Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
303 am CDT sun Oct 26 2014

Short term...(today and tonight)
issued at 244 am CDT sun Oct 26 2014

Surface analysis this morning shows large surface high pressure centered over
the central Great Lakes...maintaining its western fringes over the upper
miss River Valley...while a complex area of low pressure becomes more
organized over southern Alberta. This surface low is developing in advance
of a longwave trough moving across the northern rockies and Great
Basin...and this trough trails a ridge axis aloft that will shift
across Minnesota and WI today. As the ridge exits to the east...clouds will
steadily increase throughout the day today...particularly as a warm front
approaches from the west today. An argument can be made that the front
will be more of an occlusion since the main low...a northern stream
low...will remain wound up and north of the area while a secondary southern
stream low from The Rockies stays to the S and keeps the more Bona
fide warm air to the S. Regardless...the effects will be an increases
in cloud cover but not necessarily moisture. 1000-500mb columns
look to remain fairly shallow across the entire County warning forecast area during the
daylight hours today. So despite the increases in frontal lift with the
incoming system...precipitation generation looks meager at best so have
opted to maintain a dry forecast...even for western WI where frontal lift
and most instability look to be coincident. The approaching upper
trough looks to become sharper and dig deeper into the northern-Central
Plains overnight into Monday morning which will enhance lift while
pivoting the surface low moving into southern Manitoba. Moisture does begin
to pool tonight over eastern portions of the County warning forecast area...so this lends to
better agreement of seeing scattered showers over mainly far eastern
Minnesota into western WI overnight tonight through Monday morning. In
addition...NAM/sref/hrrr do depict some model instability to the
tune of nearly 1000 j/kg MUCAPE...so have maintained slight chance thunderstorm
mention in the forecast. Not looking for a lot of coverage at
all...but the prospects of thunder cannot be ignored so have given
it its due diligence. As for temperatures...the clear skies and light
winds this morning have allowed temperatures to bottom out in the 30s for
the entire County warning forecast area. Ample sunshine and southeast winds through the first half
of today will allow temperatures to rebound nicely into the 60-70 degree
range...with the highest temperatures in western Minnesota. Clouds tonight and strong
southerly flow associated with the warm frontal passage will produce much more
mild temperatures tonight into Monday morning. Will look for lows to only drop to
the upper 40s to lower 50s.

Long term...(monday through saturday)
issued at 244 am CDT sun Oct 26 2014

Models have been trending for a more potent shortwave/upper low to
form/move across the upper Midwest late Monday/Tuesday which
corresponds to a better chance of rain showers...especially Tuesday as the core
of the coldest air moves across the region. The only concern is
the amount of deep moisture available due to the main front well south
of our region. In addition...the phasing of the southern/northern
jet remains questionable...especially early in the period...with a
better chance of the southern stream having more influence on
deeper moisture/convection. There remains enough confidence for
scattered/isolated rain showers for Monday...especially during the afternoon...and
again Tuesday afternoon as the upper low moves near the region.

Past Tuesday...precipitation chance/S remain low considering the much
drier air mass replacing Tuesday/S system and the high amplitude
of upper ridge forecast to build across The Rockies late in the
week. In our region...this amplified pattern will lead to a sharp
contrast from the Great Lakes/Ohio Valley to the High Plains and
The Rockies by next weekend. It is likely that the coldest air of
the season will surge southward Thursday/Friday as this amplified pattern
develops. Depending upon the strength of the long wave trough in
the eastern U.S. And how it becomes blocked in the overall
pattern...will determine when the warmer air rebounds across the
upper Midwest the first week of November.

&&

Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1106 PM CDT Sat Oct 25 2014

High confidence in VFR tonight and tomorrow. Winds will remain
light or calm tonight before increasing out of the southeast in
the late morning. By the end of the taf period...00z-
Monday...light showers are possible in eastern Minnesota and western WI.
It is also entirely possible most of the light rain will pass to
the east.

Kmsp...

Little to no weather impacts through the taf period. Wind direction
will be tough to pin down late tonight with high pressure moving
right overhead. We do think the winds will finally establish a
southeast direction by 14z. Rain is not impossible by the end of
the taf period...but the chances don't look great either - maybe
some sprinkles out of a middle deck of clouds. Thunder is not out of
the question either somewhere in southeast Minnesota or western WI
tomorrow evening.

/Outlook for kmsp/
Monday...MVFR ceilings likely early. Chance rain showers. Winds becoming west-northwest 5-10 kts.
Tuesday...chance MVFR/shra. Winds west-northwest 15g25 kts.

&&

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

$$

Short term...jpc
long term...jlt
aviation...clf

National Weather Service Glossary of Abbreviations