With the weakening jet stream in the summertime, meteorologists are frustrated with the uncertainity of forecasting precipitation due to lack of a clear triggering force. Thus the broadbrush of low end precipitation probabilities for the next twenty-four hours.
What a difference a day makes. At this time on Wednesday morning much of Minnesota was cloud free. Here's a look at the 630AM visible satellite that shows south central Minnesota enjoying sunshine. Notice the bumps in the cloud cover along the South Dakota/Minnesota border where showers have more gitty-up.
Indications from tracking last night's model output support more forcing and vertical lift in the atmosphere on Friday night into Saturday night. Exactly where the potential for heavier showers might be is difficult to pin-point. See the output from the GFS model for a bulls-eye of significant rain on Saturday evening. Is this just an outlier or will this become reality? The next model run may confirm or overrule the downpour potential.
Yes that's a total of nearly two inches in central Minnesota. An example of what meteorologists examine to craft a forecast for your weekend.
You may have heard that the NWS has released and as of July 1st is now using the updated thirty year normals. As we learned over time normals are the output of the collection of the extremes. The numbers currently used have tossed out the relatively cold temperatures in the 1970s and incoporated the warmer winter temperatures of the past ten years.
I was speaking with the chief meteorologist for NOAA in the Twin Cities last evening and we agreed that the long range outlook for the winter, posted by the Climate Prediction Center is now impacted by the change in the normals.
See the graphic from NOAA on the change/warmer minimum temperatures in our neck of the woods. Most of this warming in the new normals comes from the winter season.
Based on the new normals, here's the Climate Prediction very long range outlook for the months of December 2011 to February 2012. There are several more factors that will come into play by the time we approach the winter season. Use outlooks with caution.
Equal chances of above or below temperatures for the upcoming winter; not necessarily breaking news. But you did read it here.
When you listen to a weather observation it sounds so simple. There are a number of automated meteorological observation units that take nearly continous weather observations. The official NWS automated observations are recorded and transmitted by ASOS-Automated Surface Observation System.
The FAA has augmented these observations with their own units known as AWOS-Automated Weather Observation Systems. Here is a link to the automated observation sites. In addition, the Minnesota Department of Transporation has some weather observing sites.
When I began my career with the NWS at Mitchell Field in Milwaukee I was a weather observer. Fortunately we had automated sensors already in the early 1970s. We were required to observe the cloud cover, along with the horizontal visibility on an hourly basis. This visual observation along with the temperature, dew point, wind and pressure was transmitted by teletype.
On a regular basis we would ensure the automated temperature and dew point sensor was reading accurately. Once a week the weather observer would stand in a shaded grassy area and swing a sling psychrometer that would measure the dry bulb and the web bulb temperatures. We would then calculate the dew point; ultimately deriving the relative humidity.
Here's a photo of how they still determine relative humidity when on a forest fire incident.
If you want to read more about the meteorological measurements you can check your knowledge at this NWS website.
I was partial correct when I said you would notice an increase in dew points today. The Twin Cities International Airport had a dew point of 51 degrees at this time on Wednesday. The dew point rose to 65 degrees when light rain fell at 6AM, but has since fallen back to 56 degrees. The dew point is in the lower 60s at Rochester this afternoon.
Check out the change in cloud cover from early this morning (see previous blog) to this afternoon on the visible satellite image.
Thunderstorms were firing up in portions of the Minnesota River Valley in west central Minnesota.
Latest computer model information still supports the best chance for thundershowers in central Minnesota on Saturday afternoon and evening.(2 Comments)