN/ND/SD borders. With motion of the low towards the NE, and further development of storms on the SE flank of the circulation, convective activity may still affect the TC Metro later this evening.

CFP is still looking solid at near 00Z, and behind the front flow will shift rapidly from the NW, fetching in cooler and drier air. Because the low is so deep, winds will remain breezy/gusty through Saturday. Next system is progged to move another PacNW borne wave from across the front range and up over the plains and mid-MS valley by Tuesday. Chances of showers and thunderstorms remain in the forecast grids from Sunday through Tuesday as a result, with seasonal temps (upper 70's).

Posted by pierre at 1:00 PM | Permalink

The sirens awoke Lakeville at 2:30am this morning as elevated thunderstorms erupted on the nose of the LLJ and associated warm frontal boundary, dropping .75" to 1" hail on our community right around 3am. Those cells raced northeast at 65mph on the swift flow of the LLJ. The Metro SKYWARN net (of severe weather spotters which we are a part of) activated informally and then stood down at 4:30am until further notice. That notice has been given and it looks like the NWS office in Chanhassen (MPX) is calling for net activation sometime around noon or 1300 today...which means this is when they think things will turn ugly for weather.

The upper level trough and the associated surface cold front is progged to push through MN today, making CFP around 00Z. Ahead of the front, strong to severe storms are forecast to fire in the unstable and primed atmosphere. The far eastern TC Metro and most of WI is in a "high" categorical risk for severe weather today...a rarity...and the rest of EC and Cent MN is under a moderate risk. System timing this morning, however, is a bit of a challenge. Local conditions are heating up, both temp and DewPt wise, and RUC runs have been consistent this AM in granting the highest severe weather indicies to the TC metro and SErn MN.

Now, clearing line has crossed into TC metro, as remnant stratocu from overnight has finally pushed off to the east. Question remains, however, is atmosphere destab'd enough to the west of the line to support storm development? It would appear somewhat of a dryline is occuring just to our west, as DewPts have dropped about 10 degrees on MADIS plots over the last hour. This could spell development will be imminent in the next two hours right on top of us, or just to our east....again...only time will tell. Due to congruity of the forecast elements, I am not changing my outlook for today. Please stay tuned to NOAA weather radio, or local TV and Radio stations for developing weather situations.

Posted by pierre at 10:24 AM | Permalink

On the basis of an even more explosive scenario in the cards, SPC has now placed us under a severe threat for today and tomorrow, with more emphasis on tomorrow's conditions. The low pressure system, now gaining strength as it rolls down the front ranges, is forecast to deepen to around 970mb by the time it is in the open plains later this evening. The southerly flow ahead of the low will increase as a result and the upper jet will be coming across the trough and maxing out its nose over the 970mb sfc low. Placement of these features look to be western SD in all models by 00Z tonight, in conjunction with a very strong (50kt) south-southwestly H85 flow. With shear in place, and CAPE in the 3000J/kg range over the central dakotas, explosive MCS could develop quickly today and be showing large hail and tornadoes by 5pm CDT across especially Eastern SD.

That MCS will propagate ENE into MN as upper jet turns slightly to couple with the southerly LLJ overnight, and I would expect remnants to affect much of central, but more likely NW and NC MN overnight. As this happens, any warm upper level fetch that could have capped us Thursday will be destabilized. The next piece of the puzzle is timing of the cold front as it sweeps across the area thurs. NAM and GFS both push the front to a DLH-MGG-FRM line by 23Z, and if initiation does not occur between 18Z and 22Z, I would say that the Twin Cities metro will be on the back side of the weather. However, if that front slows up today and tonight, or if there is initiation just along and ahead of the front tomorrow AM and early afternoon, our threat becomes exponentially higher for severe weather. The forecasts coming out of all offices are very categorical due to this fine-tuning of timing issue. It will be windy, warmer, getting humid through today. There is a chance we will get rain showers and thunderstorms, but not as severe today. There is a chance that we will get more thunderstorms tomorrow, and possibly more severe, but the timing is going to be a close call. Instinctively, I am going to hunch on the front slowing up a tick, as the low trajects more northbound over the next 18 hrs, and thusly my forecast...

Wednesday...40% chance of rain showers in the AM, then partly cloudy and breezy through the day. Warmer and more humid with high of 76. Gusty south winds 20-30mph, with gusts to 45. 40% chance of showers and thunderstorms after 6pm, low 65.
Thursday...50%of showers and thunderstorms before noon. Then an 80% chance of showers and thunderstorms after 2pm. Some storms could be severe with damaging winds, hail, and a possible tornado. High 84. Winds south turning southwest 15-20 mph. Rain ending after 9pm, low 55.
Friday, Mostly Sunny, High 74. Wind NW 5-10mph, low 56.

Posted by pierre at 9:11 AM | Permalink

Tricky June convection forecast coming our way for the mid week. 48-72hr period in current model runs showing many ingredients for a widespread severe weather event coming together. Having shown these elements this far out, SPC has issued threat assessments for the area both Wednesday and Thursday.

Main culprit is a longwave trough currently pushing its way into the Pac-NW, and an associated surface low now developing on the lee side of the Cascades. As the system sweeps across the MT mountain ranges, and high pressure anchors over the Appalachians, a strong southerly low level flow will develop over the plains and the upper MS valley. The low level flow will usher in high dewpoints and warmer temps from the Gulf of Mexico, and as slight blocking sets up to our east, the surface low will slow its eastward progress a bit and a well defined cold front should set up. As that front pushes east, upper jet dynamics will remain mostly zonal across the front (according to GFS), while low level flow remains firmly in place ahead of it. The potential for deep layer shear is high. Development of supercell structures will be limited to the ability of the low level flow to work its way into the H70-H50 spectrum. Some model outputs are suggesting a very elevated warm layer.

Nonetheless, I think that concurrence with the professional offices is warranted for a slight risk of severe weather for the Wednesday overnight and Thursday afternoon. Timing of system will need to be tweaked up tonight and tomorrow morning. But three day outlook is a cinch for generalities today...

Tuesday...Mostly Sunny. High 74. Calm winds turning WSW 5mph. Low 53.
Wednesday...Partly cloudy. High 83. Gusty southeast wind 10-20mph. After sundown a 40% chance of showers and thunderstorms, some with heavy rain and damaging wind. Low 55.
Thursday...Mostly cloudy. High 80. Showers and thunderstorms likely in the afternoon, some could be severe. Southeast wind 10-15mph turning southwest 5-10. Rain ending after sundown. Low 50.

Posted by pierre at 9:58 AM | Permalink