Tuesday 8/7 Update

Good Tuesday!  Overall, a very quiet weather day, so this update will be pretty short and sweet.  The lack of humidity is the big story for today.  A very dry air mass means a big spread in min/max temps...we have gone from a morning low of 63 to an afternoon reading of 96 at the time of this update.  Would expect another 30-35 degree spread in temps tomorrow, with numbers perhaps going from the mid 60's overnight to the high 90's tomorrow afternoon.

By tomorrow night, a cold front will begin to advance into the region from the north, and there could be enough energy and moisture for a few showers & t'storms, especially in S. IL & SEMO.  The best chances continue to be on Thursday, and the SPC has included at least the northern half of the Local 6 region in the Day 3 slight risk area, primarily for a chance of wind/hail producers Thursday evening:

Here's the breakdown for the second half of the week.....the GFS model shows a couple of pieces of energy (pockets of green/yellow, one over SEMO, another over MN) within a trough over the eastern U.S.  That first smaller wave could bring rain as early as Wed. PM.

The NAM shows the main pocket of energy swinging SE into the region on Thursday night:

GFS surface chart/rainfall Thursday PM:

NAM surface chart/rainfall Thursday PM:

Good news...both models generate rainfall.  Bad news....both models generate only meager rainfall.  Again, this will be another of those situations where some heavy downpours with bring localized higher amounts within stronger thunderstorms, but for most of us, I wouldn't expect more than maybe 0.10"-0.25". 

By Friday night, a very nice trough takes shape over the eastern U.S., while the big heat ridge is suppressed over the southwestern states:

This trough will mean a noticeable cool down over the weekend, as shown by the 850 mb chart (by the way, if this chart is confusing to you, the temperature scale for this chart is always shown in Celsius):

The end result should be temperatures over the weekend (Fri-Sun) running 5-10 degrees BELOW normal!  This means highs in the mid/upper 80's.  We'll also see dew points take a nosedive again, bringing in another very dry air mass, resulting in low down in the lower/mid 60's.
--------------------------------

You may be noticing that the days are getting shorter again.  We will continue to notice that continue over the next couple of months, as the time of daylight will decrease by 1-3 minutes per day over the next couple of months.  For example, today's sunrise time was 6:05am and sunset time is 7:56pm.  By the end of September, we'll be at 6:49am and 6:40pm.  This change occurs most dramatically between August & November because of the elliptical orbit of Earth around the sun.  This image from AccuWeather does a good job of visualizing this trend:

 

Finally, a quick update on Ernesto.  As of this afternoon, is it a Category 1 hurricane, with maximum sustained winds at 80 mph and gusts to 100 mph. It should make landfall late tonight on the Yucatan Peninsula, then reemerge as a tropical storm tomorrow in the Bay of Campeche.

The worst impacts should remain south of popular vacation spots such as Cancun and Cozumel.  The biggest concern with this storm will be the potential for flooding rains as it crosses more mountainous areas of Mexico, northern Belize, and northern Guatemala.