Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 132034

Area Forecast Discussion
National Weather Service Aberdeen SD
234 PM CST Mon Nov 13 2017

.SHORT TERM...(This Evening through Tuesday Afternoon)
Issued at 228 PM CST Mon Nov 13 2017

Forecast challenges include fog/low stratus potential tonight and
their impacts on temperature.

Currently, except for a small portion of northeast South Dakota into
west central Minnesota where some sct/bkn coverage of low clouds
continues, the region is experiencing full sunshine. Southerly
breezes are occurring over the eastern third of the forecast area
while the western two-thirds of the region are characterized as
light and variable. Temperatures are warming through the 40s and 50s
and in some areas into the low 60s.

The forecast is a dry one tonight and Tuesday. Behind a cold frontal
passage on Tuesday, it`s debatable whether or not an isolated shower
or two may be working its way east-southeastward across the cwa. The
atmosphere is pretty dry to support precipitation. The most note-
worthy aspect of the short term forecast period is the potential for
fog and low stratus to develop. The table is set for excellent
radiational cooling conditions on (at least) the front end of the
tonight period. Ample surface moisture (surface dewpoints at or
above 36F) to start things off this evening when the sun sets at
appx 5 PM CST. Rap soundings in BUFKIT support a fog/low stratus
sounding, particularly for the KABR and KATY areas. It`s entirely
possible that foggy conditions develop/spread as far west as the
Missouri River valley. But confidence in that scenario unfolding is
still a bit low at this point. Higher confidence in fog/stratus
developing over the eastern half of the forecast area.
Numerical/aviation guidance supports fog formation over the Prairie
Coteau and in the James River valley as well. If fog/low stratus
materializes overnight, areal coverage/depth of fog and low stratus
will play a large role in how much temperatures can fall overnight
tonight, as well as how quickly temperatures can recover on Tuesday
(time needed to mix out/dissipate fog and stratus). A couple models
are hinting at temperatures warming the most on Tuesday once the
surface cold frontal passage occurs and better northwesterly mixing
winds establish.

.LONG TERM...(Tuesday Evening through Monday)
Issued at 228 PM CST Mon Nov 13 2017

A cool snap for Wednesday, strong winds Thursday into Friday and
relatively dry conditions are the main highlights of the extended.

Will start with a shortwave crossing the northern plains Tuesday
night. The mid/surface low will have already passes into far western
Ontario, and a weak surface trough will have already crossed the
CWA. Northwest flow and a weak surface ridge will keep us mixed
overnight. The cold push of air that follows is delayed until 09-12Z
with 925mb temperatures falling from a peak of around +6C to a range
of +1 to -5C by mid day from south to north across the state. This
suggest temperatures will stall and possibly fall in the afternoon
for northern parts of the CWA.

Southeast flow develops for Thursday early, becoming more southerly
during the day with warm advection. The gradient increases to around
20mb across the state, with pressure falls of 9 to 12mb in 6 hours.
That strong gradient pushes into Minnesota by the evening but
pressure rises behind a front, along with low level westerly flow
will keep us mixed Thursday night. Breezy conditions will redevelop
for Friday thanks to the westerly component and favorable mixing
conditions, with a shot of Canadian air coming in late in the day.

As for precipitation, blended guidance supports some low chances for
Friday, however the deterministic GFS depicts best forcing splitting
the CWA. BUFKIT shows a warm/dry layer below any mid clouds and
forcing so while I decided it best to maintain blended low POPs/low
QPF, anticipate little moisture reaching the area.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday Afternoon)
Issued at 1155 AM CST Mon Nov 13 2017

With the exception of KATY, good VFR is occurring over terminal
airspace right now. KATY may eventually mix out its MVFR stratus
this afternoon and join the others in VFR flying conditions
heading into this evening. Given the synoptic pattern, time of
year and available low level moisture around tonight into Tuesday
out ahead of an approaching cold frontal passage, there is some
expectation that low (sub-vfr) stratus and/or fog will develop
overnight across the James River valley of northeast South Dakota
over into the upper Red River valley headwaters region of west
central Minnesota. Model soundings and a number of guidance
sources indicate some good radiational cooling conditions setting
up by early this evening across the region. What`s not abundantly
clear at this point is how far to the west these conditions will
develop/spread overnight. At this point, where confidence is high
enough to add mention in the TAFs, have beefed up sub-VFR forecast
conditions at KABR and KATY, and left VFR forecast conditions
going at KPIR and KMBG where adequate surface/low-level moisture
in the nocturnal boundary layer may not be sufficient to produce
any fog or low stratus. Will continue to monitor trends over the
next couple of TAF issuances.




LONG TERM...Connelly
AVIATION...Dorn is the U.S. government's official web portal to all federal, state and local government web resources and services.