SEVERE WX : Excessive Heat Warning - Severe Thunderstorm Warning View Alerts

September 19, 5:30 PM Weather Forecast Update

From 90s to rainfall, isolated severe threat & much cooler weather to frost....lots of change in this now-late October outlook.

Posted: Sep 19, 2018 3:56 PM
Updated: Sep 19, 2018 5:28 PM

A few showers/storms are possible now-Thursday morning with weak frontal boundary moving back northward through the area.  

Coverage will average 30%.  I upped percentage a hair due to the fact that the storms may tend to congregate more over this 15-hour period in the northwestern/northern areas.

This will be followed by mostly sunny, hot, humid & breezy conditions Thursday afternoon. 

Highs will run 90-95 with heat indices of 93-98.  Southwest winds will increase to 15-25 mph.  This, after lows tonight at a muggy 68-73.

As for Friday, outflow boundary from squall line to our west Thursday-Thursday night should pop new showers/storms by Friday mid- to late-morning in the area.  This may produce an isolated severe storm or two as this line progresses southeastward as outflow boundary becomes more merged with the actual cold front.  Additional scattered showers & perhaps an isolated storm are possible behind this line through the afternoon-evening at times. 

Winds at 10,000' becoming parallel to the front will prevent more in the way of severe risk as part of the rainfall tends to occur more & more behind the front.  Also, better dynamics & shear with the winds more perpendicular to the front will occur north & northeast of our area.  As said, nonetheless, isolated severe storm or two could still occur with the storms that develop on the actual front that merges with the outflow boundary.

The heaviest rainfall with this system will occur to our northwest.  Up to 9" of rainfall area possible from southern Minnesota to Iowa & Wisconsin with substantial to significant flooding expected.  Up to 6" of rain is possible in central & northern Lower Peninsula of Michigan.  The heavy rainfall & severe weather threat will continue into Ontario & Quebec, as well as New England, Friday.  A good chunk of this rainfall is courtesy of the Texas tropical low that made landfall days ago.

Here, rainfall is looking more & more variable from 0.30" to localized +1.50" amounts, rather than a widespread, solid 1-2" area-wide.  That will occur farther north & westward.

The remnants of a Pacific tropical system may bring up to 10" of rainfall from New Mexico to northern Texas to Oklahoma through Thursday night. Substantial to significant flooding is expected.

This system should ride up the front that passes south of our area Friday.  There has been question on how far north the rainfall gets for the weekend.  This has been of great consternation over the past three days. 

Ensembles show bulk of this weekend rainfall indeed shifting south of our area.  However, there is enough of a wobble & enough uncertainty to keep 30% potential of rainfall in the southern part of the area Saturday.  Kept 20% for Sunday in the southeast.  There will be more clouds in the south than north over the weekend, but it will be comfortable with nice northeast winds.

You can see the core of the heavy rainfall from Texas & Oklahoma to Kentucky, Tennessee to Ohio where up to 6" may fall.

Front will move back northward as a warm front & remnant moisture from that Pacific system will brings showers & storms Tuesday-Wednesday-Thursday of next week.

MUCH cooler weather will follow.  You think this weekend is cool, wait until the weekend after that!  How about a day or two with highs in the 50s to 60!  Lows in the 30s to 40s are likely.

Unseasonably cool weather with even some frost will occur perhaps late, late September to the start of October.

Note the chill in the Plains & some of that air coming in here.  The growing season will end from the Dakotas, through Minnesota, even parts of Nebraska to Wisconsin with lows in the 20s & 30s.

Much warmer weather should follow with temperatures surging above normal.

It appears that the remnants of a Pacific hurricane will be pulled northward into the Plains & in or near our region with rainfall near October 6.  During this time to about October 15, there is a window with a favorable MJO phase to support tropical storm/hurricane activity near/along the East Coast to perhaps even the eastern Gulf of Mexico.

Note the sudden surge of warmth with temperatures 10-20 degrees above normal possible around this time.  However, the chill will linger to the north with early Rockies snows.

It appears that the above normal temperatures for the month of October as a whole will be confined to the western & southeastern U.S.  Below normal temperatures should be confined to the north & northeast areas.

Here, I am leaning on temperatures averaging a bit below normal.  This model shows less than 0.5-degree deviation from normal here.  I prefer more like a 1- to 1.5-degree below normal trend for October here.

Rainfall looks near normal for the month.

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