First Cool Month Since March; Feels Like October!

September 16, 2018

9pm Sunday…

It’s been a very quick switch to not just early Autumn weather the past week, but it feels more like October with highs struggling to reach 70 some days.

Month Climate Temps Calendar

We’re running slightly below average for the month with no sign of warmer weather over the next 10 days.  That tells me we could actually end up with a cooler-than-average month.  That hasn’t happened since March.  And the rain is starting to (slowly) add up; we picked up another .35″ in the city today for a monthly total of 1.55″

Rainfall so far this month_compared to normal

That puts us above our typical September rain of 1.47″.

There were people worried in mid-summer that “Summer would continue into November” or it “would never rain again”.  Always keep in mind with weather that we have short-term memory.  The rain ALWAYS comes back.  And temperatures ALWAYS cool in the fall.  Even after the hottest summers we cool off.

We had a few heavy showers around the metro area earlier this afternoon but they are gone now.  I think we’ll be dry through Thursday, although a weak system might give us a sprinkle Wednesday night.  Otherwise our next wet system appears Friday.

It’s been much cooler this month due to an upper-level “dip” or trough in the jet stream.  You can see it’s still there on the GFS ensembles showing upper-level heights on Wednesday

m500za_f072_bg_NA

The cool colors represent below average 500 millibar heights.  Then the same model for next Sunday shows the continuing cool pattern.

gfs_sun_23

The ECMWF is similar and doesn’t show the upper-level trough dissipating until at least 10 days from now.  See the ECMWF ensembles showing the trough just starting to leave.

ecm_ens_wed_26th_10days

Very interesting since we were dominated by higher than average upper-level heights from late April through mid August.  I’ve always found it fascinating how a “switch can flip” and we go from one weather regime to another.  Typically it’s that late spring wet-to-dry switch.  But sometimes it goes the other way too and that appears to be the case for Autumn 2018.

Enjoy the 3-4 days of dry weather this week!

Chief Meteorologist Mark Nelsen