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TRICKS TODAY, TREATS FOR HALLOWEEN....


With just a couple of days to go, October temperatures are running cool around the Midwest. Though the core of the cold has been centered over Canada and the Plains.

Much of the coming week is projected to remain cool but beyond that some changes should lead to a much warmer period of weather by mid-November. The big tip-off is the MJO (Madden Julien Oscillation) which is projected to move into warmer phases. If you follow the green dots in the phase diagram you can see the progression into phase 2 by November 1st. Top right on the graphic is the temperature correlation. The warmth is building into the upper Midwest.

Come the middle of November, the green dots have advanced into phase 3. Phase 3 in November strongly correlates to above normal temperatures. Look at the extensive warmth top right in the diagram.

The Euro EPS ensembles are catching the potential. Here's the 500mb jet anomalies forecast November 13th. A powerful flow coming off the Pacific.

This type of pattern is well known for its warm dry conditions. The CFSv2 is certainly on board with day 15-25 temperature departures that look like this November 13th-23rd. Even for the CFSv2 this is toasty. That should brighten the day for those of you who don't embrace winter!

Back to the short term the forecast challenge is a cold front that's shown punching through Iowa Tuesday afternoon. Moisture is expected to increase ahead of the front and at some point later in the day showers and even a few thunderstorms are expected to develop.

There will be a hard line between little to no rain and heavier amounts as precipitation breaks out right over the heart of my area...much like a summer convective event. The 3k NAM has this at 4:00pm. Most of the rain shown SE of a line from Des Moines to Waterloo and eastward to Dubuque.

The hi-res HREF has this at 3:00pm. Quite similar.

With some small CAPE the potential is there for thunderstorms. With that added element rainfall amounts could be significant where this all comes together. In fact, Monday nights models have shown such a tendency and are also 30-40 miles further NW than earlier runs. Here's some rainfall forecasts from 4 different models. Note the sharp cut-off line to the NW edge of the rain.

The 3k NAM

The NAM

The GFS

The HREF

Fortunately for the ghosts and goblins of the region, this moves out quickly Tuesday evening. By Halloween we're expecting dry and seasonal conditions. Trick or treaters can expect temperatures in the upper 40s to low 50s. Nothing too spooky there as Tuesday's tricks turn to Wednesday's treats. Roll weather...TS

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© 2020 Terry Swails