FXUS63 KABR 190853

Area Forecast Discussion
National Weather Service Aberdeen SD
353 AM CDT Thu Sep 19 2019

.SHORT TERM...(Today through Friday Afternoon)
Issued at 352 AM CDT Thu Sep 19 2019

The forecast challenges include potential waa-forced convection
later tonight as a warm front advects north through the region,
along with heavy rain potential in any showers/storms that can get
going prior to 00Z Saturday.

Currently, under a clear sky and light winds, temperatures amid an
area of surface high pressure are running generally in the 50s.

Today should continue to showcase plenty of sunshine and pleasant
weather conditions (slightly above normal temps in a relatively dry
airmass) as this surface high pressure gradually works north/east
out of the area.

Convection ongoing this morning across northeast NE and the northern
half of IA is firing on a boundary that is forecast to lift north
across the region later tonight, allowing for a warm sector-like
environment of hot and muggy on southerly breezes to establish
itself on Friday. Tough to find a s/w to anchor precipitation
chances on for later tonight, but models do suggest there could be
some low level jet help for forcing a few showers or storms within
the waa sequence as the warm front lifts north later tonight. No
lack of adequately steep (for mid September) mid-level lapse rates
around overnight either.

The majority of models are still clinging to surface cold fropa
timing on Friday that brings the boundary right up to or perhaps
just into the far western forecast area by the end of the Friday
daytime forecast period. Should convection get going on Friday out
ahead of the boundary, the needed deep layer shear support for
severe storms (other than pulse-type/multi-cellular) appears to be
lacking. But, the atmosphere will be juiced (2-3 standard deviations
above normal moisture content) on Friday, so convection will
certainly have the potential to produce excessive heavy rainfall
rates. If there is a severe storm threat, it would have to be tied
directly to or perhaps just behind the frontal boundary where deep
layer shear will be closer to 25 to 40 knots. General storm motion
on Friday is south to north, so there is some concern for training
storms getting going along this slow-moving frontal boundary.

.LONG TERM...(Friday Evening through Wednesday)
Issued at 352 AM CDT Thu Sep 19 2019

By 00Z Saturday, the 500mb low or potentially open wave trough, will
be centered across ID and western MT. The broad surface low will be
set up from north central ND through eastern WY/western SD and down
through eastern CO. Expect the system to progress eastward
overnight. Although there is still some uncertainty, it looks like
the surface trough/cold front will move over central SD by 09Z
Saturday, with a reinforcing trough set up over eastern SD and
southeastern MT. PW values will remain near 1.5in with a few areas
reaching close to 1.9in. At this point, heavy rain is a serious
threat. However, figuring out where 1-2 inches or more rain will set
up is still uncertain. Despite being quickly moving storms (n to nne
30-40kts, training storms will be likely. The 00Z forecast solutions
suggest the highest threat of heavy rainfall will be over most of
our central counties. Will continue to monitor the latest trends
with this evolving storm system. As for the severe potential, hail
and winds look to be the main threats. When the cold front crosses,
LFC levels will drop below 2000m with the LCL not too far below
resulting in a higher likelihood of deep convection, and 0-km shear
jumps to around 40kts. At this point, the risk area for tornadoes is
more to our north, where there is better rotational shear.

High temperatures Saturday should end up around 10 degrees lower
than Friday, in the upper 60s to low 70s. Temperatures for the rest
of the period will remain in the mid 60s to mid 70s (warmest Monday
and Tuesday, after the surface ridge exits east).

The 500mb ridge will be overhead Monday morning-evening. A trough
moving into the Pacific Northwest Sunday morning will turn into a
cut off low over the southwestern U.S. Monday through Wednesday
night, before shifting back into the main w-e flow across the
central U.S. Unsettled weather in the form of mainly isolated
showers could return to our northeastern counties Tuesday-Thursday
as a deepening central Canadian surface low extends a trough into
that area.


.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
Issued at 1235 AM CDT Thu Sep 19 2019

VFR conditions. There will be a shift of winds to the south
southeast and increase in intensity over the next 24 hours. Storm
chances are negligible through the first half of Thursday night.




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