Tuesday, September 30, 2014

Rain likely, Snow??

Public weather briefing

After a much cooler day, clouds will remain in the area as lows will again drop into the 40s. Overnight winds will remain light and become slightly more southeasterly. Highs tomorrow will be much more comfortable and will continue this warming trend into Thursday with highs around 70. The warmth will bring a chance for rain overnight on Wednesday and increases in probability through Thursday. Winds will remain out of the south through Thursday. Friday will bring the highest chance for showers. Winds will be stronger and out of the west and highs will reach into the 50s. There will be a big cool down over the weekend especially on Saturday and a small chance for showers through Monday. 


Tonight. Partly cloudy. Low around 45. Light east winds becoming southeast around 5 mph.

Wednesday. Mostly cloudy a slight chance of showers after 4 pm. High around 67. Southeast winds 5 to 10 mph. Chance of rain 20%.

Wednesday night. Showers becoming likely mainly after midnight. Lows in the upper 50s. Light south winds. Chance of rain 70%.

Thursday.  Showers likely mainly before 1 pm. Highs around 70. Light south winds. Chance of rain 70%.

Friday. Showers likely early, then breezy and cooler. Highs in the mid 50s. West wind 10-20 mph. Chance of rain 80%.

Outlook for Saturday through Monday. Much cooler Saturday, but partly cloudy with highs in the low to mid 50s. Partly cloudy Sunday with a small chance of light showers and highs in the mid to upper 50s. Monday partly cloudy with highs in the upper 50s. [CONFIDENCE: MEDIUM]

Forecast Discussion

Look for a quiet night as the surface anticyclone remains in control through the night. Temperatures should stay right around where they are for the remainder of the night as WAA begins aloft.
Wednesday through Thursday: big difference in placement of features with the approaching upper level through to the west. There will be a small chance of showers Wednesday afternoon, becoming likely Wednesday night into Thursday as upper divergence and areas of vertical upward motion approach the area. The GFS has almost no rain overnight Wednesday into Thursday, while the NAM puts around an inch during the same time. Any sun on Thursday will boost temperatures at or above 70F. 
Thursday night: Upper trough axis approaches the area with decent upward vertical motion. Showers could get moderate to heavy overnight. Very little instability seen on soundings so no mention of thunder at this time. 
Friday and beyond: Surface cyclone moves northeast of the area drying things out and cooling things down quickly by midday Friday. Interestingly, both models are in good agreement with an area of wrap around moisture coming through overnight Friday into Saturday. Could be some snow flakes mixing in at times as the 5400 m thickness line is well south and southeast of the area. GFS has 850 mb temps well below 0C and 925 mb temps around 0C. Otherwise a weak shortwave within the northwest upper flow could bring a small chance of showers Sunday with continued cool conditions.   

Ross Braatz
Ryan Tvedt


  1. Commendable job on the accuracy of your forecast overall, guys.. looks like we're still on track to see some snow flakes mixing in tomorrow morning around here! Think we'll have enough forcing for the precip/will it be cold enough??

  2. That is a good question Andrew! While temperatures reached cool enough levels aloft, it was still too warm for snow this morning. Also much of the precipitation was to our east and it was in the form of rain. It will be interesting to see how long this blast of cold air out of the northwest will last heading into the early parts of the week next week.

  3. On my way to work Sunday morning, there was some snowflakes mixing in around 8 am, but only for about an hour. The forecast was well done except for last Tuesday. Those stubborn status clouds did NOT mix out after the frontal passage. So way off on the highs. Otherwise not bad. It was a little more breezy on Friday then anticipated, but highs were definitely since in the morning and temps fell during the remainder of day. All in all, pretty good.

  4. Ross and Ryan - Overall, I think you guys did a pretty nice job with your first cut at this forecasting exercise. You did a particularly nice job discussing the chances for snowflakes to mix in with the precipitation over the weekend and in emphasizing some of the uncertainty in precipitation amounts later in the work week. These are exactly the types of things I'd like to see in your discussions as they demonstrate the uncertainty you indicated and get more at the dynamical reasoning behind different processes. I'd encourage you to do a bit more of that in the future, particularly in the public weather briefing section. If you expect precipitation or a drastic drop in temperatures, you should still indicate that a frontal passage, or something else of the sort, is expected. Furthermore, try to tie up your dynamical descriptions a bit more as well. For example, don't just say you have divergence aloft and vertical motions moving into an area, but directly tie that to a particular feature. A sample statement could be: "the upper-level divergence associated with an approaching upper-level trough facilitates the production of precipitation late in the evening on Thursday", or something along those lines. Finally, I'd like to see a bit more of a discussion on your forecast that really gets at the dynamical processes a bit more. For instance, why did the stratus deck stay around in your opinion? Or what specifically did you do that worked well in creating your forecasts? These details will not only help you grasp the quality of your forecast better but will help the class in preparation of their own forecasts too.


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