Scientific Forecaster Discussion
fxus63 kfsd 201700
Area forecast discussion
National Weather Service Sioux Falls South Dakota
1200 PM CDT sun Oct 20 2019
Short term...(today and tonight)
issued at 334 am CDT sun Oct 20 2019
Mid to upper level clouds will continue to increase from the west
ahead of a broad upper through currently over eastern Wyoming/western South Dakota.
Dry air will keep much of this activity as sprinkles and/or isolated
showers early this morning, mainly west of the James River. However,
low to mid level moisture deepens and will allow precipitation to
become intermittent as the low approaches over the region late this
morning into the afternoon. While the instability is weak an area of
very Low Cape values and increasing Theta-E advection is possible
ahead of the front, leading to a few thunderstorms. Precipitation
becomes likely west of the I-29 corridor before 20z (3pm), then
spreads eastward into southwest Minnesota and northwest Iowa after
23z(6pm). The greatest lift and moisture today and tonight looks
to be along and north of I-90 through southwest Minnesota. This
region is where the highest quantitative precipitation forecast amounts should be. Overall, quantitative precipitation forecast
amounts in the 0.10" - 0.40" range can be expected from Sunday
through Sunday night.
Another concern this afternoon is winds. Soundings and model
guidance suggest 25 to 35 knots of wind a top of the mixed layer.
South sustained winds of 15 to 25 mph, with gusts to 35 mph are
possible through early evening.
There could be a null in precipitation for most areas late this
evening as the dry slot wraps over the forecast area. However,
expect showers will return late tonight as the main vort lobe
Long term...(monday through saturday)
issued at 334 am CDT sun Oct 20 2019
The work week starts off damp and cool as the aforementioned surface
low pressure slowly moves out of the region.
Isolated to scattered showers will continue during the day and will
slowly taper off through Monday night. Areas west of the James River
will dry out during the afternoon hours while lingering showers
could persist over portions of southwest Minnesota through early
Tuesday. Quantitative precipitation forecast amounts from 0.10" to around 0.5" of rainfall will be
possible Monday through early Tuesday morning. In terms of
temperatures, Monday looks to be cooler with highs from the upper
40s to low 50s. A tight pressure gradient on the backside of the
surface low will once again lead to strong northwest winds on
Monday. Given that, have increased winds by blending nbm with
consmos to produce gusts of 30 to 40 mph.
Tuesday should be relatively dry with temperatures slightly warmer
than Monday. Highs will generally range from the upper 40s to mid
50s. The main weather concern continues to be winds. Gusty northwest
winds are possible through the day as the main upper low system
moves into he Great Lakes and the pressure gradient slackens.
Showers return on Wednesday as a compact shortwave moves over the
region within the west to northwest flow aloft. There is model
agreement regarding this weak system suggesting light rain, mainly
focused along and north of the I-90 corridor. After the passage of
this system, a cooler airmass briefly filters in Wednesday night
into Thursday. Highs on Thursday will only reach the 40s.
Temperatures increase back into the 50s and 60s towards the end of
Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 1156 am CDT sun Oct 20 2019
Showers and isolated thunderstorms will develop across the area by
this afternoon, then push eastward through the evening hours. By
late evening there is expected to be a break in the precipitation
before there is some redevelopment on Monday morning. In addition,
ceilings will lower into the MVFR/IFR range late tonight into
Monday, affecting mainly khon and kfsd.