Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 kdvn 210250 

Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
950 PM CDT Tue Aug 20 2019

issued at 949 PM CDT Tue Aug 20 2019

Cams have been consistent with a slower arrival of storms tonight
into tomorrow. Satellite imagery and lack of convection supports
this notion. As such, have pushed pops back to after 12z across
the SW. The best chance for precip looks to be from 12z through
18z or so Wednesday.


issued at 320 PM CDT Tue Aug 20 2019

An upper level shortwave and attendant mesoscale convective system was seen on satellite
water vapor imagery and radar mosaic over Indiana and Ohio early
this afternoon. At the surface, an outflow boundary trailed from
this complex westward across northern MO, where scattered showers
and thunderstorms continued to linger. The remnant mesoscale convective vortex was over
northern Illinois with another weak boundary trailing westward into east
central IA, where skies were clearing in the shortwave
subsidence. Further north a separate mesoscale convective system that tracked southward
across Minnesota this morning had since dissipated, leaving yet another
outflow boundary over northeast Iowa. Temperatures ranged from the
upper 70s to lower 80s with dewpoints in the upper 60s to lower
70s. The main synoptic cool front across WI, Minnesota into eastern NE
marked the leading edge of much drier air with dewpoints in the
50s and 60s. This boundary is expected to advance southeast
overnight bringing cooler, drier weather for at least the north
Wednesday, while showers and thunderstorms may linger through much
of the day across the south.


Short term...(this evening through wednesday)
issued at 320 PM CDT Tue Aug 20 2019

The main challenge for tonight is the potential for showers and
thunderstorms developing along the gradient of the very high
MUCAPE axis in place over the Missouri River valley. In the near
term, shortwave subsidence and pressure rises over the local area
looks to win out over recovering low level moisture/instability
along weak boundaries to suppress new convection over the forecast
area this afternoon and evening.

Tonight, another complex of storms will likely form along the cape
gradient and low level jet focused into southeast NE into SW Iowa
late. This activity may spread eastward, in a weakening form,
reaching the Highway 34 corridor well after midnight. Unlike last
night, the potential for severe weather looks much less favorable.
Over the rest of the area, continued weak upper level subsidence
above lingering boundaries and abundant low level moisture from
recent rain may lead to at least patchy fog, which was included
over the north and central portions of the forecast area. High
dewpoints will limit lows to the upper 60s north to lower 70s

Tuesday, one or more shortwaves and possible mcvs in the zonal
flow aloft are expected to track eastward over the area,
interacting with the main synoptic front expected to reorganize
from northeast Kansas across northern MO into central Illinois. This may
lead to at least scattered showers and possible thunderstorms
across northern MO, southern Iowa into west central Illinois through the
day and high chance pops are kept in place. Temperatures will only
reach the mid to upper 70s in the north, where drier air will
begin to advect in from the north during the day, to the lower 80s
in the south.

Long term...(wednesday night through next tuesday)
issued at 320 PM CDT Tue Aug 20 2019

Wednesday night and Thursday...general agreement in several 12z
model run solutions that broad upper level troffiness will
adjust/dig down acrs the upper MS River Valley/great lks, while
undercutting sfc ridging slides down acrs these same regions. The
entire County Warning Area will look to find itself in north to Northeast Boundary
layer flow north of a low level west-to-east oriented instability
gradient- frontal system laying out from the south Central Plains,
over to the Ohio River valley. Embedded passing short waves and
isentropic lift processes will look to keep elevated areas of
showers moving acrs the southern third or so of the County Warning Area Wed night.
Still enough mid layer MUCAPES for some embedded thunder, but mid
level lapse rates look marginal. These thunder supporting parameters
really wane from midnight on into early Thu morning, and it may
transition to mainly stratiform rain.

Still enough low to mid level saturation to support general rainfall
amounts of a quarter to half inch acrs the southern third of the County Warning Area
by Thu morning, but the far south which may get in on multiple
passing elevated storms could push 0.75 to around an inch. Where
clouds thin out to the north, cool bl advection will lead to lows
well down in the 50s, while the south is held up in the low to mid
60s. May have to keep at least patchy fog in mind in the north by
early Thu morning, but confidence too low to add mention now. Some
overrunning showers may linger through Thu morning, then expect a
southward shunt of the precip-generating processes, and more cloud
thinning from north-to-south into Thu evening. High temps may be
milder over the north half of the County Warning Area in areas sooner to get less
filtered insolation. Mainly dry and cool again with many 50s Thu
night/Fri morning.

Friday through Sunday...Friday may be an ideal day for this time of
year if western Great Lakes ridging maintains it's grip with Northeast
Boundary layer(bl) flow, lower humidity and temps in the 70s to low
80s acrs much of the area. Clear skies would lead to another below
normal temp night Friday night into Sat morning. Will through out
the outlier 12z NAM which spirals a cut-off low up toward the
southern County Warning Area and produces heavy def zone rains along and south of
i80 on Friday. Then the latest suite of medium range models maintain
a partial blocking pattern acrs the north central to northeastern
Continental U.S. For a continued mainly dry fcst with some temp moderation for
much of the weekend. When that pattern starts to break down by wave
energy from the west, along with moisture return flow is when precip
chances will look to increase again which may be in the form of a
mesoscale convective system again in or near the local area by Sunday night.

Monday and next Tuesday...broad upper level troffiness to flattened
flow/westerlies interacting with moisture return acrs the upper
Midwest may lead to a more unsettled period early to mid next week,
with possible mesoscale convective system or storm clusters moving acrs the region
especially at night, depending on where the best llvl thermal
gradient/storm track lays out. ..12..


Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 633 PM CDT Tue Aug 20 2019

VFR expected to last at most taf sites for the next few hours
before fog and low clouds move into the area. Pretty high
confidence on at least MVFR restrictions and confidence increasing
that we see IFR restrictions. Late tonight into tomorrow, showers
and storms are possible again, however timing of said storms is
uncertain, so have left out of current taf issuance.


Dvn watches/warnings/advisories...


National Weather Service Glossary of Abbreviations