Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1046 PM CDT Thursday Oct 23 2014
Short term...(this evening through friday)
issued at 403 PM CDT Thursday Oct 23 2014
Clearing continues to move from eastern Minnesota into western WI this
afternoon. Good mixing occurred this afternoon across the western
and central areas of Minnesota with temperatures warming into the lower 70s
under sunny skies. As a result of the mixing and subsequent sunshine
fog is not expected across western to central Minnesota tonight. That part
of the state will see abundant sunshine Friday with temperatures a
couple degrees warmer than today.
For the western WI counties...skies will become partly cloudy by
late afternoon. A dense fog advisory will be in effect overnight for
the extreme eastern Minnesota counties and the western WI counties.
Widespread dense fog is expected to form after midnight. The lowest
visibilities will approach 1/4 mile. Visibilities will improve a few
hours after sunrise Friday with sunny skies skies by noon.
Temperatures will be several degrees warmer. Skies will be clear
Friday night with temperatures in the 40s.
Long term...(friday night through thursday)
issued at 403 PM CDT Thursday Oct 23 2014
A cyclone will develop across the Midwest early next week which will
temporarily bring an end to the above normal temperatures. The
models are in good agreement with the general depiction of the
system...but there are considerable uncertainties in the timing and
Upper level ridging across the High Plains Friday night and Saturday
will keep the region dry and mild...so continued the 0 probability of precipitation during
that time frame. Meanwhile a potent shortwave will move onshore the
Pacific northwest...and this will be the weather maker for the early
part of next week. The last few runs of the GFS...in particular the
23.12 have been very aggressive in the development with this system.
It develops a 988 low over Minnesota...while the Gem and European model (ecmwf) are
weaker...slower...and farther east with the low track.
After much interrogation...it appears that the difference Stem from
the phasing of the southern and northern stream across the Texas/OK
panhandles late Monday afternoon. The northern stream off the GFS is
less amplified and slightly quicker...so it places the main
shortwave on the foothills of Wyoming by 18z Monday. By 06z Tuesday this
pv anomaly becomes phased with the upper level front of the southern
stream...and cyclogenesis follows leading to a well developed
cyclone by Tuesday morning. However the ec and Gem are slightly more
amplified with the northern stream...and less progressive with the
initial shortwave. The phasing between the upper level front and the
polar jet is delayed and displaced...and as a result by 18z Tuesday
the surface low ends up over the eastern side of Lake Superior
compared to the western side on the GFS. The Main Point of this
discussion is that there is uncertainty in the track of the surface
low...and therefore heaviest precipitation. But confidence is high in a middle
latitude cyclone developing across central North America Monday
night and Tuesday.
The weather will remain dry through Sunday...but a few showers could
develop Sunday night with the isentropic lift along and north of the
warm front. Used 6hr grids to better show the timing of this precipitation.
Did not make changes to the forecast beyond Sunday for the reasons
mentioned above. Precipitation chances will linger through Wednesday...with
Aviation...(for the 06z tafs through 06z Friday night)
issued at 1046 PM CDT Thursday Oct 23 2014
Confidence is increasing that low MVFR/IFR ceilings across western
WI and far southeast Minnesota will back into east central Minnesota...including the Twin
Cities...overnight. Visibilities will slowly deteriorate under the
stratus during the night. Areas of eastern Minnesota where it is clear
right now have a better chance of LIFR/vlifr ceilings and
visibilities developing between 06z and 08z. Dew points are lower
for the western Minnesota terminals...resulting in a larger temperature/dew
point spreads. There is a also increasing high clouds in the west
that will help keep temperatures from falling. Hence...VFR conditions
still expected for krwf..kstc and kaxn. Ceilings and visibilities
improving by late morning across eastern Minnesota and early in the
afternoon across western WI. Light southeast winds overnight gradually
veering SW on Friday with speeds in the afternoon 8-10 knots.
Kmsp...low MVFR/IFR ceilings continue drifting northwest towards the
airfield with broken-ovc010 expected by 07z. Ceilings will persist
through much of the morning before the low level flow turns SW and
pushes things off to the east.
/Outlook for kmsp/
Sat...VFR. Winds west-northwest at 10-15kts.
Sun...chance MVFR/-shra late Sunday night. Winds becoming southeast at
08-14kts in afternoon.
Monday...chance MVFR/-shra winds east-NE at 08-13kts.
Minnesota...dense fog advisory until 10 am CDT Friday for mnz053-063-070-077-
WI...dense fog advisory until 10 am CDT Friday for wiz014>016-023>028.