Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
1053 PM CDT Wednesday Oct 22 2014

Short term...(this evening through thursday)
issued at 343 PM CDT Wednesday Oct 22 2014

Fairly Stout southeast winds out there today in response to the tight
pressure gradient between a 1028mb high over the Great Lakes and a
1002 mb low over central Manitoba. At 3 PM...a surface trough extended
from near Devils Lake south to mitchel and down to the central
Nebraska/Kansas border. Just west of this surface feature there is a negatively
tilted short wave that has a nice push of dry air on water vapor
moving across the western Dakotas. It is this upper wave that will be
the primary driver of a line of showers that will move across the
area tonight. Previous forecast had a pretty good handle on this
precipitation band...with the main change today being to shrink the width
of the band of categorical probability of precipitation moving across the area. This meant
slowing down the arrival of the precipitation by a couple of
hours...while speeding up further its departure from west to east
through Thursday morning. Did remove the thunder mention as well as best
Li/S are pegged to be barely below zero...with Storm Prediction Center sref calibrated
thunderstorm probs looking meager as well. A few folks will
undoubtedly hear a rumble of thunder or two...but would rather not
spread thunder wording across a large chunk of the area to cover a
few flashes of lightning. Less convection also means lower
rainfall rates...so did cut back on quantitative precipitation forecast amounts some...with
amounts across the area now generally a tenth to a third of an
inch.

We will see pretty aggressive clearing behind the rain band
tonight...so we will have to keep on eye on the potential for fog to
develop. Winds will go light...but not completely calm...so this may
help limit the fog development. At the moment...the greatest
potential for fog looks to exist from Mankato up through St. Cloud
given expected timing of the clearing and the placement of the surface
trough late tonight. After that...a beautiful Thursday will unfold
as strong subsidence in the wake of tonights shortwave will help
clear the skies out. Will see wrly winds develop behind tonights surface
trough as well...with a nice Chinook wind expected across the northern
plains. Favored highs Thursday toward the bias corrected
guidance...with highs ranging from the middle 70s out around
Madison...with temperatures about 20 degrees cooler over toward
Ladysmith...where more cloud cover into the early afternoon will
help keep temperatures cooler.

Long term...(thursday night through wednesday)
issued at 343 PM CDT Wednesday Oct 22 2014

Two significant changes in the extended period. First...due to the
slower model solution of the northeastern storm system over the next
few days...slightly cooler temperatures Sunday are more likely vs. The
expected 70 degree high previously forecast. Thus...due to the
slower solution...a storm system moving across the Great Lakes
Saturday will hold back the colder air across the upper Midwest. In
addition...morning lows Sunday around 40 will hold down afternoon temperatures
as clouds begin to increase from the S/SW. The second change is related
to the phasing of the southern/northern jets which leads to
precipitation chance/S across the upper Midwest as a storm system moves
out of The Rockies early next week.

One of the main weather influences over the next week is the consistent
fast/progressive pattern. The most active weather will remain across the
northeast and Pacific northwest/northern rockies. In between...problems
exist due to the phasing of the upper jets. Will remain optimistic
with a more unsettled pattern next week. In addition to the
unsettled pattern...temperatures will likely drop to near normal as the
main upper jet core and thickness values lower across the northern
U.S. Latest GFS still has a potent weather system moving across the upper
Midwest around Halloween. Thickness values and associated wet-bulb
mean layer /1km/ temperatures are near 0 to +2c...leading to some
precipitation type problems.

&&

Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1053 PM CDT Wednesday Oct 22 2014

Showers are making slow progress into eastern Minnesota late this
evening. However...they are also becoming more scattered in nature.
The showers are just ahead of a frontal boundary stretching north
to south across far western Minnesota. As the front moves east
overnight...low MVFR/IFR ceilings along the boundary will spread
into kmsp...krnh and Keau while ceilings to the west scatter out. One
change with the 06z taf package was to lower ceilings for early
Thursday morning to IFR for the eastern sites. There also remains a
threat for IFR or lower visibilities in fog across about the
central third of Minnesota. This would impact kstc. Ceilings are still
expected to lift and scatter across eastern Minnesota and western WI in
the late morning to early afternoon respectively. Southeast winds near 10 knots
ahead of the boundary becoming west-southwest with passage.

Kmsp...lowered ceilings to IFR for early Thursday morning with dew
points in the lower 50s expected along the frontal boundary.
Slowed down the clearing as well with VFR conditions developing in
the 16z-18z time frame.

/Outlook for kmsp/

Friday...VFR. Winds south-southwest at 5-10kts.
Sat...VFR. Winds northwest at 10-15kts.
Sun...chance MVFR/-shra overnight. Winds southeast at 10-15kts.

&&

Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&

$$

Short term...mpg
long term...jlt
aviation...rah

National Weather Service Glossary of Abbreviations