HEAVY RAINS, SOME ICE POSSIBLE..

February 18, 2018

The atmosphere is in the process of loading up for what promises to be a couple days of volatile weather early in the coming week. It's all centered around a full latitude trough deepening around a massive east coast ridge.

The squeeze play set-up will allow impressive amounts of water vapor to pour into the central United States. With little movement in the blocking high into mid-week, PWAT's (precipitable water vapor) will climb to unusually high levels for mid February. The 1.25" shown below is a good 3 standard deviations above normal in my area.

This is enough to drive dew points on both the GFS and EURO to near 60. Very rare this far north. The EURO shows this.

The GFS dew points Monday. Both have 59 dew points as far north as Ottumwa, Iowa.

Where the models differ some is the placement of the warm front and triple point. The EURO is further north driving highs into the 60s as far north as the Quad Cities and Iowa City. 50s to far southern Wisconsin.

The GFS is not as optimistic confining the 60s to far SE Iowa...generally south of I-80. The difference is dramatic in Cedar Rapids Monday with the EURO showing a high of 58, the GFS 45.

I guess a compromise between the 2 looks about right. However, one thing is certain and that's the fact there will be a huge temperature contrast in Iowa between upper teens in the NW and 60s in the SE (close to 50 degrees).

 

The intense thermal gradient could also cause some active thunderstorms that are heavy rain producers near the boundary.

 

The Storm Prediction Center has a risk of thunderstorms but nothing that's shown as severe. However, if full instability and CAPE can be realized some hail could fall in what should be elevated thunderstorms. The EURO does show enough CAPE for thunderstorms. 

The SPC day 2 thunderstorm outlook.

With thunderstorms the risk of heavy rain is also a real potential. It appears much of my region should see 1/2 to 1" of rain, substantially more near and east of the Mississippi. With frozen rivers and ground, run-off could cause some rapid rises on area rivers and streams. Something to watch. The EURO has this for total precipitation through Tuesday.

The GFS has this for the same period. Further east and lighter in eastern Iowa.

Last but not least, cold air may eventually undercut the slow moving front at some point Monday night or Tuesday. This could allow surface temperature to dip near or slightly below freezing. With plenty of warm air aloft at 5,000 ft the inversion would be ripe for a period of freezing rain. This could be a problem in some part of my area but it's too early to get specific on placement, amounts, or even timing. However, the EURO is aggressive in this scenario and shows this for freezing rain potential. More than 1/2" of ice in a few spots! Advisories or warnings could be posted for some.

Needless to say there is a lot of weather on the table and we'll have more in the way of specifics Sunday. Roll weather...TS 

 

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© 2019 Terry Swails