lakeville weather journal

Forecast models and supporting analyses are supporting a good stretch of autumn weather for the week ahead. The aftermath of the extremely dynamic system that spawned an F2 tornado over the northwest Twin Cities metro late last night was a relatively nice day for today. The west/northwest flow behind the front was not as intense as models first predicted, and much drier to boot. Now the trailing closed upper level low will filter in some more clouds and rain chances for Monday.

After the system totally clears...sometime late Tuesday, the jet will go zonal briefly directly overhead of MN. This will call for some watchful waiting in the models and analyses...as currently models are poo-pooing the upper level dynamics for precip chances. This is due mainly to a lack of moisture in the flow. The resulting "dryout" effect and the transport of much colder air at the lower level will give us lows in the 30's for Tuesday's overnight period. The NAM and GFS both show the feature, so unless some unexpected energy enters the picture...along with some decent moisture...we will have very fall-like weather.

Next big story could be a cold "September Rain" (homage to GNR!) for the Friday night period. Currently a deepening Pacific trough will cross the WA/OR shoreline Tuesday/Wednesday...given the track of the surface low features in the long term models, moisture transport does not return until late Thursday. And although the upper level system will be in place for a Thursday event...we may see better chances on Friday. This will deserve better analysis later on in the week, however, and for now I wouldn't scrap plans outdoors Friday night...your Lakeville forecast:

MONDAY...Cooler and cloudy. 40% chance of scattered rain showers moving in and out through the day. High 56. Wind WNW 5-10. Low 40.
TUESDAY...Mostly cloudy skies, partial clearing by sunset. High 52. NW wind 5-10. Low 35.
WEDNESDAY...Scattered clouds, High 55. Low 41.

Posted by pierre at 8:55 PM | Permalink

Last year about this time -- as the nation was reeling in awe over the devestation of Hurricane Katrina -- a line of severe thunderstorms, producing hurricane force winds, plowed through MN. (see related article in my blog here). Tonight, a similar setup as that of last September is in place for severe weather across the area. Strong southerly flow, as progged and watched all week, has arrived in force. In advance of the intense trough (now across the MO river basin of Dakotas) local height falls have been rapid (over .30" here at our station since midnight) and the gradient remains steep as you head west towards the advancing, and still deepening, trough.

This afternoon and early evening, central and eastern MN will be spared. Western MN will not, as they already are under the gun at the time of this post: thunderstorms have fired over the Sioux Empire and on the winward side of the Couteu des Prairies in SD. These locations coincide with the RUC's modeling of a 70kt mid-low level jet max nosing right up over the Couteau. SPC issued a Tornado Watch for the eastern 1/2 of SD, but attm, this looks to be a stitch to far west. These storms should evolve into a MCS that will drop off the lee side of the Couteu and train up the MN River valley towards the TC metro sometime after sunset, bringing heavy rain showers, damaging wind, and a slight chance for hail to our area from 00Z and through the night.

The trough will advance to at least western MN overnight, and become more frontal, as the jet max will shift slightly zonal behind the front and allow cooler air to filter in. Meanwhile, the models show the low pressure center stacking up over NW MN for Sunday, and with the zonal shift of the jet may become cutoff for a time. This will prolong and propogate radial bands of showers and spotty thunder over the entire Gopher State Sunday night through Monday, amidst much cooler conditions. Here is the short-term scoop for Lakeville....

TONIGHT...Thunderstorms move in after 7-8pm, some could be heavy with damaging wind and hail. Chance of rain is 80%. Lows tonight 60-65. Strong south winds 10-20 mph continue.
SUNDAY...Mostly cloudy in morning, then partial clearing in afternoon. High 74. Wind shifting to the west 10mph. Chance of showers after dark, low 55.
MONDAY...Cloudy. Rain showers likely, with high of 55. Low 45.

Posted by pierre at 4:04 PM | Permalink

This morning was spectacular...some low fog in the river and creek valleys, but after 0830 or so, any fog that had crept up the hills had burned off, and we have a bluebird sky day...calm winds, and a crispness to the air that is remarkably fall-like. 14Z METAR plot shows high pressure ridge lined up from KMSP southwest through KSPW, KMCI, and back towards the TX panhandle. 14Z run of the RUC model tags the ridge up nicely in accordance with analysis, and trends the ridgeline to get blocked, running KSAW-KSTL-KDFW by 00Z this evening. (Blocking from the last slow-moving, partially cutoff distubance running up on the Appalachains.)

Meanwhile, the next weather maker for us will continue a generous pace into the Pac-NW today. Satellite imagry already shows the trough moving over the Canadian coast southeasterly towards the Columbia basin. The GFS shows the trough deepining via a potent upper jet (125kt max). On the lee side of the Rockies, surface low pressure is already developing across the MT/WY badlands, and the pressure gradient with the blocked ridge over the MS valley will increase. This will expedite the southerly flow in advance of the Pac-NW trough, and sfc winds will increase dramatically through Thursday and into Friday.

Both the NAM and GFS have moderated on moisture transport...but only slightly. Now Fri-Sat period Pwat values have fallen below 4cm, but now that we see better transport features in the models with the dramatic southerly flow, these values, along with Td's could race up to midsummer-like values on Friday in advance of the system. Models have not generated any other convective weather indications that would warrant svr outlooks, but the GFS favors a coupled-jet structure, with the jet max nosing in over the Couteau des Prairies into western/southwestern MN for Saturday. Classic, and typical signature of a convective event for the area on Sat night. Slight modifications for the forecast...

WEDNESDAY...Sunny and warmer, High 76. Low 56. North wind 5mph shifting variably to the east-southeast.
THURSDAY...AM fog burns off, Partly Cloudy and 82. Winds SE 10-15 by evening. Low 57.
FRIDAY...Partly cloudy, more humid, gusty south winds 15-20. High 84, low 60 through.
SATURDAY...Partly cloudy, 40% chance of showers and thunderstorms after 7pm. High 83. Low 63.
SUNDAY...Partly to mostly cloudy. High 73. Chance of rain in AM and again in afternoon.

Posted by pierre at 9:49 AM | Permalink

Taking a break from the prognostications for the last week has proven to be a good idea, as post holiday weather has been cool and drab for Lakeville. As I write, however, sunshine is once again breaking through and will slowly warm the local area, as the mid-upper low pressure system finally slides down to Indiana today and out of the Upper Midwest. As we focus on the end of the week forecast models, the models have (as expected) general concurrence in the short term, and some diverging conclusions for the long term.

In the short term, solid agreement on a high pressure ridge building in through the next 24-48 hours. We can expect clearing skies, and warming temps, much more to a seasonable level over this period. Moving into late Thursday, both the GFS and NAM prog a surface low developing in the Powder River basin of WY, as the high pressure ridge gets stalled west of the Appalaichains. Both models -- but especially the NAM -- paint a strong gradient on the back side of the ridge Thursday night as a result of the blocking. Should this contribute to an even deeper southerly flow, temps could ride up in the low levels a bit. Moisture transport may bring cloudiness, however, and this could inhibit any highs beyond the 76-80 degree mark for Thurs into Friday.

As the weekend approaches, the models start to diverge a bit on the timing of another deepening trough off the Pac-NW. This feature is progged by the long-term GFS solution to race off the lee-side of the Rockies Saturday. Preceeding it, both the NAM and GFS paint the WY low to spin off a vort max that moves from Dakota into SW MN by late Friday. That vorticity could join forces with a coupled jet structure to give rise to moderate convection potentials Friday PM, but until local moisture content can be assured, timing for development (if any) is a crap shoot.

GFS has moisture plume riding up the strong-gradient low level jet from the Gulf of Mexico through the 00Z Saturday period in advance of the longwave/surface front, and widens vorticity potentials from the Couteu to the MS River. P-wat values on the current GFS for this timeframe run to 4cm, and lifting indicies jutting above a -2 over western MN. NAM dewpoint plots for the timeframe climb to 65F+ values, but push through the area faster than GFS, indicating main divergence in model construction of the system.

For now, the forecast will be somewhat conservative...but if things "heat up" later in the week, we could see a wet and stormy weekend. If not, we will have a repeat of last weekend, especially if the jet structure does not couple up (and, by the way, GFS hints at this for Sunday-Monday).

TUESDAY...Clearing skies, High 74. Low 52. North wind 5-10mph
WEDNESDAY...Sunny and warmer, High 76. Low 60. North wind 5mph.
THURSDAY...AM fog burns off, Partly Cloudy and 82. Winds turning SE 5-10.
FRIDAY through SUNDAY...Partly to mostly cloudy. Highs of 82 Friday, cooling off Saturday to mid-low 70's. Chance of precip all three days.

Posted by pierre at 12:01 PM | Permalink