Scientific Forecaster Discussion
fxus63 kmkx 220749
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
249 am CDT sun Sep 22 2019
Today and tonight...forecast confidence is medium...
We will continue to see some pesky showers as the cold front
slowly moves in this morning. This will thus bring showers and
storms to the region as it pushes through. However, the front
will not be the sole driver as this system has strong forcing and
plentiful moisture throughout the troposphere. The system will be
greatly supported by upper level longwave energy, plenty of
Theta-E advection in the low and mid levels, some enhancement from
the low level jet and some influence from a fairly strong upper level jet.
Overall this system has a lot going for it likely enabling it to
produce storms and plenty of rainfall throughout the day.
One of the concerns with this system is that some tropical
moisture from what was Imelda and Tropical Storm Lorena will
impact moisture availability and may also increase precipitation
efficiency in the system. Pwats will be near 2 inches, which is
climatologically very high for this time of year, and with
training expected as this front slowly pulls through we could see
very high rainfall totals, especially in the far southeastern
parts of Wisconsin. In addition, any storms in the region should
be mostly weak with cape mostly below 500 j/kg though would likely
be producing some torrential downpours. Thus, flash flood
potential remains through Sunday.
By early Monday morning the front will be through with rain ending
overnight from west to east, allowing temperatures to fall in to
the low to mid 50s.
Monday through Tuesday...forecast confidence is high.
We start Monday under a weak cold air advection regime as our weekend system is
well off to the east. Clouds clear through the morning and temps by
the afternoon should return to near normal with highs in the upper
60s to around 70 degrees. The biggest difference will be in the
morning lows both days where values fall into the lower 50s. High
pressure to the south of the area pushes east towards the
Appalachians on Tuesday bringing a return of southerly winds,
warmer temps and increasing moisture. Temps warm upwards of 5
degrees for Tuesday with highs in the mid 70s expected for much of
Tuesday night through Wednesday night...forecast confidence is
medium to high.
A shortwave moving out of Montana/ND will track through northern Minnesota/WI
during this period. Surface pressure falls over NE/South Dakota will trigger
the development of quick moving surface low. This feature is
forecast to track NE through northern WI and into the up of
Michigan by Wednesday morning. The associated cold front will be
the focus for another round of showers and thunderstorms. Strong
warm air advection off the surface looks to keep a cap in place over much of our
area, which could keep stronger storms focused more off to the
west. Now with that said though, the increasing forcing and strong
shear could help to clear the cap during the overnight hours on
Tuesday night into Wednesday, allowing for a few stronger storms. The
system is expected to be more progressive and quantitative precipitation forecast values will be
likely stay under a half an inch. Some locally higher amounts are
possible with any storms but widespread flooding concerns are
lower at this time.
Thursday through Saturday...forecast confidence is medium.
We get a brief break in the rain on Thursday as the front that
moved through Wednesday is south of the area. It will be a mild
day on Thursday with highs in the mid 60s. As we head into
Thursday night, the front lifts back north in response to an
approaching shortwave. Models are starting to come to an agreement
in another potentially heavy rain and flooding setup for this
period. It's a bit too far out to get into any specifics at this
point but guidance is suggesting another 2-3 inches of rain
possible. We will continue to monitor the trends for this system,
especially given the heavy rainfall this weekend.
Mfvr and IFR ceilings will dominate more much of the day today as a
cold front slowly progresses through the area. Moderate to heavy
rain will be likely throughout the day bringing at least MVFR
visibilities but heavier rain showers could result in periods of IFR
visibilities. Thunderstorms will likely be isolated to scattered
throughout the day and would be likely to bring heavier
downpours. Otherwise the period will start off with modest
south/southwest winds but as the front comes through we expect
winds to shift quickly to the northwest. The wind shift will
likely come during the late afternoon and early evening hours.
Breezy southwest winds will continue over the lake as the front
moves into the region this morning bringing lots of rain
throughout the day. There is a chance for a few thunderstorms and
any thunderstorms will likely be responsible for some torrential
downpours. Otherwise as the front moves through in the evening
expect winds to shift quickly to the northwest, though these winds
are expected to be mostly light. Rain will likely end by Monday
evening, persisting in the northern half of the lake through the
WI...Flash Flood Watch through late tonight for wiz062>072.