Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Grand Forks ND
913 am CDT Sat Aug 23 2014
issued at 915 am CDT Sat Aug 23 2014
We will add some patchy fog to the forecast for the next few
hours. Then attention turns towards potential severe weather later
this afternoon/overnight. The 12z NAM indicates the best surface
instability will remain in northeast South Dakota today...with some elevated
instability moving north tonight. There are currently plenty of
clouds for the entire forecast area...and this could limit overall
surface based convection for US. There should be an mesoscale convective system moving
northeast overnight...probably affecting the southern forecast
area after 03z. Storm Prediction Center has outlooked a good portion of the area in a
slight risk...with the main tornado threat in South Dakota...which makes
sense. In addition...with precipitable waters rising over 2 inches this
afternoon/overnight with strong forcing...heavy rainfall will also
be a concern. This is all handled well in the grids and will
continue to monitor threats today.
Short term...(today through sunday)
issued at 406 am CDT Sat Aug 23 2014
The GFS, ECMWF, Gem and NAM are in good agreement through 84 hours.
Middle term the Gem is slightly faster and the GFS and NAM slightly
slower than the European model (ecmwf). The models re-juggle by 84 hours with the Gem
and the GFS the slowest and the NAM and European model (ecmwf) the faster. Will
prefer the European model (ecmwf).
Water vapor loop indicated two short waves over Idaho and southern Colorado.
Upper level ridge axis was located over Minnesota. Upper ridge forecast to
amplify and shift east through sun then roll over. Colorado short wave to
move through later this afternoon ad evening. Idaho short wave/upper
low will follow in Tow on sun, become negatively tilted, and
Precipitable water rise to around 2 inches under 700 Theta-E ridge
this afternoon. Storm Prediction Center has slight risk for southern half or southern
2/3 for today and far eastern zones for sun.
More stable air moves in Sun night. Will have only showers in the
far north Sun night and Monday with wrap around.
Long term...(sunday night through friday)
issued at 406 am CDT Sat Aug 23 2014
/Tue through Sat/
the long range models are somewhat in agreement for next week with a
changing upper level pattern...however the GFS is faster with a
sharp short wave crossing the northern plains middle week and continues
to have a more amplified upper air pattern with ridging to our west
and an overall drier forecast for our area. European model (ecmwf) more zonal flow with
periods of low probability of precipitation as weak short waves move across southern Canada. Overall
allblend solution tonight not too bad although Tuesday probability of precipitation seemed to high
with GFS showing a strong surface low moving into Wisconsin and ridging
over ND. Lowered probability of precipitation for southern half of the County Warning Area (north was already
dry) with best chances across the extreme far south. Rest of the
week looks dry as this first systems pulls out into the Great Lakes.
Week will start with unseasonally cool temperatures in the 60s early in the
period and trend warmer through the week...with daytime highs by
Friday reaching the upper 70s to near 80.
Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 707 am CDT Sat Aug 23 2014
Mostly IFR conditions are across the area with ceiling below one thousand
feet and patchy fog with visibility as low as 1 mile. Expect ceilings to
slowly lift today but dont expect much improvement until rain moves
in from the south. Rain should clear out the fog but low ceilings will
likely remain or perhaps rise to MVFR category.