BLAME IT ON THE LAKE....
Wednesday was a tale of two seasons around my area. Readings in the far northeast never got out of the upper 40s while in SE Iowa highs hit at least 75 in Keokuk and 73 in Ft. Madison (a spread of 27 degrees over 190 miles). Those of you who remained in the 40s and 50s can blame Lake Michigan. Water temperatures are not much more than 40 degrees and when winds with an easterly component blow our way, temperature suffer thanks to the chill the water produces. Notice how the southern tip of Lake Michigan parallels I-80 and the Quad Cities (in a horizontal east west line). On days like Wednesday, the E/SE wind trajectory enhances a boundary laid out close to that I-80 position. On occasions when winds are more northeast, the boundary would likely be even further south closer to the Missouri Iowa border.
Without the impact from Lake Michigan, my southern counties are able to warm. Where the lake's involved further north, temperatures stay nice and fresh. This is a typical occurrence in spring until the water can warm up later in May and June. This streamline plot Wednesday evening (showing wind speed and direction), clearly depicts the boundary producing the 27 degree contrast in my region. You can trace the origins of the streamlines over my area directly back to Lake Michigan.
Below another view of temperatures around 4:00pm Wednesday. Visualize the streamlines above over these temperatures and it's easy to see why our day turned out the way it did. This is a fascinating mesoscale event that becomes a factor every spring when we get low pressure to the south or a big high pressure over the northern Great Lakes. It will remain an issue until we can warm Lake Michigan's water up.
In the big picture this could very well be a factor for us much of the next two weeks as the pattern remains intact in such a way that the overall wind fields will consistently have an easterly component to them. You can see that in the 16 day animation of pressure departures ending May 13th. There's either a low pressure passing south or a high pressure planted over the Great Lakes.
That's not a recipe for warm temperatures or dry weather. Here's the week 1 and week 2 temperature departures.
Week 1 (April 27th-May 4th)
Week 2 (April 5-May 13th)
As for precipitation, here's the two week departures in weekly intervals.
Week 1 (April 27-May 4th)
Week 2 (May 5th-May 13th)
The total anomaly for the 2 week period ending May 13th comes in like this.
To sum it up, the next two weeks look cool and wet at times. Oh boy, that sounds like fun!
Short term, we've got another big slug of energy due to twirl its way through the Midwest this weekend. Ahead of it, frontogenic forcing at 850mb (5,000 ft) has generated a narrow band of showers and some isolated thunderstorms overnight, mainly in my northern counties, These are expected to wane Thursday morning as the low level jet and overall forcing weakens. Some banded moderate to locally heavy rains may have fallen if model projections are achieved. Here's what they indicated Wednesday night through Thursday morning. Note the main focus is generally depicted NE of a line that extends southeast from roughly Waterloo to Maquoketa to Sterling in Illinois.
The EURO
The GFS
The HRRR
The 3K NAM
After this set-up departs, forcing appears rather unorganized Thursday afternoon, night, and into the day Friday. While there could be some spotty pockets of rain most of this period looks precipitation free. Temperatures through the day Thursday will be limited to the 50s in most areas NE of the Quad Cities where the lake enhanced front brings raw conditions to that region. The brisk SE winds will make it feel even colder. The area near and southwest of the Quad Cities looks to fair better closer to the boundary. Highs here should reach the 60s, maybe close to 70 around Keokuk and Ft. Madison. The HRRR indicates readings like this Thursday.
Friday if we can stay dry and pop a little sunshine, we should see upper 50s to low 60s areawide as the entire region is impacted by the southward retreat of the boundary and cooler southeast flow.
Friday night the primary storm advances into eastern Nebraska. The injection of moisture and the low level jet will fuel showers and thunderstorms along the boundary which occludes as it slowly pushes northward towards the southern Iowa border. Saturday additional showers and storms will end in the southwest half of the area by noon. Here, within the dry slot temperatures should surge into the upper 60s to perhaps mid 70s far south. Further north, it may take most of the day for the rain to end in my far northeastern counties. That could take a bite out of temperatures in the far north where readings could be restricted to the upper 50s to low 60s. Otherwise most of this area has a good shot as seeing highs in the low to mid 60s. Here's what the EURO is suggesting for highs Saturday. This is low confidence and could be warmer or colder being highly contingent on the speed of the front. The EURO by the way is the warmest solution currently available.
The next round of precipitation Friday night through Saturday is likely to be significant in spots, perhaps an inch or more where the heavier rain sets up. That will be better know later Friday. Meantime, here's what the EURO and GFS are suggesting during the period.
The EURO
The GFS
Late Saturday night another strong cold front spears the region and temperatures cool again Sunday with brisk westerly winds ushering in the chill. A new system looks to impact the area with rain Monday night followed by another system Wednesday. The beat goes on for our spring parade of storms. Roll weather...TS
