Scientific Forecaster Discussion
fxus63 kmpx 162342 aaa
Area forecast discussion...updated
National Weather Service Twin Cities/Chanhassen Minnesota
542 PM CST Sat Nov 16 2019
Short term...(this evening through Sunday night)
issued at 234 PM CST Sat Nov 16 2019
The main forecast concern is whether freezing precipitation
develops over the eastern 1/4 of mpx forecast area, or mainly west
central Wisconsin overnight.
First, regional radar, in conjunction of satellite imagery/moisture
profiles, indicated a large swath of moisture advection ahead of the
main short wave moving east across the western Dakotas this
afternoon. Pwats are already 0.60" across western Minnesota
indicating that once the main forcing arrives, an area of
precipitation will develop. Models are similar in developing a
narrow band of light precipitation across far western Minnesota this
evening ahead of this short wave. Both the ec/GFS support increasing
fgen at mid levels before deeper moisture arrives by midnight. Thus,
if any precipitation develops it will likely be very light, or
virga. However, once better forcing and deeper moisture coincides
with each other by midnight, there should be a band of
precipitation across central/southern Minnesota. Depending upon the
strength of the fgen and if any instability aloft can be realized,
precipitation could be locally enhanced leading to higher
precipitation rates. However, confidence is low on this scenario, so
will hold onto a blend of the models on quantitative precipitation forecast which still gives parts
of eastern Minnesota around two tenths of an inch of precipitation
between midnight and 6 am.
The other aspect to the precipitation is whether surface
temperatures will be cold enough to warrant some freezing rain,
especially in west central Wisconsin, and areas that still have some
snow on the ground in south central Minnesota. Elsewhere, and in
combination of a deeper warm layer expected overnight, any
precipitation that falls will be in the form of rain, not snow.
There is a low possibility of a localized enhancement where forcing
is maximized so a brief period of snow could develop. The best area
of cooler temperatures aloft, and better forcing will occur in west
central Wisconsin. This area will likely see the bulk of the
snowfall if any occurs. There is still a possibility of some areas
of freezing rain around Rice Lake, and Ladysmith, Wisconsin where
surface temperatures will be near the freezing mark overnight. If
any freezing precipitation develops it should be brief. However,
area roads, especially secondary roads could be impacted.
Once the short wave moves east of the region by Sunday morning, the
precipitation will end. Low clouds and breezy conditions will return
Sunday, but temperatures will still manage to rise above the
freezing mark. Sunday night looks uneventful with temperatures
falling back into the 20s.
Long term...(monday through saturday)
issued at 234 PM CST Sat Nov 16 2019
The longer term continues to look relatively quiet as the large
scale upper flow remains fairly progressive and not too amplified.
This results in a few chances for precipitation, but nothing that
looks too significant at this point. The large scale flow looks to
remain somewhat split, so the only chance for anything significant
in our area would be if we were to see some phasing of the
northern and southern streams. The GFS was suggesting this a few
runs ago, but has trended more toward the European model (ecmwf) and Canadian
solutions, which keep anything meaningful during the midweek
period well to our south. However, it should be noted that there
is a ton of spread in the ensemble guidance beyond Tuesday, which
shouldn't be too unexpected given the progresses upper flow and
timing/amplitude differences which only magnify over time. Can't
see too much reason to stray from the consensus forecast at this
point, with the main messaging being that temperatures will remain
near to slightly above normal, and that there is fairly low
confidence in forecast details from midweek Onward.
We still look to have a chance of some precipitation late Monday
into early Tuesday as the baroclinic zone lifts back to the
North/East through the area. At this point, would look to be rain
or snow depending on boundary layer temperatures (so perhaps
initially rain changing to some snow). Precipitation amounts
should be low, so not expecting much if anything in the way of
impacts. A more significant system will impact the central US
during midweek, but the bulk of the moisture and forcing look to
stay to our south. However, an inverted trough does look like it
will extend north through our region Wednesday into Wednesday
night as the main surface low moves through the mid-Mississippi
Valley. Some rain/snow chances will move across our area in
association with the surface trough and some mid-level
frontogenesis, but amounts again look limited (locations near the
Iowa border will want to keep an eye on the forecast since some of
the ensemble solutions as well as the GFS bring the primary wave
and moisture/forcing into that area). Timing and location
differences in the guidance result in a longer period of pops than
what will ultimately occur from Wednesday into Thursday, but given
the uncertainty there isn't much that can be done to refine things
too much at this point. Expect to see pops increase and the time
window to decrease as we move through the next few days. After the
midweek system, things look to dry out for the remainder of the
period, although there is substantial variation in the overall
pattern by the weekend.
Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 542 PM CST Sat Nov 16 2019
VFR conditions this evening, then a band of rain will begin
developing from rwf to stc late this evening and expand as it
heads eastward overnight. MVFR cigs likely behind this Barrow band
of precip through Sunday. The rain will encounter colder and drier
air toward eau, so odds are better for snow there very late
tonight or early Sunday morning with IFR conditions.
Kmsp...rain should arrive about 07z and continue for most of the
rest of the night. Confidence in when MVFR cigs will arrive is
low, but will likely occur sometime overnight.
/Outlook for kmsp/
Mon...VFR. MVFR ceilings possible late. Wind SW 5 kts.
Tue...VFR. Wind northwest 5 kts.
Wed...VFR. Possibly MVFR chc -ra/-sn late. Wind bcmg north 5-10 kts.