lakeville weather journal

Models and statistics are aiming once again for an unseasonably stormy Monday. Today, the first official day of Autumn, witnessed high temps better suited for mid July. Central Dakotas saw record breaking temps in the upper 90's ahead of the main culprit for the storms predicted to move into our forecast tomorrow -- a deep long wave trough digging from Alberta well south across the Intermountain West. This feature will translate slowly west through tonight and tomorrow and bringing with it monsoonal moisture tapped from the SW CONUS. Already, precipitable water levels are high, but as the low level flow from the system gets a boost from a small tropical low parked over LA tomorrow, Gulf of Mex moisture will begin to transport on the flow as well.

Dynamics for the system are a hard read thus far on the models. Notably, NWS-MPX has not had a HWO out for a good part of this evening, and I imagine they are wrestling with the same questions I have. Frontal system associated with the upper trough is driving some decent convection across the Dakotas today, and SPC put out WWa's for the activity, but without any deep shear the cells are remaining elevated across the high plains, and not acting up on the severe side of things. 00z models keep the mediocre dynamics trending through the 24-hr period, which could spell lots of soaking rain for us, but not much in the way of severe weather.

Notwithstanding the synoptic analysis thus given, the rain chance is there along with thunder (and thus, lightning). So, we could see some dangerous storms anyway. SPC also noted lack of shear dynamics in their issuance of a slight risk inclusion for the TC Metro tomorrow, but also noting that the tropical lapse rates bring pumped northward from the LA low will aid destabilization of the atmosphere tomorrow. NAM seems to manage this well, showing a late morning temps of 10°F at H70 quickly cooling through 20z-00z. Approach of LLJ ahead of the front will increase moisture and aid destab as well.

For now, it looks like common forecast grids (both commercial and NWS) are pointing to a mid-afternoon init period, probably across central MN. Relative storm motion and growth per modeling would bring rain to TC Metro near supper time, if not a touch sooner (another rush-hour storm, anyone?) Will have to do another look in the morning, particularly at RUC modeling of CAPE and shear values as the day progresses.

Posted by pierre at 11:10 PM | Permalink

Model progs have held up overnight, and shortwave has raced into Dakota and is now approaching the MN border as expected. Ahead of the front, convection is trying to work its way vertically through a moderately warm mid-layer. Visible Sat and corresponding MPX WSR echoes indicate a line that formed along the Hwy 23 route from STC-Granite Falls. CB towers will struggle in organization until the line moves further ENE into the area of weaker CIN.

I would expect the TC Metro to be affected by this line within the next 2-3 hours, with main threat to be a brief downpour. Small hail cannot be ruled out, but non-supercell nature of the line will keep us clear of any threats like we had last night. After that line clears, the front will sweep in very distinctively somewhere around 2-4pm. Winds will shift to the northwest and high pressure will build quickly behind bringing a beautiful Saturday to Lakeville. The next non-normal weather maker enters the Pacific NW concurrently, and we will see its influence push out the high, raise temps to unseasonable levels again Sunday (80-85 degrees in the grids), and then bring another round of cathartic thunder Sunday night into Monday.

Posted by pierre at 9:26 AM | Permalink

The TC Metro received a late-season surprise as a large and seasonally strong MCS roared through from the PM rush-hour to sunset. Funnel clouds and some brief tornado touchdowns were sighted all across the area. The impetus for the MCS was the edge of a well-defined warm frontal boundary that parked just over or just south of the Metro this afternoon. Initiation for the system rolled out of central MN with some surface based cells rapidly feeding off of the warm (and moist) advection overrunning the frontal zone. Deep layer shear not only gave strength to the cell growth but also developed enough spin for the funnels and 'nadoes that were reported. The MCS kicked out enough retro outflow to backbuild a smaller secondary squall in the northern metro as it entered the Badger State.

Meanwhile, the main upper impulse that stripped convective inhibition from our area this afternoon and evening continued to translate northeast, and pulling with it some of the overrunning warm and moist fuel for cells to develop along the Missabe iron range late tonight. This activity will continue to move northeast over Lake Superior and up the north shore through the early AM.

04z-05z MADIS anaysis in prep for this post showed a mesolow developed just north and east of KATY with pretty even heights at 1000mb, but definitive sfc wind fields in circulation. Late models (NAM and RUC) had a slight hint of a cap break in this region earlier tonight, and now it has happened as a supercell cluster has sprouted on the NE periphery of the mesolow and seems to have drawn up over the warm frontal boundary that is clearly defined by steep temp deltas 30 miles either side of a line from ATY-BBB-LJF-MSP. This will mean this new WC MN MCS will rapidly gain more strength as long as it can sustain some deep shear along that front. Cell movement is rapid now on ABR's WSR-88D at 40mph northeasterly. IR sat shows another cluster near Sisseton, SD and pressing toward the MN border in development. SPC jumped on a Tornado Watch when the cells fired, and that should run to 7am. The watch area borders, but does not include the TC metro at this time.

Area #2 needing nocturnal watching will be the Sioux Empire. FSD WSR now paints a cluster popping up about 60 miles NE of ONL and in an area of convergence between the mid-level trough that is leading the upstream shortwave culprit from the Bighorns across the high plains, and the strong LLJ feeding the warm sector across the Sioux Empire and into WC MN.

Tomorrow near sunrise, or sooner, it could get bumpy here in the TC metro again as a result of all the aforementioned mesosystems coming together, and to a head. The shortwave axis will join the mid-level tough axis sometime after 3am (8Z) lining up along Lake Oahe and the MO river valley across Dakota. Surface low will deepen to around 950mb near PIR, and then translate rapidly east-northeast through the AM. Storms are predicted to fire along the resulting cool front, which will unleash 2500-3000J/kg of MUCAPE bottled up under some strong low level CIN that remains in place overnight in the warm sector (assuming nocturnal activity doesn't stabilize in wake). Initiation across all models - even more recent RUC runs - all tagged at 18Z-ish, or lunchtime, and right near the I-35 corridor. Any lag in timing will spell more rain and a good severe threat for Lakeville...on time with the models or slightly quicker advance of the shortwave means not a drop.

Its not over yet....

Posted by pierre at 12:00 AM | Permalink