Tuesday 9/18 Update

Good Tuesday!  Hope you've had a chance to step outside for a bit and enjoy a little of today's fantastic weather.  I think it's safe to say that there is a fall feel to the air today.  The main issue in the forecast for the short term is how chilly it gets tonight...so here's a chance to learn a bit more on the challenges of forecasting temperatures.  Normally, we'll start with a check of the forecast model guidance to see what they are suggesting...for tonight, one model (GFS) shows 41...the other (NAM) is a tad milder at 44.  Another factor we look at are sky conditions....with clear skies tonight, things will cool down pretty quickly as the solar radiation from the sunlight today escapes back into space (clouds typically work to "blanket" the atmosphere, keeping some of that solar energy trapped & temps slightly milder).  The main factor we'll need to examine tonight is the dew point.  Temperatures cannot drop below the dew point (unless water vapor is condensed out), thus the dew point gives us a good idea of the absolute chilliest it will get.  The dew point this afternoon is not quite as low as expected, and with high pressure settling in and winds going calm tonight, the dew point will level off.  Neither model is showing dew points dropping lower than 40, so this is a pretty good indication that overnight lows will not be dropping below 40.  It does look like our record low of 41 is in serious jeopardy though.  Regardless of whether it's 39 or 42, it's still going to be a chilly night!  Just wanted to offer some insight about the complexities of forecasting.

Moving on...with high pressure parked over the region, things will be very quiet for the next couple of days.  With plenty of sunshine, we'll see a return to the mid 70's tomorrow, upper 40's Wed. night, and back to around 80 on Thursday.

By Friday morning, our next cold front will be entering the area from the west.  Models are still showing this system will bring a slight chance of rain....but not much. Here's the European model's 6-hr precip at 1PM Friday:

The GFS 6-hr precip is just a tad later in the day, but equally unimpressive:

There has been a little model disagreement on how fast this front will move through. Some push it on through by early Saturday, while other runs have the front slowing down and lingering over eastern parts of the area early Saturday.  If it hangs up, things could be a little cloudy on Saturday...a quicker progression of the front would mean more sunshine.  Either way, it will be a pleasant weekend, with highs in the low/mid 70's, lows in the mid 40's.  

Finally, a look ahead to next week, the story will be a return to average or above average temperatures.  As seen on the 850 mb chart (temperatures) above....we'll return to more of a southwest flow pattern, allowing warmer air to move back in. Early indications are the most of the week will feature highs in the low/mid 80's.