Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 190952

Area Forecast Discussion
National Weather Service Aberdeen SD
352 AM CST Sun Nov 19 2017

.SHORT TERM...(Today through Tuesday Afternoon)
Issued at 352 AM CST Sun Nov 19 2017

With dry weather continuing through the period, the main concerns
will be winds and fire weather.

Expect downslope winds to increase this morning off the Sisseton
Hills, with gusts nearing 20-30kts and continuing through early
afternoon. Above normal temperatures will continue through Monday,
on west to southwesterly winds ahead of low pressure sliding across
southern Canada (over British Columbia and Saskatchewan today, and
Manitoba by mid day Monday). Relative humidity values will fall to
20 to 30 percent across most areas west of the James River Valley
today and Monday, as winds mainly stay at or below 15 mph. The wind
will be strongest Monday, pushing the grassland fire danger index to
high and even very high for most areas west of the James River

Much cooler air and gusty northwest winds will move in late Monday
night and Tuesday, behind a passing cold front. Winds will increase
overnight, with some gusts nearing 25-30kts already by 09Z Tuesday.
Wind Chill values will fall into the single digits, with a few
single digit below readings possible. Confidence in temperatures
Tuesday afternoon are on the moderate to lower side. The ECMWF is
quicker to bring in the cooler air than the 06Z NAM, with the 06Z
GFS being more middle of the road on timing bit is warmer than both
wrt 925mb temps.

.LONG TERM...(Tuesday Evening through Saturday)
Issued at 352 AM CST Sun Nov 19 2017

00Z model solutions still showing no end in sight to the persistent
positive pna signal in the larger scale flow pattern. Other than one
or two brief periods when the flow flattens into almost zonal flow
aloft, the northwest flow saga continues.

As the dayshift alluded to, the GFS and ECMWF now appear to be
getting on the same page regarding a few hours of light
precipitation potential Wednesday afternoon/evening, when low to mid
level waa is occurring. Still a low confidence scenario whether
there is in fact any precip reaching the ground over the
northeastern forecast zones. If it is, precip-type is going to be
highly dependent on how deep and how warm (above zero celsius) the
column will become during precip`ing time. Model soundings indicate
the lowest 2k to 3k ft agl (KABR/Marshall County RAWS) will be the
slowest/weakest to respond to the warm air advection (shallow cold
layer), suggesting there could be a zone where p-type is snow,
changing/mixing with sleet before potentially (eventually)
transitioning to rain/freezing rain (surface temp? at precip time)
before ending. Again, that`s if there is any precip reaching the
ground; models indicating precip amounts would be rather scant (less
than a tenth of an inch water equivalent).

The rest of the extended forecast basically continues to be dry,
with the exception of some rather low end pops still hanging around
Friday afternoon/Friday night. Confidence remains rather low
regarding those precip chances. The only component of the Tuesday
night through Saturday forecast that maintains any semblance of
confidence is temperatures. All three 00Z GSM solutions (with
support of NAEFS ensemble 850hpa standardized anomalies output)
still pointing to things being below normal cold starting out
Tuesday night before the much anticipated warm up to above normal
warm for the second half of the week from Wednesday through Friday
(including Thanksgiving Day). And then, still expecting some push
back heading into the weekend as another blast of Canadian cold air
is forecast to impact the region.


.AVIATION...(For the 06Z TAFS through 06Z Sunday Night)
Issued at 1140 PM CST Sat Nov 18 2017

VFR conditions are expected through tonight and Sunday.




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