Storm Chances – Weather History – 4/18

Weather History

1880: A tornado struck Chester, in Eaton County, where barns were destroyed and livestock were killed. The tornado leveled A quarter-mile-wide swath of trees in a forest.

On April 18, 1975, 2.69 inches of precipitation fell in Flint, the maximum precipitation record for the month of April.

Forecast Discussion

- Much warmer with periods of showers/storms through tonight

So far convection has generally been behaving as expected, with more
of a focus across Central Lower, and not becoming strong at all so
far. This initial convection has been at the leading edge of the low
level jet and moisture plume. The next batch of convection is poised
to move in over the next few hours from Wisconsin as the low level
jet axis is feeding additional convection there. By all accounts,
the position of the low level jet, and the trajectory of the
convection indicates that it will again affect areas mostly north of
I-96 right around daybreak.

Then, finally one last round of convection now ongoing over northern
Iowa with another branch of the low level jet, will lift across the
northern section of the forecast once again.

Thus far with all convection being elevated in nature, and with
weaker updrafts, we have not had any storms even get close to being
strong. This will continue to be the case with the next round of
convection, with the caveat of a small chance of some smaller hail
with the better updrafts as mid level lapse rates are steepening
over the area with the warmer air coming in from the SW. The
convection over Iowa right now that is being warned on will tend to
diminish a bit as the low level jet feeding that line is expected to
weaken with the typical trend of weakening low level jets toward
daybreak.

We will see then a decent break for just about all of the area from
late this morning until mid evening, before the last round of
convection approaches. The break in convection comes with the
weakening of the low level jet, and with capping taking place aloft
over the area as we get into the warm sector of the system. Clouds
should give way to at least a few hours of some sunshine, helping to
build some decent instability, but that will be capped with warm mid
levels.

The cold front will approach the shoreline toward midnight, with
some convective development out ahead of the front. MU CAPE is shown
to increase to around 1500 J/kg just prior to sunset per the SPC
HREF. Deep layer shear remains favorable with values of 45 to 50
knots. The problem is both the instability and deep layer shear peak
while we are still well capped, and a few hours before the front
nudges in over the area.

We will see enough instability remain so that showers and storms
will form out ahead of the front, even with the instability
weakening. Forecast soundings support both hail and wind as threats.
There is a mid level dry wedge that will help to enhance downdrafts
due to precipitation loading. DCAPE accounts for this with values of
800-1000. Mid level lapse rates above 7.0 C/km and some thicker CAPE
in the hail generation layer will support a hail threat. While the
threat is there, the chance for severe will be tapering off at that
time.

The front will sink south of the area by Saturday morning, allowing
Canadian high pressure to build in, dry us out, and cool us down a
bit.

- Another wet and breezy system Sunday through Monday

The front will get hung up just south of the forecast area by
Saturday. This front will be waiting for a strong wave rounding the
long wave trough over the Plains to lift to the NE and interact with
the front. It looks like it will be Sunday afternoon that we see the
better moisture arrive to bring rain showers over the area. Not as
much thunder with this as the warm sector does not get as far over
the forecast area as the system does today.

It will take until later Monday for the entire system to exit the
region. Until then, rain showers will remain possible.

- Mild with small chances of rain Tuesday through Thursday

We are left with a nearly zonal flow in the wake of the stronger
system for the Sunday and Monday time frame. This flow will keep the
air mass fairly mild, but a bit unsettled. That is because numerous
waves are expected to be embedded in the flow. Moisture will be
limited, limiting the rain chances and how much rain falls.