To the left is the current forecast map from NOAA (click to enlarge).
A high-pressure area, high or anticyclone is a region where the atmospheric pressure at the surface of the planet is greater than its surrounding environment.
Winds within high-pressure areas flow outward from the higher pressure areas near their centers towards the lower pressure areas further from their centers. Gravity adds to the forces causing this general movement, because the higher pressure compresses the column of air near the center of the area into greater density – and so greater weight compared to lower pressure, lower density, and lower weight of the air outside the center.
However, because the planet is rotating underneath the atmosphere, and frictional forces arise as the planetary surface drags some atmosphere with it, the air flow from center to periphery is not direct, but is twisted due to the Coriolis effect, or the merely apparent force that arise when the observer is in a rotating frame of reference. Viewed from above this twist in wind direction is in the same direction as the rotation of the planet.
The strongest high-pressure areas are associated with cold air masses which push away out of polar regions during the winter when there is less sun to warm neighboring regions. These Highs change character and weaken once they move further over relatively warmer water bodies.
Somewhat weaker but more common are high-pressure areas caused by atmospheric subsidence, that is, areas where large masses of cooler drier air descend from an elevation of 8 to 15 km after the lower temperatures have precipitated out the water vapor.
High pressure systems have a clockwise rotation – low pressure systems rotate counterclockwise. As you can see from the Futurecast the low pressure system and rain moving towards us will slam into the high pressure located over south of Lake Michigan killing any chances of rain for today.
Quiet weather conditions are forecast today due to the high pressure situated over the Great Lakes region. An increase of high clouds will be noted this afternoon with high temperatures up around 80 degrees. A few light showers are possible Monday afternoon although most areas look to stay dry. Highs will be near 80 once again on Monday. Another mainly dry day is forecast on Tuesday with a developing warm front off to our southwest. Highs on Tuesday will push into the lower 80s. Overall fairly seasonable weather for this time of year.
HRRR and Futurecast models runs are for 12 hours beginning at 7am – a second model run begins at 3pm
Day and Week Planner
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High pressure will bring fair weather today and tonight, with an increase in high cloud with time through Monday morning. Expecting a mostly sunny day today, but there will be increasing high clouds in the afternoon. A well defined upper shortwave trough can be seen in the water vapor imagery this morning stretching from the Northern Plains south into Nebraska.
Showers are associated with the shortwave at this time well off to our west. We will stay dry through Monday morning with high pressure in place across the Great Lakes. The surface high slips away to the east on Monday allowing a weak surface trough associated with the upper wave to approach.
Have blended in with neighboring offices showing small chances for light rain showers Monday afternoon, but would not be surprised to see us stay dry. Have 20 pops (probability of precipitations) in the forecast Monday afternoon. Monday night into Tuesday the surface trough washes out with a developing warm front to our southwest. Similar reasoning in both of these forecast periods as well, small pops in the forecast to maintain consistency with neighboring offices.
Thinking the bulk of this time frame will be dry as well. An increase in cloud cover will be associated with the shortwave aloft through especially Monday and Monday night. Highs will be around 80 today, Monday and Tuesday.
The high pressure ridge will continue in control of the wx pattern Tuesday night before southerly flow brings warmer and more humid weather Wednesday. A warm front will bring scattered showers and thunderstorms Wednesday with a better chance for thunderstorms Wednesday night into early Thursday with the sfc low and cold front.
A slightly cooler and less humid airmass will gradually move in behind that system very late in the week. However a northern stream upper level disturbance and weak sfc low pressure system will bring potential for more scattered showers and storms late Friday into Saturday.